Evaluation of ABC gene polymorphisms on the pharmacokinetics and pharmacodynamics of capecitabine in colorectal patients: Implications for dosing recommendations

A polymorphism in ABCA2 is associated with neutropenia induced by capecitabine in Japanese patients with colorectal cancer

PURPOSE

Capecitabine is a prodrug that converts to 5-fluorouracil (5-FU) in three steps. A previous study showed that ABCA2 rs2271862 (C > T) and ABCG5 rs6720173 were associated with increased clearance of 5-FU and 5'-deoxy-5-fluorouridine, respectively, in Spanish patients with colorectal cancer (CRC) (Br J Clin Pharmacol 2021) and reported that ABCA2 rs2271862 was associated with decreased risk of capecitabine-induced neutropenia. Other studies have reported that ABCB1 rs1128503, rs2032592, and rs1045642 were associated with capecitabine-induced toxicity in Spanish CRC patients (Oncotarget 2015, Phamacogenomics 2010). Here, we prospectively examined the effects of ABC transporter genes polymorphisms on capecitabine pharmacokinetics and toxicity.

METHODS

We enrolled patients with postoperative CRC treated with adjuvant capecitabine plus oxaliplatin (CapeOX) and patients with metastatic CRC receiving CapeOX. Pharmacokinetic analysis of the first capecitabine dose (1000 mg/m2) was performed on day 1. We analyzed plasma concentrations of capecitabine and its three metabolites by high-performance liquid chromatography and ABC transporter genes polymorphisms using direct sequencing.

RESULTS

Patients with ABCA2 rs2271862 T/T genotype had significantly lower area under the plasma concentration-time curve of capecitabine, but not of its metabolites, which were divided by the dose of the parent drug, than patients with C/C or C/T genotype (P = 0.0238). Frequency of ≥ grade 2 neutropenia was significantly lower in patients with ABCA2 rs2271862 T/T genotype (P = 0.00915). Polymorphisms in ABCG5 and ABCB1 were not associated with capecitabine pharmacokinetics and toxicity.

CONCLUSIONS

We found that ABCA2 polymorphism was significantly associated with systemic exposure to capecitabine and capecitabine-induced neutropenia in Japanese patients with CRC.

Physiologically Based Pharmacokinetic Modeling for Prediction of 5-FU Pharmacokinetics in Cancer Patients with Hepatic Impairment After 5-FU and Capecitabine Administration

PURPOSE

5-fluorouracil (5-FU) and its prodrug capecitabine are commonly prescribed anti-tumor medications. We aimed to establish physiologically based pharmacokinetic (PBPK) models of capecitabine-metabolites and 5-FU-metabolites to describe their pharmacokinetics in tumor and plasma of cancer patients with liver impairment.

METHODS

Models including the cancer compartment were developed in PK-Sim® and MoBi® and evaluated by R programming language with 25 oral capecitabine and 18 intravenous 5-FU studies for cancer patients with and without liver impairment.

RESULTS

The PBPK models were constructed successfully as most simulated Cmax and AUClast were within two-fold error of observed values. The simulated alterations of tumor 5-FU Cmax and AUClast in cancer patients with severe liver injury compared with normal liver function were 1.956 and 3.676 after oral administration of capecitabine, but no significant alteration was observed after intravenous injection of 5-FU. Besides, 5-FU concentration in tumor tissue increases with higher tumor blood flow but not tumor size. Sensitivity analysis revealed that dihydropyrimidine dehydrogenase (DPD) and other metabolic enzymes' activity, capecitabine intestinal permeability and plasma protein scale factor played a vital role in tumor and plasma 5-FU pharmacokinetics.

CONCLUSIONS

PBPK model prediction suggests no dosage adaption of capecitabine or 5-FU is required for cancer patients with hepatic impairment but it would be reduced when the toxic reaction is observed. Furthermore, tumor blood flow rate rather than tumor size is critical for 5-FU concentration in tumor. In summary, these models could predict pharmacokinetics of 5-FU in tumor in cancer patients with varying characteristics in different scenarios.

Population pharmacokinetic and pharmacodynamic modeling of capecitabine and its metabolites in breast cancer patients

PURPOSE

The present study was performed to examine relationships between systemic exposure of capecitabine metabolites (5-FU, 5'-DFCR and 5'-DFUR) and toxicity or clinical response in patients with metastatic breast cancer.

METHODS

A population pharmacokinetic model for capecitabine and its three metabolites was built. Typical parameter values, characteristics of random distributions, associated with parameters, and covariates impact were estimated. Area under the curve (AUC) were computed for 5-FU and compared with grades of toxicity. Pharmacokinetic modeling was based on data collected on the first treatment cycle. Toxicity was assessed on the two first treatment cycles.

RESULTS

The study was conducted in 43 patients. The population pharmacokinetic model (a one-compartment model per compound) was able to capture the very complex absorption process of capecitabine. Statistically significant covariates were cytidine deaminase, alkaline phosphatase and dihydrouracilemia (UH2)/uracilemia (U) ratio. UH2/U ratio was the most significant covariate on 5-FU elimination and CDA on the transformation of 5'-DFCR in 5'-DFUR. A trend was observed between 5-FU AUC and thrombopenia toxicity grades, but not with other toxicities. Best clinical response was not linked to systemic exposure of capecitabine metabolites.

CONCLUSION

In our study, we propose a model able to describe, meanwhile, and its main metabolites, with a complex absorption process and inclusion of enzyme activity covariates such as CDA and UH2/U ratio. Trial registration Eudract 2008-004136-20, 2008/11/26.

The Road so Far in Colorectal Cancer Pharmacogenomics: Are We Closer to Individualised Treatment?

In recent decades, survival rates in colorectal cancer have improved greatly due to pharmacological treatment. However, many patients end up developing adverse drug reactions that can be severe or even life threatening, and that affect their quality of life. These remain a limitation, as they may force dose reduction or treatment discontinuation, diminishing treatment efficacy. From candidate gene approaches to genome-wide analysis, pharmacogenomic knowledge has advanced greatly, yet there is still huge and unexploited potential in the use of novel technologies such as next-generation sequencing strategies. This review summarises the road of colorectal cancer pharmacogenomics so far, presents considerations and directions to be taken for further works and discusses the path towards implementation into clinical practice.