Characterizing Imatinib’s Pharmacokinetics and Impact on Neuronal p-ERK Signaling

Abstract ID 131233 Poster Board 060 Objectives: Chemotherapy-related cognitive impairment (CRCI) is an adverse effect associated with both cytotoxic and targeted chemotherapy, including select tyrosine kinase inhibitors (TKIs). Based on recent clinical reports demonstrating that treatment with imatinib is associated with CRCI, we have been developing a preclinical model of imatinib-induced CRCI. In the development of this model, we noted a significant decrease in p-ERK staining in the hippocampi of mice chronically treated with imatinib. Based on these findings, we sought to identify an appropriate ex vivo or in vitro model to expand upon our in vivo findings. Based on findings with these models, we sought to determine physiologically relevant, steady-state concentrations of imatinib in murine plasma and brain by characterizing its pharmacokinetic (PK) profile. Methods: To determine if imatinib would decrease p-ERK in vitro, we utilized the SH-SY5Y cell line, a neuroblastoma cell line that we and others have successfully differentiated into a neuron-like state. We treated differentiated and undifferentiated SH-SY5Y cells with 1, 10, and 100 μM imatinib for 24 h, then we performed western blotting to determine the impact of imatinib on p-ERK (n=2). We also performed cell viability assays with imatinib-treated differentiated and undifferentiated SH-SY5Y cells and neurons isolated from mice. To characterize imatinib's steady-state brain pharmacokinetics, we collected plasma and brain from female wild-type (WT) C57BL/6 mice at 0.25, 0.5, 1, 3, and 6 h after 7 days of receiving imatinib (100 mg/kg; p.o.) (n = 4-5/group). Concentrations of imatinib in plasma and brain were determined by a validated method based on liquid chromatography-tandem mass spectrometry, and pharmacokinetic parameter estimates were calculated with Phoenix WinNonlin. Follow-up studies were performed by inducing p-ERK activity in neurons isolated from murine hippocampi with 12-O-tetradecanoylphorbol-13-acetate (TPA) in the presence of vehicle, imatinib, or U0126. Results: Imatinib was cytotoxic to neurons in vitro and ex vivo when applied at concentrations >10 μM for >24 hours. Based on these data and an unexpected concentration-dependent increase in p-ERK in differentiated SH-SY5Y cells at 100 μM, we investigated imatinib's brain accumulation and found the maximum concentration in the brain was around 1 μM. Using 1 μM imatinib, we found that imatinib decreased TPA-induced p-ERK activity. Conclusions: In the present study, we determined that imatinib reached concentrations as high as 1 μM in the brains of WT mice. These data suggest that concentrations beyond 1 μM for 24 h may not be physiologically relevant. Ex vivo experiments utilizing isolated murine hippocampal neurons and physiologically relevant concentrations and incubation times demonstrated that imatinib decreased p-ERK activity, consistent with our in vivo data.