Abstracts

Genomic profiling of peripheral blood using DNA microarray technology can correctly differentiate demographic differences such as gender and race and has been used to develop a genomic approach to the prediction of drug response in human cancer cell lines. We sought to determine 1) if valproic acid (VPA) therapy in children with epilepsy is associated with a characteristic blood genomic response and 2) if a distinct blood genomic pattern is noted in seizure free VPA children compared to VPA treated children with treated resistant seizures.
Informed consent was obtained, a 10-15 ml blood sample was drawn, processed and hybridized to Affymetrix human U95A gene chips. The Affymetrix GENECHIP software (MAS 4.0) was used to calculate the raw expression value of each gene from the scanned image. Analysis involved a class comparison tool (e.g. valproic acid vs controls) with p [lt] 0.01 as significant), SIGNIFICANCE ANALYSIS OF MICROARRAY (SAM) software analysis and hierarchical cluster analysis. Real-time RT-PCR was performed.
223 genes were differentially expressed when 14 VPA treated children were compared to 8 children with epilepsy pre-therapy (parametric t-test, p [lt] 0.01). These results were confirmed statistically by using the class comparison analysis, the Significance Analysis of Microarrays (SAM) software and a hierarchical cluster analysis. Among the 14 VPA treated samples, 11 were from VPA patients that were seizure free (VPA responsive) and 3 were from VPA patients still having seizures (VPA resistant). Among a total of 101 genes differentially expressed (parametric t-test, p [lt] 0.01), 56 genes had increased expression and 45 genes had decreased expression in VPA responsive samples as compared to VPA resistant samples. The class comparison, Significance Analysis of Microarrays analysis and hierarchical cluster analysis all confirmed that these genes can segregate most VPA responsive samples from the 3 VPA resistant samples. Among a total of 185 genes encoding mitochondria-dwelling proteins, 10 showed higher expression in the VPA responsive group while none showed higher expression in the VPA resistant group (p [lt] 0.01). Quantitative RT-PCR was performed and agreed well with the microarray data.
This study demonstrates 1) a significant and unique blood gene expression pattern following chronic VPA monotherapy and 2) a separate blood genomic profile that correlated with VPA anticonvulsant efficacy. These results indicate that the intrinsic variations underlying drug response among individuals can be manifested at the transcriptional level of peripheral blood cells. We speculate that in the future, it might be possible to evaluate therapeutic efficacy and toxicity based on the blood genomic profile.
[Supported by: NS28167, AG19561, NS38084, NS42774, NS43252, an American Heart Association Bugher Award and The Neuroscience Institute, University of Cincinnati (FRS) and NS40261 (TAG). ]