The sorafenib plus nutlin-3 combination promotes synergistic cytotoxicity in acute myeloid leukemic cells irrespectively of FLT3 and p53 status.

Background: Both the multi-kinase inhibitor Sorafeniband the small molecule inhibitor of the MDM2/p53 interaction Nutlin-3, used alone, have shown promising anti-leukemic activity in acute myeloid leukemiacells. Thus, in this study we have investigated the effect of Sorafenibplus Nutlin-3 combination in acute myeloid leukemia. Design and Methods: Primary acute myeloid leukemiablasts (n=13) and FLT3wild-type/p53wild-type (OCI-AML3), FLT3mutated/p53wild-type (MOLM), FLT3mutated/p53mutated (MV4-11), FLT3wild-type/p53deleted ( HL60) or FLT3wild-type/p53mutated (NB4) acute myeloidcell lines were exposed to Sorafenib, used alone or in association with Nutlin-3 at 1:1 ratio, in a range of clinically achievable concentrations (1-10 uM). Induction of apoptosis and autophagy was evaluated by transmission electron microscopy and by specific flow cytometry analyses. The levels of Mcl-1, p53 and Bak proteins were analyzed by Western blot; knock-down of Bax and Bak gene expression was performed in transfection experiments with specific siRNA. Results: The Sorafenib+ Nutlin-3 drug combination exhibits synergistic cytotoxicity in primary acute myeloid leukemiablasts and in acute myeloid leukemiacell lines with maximal cytotoxicity in FLT3mutated MV4-11 and MOLM, followed by the FLT3wild-type OCI-AML3, HL60and NB4. The cytotoxic activity of Sorafenib+ Nutlin-3 was characterized by an increase of both apoptosis and autophagy. Moreover, Bax and Bak showed a prominent role in mediating the decrease of cell viability in response to the drug combination in p53wild-type OCI-AML3 and p53deleted HL-60 cells, respectively, as demonstrated in transfection experiments performed with specific siRNA. Conclusions: Our data demonstrate that acute myeloid leukemiacells show a variable but overall good susceptibility to the innovative therapeutic combination Sorafenib+ Nutlin-3, which differentially involves the pro-apoptotic Bcl-2 familymembers Bax and Bak in p53wild-type and p53deleted cells.