RS Oncology Announces 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.

Cambridge, Mass, June 3, 2024RS 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 Professor 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 seven 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 of 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.

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.

About RS Oncology

RS Oncology is a private, clinical-stage biopharmaceutical company leading scientific discoveries and global collaborations to improve the lives of patients with the most aggressive cancers. Taking a fundamentally different approach to drug development, we are advancing a pipeline of programs based on mitochondrial dynamics and metabolic function that dictate cell processes including cell migration and tumor cell metastasis. The oral presentation will be posted to or follow us on LinkedIn and X.

Corporate contact:

Jarrett Duncan, CEO


RS Oncology Data for Novel Treatment of Aggressive Cancers Selected for an Oral Presentation at ASCO Annual Meeting

– Data from phase 1 clinical trial of RSO-021 selected for the Developmental Therapeutics session on June 3rd, 2024

– Trial in progress for the ongoing expansion cohorts will be presented as a poster in the Lung Cancer session on June 3rd, 2024

CAMBRIDGE MA, May 1, 2024 – RS Oncology, a clinical-stage biopharmaceutical company focused on developing novel treatments for aggressive and rare cancers, today announced that it will present the complete Phase 1 dose escalation data as an oral presentation at the world’s largest oncology meeting, the 2024 American Society of Clinical Oncology (ASCO) Annual Meeting.

The MITOPE phase 1 multicenter study, (clinical #NCT05278975) investigating the safety and tolerability of RSO-021, is a first-in-human trial. RSO-021 is a first-in-class therapy for treatment of mesothelioma and solid tumors in patients with malignant pleural effusion. Professor Dean Fennell from Leicester Hospitals Trust in the UK will present the complete dose escalation data as part of a rapid oral session and answer questions during a moderated panel discussion.

Aggressive cancers present tremendous challenges in treatment and management, primarily due to rapid growth and spread to other parts of the body. Malignant pleural effusion (MPE) develops as a direct extension of cancer into the pleural space and is associated with shorter life expectancies. Currently, the phase 2 expansion portion of MITOPE is underway in the UK, exploring RSO-021 as both a single agent and in combination therapy to treat stage IV metastatic cancers with MPE, including mesothelioma, lung, breast and ovarian cancers. Other causes of MPE include cancer that has spread from the stomach, kidney, ovaries, and colon. Dr. Sean Dulloo from University of Leicester will present an update of the MITOPE Phase 2 trial as a trial-in-progress poster presentation.

The data is embargoed until published by ASCO 5:00 PM (EDT) on Thursday, May 23, 2024.

Details of the Presentations

Rapid Oral Abstract

Title: First-in-human phase 1 clinical trial of RSO-021, a first-in-class covalent inhibitor of mitochondrial peroxiredoxin 3 (PRX3), in patients with malignant pleural effusion due to mesothelioma and other advanced solid tumors (MITOPE).

Presenter: Dean Fennell

Session Title: Developmental Therapeutics—Molecularly Targeted Agents and Tumor Biology

Day/Time: Monday June 3, 9:06 am (session from 8:00-9:30 am)

Abstract #3019

Poster Presentation

Title: Phase 2 study to evaluate the novel mitochondrial PRX3 inhibitor, RSO-021, as an intrapleural monotherapy and in combination with IV paclitaxel in patients with malignant pleural effusion due to mesothelioma or another advanced solid tumor.

Presenter: Sean Dulloo

Session Title: Lung Cancer—Non-Small Cell Local-Regional/Small Cell/Other Thoracic Cancers

Day/Time: Monday, June 3, from 1:30 – 4:30 PM CDT​​​​​​

Abstract: #TPS8124

Poster Bd: #381b

About RS Oncology

RS Oncology is a private, clinical-stage biopharmaceutical company leading scientific discoveries and global collaborations to improve the lives of patients with the aggressive cancers. Visit or follow us on LinkedIn and X.

