Triptolide sensitizes cancer cells to nucleoside DNA methyltransferase inhibitors through inhibition of DCTPP1-mediated cell-intrinsic resistance

Abstract

SUMMARY While nucleoside DNA methyltransferase inhibitors (DNMTi) such as decitabine and azacitidine are effective in treating myelodysplatic syndrome (MDS)/leukemia, they have had limited utility for the majority of other cancers. Through a chemical library screen, we identified that triptolide, a diterpenoid epoxide from Tripterygium wilfordii , or analogs significantly augmented the epigenetic and anti-cancer effects of decitabine in vitro and in vivo . These effects were attributable to inhibition of DCTPP1-mediated cleavage of 5-aza-deoxycytidine triphosphate, the convergent activated metabolite of nucleoside DNMTi, leading to enhanced drug incorporation into genomic DNA, increased DNMT degradation, enhanced global DNA demethylation and associated transcriptional reprogramming. We show that high DCTPP1 expression was associated with cell-intrinsic resistance to nucleoside DNMTi, and that triptolide and its analogs could overcome this resistance. SIGNIFICANCE We screened a library of existing drugs to identify those capable of enhancing the anti-cancer effects of the nucleoside DNMTi decitabine. The combination of triptolide and decitabine synergistically inhibited cancer cell growth and survival in vitro , and was highly effective in inhibiting xenograft growth in vivo . Biochemical, genetic and structural biology studies with triptolide and its analogs revealed that this synergy was due to their inhibition of DCTPP1-mediated pyrophosphate cleavage from 5-aza-deoxycytidine triphosphate, the active metabolite of DNMTi. The genomic incorporation and efficacy of decitabine in cancer cell lines were significantly correlated with DCTPP1 expression more so than those of other nucleoside metabolizing genes. Triptolide and its analogs comprise rational adjuncts to nucleoside DNMTi ripe for further pre-clinical/clinical translation. HIGHLIGHTS Triptolide synergistically sensitizes cancer cells to DNMTi in vitro . Triptolide and decitabine combination shows favorable efficacy and safety in vivo . Synergy of triptolide and decitabine is mediated through inhibition of DCTPP1. High DCTPP1 expression confers cell intrinsic resistance to DNMTi.