Ensem Therapeutics Doses First Patient in China in ETX-636 Global Phase 1/2 Study

ETX-636 is being evaluated in patients with tumors harboring activating PI3Kα mutations, including breast cancer

Expansion of global Phase 1/2 study into China is expected to accelerate enrollment and broaden patient access

Plan to disclose preliminary clinical data that supports proof-of-concept in the second half of 2026

WALTHAM, Mass. & SHANGHAI–(BUSINESS WIRE)–Ensem Therapeutics, Inc. (ENSEM), a clinical-stage, oncology-focused biopharmaceutical company, today announced that the first patient has been dosed with ETX-636 in China at Fudan University Shanghai Cancer Center as part of its ongoing global Phase 1/2 clinical trial, marking a significant advancement in ENSEM’s global development strategy.

ETX-636 is a potential first-in-class and best-in-class allosteric pan-mutant-selective PI3Kα dual inhibitor and degrader. The rapid study initiation of ETX-636 in China follows the November 19^th approval of the Investigational New Drug (IND) application by China’s National Medical Products Administration (NMPA).

“ENSEM is committed to advancing innovative precision oncology medicines for patients worldwide,” said Shengfang Jin, PhD, Co-Founder and Chief Executive Officer of ENSEM. “The expansion of the ETX-636 clinical trial into China represents a significant milestone that strengthens our global clinical presence. We are pleased that several leading oncology centers in China are joining the study, which has the potential to accelerate enrollment, expand access to a broader and underserved patient population, and further strengthen the global clinical data package supporting ETX-636.”

Hongxia Wang, MD, Principal Investigator in China at Fudan University Shanghai Cancer Center, added, “Mutant PI3Kα is a frequent and critical oncogenic driver across many cancers, including nearly half of hormone receptor-positive, HER2-negative advanced breast cancers. While first-generation PI3Kα inhibitors have clinically validated the target, their limitations – particularly toxicities associated with wild-type PI3Kα inhibition – underscore the need for improved therapies. ETX-636 employs a novel allosteric mechanism-of-action to selectively inhibit and degrade mutant PI3Kα while sparing wild-type PI3Kα, potentially offering superior tolerability with robust anti-tumor activity. We are excited to collaborate with ENSEM to evaluate ETX-636’s clinical potential and bring new treatment options to patients in China.”

The ongoing first-in-human, global Phase 1/2 study is evaluating the safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary anti-tumor activity of ETX-636 in patients with advanced solid tumors harboring PI3Kα mutations (NCT06993844). Since the first patient was dosed in the United States in June 2025, multiple leading U.S. cancer centers have joined the study. ETX-636 is being evaluated both as monotherapy and in combination with fulvestrant, an approved selective estrogen receptor degrader, for the treatment of advanced HR+/HER2- breast cancer. Dose escalation in the United States is progressing as planned, and ETX-636 has been well tolerated to date, with no observed hyperglycemia or dose-limiting toxicities. ENSEM expects to disclose preliminary clinical data supporting proof of concept in the second half of 2026.

About ETX-636

ETX-636 was rationally designed to optimally bind a specific allosteric pocket in p110α, the catalytic subunit of PI3Kα. ETX-636 allosteric binding enables selective inhibition of all activating mutant forms of PI3Kα, including hotspot kinase- and helical-domain mutations, while sparing wild-type PI3Kα. The high selectivity of ETX-636 for mutant PI3Kα is expected to reduce the risk of hyperglycemia and other wild-type PI3Kα-related adverse events compared with non-mutant-selective PI3Kα inhibitors. In preclinical toxicology studies, ETX-636 did not disrupt glucose homeostasis at predicted human efficacious doses.

In addition to potent catalytic inhibition, ETX-636 uniquely induces proteasome-dependent degradation of mutant PI3Kα while preserving wild-type protein – a feature not observed with other allosteric PI3Kα inhibitors. This dual mechanism of action drives deep and durable pathway suppression and has demonstrated robust tumor regression in kinase- and helical-domain PI3Kα-mutant breast cancer xenograft models, both as monotherapy and in combination with fulvestrant, with or without a CDK4/6 inhibitor.

About Ensem Therapeutics

ENSEM is a pioneering drug discovery and development company advancing innovative small-molecule precision medicines for oncology. Leveraging its proprietary Kinetic Ensemble^® platform, ENSEM integrates AI-driven deep learning, advanced computational modeling, and cutting-edge experimental approaches to identify non-obvious binding pockets and accelerate structure-based drug design, with a focus on high-value and historically difficult-to-drug targets.

For more information, visit www.ensemtx.com or follow ENSEM on LinkedIn.

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Media and Investor Relations

Mark Mullikin

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