Corporate Inquiries: Jarrett Duncan, CEO, RS


RS Oncology to present translational data identifying potential biomarkers associated with RSO-021 anticancer activity.

March 29th, 2024 – Cambridge MA. RS Oncology announced two abstracts with comprehensive preclinical and translational data in support of their lead clinical oncology compound RSO-021, have been accepted for poster presentations at the Annual Meeting of the American Association for Cancer Research (AACR), taking place April 5-10, 2024 in San Diego. RSO-021 is a first-in-class peroxiredoxin 3 (PRX3) covalent inhibitor that disables a critical antioxidant defense system in the mitochondria of tumor cells. Results from the completed Phase 1 clinical trial (clinical #NCT05278975) will be an oral presentation on June 3rd, at the upcoming ASCO meeting in Chicago. Currently patients are being recruited to the Phase 2 dose expansion cohorts of the MITOPE clinical trial.

“Covalent inactivation of PRX3 by RSO-021 represents a viable anticancer approach by targeting a universal tumor vulnerability of oxidative stress. The results we present at the AACR Annual Meeting will highlight fundamental tumor cell features that are exploitable by this novel treatment.” said Brian Cunniff, Chief Scientific Officer of RS Oncology.

Approximately 90% of mesotheliomas and 15-20% of solid tumors present with malignant pleural effusion (MPE) at late stage leaving the patients with poor prognoses and limited options. RSO-021 is a local therapy for patients with MPE arising from mesothelioma or advanced metastatic tumors. “The discoveries presented at AACR highlight tumor cell features that are associated with sensitivity to RSO-021, providing a potential strategy to maximize patient response to RSO-021”, added George Naumov, Chief Operations Officer of RS Oncology.

Details of the poster presentations:

Title: First-in-class peroxiredoxin 3 (PRX3) inhibitor RSO-021 triggers mesenchymal-to-epithelial transition in mesothelioma

Presenter: Brian Cunniff, CSO of RS Oncology

Session Category and Title: Experimental and Molecular Therapeutics – Other Cellular Mechanisms for Anticancer Drug Action

Session Date and Time: Tuesday Apr 9, 2024 9:00 AM – 12:30 PM

Location: Poster Section 29

Abstract Number: 4716


Title: SLC7A11 modulates sensitivity to the first-in-class mitochondrial peroxiredoxin 3 inhibitor thiostrepton (RSO-021) via a ferroptosis independent pathway

Presenter: Brian Cunniff, CSO of RS Oncology

Session Category and Title: Molecular/Cellular Biology and Genetics- Cellular Stress Responses 1

Session Date and Time: Sunday Apr 7, 2024 1:30 PM – 5:00 PM

Location: Poster Section 16

Published Abstract Number: 384


The full abstracts will be published on March 22, 2024, in an online-only proceedings supplement to the AACR journal, Cancer Research.

About RS Oncology:

RS Oncology is a private, clinical-stage biotechnology company leading scientific discoveries and global collaborations to improve the lives of patients with the most aggressive cancers. The initial focus is to develop our novel therapy for pleural mesothelioma and other cancers with metastatic disease to the lung. Our first-in-class and first-in-human drug, RSO-021, is currently in phase 2 of the MITOPE study to prove its efficacy in a multicenter clinical trial in the UK. Visit or follow us on LinkedIn and X.

Recent advancements in treating malignant pleural mesothelioma, and why localized treatment could be advantageous

George Naumov, COO at RS Oncology, summarizes a few of the recent advancements in malignant pleural mesothelioma treatment and discusses how localized administration could offer additional treatment benefits.

Malignant mesothelioma with pleural effusion, also called malignant pleural mesothelioma (MPM), is a type of cancer that primarily affects the mesothelial cells that line the protective membranes (pleura) surrounding the lungs, abdomen, and other organs. These abnormal cells cause irritation and increased fluid production in the pleural space (pleural effusion), causing chest pain, shortness of breast, and persistent cough.

