Quantitation of tazemetostat in human plasma using liquid chromatography-tandem mass spectrometry.

To support a phase 1 trial in patients with lymphomas, we developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for tazemetostat quantitation in 20 µL of human plasma. After protein precipitation, chromatographic separation employed a Kinetex C18 column and a gradient of 0.1% formic acid in both water and acetonitrile, during a 3-min run time. Detection was achieved using a SCIEX 6500+ tandem mass spectrometer with electrospray positive-mode ionization. Validation was based on the latest Food and Drug Administration guidance. With a stable isotopic internal standard, the assay was linear within the range of 10-5000 ng/mL and proved to be accurate (91.9%-103.7%) and precise (<4.4% imprecision). Recovery varied between 93.3% and 121.1%, and matrix effect ranged from -25.5% to -4.9%. Hemolysis, lipemia, and dilution did not impact quantitation. Plasma stability was confirmed after three freeze-thaw cycles, 24 h at room temperature, and 4 months at -80°C. Incurred sample reanalysis yielded 94.4% samples within 20% difference (n = 36). External validation showed a mean bias of -11.1%. Pharmacokinetic (PK) data obtained from three patients suggested variable concentration time profiles, warranting collection of further data. The assay proved to be suitable for tazemetostat quantitation in human plasma and will support clinical studies by defining tazemetostat PKs.

Rapid Homogeneous Immunoassay to Quantify Gemcitabine in Plasma for Therapeutic Drug Monitoring.

BACKGROUND: Gemcitabine (2',2'-difluoro-2'-deoxycytidine) is a nucleoside analog used as a single agent and in combination regimens for the treatment of a variety of solid tumors. Several studies have shown a relationship between gemcitabine peak plasma concentration (Cmax) and hematological toxicity. An immunoassay for gemcitabine in plasma was developed and validated to facilitate therapeutic drug monitoring (TDM) by providing an economical, robust method for automated chemistry analyzers. METHODS: A monoclonal antibody was coated on nanoparticles to develop a homogenous agglutination inhibition assay. To prevent ex vivo degradation of gemcitabine in blood, tetrahydrouridine was used as a sample stabilizer. Validation was conducted for precision, recovery, cross-reactivity, and linearity on a Beckman Coulter AU480. Verification was performed on an AU5800 in a hospital laboratory. A method comparison was performed with (LC-MS/MS) liquid chromatography tandem mass spectrometry using clinical samples. Selectivity was demonstrated by testing cross-reactivity of the major metabolite, 2',2'-difluorodeoxyuridine. RESULTS: Coefficients of variation for repeatability and within-laboratory precision were <8%. The deviation between measured and assigned values was <3%. Linear range was from 0.40 to 33.02 µ/mL (1.5-125.5 µM). Correlation with validated LC-MS/MS methods was R = 0.977. The assay was specific for gemcitabine: there was no cross-reactivity to 2',2'-difluorodeoxyuridine, chemotherapeutics, concomitant, or common medications tested. Tetrahydrouridine was packaged in single-use syringes. Gemcitabine stability in whole blood was extended to 8 hours (at room temperature) and in plasma to 8 days (2-8°C). CONCLUSIONS: The assay demonstrated the selectivity, test range, precision, and linearity to perform reliable measurements of gemcitabine in plasma. The addition of stabilizer improved the sample handling. Using general clinical chemistry analyzers, gemcitabine could be measured for TDM.

Evaluating the indotecan-neutropenia relationship in patients with solid tumors by population pharmacokinetic modeling and sigmoidal Emax regressions.

