PROTEIN TYROSINE PHOSPHATASE 1B AND CANCER
 , The present invention relates to the identification of a marker gene useful in the diagnosis and prognosis of cancer, e.g. breast cancer and prostate cancer. The invention further provides methods for determining the course of treatment of a patient with cancer. In particular the present invention relates to methods of screening for anti-cancer therapeutics and methods of cancer diagnosis and prognosis using protein tyrosine phosphatase 1 B (PTP1 B) as a marker.
BACKGROUND OF THE INVENTION
 The increased number of cancer cases reported around the world is a major concern. Currently there are only a handful of treatments available for specific types of cancer, and these provide no guarantee of success. In order to be most effective, these treatments require not only an early detection of the malignancy, but a reliable assessment of the severity of the malignancy. There is a need for clinically useful markers consistently associated with cancer and which can be used to assign treatments to a patient. Indeed a marker-based approach to tumor identification and characterization promises improved diagnostic and prognostic reliability.
 Breast cancer is the most frequent malignancy among women with a worldwide estimated one million new cases per year1. In patients with breast carcinomas, Slamon et al. first observed the amplification of the proto-oncogene ErbB2 (neu/HER-2), which encodes a receptor tyrosine kinase (RTK) belonging to the epidermal growth factor receptor (EGFR) family2. Although the other family members, EGFR (HER-1/ErbBI ), ErbB3 (HER-3), and ErbB4 (HER-4) are also expressed in various cancers, amplification of ErbB2 occurs in approximately 25% of all breast cancers3 and correlates with negative patient prognosis. Oncogenic activation of ErbB2 can either be triggered by point mutations in its transmembrane domain4'5 or by deletion or insertion in the extracellular domain (ECD)4'6'7. To explore the importance of ECD mutations in human breast cancer, transgenic mice were generated that overexpressed in mammary gland, an altered neu transgene containing an in-frame deletion in its ECD (NDL2)6. Transgenic NDL2 females develop multiple mammary tumors with frequent lung metastasis lesions. Tumor progression in this strain is associated with elevated levels of tyrosine-phosphorylated ErbB2 and ErbB37 which have also been shown to be co-expressed in the majority of human breast cancers8'9. Another important similarity between this mouse model and human breast cancer is that an alternative spliced form of ErbB2 which is analogous to the neu deletion mutant in NDL2 mice has been detected in human breast cancer6'7'10'11. For example, when the activated neu oncogene was introduced into an immortalized non-tumorigenic human breast epithelial cell line, it resulted in a striking and specific increase in protein tyrosine phosphatase 1 B (PTP1 B) expression12. Furthermore, 90% of all breast tumors co-overexpressed both ErbB2 and PTP1 B13. The significance of this link is unknown.
 Both genetic and biochemical studies have implicated this enzyme as a negative regulator of RTKs signaling. For example, genetic evidence indicates that PTP1 B is involved as a negative modulator in metabolic diseases such as obesity and diabetes14-16. Similarly, we recently reported the first in vivo genetic study suggesting that removing PTP1 B in p53-dependent tumorigenesis17 led to a slight increase in B cell lymphoma likely due to an increase number of p53-/- pre B-lymphocytes population. Yet, surprisingly, our in vitro experiments in immortalized fibroblasts demonstrated that PTP1 B exerts positive effects on Ras signaling through p62Dok and p120RasGAP regulation18.
 Prostate cancer is a leading cause of male cancer-related death, second only to lung cancer, and is estimated to afflict one out of nine men over the age of 65. In the United States alone, well over 40,000 men die annually of this disease. Despite the magnitude of these figures, there is still no effective treatment for metastatic prostate cancer. Surgical prostatectomy, radiation therapy, hormone ablation therapy, and chemotherapy remain as the main treatment options. Unfortunately, these treatments are ineffective for many and are often associated with significant undesirable consequences.  Prostate cancer is typically diagnosed with a digital rectal exam, prostate specific antigen (PSA) screening and/or trans-rectal ultrasound. PSA is used as a marker for prostate cancer because it is secreted only by prostate cells and an elevated serum PSA level can indicate the presence of prostate cancer. Although PSA screening has been a useful diagnostic tool, the specificity, sensitivity and general utility of PSA is widely regarded as lacking in several respects. Neither PSA testing, nor any other test nor biological marker has been proven capable of reliably identifying early-stage disease. Similarly, there is no marker available for predicting the emergence of the typically fatal metastatic stage of the disease. There is a need for improved diagnostic and therapeutic methods to improve the detection, prognosis, treatment and management of the disease.
 Previous studies of PTP1B activity and expression in various cancer cells and tumors have revealed variable expression levels and conflicting effects of this phosphatase in oncogenesis1634,however, the exact role of PTP1 B in tumorigenesis has remained unclear. It would therefore be desirable to understand the role of PTP1 B in cancer development and tumorigenesis, for example in human breast cancer, prostate cancer and lung cancer. It would also be desirable to have therapeutic agents for the treatment and/or prevention of cancer.
 It would also be desirable to have a clinically useful marker consistently associated with cancers which respond to particular treatments, and which can be used to assign a treatment regimen to a patient.
SUMMARY OF THE INVENTION
 It is an object of the invention to understand PTP1 B function in order to acquire new means to influence cell and body metabolism for the treatment and prevention of human diseases, particularly cancer.
 In one aspect, the present invention relates to the identification of PTP1 B as a genetic marker whose expression is correlated with cancer, for example breast cancer or prostate cancer. Specifically, the invention provides a marker whose expression can be used to select a subject who will respond to or benefit from treatment with a PTP1 B inhibitor. The invention relates to methods of using this marker to select subjects for treatment with a PTP1 B inhibitor. In one aspect, a subject with high or elevated levels of PTP1B expression is administered a PTP1 B inhibitor in a therapeutically effective amount.
 It is contemplated that any tumor or cancer with a high level of PTP1 B expression can be treated with a PTP1 B inhibitor. Therefore PTP1 B levels are a marker for treatment with PTP1 B inhibitors. Diagnostic methods and kits for measuring PTP1B levels and selecting patients for treatment with PTP1 B inhibitors are provided herein.
 In accordance with the present invention, there is further provided a diagnostic method for identifying subjects who will respond to or benefit from treatment with a PTP1 B inhibitor. Subjects with cancers expressing elevated levels of PTP1 B would be expected to respond to or benefit from treatment with a PTP1 B inhibitor. A method for monitoring progression of cancer in a subject being treated with a PTP1 B inhibitor is also provided, comprising measuring PTP1 B levels during and after treatment with a PTP1 B inhibitor and comparing to PTP1 B levels measured before treatment commences. In one aspect, PTP1 B levels may decrease in patients responding to treatment with a PTP1 B inhibitor.
 In accordance with the present invention, there is also provided a kit for diagnosing a cancer in a subject, comprising one or more than one reagent for detecting PTP1 B expression or measuring PTP1 B levels, and instructions for use of said one or more than one reagent, wherein elevated levels of PTP1 B are diagnostic of cancer or of a predisposition to cancer. The methods and kits of the invention may also be used for determining prognosis of a patient. Further in accordance with the present invention, there is provided a kit for assigning treatment to a patient, for example a breast or prostate cancer patient, comprising one or more than one reagent for detecting PTP1 B expression or measuring PTP1 B levels, and instructions for use of said one or more than one reagent, wherein a patient with elevated levels of PTP1 B is assigned treatment with one or more PTP1 B inhibitors. PTP1 B may be detected using standard methods such as PCR, antibodies, immunocytochemistry, immunoprecipitation, DNA probes, aptamers, small molecules, etc. Small molecules may be tagged with a detectable agent or labelled for imaging purposes. In one aspect, PTP1 B levels are measured in a tumor of a subject having ErbB2 positive cancer to select the subject for treatment with PTP1 B inhibitors.
 In another aspect, there is provided a kit for assigning treatment to a patient having a cancer, for example a breast or prostate cancer patient, comprising reagents for detecting PTP1 B expression or measuring PTP1B levels, and instructions for use of said reagents, wherein a patient with elevated levels of PTP1 B is assigned treatment with one or more PTP1 B inhibitors. The patient may for example have a cancer which expresses PTP1 B and one or more known oncogenic proteins, such as EGFRvIII, EGFR/HER-1/ErbB1, ErbB2/HER-2, ErbB3/HER-3, ErbB4/HER-4, ras, myc, BRCA1 , and BRCA2.
