Genomic Guided Therapy With Dasatinib or Nilutamide in Metastatic Castration-Resistant Prostate Cancer

This is a phase II multi-center study to determine the clinical impact of using a patient-specific genomic expression signature of androgen receptor (AR) activity to determine therapy for patients with castration-resistant metastatic prostate cancer (CRPC). After patient eligibility is determined, the genomic signature will be applied to fresh frozen tissue harvested from a metastatic lesion during image-guided biopsy. After assessing for androgen receptor activity, the investigators will select patients for either continued androgen manipulation with nilutamide (high AR activity) or targeted therapy with dasatinib (low AR activity). Once patients develop a first progression on either arm, patients will receive combination therapy with dasatinib and nilutamide. The primary aim is to estimate the median progression free survival in men with CRPC treated according to tumor AR activity. The investigators hypothesize that by treating men based upon AR activity, median progression free survival (PFS) will improve from a historical median of 3.0 months to 6.0 months.

Prostate cancer is the most commonly diagnosed non-cutaneous malignancy of men in the United States and remains the second leading cause of cancer-related mortality among men. Novel approaches are necessary to personalize and improve treatment. The androgen receptor (AR) plays a critical role in the normal development and function of the prostate and promotes growth in most prostate cancers. Most patients with advanced prostate cancer have cancer that will initially respond to androgen-targeting therapy (focusing on decreasing the circulating levels of testosterone which is the primary source of ligand for the AR receptor). However, castrate resistance usually develops within 18 to 24 months and the median survival of men with castration resistant prostate cancer (CRPC) ranges between 12 to 18 months. Current options are limited including: secondary hormonal manipulations, radiopharmaceuticals, and chemotherapy and only docetaxel, a taxane that targets microtubules, has been proven to prolong survival. Importantly, it has become clear that for some patients with CRPC, the prostate tumors remain dependent on AR activity. This has been supported by studies demonstrating different genetic and metabolic mechanisms by which prostate cancer cells maintain AR activity despite low levels of circulating androgen. An assay detecting AR activity that more comprehensively reflects the variety of mechanisms by which AR activity is preserved has the potential to accurately differentiate between men who have tumors still dependent on AR activity from those that are truly independent of AR activity. The identification of patients with continued AR activity has the potential to improve response to secondary hormonal manipulations; men with tumors having low levels of AR activity are likely to require alternative approaches. We have developed a transcriptional "signature" for AR activity with the goal of identifying the true status of AR in tumors of men with CRPC. After validating the AR signature on in vitro and human prostate samples to ensure that it accurately and reproducibly detects AR activity, we applied the AR signature to several independent datasets to determine the distribution of CRPC tumors with preserved AR activity. Interestingly, there is consistent heterogeneity with respect to predicted AR activity. While overall AR activity decreases in CRPC, there is a subgroup of patients with persistently elevated AR activity. In tumors with low AR activity, we observed that the probability of AR activity was negatively correlated with predicted SRC activity in localized prostate cancer and CRPC. Patients with persistently high AR activity will be treated with nilutamide, an approved oral agent used in metastatic CRPC to target the AR. Patients with tumors having low AR activity will be treated with dasatinib (an oral drug known to target the SRC family kinases). As there is compelling pre-clinical evidence of interactions between the SRC pathway and AR signaling, patients failing either single agent treatment will be treated with the combination of nilutamide and dasatinib and followed again for progression.