Potential Clinical Use of Azacitidine and MEK Inhibitor Combination Therapy in PTPN11-mutated Juvenile Myelomonocytic Leukemia

Juvenile myelomonocytic leukemia (JMML) is a rare myeloproliferative neoplasm of childhood. The molecular hallmark of JMML is hyperactivation of the Ras/MAPK pathway with the most common cause being mutations in the gene PTPN11, encoding the protein tyrosine phosphatase SHP2. Current strategies for treating JMML include using the hypomethylating agent, 5-azacitidine (5-Aza) or MEK inhibitors trametinib and PD0325901 (PD-901), but none of these are curative as monotherapy. Utilizing an Shp2 murine model of JMML, we show that the combination of 5-Aza and PD-901 modulates several hematologic abnormalities often seen in JMML patients, in part by reducing the burden of leukemic hematopoietic stem and progenitor cells (HSC/Ps). The reduced JMML features in drug-treated mice were associated with a decrease in p-MEK and p-ERK levels in Shp2 mice treated with the combination of 5-Aza and PD-901. RNA-sequencing analysis revealed a reduction in several RAS and MAPK signaling-related genes. Additionally, a decrease in the expression of genes associated with inflammation and myeloid leukemia was also observed in Shp2 mice treated with the combination of the two drugs. Finally, we report two patients with JMML and PTPN11 mutations treated with 5-Aza, trametinib, and chemotherapy who experienced a clinical response because of the combination treatment.