Callio Therapeutics has appointed Zachary “Zach” Hornby Chief Executive Officer as the clinical-stage biotechnology company advances multiple dual-payload antibody-drug conjugates for cancer.
Hornby brings experience leading biotechnology companies through clinical development, financing and strategic partnerships. He most recently served as CEO, President and a Director at Boundless Bio, which raised approximately $350 million in private and public capital and advanced three internally discovered drug candidates into clinical development.
Previously, Hornby served as CFO and COO at Ignyta, where he helped lead the company’s IPO, oversaw its development portfolio, served as team leader for cancer drug Rozlytrek and led the business development process surrounding Ignyta’s $2 billion acquisition by Roche.
As part of the transition, Callio Co-Founder and founding CEO Piers Ingram, PhD, will become Senior Advisor and remain on the board. Founding Chief Scientific Officer Jerome Boyd-Kirkup, PhD, will transition to Senior Scientific Advisor.
Callio is developing dual-payload ADCs designed to overcome treatment resistance by delivering complementary therapeutic payloads directly to tumors.
Its lead clinical candidate, CLIO-8221, is a HER2-targeted dual-payload ADC delivering a topoisomerase 1 inhibitor and an ATR inhibitor. The combination is designed to simultaneously damage cancer cells and inhibit the DNA damage response that can contribute to resistance.
CLIO-8221 is currently being evaluated in an ongoing Phase 1/2 first-in-human study in adults with metastatic or unresectable HER2-expressing solid tumors, including patients previously treated with trastuzumab deruxtecan. The first patient was dosed in March 2026, with enrollment underway in Australia and the U.S. and plans to expand the study to China.
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“Resistance is the defining challenge facing ADCs today, and Callio’s leading approach in the emerging dual-payload space tackles resistance head-on with rational combination payloads delivered in a tumor-specific manner,” said Hornby. “With CLIO-8221 in the clinic and additional programs advancing toward the clinic in the near future, I look forward to building on the strong scientific foundation to deliver meaningful impact for patients and shareholders.”
Zachary Hornby, Chief Executive Officer of Callio Therapeutics
“Callio has entered an exciting stage as we advance CLIO-8221 through a Phase 1 clinical trial and broaden the reach of our dual-payload ADC platform across a growing pipeline,” said Ingram. “Zach’s track record of leading clinical-stage companies through drug development, global registrations, and capital raising makes him the right person to guide Callio forward in this next chapter and beyond. Through a collaborative development agreement, Hummingbird will continue to provide research and development support to Callio via Hummingbird’s expertise and AI-first approach to ADC discovery. I will continue to partner with the Callio team to advance dual-payload ADCs and deliver the next generation of ADC medicines for patients.”
Piers Ingram, PhD, Co-Founder and Senior Advisor of Callio Therapeutics