PURPOSE: This study aimed at characterizing indotecan population pharmacokinetics and explore the indotecan-neutropenia relationship in patients with solid tumors. METHODS: Population pharmacokinetics were assessed using nonlinear mixed-effects modeling of concentration data from two first-in-human phase 1 trials evaluating different dosing schedules of indotecan. Covariates were assessed in a stepwise manner. Final model qualification included bootstrap simulation, visual and quantitative predictive checks, and goodness-of-fit. A sigmoidal Emax model was developed to describe the relationship between average concentration and maximum percent neutrophil reduction. Simulations at fixed doses were conducted to determine the mean predicted decrease in neutrophil count for each schedule. RESULTS: 518 concentrations from 41 patients supported a three-compartment pharmacokinetic model. Body weight and body surface area accounted for inter-individual variability of central/peripheral distribution volume and intercompartmental clearance, respectively. Estimated typical population values were CL 2.75 L/h, Q3 46.0 L/h, and V3 37.9 L. The estimated value of Q2 for a typical patient (BSA = 1.96 m2) was 17.3 L/h, while V1 and V2 for a typical patient (WT = 80 kg) was 33.9 L and 132 L. The final sigmoidal Emax model estimated that half-maximal ANC reduction occurs at an average concentration of 1416 µg/L and 1041 µg/L for the daily and weekly regimens, respectively. Simulations of the weekly regimen demonstrated lower percent reduction in ANC compared to the daily regimen at equivalent cumulative fixed doses. CONCLUSION: The final PK model adequately describes indotecan population pharmacokinetics. Fixed dosing may be justified based on covariate analysis and the weekly dosing regimen may have a reduced neutropenic effect.

Dexamethasone to prevent everolimus-induced stomatitis (Alliance MIST Trial: A221701).

mTOR inhibitors such as everolimus may cause oral stomatitis, often a dose-limiting toxicity. Prior clinical research has suggested that a dexamethasone mouth rinse might help prevent and/or treat this. Alliance A221701 was a randomized phase III trial of patients initiating 10 mg daily oral everolimus that compared dexamethasone mouthwash taken preventively (initial dexamethasone group) versus therapeutically (initial placebo group) to assess two coprimary endpoints: the incidence of mTOR inhibitor-associated stomatitis (mIAS), and the area under the curve (AUC) of mIAS-associated pain over an 8-week treatment period. A Fisher's exact test was used to compare the incidences while a Wilcoxon rank-sum test was used to compare the AUCs. In addition, we performed an exploratory analysis of the association of everolimus trough concentrations and toxicity using a Mann-Whitney U test. Due to slow accrual, this study closed after 39 patients were randomized (19 to upfront placebo and 20 to upfront dexamethasone). There were no significant differences between groups seen in either of the coprimary endpoints; furthermore, we found no association between whole blood everolimus trough concentrations and toxicity. Although limited by poor enrollment, the results of this study do not suggest that prophylactic dexamethasone mouthwash is superior to therapeutic dexamethasone mouthwash (initiated at the first sign of mouth pain) for reducing the incidence or severity of mIAS from everolimus.

Quantitation of Cabozantinib in Human Plasma by LC-MS/MS.

To support a phase III randomized trial of the multi-targeted tyrosine kinase inhibitor cabozantinib in neuroendocrine tumors, we developed a high-performance liquid chromatography mass spectrometry method to quantitate cabozantinib in 50 µL of human plasma. After acetonitrile protein precipitation, chromatographic separation was achieved with a Phenomenex synergy polar reverse phase (4 µm, 2 × 50 mm) column and a gradient of 0.1% formic acid in acetonitrile and 0.1% formic acid in water over a 5-min run time. Detection was performed on a Quattromicro quadrupole mass spectrometer with electrospray, positive-mode ionization. The assay was linear over the concentration range 50-5000 ng/mL and proved to be accurate (103.4-105.4%) and precise (<5.0%CV). Hemolysis (10% RBC) and use of heparin as anticoagulant did not impact quantitation. Recovery from plasma varied between 103.0-107.7% and matrix effect was -47.5 to -41.3%. Plasma freeze-thaw stability (97.7-104.9%), stability for 3 months at -80°C (103.4-111.4%), and stability for 4 h at room temperature (100.1-104.9%) were all acceptable. Incurred sample reanalysis of (N = 64) passed: 100% samples within 20% difference, -0.7% median difference and 1.1% median absolute difference. External validation showed a bias of less than 1.1%. This assay will help further define the clinical pharmacokinetics of cabozantinib.

A phase I study of vorinostat in combination with idarubicin in relapsed or refractory leukaemia.