 The invention further provides for methods of assigning therapeutic regimen to cancer patients, e.g. breast or prostate cancer patients. In one embodiment, the invention provides a method of assigning a therapeutic regimen to a cancer patient, comprising measuring PTP1 B levels in said patient, wherein said therapeutic regimen assigned to said patient comprises PTP1B inhibitor therapy if said PTP1B levels are high. In another specific embodiment of this method, said patient has breast cancer, e.g. ErbB2 positive cancer. In another specific embodiment of this method, said patient has prostate cancer. In yet another specific embodiment of this method, said patient is assigned PTP1 B inhibitor therapy in combination with a first anti-cancer therapy. PTP1 B inhibitor therapy and the first anti-cancer therapy may be administered concomitantly or sequentially or in any therapeutically-effective dosage and/or administration regimen.
 There is also provided a kit for monitoring progression of a cancer in a subject or response to treatment by a subject, comprising reagents for detecting PTP1 B or measuring PTP1 B levels, and instructions for use of said reagents, wherein increased levels of PTP1 B indicate progression of cancer and/or lack of response to treatment, and decreased levels indicate that the cancer has not progressed and/or a positive response to anti-cancer treatment, i.e. treatment is efficacious.
 Further provided herein are methods and kits for detecting or measuring overabundance of PTP1 B in cancerous cells, for example breast or prostate cancer cells, comprising the steps of reacting RNA or protein contained in a clinical sample with a reagent, said clinical sample having been obtained from an individual suspected of having or known to have cancerous cells; and comparing the amount of complexes formed between the reagent and the RNA or protein in the clinical sample with the amount of complexes formed between the reagent and RNA or protein in a control sample. The reagent may be any standard reagent which is specific for PTP1 B and known in the art for detecting PTP1 B RNA or protein, for example, PCR primers and reagents, antisense oligonucleotides, antibodies, etc.
 In another embodiment, the present invention encompasses a method of treating or preventing cancer in a subject in need of such treatment, comprising administering to said subject a therapeutically effective amount of an inhibitor of protein tyrosine phosphatase 1 B (PTP1 B). In one aspect, the invention relates to a method for treating or preventing breast cancer in a subject. In another aspect, ErbB2-induced mammary tumorigenesis is inhibited by administration of PTP1 B inhibitors. The methods of the invention may, for example, delay mammary tumor progression, decrease mammary tumor multiplicity, etc. In one embodiment, ErbB2 positive cancer is treated or prevented by PTP1 B inhibitors. In another aspect, the invention relates to a method for treating or preventing a cancer associated with overexpression of PTP1 B. In yet another aspect, the invention relates to a method for treating or preventing prostate cancer in a subject.
 Non-limiting examples of cancers for treatment are selected from cancers of the breast, prostate, lung, ovary, brain, genitourinary tract, lymphatic system, stomach, and larynx. Another set of forms of cancer are histiocytic lymphoma, lung adenocarcinoma, small cell lung cancers, pancreatic cancer, glioblastomas, leukemia and breast carcinoma. It is contemplated that any cancer which expresses high levels of PTP1 B may be treated or prevented by administration of PTP1 B inhibitors.
 PTP1 B inhibitors for use in the methods of the invention may be small molecules, siRNA, antisense, antibodies, etc. Many PTP1B inhibitors are known in the art and may be used in the methods of the invention. For example, PTP1 B inhibitors are described in U.S. Patent numbers 7,199,121 ; 7,179,796; 7,169,797; 7,163,932; 7,163,952; 7,141 ,596; and 7,115,624, the entire contents of which are hereby incorporated by reference in their entirety. Reports of various phosphatase inhibitors have also been published in WO 04/062664; WO 04/041799; WO 03/82841 ; WO 03/092679; WO 02/18321 ; WO 02/18323; WO 02/18363; WO 03/37328; WO 02/102359; WO 02/04412; WO 02/11722; WO 02/26707; WO 02/26743; WO 01/16122; WO 01/16123; WO 00/17211 ; WO 00/69889; WO 01/46203; WO 01/46204; WO 01/46205; WO 01/46206; WO 01/70753; WO 01/70754; WO 01/17516; WO 01/19830; WO 01/19831 ; WO 98/27065; WO 00/53583; WO 99/11606; WO 03/32916; WO 01/16097; WO 98/27092; WO 98/56376; WO 03/33496; WO 99/58514; WO 99/58518; WO 99/58519; WO 99/58521 ; WO 99/58522; WO 99/61410; WO 97/40017; WO 98/53814; and U.S. Pat. Nos. 6,166,069; 6,310,081 ; 6,110,963; 6,057,316; 6,001 ,867; and 5,798,374; and other compounds have been reported in U.S. 2003/0060419 and 2004/0167188 and in Montalibet, J. et al. (J Biol Chem 281 : 5258-66 (2006)); all of which are hereby incorporated by reference in their entirety.
 In accordance with the present invention, there is also provided a method for screening for anti-cancer therapeutics, comprising determining whether an agent is an inhibitor of PTP1 B. In another aspect, methods for identifying anti-cancer agents based on inhibition of PTP1 B are also provided.  Further in accordance with the present invention, there is provided a new use for PTP1B inhibitors in treating or preventing cancer, as described herein.
 In a further embodiment, the present invention encompasses a method of treating or preventing cancer in a subject being treated with a first anti-cancer treatment, comprising administering to said subject a therapeutically effective amount of an inhibitor of protein tyrosine phosphatase 1 B (PTP1 B). In a particular embodiment, the first anti-cancer treatment may be surgery, radiology, chemotherapy, or a targeted cancer treatment. More specifically, the targeted cancer treatment is selected from the group consisting of small molecules, monoclonal antibodies, cancer vaccines, antisense, siRNA, aptamers and gene therapy. In a further embodiment, the first anti-cancer treatment may be an anti-ErbB2 therapy. In another aspect, the first anti-cancer treatment and the PTP1 B inhibitor may be administered concomitantly or sequentially.
 Cancer is characterized by deregulated cell proliferation. Cancer refers herein to a cluster of cancer cells showing over proliferation by non- coordination of the growth and proliferation of cells, without respect to normal limits, which may be due to the loss of the differentiation ability of cells, and which may invade and destroy adjacent tissues and may spread to distant anatomic sites through a process called metastasis. In an embodiment, the encompassed cancer is selected from the group consisting of breast cancer, prostate cancer, lung cancer, ovarian cancer, lymphoma, and their metastases. Cancers of the brain, genitourinary tract, lymphatic system, stomach, and larynx and their metastases are also encompassed, as are histiocytic lymphoma, lung adenocarcinoma, small cell lung cancers, pancreatic cancer, glioblastomas and breast carcinoma and metastases thereof. In particular, breast carcinomas including lobular and duct carcinomas, and other solid tumors, carcinomas, sarcomas, and cancers including carcinomas of the lung like small cell carcinoma, large cell carcinoma, squamous carcinoma, and adenocarcinoma, stomach carcinoma, prostatic adenocarcinoma, ovarian carcinoma such as serous cystadenocarcinoma and mucinous cytadenocarcinoma, ovarian germ cell tumors, testicular carcinomas, and germ cell tumors, pancreatic adenocarcinoma, biliary adenocarcinoma, heptacellular carcinoma, renal cell adenocarcinoma, endometrial carcinoma including adenocarcinomas and mixed Mullerian tumors (carcinosarcomas), carcinomas of the endocervix, ectocervix, and vagina such as adenocarcinoma and squamous carcinoma, basal cell carcinoma, melanoma, and skin appendage tumors, esophageal carcinoma, carcinomas of the nasopharyns and oropharynx including squamous carcinoma and adenocarcinomas, salivary gland carcinomas, brain and central nervous system tumors including tumors of glial, neuronal, and meningeal origin, tumors of peripheral nerve, soft tissue sarcomas and sarcomas of bone and cartilage, and their metastases, are encompassed herein.
 In a further embodiment, the encompassed cancer expresses PTP1 B. In another embodiment, the encompassed cancer expresses PTP1 B and one or more known oncogenic proteins, such as EGFRvIII, EGFR/HER-1/ErbB1 , ErbB2/HER-2, ErbB3/HER-3, ErbB4/HER-4, ras, myc, BRCA1 , and BRCA2. In one aspect, expression of PTP1 B is elevated in the cancerous cells of a subject being treated.
