Purpose: We performed a UGT1A1 genotype-guided study to determine the maximum tolerated dose (MTD) and evaluate the toxicities and pharmacokinetics of the combination of capecitabine (CAP), oxaliplatin (OX), and irinotecan (IRIN).
Experimental design: Patients were screened for UGT1A1 *28 genotype prior to treatment. The starting dose (mg/m(2)) was IRIN (150), OX (85) and CAP (400), days 2-15. Doses were escalated or de-escalated within each genotype group (*28/*28, *1/*28 and *1/*1). IRIN pharmacokinetics was performed at the MTD.
Results: 50 patients were evaluable for toxicity [11 (*28/*28); 18 (*1/*28); 21 (*1/*1)]. UGT1A1 *28/*28 patients experienced hematologic dose limiting toxicity (DLT), requiring dose-de-escalation. The UGT1A1 *28/*28 recommended phase 2 dose (RP2D) was IRIN (75), OX (85), and CAP (400). In contrast, both UGT1A1 *1/*28 and *1/*1 tolerated higher doses of IRIN and non-hematologic toxicity was dose limiting for UGT1A1 *1/*1. The RP2D was IRIN (150), OX (85), and CAP (400) for UGT1A1*1/*28 and IRIN (150), OX (100), and CAP (1600) for UGT1A1 *1/*1. UGT1A1 *1/*28 and *1/*1 patients treated with IRIN (150) had similar AUCs for the active irinotecan metabolite, SN38 (366 +/- 278 and 350 +/- 159 ng/ml*hr, respectively). UGT1A1 *28/*28 patients (n = 3) treated with a lower IRIN dose (100) had non-significantly higher mean SN38 exposures (604 +/- 289 ng/ml*hr, p = 0.14). Antitumor activity was observed in all genotype groups.
Conclusions: UGT1A1 genotype affects the dose and pharmacokinetics of the CAPIRINOX regimen and UGT1A1 genotype-guided dosing of CAPIRINOX is ongoing in a phase II study of small bowel cancer (NCT00433550).