Suppressing Hedgehog signaling reverses drug resistance of refractory acute myeloid leukemia.

Background: Hedgehog (Hh) signaling is involved in the pathogenesis of tumors. By performing gene chip analysis, we predicted that Hh signaling might regulate multiple downstream pathways in acute myeloid leukemia (AML). Methods: In this study, the potential role of the Hh pathway in refractory AML, and the impact of Hh expression on clinical prognosis were examined. We also investigated the role of the Hh inhibitor NVP-LDE225 in reversing drug resistance of refractory primary AML cells in vitro and the roles of multiple drug-resistant HL60/Adriamycin-resistant cells in vitro and in vivo (in a xenograft mouse model). Finally, we explored the underlying mechanisms. Results: Hh pathway was highly active in chemotherapy-resistant AML cells; by contrast, activation was less pronounced in chemosensitive cells and non-refractory primary cells. Strong activation of this pathway was associated with higher recurrence rates and poorer relapse-free and overall survival. NVP-LDE225 inhibited MRP1 protein expression, increased intracellular accumulation of Adriamycin, and reversed chemotherapeutic resistance. These effects were likely mediated through inhibition of the IGF-1R/Akt/MRP1 pathway. In the AML xenograft mouse model, NVP-LDE225 plus Adriamycin resulted in marked tumor regression. Conclusion: These findings suggest that targeting the Hh pathway might be a therapeutic avenue for overcoming MDR resistance and preventing refractory AML. [ABSTRACT FROM AUTHOR]