Phase 1 dose escalation and cohort expansion study evaluating safety, PK, PD and clinical activity of STC-15, a METTL-3 inhibitor, in patients with advanced malignancies, Jun 2024, ASCO Annual Meeting 2024

Abstract 443280: Phase 1 Dose Escalation and Cohort Expansion Study Evaluating Safety, PK, PD and Clinical Activity of STC-15, a METTL-3 Inhibitor in Patients with Advanced Malignancies.

Authors: Justin C Moser, Kyriakos P. Papadopoulos, Jordi Rodon Ahnert, Yaara Ofir Rosenfeld, Josefin-Beate Holz, STC15-22101 Study Team; HonorHealth Research Institute, Scottsdale, AZ; START San Antonio, San Antonio, TX; Department of Investigational Cancer Therapeutics (Phase I Clinical Trials Program), The University of Texas MD Anderson Cancer Center, Houston, TX; Storm Therapeutics Ltd, Cambridge, United Kingdom

Background: RNA modifications are involved in cancer initiation and progression. The most abundant modification of mRNA is m6A generated by METTL3. Inhibition of METTL3 l causes double-stranded RNA formation and activation of cellular T1 IFN response. IFN signaling induces IFN-stimulated gene families i.e. IFIT and OAS, characteristic of an anti-viral response, and secretion of cytokines and chemokines. STC-15, a first in class small molecule inhibitor of METTL3 developed by Storm Therapeutics, demonstrated in pre-clinical models, activation of IFN signaling and remodeling of the TME towards pro-inflammatory state. We report the dose escalation results from a FIH trial in patients with advanced malignancies.

Methods: This is a multi-center, open-label, dose escalation study. STC-15 oral capsules are administered daily or t.i.w. in 21-d treatment cycles. Dose escalation follows 3+3 modified Fibonacci regimen. Primary objectives are safety and PK. Secondary objectives are preliminary evidence of anticancer activity and RP2D. Exploratory objectives are PD (i.e. target engagement and immune activation biomarkers) and correlation of primary pharmacology with observed clinical efficacy.

Results: As of 02/01/2024, 31 patients enrolled across 4 dose levels and 5 cohorts: 60mg QD (6 pats), 60mg t.i.w. (3 pats), 100mg t.i.w. (14 pats), 160 mg t.i.w. (5 pats) and 200mg t.i.w. (3 pats). PK profile supports t.i.w. dosing. A total of 169 AEs were observed with 45 AEs attributed to STC-15 treatment. AEs were manageable, mostly hematology (thrombocytopenia 31%; 4% Grade 3), skin (pruritis, rash 14% G1/2) and GI (N/V and diarrhea 14% G1/2). 12 SAEs occurred; 1 pt (60mg QD) had DLT with G3 pneumonitis. Of 14 patients with at least 1 on-treatment scan, DCR is 78% with 2 confirmed PR ongoing in angiosarcoma (60mg, 32 weeks) and IO-refractory NSCLC (100mg, 33 weeks) and 9 SD. An average of 63% reduction in m6A on mRNA in peripheral blood at 24h post dosing was observed in 60mg cohorts, confirming target engagement. Whole blood Nanostring and pathway analysis of gene expression confirms upregulation of innate immune pathways (i.e. T1,2 IFN activation and anti-viral responses) as early as 8h after first dose and throughout the treatment cycle. Updated PK/PD and clinical data will be presented.

Conclusions: Treatment with STC-15 is well tolerated across pharmacologically active dose range with encouraging signs of clinical activity. Early biomarker data provide proof of mechanism in target engagement, strong activation of innate immune responses and correlation of pharmacological activity with clinical response. The study is ongoing and expansion cohorts are underway to further evaluate PK/PD, safety and clinical efficacy at optimized pharmacologically active doses.