Effect of common CYP3A4 and CYP3A5 variants on the pharmacokinetics of the cytochrome P450 3A phenotyping probe midazolam in cancer patients

Toward individualized treatment: prediction of anticancer drug disposition and toxicity with pharmacogenetics

A great deal of effort has been spent in defining the pharmacokinetics and pharmacodynamics of investigational and registered anticancer agents. Often, there is a marked variability in drug handling between individual patients, which contributes to variability in the pharmacodynamic effects of a given dose of a drug. A combination of physiological variables, genetic characteristics (pharmacogenetics) and environmental factors is known to alter the relationship between the absolute dose and the concentration-time profile in plasma. A variety of strategies are now being evaluated in patients with cancer to improve the therapeutic index of anticancer drugs by implementation of pharmacogenetic imprinting through genotyping or phenotyping individual patients. The efforts have mainly focused on variants in genes encoding the drug-metabolizing enzymes thiopurine S-methyltransferase, dihydropyrimidine dehydrogenase, members of the cytochrome P450 family, including the CYP2B, 2C, 2D and 3A subfamilies, members of the UDP glucuronosyltransferase family, as well as the ATP-binding cassette transporters ABCB1 (P-glycoprotein) and ABCG2 (breast cancer resistance protein). Several of these genotyping strategies have been shown to have substantial impact on therapeutic outcome and should eventually lead to improved anticancer chemotherapy.

Medicinal Cannabis Does Not Influence the Clinical Pharmacokinetics of Irinotecan and Docetaxel

OBJECTIVE

To date, data regarding the potential of cannabinoids to modulate cytochrome P450 isozyme 3A (CYP3A) activity are contradictory. Recently, a standardized medicinal cannabis product was introduced in The Netherlands. We anticipated an increased use of medicinal cannabis concurrent with anticancer drugs, and undertook a drug-interaction study to evaluate the effect of concomitant medicinal cannabis on the pharmacokinetics of irinotecan and docetaxel, both subject to CYP3A-mediated biotransformation.

PATIENTS AND METHODS

Twenty-four cancer patients were treated with i.v. irinotecan (600 mg, n = 12) or docetaxel (180 mg, n = 12), followed 3 weeks later by the same drugs concomitant with medicinal cannabis (200 ml herbal tea, 1 g/l) for 15 consecutive days, starting 12 days before the second treatment. Blood samples were obtained up to 55 hours after dosing and analyzed for irinotecan and its metabolites (SN-38, SN-38G), respectively, or docetaxel. Pharmacokinetic analyses were performed during both treatments. Results are reported as the mean ratio (95% confidence interval [CI]) of the observed pharmacokinetic parameters with and without concomitant medicinal cannabis.

RESULTS

Medicinal cannabis administration did not significantly influence exposure to and clearance of irinotecan (1.04; CI, 0.96-1.11 and 0.97; CI, 0.90-1.05, respectively) or docetaxel (1.11; CI, 0.94-1.28 and 0.95; CI, 0.82-1.08, respectively).

CONCLUSION

Coadministration of medicinal cannabis, as herbal tea, in cancer patients treated with irinotecan or docetaxel does not significantly influence the plasma pharmacokinetics of these drugs. The evaluated variety of medicinal cannabis can be administered concomitantly with both anticancer agents without dose adjustments.

The human cytochrome P450 sub-family: Transcriptional regulation, inter-individual variation and interaction networks

The Cytochrome P450 super-family is a fundamental requirement for the viability of most life, with Cytochrome P450 proteins having been identified in organisms ranging from bacteria to man. These enzymes may be subdivided into those that metabolise purely endogenous chemicals, and those that are involved in xenobiotic metabolism. Of the latter group it can be argued that CYP3A sub-family members rank as the most important; their high expression in the liver and wide substrate specificity mean that they are clinically important in the metabolism of many therapeutic drugs, and alteration in their activity is central to many clinically-relevant drug-drug interactions. In this review I will examine the human CYP3A enzymes, discussing their genome structure, common allelic variants and, in greatest detail, their transcriptional regulation. Through examination of these characteristics we will see both striking similarities and differences between the four human CYP3A enzymes, which may have important impacts on inter-individual response to chemical exposure. Finally, the role of nuclear receptors in regulating CYP3A gene expression, and indeed that of many other proteins involved in drug metabolism, will be examined: Such an examination will show the need to utilize a systems biology approach to understand fully how the human body responds to chemical exposure.

