STC-15 is the world’s first RNA-modifying enzyme inhibitor to reach human trials. Phase 1 showed durable tumor regression in multiple sarcoma subtypes. The $56 million Series C is fully backed by existing investors, including Pfizer Ventures and M Ventures.
STORM TherapeuticsA Cambridge-based clinical-stage biotech focusing on RNA modifications to treat cancer, raised $56 million in a Series C round and dosed the first patient in a Phase 2 clinical trial of its lead drug, STC-15, in select sarcoma indications.
The round was fully funded by existing investors: M Ventures, Pfizer Ventures, Taiho Ventures LLC, IP Group plc, UTokyo Innovation Platform Co., Ltd. (UTokyo IPC) and Fast Track Initiative (FTI).
STC-15 is the first oral small molecule inhibitor of METTL3, an enzyme that methylates messenger RNA and plays a central role in the differentiation of cancer stem cells. It is the first RNA-modifying enzyme inhibitor to enter human clinical trials, having begun its Phase 1 study in November 2022.
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METTL3 adds a chemical tag called m6A to the mRNA, influencing how cells read genetic instructions; In certain cancers, this process is hijacked to keep malignant progenitor cells locked in a proliferative, undifferentiated state. Inhibiting METTL3 disrupts this process, pushing cancer cells toward cycle arrest and programmed death.
Sarcomas, cancers that arise from bone or soft tissue, including muscle, fat, cartilage, and blood vessels, account for 1% of adult cancers and 15% of pediatric cancers.
They are very difficult to treat because they often lack the driver mutations or immunogenic features that make most solid tumors amenable to targeted therapy or immunotherapy.
STORM’s thesis is that sarcomas are particularly dependent on METTL3-driven mRNA methylation for their growth and survival, making them a biologically attractive target for STC-15. In phase 1, the drug demonstrated durable tumor regression in multiple sarcoma subtypes at dose levels between 60 mg and 200 mg three times per week.
Full results from Phase 1 are expected to be presented at a medical conference in 2026.
The Phase 2 monotherapy trial is designed to support a potential accelerated regulatory approval pathway for STC-15 and lay the foundation for expanding clinical development to additional oncology indications. The first patient has already received the dose successfully. The ClinicalTrials.gov identifier for the trial is NCT06975293.
STC-15 is being evaluated simultaneously in a Phase 1b/2 combination study with LOQTORZI (toripalimab), a PD-1 inhibitor from Coherus BioSciences, in non-small cell lung cancer, head and neck squamous cell carcinoma, melanoma, and endometrial cancer, a collaboration announced in May 2025.
Jonathan Trent, MD of the University of Miami Sylvester Comprehensive Cancer Center and clinical investigator of the trial, said the mechanism of STC-15 ““targets sarcomas in their vulnerability, reprogramming malignant cells toward cell cycle arrest and apoptosis.”
STORM CEO Jerry McMahon described the Phase 2 dosing as “a fundamental advance in the fight against cancers characterized by aberrant cellular differentiation,” noting the unmet need in sarcoma, where existing options remain limited.