Histone deacetylase inhibitors (HDACi) affect chromatin remodelling and modulate the expression of aberrantly silenced genes. HDACi have single-agent clinical activity in haematological malignancies and have synergistic anti-leukaemia activity when combined with anthracyclines in vitro. We conducted a two-arm, parallel Phase I trial to investigate two schedules of escalating doses of vorinostat (Schedule A: thrice daily (TID) for 14 d; B: TID for 3 d) in combination with a fixed dose of idarubicin in patients with refractory leukaemia. Of the 41 patients enrolled, 90% had acute myeloid leukaemia, with a median of 3 prior therapies. Seven responses (17%) were documented (two complete response (5%), one complete response without platelet recovery (2.5%), and four marrow responses). The 3-d schedule of vorinostat was better tolerated than the 14-d schedule. The maximum tolerated dose for vorinostat was defined as 400 mg TID for 3 d. The most common grade 3 and 4 toxicities included mucositis, fatigue and diarrhoea. Correlative studies demonstrated histone acetylation in patients on therapy and modulation of CDKN1A and TOP2A (topoisomerase II) gene expression. Pharmacokinetic analysis confirmed a dose-related elevation in plasma vorinostat concentrations. The combination of vorinostat and idarubicin is generally tolerable and active in patients with advanced leukaemia and should be studied in the front-line setting.

A phase I, pharmacokinetic and pharmacodynamic study on vorinostat in combination with 5-fluorouracil, leucovorin, and oxaliplatin in patients with refractory colorectal cancer.

PURPOSE: We conducted a phase I study to determine the maximum tolerated dose of vorinostat in combination with fixed doses of 5-fluorouracil (FU), leucovorin, and oxaliplatin (FOLFOX). EXPERIMENTAL DESIGN: Vorinostat was given orally twice daily for 1 week every 2 weeks. FOLFOX was given on days 4 and 5 of vorinostat. The vorinostat starting dose was 100 mg twice daily. Escalation occurred in cohorts of three to six patients. Pharmacokinetics of vorinostat, FU, and oxaliplatin were studied. RESULTS: Twenty-one patients were enrolled. Thrombocytopenia, neutropenia, gastrointestinal toxicities, and fatigue increased in frequency and severity at higher dose levels of vorinostat. Two of 4 evaluable patients at dose level 4 (vorinostat 400 mg orally twice daily) developed dose-limiting fatigue. One of 10 evaluable patients at dose level 3 (vorinostat 300 mg orally twice daily) had dose-limiting fatigue, anorexia, and dehydration. There were significant relationships between vorinostat dose and the area under the curve on days 1 and 5 (Pearson, < 0.001). The vorinostat area under the curve increased (P = 0.005) and clearance decreased (P = 0.003) on day 5 compared with day 1. The median C(max) of FU at each dose level increased significantly with increasing doses of vorinostat, suggesting a pharmacokinetic interaction between FU and vorinostat. Vorinostat-induced thymidylate synthase (TS) modulation was not consistent; only two of six patients had a decrease in intratumoral TS expression by reverse transcription-PCR. CONCLUSIONS: The maximum tolerated dose of vorinostat in combination with FOLFOX is 300 mg orally twice daily x 1 week every 2 weeks. Alternative vorinostat dosing schedules may be needed for optimal down-regulation of TS expression.

In vitro circuit stability of 5-fluorouracil and oxaliplatin in support of hyperthermic isolated hepatic perfusion.

Over the years, a large number of drugs have been used in isolated perfusion of extremities or organs. To interpret the pharmacokinetics of these drugs correctly, the contributions of tissue or organ clearance and chemical degradation, respectively, to overall drug elimination from the circuit need to be identified. In support of a phase I clinical trial of isolated hepatic perfusion (IHP), delivering 5-fluorouracil (5-FU) and oxaliplatin to patients with colorectal cancer hepatic metastases, we aimed to characterize the stability of 5-FU and oxaliplatin in the IHP circuit. Stability of 5-FU and oxaliplatin was assessed in human blood, lactated Ringer infusion (LRI), and in an in vitro IHP circuit consisting of both blood and LRI. Samples were analyzed with liquid chromatography tandem mass spectrometry (5-FU) and atomic absorption spectrophotometry (oxaliplatin). 5-FU was stable under all tested in vitro conditions, but ultrafilterable platinum concentrations decreased slowly with a half-life of 85 minutes in both IHP perfusate and whole blood. The stability of 5-FU in the media containing blood is likely attributable to saturation of dihydropyrimidine dehydrogenase. The decrease of ultrafilterable platinum in blood-containing media with an 85 minutes half-life is in agreement with previous reports on oxaliplatin biotransformation. Oxaliplatin and 5-FU are sufficiently stable in the circuit for the 1-hour perfusion in ongoing and planned clinical trials.

