Individualizing dosing of irinotecan

All You Need to Know About UGT1A1 Genetic Testing for Patients Treated With Irinotecan: A Practitioner-Friendly Guide

Irinotecan is an anticancer agent widely used for the treatment of solid tumors, including colorectal and pancreatic cancers. Severe neutropenia and diarrhea are common dose-limiting toxicities of irinotecan-based therapy, and UGT1A1 polymorphisms are one of the major risk factors of these toxicities. In 2005, the US Food and Drug Administration revised the drug label to indicate that patients with UGT1A1*28 homozygous genotype should receive a decreased dose of irinotecan. However, UGT1A1*28 testing is not routinely used in the clinic, and specific reasons include lack of access to concise information on this wide issue as well as mixed recommendations by regulatory and professional entities. To assist oncologists in assessing whether and when to use UGT1A1 genetic testing in patients receiving irinotecan-based therapies, this article provided (1) essential knowledge of UGT1A1 polymorphisms; (2) an update on the impact of UGT1A1 polymorphisms on efficacy and toxicity of contemporary irinotecan-based regimens; (3) dosing adjustments based upon the UGT1A1 genotypes, and (4) recommendations from currently available guidelines from the US and international scientific consortia and major oncology societies.

Identification of the bioactive components of Banxia Xiexin Decoction that protect against CPT-11-induced intestinal toxicity via UPLC-based spectrum-effect relationship analyses

ETHNOPHARMACOLOGICAL RELEVANCE

Irinotecan (CPT-11) is a valuable chemotherapeutic compound, but its use is associated with severe diarrhea in some patients. The CPT-11 prodrug is converted into the active 7-ethyl-10-hydroxycamptothecin (SN-38) metabolite, which can then be retained for extended periods in the intestine, leading to the onset of diarrhea and related symptoms. Banxia Xiexin Decoction (BXD) is commonly employed for the treatment of gastroenteritis in traditional Chinese medicine (TCM), and in clinical settings, it is used to prevent diarrhea in patients undergoing CPT-11 treatment. To date, however, there have been no studies specifically examining which components of BXD can alleviate the gastrointestinal symptoms associated with CPT-11 administration.

AIM

This study aimed to identify the main herbal components of BXD associated with protection against CPT-11-induced intestinal toxicity in a murine model system.

MATERIALS AND METHODS

SN-38 levels were measured by UPLC-ESI-MS/MS in samples collected from mice subjected to CPT-11-induced diarrhea that had been administered BXD or different components thereof. Pearson correlation and Grey relational analyses were then used to explore spectrum-effect relationships between reductions in intestinal SN-38 levels and specific chemical fingerprints in samples from mice administered particular combinations of BXD component herbs.

RESULTS

We found that different herbal combinations were associated with significant differences in intestinal SN-38 reductions in treated mice. Our spectrum-effect analysis revealed that BXD components including chrysin 6-C-arabinoside-8-C-glucoside, coptisine, hydroxyl oroxylin A 7-O-glucuronide (hydroxyl wogonoside), baicalin, an isomer of 5,6,7-trihydroxyl-flavanone-7-O-glucuronide, berberine, palmatine, and chrysin-7-O-glucuronide were all directly linked with reductions in intestinal SN-38 levels. We therefore speculate that these compounds are the primary bioactive components of BXD, suggesting that they offer protection against CPT-11-induced diarrhea.

CONCLUSION

By utilizing UPLC to analyze SN-38 levels in mice treated with a variety of herbal combinations, we were able to effectively explore BXD spectrum-effect relationships and to thereby establish the components of this medicinal preparation that were bioactive and capable of preventing CPT-11-induced diarrhea in mice. This and similar spectrum-effect studies represent a robust means of exploring the mechanistic basis for the pharmacological activity of TCM preparations.

