GSTP1 and prostate cancer: Harmine may reactivate hypermethylated genes by inhibiting DNMTs and reducing promoter methylation of androgen receptor (AR), glutathione S-transferase Pi 1 (GSTP1), Ras association domain family member 1A (RASSF1A), Adenomatous Polyposis Coli (APC), single-strand binding protein 2 (SSBP2), hypermethylated in cancer 1 (HIC1), O-6-methylguanine-DNA methyltransferase (MGMT), endothelin receptor type B (EDNRB), prostaglandin-endoperoxide synthase 2 (PTGS2) and suppress prostate cancer cell growth [54] (Figure 2).