Acute myeloid leukemia (AML) is the most common acute leukemia in adults. More than half of older AML patients fail to respond to cytotoxic chemotherapy, and most responders relapse with drug-resistant disease. Failure to achieve complete remission can be partly attributed to the drug resistance advantage of AML blasts that frequently express P-glycoprotein (P-gp), an ATP-binding cassette transporter. Our previous work showed that elevated acid ceramidase (AC) levels in AML contribute to blast survival. Here, we investigated P-gp expression levels in AML relative to AC. Using parental HL-60 cells and drug-resistant derivatives as our model, we found that P-gp expression and efflux activity were highly upregulated in resistant derivatives. AC overexpression in HL-60 conferred resistance to the AML chemotherapeutic drugs, cytarabine, mitoxantrone, and daunorubicin, and was linked to P-gp upregulation. Furthermore, targeting AC through pharmacologic or genetic approaches decreased P-gp levels and increased sensitivity to chemotherapeutic drugs. Mechanistically, AC overexpression increased NF-κB activation whereas NF-kB inhibitors reduced P-gp levels, indicating that the NF-kappaB pathway contributes to AC-mediated modulation of P-gp expression. Hence, our data support an important role for AC in drug resistance as well as survival and suggest that sphingolipid targeting approaches may also impact drug resistance in AML.
