Activity of the multikinase inhibitor sorafenib in combination with cytarabine in acute myeloid leukemia.

BACKGROUND: Acute myeloid leukemia (AML) is a genetically heterogeneous cancer that frequently exhibits aberrant kinase signaling. We investigated a treatment strategy combining sorafenib, a multikinase inhibitor with limited single-agent activity in AML, and cytarabine, a key component of AML chemotherapy.
METHODS: Using 10 human AML cell lines, we determined the effects of sorafenib (10 μM) on antileukemic activity by measuring cell viability, proliferation, ERK1/2 signaling, and apoptosis. We also investigated the effects of sorafenib treatment on the accumulation of cytarabine and phosphorylated metabolites in vitro. A human equivalent dose of sorafenib in nontumor-bearing NOD-SCID-IL2Rγ(null) mice was determined by pharmacokinetic studies using high performance liquid chromatography with tandem mass spectrometric detection, and steady-state concentrations were estimated by the fit of a one-compartment pharmacokinetic model to concentration-time data. The antitumor activity of sorafenib alone (60 mg/kg) twice daily, cytarabine alone (6.25 mg/kg administered intraperitoneally), or sorafenib once or twice daily plus cytarabine was evaluated in NOD-SCID-IL2Rγ(null) mice bearing AML xenografts.
RESULTS: Sorafenib at 10 μM inhibited cell viability, proliferation and ERK1/2 signaling, and induced apoptosis in all cell lines studied. Sorafenib also increased the cellular accumulation of cytarabine and metabolites resulting in additive to synergistic antileukemic activity. A dose of 60 mg/kg in mice produced a human equivalent sorafenib steady-state plasma exposure of 10 μM. The more dose-intensive twice-daily sorafenib plus cytarabine (n = 15) statistically significantly prolonged median survival in an AML xenograft model compared with sorafenib once daily plus cytarabine (n = 12), cytarabine alone (n = 26), or controls (n = 27) (sorafenib twice daily plus cytarabine, median survival = 46 days; sorafenib once daily plus cytarabine, median survival = 40 days; cytarabine alone, median survival = 36 days; control, median survival = 19 days; P < .001 for combination twice daily vs all other treatments listed).
CONCLUSIONS: Sorafenib in combination with cytarabine resulted in strong anti-AML activity in vitro and in vivo. These results warrant clinical evaluation of sorafenib with cytarabine-based regimens in molecularly heterogeneous AML.