Activating internal tandem duplication (ITD) and tyrosine kinase domain (TKD) 
point mutations in Fms-like tyrosine kinase 3 (FLT3) occur in approximately 30% 
of patients with acute myeloid leukemia (AML), and confer a poor prognosis with 
standard cytarabine/anthracycline or azacitidine-based chemotherapy regimens. 
Gilteritinib is a highly-specific, potent FLT3/AXL inhibitor with demonstrated 
activity against FLT3-ITD and FLT3-TKD mutations. Compared with salvage 
chemotherapy, treatment with once-daily oral gilteritinib demonstrated a 
clinical benefit in patients with FLT3-mutated relapsed/refractory AML, which 
led to its recent approval in Japan and the United States. We investigated the 
effects of gilteritinib combined with cytarabine plus daunorubicin/idarubicin, 
or combined with azacitidine in human FLT3-ITD-positive (FLT3-ITD +) AML cell 
lines and xenografted mouse models. Gilteritinib induced G1 arrest and apoptosis 
in a dose-dependent manner. The addition of cytarabine, daunorubicin, 
idarubicin, or azacitidine potentiated apoptosis. Gilteritinib alone or combined 
with cytarabine, daunorubicin, idarubicin, or azacitidine, inhibited 
anti-apoptotic protein expression in MV4-11 cells. In xenografted mice, 
administration of cytarabine, idarubicin, or azacitidine in combination with 
gilteritinib had little impact on plasma or intratumor PK profiles of 
gilteritinib, cytarabine, idarubicin, or azacitidine. Gilteritinib combined with 
chemotherapy reduced tumor volume to a greater extent than either gilteritinib 
or chemotherapy alone. Of note, the addition of cytarabine plus 
daunorubicin/idarubicin led to tumor regression in mice, with complete 
regression observed in six out of eight mice in both triple combination groups. 
These findings support the investigation of gilteritinib combined with 
chemotherapy in patients with FLT3-ITD + AML, including those who are ineligible 
for intensive chemotherapy.