Association of Deferasirox and Vitamin D Promotes Cell Differentiation and Improves Overall Survival in Acute Myeloid Leukemia (AML) Elderly Patients After Demethylating Agents Failure: A Retrospective Case Control Study

AML is a group of heterogeneous malignant diseases characterized by uncontrolled cell growth and differentiation arrest. Following the success of differentiating therapies in APL, great hopes were placed in Vitamin D (VD) and its ability to promote differentiation of non-APL AML cells. However, results of clinical studies were disappointing and trials were interrupted due to the occurrence of life-threatening hypercalcemia. Our group has shown that iron chelators such as deferasirox (DFX) are able to promote monocytes differentiation in both normal hematopoietic progenitors and AML cells (Callens et al Jexp Med 2010). Moreover, iron deprivation synergized with VD to promote cell differentiation on leukemic cells. Most elderly patients diagnosed with AML suffer from secondary iron overload because of in some cases ineffective erythropoiesis and iterative red blood cell transfusions. Furthermore, in myelodysplastic syndromes, retrospective studies have suggested that iron chelators may increase life expectancy and decrease the risk of transformation into AML. In AML of the elderly, the use of demethylating agents such as 5-azacytidine or decitabine may induce hematological response and increase life expectancy. However, response is often of short duration. Since VD deficiency and iron overload prevalence is high in the elderly, the association of VD and DFX was given to a subgroup of patients following demethylating agents failure.

A retrospective chart review of 17 elderly AML patients after demethylating agents failure was performed in three French centers. Patients treated by the combination of DFX/VD were matched to patients treated with best supportive care (BSC). Based on ferritin, and creatinin levels the dose of DFX was adapted in each case. DFX dose was up to 2000 mg a day and VD was used at 100,000 units orally weekly. The tolerance and the overall survival (OS) were analyzed. Pre-clinical studies were conducted in vitro on cell lines (HL60, U937, OCI-AML3, THP-1, MOLM 13) to evaluate cell differentiation induced by DFX and a new VDR agonist (Inecalcitol) by cell morphology and flow cytometry (expression of CD11b and CD14 markers). VDR activity and expression were evaluated by flow cytometry, immunoblotting, luciferase reporter assays and qPCR to detect VDR-targeted genes.

Median age of DFX/VD patients and BSC control group were 76 (range 63–84) and 71 (58–85) respectively. Most patients were diagnosed with AML with multilineage dysplasia (cases 70%, controls 76%). Prognosis groups were distributed homogeneously between the treated patients and controls. There were no significant differences in blast infiltration, leukocytosis, neutropenia, systemic iron and phosphocalcium parameters. All patients received 5-azacytidine (median of 8 courses for the cases and 7 for the controls).No renal insufficiency, hepatotoxicity or hypercalcemia were observed in DFX/VD patients. At 3 months, 4 treated patients (23.5%) had significant monocyte level increase an evidence of the enhanced monocyte differentiation efficacy. The treatment did not decrease the need of transfusion. Most interestingly median survival of treated patients was significantly increased (10.4 m vs 4 m, p=0.002).

In vitro studies were conducted in parallel aiming to characterize new potential alternative therapeutic associations, which could improve patients' response. We show that the use of a new highly potent VDR agonist (Inecalcitol) potentiated the effect of DFX in promoting terminal monocyte differentiation of leukemic cell lines. It also increased VDR activity evaluated by VDR expression and phosphorylation and expression of VDR-targeted genes. In vivo studies in mice model of AML using combined DFX/inecalcitol therapy will be presented.

The prognosis of elderly patients diagnosed with AML after demethylating agents remains poor. Here we show that the differentiating therapy by the association of Deferasirox and Vitamin D was able to improve overall survival with low toxicity. New generation of highly-potent VDR agonists (which are devoided of hypercalcemic properties) significantly enhanced VDR activation and terminal monocyte differentiation of AML cells and represent potential therapeutic alternatives in the near future. These encouraging results should be verified in a large randomized prospective multicenter study.

No relevant conflicts of interest to declare.