Abstract 4592: Preclinical characterization of ATG-042-198, a novel MTAP null-selective PRMT5 inhibitor

Abstract Background: PRMT5 inhibitors are considered as a promising approach for cancer therapy due to their crucial role in the initiation and progression of many types of malignancies. Nevertheless, the crucial involvement of PRMT5 in controlling hematopoiesis, even in normal cells, resulted in significant on-target-off-tumor hematological toxicity when using first-generation, non-selective PRMT5 inhibitors in clinical settings, which hampered the clinical development of these drugs. The MTAP gene is deleted in around 10-15% of all human malignancies. As a result, the loss of MTAP leads to the buildup of MTA, which can bind to PRMT5 and partially inhibit PRMT5 activity. Inhibitors targeting the PRMT5-MTA complex become a promising strategy for treating MTAPnull cancer in a synthetically lethal manner. Herein, we report the preclinical feature of ATG-042-198, a novel MTAPnull-selective PRMT5 inhibitor. Methods: The in vitro activity and MTAP selectivity of ATG-042-198 on cell proliferation and cellular symmetric dimethylarginine (SDMA) expression were profiled using HCT116 MTAP wild type (wt) cells and HCT116 MTAP knock out (ko) cells, as well as in five MTAPnull cell lines. The in vivo efficacy was tested in cell derived xenograft (CDX) mouse models with HCT116 MTAP wt cells, HCT116 MTAP ko cells and LU99 cells (MTAPnull). The in vitro and in vivo pharmacokinetic properties were assessed with corresponding assay methods. Results: ATG-042-198 demonstrated potent and selectively inhibitory effect on HCT116 MTAP ko cells’ proliferation (IC50=44nM) and SDMA expression (IC50=0. 146nM), but very weak effect on HCT116 MTAP wt cells’ proliferation (IC50=4550nM) and SDMA expression (IC50500nM). Consistently, ATG-042-198 showed excellent anti-proliferation activities on multiple endogenous MTAPnull cell lines (A549, IC50=2nM; LU99, IC50=6nM; U87MG, IC50=11nM; NALM-6, IC50=37nM; MIA PaCa-2, IC50=43nM). ATG-042-198 demonstrated high permeability (Caco2 assay, ER=2), good metabolic stability (Human liver microsomes assay, T1/2145min), and low risk of drug interaction (CYP inhibition assay, 3A4/2C19/2D6, all IC5010μM). In vivo PK study showed that ATG-042-198 was well absorbed, with a dose-dependent increase in plasma distribution and high oral bioavailability (F=108%). Plasma free drug concentrations were continuously higher than the IC50 of cell proliferation inhibition within 24 hours after 30mpk administration. In three CDX models (HCT116 MTAP wt, HCT116 MTAP ko and LU99), ATG-042-198 at a dose of 30 mg/kg QD potently and selectively inhibited tumor growth (TGI=-1%, 89% and 106%) without inducing body weight loss. Conclusions: In summary, ATG-042-198 is an oral MTAP null-selective PRMT5 inhibitor with potent efficacy against MTAPnull tumor. It also demonstrated good tolerability and preclinical PK profiles. Citation Format: Ya Kong, Ming Zhang, Lulu Jiang, Ruiting Xu, Bin Jiang, Guoqiang Dai, Yulong He, Huiling Liu, Jay Mei, Bing Hou, Bo Shan. Preclinical characterization of ATG-042-198, a novel MTAP null-selective PRMT5 inhibitor abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 4592.