MPM is most commonly caused by asbestos exposure and, unfortunately, often diagnosed at an advanced stage where treatment options are severely limited. The average age at diagnosis is 75 years old, also making treatment that much more complicated. Prognosis is largely dependent on the disease subtype (epithelioid, sarcomatoid, or biphasic), but the average life expectancy overall is typically less than two years.

While surgery and radiotherapy are potential treatment options, most patients are too far advanced for these to be effective. As such, chemotherapy had traditionally been the prescribed regimen. The FDA-approved combination of permetrexed with cisplatin has been the standard-of-care chemotherapy, but this typically only extends survival by a few months (12.1 months combination vs. 9.3 months for cisplatin alone, as observed in the Phase III EMPHACIS study used for FDA approval).

In addition to chemotherapy, most patients will also have a catheter placed to periodically drain the pleural fluid. Doctors might also perform talc pleurodesis, in which a talc slurry is introduced via the catheter to induce inflammation and scaring to the pleural lining. This in turn reduces the amount of space that fluid can accumulate and, while not curative, helps to manage symptoms and discomfort. 

Looking Beyond Chemotherapy

Our understanding of cancer biology has grown immensely, especially over the past decade. The rise of advanced next-generation sequencing and proteomic technologies have given us a more holistic understanding of tumor biomarker signatures, gene expression profiles, and the tumor microenvironment. From this new knowledge has come new, innovative ways to treat MPM beyond traditional chemotherapies such as cisplatin.

Small molecule inhibitors

Like in any other cancer cell, MPM cells ramp up certain molecular signaling pathways to ensure their survival. Multi-omic approaches have given us a glimpse as to which proteins and functions are up- and down-regulated, and in turn we are developing small molecule inhibitors that interrogate those pathways to kill cancer cells.

One such pathway that has caught our personal interest is the mitochondrial antioxidant pathway. Because of their aggressive and uncontrolled growth, mesothelioma cells must kick their redox-responsive signaling pathways into overdrive to dispose of harmful reactive oxygen species (ROS), such as peroxides. Our lead therapeutic candidate, RSO-021, irreversibly binds to and inhibits one such enzyme in this pathway, mitochondrial peroxiredoxin 3 (PRX3), resulting in ROS accumulation and apoptotic cell death. Preclinical data have been promising thus far, and currently RSO-021 is being evaluated in a Phase 1/2 trial (MITOPE; NCT05278975) in patients with malignant pleural effusion, including those with MPM.

Other drug developers are evaluating compounds that target other pathways, either alone or in combination with other therapies. Researchers at the University of Chicago, for example, currently have an ongoing Phase 2 trial evaluating Lynparza (olaparib), a PARP inhibitor that targets poly ADP ribose polymerase, in patients with homologous recombination deficient (HRD) malignant mesothelioma (NCT04515836). There is another ongoing Phase 2 trial sponsored by the Netherlands Cancer Institute evaluating the combination of Keytruda (pembrolizumab) with Lenvima (Lenvatinib), a multikinase inhibitor that targets VEGFR1, VEGFR2, and VEGFR3, in MPM patients (PEMMELA; NCT04287829). And this is just the very tip of the iceberg in terms of ongoing trials and preclinical research.


Rather than treating cancer cells directly with drugs, immunotherapy works by rallying the body’s immune response against the tumor. Immunotherapies generally work best against “hot” tumors – those that are inflammatory in nature. Data suggest that MPM is not only inflammatory but has also has a rich T cell microenvironment, suggesting that immunotherapy might be a feasible option to treat this disease.

