Intracellular vincristine levels in lymphoblasts affect treatment outcome in childhood B-lymphoblastic leukaemia: Ma-Spore ALL 2010 study.

AIMS: Vincristine (VCR) is a key drug in the successful multidrug chemotherapy for childhood acute lymphoblastic leukaemia (ALL). However, it remains unclear how VCR pharmacokinetics affects its antileukaemic efficacy. The objective of this study is to explore the VCR pharmacokinetic parameters and intracellular VCR levels in an up-front window of Ma-Spore ALL 2010 (MS2010) study. METHODS: We randomised 429 children with newly diagnosed ALL to 15-minute vs 3-hour infusion for the first dose of VCR to study if prolonging the first dose of VCR infusion improved response. In a subgroup of 115 B-ALL and 20 T-ALL patients, we performed VCR plasma (n = 135 patients) and intracellular (n = 66 patients) pharmacokinetic studies. The correlations between pharmacokinetic parameters and intracellular VCR levels with early treatment response, final outcome and ABCB1 genotypes were analysed. RESULTS: There was no significant difference between 15-minute and 3-hour infusion schedules in median Day 8 peripheral or bone marrow blast response. Plasma VCR pharmacokinetic parameters did not predict outcome. However, in B-ALL, Day 33 minimal residual disease (MRD) negative patients and patients in continuous complete remission had significantly higher median intracellular VCR24h levels (P = .03 and P = .04, respectively). The median VCR24h intracellular levels were similar among the common genetic subtypes of ALL (P = .4). Patients homozygous for wild-type ABCB1 2677GG had significantly higher median intracellular VCR24h (P = .04) than 2677TT. CONCLUSION: We showed that in childhood B-ALL, the intracellular VCR24h levels in lymphoblasts affected treatment outcomes. The intracellular VCR24h level was independent of leukaemia subtype but dependent on host ABCB1 G2677T genotype.

Extended Evaluation of Virological, Immunological and Pharmacokinetic Endpoints of CELADEN: A Randomized, Placebo-Controlled Trial of Celgosivir in Dengue Fever Patients.

UNLABELLED: CELADEN was a randomized placebo-controlled trial of 50 patients with confirmed dengue fever to evaluate the efficacy and safety of celgosivir (A study registered at ClinicalTrials.gov, number NCT01619969). Celgosivir was given as a 400 mg loading dose and 200 mg bid (twice a day) over 5 days. Replication competent virus was measured by plaque assay and compared to reverse transcription quantitative PCR (qPCR) of viral RNA. Pharmacokinetics (PK) correlations with viremia, immunological profiling, next generation sequence (NGS) analysis and hematological data were evaluated as exploratory endpoints here to identify possible signals of pharmacological activity. Viremia by plaque assay strongly correlated with qPCR during the first four days. Immunological profiling demonstrated a qualitative shift in T helper cell profile during the course of infection. NGS analysis did not reveal any prominent signature that could be associated with drug treatment; however the phylogenetic spread of patients' isolates underlines the importance of strain variability that may potentially confound interpretation of dengue drug trials conducted during different outbreaks and in different countries. Celgosivir rapidly converted to castanospermine (Cast) with mean peak and trough concentrations of 5727 ng/mL (30.2 µM) and 430 ng/mL (2.3 µM), respectively and cleared with a half-life of 2.5 (± 0.6) hr. Mean viral log reduction between day 2 and 4 (VLR2-4) was significantly greater in secondary dengue than primary dengue (p = 0.002). VLR2-4 did not correlate with drug AUC but showed a trend of greater response with increasing Cmin. PK modeling identified dosing regimens predicted to achieve 2.4 to 4.5 times higher Cmin. than in the CELADEN trial for only 13% to 33% increase in overall dose. A small, non-statistical trend towards better outcome on platelet nadir and difference between maximum and minimum hematocrit was observed in celgosivir-treated patients with secondary dengue infection. Optimization of the dosing regimen and patient stratification may enhance the ability of a clinical trial to demonstrate celgosivir activity in treating dengue fever based on hematological endpoints. A new clinical trial with a revised dosing regimen is slated to start in 2016 (NCT02569827). Furthermore celgosivir's potential value for treatment of other flaviruses such as Zika virus should be investigated urgently. TRIAL REGISTRATION: ClinicalTrials.gov NCT01619969.

