Ona Therapeutics Advances ONA-255 Clinical Development

BARCELONA, Spain, Sept. 24, 2026 /CourierPR/ -- Ona Therapeutics, a clinical-stage biotech company developing next-generation antibody-drug conjugates (ADCs) to address treatment-resistant cancer biology, has made significant progress in its Phase 1a clinical development of ONA-255, its lead first-in-class ADC. More than half of the patients planned for the study have already been enrolled, with the trial progressing rapidly through dose escalation.

This advancement in the Phase 1a clinical development of ONA-255 marks an important milestone for the company, coming after its $86.6 million Series B financing earlier this year. The financing has enabled Ona to continue its development of innovative ADCs targeting treatment-resistant cancer biology. Alongside ONA-255, Ona is also advancing ONA-389, a first-in-class ADC designed for colorectal cancer and hepatocellular carcinoma. ONA-389 is progressing through IND-enabling studies and is expected to enter the clinic in the second half of 2027.

In addition to ONA-389, Ona is also advancing ONA-418, the third program in its ADC portfolio. This program incorporates dual-linker, dual-payload technology, designed to further expand the potential of Ona’s ADC pipeline. The company’s unique patient-led discovery engine, which allows direct access to metastatic tumor biopsies and longitudinal patient samples, has enabled the identification of clinically relevant resistance mechanisms, facilitating the development of tailored therapies.

To support the advancement of its pipeline, Ona has appointed Aleix Prat, MD, PhD, as Chief Medical Officer. An internationally recognized medical oncologist, physician-scientist, and biotech entrepreneur, Dr. Prat brings deep expertise in breast cancer, precision oncology, biomarker development, and drug development. He is currently the Director of the Clínic Barcelona Comprehensive Cancer Center, Professor of Medicine at the University of Barcelona, and co-founder of Reveal Genomics. Since becoming Chair of Ona’s Scientific Advisory Board in 2025, he has worked closely with the company and has contributed significantly to the identification and functional validation of the target underlying ONA-255.

As Chief Development Officer, Jutta Amersdorffer, MD, MBA, will continue to lead development execution, working closely with Dr. Prat on clinical strategy and with the broader team as Ona advances ONA-255 and its pipeline through the next stages of development.

The ongoing Phase 1a trial is a multicenter, open-label study evaluating the safety, tolerability, preliminary efficacy, pharmacokinetics, and pharmacodynamics of ONA-255 in patients with advanced cancer. The dose-escalation portion is evaluating ONA-255 as a monotherapy and will inform dose selection for subsequent stages of the study. These stages will further assess the safety and preliminary antitumor activity of ONA-255 in patients with HR+/HER2-negative advanced breast cancer and metastatic gastric cancer.

Ona’s lead first-in-class clinical program, ONA-255, is in advanced HR-positive/HER2-negative breast cancer and gastric cancer and is designed to address the growing unmet need among patients who have progressed on current-generation ADC therapies. The company’s second program, ONA-389, is a first-in-class ADC for advanced colorectal and liver cancers and other prevalent solid tumors. The company is also advancing ONA-418, the third program in its ADC portfolio, designed to harness the full potential of its dual-linker, dual-payload technology and expand the reach of its next-generation ADC pipeline. Supported by a strong biomarker strategy and a growing portfolio of ADC candidates targeting different resistance pathways, Ona is advancing a differentiated pipeline aimed at delivering more durable treatment options for patients.