ABSTRACT | FULL RESEARCH PROJECT 1 Puerto Rican (PR) Hispanic/Latino (H/L) men have the highest prostate cancer (PCa) mortality among Hispanic populations. According to the recent PR Cancer Registry data, PCa is the leading cancer type in terms of incidence (35% of all cancer cases) and mortality (17% of all cancer deaths) in PR H/L men. They have significantly higher PCa-specific mortality than non-Hispanic white (NHW) and non-Hispanic Black (NHB) men; addressing this gap constitutes our central efforts. While socioeconomic status and access to healthcare are contributors, manifest differences in molecular features between racial groups highlight the role of tumor biology in racially disparate outcomes in PCa. Our long-term goal is to identify DNA methylation biomarkers driving gene expression changes that underly PCa therapy resistance and aggressiveness in at-risk populations, particularly PR H/L men. The central hypothesis is that differences in tumor DNA methylation patterns and population admixture are associated with drug response and aggressiveness in PCa in PR H/L men. The rationale is that identifying the molecular basis of PCa disparities will serve to reduce the burden of lethal PCa disparities affecting PR H/L men. Our goals will be accomplished through two Specific Aims: Aim 1) Investigate associations between aggressiveness and methylated genes in PCa among the PR H/L population and the impact of methylation on their expression. (1a) Investigate differentially methylated genes associated with drug resistance and aggressiveness among PR H/L PCa patients and compare with methylation data from NHB from the Florida PCa biobank, NHW PCa patients from MCC, and TCGA. (1b) Evaluate differential DNA methylation on gene expression patterns. We will establish comparisons with previous data obtained from NHW men from MCC and TCGA. (1c) Evaluate whether population admixture will modify the methylation level of PR-specific methylated genes. Further, we will investigate whether genes that contain ancestry determinants are associated with the aggressiveness of PCa and disparity. Aim 2. Assess the contribution of DNA methylation to PCa resistance to standard therapies using drug-resistant PCa sublines and liquid biopsies from PCa patients progressing after treatment. (2a) Identify differentially methylated genes associated with drug-resistant phenotypes using cell- based models of drug resistance including castration resistance, enzalutamide resistance, and docetaxel resistance. (2b) Evaluate the expression of differentially methylated genes in resistant sublines compared to sensitive cell lines. (2c) Assess the effect of DNA methylation inhibition on drug sensitivity in resistant phenotypes. (2d) As an exploratory aim, we will evaluate resistance-associated methylation profiles in blood samples from PR and MCC patients previously treated with androgen deprivation therapy, androgen receptor- targeting agents, or taxane-based chemotherapy. The ident...