Glucuronidation by UGT1A1 is the dominant pathway of the metabolic disposition of belinostat in liver cancer patients.

UNLABELLED: Belinostat is a hydroxamate class HDAC inhibitor that has demonstrated activity in peripheral T-cell lymphoma and is undergoing clinical trials for non-hematologic malignancies. We studied the pharmacokinetics of belinostat in hepatocellular carcinoma patients to determine the main pathway of metabolism of belinostat. The pharmacokinetics of belinostat in liver cancer patients were characterized by rapid plasma clearance of belinostat with extensive metabolism with more than 4-fold greater relative systemic exposure of major metabolite, belinostat glucuronide than that of belinostat. There was significant interindividual variability of belinostat glucuronidation. The major pathway of metabolism involves UGT1A1-mediated glucuronidation and a good correlation has been identified between belinostat glucuronide formation and glucuronidation of known UGT1A1 substrates. In addition, liver microsomes harboring UGT1A1*28 alleles have lower glucuronidation activity for belinostat compared to those with wildtype UGT1A1. The main metabolic pathway of belinostat is through glucuronidation mediated primarily by UGT1A1, a highly polymorphic enzyme. The clinical significance of this finding remains to be determined. TRIAL REGISTRATION: ClinicalTrials.gov NCT00321594.

Correlation of aldo-ketoreductase (AKR) 1C3 genetic variant with doxorubicin pharmacodynamics in Asian breast cancer patients.

AIMS: Aldo-ketoreductases have been implicated in the metabolism of doxorubicin. We sought to assess the influence of AKR1C3 genetic variants on doxorubicin metabolism. METHODS: We sequenced AKR1C3 exon 5 and genotyped seven functional single nucleotide polymorphisms in CBR3, ABCB1 and SLC22A16 involved in doxorubicin pharmacology in 151 Asian breast cancer patients treated with doxorubicin-containing chemotherapy, and correlated these genotypes with doxorubicin pharmacokinetics and pharmacodynamics. RESULTS: Two previously reported AKR1C3 intronic variants, IVS4-212 C>G and IVS4+218 G>A, were detected. The AKR1C3 IVS4-212 GG genotype was associated with significantly lower cycle 1 day 15 leucocyte (mean leucocytes 2.49 ± 1.57 × 10(9) vs. 3.85 ± 3.42 × 10(9) l(-1) , P = 0.007) and neutrophil counts (mean neutrophils 0.70 ± 1.01 × 10(9) vs. 1.56 ± 2.80 × 10(9) l(-1) , P = 0.008) and significant improvement of progression-free survival [PFS, mean PFS 49.0 (95% confidence interval 42.2-55.8) vs. 31.0 (95% confidence interval 20.7-41.2) months, P = 0.017] and overall survival [OS; mean OS 64.4 (95% confidence interval 58.3-70.5) vs. 46.3 (95% confidence interval 35.1-57.5) months, P = 0.006] compared with those carrying at least one C allele. There was no significant association between AKR1C3 IVS4-212 C>G and doxorubicin pharmacokinetics. Of the other seven single nucleotide polymorphisms genotyped, CBR3 G11A correlated with doxorubicinol area under the concentration-time curve and OS, ABCB1 G2677T/A correlated with doxorubicin clearance and platelet toxicity, while ABCB1 IVS26+59 T>G correlated with OS. The AKR1C3 IVS4-212 C

Dose- and schedule-dependent protective efficacy of celgosivir in a lethal mouse model for dengue virus infection informs dosing regimen for a proof of concept clinical trial.

