Polymorphisms in UGT1A gene family and irinotecan toxicity in patients with advanced colorectal cancer

Abstract

13049 Background: The irinotecan active metabolite, SN38, is inactivated through glucuronidation mainly by uridine diphosphate glucuronosyltransferase (UGT) 1A1. The (TA)7 allele of a polymorphism in UGT1A1 promoter has been associated with reduced SN38-glucuronidation rate and more severe toxicity. Since other UGT1A family isoforms, the extrahepatic UGT1A7 and the hepatic UGT1A9, are involved in SN38 glucuronidation, it has been suggested that also polymorphic variants of these genes may affect irinotecan toxicity. Methods: 84 patients with advanced colorectal cancer received an irinotecan-based (180 mg/m2 q.2wks) combination treatment. Polymorphisms of UGT1A1 [(TA)6>7], UGT1A7 [387T > G, 391–2CG > AA, 622T > C] and UGT1A9 [-118(T)9>10, -87G > A, 98T > C, I152G > A] were identified by sequencing on DNA from blood samples obtained under an IRB approved protocol. Toxicity has been graded according to NCI-CT criteria. Results: Patient median age was 64 y (range: 31–82); median PS was 0 (range: 0–2). Severe toxicity (diarrhea or/and neutropenia ≥G3) has been observed in 32 patients: diarrhea in 11, neutropenia in 25 (4 patients had both). The estimated allele frequencies were as follows: UGT1A1, (TA)7 (0.35); UGT1A7, 387T and the completely linked 391–2CG (0.39), 622C (0.39); UGT1A9, -118(T)10 (0.39), -87A (0.05), T98C (0.02), I152A (0.21). Severe toxicity was significantly associated only with: (a) the UGT1A1 (TA)7 allele [severe toxicity in 25% of (TA) 6/6, in 46% of (TA) 6/7, in 55% of (TA) 7/7 (Mantel-Haenszel trend test, P < 0.03)]; and (b) the low activity UGT1A7 622C allele [severe toxicity in 26% of 622 T/T, in 39% of 622 T/C, in 67% of 622 C/C (Mantel-Haenszel, P < 0.02)]. In addition, the analysis of the combined genotypes [(TA)6>7 and 622T > C] has shown severe toxicity in 21% of patients with none of (TA)7 and of 622C alleles, in 43% of patients in which the sum of the number of (TA)7 and of 622C alleles is 1 or 2, in 57% of patients in which this sum is ≥3 (the latter includes all patients with both toxicities) (Mantel-Haenszel, P < 0.02). Conclusions: These data show that both the low activity UGT1A1 (TA)7 and UGT1A7 622C alleles are significantly associated with irinotecan severe toxicity. It is to evaluate if their combined genotype may be a better predictor of toxicity. No significant financial relationships to disclose.