CarboxylesteraseIsoform2mRNAExpressioninPeripheralBlood Mononuclear Cells Is a Predictive Markerof the Irinotecan toSN38ActivationStepinColorectalCancerPatients Erika Cecchin, 1 Giuseppe Corona, 1 Sara Masier, 1 Paola Biason, 1 Giulio Cattarossi, 1 Sergio Frustaci, 2 Angela Buonadonna, 2 Annamaria Colussi, 2 and Giuseppe Toffoli 1 Abstract Purpose: Irinotecan (CPT11) is a prodrug activated in humans mainly by carboxylesterase 2 (CES2) generating the SN38 metabolite responsible for the drug efficacy and toxicity. The inter- patients variability in CPT11activation step could cause unpredictable toxicity. To identify a pre- dictive molecular marker for CPT11activation in cancer patients, we investigated the CES2 mRNA expression in peripheral blood mononuclear cells (PBMC) and correlated it to CPT11 acti- vation rate, toxic effects, and response. ExperimentalDesign: Forty-five colorectal cancer patients were treated with a CPT11-including regimen (FOLFIRI). CES2 mRNA expression in PBMC was quantified by reverse transcription- PCR in real time. Plasma concentrations of CPT11, SN38, and SN38-glucuronide were determined by high-performance liquid chromatography and the pharmacokinetic variables calculated adopting the noncompartmental model. Toxicity was evaluated by the National Cancer Institute CommonToxicity Criteria scale and response by the WHO criteria. Results: A high interindividual variability in CES2 mRNA relative expression was observed (median, 1.45; range, 0.01-28.21). CES2 mRNA expression level was significantly associated with CPT11activation ratio [(AUC SN38 + AUC SN38G )/AUC CPT11 ]. Patients with CES2 mRNA expression above the median cutoff value presented an activation ratio higher (median, 0.25; range, 0.15- 0.42) than those with CES2 mRNA below the median (median, 0.20; range, 0.10-0.40; P = 0.013). This was associated with a nonsignificant trend of 1.34-fold increase of SN38 AUC in the group of patients with high CES2 mRNA expression (mean, 1.03 F 0.62 versus 0.77 F 0.32 Amol/L hour). Eight of 23 high CES2 mRNA ^ expressing patients (34.8%) developed grade 3 to 4 neutropenia or diarrhea compared with 2 of 22 (9.1%) in the low CES2-expressing group (P = 0.071). Conclusion: Our data support a predictive power of CES2 mRNA expression in PBMC for the activation rate of CPT11. Irinotecan {7-ethyl-10-[4-(1-piperidino)-1-piperidino]carbo- nyloxycamptothecin, CPT11} is a topoisomerase I inhibitor, active in cancer chemotherapy. It is used as a first-line treatment for metastatic colorectal cancer in association with 5-fluoro- uracil and leucovorin and is active in ovarian, lung, breast, pancreatic, and cervix cancer (1). A great interpatient variability has been reported in terms of toxicity to CPT11, especially diarrhea and neutropenia, possibly related to differential plasma levels of the active metabolite SN38 (2). This depends on several factors such as the activation of CPT11 to SN38, the glucuronidation of SN38 to the inactive SN38 glucuronide (SN38G), or to the biliary excretion levels of SN38 (3). Presently, an impaired glucuronidation activity of the uridine diphosphoglucuronosyltransferase isoform 1 (UGT1A1) enzyme, possibly due to the genetic polymorphism of the UGT1A1 gene, has been considered to explain toxicity variabil- ity. In particular, UGT1A1*28 polymorphism, characterized by a variation in the number of TA repeats in the promoter region of the gene, is thought to be associated with interpatient differential glucuronidation of SN38 possibly leading to CPT11 pharmacokinetics and pharmacodynamics variability (4 – 6). The possibility of using a genetic marker for toxicity or response allows a simple methodologic approach of analysis that can be easily done in peripheral blood mononuclear cells (PBMC) allowing CPT11 dosage on the individual genetic profile. Nonetheless, data reported until now (7, 8) seem to suggest that UGT1A1 polymorphisms are not by themselves sufficient and should be enclosed in a more complete set of markers involved in drug metabolism, to increase their predictive power. A limiting step in CPT11 activation to SN38 in vivo is the CPT11 dipiperidino side chain hydrolysis mainly mediated by Cancer Therapy: Clinical Authors’Affiliations: 1 Experimental and Clinical Pharmacology and 2 Medical Oncology C, Centro di Riferimento Oncologico, National Cancer Institute, Aviano, Italy Received 3/17/05; revised 6/6/05; accepted 7/6/05. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Requestsforreprints: Giuseppe Toffoli, Experimental and Clinical Pharmacology, via Pedemontana Occidentale 12, 33081Aviano, Italy. Phone: 39-0434-659612; Fax: 39-0434-659659; E-mail: gtoffoli@cro.it. F 2005 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-05-0602 www.aacrjournals.org ClinCancerRes2005;11(19)October1,2005 6901 Cancer Research. on October 14, 2021. © 2005 American Association for clincancerres.aacrjournals.org Downloaded from