While deletions of the p16/CDKN2A tumor suppressor were first discovered more than 30 years ago, therapeutics that selectively target such tumors have proven elusive. Recent work utilizing functional genomics has identified a synthetic lethal vulnerability that arises due to co-deletion of the adjacent metabolic gene, methylthioadenosine phosphorylase (MTAP). Loss of MTAP in these tumors leads to an accumulation of MTAP substrate 5'-methylthioadenosine (MTA), which partially inhibits the arginine methyltransferase PRMT5 and sensitizes tumors to shRNA-mediated depletion of PRMT5 and the upstream metabolic enzyme, methionine adenosyltransferase 2 alpha (MAT2A). To investigate the therapeutic potential of this finding, we utilized a biophysical binding screen followed by iterative structure-guided design to make the first highly potent, selective, and orally bioavailable inhibitors of MAT2A. MAT2A inhibitor treatment leads to potent inhibition of the growth of HCT116 MTAP-/- cells while sparing isogenic HCT116 MTAP+/+ cells. Tumor xenograft studies similarly demonstrated MTAP-selective growth inhibition in HCT116 MTAP-/- tumors compared to isogenic HCT116 MTAP+/+ tumors. Further, MTAP-deletion correlated with MAT2A inhibitor efficacy across a panel of >300 cell lines in vitro, and MAT2A inhibitor treatment was efficacious in a variety of MTAP-deleted patient-derived xenografts in vivo. Having demonstrated that potent MAT2A inhibitors selectively block the proliferation of MTAP-deleted cells and tumors, we sought to investigate the mechanism by which these effects arise. Using methylation proteomics we noted that MAT2A inhibitor treatment leads to selective inhibition of PRMT5 methylation activity in MTAP-deleted cancers in vitro and in vivo. RNA-seq analyses revealed that MAT2A inhibition leads to substantial defects in RNA splicing in MTAP-deleted cancers, consistent with published findings that PRMT5-mediated methylation of splicing complex proteins is critical for their function. MAT2A inhibitor treatment led to a substantial increase in detained introns, which were enriched in genes involved in cell cycle regulation and DNA damage response, thus implicating dysregulated splicing in the antiproliferative effects of MAT2A inhibition in MTAP-deleted cancer cells. Furthermore, we demonstrated substantial drug-drug synergy between MAT2A inhibitors and select agents inhibiting cell cycle progression or DNA repair. Importantly we validated key combination findings in vivo, including demonstration of synergy with the MAT2A inhibitor AG-270 and anti-mitotic taxanes. AG-270 is the first MAT2A inhibitor to enter clinical development and is under investigation in a Phase I trial that is currently enrolling patients with MTAP-deleted solid tumors (NCT03435250). Our findings suggest clinically-applicable combination strategies which may further enhance the efficacy of AG-270 in malignancies with this genetic lesion.
Citation Format: Katya Marjon, Peter Kalev, Marc Hyer, Mark Fletcher, Peili Zhang, Elia Aguado-Fraile, Everton Mandley, Zenon Konteatis, Jeremy Travins, Kevin Marks. Targeting MAT2A in CDKN2A/MTAP-deleted cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 2714.