Ketoconazole pharmacokinetics during chronic dosing in adults with haematological malignancy

Phase I study of cabazitaxel plus cisplatin in patients with advanced solid tumors: study to evaluate the impact of cytochrome P450 3A inhibitors (aprepitant, ketoconazole) or inducers (rifampin) on the pharmacokinetics of cabazitaxel

PURPOSE

Cabazitaxel is primarily metabolized by CYP3A. This study evaluated the impact of moderate/strong CYP3A inhibitors [aprepitant (Study Part 2); ketoconazole (Study Part 3)] or strong CYP3A inducers [rifampin (Study Part 4)] on the pharmacokinetics of cabazitaxel.

METHODS

Adult patients received IV cabazitaxel/cisplatin 15/75 mg/m(2) on Day 1 of 3-week cycles (5/75 mg/m(2) in Cycles 1 and 2 of Part 3 to allow a safety margin to the cabazitaxel MTD). Patients received repeated oral doses of aprepitant, ketoconazole or rifampin before/during Cycle 2. Cabazitaxel clearance was the primary endpoint; clearance and area under the plasma concentration-time curve (AUC) were normalized to body surface area and dose, respectively.

RESULTS

The PK population included 13 (Part 2), 23 (Part 3) and 21 patients (Part 4). Repeated aprepitant administration did not affect cabazitaxel clearance [geometric mean ratio (GMR) 0.98; 90 % confidence interval (CI) 0.80-1.19]. Repeated ketoconazole administration resulted in 20 % decrease in cabazitaxel clearance (GMR 0.80; 90 % CI 0.55-1.15), associated with 25 % increase in AUC (GMR 1.25; 90 % CI 0.86-1.81). Repeated rifampin administration resulted in 21 % increase in cabazitaxel clearance (GMR 1.21; 90 % CI 0.95-1.53), associated with 17 % decrease in AUC (GMR 0.83; 90 % CI 0.65-1.05). The GMR of AUC0-24 with rifampin administration was 1.09 (90 % CI 0.9-1.33), suggesting that rifampin had a low impact during the initial phases of cabazitaxel elimination. Safety findings were consistent with previous results.

CONCLUSIONS

Cabazitaxel pharmacokinetics are modified by drugs strongly affecting CYP3A. Co-administration of cabazitaxel with strong CYP3A inhibitors or inducers should be avoided.

Tissue-specific regulation of pregnane X receptor in cancer development and therapy

As a ligand-dependent transcription factor of the nuclear hormone receptor superfamily, the pregnane X receptor (PXR) has a multitude of functions including regulating xenobiotic and cholesterol metabolism, energy homeostasis, gut mucosal defense, and cancer development. Whereas the detoxification functions of PXR have been widely studied and well established, the role of PXR in cancer has become controversial. With more than 60% of non-prescription and prescription drugs being metabolized by cytochrome P450 enzyme 3A4 (CYP3A4), a transcriptional target of PXR, insights into the regulation of PXR during systemic administration of novel treatment modalities will lead to a better understanding of PXR function in the context of human disease. Previous studies have suggested that PXR activation decreases drug sensitivity and augments chemoresistance in certain colon cancers mainly through the upregulation of CYP3A4 and multidrug resistance protein-1 (MDR1). Later studies suggest that downregulation of PXR expression may be oncogenic in hormone-dependent breast and endometrial cancers by reducing estrogen metabolism via CYP3A4; thus, higher estradiol concentrations contribute to carcinogenesis. These results suggest a differential role of PXR in tumor growth regulation dependent on tissue type and tumor microenvironment. Here, we will summarize the various mechanisms utilized by PXR to induce its diverse effects on cancerous tissues. Moreover, current approaches will be explored to evaluate the exploitation of PXR-mediated pathways as a novel mechanistic approach to cancer therapy.

Activated pregnenolone X-receptor is a target for ketoconazole and its analogs

PURPOSE

Variations in biotransformation and elimination of microtubule-binding drugs are a major cause of unpredictable side effects during cancer therapy. Because the orphan receptor, pregnenolone X-receptor (PXR), coordinately regulates the expression of paclitaxel metabolizing and transport enzymes, controlling this process could improve therapeutic outcome.

EXPERIMENTAL DESIGN

In vitro RNA-, protein-, and transcription-based assays in multiple cell lines derived from hepatocytes and PXR wild-type and null mouse studies were employed to show the effects of ketoconazole and its analogues on ligand-activated PXR-mediated gene transcription and translation.

