Callio Therapeutics Names Chris Hassig as Chief Scientific Officer

SAN DIEGO and SEATTLE and SINGAPORE, Sept. 28, 2026 /CourierPR/ -- Callio Therapeutics, a global clinical-stage biotechnology company advancing dual-payload antibody-drug conjugates (ADCs) as the next frontier of rationally designed targeted cancer therapy, has appointed Chris Hassig, PhD, as Chief Scientific Officer (CSO). Hassig will lead Callio's research and discovery organization, overseeing the advancement of the Company's dual-payload ADC platform and pipeline.

Hassig joins Callio from Boundless Bio, where he served as CSO, building the company's drug discovery organization from its inception through advancement of three internally discovered first-in-class molecules into clinical development. Prior to Boundless Bio, he was CSO of Sierra Oncology (acquired by GSK) and Vice President of Drug Discovery at Sanford Burnham Prebys Medical Discovery Institute. He previously held drug discovery and research roles at Kalypsys, Inc. and the Scripps Research Institute.

Callio Therapeutics is developing dual-payload ADCs to address high incidence tumors where better therapies are needed. The company's proprietary platform pairs modular, adaptable linker technology with rationally selected synergistic payload combinations designed to block key resistance mechanisms that enable cancer's escape. The lead clinical program, CLIO-8221, is a HER2-targeted dual-payload ADC with potential to prevent and overcome treatment resistance that limits efficacy of current ADCs.

CLIO-8221 delivers two mechanistically complementary payloads, a topoisomerase 1 (Topo1) inhibitor and an ATR inhibitor, directly to HER2-expressing tumors. While Topo1 inhibitors have shown strong clinical activity, activation of the DNA damage response following Topo1 inhibitor-induced replication stress represents a potential major driver of resistance. By simultaneously inhibiting Topo1 and blocking the DNA damage response through ATR inhibition, CLIO-8221 is engineered to overcome payload insensitivity and further sensitize tumors to Topo1 inhibition.

The team has already advanced CLIO-8221 into the clinic and built an ADC platform that systematically tests rationally designed dual-payload combinations for ADCs, optimized for specific tumor targets. The first patient was dosed in March 2026, and enrollment is ongoing in Australia and the US, with plans to open the study in China (NCT07300943).

Hassig earned a BA in Chemistry and Biochemistry from the University of California, San Diego, and a PhD in Molecular and Cellular Biology from Harvard University. He completed a postdoctoral fellowship at the University of California, Berkeley.