<i>In‐vitro</i> Assessment of BCRP‐Mediated Efflux of Antiseizure Medications in Human Blood‐Brain Barrier Cell Model

Drug-resistant epilepsy (DRE), where current antiseizure medications (ASMs) are ineffective in controlling seizures, affects approximately one-third of epilepsy patients. One potential mechanism that explains DRE is the presence of efflux transporters, like breast cancer resistance protein (BCRP) at the blood-brain barrier (BBB), that hamper the exposure of several ASMs to the brain. Here, we employed ATPase assay, competitive substrate efflux assay, and bidirectional transport assay to explore the interaction of BCRP with frequently prescribed eight ASMs. Immortalized human cerebral microvascular endothelial cells (hCMEC/D3) were used as a human BBB cell model. The obtained ATPase assay data revealed N-desmethyl clobazam at 12 µM and oxcarbazepine at 40 µM stimulated baseline ATPase activity of BCRP (p < 0.05). They also influenced the BCRP-mediated BODIPY-prazosin efflux in competitive substrate efflux assay, since N-desmethyl clobazam (1 µM & 10 µM) and oxcarbazepine (12 µM & 140 µM) increased the BODIPY-prazosin intracellular accumulation (p < 0.01). Bidirectional transport experiments demonstrated significant directional transport of N-desmethyl clobazam (efflux ratios: 2.0 at 5 µM & 10 µM), and oxcarbazepine (efflux ratios: 1.81 & 2.37 at 25 µM & 140 µM). Co-incubation with the BCRP inhibitor significantly reduced the efflux ratios for these two ASMs (p < 0.01), confirming active BCRP-mediated efflux of N-desmethyl clobazam and oxcarbazepine. Collectively, these findings provide evidence that among eight ASMs, N-desmethyl clobazam, and oxcarbazepine may be transported by BCRP at clinically relevant concentrations, and targeting BCRP may potentially enhance future epilepsy treatments.