title: The multidrug transporter hypothesis of drug resistance in epilepsy: Proof-of-principle in a rat model of temporal lobe epilepsy.
abstract: Resistance to drug treatment is an important hurdle in the therapy of many diseases, including cancer, infectious diseases and brain disorders such as epilepsy. A phenotype that is referred to as multidrug resistance was first described for chemotherapy-resistant cancer cells that overexpressed the drug efflux transporter P-glycoprotein (P-gp). More recently, overexpression of P-gp has been found in capillary endothelial cells of epileptogenic brain tissue from patients with medically intractable epilepsy. Such regionally restricted P-gp overexpression in the blood-brain barrier is likely to reduce the concentration of antiepileptic drugs at epileptic neurons, which would be a plausible explanation for multidrug resistance in epilepsy. However, a definite proof-of-principle for this hypothesis is lacking. In the present study, we used a rat model of temporal lobe epilepsy that allows selecting drug-resistant and drug-responsive subgroups of epileptic rats by prolonged treatment with the antiepileptic drug phenobarbital at maximum tolerated doses. We have shown recently that drug-resistant rats selected from this model exhibit a marked overexpression of P-gp in the hippocampus and other limbic brain regions. This model is thus ideally suited to prove the multidrug transporter hypothesis of drug resistance. For this purpose, we selected a group of phenobarbital-resistant rats, which was subsequently treated by combinations of phenobarbital with the selective P-gp inhibitor tariquidar. Coadministration of tariquidar (15-20 mg/kg) fully restored the anticonvulsant activity of phenobarbital without altering plasma pharmacokinetics or neurotoxicity of the antiepileptic drug. These data demonstrate that inhibiting P-gp in epileptic rats with proven drug resistance counteracts resistance, providing the first proof-of-principle of the multidrug transporter hypothesis of medically refractory epilepsy.
authors.affiliation: Department of Pharmacology, Toxicology and Pharmacy, University of Veterinary Medicine, Bünteweg 17, D-30559 Hannover, Germany.
authors.forename: Claudia
authors.initials: C
authors.lastname: Brandt
authors.forename: Kerstin
authors.initials: K
authors.lastname: Bethmann
authors.forename: Alexandra M
authors.initials: AM
authors.lastname: Gastens
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Löscher
mesh_terms: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors; D000818:Animals; D000927:Anticonvulsants / Q000493:pharmacokinetics / Q000494:pharmacology*; D002352:Carrier Proteins / Q000235:genetics*; D018432:Drug Resistance, Multiple / Q000235:genetics*; D004567:Electrodes, Implanted; D004569:Electroencephalography / Q000187:drug effects; D004833:Epilepsy, Temporal Lobe / Q000235:genetics* / Q000378:metabolism*; D005260:Female; D010634:Phenobarbital / Q000493:pharmacokinetics / Q000494:pharmacology; D011804:Quinolines / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D012640:Seizures / Q000503:physiopathology; D013238:Stereotaxic Techniques
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D000927:Anticonvulsants; D002352:Carrier Proteins; D011804:Quinolines; C402343:tariquidar; D010634:Phenobarbital