San Diego, Seattle and Singapore, September 9, 2026
Callio Therapeutics has appointed Zachary “Zach” Hornby as Chief Executive Officer, bringing an experienced biotechnology executive to lead the company as it advances its dual-payload antibody-drug conjugate (ADC) pipeline through clinical development. The leadership transition comes as Callio progresses its lead program, CLIO-8221, a novel HER2-targeted dual-payload ADC currently being evaluated in a first-in-human clinical study for patients with advanced solid tumors. The company announced the appointment on September 9, 2026, alongside leadership changes involving its founding executives.
New Leadership to Support Clinical Development
Hornby brings experience in biotechnology leadership, oncology drug development, financing and strategic partnerships. Before joining Callio, he served as CEO, President and a director of Boundless Bio, where he helped advance internally discovered oncology programs into clinical development and supported significant private and public financing activities. Earlier in his career, Hornby held Chief Financial Officer and Chief Operating Officer positions at Ignyta, where he contributed to the development of the company’s oncology portfolio and helped lead the business-development process associated with its acquisition by Roche. At Callio, Hornby will guide the company during an important stage of its clinical and corporate development. The company is building its pipeline around dual-payload ADCs, an approach designed to combine complementary anticancer mechanisms within a single targeted therapeutic. Callio said its platform uses modular linker technology and rationally selected payload combinations intended to address tumor resistance mechanisms that can limit the effectiveness of conventional ADCs.
CLIO-8221 Advances in Phase 1/2 Study
Callio’s lead clinical candidate, CLIO-8221, is a HER2-targeted dual-payload ADC designed to deliver two mechanistically complementary payloads to HER2-expressing tumor cells. The candidate combines a topoisomerase 1 (Topo1) inhibitor with an ATR inhibitor. The scientific rationale is based on targeting tumor-cell DNA damage and simultaneously inhibiting the DNA damage response that may contribute to resistance to Topo1 inhibition. The investigational therapy is being evaluated in an ongoing Phase 1/2 first-in-human dose-escalation and expansion study in adults with metastatic or unresectable HER2-expressing solid tumors. The study includes patients who have previously received trastuzumab deruxtecan (T-DXd), an important population because resistance to established ADC therapies remains a challenge in HER2-positive cancers. The first patient was dosed in March 2026, and enrollment is ongoing in Australia and the United States, with plans to expand the study to China.
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Leadership Transition Supports Pipeline Expansion
As part of the transition, Piers Ingram, PhD, Callio’s co-founder and founding CEO, will become Senior Advisor while continuing to serve on the company’s Board of Directors. Jerome Boyd-Kirkup, PhD, the company’s founding Chief Scientific Officer, will transition to Senior Scientific Advisor. Both executives will continue contributing to the broader scientific and strategic direction of the company. Callio also plans to continue working with Hummingbird Bioscience through a collaborative development agreement. Hummingbird, from which Callio exclusively licensed its multi-payload ADC platform and associated intellectual property and pipeline assets in 2025, will provide ongoing research and development support, including expertise in AI-enabled ADC discovery. The appointment of Hornby comes as Callio seeks to translate its dual-payload ADC technology into a broader clinical pipeline. With CLIO-8221 already in human testing and additional programs moving toward the clinic, the company is positioning its platform around the potential to address treatment resistance in cancer while maintaining targeted delivery of cytotoxic therapies.
Source: Callio Therapeutics press release