Pharmacokinetic and Pharmacogenetic Markers of Irinotecan Toxicity

BACKGROUND

Irinotecan (IRI) is a widely used chemotherapeutic drug, mostly used for first-line treatment of colorectal and pancreatic cancer. IRI doses are usually established based on patient's body surface area, an approach associated with large inter-individual variability in drug exposure and high incidence of severe toxicity. Toxic and therapeutic effects of IRI are also due to its active metabolite SN-38, reported to be up to 100 times more cytotoxic than IRI. SN-38 is detoxified by the formation of SN-38 glucuronide, through UGT1A1. Genetic polymorphisms in the UGT1A1 gene are associated to higher exposures to SN-38 and severe toxicity. Pharmacokinetic models to describe IRI and SN-38 kinetic profiles are available, with few studies exploring pharmacokinetic and pharmacogenetic-based dose individualization. The aim of this manuscript is to review the available evidence supporting pharmacogenetic and pharmacokinetic dose individualization of IRI in order to reduce the occurrence of severe toxicity during cancer treatment.

METHODS

The PubMed database was searched, considering papers published in the period from 1995-2017, using the keywords irinotecan, pharmacogenetics, metabolic genotyping, dose individualization, therapeutic drug monitoring, pharmacokinetics and pharmacodynamics, either alone or in combination, with original papers being selected based on the presence of relevant data.

CONCLUSION

The findings of this review confirm the importance of considering individual patient characteristics to select IRI doses. Currently, the most straightforward approach for IRI dose individualization is UGT1A1 genotyping. However, this strategy is sub-optimal due to several other genetic and environmental contributions to the variable pharmacokinetics of IRI and its active metabolite. The use of dried blood spot sampling could allow the clinical application of limited sampling and population pharmacokinetic models for IRI doses individualization.

Determination of irinotecan, SN-38 and SN-38 glucuronide using HPLC/MS/MS: Application in a clinical pharmacokinetic and personalized medicine in colorectal cancer patients

BACKGROUND

Irinotecan (CPT-11) is chemotherapy used mainly in the metastatic colorectal cancer. The purpose of this study was to develop and validate the LC-MS/MS for the simultaneous determination of CPT-11, SN-38, and SN-38G.

METHODS

A 100 μL of plasma was prepared after protein precipitation and analyzed on a C18 column using 0.1% acetic acid in water and 0.1% acetic acid in acetonitrile as mobile phases. The mass spectrometer worked with multiple reaction monitoring (MRM) in positive scan mode. The standard curves were linear on a concentration range of 5-10 000 ng/mL for CPT-11, 5-1000 ng/mL for SN-38, and 8-1000 ng/mL for SN-38G.

RESULTS

In this assay, the intra and interday precision consisted of ≤9.11% and ≤11.29% for CPT-11, ≤8.70% and 8.31% for SN-38, and ≤9.90 and 9.64% for SN-38G.

CONCLUSION

This method was successfully used to quantify CPT-11, SN-38, and SN-38G and applied to a pharmacokinetic study.

Sequential designs for individualized dosing in phase I cancer clinical trials

This paper addresses dose finding in clinical trials where individuals exhibit biologic characteristics that alter the toxicity risks of the individuals. In these situations, instead of determining a dose that works for every patient, the trial aims to identify a dosing algorithm that prescribes dose according to the patient's biomarker or pharmacokinetic expression. Specifically, we aim to dose patients around a pre-specified level of area under the curve of irinotecan concentration using the patients' baseline phenotypes that predict drug clearance. We propose least squares recursion procedures to estimate the dosing algorithm sequentially with an aim to treat patients in the trial around the true unknown dosing algorithm, and introduce a novel application of an eigenvalue theory that guarantees convergence to the true dosing algorithms. Our simulation study demonstrates that using an eigenvalue constraint improves the efficiency of the recursion by as large as 40%, while concentrating in-trial patient allocation around the true dosing algorithm. We also provide practical guidance on design calibration, and design future irinotecan studies based on data from our first trial.

Pre-treatment serum total bilirubin level as an indicator of optimal CPT-11 dosage

BACKGROUND

Irinotecan (CPT-11), a highly effective chemotherapeutic agent, can cause severe neutropenia and diarrhea. The area under the curve of plasma levels over time of SN-38, an active metabolite of CPT-11, was previously reported to correlate with the pre-treatment serum total bilirubin level (PTB). However, there are no established criteria for selecting CPT-11 dose on the basis of PTB. Therefore, we evaluated PTB as an indicator for the optimal CPT-11 dose.

