Abstract 1073: PRMT5 Inhibition Synergizes with a Natural Small Molecule Compound to Kill MTAP-deleted Cells and Suppress Tumor Growth

Homozygous deletion of MTAP occurs in about 15% of all human cancers, such as glioblastoma, pancreatic cancer, mesothelioma, urothelial bladder carcinoma, and lung squamous cell carcinoma. PRMT5 inhibitors show activity against MTAP-deleted cancer cells in culture and xenografts with a mechanism that relies on the significant elevation of the MTAP substrate, methylthioadenosine (MTA). Previously, we have shown that unlike cells in culture, MTA levels in MTAP-deleted primary human GBM tumors are not significantly higher than in MTAP-intact tumors. Therefore, combining the PRMT5 inhibitor with another drug may be required to increase the therapeutic window and clinical efficacy of a PRMT5 inhibitor in MTAP-deleted patients. Here, we identified a natural small molecular chemical compound with a good safety profile that synergizes with a PRMT5-MTA complex inhibitor, which boosts the efficacy of MTAP-deleted selective cell killing in the presence of MTA sequestering cells. This combination therapy significantly increases the potency of PRMT5 inhibitor treatment in MTAP-deleted cells across various tumor cell lines and lowers the IC50 of PRMT5 inhibitor treatment. In vivo, PRMT5 inhibitor combination treatment leads to smaller tumor volumes in MTAP-deleted CDX tumors (U87, glioma cell line) compared to PRMT5 inhibitor monotherapy. In summary, our proposed combination therapy of PRMT5 inhibition with a natural compound may increase the therapeutic window and clinical efficacy of PRMT5 inhibitors leading to better treatment options for patients harboring MTAP-deleted cancer. Citation Format: Yasaman Barekatain, Kyle LaBella, Hikaru Sugimoto, Kristen Harris, Sunada Khadka, Florian Muller, Raghu Kalluri. PRMT5 inhibition synergizes with a natural small molecule compound to kill MTAP-deleted cells and suppress tumor growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1073.