Quantitation of iohexol, a glomerular filtration marker, in human plasma by LC-MS/MS.

We developed a high-performance liquid chromatography mass spectrometry method for quantitating iohexol in 50 µL human plasma. After acetonitrile protein precipitation, chromatographic separation was achieved with a Shodex Asahipak NH2P-50 2D (5 µm, 2 × 150 mm) column and a gradient of 0.1 % formic acid in acetonitrile and 0.1 % formic acid in water over a 10 min run time. Mass spectrometric detection was performed on a Micromass Quatromicro triple-stage bench-top mass spectrometer with electrospray, positive-mode ionization. The assay was linear from 1 to 500 µg/mL for iohexol, proved to be accurate (101.3-102.1 %) and precise (<3.4 %CV), and fulfilled Food and Drug Administration (FDA) criteria for bioanalytical method validation. Recovery from plasma was 53.1-64.2 % and matrix effect was trivial (-3.4 to -1.3 %). Plasma freeze thaw stability (97.4-99.4 %), stability for 5 months at -80 °C (95.5-103.3 %), and stability for 4 h at room temperature (100.6-103.3 %) were all acceptable. This validated assay using a deuterated internal standard will be an important tool in measuring iohexol clearance and determining glomerular filtration rate (GFR) in patients.

Evaluation of the pharmacokinetic drug-drug interaction potential of iohexol, a renal filtration marker.

PURPOSE: Carboplatin dose is calculated based on kidney function, commonly estimated with imperfect creatinine-based formulae. Iohexol is used to measure glomerular filtration rate (GFR) and allows calculation of a more appropriate carboplatin dose. To address potential concerns that iohexol administered during a course of chemotherapy impacts that therapy, we performed in vitro and in vivo pharmacokinetic drug-drug interaction evaluations of iohexol. METHODS: Carboplatin was administered IV to female mice at 60 mg/kg with or without iohexol at 300 mg/kg. Plasma ultrafiltrate, kidney and bone marrow platinum was quantitated by atomic absorption spectrophotometry. Paclitaxel microsomal and gemcitabine cytosolic metabolism as well as metabolism of CYP and UGT probes was assessed with and without iohexol at 300 µg/mL by LC-MS/MS. RESULTS: In vivo carboplatin exposure was not significantly affected by iohexol co-administration (platinum AUC combination vs alone: plasma ultrafiltrate 1,791 vs 1920 µg/mL min; kidney 8367 vs 9757 µg/g min; bone marrow 12.7 vs 12.7 µg/mg-protein min). Paclitaxel microsomal metabolism was not impacted (combination vs alone: 6-α-OH-paclitaxel 38.3 versus 39.4 ng/mL/60 min; 3-p-OH-paclitaxel 26.2 versus 27.7 ng/mL/60 min). Gemcitabine human cytosolic elimination was not impacted (AUC combination vs gemcitabine alone: dFdU 24.1 versus 23.7 µg/mL/30 min). Iohexol displayed no relevant inhibition of the CYP and UGT enzymes in human liver microsomes. CONCLUSIONS: Iohexol is unlikely to affect the clinical pharmacokinetics of carboplatin, paclitaxel, gemcitabine, or other agents used in combination with carboplatin treatment. Measuring GFR with iohexol to better dose carboplatin is unlikely to alter the safety or efficacy of chemotherapy through pharmacokinetic drug-drug interactions.

A phase I study of hyperthermic isolated hepatic perfusion with oxaliplatin in the treatment of unresectable liver metastases from colorectal cancer.