BRIEF DESCRIPTION OF THE DRAWINGS
 Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration, an embodiment or embodiments thereof, and in which:
 Figure 1 illustrates the reduced rate of tumor development, number of tumors and lung metastases in NDL2-PTP1 B-/- mice. A: Kaplan-Meier kinetic analysis of tumor occurrence in NDL2-PTP1B female transgenic mice. In order to detect mammary tumors, mice were examined twice a week after weaning of the second litter. The curves were drawn and analyzed using Prism software. Logrank tests of survival plots of the data indicated a statistically significant difference between each survival curves: NDL2-PTP1 B+/+ versus NDL2- PTP1 B+/- P = 0.004; NDL2-PTP1 B+/+ versus NDL2-PTP1 B-/- P = 0.0001 ; NDL2-PTP1 B+/- versus NDL2-PTP1 B-/- P = 0.001. The number of animals analyzed for each genotype (n) and the median time to tumor onset (T50) are also shown. B: Female mice described in (A) were sacrificed at different time points (0.3, 4, or 6 weeks) after tumor initiation stage and the number of tumors was determined, (n) = number of mice per group. C: Lung metastases were monitored by histopathological analysis from H & E-stained lung sections from all animals presented in (A), n = number of mice per group;
 Figure 2 illustrates the distinct mammary gland histopathology in NDL2-PTP1 B+/+ compared to NDL2-PTP1 B-/-. H&E-stained tissue sections of abdominal mammary gland number four from NDL2-PTP1 B+/+ (left; panels B, D, F) and NDL2-PTP1 B-/- (right; panels C, E, G) transgenic mice breast tumors (BT) at 0.3 (BT0.3), 4 (BT4) and 6 (BT6) weeks after tumor occurrence. The representative sections were obtained from the mice described in Supplementary Fig. 1 , respectively. Arrows indicate mitotic figures (panels F-G). Tissue section from a 3 month-old non-transgenic FVB mouse is presented as a control (panel A). Bar, 50/vm (panel A); 200 μm (panels B-E); 100 μm (panels F- G) and 20μm (enlargement);
 Figure 3 illustrates the reduced expression levels of ErbB2 and ErbB3 in breast tumors of NDL2- PTP1 B-/- transgenic mice. Breast tumor tissue (BT) was isolated from NDL2-PTP1 B+/+ and NDL2-PTP1 B-/- transgenic mice at week 0.3 (BT0.3), 4 (BT4), and 6 (BT6) after tumor occurrence. Normal mammary epithelium adjacent to the tumors at week 6 after tumor onset (normal breast, NB6) was used as a control. A: ErbB2 was immunoprecipitated (IP) from breast tumor tissue lysates and immunoprecipitates were subjected to SDS-PAGE and immunoblot (IB) analysis was performed using anti- phosphotyrosine antibodies (4G10), followed by a reprobe with anti-ErbB2 antibodies. Phosphorylated-ErbB2 (P-ErbB2) and ErbB2 bands are indicated by the arrows at molecular weight 185 kDa. Mammary tissue from non-transgenic FVB mouse (lane 1 ) was included as a control for endogenous ErbB2 expression. The experiment was performed three times, using three mice per time point in total. The diagram illustrates the densitometry analysis of the phosphorylated ErbB2/ErbB2 ratio obtained from all the experiments. Results represent the mean ± SD. * P<0.001 NDL2-PTP1 B+/+ versus NDL2-PTP1 B-/-. B: Breast tumor tissue (BT) lysates from NDL2-PTP1 B+/+ and NDL2-PTP1 B-/- transgenic mice were separated by 4-12% gradient SDS-PAGE and transferred to PVDF membrane. The membrane was blotted with anti-ErbB2 antibodies and reprobed with anti-ErbB3 antibodies. The anti-Grb2 immunoblot is used as a loading control. The experiment was repeated three times, using three mice per time point;
 Figure 4 illustrates the decreased Ras-MAPK signaling in breast tumors of NDL2-PTP1 B-/- mice. Breast tumor tissue (BT) was isolated from NDL2-PTP1 B+/+ and NDL2-PTP1 B-/- transgenic mice at week 0.3 (BT0.3), 4 (BT4), and 6 (BT6) after tumor occurrence. Normal mammary epithelium adjacent to the tumors at week 6 after tumor onset (normal breast, NB6) was used as a control. A: Breast tumor tissue (BT) lysates (20 μg) were analyzed by Western blotting with anti-phosphoY449-p62Dok antibodies and reprobed with anti-Dok1 antibodies to ensure equal loading. B: p120RasGAP phosphorylation was analyzed by immunoprecipitating p120RasGAP, probing with anti- phosphotyrosine antibodies (4G10), and then reprobing with anti-p120RasGAP antibodies. C: Phosphorylation of p42/p44MAPK in breast tumor samples described in (A). The samples were analyzed for p42/p44 MAPK protein and phosphorylation levels by using phosphospecific antibodies (anti- phosphoT202/Y204-MAPK). The diagrams illustrate the densitometry analysis of the blots. Results represent the mean ± SD of three independent experiments with a total of n = 3 mice per group.* P<0.005 NDL2-PTP1 B+/+ versus NDL2- PTP 1 B-/- ;
 Figure 5 illustrates the downregulation of Akt activation in NDL2- PTP 1 B-/- transgenic mice. Breast tumor tissue (BT) was isolated from NDL2- PTP1 B+/+ and NDL2-PTP1 B-/- transgenic mice at week 0.3 (BT0.3), 4 (BT4), and 6 (BT6) after tumor occurrence. Normal mammary epithelium adjacent to the tumors at week 6 after tumor onset (normal breast, NB6) was used as a control. A: 20 μg of the samples were analyzed for Akt protein and phosphorylation levels by using phosphospecific antibodies (anti-phosphoS473- Akt). B and C: p27 and Cyclin D1 expression levels were determined in the breast tumor samples described in (A). Grb2 expression was used as a loading control. The diagrams illustrate the densitometry analysis of the blots. Results represent the mean ± SD of three independent experiments with a total of n = 3 mice per group.* P<0.005 NDL2-PTP1B+/+ versus NDL2-PTP1B-/- ;
 Figure 6 illustrates the increased apoptosis in breast tumor samples of NDL2-PTP1 B-/- mice. A: Western blot analysis of PARP expression and cleavage from breast tumor lysates from NDL2-PTP1 B+/+ and NDL2-PTP1 B-/- transgenic mice at 0.3 (BT0.3), 4 (BT4) and 6 (BT6) weeks after tumor occurrence. The full-length (113 kDa) and the cleaved fragments (85 kDa) are indicated by the arrows. B: lmmunoblot analysis was performed with anti- caspase-3 antibodies on breast tumor total lysates as described in (A). Full- length (35 kDa) and cleaved caspase-3 fragment (17 kDa) are indicated by the arrows. The experiments described in A and B were repeated three times using three different mice for each time point and similar results were obtained. C: lmmunohistochemical detection of PCNA-positive and cleaved-caspase 3- positive cells (black and white arrows, respectively) in breast tumor sample 6 weeks after tumor occurrence. Samples shown are representative of three independent experiments with a total of n = 3 mice per genotype. The average percentages of PCNA-positive and cleaved-caspase-3-positive cells are indicated in the lower left corner of each panel. Magnification: *63;
 Figure 7 illustrates the PTP1 B inhibitor administration delays the onset of mammary tumor development in NDL2-PTP1 B+/+ mice. Kaplan-Meier kinetic analysis of tumor occurrence in NDL2-PTP1 B female transgenic mice , that received the PTP1 B inhibitor or vehicle. Mice were examined twice a week after the end of treatment in order to detect mammary tumors. The curves were drawn and analyzed using Prism software. Logrank tests of survival plots of the data indicate a statistically significant difference between compound administered-NDL2-PTP1 B+/+ and vehicle-administered NDL2-PTP1 B+/+ (P <0.001 ). The number of animals analyzed for each genotype (n) and the median time to tumor onset (T50) are indicated on the graph;
 Figure 8 illustrates the overexpression of PTP1 B in breast induces mammary gland tumorigenesis. A: Schematic diagram of the human PTP1B transgene. The unshaded region represents sequences within the pBSKK vector backbone. The transcriptional start site within the MMTV-LTR is illustrated by the lower arrow and the 5' non coding sequences derived from the MMTV-v-Has-Ras vector pA9 are illustrated by the shaded box. The boundaries of the cDNA PTP1 B wild-type (WT), and SV40 processing signals are shown by the appropriate arrows. Relevant restriction endonuclease sites are also identified in the figure.B: 20 μg of total breast or tumor tissue lysates from MMTV-EGFP-PTP1 B transgenic mice were separated by SDS-PAGE, transferred to a PVDF membrane and immunoblotted with anti-PTP1 B antibodies. Breast tissue lysate from FVBN mouse was used as a negative control (lanes 3). Equal loading was verified by reprobing the membrane with anti-Grb2 antibodies. C: H&E-stained tissue sections of abdominal mammary gland number four from MMTV-EGFP-PTP1 B transgenic mice which had no litter (panel B), 2 litters (panel C) or 7 litters (panel D). Tissue section from a non-transgenic FVB mouse which had 2 litters is presented as a control (panel A). The representative sections were obtained from the mice described in B. Bar, 200 μm;
