# Callio Therapeutics

Source: https://onco.cc/companies/callio-therapeutics/  
OnCo record `callio-therapeutics` (Company). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

Callio Therapeutics makes antibodies that carry two different cancer-killing drugs at once to HER2-positive tumours, to stop cancers escaping treatment. Its first medicine entered human trials in 2026.

## Summary

Callio Therapeutics is a clinical-stage biotech headquartered in Seattle and Singapore, launched in March 2025 by Frazier Life Sciences with technology and programmes exclusively licensed from Hummingbird Bioscience. Its platform pairs a modular linker with two rationally selected synergistic payloads on one antibody, aiming to block the dominant resistance mechanisms that limit single-payload ADCs. The lead candidate CLIO-8221 is a HER2-targeted dual-payload ADC co-delivering exatecan (a topoisomerase 1 inhibitor) and an ATR inhibitor; a phase 1/2 study in advanced HER2-expressing solid tumours was presented as a trials-in-progress poster at ASCO 2026 after preclinical data at AACR 2026. A second undisclosed ADC programme is also funded. The USD 187 million Series A was led by Frazier Life Sciences with significant participation from Jeito Capital. Zachary Hornby was appointed CEO in September 2026.

## Fields

- Kind: Company
- Last checked: 2026-09-10
- HQ: Seattle, WA
- Type: biotech
- Website: https://calliotx.com/

## Sources

- Official website: https://calliotx.com/
- Series A press release: https://www.prnewswire.com/news-releases/callio-therapeutics-launches-with-us187-million-series-a-to-advance-multi-payload-antibody-drug-conjugate-platform-through-clinical-proof-of-concept-302388161.html
- News and publications: https://calliotx.com/news/

## Connected records

- cancers: [HER2-positive breast cancer](https://onco.cc/cancers/breast-her2-positive/)
- fronts: [Antibody-Drug Conjugates](https://onco.cc/fronts/adcs/)
- technologies: [Antibody-drug conjugate (ADC)](https://onco.cc/technologies/adc/), [Dual-payload ADC](https://onco.cc/technologies/dual-payload-adc/)
- targets: [ATR](https://onco.cc/targets/atr/), [HER2](https://onco.cc/targets/her2/)
- trials: [Study in Advanced Solid Tumor Patients](https://onco.cc/trials/nct07300943/)
- companies: [Frazier Life Sciences](https://onco.cc/companies/frazier-life-sciences/), [Jeito Capital](https://onco.cc/companies/jeito-capital/), [Novo Holdings](https://onco.cc/companies/novo-holdings/), [Omega Funds](https://onco.cc/companies/omega-funds/)

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