After a therapeutic dry spell, a landmark milestone for MPM came in 2020 with the FDA approval of Opdivo (nivolumab) in combination with Yervoy (ipilimumab) as the new first-line treatment for MPM – 16 years following the approval of permetrexed and cisplatin combination chemotherapy. Further, this was also the first immunotherapy combination approved for this disease. The approval was based on the Phase 3 CheckMate 743 study, a randomized, open-label trial in 605 patients with previously untreated, unresectable MPM. Patients who received Opdivo in combination with Yervoy survived a median of 18.1 months while patients who underwent chemotherapy survived a median of 14.1 months. Although the median difference was only a few months, it was still an achievement very much worth celebrating for such a difficult disease. Further, it fueled a continuing interest in evaluating other immunotherapies.

While results with other immunotherapy regimens have been variable in MPM, many early-phase studies have shown some promise for additional immune checkpoint blockade. There are also numerous studies ongoing, such as this NCI-sponsored Phase 1/2 study evaluating Keytruda (pembrolizumab) alone and in combination with anetumab ravtansine in MPM (NCT03126630). Others are also evaluating the combination of immunotherapy plus chemotherapy rather than immunotherapy alone. Rondon et al recently wrote an informative review article summarizing this and a number of other ongoing immunotherapy clinic trials against MPM.

While promising, it’s important to note that immunotherapy is not always the right choice for patients, as there are significant side-effects that can significantly lower quality of life. Going forward, identifying additional treatment options that work alone or in combination with immunotherapy will be critical.

Cell Therapy

Cell therapies have caught considerable interest from drug developers, especially after seeing the success of CAR T-cell therapies for hematologic cancers. Solid tumors have been notoriously trickier to treat with cell therapy in comparison, and MPM is no exception. While there has not yet been an approved cell therapy for MPM, preclinical data have been promising, and there are numerous clinical trials in progress.

Part of the challenge of cell therapy is finding a suitable target that is selectively expressed on tumor cells. In the case of MPM, mesothelin has been one such target of interest, as it’s been shown to be broadly overexpressed on malignant tumor cells. An ongoing Phase 1/2 study conducted by Memorial Sloan Kettering (NCT02414269) published preliminary results in 2021 showing that intrapleural administration of 0.3M-60M CAR T cells/kg in 27 patients (25 with MPM) was safe and well tolerated. CAR T-cells were detected in peripheral blood for >100 days in 39% of patients. 18 patients with MPM also received pembrolizumab safely. Among those patients, median overall survival from CAR T-cell infusion was 23.9 months (1-year overall survival, 83%). Stable disease was sustained for ≥6 months in 8 patients; 2 exhibited complete metabolic response on PET scan.

There are numerous additional studies also in progress.  Memorial Sloan Kettering, for example, is performing an additional Phase 1 study to evaluate the safety of autologous mesothelin-targeted CAR T-cells in combination with cyclophosphamide chemotherapy in mesothelioma patients (NCT04577326). Another trial, a Phase 1/2 sponsored by TCR2 Therapeutics, is evaluating an autologous CAR T-cell therapy consisting of two synthetic constructs – a single-domain antibody targeting mesothelin, and a PD-1:CD28 switch receptor designed to elicit a costimulatory signal upon PD-L1 engagement on the cancer cell (NCT05451849).

Beyond T-cell therapy, others are exploring other types of immune cells. The Amphera-sponsored DENdritic Cell Immunotherapy for Mesothelioma (DENIM; NCT03610360) study is a randomized Phase 2/3 trial evaluating the administration of dendritic cells encapsulated with allogenic tumor cell lysate plus best supportive care (BSC) vs those receiving BSC alone.

Localized Administration – Giving Next-Generation Therapies a Potential Added Boost

Cancer therapies can either be administered systemically or locally at the specific site of the tumor. When possible, localized therapy (also called “locoregional” therapy) is the ideal treatment regimen because it allows for direct contact between the drug therapy and the tumor(s). This results in an increased concentration of drug in the local environment, which may have the added advantage of reducing off-target side effects associated with drugs entering the bloodstream.

