Dexamethasone as a probe for vinorelbine clearance

CYP3A activity: towards dose adaptation to the individual

INTRODUCTION

Co-medication, gene polymorphisms and co-morbidity are main causes for high variability in expression and function of the CYP3A isoenzymes. Pharmacokinetic variability is a major source of interindividual variability of drug effect and response of CYP3A substrates. While CYP3A genotyping is of limited use, direct testing of enzyme function ('phenotyping') may be more promising to achieve individualized dosing of CYP3A substrates.

AREAS COVERED

We will discuss available phenotyping strategies for CYP3A isoenzymes and causes of intra- and interindividual variability of CYP3A. The impact of phenotyping on the dose selection and pharmacokinetics of CYP3A substrates (docetaxel, irinotecan, tyrosine kinase inhibitors, ciclosporin, tacrolimus) are reviewed. Pubmed searches were conducted during March-November 2015 to retrieve articles related to CYP3A enzyme, phenotyping, drug interactions with CYP3A probe substrates, and phenotyping-guided dosing algorithms.

EXPERT OPINION

While ample data is available on the choice appropriate phenotyping drugs (midazolam, alfentanil, aplrazolam, buspirone, triazolam), less clinical trial data is available concerning strategies to usefully guide dosing in the clinical practice. Implementation into the clinical routine necessitates further research to identify (1) an easy-to-use and cheap test for CYP3A activity that (2) adequately predicts drug exposure to (3) allow a sound decision on dose adaptation and hence (4) improve clinical outcome and/or reduce the intensity or frequency of adverse drug effects.

Sex differences in the drug therapy for oncologic diseases

There are clear gender-dependent differences in response rates and the probability of side effects in patients treated with chemotherapy. Sex-biased expression levels of metabolic enzymes and transporters in liver and kidney leading to different pharmacokinetics have been described for most common anti-cancer drugs. In women, half-life is often longer, which is associated with improved survival, but also increased toxicity.Some chemotherapy protocols lead to a better response rate in women without increasing toxicity (e.g., cisplatin and irinotecan), while others only increase toxicity, but do not improve response rates in women (e.g., 5-fluorouracil). The increased toxicity often correlates with different pharmacokinetics, but women also show a higher sensitivity to some agents with shorter half-life (e.g., steroids). Organ-specific toxicities like cardiac toxicity after doxorubicin treatment or neurotoxicity associated with ifosfamide are more severe in women due to gender-specific changes in gene expression. Novel therapies like tyrosine kinase inhibitors or monoclonal antibodies show very complex, but clinical significant differences depending on gender. Antibodies often have a longer half-life in women, which is associated with an improved response to therapy.Side effects appear to be highly dependent on different tissue properties, as women have a higher incidence of oral mucositis, but lower rates of gut toxicity. Nausea and vomiting is a greater problem in females during therapy due to the lower activity of anti-emetic drugs. Nausea and vomiting pose a bigger challenge in female patients, as anti-emetic drugs seem to be less effective.

Pharmacokinetic modeling of an induction regimen for in vivo combined testing of novel drugs against pediatric acute lymphoblastic leukemia xenografts

Current regimens for induction therapy of pediatric acute lymphoblastic leukemia (ALL), or for re-induction post relapse, use a combination of vincristine (VCR), a glucocorticoid, and L-asparaginase (ASP) with or without an anthracycline. With cure rates now approximately 80%, robust pre-clinical models are necessary to prioritize active new drugs for clinical trials in relapsed/refractory patients, and the ability of these models to predict synergy/antagonism with established therapy is an essential attribute. In this study, we report optimization of an induction-type regimen by combining VCR, dexamethasone (DEX) and ASP (VXL) against ALL xenograft models established from patient biopsies in immune-deficient mice. We demonstrate that the VXL combination was synergistic in vitro against leukemia cell lines as well as in vivo against ALL xenografts. In vivo, VXL treatment caused delays in progression of individual xenografts ranging from 22 to >146 days. The median progression delay of xenografts derived from long-term surviving patients was 2-fold greater than that of xenografts derived from patients who died of their disease. Pharmacokinetic analysis revealed that systemic DEX exposure in mice increased 2-fold when administered in combination with VCR and ASP, consistent with clinical findings, which may contribute to the observed synergy between the 3 drugs. Finally, as proof-of-principle we tested the in vivo efficacy of combining VXL with either the Bcl-2/Bcl-xL/Bcl-w inhibitor, ABT-737, or arsenic trioxide to provide evidence of a robust in vivo platform to prioritize new drugs for clinical trials in children with relapsed/refractory ALL.

