Article

TOS-358 is a covalent, pan-mutant, α-specific PI3K inhibitor designed to address key limitations of existing PI3Kα therapies which include limited mutation coverage and poor tolerability

Data will include efficacy, durability and safety findings in heavily pretreated patients with PI3Kα-mutant, HR+/HER- breast cancer

Poster to be presented May 7, at ESMO Breast Cancer Annual Congress 2026 in Berlin, Germany

EMERYVILLE, Calif., April 30 2026/PRNewswire/ --Totus Medicines, a clinical stage, precision medicines company leveraging AI-powered small molecule drug discovery to advance a differentiated pipeline of therapeutics against high-value, historically difficult to drug targets in multiple therapeutic areas, today announced that interim Phase 1b clinical data from its ongoing study of TOS-358, a next-generation pan-mutant, covalent, alpha-specific PI3K inhibitor, in combination with Fulvestrant, in heavily pre-treated metastatic HR+/HER- breast cancer patients, will be presented at the European Society for Medical Oncology (ESMO) Breast Cancer Annual Congress, taking place in Berlin, Germany, May 5-8, 2026.

Presentation Details:
Conference: ESMO Breast Cancer 2026
Session: Poster Presentation
Date / Time: 13:15, Thursday, May 7, 2026

TOS-358 is an oral, highly selective, pan-mutant, covalent PI3Kα inhibitor that achieves >95% continuous target engagement at clinically relevant doses for deep and durable inhibition of PI3K-AKT signaling. PI3Kα driver mutations are present in approximately 40% of ER-positive/HER2-negative breast cancer, 50% of endometrial adenocarcinoma, and a meaningful subset of head and neck squamous cell carcinoma (HNSCC) patients. Totus Medicines is advancing TOS-358 as a potential best-in-class PI3Kα inhibitor into Ph1b clinical development across selected solid tumor indications.

About Totus Medicines:

Totus Medicines is a clinical-stage, precision medicines company, discovering novel covalent small molecules against previously undrugged or difficult to drug targets, based on its proprietary AI-powered OmniDEL platform (DNA-encoded covalent library technology). The company's lead program, TOS-358, the first and only covalent PI3Kα inhibitor in clinical development, has shown efficacy, response and long-term disease control with class-leading tolerability in breast, endometrial and head & neck cancers.  The company's lead pre-clinical program is targeting IRF5, a key genetically validated but previously undrugged target across multiple I&I indications. For more information, please visit www.totusmedicines.com