Effects of tetrahydrouridine on pharmacokinetics and pharmacodynamics of oral decitabine.

The deoxycytidine analog decitabine (DAC) can deplete DNA methyl-transferase 1 (DNMT1) and thereby modify cellular epigenetics, gene expression, and differentiation. However, a barrier to efficacious and accessible DNMT1-targeted therapy is cytidine deaminase, an enzyme highly expressed in the intestine and liver that rapidly metabolizes DAC into inactive uridine counterparts, severely limiting exposure time and oral bioavailability. In the present study, the effects of tetrahydrouridine (THU), a competitive inhibitor of cytidine deaminase, on the pharmacokinetics and pharmacodynamics of oral DAC were evaluated in mice and nonhuman primates. Oral administration of THU before oral DAC extended DAC absorption time and widened the concentration-time profile, increasing the exposure time for S-phase-specific depletion of DNMT1 without the high peak DAC levels that can cause DNA damage and cytotoxicity. THU also decreased interindividual variability in pharmacokinetics seen with DAC alone. One potential clinical application of DNMT1-targeted therapy is to increase fetal hemoglobin and treat hemoglobinopathy. Oral THU-DAC at a dose that would produce peak DAC concentrations of less than 0.2µM administered 2×/wk for 8 weeks to nonhuman primates was not myelotoxic, hypomethylated DNA in the γ-globin gene promoter, and produced large cumulative increases in fetal hemoglobin. Combining oral THU with oral DAC changes DAC pharmacology in a manner that may facilitate accessible noncytotoxic DNMT1-targeted therapy.

Characterization of acute biliary hyperplasia in Fisher 344 rats administered the indole-3-carbinol analog, NSC-743380.

NSC-743380 (1-[(3-chlorophenyl)-methyl]-1H-indole-3-carbinol) is in early stages of development as an anticancer agent. Two metabolites reflect sequential conversion of the carbinol functionality to a carboxaldehyde and the major metabolite, 1-[(3-chlorophenyl)-methyl]-1H-indole-3-carboxylic acid. In an exploratory toxicity study in rats, NSC-743380 induced elevations in liver-associated serum enzymes and biliary hyperplasia. Biliary hyperplasia was observed 2 days after dosing orally for 2 consecutive days at 100mg/kg/day. Notably, hepatotoxicity and biliary hyperplasia were observed after oral administration of the parent compound, but not when major metabolites were administered. The toxicities of a structurally similar but pharmacologically inactive molecule and a structurally diverse molecule with a similar efficacy profile in killing cancer cells in vitro were compared to NSC-743380 to explore scaffold versus target-mediated toxicity. Following two oral doses of 100mg/kg/day given once daily on two consecutive days, the structurally unrelated active compound produced hepatic toxicity similar to NSC-743380. The structurally similar inactive compound did not, but, lower exposures were achieved. The weight of evidence implies that the hepatotoxicity associated with NSC-743380 is related to the anticancer activity of the parent molecule. Furthermore, because biliary hyperplasia represents an unmanageable and non-monitorable adverse effect in clinical settings, this model may provide an opportunity for investigators to use a short-duration study design to explore biomarkers of biliary hyperplasia.

Subchronic oral toxicity study of decitabine in combination with tetrahydrouridine in CD-1 mice.

Decitabine (5-aza-2'-deoxycytidine; DAC) in combination with tetrahydrouridine (THU) is a potential oral therapy for sickle cell disease and ß-thalassemia. A study was conducted in mice to assess safety of this combination therapy using oral gavage of DAC and THU administered 1 hour prior to DAC on 2 consecutive days/week for up to 9 weeks followed by a 28-day recovery to support its clinical trials up to 9-week duration. Tetrahydrouridine, a competitive inhibitor of cytidine deaminase, was used in the combination to improve oral bioavailability of DAC. Doses were 167 mg/kg THU followed by 0, 0.2, 0.4, or 1.0 mg/kg DAC; THU vehicle followed by 1.0 mg/kg DAC; or vehicle alone. End points evaluated were clinical observations, body weights, food consumption, clinical pathology, gross/histopathology, bone marrow micronuclei, and toxicokinetics. There were no treatment-related effects noticed on body weight, food consumption, serum chemistry, or urinalysis parameters. Dose- and gender-dependent changes in plasma DAC levels were observed with a Cmax within 1 hour. At the 1 mg/kg dose tested, THU increased DAC plasma concentration (∼ 10-fold) as compared to DAC alone. Severe toxicity occurred in females receiving high-dose 1 mg/kg DAC + THU, requiring treatment discontinuation at week 5. Severity and incidence of microscopic findings increased in a dose-dependent fashion; findings included bone marrow hypocellularity (with corresponding hematologic changes and decreases in white blood cells, red blood cells, hemoglobin, hematocrit, reticulocytes, neutrophils, and lymphocytes), thymic/lymphoid depletion, intestinal epithelial apoptosis, and testicular degeneration. Bone marrow micronucleus analysis confirmed bone marrow cytotoxicity, suppression of erythropoiesis, and genotoxicity. Following the recovery period, a complete or trend toward resolution of these effects was observed. In conclusion, the combination therapy resulted in an increased sensitivity to DAC toxicity correlating with DAC plasma levels, and females are more sensitive compared to their male counterparts.

