# CLIO-8221

Source: https://onco.cc/drugs/clio-8221/  
OnCo record `clio-8221` (Treatment). Data CC BY-NC 4.0, attribute "Data from OnCo (onco.cc)"; commercial use needs a licence.

## TL;DR

CLIO-8221 is an experimental dual-payload antibody-drug conjugate from Callio Therapeutics, in phase 1 trials for HER2-expressing advanced solid tumours and metastatic breast cancer.

## Summary

CLIO-8221 is a dual-payload antibody-drug conjugate from Callio Therapeutics, with Hummingbird Bioscience as partner. A HER2-targeted ADC carrying two payloads at once, the topoisomerase 1 inhibitor exatecan and the ATR inhibitor berzosertib, paired to address resistance that emerges on existing HER2 ADCs. Its furthest stage is phase 1, for HER2-expressing advanced solid tumours and metastatic breast cancer. ClinicalTrials.gov registers it in one study linked below. Phase 1/2 recruiting in the US and Australia, China planned (NCT07300943). Whether it works in people has not been established unless a trial below reports it.

## Fields

- Kind: Treatment
- Status: phase-1
- Last checked: 2026-11-03
- Tags: pipeline; ctgov-ingest
- Code: CLIO-8221
- Modality: Dual-payload antibody-drug conjugate
- Mechanism: A HER2-targeted ADC carrying two payloads at once, the topoisomerase 1 inhibitor exatecan and the ATR inhibitor berzosertib, paired to address resistance that emerges on existing HER2 ADCs.

## Sources

- Callio Therapeutics: calliotx.com: https://calliotx.com/
- Callio Therapeutics: biospace.com: https://www.biospace.com/press-releases/callio-therapeutics-to-present-phase-1-trial-design-of-clio-8221-novel-dual-payload-adc-at-asco-2026
- Callio Therapeutics: biospace.com: https://www.biospace.com/press-releases/callio-therapeutics-to-present-phase-1-trial-design-of-clio-8221-novel-dual-payload-adc-at-asco-2026
- Callio Therapeutics: clinicaltrials.gov: https://clinicaltrials.gov/study/NCT07300943
- ClinicalTrials.gov: trials of CLIO-8221: https://clinicaltrials.gov/search?intr=CLIO-8221

## Connected records

- cancers: [Metastatic cancer (cancer that has spread)](https://onco.cc/cancers/metastatic-cancer/)
- targets: [HER2](https://onco.cc/targets/her2/)
- companies: [Callio Therapeutics](https://onco.cc/companies/callio-therapeutics/)
- trials: [Study in Advanced Solid Tumor Patients](https://onco.cc/trials/nct07300943/)

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