Phoenix Molecular Designs Expands PMD-026 into Second Clinical Indication with Myelofibrosis Trial at WashU Medicine

Dauntless-3 Phase 1 trial extends first-in-class RSK inhibitor PMD-026 into hematologic cancers, building on Nature Communications findings that identified RSK1 as a vulnerability in myeloproliferative neoplasms

SAN DIEGO, California – VANCOUVER, British Columbia, May 27, 2026 – Phoenix Molecular Designs (PhoenixMD), a clinical-stage precision oncology company developing first-in-class RSK kinase inhibitors, today announced the expansion of its lead asset PMD-026 into a second clinical indication with the initiation of Dauntless-3, an investigator-initiated Phase 1 trial in myelofibrosis at Washington University School of Medicine in St. Louis. Conducted at Siteman Cancer Center, based at Barnes-Jewish Hospital and WashU Medicine, the trial extends the PMD-026 program from breast cancer into hematologic cancers.

Myelofibrosis (MF) is a serious form of myeloproliferative neoplasm in which the bone marrow develops scar tissue, disrupting normal blood cell production. Current therapies are not curative, and patients who cannot tolerate or progress on treatment have limited options. Dauntless-3 is led by Principal Investigator Dr. Amy Zhou, a WashU Medicine hematologist at Siteman Cancer Center, and will evaluate PMD-026 as a monotherapy in chronic myelofibrosis patients who have failed prior or are intolerant to JAK inhibitor treatment(s). The study is registered on ClinicalTrials.gov under identifier NCT07379125.

In January 2025, the laboratory of Dr. Stephen T. Oh, a WashU Medicine hematologist at Siteman Cancer Center and a leader in myeloproliferative neoplasm research, published a study in Nature Communications. The study identified RSK1 as an exploitable dependency in myeloproliferative neoplasms and secondary acute myeloid leukemia (secondary AML). In myelofibrosis mouse models, PMD-026 reduced leukocytosis, splenomegaly, and bone marrow fibrosis, while shifting bone marrow histology back to normal. Moving from that publication to a clinical trial in roughly 16 months reflects both the strength of the underlying science and PhoenixMD's position as the only company advancing a clinical-stage pan-RSK inhibitor across solid tumors and hematologic cancers.

"PMD-026 was designed to target a kinase that drives some of the hardest cancers to treat, and our focus has always been on helping patients live longer, better lives. The work from the Oh lab reinforced our belief that RSK biology may play a meaningful role across multiple cancer settings beyond breast cancer. PMD-026 has the potential to address the root drivers of myelofibrosis by inhibiting megakaryocytes and resolving fibrosis — features unique to RSK inhibition that are not commonly observed with JAK inhibitors, the current standard of care. Our hope is that PMD-026 will move the field toward a more curative approach to treating myelofibrosis. Dauntless-3 brings us closer to delivering on that promise for patients with myelofibrosis and secondary AML, who deserve every opportunity for better outcomes," said Dr. Sandra Dunn, Founder and CEO of Phoenix Molecular Designs.

"We found the preclinical data from Dr. Oh’s research lab, identifying RSK1 as a vulnerability in myeloproliferative neoplasms provided a strong scientific rationale to move forward and evaluate PMD-026 in a clinical trial for myelofibrosis," said Dr. Zhou, who treats patients at Siteman Cancer Center.” While myelofibrosis treatments have advanced in the last decade, there is still an unmet need for treatments in patients who have disease progression despite the standard therapies. Since this is a Phase 1 study, it was designed to assess the safety of PMD-026 and explore its potential to impact disease biology in this patient population. Through the dedicated efforts between WashU Medicine and PhoenixMD teams we are pleased to open this trial and look forward to evaluating this novel therapy for our patients.”

Dauntless-3 marks the second active clinical program for PMD-026 and reinforces PhoenixMD's strategy of advancing RSK inhibition across cancers with the greatest unmet need. The company expects to share additional updates from its broader RSK pipeline in the coming year.

For more information about the Dauntless-3 trial, please visit https://clinicaltrials.gov/study/NCT07379125.

About PMD-026 PMD-026 is a first-in-class, orally administered RSK inhibitor. It is being evaluated in PhoenixMD's Phase 2 Dauntless-1 trial in advanced HR+/HER2-/RSK2-high metastatic breast cancer, and is now being investigated in myelofibrosis through Dauntless-3, an investigator-initiated Phase 1 trial at Washington University School of Medicine. PMD-026 is a pan-RSK inhibitor that targets all four RSK isoforms (RSK1, RSK2, RSK3, and RSK4).

Disclosures Dr. Stephen T. Oh, whose laboratory led the preclinical research underlying this trial, serves on the Scientific Advisory Board of Phoenix Molecular Designs. Dr. Sandra E. Dunn holds patents related to RSK inhibitors for the treatment of cancer.