 Figure 9 shows prostate-specific antigen recurrence-free survival curves plotted using the Kaplan-Meier analysis and the log-rank test, wherein the lower curve (pink) illustrates survival for patients expressing a high level of PTP- 1 B in prostate tumors, and the upper curve (green) illustrates survival for patients expressing low levels of PTP- 1 B in prostate tumors. The cut-off value of 1.29 (average intensity of staining) was used to assign patients to the High PTP1 B expression group (> 1.29) or the Low PTP1 B expression group (<1.29). The graph represents the proportion of patients without biochemical recurrence (Y axis) at a specific time-point (X axis), wherein censored means patients with <150 months of follow-up that did not relapse, the Log Rank is 1.78, p=0.1819 and n=63;
 Supplementary Figure 1 illustrates the comparative pathology of breast tumors in NDL2-ptpn1-7- and NDL2-ptpn1 +/+ mice. In addition to the analysis of tumor burden and multiplicity, we compared mammary whole mounts from MMTV-NDL2 mice containing either PTP1 B wild-type or homozygous mutants (Supplementary Fig. 1 ). Careful examination of mammary gland whole mounts revealed that NDL2-ptpn1+/+ animals exhibited a number of nodular masses amongst hyperplastic and dysplastic tissue at 0.3 week after palpable tumor, whereas NDL2-ptpn1-/- mice only presented hyperplastic lobuloalveloar endbuds (Supplementary Fig. 1 B vs C). After 4 to 6 weeks of tumor initiation, both groups presented a severe altered branching, hyperplastic progression and neoplasia in the fat pad (Supplementary Fig. 1 D-E vs A). However, all these features were less pronounced in the absence of PTP1 B (Supplementary Fig. 1 D-F vs E-G, respectively);
 Supplementary Figure 2 illustrates the unaltered Src phosphorylation during mammary tumor progression in NDL2-ptpn1 null mice. Since numerous tumors and cell lines overexpressing ErbB2 show high levels of activated Src 19 and because previous in vitro studies have identified PTP1 B as a potent activator of Src by dephosphorylating its negative tyrosine regulatory site in human breast cancer cell lines 20, we examined the relative levels of Src activity and expression in breast tumor samples of our NDL2-ptpn1 wild-type and null animals (Supplementary Fig. 2). Tumor lysates were subjected to western blot analysis using phosphospecific antibodies against the inhibitory phosphorylation site of Src (Y529). To confirm this result, we also performed immunoblot using a phosphospecific antibody against the activating phosphorylation site of Src (Y418) and we observed a time-dependent decrease in Y418 phosphorylation resulting in decreased Src activity during tumor progression in both group of animals (data not shown);
 Supplementary Figure 3 shows that administration of PTP1 B inhibitor in NDL2-ptpn1 +/+ normalizes glucose levels. Glucose levels remains similar and lower than wild-type animals (5.71 ± 0.13 mmol.L-1 ; P < 0.05, data not shown) in both PTP1 B inhibitor-administered NDL2-ptpn1 -7- group (4.40 ± 0.09 mmol.L-1 ; P < 0.05) and vehicle-administered NDL2-ptpn1-7- group (4.35 ± 0.12 mmol.L-1 ; P < 0.05) all over the 21-days treatment and further in time. PTP1 B inhibitor administration lowered glucose levels in the NDL2-ptpn1 +/+ group between day-6 of treatment up to 10 days after the end of treatment with an average of 4.50 ± 0.09 mmol.L-1 (P < 0.05) as compared to vehicle- administered NDL2-ptpn1+/+ group (5.58 ± 0.17 mmol.L-1 ; P < 0.05)( Supplementary Fig. 3);
 Supplementary Tablei illustrates a summary of phenotypic abnormalities in MMTV-PTP1 B transgenic mice. Four different female funders (A, B C and D from a second generation F2) were bred to FVB male to induce pregnancy in order to activate MMTV promoter and to synchronize tumor occurrence. Female were sacrificed after the weaning of the second, fifth or seventh pregnancy. Tissue mammary gland were processed according to routine procedures and embedded in paraffin. Sections were cut and stained with H&E for histopathological diagnosis. A minimal diffuse mammary gland acinar hyperplasia was observed after 2 litters. However, after 5 or 7 litters mice developed mammary gland carcinoma papillary type. This tumor is well differentiated and composed of numerous finger-like projections supported by a fibrovascular stroma and covered by neoplastic epithelium. The rest of mammary gland was composed of hyperplastic acini, mild, with few mitoses and little atypia (nuclear pleomorphism). There was also focal squamous metaplasia in the mammary gland of one mouse analyzed. The rest of the mammary gland was composed of hyperplastic acini, minimal, with few mitoses and little atypia (nuclear pleomorphism). All these data provide unambiguous evidence that PTP1 B transgene may drive tumors by its own.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
 Because most oncogenes originally described were tyrosine kinases, PTPs were first postulated to be tumor suppressor genes. The role of PTP1 B is unclear: PTP1 B protein levels have been found to be increased in an important proportion of breast and ovarian cancers, but decreased in the esophageal cancers. Our findings presented herein have revealed the oncogenic properties of PTP1 B.  It has been demonstrated that PTP1 B-deficient fibroblasts display increased IGF-I receptor, PDGRF and EGFR tyrosine phosphorylation and associated PI3K-mediated signaling, but activation of their Ras/MAPK-mediated pathways is significantly impaired. Examining this phenomenon further, we showed that loss of PTP1 B resulted in decreased Ras activity and that this event occurred through increased p120RasGAP expression and augmented p62Dok phosphorylation. These results suggested that if increased in expression, PTP1 B could potentially play a prooncogenic role by enhancing Ras signaling. We have evaluated the consequence of removing PTP1 B in the MMTV-ErbB2 model of breast cancer developed. Our data indicate that PTP1 B+/+ and PTP1 B+/- ErbB2 transgenic (TG) mice present a defect in lactation and postnatal death of their progeny occurs due to tumor initiation. In contrast, PTP1 B deficient -/- ErbB2 transgenic (TG) mice have normal pups and they are able to nurse their young to a normal weight. Even more striking, PTP1 B WT and heterozygote ErbB2 transgenic animals have detectable tumors at 4 months of age, but knockout PTP1 B MMTV-ErbB2 animals have yet to develop tumors at the same age. These findings are remarkable and indicate that PTP1 B could be an important factor in the process of breast cancer initiation and development. Our main objective remains understanding PTP1 B function in order to acquire new means to influence cell and body metabolism for the treatment of human diseases, particularly cancer. We report herein that PTP1 B is a novel therapeutic target in cancer, for example in breast cancer, prostate cancer and in lung cancer.
 In order to clarify the role of PTP1 B in oncogenesis we used both genetic and pharmacological approaches to investigate the function of PTP1 B in breast cancer. We show here that mice lacking PTP1 B or PTP1 B inhibitor- administered mice display ErbB2-induced breast tumor latency. Finally, mouse mammary tumor virus (MMTV)-dependent over-expression of PTP1 B in mammary gland leads to spontaneous breast cancer development following multiple pregnancies. Taken together, our findings support that inhibition of PTP1 B activity could be used as a new therapeutic approach in human breast cancer.  We found that the predominant phenotype of MMTV-NDL2-PTP1 B deficient mice was delayed mammary tumor formation and decreased tumor multiplicity.
