Diacylglycerol kinases (DGKs), a family of isozymes that phosphorylate the membrane lipid, diacylglycerol (DAG), to phosphatidic acid (PA), are important players in signal transduction cascades. DAG and PA act as vital second messengers that regulate multiple cellular signal transduction pathways including PKC and MAPK. DGKα (DGKA), one of the ten human DGK isoforms, has been reported to play a role in mediating numerous aspects of cancer progression including survival, migration, and invasion of cancer cells. Emerging data indicate that DGKA mediates T-cell dysfunction during anti-PD-1 therapy, playing a role in the development of resistance to PD-1 blockade. This suggests that DGKA inhibition offers a promising strategy to improve the efficacy of immunotherapy in the treatment of cancer. Although serotonin (5-HT) antagonists ritanserin, R59022 and R59949 have been previously repurposed as DGKA inhibitors, their potency and selectivity profiles are largely unsatisfactory. Therefore, there is a significant unmet clinical need to develop potent and selective DGKA inhibitors.

Here, we used our proprietary PandaOmics platform to explore targets that can overcome the resistance to anti-PD1 therapy. In order to do so, we created a project that included bulk RNAseq data from 4 datasets alongside with 2 single-cell RNAseq datasets. Based on the calculation results, DGKA inhibitors may overcome anti-PD-1 resistance and expand the responder patient population in cancer immunotherapy. We then designed and evaluated a series of compounds in biochemical and cellular assays, and report that ISM4312A is a novel DGKA inhibitor with excellent potency (IC50 of 120 pM) and high selectivity (>25000 fold) for DGKA versus 5-HT1A, 5-HT1B, 5-HT2A, and 5-HT2B. Further, ISM4312A showed high selectivity against 468 other kinases. In the cellular T-cell activation assay, ISM4312A induced IL-2 production in a dose-dependent manner and enhanced T-cell activity at concentrations as low as 20 nM.

In the MC38 in vivo syngeneic model, ISM4312A at 3 mg/kg BID showed robust anti-tumor activities with (Tumor Growth Inhibition, TGI, 93.4%, 37.5% mice achieved CR) or without (TGI, 25.2%) anti-PD-1 therapy. Data from this combination study indicate synergistic activity as compared with the single anti-PD-1 treatment (TGI, 50.8% at 5 mg/kg BID, no mice achieved CR). ISM4312A also exhibited favorable ADME, excellent oral bioavailability, and tolerance.

Together, the data support the ongoing clinical development of ISM4312A as a potential first-in-class DGKA inhibitor in cancer immunotherapy.

Citation Format: Deheng Sun, Hongfu Lu, Huaxing Yu, Feng Wang, Mike Korzinkin, Xin Cai, Xiao Ding, Sujata Rao, Feng Ren, Alex Zhavoronkov. Targeting DGKA for immuno-oncology therapy: ISM4312A, a novel DGKA inhibitor with robust anti-tumor activity [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 1855.