The decision to administer treatments systemically vs locally is largely influenced by the type of cancer. Melanomas, for example, are a prime candidate for localized treatment because the primary tumor is easily visible on a patient’s skin, making it easy to inject. Other solid tumors, however, require deep radiology or surgical expertise to gain access to the tumor, which is burdensome to the patient and can be risky.

In the case of MPM, patients could immensely benefit from a localized treatment approach because they often will already have a catheter port in place to drain the pleural fluid. This is a unique situation that warrants an opportunity for further study, not only with small molecule drugs but also with immunotherapies and perhaps even cell therapies. Indeed, this is exactly the strategy we at RS Oncology are taking with our MITOPE clinical trial.

A Hopeful Future

Mesothelioma in general has been an incredibly tough nut to crack in terms of finding effective treatments, and MPM is no exception. There has been significant progress in the field, but also immense frustration as many approaches haven’t quite panned out. Nonetheless, we and others are dedicated to this mission and refuse to back down. While asbestos use has been banned in many countries across the world, including the United States, we’re still seeing the lingering effects from decades ago as those who were exposed continue to age.

As newer therapies are being evaluated, we encourage drug developers and oncologists to explore the option for localized therapy, as this is a unique opportunity that many other solid tumor cancers do not have. And, of course, we will continue to move forward with our own MITOPE study and will share results when available.

RS Oncology Announces First Patient Dosed in Phase 2 Clinical Study (MITOPE) Investigating RSO-021 for the Treatment of Malignant Pleural Mesothelioma and Metastatic Disease to the Lung

Cambridge, MA, USA and Leicester, UK, February 1, 2024 — RS Oncology (RSO), a clinical stage biotechnology company developing innovative therapies to eradicate mesothelioma and other diseases, today announced the successful dosing of the first patient in the Phase 2 dose expansion portion of its United Kingdom multicenter study (MITOPE; NCT05278975).

Malignant pleural effusion (MPE) is the build up of fluid in the lining membrane (pleura) of the lungs. MPE is a common clinical symptom in patients with various malignancies (~15% of end-stage cancer patients) and produces significant morbidity in the majority of affected patients. RSO’s novel, investigational anti-cancer treatment, RSO-021, is administered weekly directly into the pleural space following MPE drainage via an indwelling pleural catheter. RSO recently (4Q 2023) completed the Phase 1 dose escalation portion of its MITOPE trial and established a recommended Phase 2 dose and safety/tolerability profile of RSO-021 in a relapse setting.

Recently, RSO has expanded the Phase 2 portion of MITOPE and is now investigating RSO-021 anticancer activity in patients:

  • First presenting with MPE due to malignant pleural mesothelioma (MPM) and before standard-of-care (SOC) treatment (a window of opportunity arm).
  • With MPE who have failed first line SOC treatment and have relapsed disease.
  • With local metastatic lung disease and MPE.
  • With MPE due to advanced metastatic breast, ovarian and non-small cell lung cancers (in combination with systemic paclitaxel).

“Mesothelioma has notoriously been a difficult cancer to treat, especially since patients are often diagnosed in the more advanced stages,” said Prof. Dean Fennell, Director of the Mesothelioma Research Programme at Leicester University Hospitals. “RSO-021 exhibits a unique mechanism of action that we believe could provide new hope to patients with this disease.”

“RSO-021 is an exciting novel anti-cancer treatment that can potentially help a global population of cancer patients who are left with little to no options,” said Jarrett Duncan, CEO of RS Oncology. “Commencing the Phase 2 portion of our trial presents a major milestone for patients and their caregivers.”

About RSO-021
RSO-021 is a novel small molecule treatment that irreversibly binds mitochondrial peroxiredoxin 3 (PRX3). Preclinical studies with RSO-021 have shown that inhibition of the antioxidant signaling network results in selective killing of malignant cells by upregulating oxidative stress; in contrast, healthy cells are spared.

