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.

Regulation of carboxylesterase-2 expression by p53 family proteins and enhanced anti-cancer activities among 5-fluorouracil, irinotecan and doxazolidine prodrug

BACKGROUND AND PURPOSE

For four decades, 5-fluorouracil (5-FU) has been a major anti-cancer medicine. This drug is increasingly used with other anti-cancer agents such as irinotecan. Irinotecan and many others such as PPD (pentyl carbamate of p-aminobenzyl carbamate of doxazolidine) require activation by carboxylesterase-2 (CES2). 5-FU, on the other hand, reportedly induces CES2 in colorectal tumour lines. The aims of this study were to determine the molecular basis for the induction and to ascertain interactive cell-killing activity between 5-FU and ester prodrugs.

EXPERIMENTAL APPROACH

Colorectal and non-colorectal lines and xenografts were treated with 5-FU and the expression of CES2 was determined. Cell-killing activity of irinotecan and PPD were determined in the presence or absence of CES2 inhibitor. Several molecular experiments were used to determine the molecular basis for the induction.

KEY RESULTS

Without exceptions, robust induction was detected in cell lines expressing functional p53. High-level induction was also detected in xenografts. 5-FU pretreatment significantly increased cell-killing activity of irinotecan and PPD. Molecular experiments established that the induction was achieved by both transactivation and increased mRNA stability through p53. Either p63 or p73, functionally related to p53, did not support the transactivation.

CONCLUSIONS AND IMPLICATIONS

The results in this study suggest that FOLFIRI, a common regimen combining irinotecan and 5-FU, should switch the dosing sequence, namely from 5-FU to irinotecan, to enhance hydrolytic activation of irinotecan. This modified order likely reduces the dose of anti-cancer agents, thus minimizing overall toxicity. The results also conclude that p53 family members act differently in regulating gene expression.

The impact of dose/time modification in irinotecan- and oxaliplatin-based chemotherapies on outcomes in metastatic colorectal cancer

PURPOSE

This study was designed to evaluate (1) the impact of relative dose intensity (RDI) on tumor response and survival outcomes and (2) the influence of dose reduction and schedule modification on outcomes in patients with metastatic colorectal cancer (mCRC).

METHODS

Pooled datasets from two previous phase II trials of FOLFIRI (CCOG-0502; n = 36) and mFOLFOX6 (CCOG-0704; n = 30) in patients with mCRC were analyzed retrospectively. The RDIs of irinotecan and oxaliplatin were compared to response rate (RR), disease control rate (DCR), progression-free survival (PFS) and overall survival (OS). To assess the effects of dose reduction and schedule modification, the effects of dose index (DI) and time index (TI) on outcomes were evaluated.

RESULTS

The median RDIs of irinotecan in FOLFIRI and oxaliplatin in mFOLFOX6 were 80 and 79 %, respectively. Higher RDI of irinotecan in FOLFIRI was associated with significant improvements in RR (65 vs. 6 %, p < 0.01), DCR (100 vs. 59 %, p < 0.01), PFS (9.9 vs. 5.6 months, p < 0.01) and OS (26.7 vs. 12.9 months, p = 0.01) and was the only independent factor associated with PFS [hazard ratio (HR) 8.48, p < 0.01). Higher RDI of oxaliplatin in FOLFOX was significantly associated with DCR (65 vs. 6 %, p < 0.01), and higher TI of oxaliplatin was the only independent factor associated with PFS (HR 2.74, p = 0.04).

CONCLUSION

RDIs of irinotecan and oxaliplatin affected clinical outcomes. Dose reductions in irinotecan, as indicated by DI, and time delays in oxaliplatin, as indicated by TI, were the only independent prognostic factors predicting PFS in patients receiving FOLFIRI and FOLFOX6, respectively.

A genotype-directed phase I-IV dose-finding study of irinotecan in combination with fluorouracil/leucovorin as first-line treatment in advanced colorectal cancer

Background:

Infusional fluorouracil/leucovorin (FU/LV) plus irinotecan (FOLFIRI) is one of the standard first-line options for patients with metastatic colorectal cancer (mCRC). Irinotecan is converted into 7-ethyl-10-hydroxycamptothecin (SN-38) by a carboxylsterase and metabolised through uridine diphosphate glucuronosyl transferase (UGT1A1). The UGT1A1^*28 allele has been associated with the risk of developing severe toxicities. The present trial was designed to define the maximum tolerated dose according to UGT1A1 genotype. This report focuses on the results of tolerance to different escalated doses of FOLFIRI first-line of chemotherapy.

Patients and methods:

Patients undergoing first-line treatment for mCRC and eligible for treatment with FOLFIRI were classified according to UGT1A1 genotype. A total of 94 patients were eligible for dose escalation of irinotecan. The starting dose of biweekly irinotecan was 180 mg m⁻² for the ^*1/^*1, 110 mg m⁻² for the ^*1/^*28 and 90 mg m⁻² for the ^*28/^*28 genotypes.

Results:

The dose of irinotecan was escalated to 450 mg m⁻² in patients with the ^*1/^*1 genotype, to 390 mg m⁻² in those with the ^*1/^*28 genotype and to 150 mg m⁻² in those with the ^*28/^*28 genotype. Neutropenia and diarrhoea were the most common grade 3 or 4 toxicities.

Conclusions:

Our results demonstrated that the recommended dose of 180 mg m⁻² for irinotecan in FOLFIRI is considerably lower than the dose that can be tolerated for patients with the UGT1A1 ^*1/^*1 and ^*1/^*28 genotypes. The maximum tolerable dose (MTD) in patients with a high-risk UGT1A1 ^*28/^*28 genotype is 30% lower than the standard dose of 180 mg m⁻².