Pharmacogenetics
In consenting patients, prior to the first palbociclib dose, whole blood (5 mL) was collected for DNA extraction with a Gentra Puregene Blood Kit (#158389, Qiagen). DNA was quantified by using Nanodrop 2000 Spectrophotometer (Thermo Fisher Scientific). Genome-wide genotyping was performed in germline DNA with an Illumina Infinium Omni2.5Exome-8 Bead-Chip (Illumina Inc.) Selected genes included CYP3A4 ,CYP3A5 , and SULT2A1 involved in palbociclib metabolism, and ABCB1 , ABCG2 , ABCC1 , and ABCC4 which encode genes for known drug transporters. All available single nucleotide polymorphisms (SNPs) from these genes with a reported minor allelic frequency >5% (https://www.ncbi.nlm.nih.gov/snp/) were extracted.
Associations between palbociclib Cmax and AUC0-Tlast after single and repeated doses and genotypes were evaluated using non-parametric Kruskal-Wallis tests, Mann-Whitney U-tests, and linear regression. For SNPs including data from wild-type (0), heterozygous (1), and homozygous mutant (2) patients, the distribution of the pharmacokinetic variables was compared between 0,1, and 2, and between 0+1 vs 2, and 0 vs 1+2. Statistical significance was defined by a p-value P < 0.05. Strong linkage disequilibrium (LD) between SNPs, defined as r2>0.80, was verified using the LD matrix tool (https://ldlink.nci.nih.gov/ ). Based on the population size, associations were tested using a univariate analysis only. All the tests were performed using R® software.