Callio Therapeutics to Present Phase 1 Trial Design of CLIO-8221, Novel Dual-Payload ADC, at ASCO 2026

Callio Therapeutics, a biotherapeutics company specializing in dual-payload antibody-drug conjugates (ADCs), announced it will present Phase 1 trial design details for CLIO-8221 at the 2026 American Society of Clinical Oncology (ASCO) Annual Meeting in Chicago. The trial, active under identifier NCT07300943, focuses on HER2-expressing solid tumors, including those resistant to trastuzumab deruxtecan. CLIO-8221 combines a topoisomerase 1 inhibitor (exatecan) and an ATR inhibitor (berzosertib) to target key resistance mechanisms in HER2-targeted therapies. Enrollment is ongoing in Australia and the U.S., with plans to expand to China. The Phase 1 study follows a dose-escalation design, potentially including dose expansions for patients with HER2-expressing cancers, regardless of prior response to trastuzumab deruxtecan. Chief Medical Officer Naomi Hunder emphasized the trial’s potential to provide differentiated treatment options for hard-to-treat tumors. Preclinical data, previously disclosed at AACR 2026, supports CLIO-8221’s efficacy and safety. The ADC demonstrated superior tumor regression in both sensitive and resistant models, with a favorable safety profile in non-human primates at doses exceeding those of trastuzumab deruxtecan. Lead investigator Timothy A. Yap of The University of Texas MD Anderson Cancer Center highlighted the need for innovative approaches to address limited treatment options for patients progressing on existing HER2-targeted therapies. The trial’s design aims to evaluate whether dual-payload inhibition can expand therapeutic possibilities for HER2-expressing solid tumors. Callio Therapeutics plans to activate additional clinical sites in China to accelerate patient enrollment and data collection.