Isolated hepatic perfusion (IHP) is a proven approach for regional delivery of chemotherapy in patients with unresectable primary and metastatic tumors of the liver. Most trials of IHP have utilized melphalan as the active drug in the perfusate. We performed a phase I trial to evaluate the efficacy, safety, and maximum tolerated dose (MTD) of oxaliplatin delivered by hyperthermic isolated hepatic perfusion. A phase I dose-escalation trial of hyperthermic IHP with oxaliplatin in patients with unresectable metastatic colorectal cancer scheduled to undergo placement of a hepatic arterial infusion (HAI) pump was carried out. Thirteen patients were enrolled between November 2003 and September 2006. Dose-limiting veno-occlusive disease was observed at 60 mg/m(2). At the MTD of 40 mg/m(2) only minor transient liver dysfunction was observed. Ultrafilterable platinum area under the curve and maximum concentration delivered by IHP increased nonlinearly with dose as did platinum concentrations in liver biopsies obtained at the end of the 60 min IHP. Seventy-seven percent of patients had a >50% decrease in serum carcinoembryonic antigen (CEA) after IHP. The overall response rate to the combined IHP and HAI therapy was 66%. One patient had a durable complete response (>4 years). We conclude that hyperthermic IHP with oxaliplatin was safe and feasible at a dose of 40 mg/m(2). The ability to obtain complete vascular isolation with open IHP was confirmed. The response rate in this small phase I study was encouraging.

Enhancement of cisplatin [cis-diammine dichloroplatinum (II)] cytotoxicity by O6-benzylguanine involves endoplasmic reticulum stress.

O6-Benzylguanine (BG) enhances cisplatin [cis-diammine dichloroplatinum (II)]-induced cytotoxicity and apoptosis in head and neck cancer cell lines by an unknown mechanism. We investigated the effect of cisplatin with and without BG on two targets of damage: DNA and the endoplasmic reticulum (ER). We chose three cancer cell lines to ascertain the mechanism of BG-enhanced cytotoxicity: SQ20b head and neck and SKOV-3x ovarian cancer cell lines, where BG enhanced cisplatin cytotoxicity, and A549 nonsmall cell lung cancer line, where BG did not enhance cisplatin cytotoxicity. All three lines had an increase in DNA damage when BG was added to cisplatin treatment, as evidenced by increased platination and phosphorylated histone H2AX formation. The increase in cisplatin-induced DNA damage after treatment with BG plus cisplatin is not sufficient to increase cytotoxicity or apoptosis in A549 cells. We evaluated the effect of cisplatin on the ER and observed increased caspase 12 cleavage in SQ20b and SKOV-3x cells, but not in A549 cells, after treatment with BG plus cisplatin versus cisplatin alone. Growth arrest and DNA damage inducible (GADD) 153, an ER stress-response gene, is up-regulated after treatment with BG plus cisplatin compared with cisplatin alone in SQ20b and SKOV-3x cells, but not in A549 cells. ER stress-induced apoptosis is an integral part of the mechanism by which BG enhances cisplatin. Inhibition of ER stress in the SQ20b cell line by salubrinal, an inhibitor of eIF2alpha dephosphorylation, or GADD153 small interfering RNA, abrogated BG-enhancement of cisplatin cytotoxicity and apoptosis through caspase 3 and 12 cleavage. These data indicate GADD153 up-regulation plays an important role in BG-enhanced cisplatin cytotoxicity and apoptosis.

Liquid chromatography-mass spectrometric assay for quantitation of the short-chain fatty acid, 2,2-dimethylbutyrate (NSC 741804), in rat plasma.

2,2-Dimethylbutyrate (DMB) is a potential treatment for thalassemia and hemoglobinopathies. To facilitate pharmacokinetic evaluation of DMB, we developed an LC-MS assay and quantitated DMB in plasma of rats after an oral dose of 500mg/kg. After acetonitrile protein precipitation, DMB and dimethylvaleric acid (DMV) internal standard were derivatized to benzylamides, chromatographed on a Hydro-RP column with acetonitrile, water, and 0.1% formic acid, and detected by electrospray positive-mode ionization mass spectrometry. The assay was accurate (97-107%) and precise (3.4-6.2%) between 100 and 10,000ng/mL. Recovery from plasma was >62%. Plasma freeze-thaw and room temperature stability were acceptable.

