Determination of Capecitabine and Its Metabolites in Plasma of Egyptian Colorectal Cancer Patients

Abstract

The incidence of colorectal cancer (CRC) is increasing worldwide. It has variable signs and symptoms starting from changes in bowel habit to nausea and vomiting. Chemotherapeutic agents are often prescribed in CRC such as Capecitabine (CCB) and 5-Fluorouracil (FU). CCB is the prodrug of FU in oral dosage form, which makes it preferable by physicians, since no hospitalization is needed for drug administration. CCB is activated to FU in a three-step reaction producing 5′-deoxy-5-fluorocytidine (DFCR) (by carboxylesterase (CES) enzyme), then 5′-deoxy-5-fluorouridine (DFUR) (by cytidine deaminase (CDD) enzyme) and finally FU (by thymidine phosphorylase (TP) enzyme), the active form, which is later deactivated to give 5,6-dihydro-5-fluorouracil (DHFU). Different patients exhibit variable drug responses and adverse in response to CCB therapy, despite being treated by the same dose, which could be attributed to the occurrence of different possible enzyme single nucleotide polymorphisms (SNPs) along the activation and deactivation pathways of CCB. The most commonly occurring toxicities in CCB therapy are hand-foot syndrome and diarrhea. This study aims at developing and validating a new method for the simultaneous determination of CCB and its metabolites by HPLC-UV, followed by a correlation study with the toxicities occurring during therapy, where predictions of toxicity could be based on metabolites’ levels instead of the tedious process of genotyping. A new superior analytical method was optimized by a quality-by-design approach using DryLab® 2000 software achieving a baseline resolution of the six analytes within the least possible gradient time of 10 min. The method also showed linearity (in a range from 1 to 500 μg/mL), accuracy, precision and robustness upon validation: The LOD was found to be 3.0 ng/mL for DHFU and CCB, and 0.3 ng/mL for DFUR, DFCR and FU. The LOQ was found to be 10.0 ng/mL for DHFU and CCB, and 1.0 ng/mL for DFUR, DFCR and FU. The clinical results showed a positive correlation between the concentration of DFCR and mucositis and between the concentration of DFUR and hand-foot syndrome, confirming that this technique could be used for predicting such toxicities.