Mouse pharmacokinetics and metabolism of the phenylurea thiocarbamate NSC 161128.

PURPOSE: NSC 161128, a phenylurea thiocarbamate, displays activity against the NCI60 anti-cancer cell line panel and xenograft models. The metabolite N-methyl-N'-phenylurea (M10) has been detected in animal plasma; however, detection and quantification of other putative NSC 161128 metabolites have not been undertaken. The purpose of this study was to characterize the pharmacokinetics and metabolism of NSC 161128 in mice and under in vitro conditions. METHODS: An LC-MS/MS assay was developed to evaluate stability and in vitro metabolism of NSC 161128 in liver microsomes and S9 fractions. Single-dose pharmacokinetic profiles for NSC 161128 and its metabolite M10 were obtained following intraperitoneal (I.P.) administration. RESULTS: A sensitive and specific positive ionization LC-MS/MS method for measuring NSC 161128 and its metabolites was developed. HPLC separation was achieved under gradient elution using an aqueous methanol mobile phase containing 0.05% formic acid and 0.05% ammonium hydroxide. The assay was linear over the range 1.0-1000 ng/mL. NSC 161128 was stable in aqueous solution and tissue culture media, but not in plasma, where rapid degradation of NSC 161128 to the metabolite M10 was observed. Following I.P. administration of a 200 mg/kg dose to male CD1 mice, the peak plasma concentration of NSC 161128 was 255 ng/mL after 5 min with a plasma half-life of 138 min. Potential bioactivation of NSC 161128 was explored using mouse S9. CONCLUSIONS: An analytical LC-MS/MS method was successfully developed for the detection and quantification of NSC 161128 and its metabolites. These results increase the understanding of NSC 161128 pharmacokinetic and metabolic properties.

Population Pharmacokinetics of Z-Endoxifen in Patients With Advanced Solid Tumors.

The purpose of this study was to develop and validate a population pharmacokinetic model for Z-endoxifen in patients with advanced solid tumors and to identify clinical variables that influence pharmacokinetic parameters. Z-endoxifen-HCl was administered orally once a day on a 28-day cycle (±3 days) over 11 dose levels ranging from 20 to 360 mg. A total of 1256 Z-endoxifen plasma concentration samples from 80 patients were analyzed using nonlinear mixed-effects modeling to develop a population pharmacokinetic model for Z-endoxifen. A 2-compartment model with oral depot and linear elimination adequately described the data. The estimated apparent total clearance, apparent central volume of distribution, and apparent peripheral volume of distribution were 4.89 L/h, 323 L, and 39.7 L, respectively, with weight-effect exponents of 0.75, 1, and 1, respectively. This model was used to explore the effects of clinical and demographic variables on Z-endoxifen pharmacokinetics. Weight, race on clearance, and aspartate aminotransferase on the absorption rate constant were identified as significant covariates in the final model. This novel population pharmacokinetic model provides insight regarding factors that may affect the pharmacokinetics of Z-endoxifen and may assist in the design of future clinical trials.

Comparative Oncology Assessment of a Novel Inhibitor of Valosin-Containing Protein in Tumor-Bearing Dogs.