Part II: Liver function in oncology: towards safer chemotherapy use

The liver is fundamentally important in drug metabolism. In oncology, the astute clinician must not only understand the meaning and limitations of commonly ordered liver biochemical tests, but also be aware of which anticancer agents might induce liver dysfunction, and of the strategies for appropriate dosing of patients with pre-existing liver dysfunction. In part I of our Review, we highlighted both the importance and inadequacies of identifying serum biochemical liver abnormalities in oncology; we also discussed a lack of routine formal investigation of liver function. We summarised chemotherapy-related hepatotoxicity and other causes of liver toxic effects in patients with cancer. Here in part II, we discuss trials that have specifically assessed chemotherapy dosing strategies in the setting of overt biochemical liver dysfunction and we note their recommendations. Furthermore, we review other assessments of liver metabolic and excretory function, particularly in the setting of chemotherapy drug handling. We discuss the potential use of these metabolic probes in practice.

Asparaginase may influence dexamethasone pharmacokinetics in acute lymphoblastic leukemia

PURPOSE

Dexamethasone is used widely in oncology, but pharmacokinetic studies are lacking. We evaluated dexamethasone pharmacokinetics in children with acute lymphoblastic leukemia.

PATIENTS AND METHODS

We assessed 214 children with acute lymphoblastic leukemia who received 418 courses of oral dexamethasone (8 mg/m(2)/d) on days 1 and 8 of reinduction. Extensive asparaginase use preceded reinduction in the 101 children in the standard/high-risk treatment arm but not in the 113 children in the low-risk treatment arm. A one-compartment model with first-order absorption and disposition was fit to dexamethasone plasma concentrations by using maximum a posteriori probability estimation; we evaluated covariates by using linear mixed models.

RESULTS

Interpatient and intrapatient variabilities in apparent clearance were substantial; they were 46% and 53%, respectively. Variability was explained by the serum albumin concentration (P < .0001), concomitant use of fentanyl (P = .008) and ketoconazole (P = .03), and age (P = .006). Apparent clearance was higher in the low-risk arm (P < .001) and was related to a greater serum albumin concentration (P < .001) and to a lower exposure to asparaginase than in the standard/high-risk arm. Hypoalbuminemia, a biomarker of asparaginase activity, was associated with a lower dexamethasone apparent clearance (P = .04) in patients in the standard/high-risk arm that was more pronounced in those not allergic to asparaginase. Ethnicity or gender did not explain apparent clearance variability.

CONCLUSION

Dexamethasone pharmacokinetics are highly variable and are related to the concurrent use of particular drugs, age, and treatment intensity. Patients allergic to asparaginase may be doubly disadvantaged: they not only suffer from diminished exposure to asparaginase but also, by maintaining high clearance of dexamethasone, may experience fewer antileukemic effects of dexamethasone.

MDR1 single nucleotide polymorphisms predict response to vinorelbine-based chemotherapy in patients with non-small cell lung cancer

BACKGROUND

The polymorphisms of genes participate in metabolism and transport, and therefore may have an impact on the response to vinorelbine.

OBJECTIVES

To investigate whether genotypes of CYP3A5, MDR1 and cyclooxygenase-2 (COX-2) are associated with the response to vinorelbine in non-small cell lung cancers (NSCLC).