NCI Comparative Oncology Program Testing of Non-Camptothecin Indenoisoquinoline Topoisomerase I Inhibitors in Naturally Occurring Canine Lymphoma.

PURPOSE: Only one chemical class of topoisomerase I (TOP1) inhibitors is FDA approved, the camptothecins with irinotecan and topotecan widely used. Because of their limitations (chemical instability, drug efflux-mediated resistance, and diarrhea), novel TOP1 inhibitors are warranted. Indenoisoquinoline non-camptothecin topoisomerase I (TOP1) inhibitors overcome chemical instability and drug resistance that limit camptothecin use. Three indenoisoquinolines, LMP400 (indotecan), LMP776 (indimitecan), and LMP744, were examined in a phase I study for lymphoma-bearing dogs to evaluate differential efficacy, pharmacodynamics, toxicology, and pharmacokinetics. EXPERIMENTAL DESIGN: Eighty-four client-owned dogs with lymphomas were enrolled in dose-escalation cohorts for each indenoisoquinoline, with an expansion phase for LMP744. Efficacy, tolerability, pharmacokinetics, and target engagement were determined. RESULTS: The MTDs were 17.5 mg/m2 for LMP 776 and 100 mg/m2 for LMP744; bone marrow toxicity was dose-limiting; up to 65 mg/m2 LMP400 was well-tolerated and MTD was not reached. None of the drugs induced notable diarrhea. Sustained tumor accumulation was observed for LMP744; γH2AX induction was demonstrated in tumors 2 and 6 hours after treatment; a decrease in TOP1 protein was observed in most lymphoma samples across all compounds and dose levels, which is consistent with the fact that tumor response was also observed at low doses LMP744. Objective responses were documented for all indenoisoquinolines; efficacy (13/19 dogs) was greatest for LMP744. CONCLUSIONS: These results demonstrate proof-of-mechanism for indenoisoquinoline TOP1 inhibitors supporting their further clinical development. They also highlight the value of the NCI Comparative Oncology Program (https://ccr.cancer.gov/Comparative-Oncology-Program) for evaluating novel therapies in immunocompetent pets with cancers.

Pharmacokinetics, metabolism, and oral bioavailability of the DNA methyltransferase inhibitor 5-fluoro-2'-deoxycytidine in mice.

PURPOSE: In vivo, 5-fluoro-2'-deoxycytidine (FdCyd) is rapidly and sequentially converted to 5-fluoro-2'-deoxyuridine, 5-fluorouracil, and 5-fluorouridine. The i.v. combination of FdCyd and 3,4,5,6-tetrahydrouridine (THU), a cytidine deaminase (CD) inhibitor that blocks the first metabolic step in FdCyd catabolism, is being investigated clinically for its ability to inhibit DNA methyltransferase. However, the full effects of THU on FdCyd metabolism and pharmacokinetics are unknown. We aimed to characterize the pharmacokinetics, metabolism, and bioavailability of FdCyd with and without THU in mice. EXPERIMENTAL DESIGN: We developed a sensitive high-performance liquid chromatography tandem mass spectrometry assay to quantitate FdCyd and metabolites in mouse plasma. Mice were dosed i.v. or p.o. with 25 mg/kg FdCyd with or without coadministration of 100 mg/kg THU p.o. or i.v. RESULTS: The oral bioavailability of FdCyd alone was approximately 4%. Coadministration with THU increased exposure to FdCyd and decreased exposure to its metabolites; i.v. and p.o. coadministration of THU increased exposure to p.o. FdCyd by 87- and 58-fold, respectively. FdCyd exposure after p.o. FdCyd with p.o. THU was as much as 54% that of i.v. FdCyd with i.v. THU. CONCLUSIONS: FdCyd is well absorbed but undergoes substantial first-pass catabolism by CD to potentially toxic metabolites that do not inhibit DNA methyltransferase. THU is sufficiently bioavailable to reduce the first-pass effect of CD on FdCyd. Oral coadministration of THU and FdCyd is a promising approach that warrants clinical testing because it may allow maintaining effective FdCyd concentrations on a chronic basis, which would be an advantage over other DNA methyltransferase inhibitors that are currently approved or in development.

