Abstract P3-06-43: A genetic deletion in the uridine diphosphate glucuronosyltransferase 2B17 affects the pharmacokinetics of exemestane
Authors: Johansson Harriet , Aristarco Valentina , Gjerde Jennifer , Gandini Sara , Guerrieri-Gonzaga Aliana , Lazzeroni Matteo , Mora Serena , Macis Debora , Serrano Davide , Toesca Antonio , Bottiglieri Luca , Mellgren Gunnar , Viale Giuseppe , DeCensi Andrea , Bonanni Bernardo 
Published: May 2015

Background Exemestane (EXE) is an aromatase inactivator used in the prevention and treatment of breast cancer (BC). The majority of EXE and its active metabolite 17-dihydroEXE are excreted as glucuronide conjugates by uridine diphosphate glucuronosyltransferase (UGT). The UGT2B17 enzyme is the most expressed in human liver. A deletion spanning the entire UGT2B17 gene (*2) decreased the EXE glucuronidation process by 14-fold in human liver microsomes (HLM) from UGT2B17(*2/*2) genotype subjects compared to wild-type UGT2B17(*1/*1) HLMs.

Aim The aim of this study was to investigate whether the UGT2B17 deletion is associated with increased serum levels of EXE and 17-dihydroEXE and to assess if this deletion predicts the anti-proliferative effect of EXE in BC tissue as measured by Ki67 changes 6 weeks apart.

Methods In a phase II pre-surgical trial, 50 postmenopausal women with histologically-confirmed ER positive BC; stage T1-2, N0-1, M0 were assigned to EXE 25 mg/d for 6 weeks before surgery. Morning fasting blood was collected at baseline (B) and after 6 weeks and stored at -80° C until assayed. Time of last drug intake was collected at blood draw. DNA was extracted from whole blood (Qiagen, Italy). We used Taqman copy number variation assay (Life Technologies, Monza, Italy) for the UGT2B17 genotyping. EXE and 17-dihydroEXE concentrations were determined by mass spectrometry (MS) using Waters® Xevo™ TQ MS in electrospray positive ionization mode (Waters, Manchester, UK), optimized by multiple reaction monitoring mode. We used Zorbax Eclipse Plus C18 columns and mobile phase MeOH/H2O with 0.1% formic acid. EXE pure substance was provided by Pfizer Inc.,17β-hydroxy EXE and EXE-19-d3 purchased from Toronto Research Chemicals (Toronto, Ontario, Canada).

Wilcoxon Signed Rank Test was used to assess differences in serum concentrations of EXE, its metabolites, and post-pretreatment tissue Ki67 changes according to UGT2B17 genotypes.

Results Median age and BMI were 62 years and 26 kg/m2, respectively. The UGT2B17 genotype (n=50) was 24 homozygote wt (*1/*1), 20 heterozygote (*1/*2) and 6 homozygote variant (*2/*2). Minor allele frequency = 0.32. Hardy-Weinberg Equilibrium (P=0.57) was respected.

Median and interquartile ranges (IQRs) of EXE and 17-dihydroEXE at 6 weeks, by time elapsed since last drug intakeTime since last drugEXE (nM)17-dihydroEXE (nM)≤24 hours (n=32)10.25 (5.55, 17.25)2.75 (1.85, 3.6)&gt;24 hours (n=15)2.10 (1.20, 2.20)*1.50 (1.20, 2.00)*** P=.0001 vs ≤24h; **P=.0003 vs ≤24h

;

Median and IQRs of EXE, 17-dihydroEXE and Ki67 change from B by UGT2B17 genotypesGenotypeEXE (nM)17-dihydroEXE (nM)Ki67 changeBMIUGT2B17 *1/*1 (n=22)5.3 (2.2, 11.4)1.85 (1.4, 3.06)-9 (-16, -5)28 (24, 32)UGT2B17 *1/*2, *2/*2 (n=25)9.3 (2.6, 17.6)*2.5 (2.0, 3.6)**-11 (-19, -3)♦26 (23, 30)♦♦P-values between genotype groups:*P=.28; **P=.04; ♦P=.82; ♦♦P=.41

Conclusions Our study demonstrates a significant association of the UGT2B17 deletion with increased serum concentrations of 17-dihydroEXE, irrespective of time since last drug intake. Neither 17-dihydroEXE, nor genotype explained the significant anti-proliferative effect of EXE on BC tissue. Larger studies should determine the clinical implications of this gene on EXE efficacy.

Citation Format: Harriet Johansson, Valentina Aristarco, Jennifer Gjerde, Sara Gandini, Aliana Guerrieri-Gonzaga, Matteo Lazzeroni, Serena Mora, Debora Macis, Davide Serrano, Antonio Toesca, Luca Bottiglieri, Gunnar Mellgren, Giuseppe Viale, Andrea DeCensi, Bernardo Bonanni. A genetic deletion in the uridine diphosphate glucuronosyltransferase 2B17 affects the pharmacokinetics of exemestane [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P3-06-43.