The role of multidrug transporters in causing pharmacoresistance in epilepsy
Lead Research Organisation:
University of Liverpool
Department Name: UNLISTED
Abstract
A third of people with epilepsy continue to have seizures despite treatment with antiepileptic drugs.
The ‘drug transporter hypothesis‘ states that an increased expression of multidrug transporters (MDTs) occurs in seizure-generating areas of the brain (seizure focus). These MDTs transport antiepileptic drugs away resulting in lower levels of the drugs where they are needed most.
There are hundreds of human MDTs, but studies in epilepsy have so far focused only on a small number of these and have produced conflicting results.
The questions we want to answer are: Can MDTs contribute to treatment failure in epilepsy? If so, which MDTs?
Some patients with drug-resistant epilepsy have the seizure focus surgically removed from their brains. We will identify which MDTs are overexpressed in these surgically-removed seizure foci. I will then check if drug-resistance could be due to differences in the genes for these MDTs. Finally, I will determine if the MDTs identified in the above studies can transport antiepileptic drugs away from seizure foci.
These discoveries will allow us to develop new strategies for treating refractory epilepsy with current antiepileptic drugs and to develop newer antiepileptic drugs which are not transported by the implicated MDTs.
The ‘drug transporter hypothesis‘ states that an increased expression of multidrug transporters (MDTs) occurs in seizure-generating areas of the brain (seizure focus). These MDTs transport antiepileptic drugs away resulting in lower levels of the drugs where they are needed most.
There are hundreds of human MDTs, but studies in epilepsy have so far focused only on a small number of these and have produced conflicting results.
The questions we want to answer are: Can MDTs contribute to treatment failure in epilepsy? If so, which MDTs?
Some patients with drug-resistant epilepsy have the seizure focus surgically removed from their brains. We will identify which MDTs are overexpressed in these surgically-removed seizure foci. I will then check if drug-resistance could be due to differences in the genes for these MDTs. Finally, I will determine if the MDTs identified in the above studies can transport antiepileptic drugs away from seizure foci.
These discoveries will allow us to develop new strategies for treating refractory epilepsy with current antiepileptic drugs and to develop newer antiepileptic drugs which are not transported by the implicated MDTs.
Technical Summary
Seizures remain uncontrolled in 30% of patients with epilepsy, despite optimum treatment with two or more antiepileptic drugs (AEDs). The drug transporter hypothesis states that localized overexpression of multidrug transporter (MDT) proteins around the epileptic focus can reduce the efficacy of AEDs by limiting their ability to penetrate the blood-brain barrier. Previous studies have focused on a small number of these transporters, primarily P-glycoprotein, but have produced conflicting results. An objective search to find which MDTs have the highest relative change in epileptic compared to normal brain tissue has not been performed. The present study proposes to fill this gap.
Hypothesis
Multiple MDTs are altered in epileptic brain tissue of patients with treatment-refractory temporal lobe epilepsy (TLE) and contribute to pharmacoresistance through altered transport of AEDs.
Methodology
All laboratory studies will be performed in the Department of Pharmacology, University of Liverpool, which has all the necessary equipment and expertise to successfully complete this project. All patient material will be obtained locally as well as from collaborators.
I will initially focus on the 4 published cDNA microarray analyses of temporal lobe tissue from patients with TLE and will undertake a meta-analysis of these data to identify any differences in expression of MDT genes between normal and epileptic tissue. This will be followed by validation studies which will (a) recruit patients having epilepsy surgery; (b) obtain normal and epileptic brain tissue; and (c) use a custom-designed low density array to validate the expression of the candidate MDTs, and in particular their variation between normal and diseased tissue.
The implicated transporter genes will then be investigated to determine whether genetic variation predisposes to the development of pharmacoresistance. A tag SNP approach will identify individual SNPs and haplotypes associated with pharmacoresistance. Large patient cohorts for the test and validation sets are available in Liverpool.
Finally, using the top transporters identified in the above studies, I will investigate whether currently available AEDs are substrates for the transporters using a Xenopus oocyte expression system.
Medical opportunities
In the short term, identifying MDTs that contribute to pharmacoresistance will allow us to identify patients that are likely to be drug refractory and tailor their management accordingly, e.g. consider early resective surgery. In the longer term, we will be able to develop a test system which will allow for screening of new AEDs to determine whether they are transported by the implicated MDTs.
Hypothesis
Multiple MDTs are altered in epileptic brain tissue of patients with treatment-refractory temporal lobe epilepsy (TLE) and contribute to pharmacoresistance through altered transport of AEDs.
Methodology
All laboratory studies will be performed in the Department of Pharmacology, University of Liverpool, which has all the necessary equipment and expertise to successfully complete this project. All patient material will be obtained locally as well as from collaborators.
I will initially focus on the 4 published cDNA microarray analyses of temporal lobe tissue from patients with TLE and will undertake a meta-analysis of these data to identify any differences in expression of MDT genes between normal and epileptic tissue. This will be followed by validation studies which will (a) recruit patients having epilepsy surgery; (b) obtain normal and epileptic brain tissue; and (c) use a custom-designed low density array to validate the expression of the candidate MDTs, and in particular their variation between normal and diseased tissue.
The implicated transporter genes will then be investigated to determine whether genetic variation predisposes to the development of pharmacoresistance. A tag SNP approach will identify individual SNPs and haplotypes associated with pharmacoresistance. Large patient cohorts for the test and validation sets are available in Liverpool.
Finally, using the top transporters identified in the above studies, I will investigate whether currently available AEDs are substrates for the transporters using a Xenopus oocyte expression system.
Medical opportunities
In the short term, identifying MDTs that contribute to pharmacoresistance will allow us to identify patients that are likely to be drug refractory and tailor their management accordingly, e.g. consider early resective surgery. In the longer term, we will be able to develop a test system which will allow for screening of new AEDs to determine whether they are transported by the implicated MDTs.