Simultaneous quantitation of abiraterone, enzalutamide, N-desmethyl enzalutamide, and bicalutamide in human plasma by LC-MS/MS.

Inhibiting the androgen receptor (AR) pathway is an important clinical strategy in metastatic prostate cancer. Novel agents including abiraterone acetate and enzalutamide have been shown to prolong life in men with metastatic, castration-resistant prostate cancer (mCRPC). To evaluate the pharmacokinetics of AR-targeted agents, we developed and validated an LC-MS/MS assay for the quantitation of enzalutamide, N-desmethyl enzalutamide, abiraterone and bicalutamide in 0.05mL human plasma. After protein precipitation, chromatographic separation was achieved with a Phenomenex Synergi Polar-RP column and a linear gradient of 0.1% formic acid in methanol and water. Detection with an ABI 4000Q mass spectrometer utilized electrospray ionization in positive multiple reaction monitoring mode. The assay was linear over the ranges of 1-1000ng/mL for abiraterone and bicalutamide and 100-30,000ng/mL for N-desmethyl enzalutamide and enzalutamide and proved to be accurate (92.8-107.7%) and precise (largest was 15.3% CV at LLOQ for bicalutamide), and fulfilled FDA criteria for bioanalytical method validation. We demonstrated the suitability of this assay in plasma from patients who were administered enzalutamide 160mg, abiraterone 1000mg and bicalutamide 50mg once a day as monotherapy or in combination. The LC-MS/MS assay that has been developed will be an essential tool that further defines the pharmacology of the combinations of androgen synthesis or AR-receptor targeted agents.

Phase I study of veliparib in combination with gemcitabine.

BACKGROUND: Veliparib (ABT-888) is an oral PARP inhibitor expected to increase gemcitabine activity. This phase I determined the maximal tolerable dose (MTD), dose-limiting toxicities (DLT), antitumor activity, pharmacokinetics (PK), and pharmacodynamics (PD) of veliparib combined with gemcitabine. METHODS: Patients with advanced solid tumors received veliparib (10-40-mg PO BID) on chemotherapy weeks with gemcitabine 500-750-mg/m2 IV on days 1, 8, and 15 (28-day cycle), or on days 1 and 8 (21-day cycle). The MTD, DLT, adverse events, PK, and PD were evaluated. RESULTS: Eleven patients were enrolled on the 28-day schedule. The 28-day schedule was considered intolerable and amended to a 21-day schedule, with 20 patients enrolled. Grade ≥ 3 adverse events were myelosuppression-related. The MTD was determined to be 750-mg/m2 gemcitabine IV on days 1 and 8- and 20-mg PO veliparib BID days 1-14 on a 21-day schedule. Of 27 patients evaluable for response, 3 had PR and 15 had SD. There was no evidence of any major drug-drug interaction, and PK parameter values for veliparib, gemcitabine, and dFdU were as expected. Analysis of PBMCs showed evidence of PARP inhibition and DNA damage associated with therapy. CONCLUSIONS: Gemcitabine at 750-mg/m2 IV on days 1 and 8 combined with veliparib at a dose of 20-mg PO BID days 1-14 on a 21-day schedule is relatively well-tolerated, with manageable, expected toxicities. Clinical responses were observed in a pretreated population of patients, suggesting that this combination should be further evaluated in the phase II setting.

A liquid chromatography-electrospray ionization tandem mass spectrometric assay for quantitation of the histone deacetylase inhibitor, vorinostat (suberoylanilide hydroxamicacid, SAHA), and its metabolites in human serum.

Vorinostat (suberoylanilide hydroxamic acid, SAHA) is undergoing evaluation as an antineoplastic agent. We developed a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for quantitating vorinostat and its major metabolites, vorinostat glucuronide and 4-anilino-4-oxobutanoic acid, in human serum. The assay uses: deuterated internal standards; acetonitrile protein precipitation; a BDS Hypersil C18 (3 microm, 100 mm x 3 mm) column; a gradient mobile phase of 0.5% acetic acid in acetonitrile and water; and electrospray positive-mode ionization with selected reaction monitoring (SRM) detection. The lower limit of quantitation was 3.0 ng/ml for each analyte. The assay is being employed in at least 12 clinical studies of vorinostat-containing regimens.

