Salkeni, Mohamad Adham

TPS3182 Background: MTAP deletion in solid tumors causes intracellular accumulation of methylthioadenosine (MTA) which partially inhibits activity of the key methylating enzyme, protein arginine methyltransferase 5 (PRMT5) and creates synthetic lethal dependencies on PRMT5 and methionine adenosyltransferase 2A (MAT2A), the rate limiting step in the synthesis of PRMT5 substrate, S-adenosyl methionine. PRMT5 and MAT2A are essential to transcription modulation, gene splicing, and DNA damage response. IDE892 is an MTA-cooperative PRMT5 inhibitor designed to exploit this vulnerability in MTAPdel tumors. Preclinical studies report robust antitumor activity with IDE892 monotherapy in MTAPdel xenograft models and an enhanced response when combined with IDE397 (an allosteric MAT2A inhibitor). IDE892-001 is a Phase 1 study evaluating safety, pharmacokinetics (PK), pharmacodynamics (PD), and preliminary antitumor activity of IDE892 alone and in combination with IDE397. Methods: IDE892-001 is an ongoing, open-label, multicenter four-part study: IDE892 monotherapy dose escalation (Part 1), monotherapy dose expansion in MTAPdel NSCLC (Part 2), IDE892 + IDE397 dose escalation (Part 3), and combination expansion in MTAPdel NSCLC (Part 4). Adults with advanced or metastatic MTAPdel solid tumors including lung, urothelial, gastrointestinal cancers (including pancreatic and biliary tract cancers) and mesothelioma are eligible following disease progression on standard therapies. Key exclusion criteria include symptomatic brain metastases, cardiac disease, active severe infection, and prior treatment with a PRMT5 or MAT2A inhibitor. Part 1 uses a Bayesian optimal interval design to determine maximum tolerated dose (MTD) and recommended doses for expansion (RDE). Part 3 uses a modified toxicity probability interval design to evaluate escalating combinations of IDE892 and IDE397. Oral treatment is given QD in 21-day cycles until progression or unacceptable toxicity. Serial blood samples are collected for PD analyses. Imaging will be performed every 6 weeks through week 24, then every 9–12 weeks. Efficacy endpoints will be assessed by RECIST v1.1. Primary objectives for dose-escalation cohorts (Parts 1 and 3) are safety and tolerability, including determination of MTD/RDE. In expansion cohorts (Parts 2 and 4), co-primary objectives include safety and preliminary antitumor activity (objective response rate and duration of response). Secondary endpoints for all parts include PK of IDE892 alone and in combination with IDE397. Exploratory assessments include progression free survival, changes in circulating and tumor-based markers of PRMT5 pathway modulation, molecular predictors of response, exposure–response relationships, and metabolite characterization. Clinical trial information: NCT07277413 .

Abstract Purpose: This open-label, multicenter, phase IB/II study evaluated sapanisertib, a dual inhibitor of mTOR kinase complexes 1/2, plus exemestane or fulvestrant in postmenopausal women with hormone receptor–positive (HR+)/HER2-negative (HER2−) advanced/metastatic breast cancer. Patients and Methods: Eligible patients had previously progressed on everolimus with exemestane/fulvestrant and received ≤3 (phase IB) or ≤1 (phase II) prior chemotherapy regimens. Patients received sapanisertib 3 to 5 mg every day (phase IB), or 4 mg every day (phase II) with exemestane 25 mg every day or fulvestrant 500 mg monthly in 28-day cycles. Phase II enrolled parallel cohorts based on prior response to everolimus. The primary objective of phase II was to evaluate antitumor activity by clinical benefit rate at 16 weeks (CBR-16). Results: Overall, 118 patients enrolled in phase IB (n = 24) and II (n = 94). Five patients in phase IB experienced dose-limiting toxicities, at sapanisertib doses of 5 mg every day (n = 4) and 4 mg every day (n = 1); sapanisertib 4 mg every day was the MTD in combination with exemestane or fulvestrant. In phase II, in everolimus-sensitive versus everolimus-resistant cohorts, CBR-16 was 45% versus 23%, and overall response rate was 8% versus 2%, respectively. The most common adverse events were nausea (52%), fatigue (47%), diarrhea (37%), and hyperglycemia (33%); rash occurred in 17% of patients. Molecular analysis suggested positive association between AKT1 mutation status and best treatment response (complete + partial response; P = 0.0262). Conclusions: Sapanisertib plus exemestane or fulvestrant was well tolerated and exhibited clinical benefit in postmenopausal women with pretreated everolimus-sensitive or everolimus-resistant breast cancer.