Irinotecan dose reduction in metastatic colorectal cancer patients with homozygous UGT1A1*28 polymorphism: a single-center case series

Mechanisms and emerging strategies for irinotecan-induced diarrhea

Irinotecan (also known as CPT-11) is a topoisomerase I inhibitor first approved for clinical use as an anticancer agent in 1996. Over the past more than two decades, it has been widely used for combination regimens to treat various malignancies, especially in gastrointestinal and lung cancers. However, severe dose-limiting toxicities, especially gastrointestinal toxicity such as late-onset diarrhea, were frequently observed in irinotecan-based therapy, thus largely limiting the clinical application of this agent. Current knowledge regarding the pathogenesis of irinotecan-induced diarrhea is characterized by the complicated metabolism of irinotecan to its active metabolite SN-38 and inactive metabolite SN-38G. A series of enzymes and transporters were involved in these metabolic processes, including UGT1A1 and CYP3A4. Genetic polymorphisms of these metabolizing enzymes were significantly associated with the occurrence of irinotecan-induced diarrhea. Recent discoveries and progress made on the detailed mechanisms enable the identification of potential biomarkers for predicting diarrhea and as such guiding the proper patient selection with a better range of tolerant dosages. In this review, we introduce the metabolic process of irinotecan and describe the pathogenic mechanisms underlying irinotecan-induced diarrhea. Based on the mechanisms, we further outline the potential biomarkers for predicting the severity of diarrhea. Finally, based on the current experimental evidence in preclinical and clinical studies, we discuss and prospect the current and emerging strategies for the prevention of irinotecan-induced diarrhea.

Irinotecan dosing and pharmacogenomics: a comprehensive exploration based on UGT1A1 variants and emerging insights

Irinotecan is a critical anticancer drug used to treat metastatic colorectal cancer and advanced pancreatic ductal adenocarcinoma by obstructing topoisomerase 1; however, it can cause minor-to-severe and life-threatening adverse effects. UDP glucuronosyltransferase family 1 member A1 (UGT1A1) polymorphisms increase the risk of irinotecan-induced neutropenia and diarrhea. Hence, screening for UGT1A1 polymorphisms before irinotecan-based chemotherapy is recommended to minimize toxicity, whereas liposomes offer the potential to deliver irinotecan with fewer side effects in patients with pancreatic ductal adenocarcinoma. This review presents a comprehensive overview of the effects of genotype-guided dosing of irinotecan on UGT1A1*28 and UGT1A1*6 variants, incorporating pharmacogenomic research, optimal regimens for metastatic colorectal and pancreatic cancer treatment using irinotecan, guidelines for toxicity reduction, and an evaluation of the cost-effectiveness of UGT1A1 genotype testing.

A phase-II study based on dose adjustment according to UGT1A1 polymorphism: is irinotecan underdosed in first-line FOLFIRI regimen for mCRC?

PURPOSE

Irinotecan has considerable importance in the treatment of metastatic colorectal cancer (mCRC). UDP-glucoronyltransferase (UGT) 1A1 is responsible for the inactivation of SN-38, a metabolite of irinotecan. Depending on UGT1A1 polymorphism, the activity of the UGT enzyme can be reduced leading to more frequent occurrence of adverse events related to irinotecan. The present study aimed to assess the safety and efficacy of different doses of irinotecan adjusted according to UGT1A1 polymorphism.

METHODS

Thirty-four patients treated with FOLFIRI as first-line treatment for mCRC were included in this study. The irinotecan dosage was adapted on the basis of UGT1A1 polymorphisms: *1/*1 (370 mg/m2); *1/*28 (310 mg/m2), and *28/*28 (180 mg/m2). The incidence of grades 3 and 4 toxicities (neutropenia, febrile neutropenia, and diarrhoea) was recorded. Response was assessed according to the RECIST 1.1 criteria.

RESULTS

On the basis of UGT1A1 genotyping, 20 patients were *1/*1 (58.8%), 12 were *1/*28 (35.3%) and 2 were *28/*28 (5.9%). Seven patients experienced at least one severe toxicity, i.e., 21% of the population, amounting to eleven adverse events. Concerning the response rate, 15 patients (44%) had partial or complete response.

CONCLUSION

This study demonstrates that mCRC patients treated with FOLFIRI can tolerate a higher dose of irinotecan than the standard dose, i.e., > 180 mg/m2, on the basis of their UGT1A1 genotype, without increased toxicities.

TRIAL REGISTRATION

NCT01963182 (registered on 16/10/2013, Clermont-Ferrand, France).

Real-World Outcomes of First-Line FOLFIRI Plus Bevacizumab with Irinotecan Dose Escalation versus FOLFOXIRI Plus Bevacizumab in BRAFV600E-Mutant Metastatic Colorectal Cancer: The Preliminary Data from a Single-Center Observational Study

Background and Objectives: Approximately 5-10% of all patients with metastatic colorectal cancer (mCRC) harbor a BRAFV600E mutation. These patients exhibit distinct metastatic patterns, poor prognosis, and heterogenous survival outcomes. The findings from the TRIBE study indicated that the administration of FOLFOXIRI plus bevacizumab as first-line treatment extended the median duration of overall survival (OS). In this study, we explored the effects of UGT1A1 polymorphism on the outcomes of irinotecan dose escalation versus FOLFOXIRI plus bevacizumab in patients with BRAFV600E-mutant mCRC. Materials and Methods: We retrospectively reviewed the medical records of 25 patients who had received a diagnosis of BRAFV600E-mutant mCRC between October 2015 and August 2022. All patients underwent UGT1A1 genotyping before receiving bevacizumab plus FOLFIRI. The primary end point was progression-free survival (PFS), and secondary endpoints were OS and adverse events (AEs). The two treatment arms were compared in terms of 6-month PFS and 12-month OS. Results: Over a median follow-up duration of 15.0 (interquartile range, 10.0-30.5) months, no significant differences were noted between the treatment arms in severe AEs (SAEs), 6-month PFS, or 12-month OS (all p < 0.05). Regarding AEs, the FOLFIRI plus bevacizumab regimen was associated with a lower incidence of anorexia than was the FOLFOXIRI plus bevacizumab regimen (p = 0.042). Conclusions: Our findings indicate that FOLFIRI plus bevacizumab with irinotecan dose escalation is an effective first-line treatment regimen for patients with BRAFV600E-mutant mCRC. This regimen leads to acceptable clinical outcomes with manageable AEs. However, the effects on survival and safety outcomes could only be speculated, and further studies are needed because of the sample size, the follow-up for the OS evaluation, and the non-uniformity in all the variables considered in the two groups.