Enhanced plasma and brain concentrations and medulloblastoma cytotoxicity of asciminib and nilotinib by P-glycoprotein inhibition with tariquidar.

ABL1 and ABL2 are putative drivers of medulloblastoma leptomeningeal dissemination. ABL1/ABL2 inhibitors, nilotinib and asciminib, are P-glycoprotein substrates. The purpose of this work is to elucidate P-glycoprotein expression in the brain/brain tumors and to determine if P-glycoprotein inhibition increases plasma and brain concentrations and medulloblastoma cytotoxicity of nilotinib and asciminib. ABCB1 (P-glycoprotein) mRNA expression was analyzed from multiple datasets of brain and brain tumor specimens. Cytotoxicity assays of medulloblastoma cells were conducted. In a mouse model, the pharmacokinetics of asciminib and nilotinib, with and without tariquidar, were determined using LC/MS. ABCB1 mRNA expression varied by brain region and was significantly lower in the cerebellum ( P  < 0.05). There was a bimodal increase in brain ABCB1 expression at ages 0-3 and 21-23 ( P  < 0.05). ABCB1 expression in pediatric brain tumors was similar to normal brain. The addition of tariquidar significantly reduced medulloblastoma cell viability compared to asciminib alone ( P  < 0.01). Tariquidar increased asciminib plasma and brain concentrations at 24 h ( P  = 0.0005 and P  = 0.0002, respectively) and nilotinib brain concentrations at 3 h ( P  = 0.0009). Tariquidar increased the area under the curve (AUC) brain : plasma ratio of asciminib from 0.33 to 10.16% and of nilotinib from 1.16 to 9.61%. Tariquidar prolonged the plasma half-life of asciminib from 2.21 to 10.49 h and nilotinib from 7.63 to 14.64 h. P-glycoprotein inhibition increased the brain concentrations, AUC, and half-life of asciminib and nilotinib and increased cytotoxicity in medulloblastoma cells.