Synergy in Immunostimulatory and Pro-Differentiation Effects of Vitamin D Analog and Fludarabine in Acute Myeloid Leukemias

Acute myeloid leukemia (AML) is an aggressive and often fatal hematopoietic malignancy, diagnosed predominantly in the elderly. The five-year survival of patients with AML is as low as 30%. Differentiation therapy of a subtype of AML, named acute promyelocytic leukemia (APL), using all-<i>trans</i> retinoic acid (ATRA) was the most successful example of a targeted therapy against AML. Epigenetic-based differentiation therapies for other subtypes of AML are also showing improvements in response and in survival rates. Thus, in this study, we investigated a potential differentiation therapy with a combination of 1,25-dihydroxyvitamin D (1,25D) analog (named PRI5202) and low concentration of Fludarabine. We show that such a combination elicits immunostimulatory and pro-differentiation effects in AML cells, specifically in those with activating mutations in fibroblast growth factor receptor (FGFR) and Janus kinase (JAK) pathways. We show here that both PRI5202 and Fludarabine are potent activators of the transcription of many innate immunity-related genes, and that, in combination, their effects are in many aspects synergistic. We propose that such a low-intensity regimen may be suitable for older patients with AML, who are unfit for intensive chemotherapy. We also present data indicating that PRI5202 induces myeloid differentiation in blasts from patients with myelodysplastic syndrome (MDS), and we propose to further investigate PRI5202 as a differentiation therapy for patients suffering from MDS.