 To explore the role of PTP1 B in ErbB2-dependent breast tumor development PTP1 B-deficient mice were crossed with the MMTV-NDL2 transgenic mouse strain which have been shown to develop mammary carcinomas7. In order to accelerate and synchronize mammary tumor onset, multiple pregnancies by mating the females with FVB males were initiated7. Thus, tumors arose in a synchronous manner between 131 to 155 days of age in all NDL2-1 B+/+ mice, whereas the NDL2-PTP1 B-/- mice had yet to develop tumors at that stage (Fig. 1A). Compared to the NDL2-PTP1 B+/+ mice (T50=147.5 days), the time course of mammary tumor development in the NDL2-PTP1 B-/- mice was significantly delayed (T50=205 days, P<0.0001 ). In fact tumor development was delayed by approximately 85 days in the NDL2- PTP1 B-/- strain compared to the NDL2-1 B+/+ mice. The first palpable tumor in the NDL2-PTP1 B-/- strain occurred at 147 days of age and by day 230, 90% of the animals had developed tumors. Interestingly, NDL2-PTP1 B+/- mice exhibited an intermediate profile of tumor occurrence, suggesting that the absence of one allele of PTP1 B is sufficient to delay the onset of breast tumor development by 35 days compared to NDL2-PTP1 B+/+ mice (Fig. 1A). These results indicate that the PTP1 B gene dosage is limiting for tumorigenesis.
 Subsequently, mice were sacrificed at week 0.3, 4 and 6 after tumor occurrence and diagnosis of mammary tumorigenesis and tumor multiplicity was confirmed by visual examination following necropsy. Up to 4 weeks after tumor formation, there was no significant difference in tumor burden between the groups. However, 6 weeks after tumor occurrence, the NDL2-PTP1 B+/+ mice showed twice as many tumors (15 ± 2) than the NDL2-PTP1 B-/- mice (6.7 ± 1.8, PO.01 ) (Fig. 1 B). In addition to mammary tumor onset, the occurrence of lung metastatic lesions was also monitored. Whereas, all NDL2-PTP1 B+/+ mice, 4 weeks after breast tumor onset, developed lung metastases (Fig. 1C), the level of lung metastases was attenuated in both the heterozygous and homozygous PTP1 B-deficient NDL2 strains (Fig. 1 C). For example, six weeks after mammary tumor formation, the penetrance of lung metastases was decreased respectively by 66.6 % and 33.3 % (P=O.01) in the absence of one or two alleles of PTP1 B in the NDL2 strain compared to the parent strain (Fig. 1C). Taken together, these results constitute the first genetic evidence that PTP1B contributes positively to ErbB2-induced mammary tumor occurrence and malignancy.
 Although the macroscopic appearance was quite similar as illustrated in Supplementary Fig.1 , microscopic analyses revealed that the histopathology of the mammary gland in the MMTV-NDL2-PTP1 B-/- mice was markedly different than that of the NDL2-PTP1 B+/+ mice (Fig. 2). Indeed, at 0.3 week after palpable tumor occurrence, NDL2-PTP1 B+/+ mice presented mammary proliferative ductal lesions (Fig. 2B) compared to the benign ductal hyperplasia present in breast of NDL2-1 B-/- females (Fig. 2C). Four weeks later, the morphology of the mammary tissue was dominated by adenocarcinoma infiltrating the fat pad in NDL2-PTP1 B+/+ animals (Fig. 2D), whereas the NDL2- PTP1 B null mice exhibited benign intraductal papilloma (Fig. 2E). Finally, 6 weeks after tumor occurrence, adenocarcinomas were also present in null PTP1 B-NDL2 females (Fig. 2G). We observed larger tumor cells size, higher nuclear/cytoplasmic ratio, nuclear pleomorphism and more prominent nucleoli in NDL2-PTP1 B+/+ tumors (panel F, enlargement) as compared to NDL2-PTP1 B- /- tumors (panel G, enlargement) which still present some heterochromatic cells within adenocarcinomas. These results clearly demonstrate that PTP1 B deficiency in the NDL2 strain delays the progression from hyperplasia to blunt carcinoma at least during the first 6 weeks of mammary gland tumor development.
 It is also reported herein that activated ErbB2 and ErbB3 levels decreased during mammary tumor progression in NDL2-PTP1 B null mice.
 In order to assess the relationship between the rapid onset of multifocal adenocarcinomas and high expression levels of ErbB2 driven by the MMTV promoter in our animal model, we first examined the level of activated ErbB2 during mammary tumor development at 0.3, 4 and 6 weeks after tumor onset (Fig. 3). Tumor samples at 4 and 6 weeks exhibited high levels of total and tyrosine-phosphorylated ErbB2 compared to normal adjacent mammary epithelium (Normal Breast, NB, Fig. 3A, lanes 4 versus 5-7 and 8 versus 9-11 ), a feature associated with breast tumor progression 7. In NDL2-PTP1 B+/+ tumor samples phospho-ErbB2 levels were detectable at the time of tumor onset (Fig. 3A upper panel, lane 5 versus 9) and higher than in NDL2-PTP1 B-/- tumor samples (Fig. 3A upper panel, lanes 6-7 versus 10-11 , P<0.001 ). Since heterodimerization of ErbB receptors is crucial for cellular signaling and the ErbB2-ErbB3 receptor pair forms the most potent signaling module of the ErbB- receptor family in terms of cell growth and transformation8 the kinetics of ErbB3 expression during breast tumor progression from 0.3 to 6 weeks was examined. Whereas, the ErbB3 and ErbB2 expression patterns were quite similar (Fig. 3B) and the ErbB3 receptor was overexpressed in tumor samples7 there was a much higher level observed in tumors expressing PTP1B compared to the PTP1 B null samples at each time point examined (Fig. 3B, lanes 2-4 versus 6- 8).
 Numerous tumors and cell lines over-expressing ErbB2 show high levels of activated Src19 and PTP1 B has been proposed to activate Src through dephosphorylation of the inhibitory tyrosine Y529, thereby providing a mechanism by which PTP1 B over-expression might promote tumorigenesis20. Bjorge et al. also showed that PTP1 B expression is increased in human breast cancer cell lines compared to a normal breast cell line. In contrast, others have argued for a negative role for PTP1 B in signaling downstream of HER2, using v- src in fibroblast models21'22. These conflicting in vitro observations leave the relationship between PTP1 B and HER2 ambiguous. We examined the relative levels of Src activity and expression in breast tumor samples of our NDL2- PTP1 B wild-type and null animals (Supplementary Fig. 2). The diagram that summarizes the quantification of the blots shows no difference of the Y529 phosphorylation levels between NDL2-PTP1 B+/+ and NDL2-PTP1 B null breast tumor tissue. This contradicts the current in vitro paradigm that activation of Src kinases is essential for Neu-induced oncogenesis. However our in vivo results are in accordance with a recent study which was the first to distinguish between the kinase-dependent and kinase-independent actions of Src and showed that its kinase-dependent properties are not requisite for Neu-induced tumorigenesis23.
 We also show that PTP1 B deficiency in the NDL2 strain down- regulates the Ras-MAPK signaling pathway through p62dok activation.
 We investigated the role of PTP1 B in the ErbB2 downstream signaling pathways that may contribute to mammary tumor development. The ErbB2-ErbB3 heterodimer potently triggers proliferative signals through the Ras-MAPK pathway8. Moreover, we recently demonstrated that PTP1 B positively regulates Ras activity by acting on p62Dok and p120RasGAP18. Based on these findings, we examined whether the loss of PTP1 B influences Ras signaling downstream of ErbB2/ErbB3 in mammary tumors (Fig. 4). We found that p62Dok was phosphorylated in samples at 6 weeks after tumor onset, but phospho-p62Dok was significantly enhanced 48% in PTP1 B deficient tumor samples (Fig. 4A, P<0.005). Previous studies have shown that p62Dok binds to p120RasGAP, resulting in inhibition of ERK activation24'25. To determine whether activated p62Dok may have a direct impact on the Ras/MAPK pathway, through RasGAP, p120RasGAP was immunoprecipitated from breast tumor lysates at different time point after tumor initiation (0.3, 4 or 6 weeks) and western blot analysis was performed using anti-phosphotyrosine antibodies. As shown in Fig. 4B, BT4 and BT6 samples display RasGAP phosphorylation, which inversely correlates with p62Dok phosphorylation (Fig. 4A). RasGAP phosphorylation was attenuated in the absence of PTP1 B compared to the wild- type samples (Fig. 4B lanes 7-8 versus 3-4, P<0.005) and consistent with our previous data18 there appeared to be decreased levels of RasGAP protein in the PTP1 B expressing samples compared to the PTP1 B deficient samples. Furthermore, when p42/p44 MAPK phosphorylation was examined in these same samples MAPK activation was totally inhibited in NDL2-PTP1B-/- breast tumor samples (Fig. 4C, lane 3 versus 6, P<0.005). These results show that the absence of PTP1 B attenuated the Ras-MAPK-induced ErbB2 activation in breast tumor progression. Indeed, PTP1 B may act as a positive regulator downstream of ErbB2 at least through the downregulation of p62Dok activity, leading to increased Ras and p42/p44 MAPK activation.