About RS Oncology
RS Oncology is a biotechnology company leading scientific discoveries and global collaborations to improve the lives of patients with the most aggressive cancers. The initial focus is to develop our novel therapy for pleural mesothelioma and other cancers with metastatic disease to the lung. Our novel investigational therapy, RSO-021, is currently being evaluated in the Phase 2 portion of the UK-based, multicenter MITOPE study (NCT05278975).


Corporate Inquiries: Jarrett Duncan, CEO, RS Oncology


RS Oncology presents new drug in early clinical development for Mesothelioma and lung cancer patient

Start-up US biotech company tackling rare diseases presents three case studies in France

Lille, France (2023) RS Oncology is bringing exciting new science to patients who will have the best chance of benefiting from new therapies. PRX3 is a novel drug target with potential for treating patients with the asbestos related cancer, mesothelioma. It is a key defense against oxidative stress and is located in the mitochondria, the energy generating factories. Inhibiting PRX targets cancer, not normal cells.

MITOPE, a first-in-human Phase 1 clinical trial, is investigating a first-in-class PRX3 inhibitor, RSO-021 ( using the identifier NCT05278975, sponsor RS Oncology, LLC [RSO], Boston, USA). Dose escalation is ongoing across four UK sites with a planned enrollment by Q2 2024. Phase 2 expansion will bring on board additional sites in Q4 of 2023.

Early experience with RSO-021 in MITOPE was presented to a global audience of mesothelioma clinicians, scientists, and allied professionals at the 2023 International Mesothelioma Interest Group (iMig) conference hosted in Lille, France in June. The industrial symposium was entitled New Horizons for Cancer Therapy – Targeting Oxidative Stress Vulnerabilities.

Brian Cunniff, Ph.D., Chief Science Officer for RSO, and Assistant Professor of Pathology and Laboratory Medicine at the University of Vermont Cancer Center, explained how tumor cells utilize increased levels of Reactive Oxygen Species (ROS) as a driver of pro-tumor signaling pathways. He also described the discovery of PRX3 as a target to leverage ROS dependency in cancer. RSO-021 irreversibly binds and inhibits PRX3, leading to tumor-specific cell death. Dr. Cunniff stated that “RSO-021 is an exciting new therapeutic option for patients suffering with mesothelioma. RSO-021 exploits a universal vulnerability of tumor cells through a novel mechanism of action, leaving tumor cells unable to clear toxic waste products. We are excited to see our laboratory findings translated to patients in collaboration with RS Oncology.”

Dr. Sean Dulloo, a UK investigator based at the University Hospitals of Leicester and University of Leicester, shared early insights in the safety and activity in MITOPE. Three cases were presented demonstrating the impactful tumor responses and reduced MPE levels with disease stabilization and improved quality of life.

Key opinion leader and IMIG 23 research medal winner, Professor Dean Fennell, also from Leicester, summarized the evolving mesothelioma treatment landscape and unmet needs. “PRX3 is a novel and interesting therapeutic drug target with potential for treating cancers, especially those with unmet need such as mesothelioma. We await the first clinical results with interest.”

For more information about MITOPE clinical trial visit Mesothelioma UK. The study is supported by NIHR.

About RS Oncology

RSO is a clinical stage biotechnology company based in Cambridge, Massachusetts with a mission to eradicate mesothelioma and other diseases worldwide through novel science and an innovative business model. The lead program is currently focused on development of novel therapies that modulate mitochondrial pathways driving diseases of oxidative stress, including mesothelioma and other cancers.

Corporate Inquiries:
Jarrett Duncan, CEO, RS Oncology

Media Inquiries:
Christine Sununu, Marketing & Communications, RS Oncology

AACR 2023, RSO-021, a first-in-class treatment

Our Chief Science Officer, Dr. Brian Cunniff successfully presented key research at AACR 2023. Characterization of immune cell phenotypes in patient derived malignant pleural effusion treated with thiostrepton. Thiostrepton (TS) is a covalent inhibitor of mitochondrial Peroxiredoxin 3 (PRX3).


