Irinotecan pharmacogenetics: influence of pharmacodynamic genes.
OBJECTIVE
Irinotecan is an important drug for the treatment of solid tumors. Although genes involved in irinotecan pharmacokinetics have been shown to influence toxicity, there are no data on pharmacodynamic genes. CDC45L, NFKB1, PARP1, TDP1, and XRCC1 have been shown to influence the cytotoxic action of camptothecins, including irinotecan. Polymorphisms in the drug target of camptothecins, topoisomerase I (TOP1), and downstream effectors may influence patient outcomes to irinotecan therapy. We undertook a retrospective candidate gene haplotype association study to investigate this hypothesis.


METHODS
Haplotype compositions of six candidate genes were constructed in European (n = 93), East Asian (n = 94), and West African (n = 95) populations. Haplotype-tagging single nucleotide polymorphisms (htSNP) were selected based on genealogic relationships between haplotypes. DNA samples from 107 European, advanced colorectal cancer patients treated with irinotecan-based regimens were genotyped for htSNPs as well as three coding region SNPs. Associations between genetic variants and toxicity (grade 3/4 diarrhea and neutropenia) or efficacy (objective response) were assessed.


RESULTS
TOP1 and TDP1 htSNPs were related to grade 3/4 neutropenia (P = 0.04) and response (P = 0.04), respectively. Patients homozygous for an XRCC1 haplotype (GGCC-G) were more likely to show an objective response to therapy than other patients (83% versus 30%; P = 0.02). This effect was also seen in a multivariate analysis (odds ratio, 11.9; P = 0.04). No genetic variants were associated with diarrhea.


CONCLUSIONS
This is the first comprehensive pharmacogenetic investigation of irinotecan pharmacodynamic factors, and our findings suggest that genetic variation in the pharmacodynamic genes may influence the efficacy of irinotecan-containing therapies in advanced colorectal cancer patients.
Hoskins
Janelle M
JM
Department of Internal Medicine, Washington University School of Medicine, St. Louis, Missouri, USA.
Marcuello
Eugenio
E
Altes
Albert
A
Marsh
Sharon
S
Maxwell
Taylor
T
Van Booven
Derek J
DJ
Paré
Laia
L
Culverhouse
Robert
R
McLeod
Howard L
HL
Baiget
Montserrat
M
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000972:Antineoplastic Agents, Phytogenic / Q000009:adverse effects / Q000493:pharmacokinetics / Q000627:therapeutic use; D002166:Camptothecin / Q000009:adverse effects / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000627:therapeutic use; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000188:drug therapy / Q000235:genetics; D018450:Disease Progression; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects*; D014453:Glucuronosyltransferase / Q000235:genetics; D006239:Haplotypes; D006801:Humans; D000077146:Irinotecan; D008297:Male; D008875:Middle Aged; D010597:Pharmacogenetics; D020641:Polymorphism, Single Nucleotide; D012189:Retrospective Studies; D000099148:UGT1A1 Enzyme
D000972:Antineoplastic Agents, Phytogenic; D002166:Camptothecin; D014453:Glucuronosyltransferase; D000077146:Irinotecan; D000099148:UGT1A1 Enzyme