Methylthioadenosine phosphorylase inhibition suppresses prostate cancer

Abstract

Methylthioadenosine phosphorylase (MTAP) is the only human enzyme for MTA metabolism. MTAP inhibition may alter polyamine levels, cause accumulation of MTA, and disrupt S-adenosylmethionine (SAM) recycling. Depleted SAM and increased MTA may affect methylation reactions resulting in epigenetic changes and anti-proliferative effects.;MT-DADMe-ImmA is an orally available, 86 pM transition state analogue inhibitor of human MTAP. Treatment of PC3 (human androgen-independent prostate cancer) cells with1 muM MT-DADMe-ImmA for 24 hours results in a >97% inhibition of MTAP activity. Treatment of PC3 cells with 20 muM MTA (to compensate for export of intracellular MTA) and MT-DADMe-ImmA >10 nM for 5 days decreased proliferation in comparison to controls. Combination-treatment of PC3 cells caused accumulation of MTA, alteration of polyamines, and a decrease in SAM in comparison to controls. Decreased SAM had no effect on histone H3 or H4 post-translational modifications. Methylation-specific CpG microarrays revealed a decrease in hypermethylated CpG islands in combination-treated PC3 cell DNA. Gene expression analysis of combination-treated PC3 cells revealed 59 >2-fold up-regulated mRNA's and 14 >2-fold down-regulated mRNA's. Combination-treatment of PC3 cells for 4 cell doublings resulted in decreased incorporation of [ 3H3-Me]SAM into DNA.;MT-DADMe-ImmA effects have been characterized in vivo using PC3 xenografts developed in male Rag2-yc double knockout mice and transgenic adenocarcinoma of mouse prostate (TRAMP) mice. A single dose of 150 nmol MT-DADMe-ImmA either orally or i.p. inhibited MTAP activity in mice. Treatment of mice for 48 hours with 250 muM MT-DADMe-ImmA orally increased MTA to 0.5 muM in the plasma and 18 muM in the urine. Tumors from PC3 xenograft mice treated with 250 muM MT-DADMe-ImmA for 1 month showed decreased SAM. Treatment of xenografts for 96 days with MT-DADMe-ImmA resulted in decreased tumor growth. TRAMP mice treated with 100 muM MT-DADMe-ImmA orally for 8 to 9 months had decreases in the size of preinvasive lesions and in the incidence of invasive cancer. No toxicities were observed with MT-DADMe-ImmA treatment.;Inhibition of MTAP causes accumulation of MTA, decreases in SAM, decreases in methylation of genomic DNA, and anti-proliferative effects. MT-DADMe-ImmA shows promise as an orally available, non-toxic tumor suppressive agent.