Biotech Startup Announces Preclinical Success for Novel Therapeutic Candidate
Novel Antibody-Drug Conjugate Demonstrates Superior Therapeutic Index and Complete Tumor Regression in Multiple Preclinical Models
SOUTH SAN FRANCISCO, Calif., November 28, 2025 – Vexillum Therapeutics, a privately held biotechnology company developing next-generation antibody-drug conjugates (ADCs) for solid tumors, today announced positive preclinical data for its lead candidate VXM-407, a HER3-targeting ADC engineered with a proprietary tumor-selective cleavable linker-payload system. The findings, presented at the 2025 AACR-NCI-EORTC International Conference in Boston, demonstrate robust anti-tumor activity across breast, lung, and colorectal cancer models with a notably improved safety profile compared to first-generation HER3 ADCs.
The preclinical program evaluated VXM-407 in 12 patient-derived xenograft (PDX) models representing HER3-high and HER3-low expressing tumors. Treatment with VXM-407 resulted in complete tumor regression in 8 of 12 models and partial regression in three additional models, achieving a 92% overall response rate. Notably, the candidate maintained full efficacy at doses 50% lower than the maximum tolerated dose, indicating a substantially wider therapeutic window—a critical limitation that has historically plagued HER3-directed therapies. According to recent market analysis, the global oncology market is projected to reach $600.97 billion by 2034, driven by escalating demand for targeted therapies addressing treatment-resistant cancers .
The VXM-407 program addresses a significant unmet need in oncology, as HER3 overexpression occurs in approximately 30% of solid tumors and correlates with poor prognosis and resistance to standard-of-care therapies, including EGFR inhibitors and anti-PD-1 agents. Unlike conventional ADCs that utilize non-selective cleavage mechanisms, Vexillum’s proprietary Vx-Linker technology enables payload release exclusively within the tumor microenvironment, minimizing off-target toxicity to healthy tissues. Pharmacokinetic studies demonstrated a 12-fold higher tumor-to-plasma concentration ratio versus benchmark ADCs, while safety assessments revealed no evidence of ocular toxicity or severe neutropenia—common dose-limiting toxicities associated with existing payloads.
The company has completed IND-enabling studies, including GLP toxicology in non-human primates and CMC manufacturing at 200-liter scale, achieving >95% conjugation efficiency and <5% free drug content. Based on these results, Vexillum intends to submit an Investigational New Drug (IND) application to the FDA in Q1 2026, with plans to initiate a Phase 1/2a clinical trial in patients with metastatic breast cancer and non-small cell lung cancer who have progressed on at least two prior lines of therapy. The trial will employ a novel basket design to evaluate VXM-407 across HER3 expression levels, with adaptive expansion cohorts in tumor types demonstrating early signals of activity.
“These preclinical data validate our hypothesis that engineering linker-payload selectivity can fundamentally transform the therapeutic index of HER3-targeted ADCs,” said Dr. Sarah Chen, Chief Executive Officer of Vexillum Therapeutics. “The consistent complete responses we observed, even in HER3-low models, suggest VXM-407 could address patient populations historically considered undruggable. With manufacturing readiness and a clear regulatory path forward, we are positioned to rapidly advance this candidate into the clinic and potentially offer a meaningful option for patients who have exhausted currently approved therapies.”
About Vexillum Therapeutics
Founded in 2021 and headquartered in South San Francisco, Vexillum Therapeutics is a preclinical-stage biotechnology company dedicated to developing precision ADCs for treatment-resistant solid tumors. The company’s proprietary Vx-Linker platform integrates AI-driven tumor proteomics with advanced medicinal chemistry to design linkers that are selectively cleaved by tumor-enriched proteases, sparing healthy tissue. Vexillum has established strategic partnerships with leading CROs and CDMOs to accelerate development and maintains a pipeline of three additional ADC candidates targeting novel tumor antigens. The company is backed by leading life science investors including Omega Funds and Clarivate Capital, having raised $85 million in Series B financing in June 2025.
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