 Further, we report herein that the absence of PTP1 B downregulates the ErbB2-induced PI3K/Akt pathway in the NDL2 strain.
 As previously mentioned, ErbB2-ErbB3 heterodimer has the capacity to signal very potently through Ras-MAPK for proliferation, but also through the PI3K/Akt pathway for survival8. Akt is one of the most activated serine/threonine kinase in human cancer26 and its activation occurs during ErbB2 overexpression. Thus the effects of PTP1 B deficiency on Akt activation in this ErbB2-induced mammary tumor model were examined. In NDL2-PTP1 B+/+ breast tumor samples as early as tumor initiation (0.3 weeks) and up to 6 weeks after tumor onset there was increased compared to normal adjacent mammary epithelium and sustained S473 Akt phosphorylation in all tumor samples (Fig 5A, lane 1 versus 3-5, P<0.005). This was in contrast to the NDL2-PTP1B-/- samples which displayed an attenuated Akt phosphorylation level compared to NDL2-PTP1 B+/+ samples, and further decreased during breast tumor progression (Fig. 5A, lanes 6-8 versus lanes 3-5, P<0.005).
 Both MAPK and PI3K/Akt signaling pathways regulate cell cycle progression by modulating the levels of effectors such as cyclin D1 and the CDK inhibitor p27kip 27'28. Morever, cyclin D1 is required for ErbB2-induced tumorigenesis29. Based on this data, we explored the expression levels of these effectors in NDL2-PTP1 B+/+ and NDL2-PTP1 B-/- breast tumor samples (Fig. 5B and C). Both groups exhibit a dramatic decrease in p27kιp expression level during tumor progression (Fig. 5B). In contrast, and in accordance with previous reports, cyclin D1 was overexpressed at the tumor initiation stage and up to 6 weeks after tumor occurence compared to control adjacent tissue (Fig. 5C, lanei and 4 versus lanes 2-3 and 5-6, respectively)30'31. Moreover, the cyclin D1 protein levels showed a reciprocal response to p27kιp, with elevated expression observed in absence of p27kιp (Fig. 5B versus Fig. 5C). Consistent with the tumor progression data described above, cyclin D1 expression levels were significantly higher when PTP1 B was present (Fig. 5C, lanes 2-3 versus 5-6). These results strongly suggest that the requirement for cyclin D1 in ErbB2- induced mammary gland tumorigenesis is dependent on PTP1 B.
 It is also reported herein that PTP1 B deficiency triggers apoptosis earlier in ErbB2-induced breast tumors.
 Since hyperactivation of the PI3K/Akt pathway in tumors overexpressing ErbB2 has been reported to prevent tumor cell apoptosis in breast cancer32, the apoptotic status in tumor samples was monitored by cleavage analysis of poly(ADP-ribose) polymerase (PARP). Full-length PARP (115 kDa) is known to be cleaved by activated caspase-3, which yields a 85 kDa cleavage product. In NDL2-PTP1 B+/+ animals PARP cleavage was visibly evident only 6 weeks after tumor onset whereas this cleavage event was readily detected 2 weeks earlier in NDL2-PTP1 B null mice (Fig. 6A, lanes 3-4 versus 7- 8). To further confirm these results caspase-3 activation in these samples was also determined. As expected, the 17 kDa activated caspase-3 cleavage product is increased in NDL2-PTP1 B-/- breast tumor samples 6 weeks following tumorigenesis onset compared to NDL2-PTP1 B+/+ samples (Fig. 6B, lane 6 versus 3), suggesting a higher number of apoptotic events in breast tumor in the absence of PTP1 B.
 As determined by immunohistochemistry of breast tumor samples at 6 weeks after tumor occurence, the percentage of PCNA-positive nuclei was significantly higher in NDL2-PTP1B+/+ tumors (85 ± 11 %) than in NDL2- PTP1 B-/- tumors (36 ± 15 %; P<0.05) (Fig. 6C). In contrast, the percentage of cleaved-caspase 3-positive cells was almost undetectable in NDL2-PTP1 B+/+ tumors (1.2 ± 0.7%) compared to NDL2-PTP1 B-/- tumors (2.9 ± 1.1 %; P<0.05) (Fig. 6C). This suggests that protection from invasiveness in NDL2-PTP1 B null mice may be due to both decreased proliferation and increased cell loss.
 We also show that administration of a selective orally available PTP1 B inhibitor to NDL2-PTP1 B+/+ mice delays breast tumor development.
 The genetic results presented here provide strong evidence that PTP1 B plays a critical and positive role in human related ErbB2-induced breast cancer and suggest that inhibition of this enzyme may be beneficial in the treatment of this disease. To determine if PTP1 B inhibition would provide the same delay in tumorigenesis as was observed for the PTP1 B genetic deficiency a specific orally available PTP1 B inhibitor33 was used to treat NDL2-PTP1B transgenic mice. The effect of PTP1 B inhibition in these animals was monitored by measurement of glucose levels during the 21 days of treatment. It is known that PTP1 B deficiency results in enhanced insulin sensitivity and decreases in blood glucose levels. Treatment of the NDL2 transgenic mice with the PTP1 B inhibitor resulted in blood glucose lowering during the time course of treatment comparable to the levels observed in the NDL2-PTP1 B-/- mice. Treatment of NDL2-PTP1B-/- mice with the compound had no effect on blood glucose levels suggesting specific target engagement (Supplementary Fig. 3).
 When the time course of tumor development (Fig. 7) was determined there was a significant delay in the onset of mammary tumor development in the PTP1 B inhibitor-administered NDL2-PTP1B+/+ mice group (T50=28 days) compared to the vehicle-administered NDL2-PTP1B+/+ group (T50=75 days, P<0.001 ). Tumors arose in a synchronous manner between 20 to 50 days after the end of treatment in all vehicle-administered NDL2-1 B+/+ mice. The first palpable tumor in the PTP1 B inhibitor-administered NDL2-PTP1 B+/+ group occurred 48 days after the end of treatment and 20 days later, 90% of the animals had developed tumors, with a significant delay of approximately 29 days compared to the vehicle-administered NDL2-1 B+/+ mice. Two mice still remained tumor-free after more than 75 days after the end of treatment. These results strongly suggest that PTP1 B may represent a valuable therapeutic target for anti-cancer applications.
 It is also reported herein that tissue specific over-expression of PTP1 B in breast induces mammary gland tumorigenesis.
 In order to evaluate the potential of over-expressed PTP1 B to promote mammary gland tumor initiation and progression, transgenic mice were generated in which wild-type PTP1 B, fused to enhanced green fluorescent protein (EGFP), was expressed specifically in the mammary gland (Fig. 8A). Transgenic protein expression was directly correlated to the increased numbers of litters (Fig. 8B, lane 2 versus lanes 1 and 4) and was also concomitant to a dramatic increased in endogenous PTP1 B protein levels (Fig. 8B, lane 2 versus lanes 1 and 4) and to mammary gland transformation (Fig. 8C). Indeed, microscopic analyses revealed that the histopathology of the mammary gland in MMTV-EGFP-PTP1 B transgenic mice was markedly different depending on the numbers of litters delivered by the mothers. After only 2 pregnancies, mice presented usual mammary ductal hyperplasia (Fig 8C, panel C) whereas 7 litters have induced adenocarcinoma infiltrating the fat pad (Fig. 8C, panel D). Supplementary Table 1 summarizes the phenotypic abnormalities derived from 4 different mouse lines. Taken together our findings confirm that PTP1 B alone is capable to drive the observed carcinoma and that it possesses oncogenic properties or at least, positively contributes to the transformation process on its own.
