Randomized crossover pharmacokinetic study of solvent-based paclitaxel and nab-paclitaxel.

PURPOSE: Abraxane (ABI-007) is a 130-nm albumin-bound (nab) particle formulation of paclitaxel, devoid of any additional excipients. We hypothesized that this change in formulation alters the systemic disposition of paclitaxel compared with conventional solvent-based formulations (sb-paclitaxel; Taxol), and leads to improved tolerability of the drug. PATIENTS AND METHODS: Patients with malignant solid tumors were randomized to receive the recommended single-agent dose of nab-paclitaxel (260 mg/m(2) as a 30-minute infusion) or sb-paclitaxel (175 mg/m(2) as a 3-hour infusion). After cycle 1, patients crossed over to the alternate treatment. Pharmacokinetic studies were carried out for the first cycle of sb-paclitaxel and the first two cycles of nab-paclitaxel. RESULTS: Seventeen patients were treated, with 14 receiving at least one cycle each of nab-paclitaxel and sb-paclitaxel. No change in nab-paclitaxel pharmacokinetics was found between the first and second cycles (P = 0.95), suggesting limited intrasubject variability. Total drug exposure was comparable between the two formulations (P = 0.55) despite the dose difference. However, exposure to unbound paclitaxel was significantly higher after nab-paclitaxel administration, due to the increased free fraction (0.063 +/- 0.021 versus 0.024 +/- 0.009; P < 0.001). CONCLUSION: This study shows that paclitaxel disposition is subject to considerable variability depending on the formulation used. Because systemic exposure to unbound paclitaxel is likely a driving force behind tumoral uptake, these findings explain, at least in part, previous observations that the administration of nab-paclitaxel is associated with augmented antitumor efficacy compared with solvent-based paclitaxel.

Thalidomide metabolism and hydrolysis: mechanisms and implications.

Despite its controversial past, thalidomide is currently under investigation for the treatment of several disease types, ranging from inflammatory conditions to cancer. The mechanism of action of thalidomide is complex and not yet fully understood, but there is some evidence to suggest that metabolism may play a role. Consequently, there has been a considerable effort to characterize the metabolism of thalidomide in recent years. Thalidomide undergoes biotransformation by non-enzymatic hydrolysis and enzyme-mediated hydroxylation to form a multitude of metabolites. Metabolite identification and reaction phenotyping studies have been performed and will be discussed in this review in addition to interspecies differences in thalidomide metabolism.

The role of drug-metabolising enzymes in clinical responses to chemotherapy.

Interindividual differences in efficacy and toxicity of cancer chemotherapy are especially important given the narrow therapeutic index of these drugs. Pharmacokinetic and pharmacodynamic responses to chemotherapy are difficult to predict in a particular patient as numerous variables (e.g., age, gender, concomitant medications and concomitant illness) can alter drug responses. Inherited variations in genes involved in drug metabolism have also been shown to contribute to altered responses to cancer treatment. There are several clinically relevant examples of genetic polymorphisms in drug-metabolising enzymes that alter outcomes of patients treated with chemotherapy agents. It may be possible to predict a patient's response to a particular chemotherapy agent based on knowledge of their genetic composition through in vivo phenotyping of drug-metabolising enzymes.

Drug interactions in cancer therapy.

Drug interactions in oncology are of particular importance owing to the narrow therapeutic index and the inherent toxicity of anticancer agents. Interactions with other medications can cause small changes in the pharmacokinetics or pharmacodynamics of a chemotherapy agent that could significantly alter its efficacy or toxicity. Improvements in in vitro methods and early clinical testing have made the prediction of potentially clinically significant drug interactions possible. We outline the types of drug interaction that occur in oncology, the mechanisms that underlie these interactions and describe select examples.

Determination of the heat shock protein 90 inhibitor 17-dimethylaminoethylamino-17-demethoxygeldanamycin in plasma by liquid chromatography-electrospray mass spectrometry.

A rapid method was developed for the quantitative determination of the novel heat shock protein 90 inhibitor, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG; NSC707545), in human plasma. Calibration curves were constructed, and were analyzed using a weight factor proportional to the nominal concentration. Sample pretreatment involved a one-step extraction with ethyl acetate of 0.5-ml samples. The analysis was performed in the range of 1-100 ng/ml on a column (75 mm x 2.1 mm internal diameter with 3.5 microm C18 particle size), using 55% methanol in water containing formic acid as the mobile phase. The column effluent was monitored by mass spectrometry with positive electrospray ionization. The values for precision and accuracy were always <8% and <10% relative error, respectively. The method was successfully applied to examine the pharmacokinetics of 17-DMAG in a cancer patient.

