The utility of genomics and functional imaging to predict irinotecan pharmacokinetics and pharmacodynamics: The PREDICT IR study.

Abstract

2564 Background: BSA-based dosing of Irinotecan (IR), does not account for its pharmacokinetic (PK) and pharmacodynamic (PD) variability. Given IR’s unique metabolism, functional hepatic nuclear imaging (HNI) with probes for hepatic transporters correlated with its PK. This study further evaluated the utility of HNI combined with extensive excretory/metabolic/PD pharmacogenomics (PG) to predict IR PK and PD in patients (pts) treated with FOLFIRI to enable dose individualization. Methods: Eligible pts had advanced colorectal cancer, suitable for 1st/2nd-line FOLFIRI± Bevacizumab. Pts had blood analyzed by Affymetrix DMET™ Plus Array and additional SNPs were genotyped. For HNI, pts were given IV 250MBq 99mTc-IDA and imaging data analyzed for hepatic extraction/excretion parameters (clearance [CL], 1hour retention [1hRET], deconvulutional CL [DeCL], hepatic extraction fraction [HEF]). Pts treated with chemotherapy, q2-weekly, and restaged after 4 cycles. Blood taken for IR and metabolite (SN38, SN38G) analysis on day 1 cycle 1, PK parameters derived by non-compartmental analysis. Statistical correlations were evaluated between (i) IDA HNI and (2) PGs, with IR PK, toxicity, objective response (ORR) and progression-free survival (PFS). Results: 32 pts analysed, 31 pts completed 4 cycles. (1) PK correlates: (a) HNI CL and 1hRET with SN38 Metabolic CL, (P = 0.04) and (b) HNI DeCL with IR AUC(0-∞) (P = 0.04). (2) Grade 3+ diarrhea (N = 4, 13%) predicted by SN38 AUC(0-∞) and Metabolic CL (P = 0.04), and gene variants for SCL22A2 and -28A3, ABCC2, UGT2B17, CYP2C18 and DPYD (P < 0.05). (3) Grade 3+ neutropenia (N = 9, 28%) predicted by SN38 PK exposure (P < 0.02), HNI CL and 1hRET (P < 0.0001) and variants for SLC7A7-, SLC22A2-, CHST1-, UGT1A1-, -2B7, ABCB1. (4) ORR (N = 6, 20%) predicted by Methylene tetrahydrofolate reductase (MTHFR) 677C > T (P = 0.002), SN38 exposure (P < 0.003), and variants in metabolic/transporter genes (P < 0.05). (5) PFS by SN38 PK exposure, MTHFR 677C > T, HNI CL, HNI HEF and variants in PK genes (P < 0.05). Conclusions: Hepatic functional imaging with extensive pharmacogenomics correlate with Irinotecan PK and PD enabling the development of nomograms to individualize dosing. Clinical trial information: ACTRN12610000898055.