Mesothelioma UK

Mesothelioma MattersMesothelioma Matters UK highlighted RS Oncology in their Autumn Newsletter.

15% of cancer patients develop pleural effusion as their disease spreads to the lungs and accumulates excess fluid. This condition is common among mesothelioma patients. Earlier this year, RS Oncology, LLC, a US-based biotechnical company focused on the treatment of patients with malignant pleural effusion (MPE) and mesothelioma, initiated its MITOPE clinical trial, a first-in-human Phase 1/2 clinical trial in the UK.

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RS Oncology, LLC Announces Initiation of Patient Dosing in Phase 1/2 MITOPE Clinical Trial of RSO-2

4 April 2022, Cambridge, MA — RS Oncology, LLC, (RSO) a biotechnical company focused on the treatment of patients with malignant pleural effusion and mesothelioma, announces the dosing of the first patient with RSO-021 as part of its first-in-human Phase 1/2 clinical trial (MITOPE) at the University Hospitals of Leicester in the U.K. RSO will be evaluating its novel treatment, RSO-021, against a specific mitochondrial enzyme regulating oxidative stress pathways in cancer cells.

This novel therapeutic approach has proven in pre-clinical studies to significantly reduce tumor burden in malignant mesothelioma and other cancer types by irreversibly binding and inhibiting a key enzyme in the antioxidant signaling network within the mitochondria of malignant cells.

“Our team is excited to begin patient dosing with our novel metabolic therapy. This is a significant milestone in developing a treatment for people suffering from this horrible disease,” stated CEO Jarrett Duncan. “We are eager to see activity of our drug in humans following our successful pre-clinical studies in multiple indications,” added COO and Head of Business Development, George Naumov, Ph.D.

“Mesothelioma remains a lethal cancer lacking effective treatments, particularly in patients with relapsed disease. This exciting study of a first in class PRX3 inhibitor is hoped to show promising signals that could lead to development of a new approach to tackle this cancer.” said the clinical investigator from Leicester Hospital, Professor Dean Fennell, FRCP FRSB.

About MITOPE clinical trial

The MITOPE Phase 1/2 clinical trial is a first-in-human study that will evaluate RSO-021 as a treatment for patients suffering from MPE and mesothelioma. RSO-021 is a novel irreversible inhibitor of a key mitochondrial enzyme (upregulated in cancer cells) regulating oxidative stress pathways. Treatment with RSO-021 will be administered weekly via an intrapleural catheter after routine pleural effusion drainage. The MITOPE trial is planned to open in six UK-based clinical institutions and will be recruiting patients in collaboration with Mesothelioma UK. For more MITOPE information review visit Mesothelioma UK Clinical Trials or contact The study is supported by NIHR.

About RS Oncology

RSO is a clinical stage biotechnology company based in Cambridge, Massachusetts with a mission to eradicate mesothelioma worldwide through new science and an innovative business model. The lead program RSO-021 is currently focused on development of novel therapies that modulate mitochondrial pathways that drive diseases of oxidative stress for treatment of malignant pleural effusion and malignant mesothelioma.

About NIHR

The National Institute for Health Research is UK’s largest funder of health and care research. The NIHR: funds, supports and delivers high quality research that benefits the UK National Health System, public health and social care; engages and involves patients, caregivers and the public in order to improve the reach, quality and impact of research; attracts, trains and supports the best researchers to tackle the complex health and care challenges of the future; invests in world-class infrastructure and a skilled delivery workforce to translate discoveries into improved treatments and services; partners with other public funders, charities and industry to maximize the value of research to patients and the economy.

For Corporate Inquiries:
Jarrett Duncan, CEO, RS Oncology

For Media Inquiries:
Nichole Pfeiffer Hicks, Patient Advocacy, RS Oncology