Peripheral neuropathy induced by paclitaxel: recent insights and future perspectives.

Paclitaxel is an antineoplastic agent derived from the bark of the western yew, Taxus brevifolia, with a broad spectrum of activity. Because paclitaxel promotes microtubule assembly, neurotoxicity is one of its side effects. Clinical use of paclitaxel has led to peripheral neuropathy and this has been demonstrated to be dependent upon the dose administered, the duration of the infusion, and the schedule of administration. Vehicles in the drug formulation, for example Cremophor in Taxol, have been investigated for their potential to induce peripheral neuropathy. A variety of neuroprotective agents have been tested in animal and clinical studies to prevent paclitaxel neurotoxicity. Recently, novel paclitaxel formulations have been developed to minimize toxicities. This review focuses on recent advances in the etiology of paclitaxel-mediated peripheral neurotoxicity, and discusses current and ongoing strategies for amelioration of this side effect.

Modulation of cytochrome P450 activity: implications for cancer therapy.

Although metabolism mediated by cytochrome P450 isoenzymes is known to play a major part in the biotransformation of anticancer agents in vivo, few clinical studies have investigated activity of cytochrome P450s and therapeutic outcome in people with cancer. Variability between individuals in the pharmacokinetics of cancer chemotherapy has important consequences in terms of therapeutic efficacy and safety. We discuss here the effect of drug metabolism mediated by cytochrome P450 on therapeutic outcome. As examples, the biotransformation pathways of cyclophosphamide, ifosfamide, tamoxifen, docetaxel, paclitaxel, and irinotecan are discussed. Since most anticancer agents are transformed by enzymes, better knowledge of their metabolic pathways could help improve treatment outcome and safety. Furthermore, a more complete understanding of the metabolism of anticancer agents through phenotyping and genotyping approaches will facilitate the prediction of interactions between drugs. More clinical evidence is needed on the metabolic transformation and drug interactions with these agents to improve cancer therapeutics.

Leuprolide acetate given by a subcutaneous extended-release injection: less of a pain?

Androgen deprivation therapy is a mainstay for the treatment of advanced prostate cancer. Hormonal therapy commonly consists of injection of gonadotropin hormone-releasing hormone agonists. Based on the need for improved convenience of administration, a novel formulation of leuprolide acetate (Eligard; Atrix Laboratories Inc. & Sanofi Aventis) which incorporates a mixture of selected polymers and solvents to achieve sustained drug delivery after subcutaneous injection, was developed. The US Food and Drug Administration has approved 1-, 3-, 4- and 6-month formulations of leuprolide acetate. In clinical trials, leuprolide acetate achieves sustained suppression of serum testosterone to castration levels (< or =50 ng/dl). The adverse-event profile is consistent with the effects of testosterone suppression. This novel delivery system in addition to the availability of a 6-month formulation of leuprolide acetate, offers patients the option of a convenient twice-yearly injection schedule.

Comparative preclinical and clinical pharmacokinetics of a cremophor-free, nanoparticle albumin-bound paclitaxel (ABI-007) and paclitaxel formulated in Cremophor (Taxol).

PURPOSE: To compare the preclinical and clinical pharmacokinetic properties of paclitaxel formulated as a Cremophor-free, albumin-bound nanoparticle (ABI-007) and formulated in Cremophor-ethanol (Taxol). EXPERIMENTAL DESIGN: ABI-007 and Taxol were given i.v. to Harlan Sprague-Dawley male rats to determine pharmacokinetic and drug disposition. Paclitaxel pharmacokinetic properties also were assessed in 27 patients with advanced solid tumors who were randomly assigned to treatment with ABI-007 (260 mg/m(2), 30 minutes; n = 14) or Taxol (175 mg/m(2), 3 hours; n = 13), with cycles repeated every 3 weeks. RESULTS: The volume of distribution at steady state and clearance for paclitaxel formulated as Cremophor-free nanoparticle ABI-007 were significantly greater than those for paclitaxel formulated with Cremophor (Taxol) in rats. Fecal excretion was the main elimination pathway with both formulations. Consistent with the preclinical data, paclitaxel clearance and volume of distribution were significantly higher for ABI-007 than for Taxol in humans [21.13 versus 14.76 L/h/m(2) (P = 0.048) and 663.8 versus 433.4 L/m(2) (P = 0.040), respectively]. CONCLUSIONS: Paclitaxel formulated as ABI-007 differs from paclitaxel formulated as Taxol, with a higher plasma clearance and a larger volume of distribution. This finding is consistent with the absence of paclitaxel-sequestering Cremophor micelles after administration of ABI-007. This unique property of ABI-007 could be important for its therapeutic effectiveness.