METHODS

We determined the genotypes of CYP3A5(*3), MDR1 (2677G-->T at exon 21 and 3435C-->T at exon 26 and their haplotypes) and COX-2 (-1195G-->A) polymorphisms by PCR-RFLP and chemotherapy response in 69 Chinese Han patients with NSCLC who received a combination chemotherapy of vinorelbine-cisplatin (VC). The chi(2) test was used to investigate potential associations between genotypes and response to chemotherapy. Odds ratios and 95% confidence intervals were calculated.

RESULTS

The 3435 CC genotype was associated with a significantly better chemotherapy response compared with the combined 3435 CT and TT genotypes (p = 0.025). The 2677 GG genotype was also associated with a better chemotherapy response compared with the combined 2677 GT and TT genotype, although it was not statistically significant. Moreover, we analyzed the haplotypes of MDR1 3435-2677: patients harboring the 2677G-3435C haplotype had a statistically significantly better response to chemotherapy compared with those with the other haplotypes combined (p = 0.015). CYP3A5*3 is not likely to correlate with sensitivity to vinorelbine in NSCLC. COX-2 (-1195G) is likely to result in a better response to vinorelbine (nonsignificant).

CONCLUSIONS

Our findings suggest that MDR1 2677G-->T/A and 3435C-->T polymorphisms can be used to predict treatment response to VC chemotherapy in NSCLC patients.

Molecular pharmacokinetics of catharanthus (vinca) alkaloids

This review focuses on the published data regarding the molecular determinants (enzymes, transporters, orphan nuclear receptors) of Catharanthus (vinca) alkaloids pharmacokinetics in humans. The clinical impact of these determinants (drug disposition, drug-drug interactions) is also discussed.

Dexamethasone as a probe for CYP3A4 metabolism: evidence of gender effect

BACKGROUND

A study was conducted to evaluate prospectively the correlation between docetaxel clearance and pharmacokinetics of dexamethasone previously obtained in 21 patients.

PATIENTS AND METHODS

Dexamethasone pharmacokinetics were performed in 17 patients 24 h before docetaxel treatment as monochemotherapy. Dexamethasone and docetaxel plasma concentrations were determined by HPLC methods. Determination of docetaxel unbound fraction in plasma was performed using microequilibrium dialysis.

RESULTS

Significant correlation was observed between observed plasma docetaxel clearances (CL(docetaxel)) and values predicted from dexamethasone plasma clearance (CL(dexa)), unbound plasma docetaxel fraction estimated from serum alpha1-acid glycoprotein level (fu(alpha1-AAG)), and hepatic metastasis status. However, after splitting of the prospective data set according to gender, no correlation was observed for males (R(2) = 0.08, NS, n = 10), then strong correlation was observed for females (R(2) = 0.78, P < 0.01, n = 7). Multivariate analysis was performed from data obtained in the women included in the first study and those of this prospective study (n = 18). Docetaxel CL was significantly correlated with CL(dexa) (P = 0.001) and fu(alpha1-AAG) (P = 0.01) according to the relationship (with +/-95% confidence intervals): CL(docetaxel) (l/h) = 1.92 (+/-0.94) x CL(dexa) (l/h) + 2.68 (+/-1.95) x fu(alpha1-AAG) (%) (R(2) = 0.68).

CONCLUSION

Dexamethasone may be used to predict docetaxel clearances in females, but not in males.

Genotyping and phenotyping cytochrome P450: Perspectives for cancer treatment

As most anticancer agents display a narrow therapeutic window, patients may be susceptible to (extreme) toxicities or a lowered therapeutic outcome if not dosed adequately. Therefore, it is important to study factors which affect the pharmacokinetics and pharmacodynamics of these drugs. Among these, the contribution of genetic variation in drug metabolizing enzymes on the metabolism of anticancer agents has gathered interest, as it may potentially explain a substantial amount of interpatient variability in pharmacokinetics and drug response. Cytochrome P450, an oxidative enzyme-system involved in the breakdown of many drugs, is currently studied for correlations between genetic polymorphisms and anticancer drug metabolism. Also, alternative ways to predict the expression of cytochrome P450 have been developed (phenotyping measures) which may have additional value in creating a lowered interpatient variability, to minimize side-effects and maximize therapeutic efficacy.