METHODS

Retrospective analyses were conducted in patients administered CPT-11 as a single agent at the Osaka National Hospital from June 2006 to July 2013. Data obtained during the first 28 days following CPT-11 administration were analyzed to compare PTB between patients with and without grade 3-4 neutropenia and grade 3-4 diarrhea. Receiver operating characteristics (ROC) curve analysis was performed to determine the optimal PTB cutoff value for PTB-associated toxicity. Subgroup analysis was performed comparing the incidence of toxicity in patients with PTB values below or above the cutoff value.

RESULTS

Although PTB incidence was significantly higher in patients who developed grade 3-4 neutropenia than in those who did not, PTB was not associated with grade 3-4 diarrhea. The PTB cutoff value for association with grade 3-4 neutropenia occurrence was set at 0.8 mg/dL. The incidence of febrile neutropenia (FN) significantly elevated to 21% in patients with PTB ≥0.8 mg/dL, whereas that of patients with PTB <0.8 mg/dL was 4%. In the subgroup analysis, no difference was found in the neutropenia incidence between patients treated with a dose below 80 mg/m(2) and those treated on a weekly schedule.

CONCLUSIONS

PTB can be used as a predictive marker of CPT-11-induced severe neutropenia and FN. In patients with PTB ≥0.8 mg/dL, the CPT-11 dose should be reduced to less than 80 mg/m(2) with weekly dosing.

Understanding patient and provider perceptions and expectations of genomic medicine

Advances in genome sequencing technology have fostered a new era of clinical genomic medicine. Genetic counselors, who have begun to support patients undergoing multi-gene panel testing for hereditary cancer risk, will review brief clinical vignettes, and discuss early experiences with clinical genomic testing. Their experiences will frame a discussion about how current testing may challenge patient understanding and expectations toward the evaluation of cancer risk and downstream preventive behaviors.

Correlation between plasma concentration ratios of SN-38 glucuronide and SN-38 and neutropenia induction in patients with colorectal cancer and wild-type UGT1A1 gene

In irinotecan (CPT-11)-based chemotherapy, neutropenia and diarrhea are often induced. In the present study, the clinical significance of the concentration ratios of 7-ethyl-10-hydroxycamptothecin (SN-38) glucuronide (SN-38G) and SN-38 in the plasma in predicting CPT-11-induced neutropenia was examined. A total of 17 patients with colorectal cancer and wild-type UDP-glucuronosyltransferase (UGT)1A1 gene were enrolled and treated with CPT-11 as part of the FOLFIRI regimen [CPT-11 and fluorouracil (5-FU)]. Blood was taken exactly 15 min following a 2-h continuous infusion of CPT-11. Plasma concentrations of SN-38, SN-38G and CPT-11 were determined by a modified high-performance liquid chromatography (HPLC) method. The median, maximum and minimum values of plasma SN-38G/SN-38 ratios were 4.25, 7.09 and 1.03, respectively, indicating that UGT activities are variable among patients with the wild-type UGT1A1 gene. The plasma SN-38G/SN-38 ratios decreased with an increase in the trial numbers of chemotherapy (r=0.741, p=0.000669), suggesting that CPT-11 treatment suppresses UGT activity, and the low plasma SN-38G/SN-38 ratios resulted in the induction of greater neutropenia. However, in this analysis, 2 clearly separated regression lines were observed between plasma SN-38G/SN-38 ratios and neutropenia induction. In conclusion, UGT activity involved in SN-38 metabolism is variable among patients with the wild-type UGT1A1 gene, and each CPT-11 treatment suppresses UGT activity. One-point determination of the plasma SN-38G/SN-38 ratio may provide indications for the prediction of CPT-11-induced neutropenia and adjustment of the optimal dose, although further studies are required.

Irinotecan pharmacogenomics

Irinotecan is a camptothecin analog used as an anticancer drug. Severe, potentially life-threatening toxicities can occur from irinotecan treatment. Although multiple genes may play a role in irinotecan activity, the majority of evidence to date suggests that variation in expression of UGT1A1 caused by a common promoter polymorphism (UGT1A1*28) is strongly associated with toxicity; however, this link is dose dependent. Variations in other pharmacokinetic genes, particularly the transporter ABCC2, also contribute to irinotecan toxicity. In addition, recent studies have shown that pharmacodynamic genes such as TDP1 and XRCC1 can also play a role in both toxicity and response.