A personalized medicine approach to identifying dysregulated epigenetic enzymes in the development of castrate-resistant prostate cancer

237 Background: Recent advances in proteomic and chromatin immunoprecipitation tools have been crucial in studying cancer epigenetics but the ability to measure directly the enzyme activities of dysregulated histone-modifiers is lacking. We utilize a novel approach to identify altered histone-modifying enzymes in the progression from hormone sensitive (HS) to castrate-resistant prostate cancer (CRPC) progression. Methods: We developed, validated and utilized a high-throughput peptide microarray assay to identify altered histone lysine (de)acetylation activity in tumor lysates. Functional assays, novel HS and CRPC human tumor arrays and xenografts were utilized to confirm these findings. Results: This microarray-based activity assay revealed up-regulated histone acetyltransferase (HAT) activity against specific histone H3 sites in a castrate-resistant CR cell line compared to its hormone-sensitive (HS) isogenic counterpart. NAD+-dependent deacetylation assays revealed down-regulated Sirtuin activity in validated CR lines. Levels of acetyltransferases GCN5, PCAF, CBP and p300 were unchanged between matched HS and CR cell lines. However, auto-acetylation of p300 at K1499, a modification known to enhance HAT activity and a target of deacetylation by SIRT2, was highly elevated in CR cells. Among all 7 Sirtuins, only SIRT2 and SIRT3 protein levels were reduced in CR lines. Interrogation of HS and matched CR xenograft lines reveals that H3K18 hyperacetylation, increased p300 activity, and decreased SIRT2 expression are associated with progression to CR in 8/12 (66%). Tissue microarray analysis revealed that hyperacetylation of H3K18 is a feature of CRPC. Inhibition of p300 results in lower H3K18ac levels and increased expression of androgen receptor. Conclusions: This novel microarray approach provides a method to identify commonly dysregulated chromatin enzymes during progression providing a personalized therapeutic strategy to direct available drugs to target enzymes. Reduced SIRT2 expression and increased p300 activity lead to a concerted mechanism of hyperacetylation at specific histone lysine sites (H3K9, H3K14, and H3K18)