Phoenix Molecular Designs Announces First Patient Dosed in Dauntless-3, Expanding PMD-026 into a Second Cancer Type

Phoenix Molecular Designs' first-in-class RSK inhibitor is now being administered to patients in both metastatic breast cancer and myelofibrosis, following the start of an investigator-initiated Phase 1 trial at WashU Medicine.

SAN DIEGO, California and VANCOUVER, British Columbia, September 21, 2026 – Phoenix Molecular Designs (PhoenixMD), a clinical-stage precision oncology company developing first-in-class RSK kinase inhibitors, today announced that the first patient has been dosed in Dauntless-3, an investigator-initiated Phase 1 trial of PMD-026 in myelofibrosis at Washington University School of Medicine in St. Louis. The first patient received treatment on September 17, 2026, at Siteman Cancer Center, based at Barnes-Jewish Hospital and WashU Medicine.

With this milestone, PMD-026 becomes the only clinical-stage pan-RSK inhibitor being given to patients in both solid tumors and blood cancers. The compound is currently under evaluation in PhoenixMD's Phase 2 Dauntless-1 trial in advanced HR+/HER2-/RSK2-high metastatic breast cancer and now in chronic myelofibrosis through Dauntless-3.

Myelofibrosis is a serious myeloproliferative neoplasm in which the bone marrow develops scar tissue, disrupting normal blood cell production. Dauntless-3 is enrolling patients with myelofibrosis who have failed prior JAK inhibitor treatment or are intolerant of it, a population with limited remaining treatment options. The trial is led by principal investigator Dr. Amy Zhou, a WashU Medicine hematologist at Siteman Cancer Center, and is registered on ClinicalTrials.gov under identifier NCT07379125. It builds on preclinical work from the laboratory of Dr. Stephen Oh, published in Nature Communications in January 2025, which identified RSK1 as an exploitable dependency in myeloproliferative neoplasms.

"Every patient enrolling in this trial has already been told their options are running out beyond trying yet another JAK inhibitor. Inhibiting RSK with PMD-026 suppresses inflammation and reduces spleen size in preclinical models. It has the added benefit of suppressing abnormal megakaryocyte and resolving reticulin by restoring normal bone marrow architecture. This is unlike the way approved JAK inhibitors work," said Dr. Sandra Dunn, Founder and CEO of Phoenix Molecular Designs. "We believed from the start that RSK biology matters far beyond breast cancer, and the work from Dr. Oh's lab gave us the rationale to move quickly. I am proud of how fast our team got here."

"We have made real headway in myelofibrosis over the past decade, and many patients now get meaningful relief from their symptoms," said Dr. Zhou. "But when those therapies stop working, we are largely out of options, and this study is for those individuals. RSK is a different target from anything currently used in this disease, and the work made a strong case for evaluating it in patients."

Dauntless-3 is the second active clinical program for PMD-026. 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.

Disclosures

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