GENETIC ALTERATIONS IN PROSTATE CANCER: EVALUATING THEIR BIOMARKER POTENTIAL AND ROLES IN THERAPEUTIC RESPONSE AND RESISTANCE

Prostate cancer (PCa) continues to be a leading cause of cancer-related death in United States men due to the subset of patients who develop metastatic disease. In spite of recent advances, two substantial clinical challenges remain today: identifying who is at risk for (1) metastatic recurrence and (2) developing resistance to current therapies. In order to address these two main challenges, three novel approaches were taken to evaluate the potential of PCa genetic alterations as biomarkers and the roles that these genetic alterations have in therapeutic response and resistance. For our first study, genetic aberrations discovered by the next-generation sequencing (NGS) of patients’ primary tumor DNA (which was isolated from radical prostatectomy samples) were probed for by droplet digital PCR (ddPCR) in the corresponding patient’s plasma-derived cell-free DNA (cfDNA) isolated before radical prostatectomy. Determining if it is possible to assess the genetic landscape of primary PCa by liquid biopsy, may ultimately lead to the discovery of biomarkers for disease risk stratification as well as the ability to better predict disease outcomes and treat localized PCa patients. For our second study, metastatic castration-resistant prostate cancer (mCRPC) patients were prospectively enrolled in order to validate gene alterations, such as androgen receptor (AR) ligand-binding domain (LBD) mutations and/or AR copy number (CN) gain, detected in cfDNA as markers of enzalutamide and abiraterone resistance. Here, we show that AR LBD missense mutations are associated with a shorter progression-free survival (PFS). In addition, loss of the tumor protein p53 (TP53) gene and defects in the phosphoinositide 3-kinase (PI3K) pathway are associated with a worse overall survival (OS). In our third study, the CRISPR/Cas9 system was used to generate an isogenic panel of PCa cell lines, containing both individual and multiple hotspot AR LBD mutations. The findings from these in vitro models will illuminate the biological role that these genetic alterations have in resistance to contemporary next-generation therapies, such as abiraterone and enzalutamide. Taken together, our studies provide valuable insight on how to better identify which PCa patients are at risk for developing lethal disease and resistance to current treatments