RESULTS

The transcriptional activation of genes regulating biotransformation and transport by the liganded human nuclear xenobiotic receptor, PXR, was inhibited by the commonly used antifungal ketoconazole and related azole analogs. Mutations at the AF-2 surface of the human PXR ligand-binding domain indicate that ketoconazole may interact with specific residues outside the ligand-binding pocket. Furthermore, in contrast to that observed in PXR (+/+) mice, genetic loss of PXR results in increased (preserved) blood levels of paclitaxel.

CONCLUSIONS

These studies show that some azole compounds repress the coordinated activation of genes involved in drug metabolism by blocking PXR activation. Because loss of PXR maintains blood levels of paclitaxel upon chronic dosing, ketoconazole analogues may also serve to preserve paclitaxel blood levels on chronic dosing of drugs. Our observations may facilitate new strategies to improve the clinical efficacy of drugs and to reduce therapeutic side effects.

Comparison of prediction methods for in vivo clearance of (S,S)-3-[3-(methylsulfonyl)phenyl]-1-propylpiperidine hydrochloride, a dopamine D2 receptor antagonist, in humans

The purpose of this study is to investigate reliable prediction methods for in vivo pharmacokinetics and the likelihood of drug interactions with several cytochrome P450 inhibitors in humans for (S,S)-3-[3-(methylsulfonyl)phenyl]-1-propylpiperidine (PNU-96391). By allometric scaling of in vivo animal data, clearance of PNU-96391 in humans was over-predicted by 4-fold, half-life was under-predicted by 3-fold, and volume of distribution was accurately predicted. High correlation coefficients (>0.99) were observed for these parameters. Neither the in vitro-in vivo correlation approach nor the modified allometric scaling with maximum life span potential or brain weight accurately provided the predicted clearance value. Using an alternative method, based on normalization of in vitro human data with the ratio of in vivo to in vitro animal data, the in vivo clearance in humans was predicted to be 0.39 l/h/kg. This value correlated well with the in vivo value (0.43 l/h/kg). Regarding the interactions of PNU-96391 with cytochrome P450 inhibitors, only quinidine, haloperidol, and ketoconazole showed significant inhibition on the metabolic clearance of PNU-96391 in human hepatocytes. By comparing in vitro K(i) values with in vivo maximum unbound concentrations of the inhibitor, the increases in systemic exposure of PNU-96391 by coadministration of the inhibitors were estimated to be less than 1.5-fold. A preliminary comparison of pharmacokinetics of PNU-96391 between CYP2D6 extensive and poor metabolizers in the clinical study showed only a slight increase in systemic exposure in poor metabolizers (approximately 1.4-fold as area under the concentration-time curve). Therefore, clinically significant drug-drug interactions of PNU-96391 would be unlikely to occur with coadministration of CYP2D6 inhibitors.

Liquid chromatographic determination of ketoconazole, a potent inhibitor of CYP3A4-mediated metabolism

A high-performance liquid chromatographic assay with UV detection has been developed for the determination of ketoconazole in human plasma. Quantitative extraction was achieved by a single solvent extraction involving a mixture of acetonitrile-n-butyl chloride (1:4, v/v). Ketoconazole and the internal standard (clotrimazole) were separated on a column packed with Inertsil ODS-80A material and a mobile phase composed of water-acetonitrile-tetrahydrofuran-ammonium hydroxide-triethylamine (45:50.2:2.5:0.1:0.1, v/v). The column effluent was monitored at a wavelength of 206 nm with a detector range set at 0.5. The calibration graph was linear in the range of 20-2000 ng/ml, with a lower limit of quantitation of 20.0 ng/ml. The extraction recoveries for ketoconazole and clotrimazole in human plasma were 93+/-9.7% and 83+/-10.0%, respectively. The developed method has been successfully applied to a clinical study to examine the pharmacokinetics of ketoconazole in a cancer patient.

Oral antifungals as prophylaxis in haematological malignancy

In the standard treatment of patients with haematological malignancy, immunosuppressive therapy produces prolonged periods of neutropenia and mucositis, which increase the risk of systemic fungal infection. In allogeneic bone marrow transplantation, this risk extends well beyond the period of neutropenia when graft-versus-host disease, and its treatment, result in prolonged lymphocytopenia. Various agents are used for antifungal prophylaxis and treatment but all have limitations: amphotericin B is restricted by the need for intravenous infusion and the occurrence of adverse events, fluconazole by its narrow spectrum of activity and the emergence of fluconazole-resistant fungi and itraconazole capsules by erratic absorption. Oral administration of antifungals has clear advantages in prophylaxis and an important current strategy is to maximize the extent and reliability of the oral bioavailability of antifungal agents. Mucositis is the main obstacle for success of strategies based on oral delivery. In this review, the ability of these new oral formulations to deliver sufficient antifungal prophylaxis is evaluated.