Pharmacogenomic Research for Avoiding Adverse Reactions by Anti-cancer Drugs

Anti-cancer drugs have relatively low effective rates and high frequencies of adverse reactions, occasionally leading to cessation of their treatments. Use of pharmacogenomic (PGx) information could be able to select the patients with high-response and less-adverse reactions, resulting in increase of patients' QOL and proper use of drugs. We have been collaborating with National Cancer Center for PGx analysis of anti-cancer drugs including irinotecan and gemcitabine in Japanese cancer patients. Irinotecan, now used for treatments of many cancers, is metabolically activated to SN-38 and then inactivated to SN-38 glucuronide by a UDP-glucuronosyltransferase UGT1A1. In the UGT1A1 gene, two representative genetic polymorphisms, *28 and *6, were detected at 0.138 and 0.167, respectively in 177 Japanese cancer patients. When the patients were homozygotes of *28 or *6, or compound heterozygotes of them, statistically significant decreases were observed in the SN-38 glucuronidation activity and increases in the rate of severe neutropenia, compared to those in the patients without *28 or *6. Our results and papers were cited in the Japanese package inserts of irinotecan. Gemcitabine was inactivated by cytidine deaminase (CDA) into 2'-2'-difluorodeoxyuridine. A CDA polymorphism 208G>A (Ala70Thr) was detected at 0.037 frequency in 256 Japanese cancer patients and associated with reduced gemcitabine clearance as well as increased frequency of severe neutropenia. In the 4 patients suffered from very severe bone marrow toxicities, 3 patients were homozygous CDA*3, suggesting that this polymorphism is exquisite for predicting severe adverse reactions by gemcitabine in Japanese.