Celgosivir (6-O-butanoyl castanospermine), a pro-drug of the naturally occurring castanospermine, is an inhibitor of α-glucosidase I and II that is found to be a potent inhibitor of several enveloped viruses including all four serotypes of dengue virus. We showed previously that the compound fully protected AG129 mice from lethal infection with a mouse adapted dengue virus at a dose of 50mg/kg twice daily (BID) for 5days and was effective even after 48h delayed treatment. Here we show that the protection by celgosivir is dose- and schedule-dependent and that a twice-a-day regimen of 50, 25 or 10mg/kg is more protective than a single daily dose of 100mg/kg. Treatment with 50mg/kg BID castanospermine had comparable efficacy as 25mg/kg BID celgosivir, suggesting that celgosivir is approximately twice as potent as castanospermine with respect to in vivo antiviral efficacy. Pharmacokinetics (PK) studies of celgosivir in mice showed that it rapidly metabolized to castanospermine. Simulation of the PK data with the survival data for the various doses of celgosivir tested suggests that the steady-state minimum concentration is a critical parameter to note in choosing dose and schedule. These results influenced the selection of the dose regimen for a proof-of-concept clinical trial of celgosivir as a treatment against dengue fever.

Population pharmacokinetics of modafinil and its acid and sulfone metabolites in Chinese males.

BACKGROUND: Modafinil is a psychostimulant used to treat excessive sleepiness. The aim of this study was to develop a population pharmacokinetic model of modafinil and its major metabolites in Chinese male adults and to identify covariates that predict variability in disposition. METHODS: Eighty healthy volunteer subjects were randomized to 4 oral dose groups: 3 doses of 50 mg of modafinil, 3 doses of 100 mg of modafinil, 2 doses of 200 mg of modafinil plus 1 dose of placebo, or 3 doses of placebo (each dose given 8 hourly). Blood samples were collected up to 58 hours post-first dose for plasma concentrations of modafinil and its metabolites. Pharmacokinetic data analyses were performed using noncompartmental and compartmental approaches. The population pharmacokinetic study was conducted using the nonlinear mixed-effects model software, NONMEM, and validated using the bootstrap, crossvalidation and visual predictive check approaches. RESULTS: Data were best described by a 5-compartment model: 2 compartments for modafinil (first-order absorption from gut compartment) and 1 each for modafinil acid and modafinil sulfone. A covariate analysis identified body weight as influencing volumes of the central and peripheral compartments for modafinil. All the parameters were estimated with good precision (relative standard error < 39%). The visual predictive check found that the final pharmacokinetic model adequately predicted observed concentrations of all 3 molecular species. The authors developed dosing schedules to achieve minimum trough plasma modafinil concentrations of 3 mcg/mL. CONCLUSIONS: A robust population pharmacokinetic model for modafinil and its metabolites was developed for the first time. Based on this model, individualized dosing based on weight is now possible.

Regulation of heart function by endogenous gaseous mediators-crosstalk between nitric oxide and hydrogen sulfide.

Both nitric oxide (NO) and hydrogen sulfide (H(2)S) are two important gaseous mediators regulating heart function. The present study examined the interaction between these two biological gases and its role in the heart. We found that l-arginine, a substrate of NO synthase, decreased the amplitudes of myocyte contraction and electrically induced calcium transients. Sodium hydrogen sulfide (an H(2)S donor), which alone had minor effect, reversed the negative inotropic effects of l-arginine. The effect of l-arginine + sodium hydrogen sulfide was abolished by three thiols (l-cysteine, N-acetyl-cysteine, and glutathione), suggesting that the effect of H(2)S + NO is thiol sensitive. The stimulatory effect on heart contractility was also induced by GYY4137, a slow-releasing H(2)S donor, when used together with sodium nitroprusside, an NO-releasing donor. More importantly, enzymatic generation of H(2)S from recombinant cystathionine-γ-lyase protein also interacted with endogenous NO generated from l-arginine to stimulate heart contraction. In summary, our data suggest that endogenous NO may interact with H(2)S to produce a new biological mediator that produces positive inotropic effect. The crosstalk between H(2)S and NO also suggests an intriguing potential for the endogenous formation of a thiol-sensitive molecule, which may be of physiological significance in the heart.

A sensitive and specific liquid chromatography-tandem mass spectrometric method for determination of belinostat in plasma from liver cancer patients.

