Abstract PR006: Initial results from first-in-human study of AMG 193, an MTA-cooperative PRMT5 inhibitor, in biomarker-selected solid tumors

Abstract Background: AMG 193 is a second-generation protein arginine methyltransferase 5 (PRMT5) inhibitor that targets the MTA-bound state of PRMT5 in methylthioadenosine phosphorylase (MTAP)-null tumors. PRMT5 is responsible for methylation and gene silencing of cell-essential proteins dysregulated in cancer and is partially inhibited in tumors harboring MTAP deletion, which occurs in ~15% of solid tumors. First generation PRMT5 inhibitors were intolerable due to indiscriminate inhibition of PRMT5 leading to dose-limiting myelosuppression. In preclinical studies, AMG 193 demonstrated selective antitumor activity in MTAP-null models by further suppressing PRMT5 function while sparing normal function, thereby improving upon first generation molecules. We report the initial clinical results from dose-escalation in the ongoing first-in-human (FIH) study. Methods: AMG193 was orally administered in continuous 28-day cycles to patients (pts) with advanced MTAP-null solid tumors. Dose escalation proceeded via a BLRM method. The primary objectives include safety, tolerability, and identification of the maximum tolerated dose (MTD). Secondary objectives include preliminary antitumor activity by investigator-assessed RECIST, pharmacokinetics (PK) and pharmacodynamic (PD) effects. Results: As of August 8, 2023, 47 pts with MTAP-null cancer (PDAC n = 10; NSCLC n = 6; CCA = 5; MESO n = 3; others n = 23) were enrolled in seven escalating cohorts. Five pts had DLTs, and exploration continues per protocol to identify the MTD. The most common TRAEs were nausea (45%), fatigue (26%), decreased appetite (17%), and vomiting (17%). Preliminary PK analyses showed dose-proportional systemic exposure with a half-life of 7–11 hrs. Among 31 pts who had at least one postbaseline scan, there were 5 with confirmed PRs [PDAC (–100%), ovarian Sertoli-Leydig (–59%), RCC (–58%), esophageal (–46%), and gallbladder cancer (–63%), 1 each], 14 with stable disease (including 9 with some degree of tumor shrinkage), and 12 with disease progression. All PRs were ongoing at the data cutoff with treatment durations of 140–275 days. PD effects demonstrated dose-dependent reduction in serum total SDMA levels and complete PRMT5 inhibition was confirmed in five pts with on-treatment biopsies spanning multiple dose levels. Exploratory analysis of changes in variant allele frequency by ctDNA demonstrated rapid treatment effects that was predictive and correlated with response. Conclusion: AMG 193 is an MTA-cooperative PRMT5 inhibitor designed to induce synthetic lethality in MTAP-null solid tumors while sparing hematologic toxicity. The initial results of the FIH study demonstrate proof-of-concept with encouraging signs of preliminary clinical activity without evidence of myelosuppression. Dose escalation continues to proceed to establish the MTD. AMG 193 has demonstrated promise as a potential new therapeutic for pts with tumors that have MTAP loss. Citation Format: Jordi Rodon, Noboru Yamamoto, Toshihiko Doi, François Ghiringhelli, Maria-Elisabeth Goebeler, Yutaka Fujuwara, Miguel Villalona-Calero, Nicolas Penel, Amita Patnaik, Jean-Pascal Machiels, Alfredo Addeo, James Abbruzzese, Sophie Postel-Vinay, Sylvie Rottey, Chunxu Liu, Chen-Hua Chuang, William Kormany, Paul Hughes, Kiana Keyvanjah, Bert O'Neil. Initial results from first-in-human study of AMG 193, an MTA-cooperative PRMT5 inhibitor, in biomarker-selected solid tumors [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr PR006.