 To investigate the role of PTP1 B in tumorigenesis, we used a genetic approach by breeding PTP1 B null mice35 with a breast cancer transgenic strain expressing the Neu/ErbB2 mutant (Neu deletion in extracellular domain 2, NDL2) driven by the MMTV-LTR promoter6'7. The NDL2 mouse is a well established breast cancer model6 and replicates many of the events that occur in human breast tumor progression, including the erbB2 in-frame deletion mutation7'10. In the present study, we report that the genetic deletion or pharmacological inhibition of PTP1 B results in delayed ErbB-2-induced breast tumorigenesis. In addition, NDL2-PTP1 B-/- mice are resistant to lung metastasis and the effects may cumulate through the regulation of cyclin D1 expression, as well as apoptosis triggered by the down-regulation of MAPK and AKT signaling pathways. These results constitute the first genetic and pharmacological evidence that PTP1 B plays a critical role in breast tumor development.
 The findings presented herein are surprising and unexpected since PTP1 B acts as negative regulator of multiple RTKs and consequently, inhibition of this enzyme leads to increased activation of these receptors and should promote oncogenic signaling. We have recently reported that this is indeed the case in a p53 deficient background, where genetic ablation of PTP1 B accelerates the rate of tumor development17. However, in this case the total removal of PTP1 B appears to lead to an increase in the pre B-cell population, which in the absence of p53 is seemingly more prone to develop B lymphomas. In addition, tissue-specific over-expression of PTP1 B in mammary gland leads to breast tumorigenesis suggesting true oncogenic property for this phosphatase. Interestingly, we observed a dramatic increase of endogenous PTP1 B in mammary gland with increased numbers of litters concomitant with breast transformation. Our findings clearly support a positive role for PTP1B during immortalization and transformation and probably by a cell autonomous manner.
 Our results also demonstrate that loss of PTP1B decreases ErbB2 activity, as well as ErbB2 and ErbB3 expression levels during mammary tumor progression. Consequently, a decrease in activation of downstream effectors such as MAPK and AKT is observed. This is in agreement with recent studies reporting AKT activation in breast cancer, due to the ability of ErbB3 to couple preferentially with the PI3-K/AKT pathways32 36'42. Finally, we propose that PTP1B may directly link ErbB2/ErbB3 signaling to cyclin D1 regulation and p27 stabilization via its substrate p62Dok, thus subsequently acting in a synergistic fashion on both MAPK and AKT pathways.
 The induction of the cell-death pathway in NDL2-PTP1 B null mice is an important feature since it could be combined to chemotherapy in the treatment of breast cancer. For instance, resistance to chemotherapy-induced apoptosis could be overcome by blocking the anti-cell death pathway with a PTP1 B inhibitor. Interestingly, ablation of PTP1 B has no consequences on adult mouse physiology, suggesting that anti-PTP1 B therapy might be highly selective in preventing breast tumorigenesis. Moreover, since NDL2-PTP1 B-/- animals are resistant to lung metastasis, shorter treatments with a PTP1 B inhibitor should be investigated in clinical studies in patients suffering of breast cancer. Indeed, we obtained strong and hopeful results with PTP1B inhibitor in our in vivo assay as shown in Fig. 7.  Our findings have therapeutic implications and we propose, as described herein, that patients having cancer, e.g. ErbB-2 positive breast cancer, might benefit from pharmaco-inhibition of PTP1 B activity alone or in combination with anti-ErbB2 therapies.
 In order to clarify the role of PTP1 B in oncogenesis we also investigated the function of PTP1 B in prostate cancer. PTP1 B expression in prostate tumor sections from human prostate cancer patients was assessed using immunohistochemistry. Progression of disease in the patients was also assessed by measuring PSA levels in the samples, where a PSA increase above 0.3 ng ml 1 was defined as postoperative recurrence of the disease. It was found that elevated PTP1 B expression in prostate tumors correlates with disease recurrence as measured by PSA levels, Gleason grade, Extracapsular invasion, seminal vesicle invasion and survival functions, as shown in Tables 1 and 2 below and in Figure 9.
 Table 1 indicates correlations between PTP1 B staining intensity in tumors and clinico-pathological parameters. Table 2 indicates correlations between PTP1B staining intensity in normal tissues and clinico-pathological parameters. This data shows a strong correlation between elevated PTP1B expression in prostate tumors and prostate cancer. Figure 9 shows prostate- specific antigen recurrence-free survival curves plotted using the Kaplan-Meier analysis and the log-rank test, wherein the lower curve (pink) illustrates survival for patients expressing a high level of PTP- 1 B in prostate tumors, and the upper curve (green) illustrates survival for patients expressing low levels of PTP- 1 B in prostate tumors. It can be seen that approximately 70% of patients expressing a high level of PTP-1 B had relapsed within 80 months, whereas for patients expressing low levels of PTP-1 B, approximately 50% still had not relapsed after 150 months. Thus elevated PTP- 1 B expression in prostate tumors is correlated with disease progression and may predict an earlier biochemical relapse.
 These results suggest that PTP1 B plays an important role in prostate cancer tumor development and that patients having prostate cancer might benefit from pharmaco-inhibition of PTP1 B activity alone or in combination with other anti-cancer therapies. In addition, the results also suggest that PTP1 B expression will be a valuable marker or tool for diagnosis, prognosis and monitoring of disease progression for cancers such as prostate cancer.
 The examples described herein are given to illustrate the invention rather than to limit its scope, and were performed using the methods described below.
 The following antibodies were used for immunoblotting and immunoprecipitation: anti-phosphoT202/Y204-anti-p42/p44 MAPK, anti-p42/p44 MAPK, anti-caspase-3, anti-cleaved caspase-3, anti-phosphoS473-AKT, anti- AKT, anti-p27 (Cell Signaling Technology, Beverly, MA); anti-phosphotyrosine 4G10, anti-ErbB3, anti-PTP1 B (Upstate Biotechnology, Lake Placid, NY); anti- Grb2, anti-cyclinD1 , anti-PARP, anti-Dok1 (Santa Cruz Biotechnology, Santa Cruz, CA); anti-p120RasGAP (Transduction Laboratories, Lexington, KY); anti- phosphoY529Src, anti-Src (Biosource International, Inc.Camarillo, CA); anti- ErbB2, anti-PCNA (EMD Biosciences, San Diego, CA). Anti- phosphoY449p62Dok was a generous gift of American Proteomix (Carlsbad, CA).
Mouse experimental procedure
 PTP1 B+/' and ~'~ mice were generated as previously described35 and were backcrossed with FVB/J wild-type mice for seven generations to introduce the targeted PTP1 B alleles onto a FVB background. ErbB2/neu transgenic (TG) mice have been generated in FVB strain by the expression of a neu deletion mutant (NDL2) cDNA under the transcriptional control of the MMTV-LTR6'7. MMTV/NDL2 and PTP1 B mice were interbred to generate females of the required genotypes: NDL2-PTP1 B+/+ (ErbB2/neu TG- WT PTP 1 B-), NDL2- PTP1B+/- (ErbB2/neu TG- heterozygous PTP1B), and NDL2-PTP1B-7- (ErbB2/neu TG- null PTP1 B). Genotypes for PTP1 B and Neu were determined by Southern blot and PCR analysis respectively7'35. Mice were kept on a 12h light/12h dark cycle and were allowed free access to food and water. Animals were monitored daily for physical well-being and were examined twice a week for tumor occurrence. We generated MMTV_EGFP_PTP1B transgenic mice by microinjecting the linearized expression construct into the pronucleus of FVBN mouse embryos at day 0.5 p.c. Injected embryos were implanted into pseudopregnant CD-1 female mice. Progenies were screened by PCR of tail biopsies. Mice positive for the transgene were mated to WT FVBN mice. All procedures were carried out according to the Canadian Council on Animal Care ethical regulations and were approved by the McGiII University Research and Ethics Animal committee.
PTP1B inhibitor treatment
 PTP1 B inhibitor was synthesized at Merck Frosst Canada Ltd., and the methods of synthesis have been described33. PTP1 B compound was administered (30 mg/kg body weight) daily by oral gavage with an injection volume of 10 ml/kg body weight for 21 days. Vehicle solution consisted of 0.5% methylcellulose (Sigma Aldrich). Solutions were freshly prepared before each administration. Mice were sacrificed 10 days after tumor occurrence.
Mammary tissue harvesting
 Tissue samples were ground into a powder under liquid nitrogen and lysed for 30min on ice in a modified TLCK lysis buffer (50 mM HEPES pH 7.4; 10% Glycerol; 1 % Triton X-100, 150 mM NaCI; 1 mM EGTA, pH 8.0; 1 mM sodium orthovanadate; 20 mM NaF; Complete EDTA-free protease cocktail inhibitors). The cell lysates were cleared by centrifugation at 12,000 g for 15min at 4°C.