A novel, sensitive and reliable liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed and validated for the determination of belinostat (PXD101) in human plasma. Oxamflatin was used as the internal standard. Liquid-liquid extraction of the plasma sample was performed using tert-butyl methyl ether as the organic solvent. Chromatographic separation was achieved on a BDS Hypersil C18 column (2.1 mm x1 00 mm, 5 microm) using gradient elution mode using 0.05% formic acid in water and 0.05% formic acid in acetonitrile as solvents A and B, respectively, 60/40. The run time was 6 min. The mass spectrometer was operated under a positive electrospray ionization condition and a multiple reaction monitoring mode. An excellent linear calibration was achieved in the range of 0.5-1000 ng/mL. An average recovery of belinostat for four quality controls was 72.6% and the recovery of the internal standard at 1000 ng/mL was 67.8%. The intra-day and inter-day precisions for belinostat were

The use of submicron/nanoscale PLGA implants to deliver paclitaxel with enhanced pharmacokinetics and therapeutic efficacy in intracranial glioblastoma in mice.

Pharmacokinetics and therapeutic efficacy of submicron/nanoscale, intracranial implants were evaluated for treating malignant glioblastoma in mice. 9.1% (w/w) paclitaxel-loaded polylactide-co-glycolide (PLGA) nanofiber discs (F3) were fabricated and characterized for morphology and size distribution. Along with F3, three other formulations, 9.1% (w/w) paclitaxel-loaded PLGA submicron-fiber discs (F2), 16.7% (w/w) paclitaxel-loaded PLGA microspheres entrapped in hydrogel matrices (H80 and M80) were intracranially implanted in BALB/c mice and the coronal brain sections were analyzed for bio-distribution of paclitaxel on 14, 28 and 42 days post-implantation. BALB/c nude mice with intracranial human glioblastoma (U87 MG-luc2) were used in the therapeutic efficacy study. Animals were randomized to intracranial implantation of F3 and H80 with paclitaxel dose of 10mg/kg, placebo F3, placebo H80, weekly intratumoral injection of Taxol (10mg/kg) or no treatment and the treatment response was analyzed by bioluminescence imaging and histological (H&E, Ki-67) examinations. Enhanced, therapeutic paclitaxel penetration (approximately 1 microm) in the mouse brain up to 5mm from the implant site even after 42 days post-implantation from F3 and H80 was confirmed and deduced to be diffusion/elimination controlled. F3 and H80 demonstrated significant (approximately 30 fold) tumor inhibition and significantly low tumor proliferation index after 41 days of treatment in comparison to sham and placebo controls. The submicron/nanoscale implants are able to demonstrate optimal paclitaxel pharmacokinetics in the brain/tumor with significant tumor inhibition in a glioblastoma xenograft model in mice and hence could be potentially useful to treat highly recurrent GBM.

Paclitaxel delivery from PLGA foams for controlled release in post-surgical chemotherapy against glioblastoma multiforme.

Paclitaxel loaded biodegradable poly-(DL-lactic-co-glycolic) acid (PLGA) foams with microporous matrix were fabricated by a novel pressure quenching approach to provide a sustained paclitaxel release. The foams with micropores provided increased surface area to volume ratio and were also implantable for post-surgical chemotherapy applications. The two formulations 5% (w/w) paclitaxel loaded PLGA 85:15 foam (F1) and 10% (w/w) paclitaxel loaded PLGA 50:50 foam (F2), were evaluated in vitro and in vivo. Both the foams were found to provide a paclitaxel release beyond a month in vitro with a near zero-order kinetics and with minimum burst release. Furthermore, apoptosis of C6 glioma cells in vitro demonstrated the benefits of sustained paclitaxel release by the foams in comparison to acute Taxol exposure. Both the foams exhibited continuous paclitaxel release in an in vivo (subcutaneous) environment up to a month which correlated well with the in vitro release profiles. Bio-distribution results in the rat brain showed paclitaxel penetration at therapeutic levels up to 3mm into the tissue from the site of foam implantation. Hence these foams could be employed as potential implants for post-surgical chemotherapy against malignant glioma.

A high-performance liquid chromatography method for the quantification of cysmethynil, an inhibitor of isoprenylcysteine carboxylmethyl transferase, in mouse plasma.

Cysmethynil, a newly identified small molecule inhibitor of isoprenylcysteine carboxylmethyl transferase (Icmt) is involved in the post-translational modification of CaaX proteins. Cysmethynil causes cell death in many human cancer cells in vitro, and inhibits tumor growth in the xenograft mouse model in vivo. A HPLC method for the quantification of cysmethynil in mouse plasma was developed and validated. The lower limit of quantification of this method was 0.01microg/ml. Inter- and intra-day variability ranged from 0.38-8.5% and accuracy was between 86% and 98%. This sensitive method was used to quantify cysmethynil in plasma of mice after intraperitoneal dosing for preliminary pharmacokinetic studies.

