Glucosylceramide Synthase Is a Novel Biomarker of Midostaurin-Induced Cytotoxicity in Non-Mutant FLT3 Positive Acute Myeloid Leukemia Cells

Abstract

Objective: Glucosylceramide (GC) synthesized by glucosylce- ramide synthase (GCS) favors cell survival and proliferation in many cancers. However, it’s role in Fms-like tyrosine kinase 3 (FLT3) non-mutant Acute Myeloid Leukemia (AML) pathogenesis is not clarified. Midostaurin, a multi-kinase inhibitor, clinically benefits FLT3-mutated AML, however, its clinical efficacy is under-estimat- ed in FLT3 non-mutant AML. This study aimed to investigate the efficacy of combination of midostaurin with GCS inhibitor in FLT3 AML cell carrying wild-type FLT3 and the underlying molecular mechanisms. Material and Method: Cytotoxic and cytostatic effects of mido- staurin, PDMP (GCS inhibitor) alone and in combination on THP1 cells were determined by MTT assay and flow cytometric propidi- um iodide (PI) staining, respectively. Calcusyn software was used to calculate combination indexes (CIs). GCS expression was checked by western blot. Results: Midostaurin downregulated GCS. Simultaneous inhibi- tion of FLT3 and GCS resulted in suppression of cell proliferation as compared to untreated control. Combinations showed synergistic cytotoxic effects (CI<1). Co-treatments increased cell cycle popula- tion at G2/M phase. Conclusion: Inhibition of GCS enhances the efficacy of midostau- rin in FLT3 non-mutant AML, which could be a novel therapeutic approach to increase midostaurin’s limited usage in the clinic after detailed mechanistic studies.