Comparative in vitro properties and clinical pharmacokinetics of Paclitaxel following the administration of taxol(r) and paxene(r).

PURPOSE: Taxol contains paclitaxel formulated in Cremophor EL-P (CrEL-P) and ethanol. Paxene is similar to Taxol, except for the use of Cremophor EL (CrEL) and the addition of citric acid. Here, we investigated the physicochemical properties and clinical pharmacokinetics of the two paclitaxel formulations. EXPERIMENTAL DESIGN: The size and modality of distribution of CrEL-P and CrEL micelles was determined by dynamic-light scattering. The effect of vehicle composition on the fraction unbound paclitaxel in vitro was determined by equilibrium dialysis. Paclitaxel pharmacokinetics were studied in 61 cancer patients receiving Taxol and 26 patients receiving Paxene. Comparative pharmacokinetics of CrEL-P and CrEL were obtained in 14 and 6 patients, respectively. RESULTS: The size of micelles present in Taxol was slightly smaller (9 to 13%) than those present in Paxene. Surface tension and critical micellar concentration were also similar for the two formulations, with mean values of 37.0 and 38.1 mN/m and 0.0387 and 0.0307 mg/mL, respectively. The fraction unbound paclitaxel was not significantly different for Taxol and Paxene (p > 0.05). Over the tested dose range, the mean clearance of paclitaxel decreased from 45.1 to 16.9 L/h for Taxol, and from 50.7 to 16.4 L/h for Paxene (p > 0.05). Concentrations of the excipient following the administration of CrEL-P or CrEL were also similar. CONCLUSION: The differences in formulation between Taxol and Paxene do not significantly affect micelle formation and/or quantitative aspects of the vehicle-paclitaxel interaction in vitro and in vivo.

Paclitaxel chemotherapy: from empiricism to a mechanism-based formulation strategy.

Paclitaxel is an anticancer agent effective for the treatment of breast, ovarian, lung, and head and neck cancer. Because of water insolubility, paclitaxel is formulated with the micelle-forming vehicle Cremophor EL to enhance drug solubility. However, the addition of Cremophor EL results in hypersensitivity reactions, neurotoxicity, and altered pharmacokinetics of paclitaxel. To circumvent these unfavorable effects resulting from the addition of Cremophor EL, efforts have been made to develop new delivery systems for paclitaxel administration. For example, ABI-007 is a Cremophor-free, albumin-stabilized, nanoparticle paclitaxel formulation that was found to have significantly less toxicity than Cremophor-containing paclitaxel in mice. Pharmacokinetic studies indicate that in contrast to Cremophor-containing paclitaxel, ABI-007 displays linear pharmacokinetics over the clinically relevant dose range of 135-300 mg/m(2). In a phase III study conducted in patients with metastatic breast cancer, patients treated with ABI-007 achieved a significantly higher objective response rate and time to progression than those treated with Cremophor-containing paclitaxel. Together these findings suggest that nanoparticle albumin-bound paclitaxel may enable clinicians to administer paclitaxel at higher doses with less toxicity than is seen with Cremophor-containing paclitaxel. The role of this novel paclitaxel formulation in combination therapy with other antineoplastic agents needs to be determined.

Activities of cytochrome P450 1A2, N-acetyltransferase 2, xanthine oxidase, and cytochrome P450 2D6 are unaltered in children with cystic fibrosis.

The activities of hepatic cytochrome P450 (CYP) 1A2, N-acetyltransferase 2 (NAT-2), xanthine oxidase (XO), and CYP2D6 were evaluated in 12 young children (aged 3-8 years) with mild cystic fibrosis (CF) and 12 age-matched healthy control subjects by use of standard caffeine and dextromethorphan phenotyping methods. Subjects were given 4 oz of Coca-Cola (approximately 35 mg caffeine) (The Coca-Cola Company, Atlanta, Ga) and a single 0.5-mg/kg dose of dextromethorphan. Urine was collected for 8 hours after biomarker administration, and enzyme activity was assessed by use of previously validated caffeine and dextromethorphan molar ratios. CYP2D6 genotyping was also performed in 10 of 12 subjects with CF and 11 of 12 control subjects. There were no significant differences in the urinary molar ratios for any of the enzyme systems evaluated. These data suggest that CF does not alter the activities of CYP1A2, NAT-2, XO, and CYP2D6. Altered biotransformation of drugs in this patient population is likely enzyme- and isoform-specific and thus is apparent for only selected compounds that are substrates for enzymes other than CYP1A2, NAT-2, XO, and CYP2D6.