MDM2- and FLT3-inhibitors in the treatment of FLT3-ITD acute myeloid leukemia, specificity and efficacy of NVP-HDM201 and midostaurin.

Prognosis for FLT3-ITD positive acute myeloid leukemia with high allelic ratio (>0.5) is poor, particularly in relapse, refractory to or unfit for intensive treatment, thus highlighting an unmet need for novel therapeutic approaches. The combined use of compounds targeting both the mutated FLT3 receptor and cellular p53 inhibitors might be a promising treatment option for this poor risk leukemia subset. We therefore assessed MDM2 and FLT3 inhibitors as well as cytotoxic compounds used for conventional induction treatment as single agents and in combination for their ability to induce apoptosis and cell death in leukemic cells. Acute myeloid leukemia cells represented all major morphologic and molecular subtypes with normal karyotype, including FLT3-ITD (>0.5) and FLT3 wild type, NPM1 mutant and NPM1 wild type, as well as TP53 mutant and TP53 wild type cell lines. Acute myeloid leukemia cells with mutated or deleted TP53 were resistant to MDM2- and FLT3-inhibitors. FLT3-ITD positive TP53 wild type acute myeloid leukemia cells were significantly more susceptible to FLT3-inhibitors than FLT3-ITD negative TP53 wild type cells. The presence of a NPM1 mutation reduced the susceptibility of TP53 wild type acute myeloid leukemia cells to the MDM2 inhibitor NVP-HDM201. Moreover, the combined use of MDM2- and FLT3-inhibitors was superior to single agent treatment, and the combination of midostaurin and NVP-HDM201 was as specific and effective against FLT3-ITD positive TP53 wild type cells as the combination of midostaurin with conventional induction therapy. In summary, the combined use of the MDM2 inhibitor NVP-HDM201 and the FLT3 inhibitor midostaurin was a most effective and specific treatment to target TP53 and NPM1 wild type acute myeloid leukemia cells with high allelic FLT3-ITD ratio. These data suggest that the combined use of NVP-HDM201 and midostaurin might be a promising treatment option particularly in FLT3-ITD positive acute myeloid leukemia relapsed or refractory to conventional therapy.

The Cellular p53 Inhibitor MDM2 and the Growth Factor Receptor FLT3 as Biomarkers for Treatment Responses to the MDM2-Inhibitor Idasanutlin and the MEK1 Inhibitor Cobimetinib in Acute Myeloid Leukemia.

The tumor suppressor protein p53 is inactivated in a large variety of cancer cells. Cellular p53 inhibitors like the mouse double minute 2 homolog (MDM2) commonly suppress the p53 function in acute myeloid leukemia (AML). Moreover, fms like tyrosine kinase 3 (FLT3) growth factor signaling pathways including the mitogen-activated kinase (MAPK) cascade (RAS-RAF-MEK-ERK) are highly active in AML cells. Consequently, the combined administration of MDM2 and MEK inhibitors may present a promising anti-leukemic treatment strategy. Here we assessed the MDM2 antagonist idasanutlin and the MEK1 inhibitor cobimetinib as single agents and in combination in a variety of AML cell lines and primary AML blast cells for their ability to induce apoptosis and cell death. AML cell lines and blast cells comprised all major AML subtypes based on the mutational status of TP53, FLT3 and NPM1 genes. We observed a considerably varying anti-leukemic efficacy of idasanutlin and cobimetinib. AML cells with high sensitivity to the single compounds as well as to the combined treatment emerged with normal karyotype, wild-type TP53 and elevated FLT3 and MDM2 protein levels. Our data indicate that AML cells with normal karyotype (NK) and wild-type status of TP53 with elevated FLT3 and MDM2 expression emerge to be most sensitive to the combined treatment with cobimetinib and idasanutlin. FLT3 and MDM2 are biomarkers for treatment response to idasanutlin and cobimetinib in AML.