Distribution of gemcitabine pathway genotypes in ethnic Asians and their association with outcome in non-small cell lung cancer patients.

OBJECTIVE: Pharmacogenetics suggests variants of genes involved in gemcitabine pharmacology could be useful markers for predicting inter-ethnic and inter-patient outcomes from treatment with the agent. Here, we have characterized the distribution of variants of genes involved in gemcitabine pharmacology in ethnic Asian populations and their association with non-small cell lung cancer (NSCLC) patient outcome. METHODS: All genes involved in gemcitabine transport, metabolism and activity were screened for suitable variants for analysis using publications and public databases. By pyrosequencing, the frequency of qualifying variants was characterized from germline DNA of 94 healthy Asian donors and 53 NSCLC patients receiving gemcitabine-based chemotherapy. RESULTS: Significant differences in genotype distribution between Caucasians and Asians were seen at 10/25 (45%) variant loci. In NSCLC patients, CDA+435 C>T variants were associated with response (p=0.026) and time to progression (p=0.016) and SLC28A1+1561 G>A variants were associated with neutropenia (p=0.030) and thrombocytopenia nadir (p=0.037). CONCLUSIONS: Many genotypes in gemcitabine pharmacology vary in their frequency between Caucasians and Asians. CDA+435, and SLC28A1+1561 are worthy of further investigation as potential indicators of patient outcome after gemcitabine treatment.

A pharmacodynamic model for the time course of tumor shrinkage by gemcitabine + carboplatin in non-small cell lung cancer patients.

PURPOSE: This tumor response pharmacodynamic model aims to describe primary lesion shrinkage in non-small cell lung cancer over time and determine if concentration-based exposure metrics for gemcitabine or that of its metabolites, 2',2'-difluorodeoxyuridine or gemcitabine triphosphate, are better than gemcitabine dose for prediction of individual response. EXPERIMENTAL DESIGN: Gemcitabine was given thrice weekly on days 1 and 8 in combination with carboplatin, which was given only on day 1 of every cycle. Gemcitabine amount in the body and area under the concentration-time curves of plasma gemcitabine, 2',2'-difluorodeoxyuridine, and intracellular gemcitabine triphosphate in white cells were compared to determine which best describes tumor shrinkage over time. Tumor growth kinetics were described using a Gompertz-like model. RESULTS: The apparent half-life for the effect of gemcitabine was 7.67 weeks. The tumor turnover time constant was 21.8 week.cm. Baseline tumor size and gemcitabine amount in the body to attain 50% of tumor shrinkage were estimated to be 6.66 cm and 10,600 mg. There was no evidence of relapse during treatment. CONCLUSIONS: Concentration-based exposure metrics for gemcitabine and its metabolites were no better than gemcitabine amount in predicting tumor shrinkage in primary lung cancer lesions. Gemcitabine dose-based models did marginally better than treatment-based models that ignored doses of drug administered to patients. Modeling tumor shrinkage in primary lesions can be used to quantify individual sensitivity and response to antitumor effects of anticancer drugs.

Genotype of human carbonyl reductase CBR3 correlates with doxorubicin disposition and toxicity.

OBJECTIVES: Doxorubicin is a cytotoxic drug with potential for severe myelosuppression that is highly variable and poorly predictable. METHODS: We correlated CBR1 and CBR3 genotypes with the pharmacokinetics and pharmacodynamics of doxorubicin in 101 Southeast Asian breast cancer patients receiving first-line doxorubicin. RESULTS: A common CBR3 11G>A variant was associated with lower doxorubicinol area under the concentration-time curve (AUC)/doxorubicin AUC metabolite ratio (P=0.009, GG vs. AA; trend test, P=0.004), lower CBR3 expression in breast tumor tissue (P=0.001, GG vs. AA), greater tumor reduction (P=0.015, GG vs. AA), and greater percentage reduction of leukocyte and platelet counts at nadir (trend test, P < or = 0.03). Chinese and Malays had higher frequency of the CBR3 11G>A variant than Indians (P < or = 0.002). Another variant CBR3 730G>A was associated with higher doxorubicinol AUC (P=0.009, GG vs. AA) and CBR3 expression in breast tumor tissue (P=0.001, GG vs AA). CONCLUSION: Polymorphisms in CBR3 may explain interindividual and interethnic variability of doxorubicin pharmacokinetics and pharmacodynamics.