 Total mammary gland lysates (200μg) were incubated with 20 μ\ of protein A-Agarose and with 2//g of anti-ErbB2 antibody for 3h, rotating at 4C° in 400 μ\ of modified TLCK lysis buffer. After five washes with the lysis buffer, precipitated proteins were released by boiling in sample buffer and then subjected to western blot analysis.
 20 μg of total mammary gland proteins was separated by SDS-PAGE using 4-12% gradient gel or 10% gels and then transferred to PVDF membranes, which were then blocked with 6% (w/v) milk-3% BSA in Tris- Buffered saline (TBS) containing 0.1% Tween-20. Membranes were probed overnight with primary antibodies (1/1000 dilution for all antibodies used). After incubation with specific HRP-conjugated antibodies, protein bands were revealed by the ECL detection system.
 Complete necropsies were performed and tissues used for histology and immunohistology were fixed in 10% neutral buffered formalin and embedded in paraffin, sectioned at 4μm, stained with hematoxilin and eosin, and examined for pathological findings. PCNA-positive nuclei and cleaved caspase-3-positive cells were visualized in paraffin sections. HRP-linked secondary antibodies were used (Cell Signaling Technology, Beverly, MA). The color reaction was developed using 3-3_-diaminobenzidine tetrahydrochloride (DAB) as a chromogen (SigmaFast DAB tablets; Sigma).
Mammary glands whole mounts
 Inguinal mammary glands number four were dissected and spread onto glass slides. Samples were fixed overnight in acetone and then stained for 24 hours in Modified Harris Hematoxilin. After several washes in 1 % HCI/70% ethanol, samples were cleared overnight in xylene and mounted with permount. Samples were examined under a dissecting microscope.
 Animals were monitored and examined twice a week for blood glucose and tumor occurrence. The measurements were made by removing blood from the tail vein and placing one drop on Advantage II® reactive tape. The glycemia level was read using the Glucometer® apparatus. Mice were sacrificed 10 days after tumor occurrence.
Patient cohort for prostate cancer studies
 Paraffin-embedded human primary prostate cancer specimens from patients having provided informed consent and operated from 1993 to 2000 were reviewed. In total, 64 specimens were included in the study to create a tissue array. Criteria for the retrospective cohort study to create the tissue arrays were: no preoperative treatment was used in this cohort, and all cases had clinical follow up of at least 5 years or until death. Patients were followed for an average range of 72 months. No age difference was observed between the group of patients who relapsed and the group that did not. Preoperative PSA level was available for 62 patients. Postoperative PSA was available for all patients. PSA nonfailure was defined as PSA remaining below 0.3 ng/ml 1 after radical prostatectomy. Biochemical recurrence-free survival was defined as the time between date of surgery and the date of first PSA increase above 0.3 ng/ml 1. The final staging, grading and histologic diagnosis was based on the Hospital Notre-Dame (Montreal, QC, Canada) pathology report in agreement with the review from an independent pathologist. Ethics approval was obtained from the local IRB committee.
lmmunohistochemistry for prostate cancer studies
 PTP1 B expression in prostate tumor sections was assessed using the polyclonal Rabbit Anti-human PTP1 B Antibody AF1366 (R&D Systems, Minneapolis, MN). lmmunostaining was performed using the biotin-streptavidin- peroxydase method. Briefly, formalin-fixed paraffin-embedded sections were deparaffinized in toluene and rehydrated through graded ethanol followed by distilled water. Antigen retrieval was done heating slides in the microwave for 15 minutes in citrate buffer (pH 6,0). Non specific sites were blocked with goat serum and slides were then incubated with the primary antibody at a 1/300 dilution for 2 hrs at room temperature. Endogenous peroxydase was quenched in 3% hydrogen peroxide. A biotinylated goat anti-rabbit secondary antibody followed by streptavidin-HRP (Lab Vision, Fremont, CA) were applied for 20 minutes each. All rinsing steps between antibodies were done in PBS-T for 5 minutes. Chromogen reaction using a 3,3'-diaminobenzidine tetrahydrochloride (DAB) solution kit (Lab Vision, Fremont, CA) was carried out for 5 minutes. Slides were counterstained with Harris Hematoxylin for 10 seconds, dehydrated in ethanol and toluene and then mounted.
Scoring and statistical analysis for prostate cancer studies
 Tumour sections were inspected at 2Ox and 4OX magnification. Epithelial zones were scored according to the intensity of staining of the cytoplasm (value of 0 for absence, 1 for weak, 2 for moderate, 3 for high intensity). In cores where staining was of variable intensity the average intensity was reported. The Spearman and Pearson correlation coefficient tests (two tailed) were used to estimate the correlation with clinicopathologic variables. Prostate-specific antigen recurrence-free survival curves were plotted using the Kaplan-Meier analysis and the log-rank test was used to test for significant differences. Receiver operative characteristic (ROC) curves were used to determine the threshold value.
 While the invention has been described in connection with specific embodiments thereof, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses, or adaptations of the invention following, in general, the principles of the invention and including such departures from the present disclosure as come within known or customary practice within the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth, and as follows in the scope of the appended claims.
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WHAT IS CLAIMED IS:
1. A method of screening for an anti-cancer therapeutic or for identifying an anti-cancer agent, comprising assaying for inhibition of PTP1B.
2. A method of diagnosing or prognosing cancer in a subject, comprising measuring PTP1 B expression or levels in a subject, wherein elevated PTP1 B levels are diagnostic of cancer or of a predisposition to cancer.
3. A method of selecting a subject for treatment with a PTP1 B inhibitor, comprising measuring PTP1 B levels in a tumor in a subject, wherein a subject with elevated PTP1 B levels is selected for treatment with a PTP1 B inhibitor.
4. A kit for assigning a treatment to a patient, comprising one or more than one reagent for measuring PTP1 B expression in a sample from said patient and instructions for use of said one or more than one reagent, wherein a patient with elevated PTP1 B expression is assigned treatment with one or more PTP1B inhibitors.
5. The kit of claim 4, wherein the patient has cancer.
6. The kit of claim 5, wherein the patient has breast cancer, prostate cancer, lung cancer, ovarian cancer, lymphoma, or metastases thereof.
7. The kit of claim 4, 5 or 6 wherein the sample comprises cancerous cells.
8. The kit of claim 4, 5, 6, or 7 wherein the reagents are PCR reagents.
9. The kit of claim 4, 5, 6, or 7 wherein the reagent is an antibody.
10. The kit of claim 4, 5, 6, or 7 wherein the reagent is a DNA probe.
11.The kit of claim 4, 5, 6, or 7 wherein the reagent is an aptamer.
12. The kit of claim 4, 5, 6, or 7 wherein the reagent is a small molecule.
13. The kit of claim 13, wherein the small molecule is tagged with a detectable agent for imaging purposes.
14. A method for assigning a treatment to a patient, comprising isolating a sample from said patient and measuring PTP1 B expression in the sample, wherein the patient is assigned treatment with one or more PTP1 B inhibitors if PTP1 B expression is high.
15. The method of claim 14, wherein the patient has cancer.
16. The method of claim 15, wherein the patient has breast cancer, prostate cancer, lung cancer, ovarian cancer, lymphoma, or metastases thereof.
17. The method of claim 14, 15 or 16 wherein the sample comprises cancerous cells.
18.A method of treating or preventing cancer in a subject in need thereof, comprising administering to said subject a therapeutically effective amount of an inhibitor of PTP1 B.
19. The method of claim 18, wherein the cancer is breast cancer or its metastases.
20. The method of claim 18, wherein the cancer is ovarian cancer or its metastases.
21. The method of claim 18, wherein the cancer is lung cancer or its metastases.
22. The method of claim 18, wherein the cancer is a lymphoma or its metastases.
23. The method of claim 18, wherein the cancer is prostate cancer or its metastases.
24.A method of treating or preventing cancer in a subject being treated with a first anti-cancer treatment, comprising administering to said subject a therapeutically effective amount of an inhibitor of PTP1 B.
25.A method of treating or preventing cancer in a subject in need thereof, comprising administering to said subject a first anti-cancer treatment in combination with a therapeutically effective amount of an inhibitor of PTP1 B.