Patients with advanced prostate cancer typically undergo hormonal therapy to block androgen production (LHRH agonist) and/or block androgen receptor (AR) activity (antiandrogens). Unfortunately, development of resistance to hormonal treatments is common, resulting in hormone-refractory prostate cancer. Despite this hormone-refractory state, tumors retain dependence upon the AR for growth. Indeed, recent studies suggest that AR overexpression is a critical step in the progression to a hormone-refractory state. Thus, the identification of new antiandrogens, designed to inhibit prostate cancer cell growth in systems where AR is overexpressed, is an important step in the design of novel therapies for the treatment of this disease. Traditionally, AR antagonists have been identified in an empirical manner with chemistry being guided primarily by in vitro ligand binding assays, followed by secondary transcriptional reporter gene assays that measure functional antagonism. These approaches have been successful, however, the clinically approved antiandrogens appear to be mechanistically similar and exhibit partial agonist activity that limits their effectiveness in treating hormone-refractory disease. The rational design of next generation antiandrogens will require more sophisticated screening methodologies. During this Phase 1 program, we will employ a novel strategy to tackle this important problem by using an approach that takes advantage of our current understanding of the molecular determinants of AR action and the observation that nuclear receptor pharmacology is mediated in large part by the ability of these transcription factors to interact in a differential manner with either transcriptional co-activators or co-repressors. We will use an optimized T7 phage display technology to perform a comprehensive screen for proteins that interact with antagonist bound AR. These interacting proteins will then be used to develop a """"""""receptor conformation profiling tool"""""""" (RCPT) that will allow us to identify compounds that enable differential cofactor interactions. Using this tool, we will attempt to identify several mechanistically distinct antiandrogens, some of which may be predicted to dramatically suppress AR activity and effectively suppress hormone-refractory tumor growth. In the estrogen receptor field, compounds of this nature (Faslodex(R)) have proven to be useful in the treatment of breast cancer that has become refractory to first line hormonal therapy. The stated objective of this proposal is to generate a RCPT capable of discriminating between mechanistically distinct antiandrogens. The validity of the RCPT will be tested by assessing its ability to predict the activity of compounds in pre-clinical models of androgen-dependent and -independent disease. Insights gained from this Phase 1 study will then be used to optimize novel lead compounds for the treatment of hormone-refractory prostate cancer in a Phase 2 funding period aimed at commercialization.
Androgens like testosterone, acting through the androgen receptor (AR), are not only responsible for the development and maintenance of the normal secondary sexual characteristics (growth of sex accessory organs, body and facial hair growth, increase in muscle mass) associated with adolescence in males, but are also critical for prostate gland development and are causally linked to the progression of prostate cancer. Indeed, prostate cancer is often initially responsive to hormonal therapies targeting androgen production or the AR itself. However, through mechanisms that often result in heightened AR activity, resistance to currently available therapies arises and the cancer progresses to a hormone-refractory state. Our proposed goal is to use state-of-art protein-protein interaction screening technology to develop and validate a novel drug discovery tool capable of identifying novel antiandrogens that function in a different way from currently used AR antagonists. Successful completion of this Phase 1 project will allow the implementation of this novel screening tool for use in the discovery and validation of new classes of mechanistically unique AR antagonists predicted to have efficacy in hormone-refractory disease during a Phase 2 funding period.
