Population Pharmacokinetics of Gemcitabine and dFdU in Pancreatic Cancer Patients Using an Optimal Design, Sparse Sampling Approach

Liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) methods for the therapeutic drug monitoring of cytotoxic anticancer drugs: An update

In the era of precision medicine, there is increasing evidence that conventional cytotoxic agents may be suitable candidates for therapeutic drug monitoring (TDM)- guided drug dosage adjustments and patient's tailored personalization of non-selective chemotherapies. To that end, many liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) assays have been developed for the quantification of conventional cytotoxic anticancer chemotherapies, that have been comprehensively and critically reviewed. The use of stable isotopically labelled internal standards (IS) of cytotoxic drugs was strikingly uncommon, accounting for only 48 % of the methods found, although their use could possible to suitably circumvent patients' samples matrix effects variability. Furthermore, this approach would increase the reliability of cytotoxic drug quantification in highly multi-mediated cancer patients with complex fluctuating pathophysiological and clinical conditions. LC-MS/MS assays can accommodate multiplexed analyses of cytotoxic drugs with optimal selectivity and specificity as well as short analytical times and, when using stable-isotopically labelled IS for quantification, provide concentrations measurements with a high degree of certainty. However, there are still organisational, pharmacological, and medical constraints to tackle before TDM of cytotoxic drugs can be more largely adopted in the clinics for contributing to our ever-lasting quest to improve cancer treatment outcomes.

Correlation Between the Metabolic Conversion of a Capecitabine Metabolite, 5'-Deoxy-5-fluorocytidine, and Creatinine Clearance

AIM

Capecitabine is a prodrug that is metabolized to its active form, 5-fluorouracil (5-FU), in three enzymatic steps. This prospective pharmacokinetic study evaluated cytidine deaminase (CDA) activity, the second drug-metabolizing enzyme that generates 5'-deoxy-5-fluorouridine (5'-DFUR) from 5'-deoxy-5-fluorocytidine (5'-DFCR), as well as creatinine clearance (CLcr).

PATIENTS AND METHODS

Patients with colorectal cancer who received capecitabine plus oxaliplatin were selected. Pharmacokinetics of capecitabine and its metabolites, and CDA activity in plasma were analyzed.

RESULTS

Eighteen patients were examined. The area under the plasma concentration-time curve (AUC) of 5'-DFUR showed a significant inverse correlation with CLcr (p=0.003). The metabolic ratio, i.e. the ratios of the AUC of 5'-DFUR plus that of 5-FU to the AUC of 5'-DFCR, significantly increased when CLcr decreased (p=0.001) but did not depend on plasma CDA activity.

CONCLUSION

Metabolism of 5'-DFCR to form 5'-DFUR increased as CLcr decreased but the mechanism remains unknown.

CDA as a predictive marker for life-threatening toxicities in patients with AML treated with cytarabine

Cytarabine (Ara-C) is the backbone of acute myeloid leukemia (AML) chemotherapy. Little is known about possible risk factors predictive for the frequent (ie, up to 16%) life-threatening or lethal toxicities caused by Ara-C. Ara-C is detoxified in the liver by a single enzyme, cytidine deaminase (CDA), coded by a gene known to be highly polymorphic. In this proof-of-concept study, we particularly investigated the role of the CDA poor metabolizer (PM) phenotype in Ara-C toxicities. CDA phenotyping (measurement of CDA residual activity in serum) and genotyping (search for the CDA*2 allelic variant) were performed in 58 adult patients with AML treated with the standard 7+3 (Ara-C + anthracyclines) protocol. Statistically significantly lower CDA activity was observed in patients experiencing severe/lethal toxicities as compared with patients who did not (1.5 ± 0.7 U/mg vs 3.95 ± 3.1 U/mg; Student t test P < .001). Subsequent receiver operating characteristic analysis identified a threshold in CDA activity (ie, 2 U/mg) associated with PM syndrome and increased risk of developing severe toxicities. Five percent of patients experienced lethal toxicities, all displaying CDA PM status (1.3 ± 0.5 U/mg). In terms of efficacy, a trend toward higher response rates and longer progression-free survival and overall survival were observed in patients with low CDA activity. Taken together, the results of this study strongly suggest that CDA is a predictive marker of life-threatening toxicities in patients with AML receiving induction therapy with standard Ara-C.