From Bench to Bedside: Positive Data from a Phase 1 Clinical Trial of RSO-021

June 17, 2024 by Kate Strotmeyer

Dean Fennell, FRCP, PhD, principal investigator, presents results from the Phase 1 MITOPE clinical study of a first-in-human, and potential first-in-class therapeutic, RSO-021at ASCO (Photo: Business Wire)

From Bench to Bedside: Positive Data from a Phase 1 Clinical Trial of RSO-021, a First-in-Class Therapeutic for Malignant Pleural Mesothelioma

  • First-in-human MITOPE clinical study meets primary objective of Phase 1 safety and tolerability
  • First-in-Class therapy shows early signs of efficacy and offers new hope to patients with malignant pleural mesothelioma with pleural effusion and other cancers.

Using a novel therapy discovered in the Cunniff Lab at the University of Vermont Cancer Center, RS Oncology, a privately held biopharmaceutical company focusing on novel treatments for rare and aggressive cancers presented positive results from its Phase 1 study in patients with Malignant Pleural Mesothelioma (MPM) with Malignant Pleural Effusion (MPE) or MPE associated with other solid tumors at the 2024 American Society of Clinical Oncology (ASCO) Annual Meeting.

The Phase 1 data was presented by principal investigator Dean Fennell, MRCP, FRCP (MD/PhD) on behalf of all the MITOPE investigators at an oral presentation session. In the 15 recruited patients, safety data demonstrated weekly treatment of RSO-021 was well tolerated at 90 mg. The pharmacokinetic data showed minimal systemic exposure to RSO-021 after intrapleural administration. Efficacy data showed a long-term partial response in one patient as well as encouraging survival in 7 of the 10 evaluable patients. In addition to responses in mesothelioma, the drug showed promising responses in non-target lesions and other cancers with metastatic disease to the lung.

“The MITOPE trial would not have been possible without the support of the outstanding investigation teams throughout the UK who are dedicated to the treatment of patients with mesothelioma. We thank all the MITOPE trial participants and their supportive families, and look forward to hearing about their continued benefit,” said George Naumov, PhD, RS Oncology Chief Operations Officer.

“RSO-021 represents a new class of drugs with a first-in-class anticancer mechanism. The safety and efficacy observed in the Phase 1 trial is supported by strong pre-clinical rationale” said Brian Cunniff, PhD, Chief Science Officer for RS Oncology and assistant professor at the University of Vermont Larner College of Medicine.

MPM is a rare and aggressive form of cancer that typically develops years after asbestos inhalation and/or exposure. Most cases (70%) originate in the pleura, but it can also be found the peritoneum and the pericardium. A mesothelioma prognosis remains poor with a shorter life expectancy and decreased quality of life.

Phase 2 exploration of this novel agent is ongoing at two doses, as a single agent and in combination with chemotherapy. Clinical trial information: NCT05278975.

About RS0-021

RSO-021 is a naturally occurring, sulfur-rich, cyclic oligopeptide of the thiopeptide class, which covalently inactivates PRX3, leading to catastrophic oxidative stress and cell death.

The oral and poster presentations will be available for viewing on

About the MITOPE study

MITOPE is an open-label, non-randomized, multicenter, translational Phase 1/2 dose-escalation and expansion study. It is designed to determine the safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary anti-tumor activity of RSO-021 after intrapleural (IP) administration in patients with MPE associated with either MPM or other solid tumors.