TASK ORDER: EVALUATION OF TWO DIFFERENT CLASSES OF COMPOUNDS (STAT3 INHIBITORS AND SERMS) FOR THE PREVENTION OF URINARY BLADDER CANCER

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Urinary bladder cancer is one of the most prevalent malignancies of the urinary system, with over 80,000 new cases predicted in the United States in 2019. Although 70% of patients initially present with non-muscle-invasive disease, urinary bladder tumors have a high rate of recurrence (50 –70%), and 10-15% will progress to muscle-invasive disease within a 5-year period, making the prevention of bladder cancer an important priority. Throughout the years, a relatively large number of compounds have been tested for efficacy in the prevention of early stage bladder cancers. However, many of these agents have proven to be largely ineffective or toxic to various organs. Thus, there is a need for the identification of new chemopreventive agents with novel mechanisms of action. Estrogen receptor α (ERα) is expressed in 18% of patients with bladder cancer and is associated with highly proliferative tumors and lower overall survival; ERβ is expressed in 63% of bladder cancer tumors, and the degree of ERβ expression increases with increasing stage and grade of differentiation. These correlations, combined with the findings that N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN)-treated mice lacking ERβ have a reduced incidence of bladder cancer, suggest that the ER could serve as a target for preventive intervention. In support of this, several groups have reported that estrogen receptor modulators reduce bladder cancer cell proliferation in vitro, and reduce cancer incidence in BBN-treated mice. This Task Order will evaluate the selective estrogen receptor modulator bazedoxifene for bladder cancer prevention. Bazedoxifene has affinity for both the ERα and ERβ receptors, and it is a competitive inhibitor of 17-β-estradiol at either estrogen receptor. It is also highly effective as a chemopreventive agent in the N-Nitroso-N-methylurea (MNU)-rat model, in which breast cancer development is driven by expression of the ER. Signal transducer and activator of transcription 3 (STAT3) is one of the seven members of a family of transcription factors that regulates cell proliferation, differentiation, apoptosis, and the immune response. Although the activation of STAT3 is transient and highly regulated in normal cells, it is constitutively active in several types of cancer, including bladder cancer. The findings that the expression of dominant-negative STAT3 inhibits bladder tumor formation and that the STAT3 inhibitor WP1066 reduces cell survival and proliferation of bladder cancer cells support a role for STAT3 in bladder cancer carcinogenesis and suggest that STAT3 could serve as a target for preventive intervention. This Task Order will also investigate the chemopreventive potential of the STAT3 inhibitor GLG-302 and its structural analogs in a model of human bladder cancer. GLG-302 reduces tumor multiplicity in the MMTV-Neu mouse model of mammary cancer, and its structural analogs, including SH5-07, BP-1-102, and SH4-54, are reported to have improved bioavailability and in vitro potency. The Chemopreventive Agent Development Research Group is currently in the process of further optimizing this class of STAT3 inhibitors.