Bevacizumab and rapamycin induce growth suppression in mouse models of hepatocellular carcinoma.

BACKGROUND/AIMS: Hepatocellular carcinoma is a leading cause of global cancer mortality, with standard chemotherapy being minimally effective in prolonging survival. We investigated if combined targeting of vascular endothelial growth factor protein and expression might affect hepatocellular carcinoma growth and angiogenesis. METHODS: We treated patient-derived hepatocellular carcinoma xenografts with (i) bevacizumab; (ii) rapamycin; and (iii) bevacizumab plus rapamycin. Western blotting was employed to determine changes in the proteins. Apoptosis, vascular endothelial growth factor expression, microvessel density, and cell proliferation were analyzed by immunohistochemistry. RESULTS: Hepatocellular carcinoma growth was inhibited by bevacizumab plus rapamycin treatment to a significantly greater degree than bevacizumab or rapamycin monotherapy. Reductions in tumor growth by bevacizumab plus rapamycin were associated with inhibition of downstream targets of the mammalian target-of-rapamycin pathway, reductions in vascular endothelial growth factor expression, and tumor microvessel density. Potentially additive effects of bevacizumab plus rapamycin included reductions in vascular endothelial growth factor expression, cyclin D1, and cyclin B1. In an intra-peritoneal model of hepatocellular carcinoma, bevacizumab plus rapamycin potently inhibited both intra-liver and intra-abdominal tumor growth, reduced ascites levels, and significantly prolonged mouse survival. CONCLUSIONS: Bevacizumab and rapamycin, which are both clinically approved drugs, may represent a novel molecularly-targeted combination treatment for hepatocellular carcinoma.

A small molecule inhibitor of isoprenylcysteine carboxymethyltransferase induces autophagic cell death in PC3 prostate cancer cells.

A number of proteins involved in cell growth control, including members of the Ras family of GTPases, are modified at their C terminus by a three-step posttranslational process termed prenylation. The enzyme isoprenylcysteine carboxylmethyl-transferase (Icmt) catalyzes the last step in this process, and genetic and pharmacological suppression of Icmt activity significantly impacts on cell growth and oncogenesis. Screening of a diverse chemical library led to the identification of a specific small molecule inhibitor of Icmt, cysmethynil, that inhibited growth factor signaling and tumorigenesis in an in vitro cancer cell model (Winter-Vann, A. M., Baron, R. A., Wong, W., dela Cruz, J., York, J. D., Gooden, D. M., Bergo, M. O., Young, S. G., Toone, E. J., and Casey, P. J. (2005) Proc. Natl. Acad. Sci. U. S. A. 102, 4336-4341). To further evaluate the mechanisms through which this Icmt inhibitor impacts on cancer cells, we developed both in vitro and in vivo models utilizing PC3 prostate cancer cells. Treatment of these cells with cysmethynil resulted in both an accumulation of cells in the G(1) phase and cell death. Treatment of mice harboring PC3 cell-derived xenograft tumors with cysmethynil resulted in markedly reduced tumor size. Analysis of cell death pathways unexpectedly showed minimal impact of cysmethynil treatment on apoptosis; rather, drug treatment significantly enhanced autophagy and autophagic cell death. Cysmethynil-treated cells displayed reduced mammalian target of rapamycin (mTOR) signaling, providing a potential mechanism for the excessive autophagy as well as G(1) cell cycle arrest observed. These results identify a novel mechanism for the antitumor activity of Icmt inhibition. Further, the dual effects of cell death and cell cycle arrest by cysmethynil treatment strengthen the rationale for targeting Icmt in cancer chemotherapy.

Does saturable formation of gemcitabine triphosphate occur in patients?

