Prostate cancer is listed as a primary diagnosis for approximately 16% of older male VHA users, and contributes significantly to morbidity and mortality rates in these individuals. The majority of VA patients with metastatic prostate cancer, similar to most non-VA patients in the United States, receives hormonal treatment which is initially effective, but frequently fail indicative of the development of castration resistant prostate cancer (CRPC). The treatment options for patients who fail hormonal therapy are limited, despite numerous clinical trials testing multiple drugs. Hence, our laboratory has undertaken the innovative overall strategy of identifying therapeutic targets that can prevent prostate cancer progression to castration resistance, rather than trying to cure it after it has already developed. Studies performed during the previous funding period, which resulted in 14 publications in related topics, contributed to understanding the importance of the cell survival regulator Akt in prostate cancer development and progression. While a number of Akt inhibitors have been developed commercially, their utility has been compromised by high levels of toxicity when used in human patients, caused by the induction of apoptosis in normal tissue including non-tumor prostate regions. As a result, a goal of the project was to identify natural antagonists of Akt that selectively counteract the effects of the increase in Akt phosphorylation in the tumor without affecting basal levels of Akt activation in other cells. Two of our recent publications demonstrate that Filamin A (FlnA) may be one such protein. In vitro studies showed that FlnA localization to the nucleus resulted in castration sensitive growth of prostate cancer cells which was mediated by antagonism of Akt phosphorylation and its downstream effectors. FlnA nuclear localization is regulated by its phosphorylation, which in turn is regulated by PKA activity. The effects of FlnA nuclear localization are likely caused by its interaction with the androgen receptor (AR), a nuclear steroid receptor mediating the effects of the androgens on cell mechanisms. Therefore, in the current application, we will investigate the role nuclear FlnA plays in regulating castration sensitive cell behavior. We hypothesize that FlnA counters the effects of Akt phosphorylation and its downstream effectors, and that its localization is in turn regulated by its phosphorylation. The following aims will test this hypothesis.
Specific Aim 1 : To test the hypothesis that FlnA 16-24 nuclear localization sensitizes prostate cancer cells to androgen withdrawal by preventing the effects of Akt on AR activity and cell survival. We will determine whether FlnA16-24 induces sensitivity to androgen blockade in CRPC cells by antagonizing an Akt- dependent signaling pathway and preventing AR/TIF2 interactions. We will also investigate whether nuclear localization of FlnA 16-24 induces apoptosis by repressing NF-kB activation and stimulating AR-dependent p21Cip1 transcription.
Specific Aim 2 : To test the hypothesis that FlnA phosphorylation is a key factor responsible for preventing FlnA nuclear localization in castrate resistant prostate cancer. We will examine whether FlnA phosphorylation prevents FlnA nuclear localization and causes castration resistance in prostate cancer cell lines expressing a functional AR. We will also determine whether inhibition of FlnA phosphorylation prevent the development of castration resistance in a mouse model of recurrent prostate cancer.
Specific Aim 3 : To test the hypothesis that increased FlnA phosphorylation and decreased FlnA nuclear localization predict time to treatment failure in VA patients with metastatic prostate cancer on androgen withdrawal therapy who did not undergo radical prostatectomy. We have identified patients within the VA Northern California System who presented with metastatic prostate cancer. We will determine in biopsies of the prostates of these patients the localization of Filamin A, FlnA phosphorylation, AR levels and Akt phosphorylation and determine whether they respond to androgen withdrawal therapy.