shCDK9 or shDHODH sensitizes cells to gilteritinib treatment by altering transcriptomes of AML cells

Acquisition of an internal tandem duplication of the juxtamembrane region of FLT3 (FLT3-ITD) is a common event in Acute myeloid leukemia (AML) patients and is associated with poor outcomes at high allelic frequency. Although targeted therapies against FLT3-ITD exist, narrow therapeutic index as monotherapies and failure to achieve complete remission limits their clinical application. Using a genome-wide CRISPR knockout screen, we identified cyclin-dependent kinase (CDK9), protein arginine methyltransferase (PRMT5) and dihydroorotate dehydrogenase (DHODH) as novel synthetic lethal partners with gilteritinib treatment. We demonstrated that genetic or pharmacologic inhibition of these targets in combination with gilteritinib synergistically kill AML cells. The presence of FLT3-ITD was shown to cause a significant increase in aerobic glycolysis, rending the leukemia cells highly sensitive to pharmacological inhibition of glycolytic activity. Supportive of this, our screen shows that sgRNAs targeting ~28 genes in the glycolysis pathway are enriched in cells treated with gilteritinib, suggesting that switching to oxidative phosphorylation from aerobic glycolysis may represent a metabolic adaption of the leukemic cells to resistance to FLT3-targeted therapy. Interestingly, the knockdown of CDK9, PRMT5 or DHODH in presence of gilteritinib cooperatively shuts down oxidative phosphorylation and associated purine biosynthesis and mevalonate pathway, implying inhibition of these genes along with proteins involved in the mitochondria respiratory chain complexes and energy metabolism may represent an attractive strategy to resensitize leukemic cells to gilteritinib treatment. Overall, these findings provide the basis for maximizing therapeutic impact of FLT3-ITD inhibitors and provide a rationale for a clinical trial of these novel combinatorial therapies. shCDK9 or shDHODH -stable MOLM13 cells were treated with sublethal doses of gilteritinib before being subject to RNA-seq analysis shCDK9, shDHODH or scrambled shRNA-stable MOLM13 were treated with DMSO or 8nM gilteritinib for 48 or 96 hrs in triplicates before RNA was extracted.