AIM: This study aims to determine if intracellular formation of gemcitabine triphosphate (dFdCTP), an active metabolite of gemcitabine, is saturable at doses used for treatment of Asian patients with lung cancer. METHODS: From a phase II trial, plasma concentrations of gemcitabine, its inactive metabolite 2'-2'-difluorodeoxyuridine (dFdU), and mononuclear cell concentrations of gemcitabine-triphosphate were measured in 56 and 33 patients, respectively. The pharmacokinetics of gemcitabine and metabolites were modeled using nonlinear mixed effects modeling (NONMEM). A reduced dataset of ten randomly selected patients was employed to compare first-order and saturable formation of dFdCTP from gemcitabine. RESULTS: The median population clearance estimate for dFdCTP formation with the full dataset was 70.2 L/h/70 kg/1.7 m. Modeling Michaelis-Menten formation of dFdCTP on a reduced dataset estimated K(m) to be 3.6 times higher than the maximum gemcitabine concentration (72.2 microM) measured in this study. CONCLUSIONS: The results showed that first-order and nonsaturable clearance described intracellular dFdCTP formation at clinically applied doses of gemcitabine.

A phase I study of docetaxel with ketoconazole modulation in patients with advanced cancers.

PURPOSE: The aims were to determine the maximum tolerable dose (MTD) of docetaxel with CYP3A inhibition by ketoconazole, and to correlate the pharmacokinetics of docetaxel with midazolam phenotyping of CYP3A activity. METHODS: Forty-one patients with refractory metastatic cancers were treated with an escalating dose of intravenous docetaxel once in every 3 week of 10 mg/m(2), concurrently with oral ketoconazole 200 mg twice daily for 3 days starting 2 days before the administration of docetaxel. Midazolam phenotyping test with ketoconazole modulation was performed before the first cycle of docetaxel. Docetaxel and midazolam pharmacokinetics were compared to our previous study of docetaxel treatment without ketoconazole modulation. RESULTS: Neutropenia was the dose-limiting toxicity. The maximum tolerated dose was 70 mg with mean AUC at 70 mg similar to 75 mg/m(2) of docetaxel without ketoconazole. The plasma clearances of docetaxel and midazolam were reduced by 1.7- and 6-fold, respectively. The variability of midazolam AUC was reduced from 157 to 67%, but variability of docetaxel clearance was not reduced by CYP3A inhibition. Docetaxel clearance correlated with renal function and maximum concentration of ketoconazole, but not midazolam clearance or other variables of hepatic function. CONCLUSION: Fixed dosing was found to be feasible, without increased variability of clearance or neutrophil toxicity compared to BSA-based dosing. With ketoconazole modulation, docetaxel clearance correlated with renal function but not CYP3A phenotype.

Lack of association of single-nucleotide polymorphisms in pregnane X receptor, hepatic nuclear factor 4alpha, and constitutive androstane receptor with docetaxel pharmacokinetics.

PURPOSE: This study aims to describe a population pharmacokinetic model for docetaxel in Asian breast cancer patients and to evaluate the effects of single-nucleotide polymorphisms (SNP) in the cytochrome P450 3A (CYP3A) gene expression regulators, constitutive androstane receptor (CAR), pregnane X receptor (PXR), and hepatic nuclear factor 4alpha (HNF4alpha), on the pharmacokinetics of docetaxel. EXPERIMENTAL DESIGN: Docetaxel was given as an i.v. infusion of 75 mg/m(2) over 1 h to 101 female breast cancer patients. CAR, PXR, and HNF4alpha were comprehensively sequenced. Docetaxel concentrations were measured using a liquid chromatography/tandem mass spectrometry method and its population pharmacokinetic variables, and the covariate effects of clearance predictors were estimated using a nonlinear mixed effects model. RESULTS: Final estimates for docetaxel clearance was 47.1 L/h/70 kg/1.75 m. Between subject variability in docetaxel clearance was 22.5%. Covariates that showed significant association with docetaxel clearance included body size, alpha1 acid glycoprotein and liver function. SNPs identified in the coding regions of CAR and HNF4alpha and 5' untranslated region of PXR in this Asian breast cancer cohort did not seem to improve predictability of docetaxel clearance. CONCLUSIONS: SNPs identified in CYP3A gene expression regulators CAR, HNF4alpha, and PXR in the Asian female breast cancer population do not seem to have any significant effect on the clearance of docetaxel, a CYP3A substrate.