Plasma pharmacokinetics, oral bioavailability, and interspecies scaling of the DNA methyltransferase inhibitor, zebularine.

PURPOSE: Zebularine is a DNA methyltransferase inhibitor proposed for clinical evaluation. EXPERIMENTAL DESIGN: We developed a liquid chromatography/mass spectrometry assay and did i.v. and oral studies in mice, rats, and rhesus monkeys. RESULTS: In mice, plasma zebularine concentrations declined with terminal half-lives (t(1/2)) of 40 and 91 minutes after 100 mg/kg i.v. and 1,000 mg/kg given orally, respectively. Zebularine plasma concentration versus time curves (area under the curve) after 100 mg/kg i.v. and 1,000 mg/kg given orally were 7,323 and 4,935 mug/mL min, respectively, corresponding to a total body clearance (CL(tb)) of 13.65 mL/min/kg, apparent total body clearance (CL(app)) of 203 mL/min/kg, and oral bioavailability of 6.7%. In rats, plasma zebularine concentrations declined with t(1/2) of 363, 110, and 126 minutes after 50 mg/kg i.v., 250 mg/kg given orally, and 500 mg/kg given orally, respectively. Zebularine areas under the curve after 50 mg/kg i.v., 250 mg/kg given orally, and 500 mg/kg given orally were 12,526, 1,969, and 7,612 mug/mL min, respectively, corresponding to a CL(tb) of 3.99 mL/min/kg for 50 mg/kg i.v. and CL(app) of 127 and 66 mL/min/kg for 250 and 500 mg/kg given orally, respectively. Bioavailabilities of 3.1% and 6.1% were calculated for the 250 and 500 mg/kg oral doses, respectively. In monkeys, zebularine t(1/2) was 70 and 150 minutes, CL(tb) was 3.55 and 10.85 mL/min/kg after i.v. administration, and CL(app) was 886 and 39,572 mL/min/kg after oral administration of 500 and 1,000 mg/kg, respectively. Zebularine oral bioavailability was <1% in monkeys. Interspecies scaling produced the following relationship: CL(tb) = 6.46(weight(0.9)). CONCLUSIONS: Zebularine has limited oral bioavailability. Interspecies scaling projects a CL(tb) of 296 mL/min in humans.

LC-MS/MS assay for the quantitation of FdCyd and its metabolites FdUrd and FU in human plasma.

The hypomethylating agent 5-fluoro-2'-deoxycytidine (FdCyd, NSC 48006) is being evaluated clinically both via the intravenous route and via the oral route in combination with 3,4,5,6-tetrahydrouridine (THU), a potent inhibitor of FdCyd catabolism. To determine the pharmacokinetics of FdCyd and downstream metabolites, we developed and validated an LC-MS/MS assay for the quantitation of FdCyd, 5-fluoro-2'-deoxyuridine (FdUrd), and 5-fluorouracil (FU) in 0.2mL human plasma. After acetonitrile protein precipitation, the sample was split and separate chromatography was achieved for FdCyd with a Synergi Polar-RP column and for FdUrd and FU with a Shodex Asahipak NH2P-50 2D column. Gradients of 0.1% acetic acid in acetonitrile and water were used. Detection with a Quattromicro quadrupole mass spectrometer with electrospray ionization in positive-ion (FdCyd) or negative-ion (FdUrd and FU) multiple reaction monitoring (MRM) mode. The assay was linear from 5 to 3000ng/mL for all three analytes and proved to be accurate (96.7-105.5%) and precise (<8.1%CV), and fulfilled FDA criteria for bioanalytical method validation. We demonstrated the suitability of this assay for measuring FdCyd and metabolites FdUrd and FU in plasma from a patient who was administered 120mg PO FdCyd 30min after 3000mg THU. Our LC-MS/MS assay will be an essential tool to further define the pharmacology of FdCyd in ongoing and future studies.