Role of pharmacogenetic studies in early clinical development: Phase I studies with lapatinib

Abstract

3029 Background: Rash and diarrhea are a class effect of ERBB1 inhibitors. These events are relatively mild with Lapatinib (a dual ERBB1/ERBB2 kinase inhibitor). Finding a genetic basis for patients who may be predisposed to these adverse events, from the outset of clinical development, may improve the understanding of the mechanisms of these side effects and may have implications for use and dosing. Methods: DNA was isolated from peripheral blood of 107 Caucasian subjects from eight monotherapy phase I studies including 73 healthy volunteers and 34 cancer patients, 100 of whom had associated pharmacokinetic data. 284 single nucleotide polymorphisms (SNPs) from five candidate genes of transporters (ABCB1, ABCG2) and enzymes (CYP 3A4 and 3A5, and 2C19) for which lapatinib is a substrate were genotyped and examined for associations with pharmacokinetic variables (dose-normalized AUC, Cmax, and Tmax) as well as rash (15 cases) and diarrhea (18 cases). Results: Skin rash and diarrhea in this phase I cohort were only mild, (i.e. grade I or II). Statistically significant associations were observed between 34 SNPs in CYP2C19, rash (22 SNPs) and diarrhea (6 SNPs), and between 15 SNPs in ABCB1 and Tmax. Notably, 3/3 subjects (2 healthy volunteers, one patient) homozygous for the CYP2C19*2 allele experienced both mild rash and diarrhea. Extensive linkage disequilibrium was observed among these associated SNPs. Conclusions: Our results suggest that it is possible to determine pharmacogenetic associations with side effect phenotypes during the earliest phase of clinical drug development. These results are currently being validated on a larger cohort of patients from phase II lapatinib clinical trials. [Table: see text]