Chemotherapy Dosing Part I: Scientific Basis for Current Practice and Use of Body Surface Area

Cytotoxic chemotherapy is characterised by a low therapeutic index and significant variability in therapeutic and toxic effects. In an attempt to reduce this variability, most chemotherapy doses are individualised according to patient body surface area (BSA). This practice, which was introduced almost 50 years ago, clearly has practical and economic implications for the healthcare system. Furthermore, the clinical value of this approach has, in recent years, been questioned. Despite established practice, chemotherapy dose selection remains complicated, partly because treatment effects are difficult to measure, partly because drugs are used in combination with other treatment modalities, and also because the patient's condition may change with disease progression. Various patient-related factors can affect drug pharmacokinetics (PK) and pharmacodynamics (PD), for example organ function, expression and activity of metabolising enzymes, drug resistance, body size, gender, age, concomitant disease and co-administration of other drugs. These factors may be of clinical significance in chemotherapy dose determination and measures of PK, PD or both feature in attempts to devise more rigorous methods for chemotherapy dosing. Part I of this series of two reviews describes the history and clinical impact of BSA-based chemotherapy, and examines the scientific evidence to support BSA dosing. It evaluates the factors affecting PK and PD for specific drugs that could inform and refine dose determination.

Transcriptional Repression of Hepatic Cytochrome P450 3A4 Gene in the Presence of Cancer

PURPOSE

Many chemotherapeutic drugs have an inherent lack of safety due to interindividual variability of hepatic cytochrome P450 (CYP) 3A4 drug metabolism. This reduction in CYP3A4 in cancer patients is possibly mediated by cytokines associated with tumor-derived inflammation. We sought to examine this link by using an explant sarcoma in a novel transgenic mouse model of human CYP3A4 regulation.

EXPERIMENTAL DESIGN

Engelbreth-Holm-Swarm sarcoma cells were injected into the hindlimb of transgenic CYP3A4/lacZ mice. Hepatic expression of the human CYP3A4 transgene was analyzed by direct measurement of the reporter gene product, beta-galactosidase enzyme activity. Hepatic expression of murine Cyp3a was analyzed at the mRNA, protein, and function levels. The acute phase response was assessed by examining cytokines [interleukin-6 (IL-6) and tumor necrosis factor] in serum, liver, or tumor as well as hepatic expression of serum amyloid protein P.

RESULTS

Engelbreth-Holm-Swarm sarcoma elicited an acute phase response that coincided with down-regulation of the human CYP3A4 transgene in the liver as well as the mouse orthologue Cyp3a11. The reduction of murine hepatic Cyp3a gene expression in tumor-bearing mice resulted in decreased Cyp3a protein expression and consequently a significant reduction in Cyp3a-mediated metabolism of midazolam. Circulating IL-6 was elevated and IL-6 protein was only detected in tumor tissue but not in hepatic tissue.

CONCLUSIONS

The current study provides a mechanistic link between cancer-associated inflammation and impaired drug metabolism in vivo. Targeted therapy to reduce inflammation may provide improved clinical benefit for chemotherapy drugs metabolized by hepatic CYP3A4 by improving their pharmacokinetic profile.

Genetic markers of treatment response in rheumatoid arthritis

Rheumatoid arthritis patients exhibit a considerable interindividual variability in response to drug treatment. Although many disease-related and demographic factors have been studied to predict treatment outcome, the effective disease-modifying antirheumatic drug (DMARD) therapy is not yet allocated based on factors that predict efficacy. Individual genetic characteristics are thought to play an important role in treatment response; therefore, current research aims to identify these genetic predictors for clinical response. Pharmacogenetic studies are beginning to provide results, which suggests that personalized treatment maximization of DMARD efficacy and minimization of adverse drug reactions are feasible.