Integrated Human and Murine Clinical Study Establishes Clinical Efficacy of Ruxolitinib in Chronic Myelomonocytic Leukemia

Purpose: Chronic myelomonocytic leukemia (CMML) is a rare leukemia characterized by peripheral monocytosis with no disease-modifying therapies. CMML cells are uniquely hypersensitive to granulocyte-macrophage colony-stimulating factor (GM-CSF) and robustly engraft in immunocompromised mice that secrete human cytokines. To leverage these unique biological features, we conducted an integrated human and murine study evaluating ruxolitinib, a JAK1/2 inhibitor that potently downregulates intracellular GM-CSF signaling. Patients and Methods: A total of 50 patients with WHO-defined CMMLwere enrolled in this open-label, multi-institution phase I/II clinical study, with a ruxolitinib dose of 20 mg twice daily studied in phase II. In parallel, 49 patient-derived xenografts (PDX) derived from 13 study participants were generated and randomized to receive ruxolitinib or vehicle control. Results: The most common grade 3/4 treatment-related toxicities observed were anemia (10%) and thrombocytopenia (6%). The clinical overall response rate was 38% by Myelodysplastic Syndrome/Myeloproliferative Neoplasm(MDS/MPN) International Working Group (IWG) criteria and 43% of patients with baseline splenomegaly achieved a spleen response. Profiling of cytokine levels and somatic mutations at baseline failed to identify predictive biomarkers. PDX models derived from screening samples of study participants recapitulated responses seen in humans, particularly spleen responses, and corroborated ruxolitinib's clinical efficacy in a randomized murine study not feasible in human trials. Conclusions: Ruxolitinib demonstrated clinical efficacy and an acceptable adverse event profile in patients with CMML, identifying a potential novel therapeutic in this rare malignancy. Furthermore, this study demonstrates proof of concept that PDX modeling can recapitulate responses of patients treated on clinical trial and represents a novel correlative study that corroborates clinical efficacy seen in humans.