Resistance to topoisomerase inhibitor payloads is already measurable in the clinic: a 2025 study in Clinical Cancer Research found TOP1 mutations at disease progression in 12.9% of metastatic breast cancer patients who had received ADCs, compared with 0.7% at baseline. That signal is exactly what Genentech is paying $45 million upfront to get ahead of, through a new collaboration with DualityBio anchored on the company’s DUPAC payload platform, with milestone eligibility exceeding $1 billion across all programs.
The strategic logic is tight. Approved topoisomerase inhibitor ADCs, including sacituzumab govitecan and fam-trastuzumab deruxtecan, are moving into earlier lines of therapy across major solid tumor indications. That success is also creating a downstream problem: a larger, earlier-emerging population of patients whose tumors are resistant or less responsive to that payload class. DUPAC is built specifically for that population, with payloads DUP5, DUP9, and DUP10 each operating through distinct antitumor mechanisms, paired with linker technologies engineered for systemic stability and tumor-specific release. Preclinical data, presented across AACR 2025 and 2026, show activity in tumor models that are relatively insensitive to topoisomerase inhibitor payloads, plus non-human primate tolerability data.
The deal structure reflects a clean division of labor. DualityBio leads discovery and early global clinical development through Phase 1a, applying its platform against Genentech-defined oncology targets. At the Phase 1a handoff, Genentech takes exclusive worldwide responsibility for further development and commercialization. That arrangement is deliberate: DualityBio retains the asset-generation engine while Genentech absorbs the capital-intensive late-stage and commercial burden. For DualityBio, which is already running multicenter trials across nearly 20 countries with more than 3,500 patients enrolled, this is not a capacity question. It is a reach question, and Roche’s global commercialization infrastructure answers it.
The number to watch as these programs advance is Phase 1a tumor-response rates in patients previously treated with topoisomerase inhibitor ADCs. That subgroup readout will be the first real-world test of whether DUPAC’s preclinical resistance-bypass profile translates into clinical differentiation, and it will set the valuation floor for the milestone payments that follow.
Jon Napitupulu is Director of Media Relations at The Clinical Trial Vanguard. Jon, a computer data scientist, focuses on the latest clinical trial industry news and trends.