Pet dogs with naturally occurring cancers play an important role in studies of cancer biology and drug development. We assessed tolerability, efficacy, and pharmacokinetic/pharmacodynamic relationships with a first-in-class small molecule inhibitor of valosin-containing protein (VCP/p97), CB-5339, administered to 24 tumor-bearing pet dogs. Tumor types assessed included solid malignancies, lymphomas, and multiple myeloma. Through a stepwise dose and schedule escalation schema, we determined the maximum tolerated dose to be 7.5 mg/kg when administered orally on a 4 days on, 3 days off schedule per week for 3 consecutive weeks. Adverse events were minimal and mainly related to the gastrointestinal system. Pharmacokinetic/pharmacodynamic data suggest a relationship between exposure and modulation of targets related to induction of the unfolded protein response, but not to tolerability of the agent. An efficacy signal was detected in 33% (2/6) of dogs with multiple myeloma, consistent with a mechanism of action relating to induction of proteotoxic stress in a tumor type with abundant protein production. Clinical trials of CB-5339 in humans with acute myelogenous leukemia and multiple myeloma are ongoing.

Development and validation of an LC-MS/MS generic assay platform for small molecule drug bioanalysis.

AIM: We developed a generic high-performance liquid chromatography mass spectrometry approach for quantitation of small molecule compounds without availability of isotopically labelled standard. METHODS: The assay utilized 50 µL of plasma and offers 8 potential internal standards (IS): acetaminophen, veliparib, busulfan, neratinib, erlotinib, abiraterone, bicalutamide, and paclitaxel. Preparation consisted of acetonitrile protein precipitation and aqueous dilution in a 96 well-plate format. Chromatographic separation was achieved with a Kinetex C18 reverse phase (2.6 µm, 2 mm x 50 mm) column and a gradient of 0.1 % formic acid in acetonitrile and water over an 8 min run time. Mass spectrometric detection was performed on an AB SCIEX4000QTRAP with electrospray, positive-mode ionization. Performance of the generic approach was evaluated with seven drugs (LMP744, olaparib, cabozantinib, triapine, ixabepilone, berzosertib, eribulin) for which validated assays were available. RESULTS: The 8 IS covered a range of polarity, size, and ionization; eluted over the range of chromatographic retention times; were quantitatively extracted; and suffered limited matrix effects. The generic approach proved to be linear for test drugs evaluated over at least 3 orders of magnitude starting at 1-10 ng/mL, with extension of assay ranges with analyte isotopologue MRM channels. At a bias of less than 16 % and precision within 15 %, the assay performance was acceptable. CONCLUSION: The generic approach has become a useful tool to further define the pharmacology of drugs studied in our laboratory and may be utilized as described, or as starting point to develop drug-specific assays with more extensive performance characterization.

Phase 1 study of Z-endoxifen in patients with advanced gynecologic, desmoid, and hormone receptor-positive solid tumors.

BACKGROUND: Differential responses to tamoxifen may be due to inter-patient variability in tamoxifen metabolism into pharmacologically active Z-endoxifen. Z-endoxifen administration was anticipated to bypass these variations, increasing active drug levels, and potentially benefitting patients responding sub-optimally to tamoxifen. MATERIALS AND METHODS: Patients with treatment-refractory gynecologic malignancies, desmoid tumors, or hormone receptor-positive solid tumors took oral Z-endoxifen daily with a 3+3 phase 1 dose escalation format over 8 dose levels (DLs). Safety, pharmacokinetics/pharmacodynamics, and clinical outcomes were evaluated. RESULTS: Thirty-four of 40 patients were evaluable. No maximum tolerated dose was established. DL8, 360 mg/day, was used for the expansion phase and is higher than doses administered in any previous study; it also yielded higher plasma Z-endoxifen concentrations. Three patients had partial responses and 8 had prolonged stable disease (≥ 6 cycles); 44.4% (8/18) of patients at dose levels 6-8 achieved one of these outcomes. Six patients who progressed after tamoxifen therapy experienced partial response or stable disease for ≥ 6 cycles with Z-endoxifen; one with desmoid tumor remains on study after 62 cycles (nearly 5 years). CONCLUSIONS: Evidence of antitumor activity and prolonged stable disease are achieved with Z-endoxifen despite prior tamoxifen therapy, supporting further study of Z-endoxifen, particularly in patients with desmoid tumors.

Discovery and Optimization of 2H-1λ2-Pyridin-2-one Inhibitors of Mutant Isocitrate Dehydrogenase 1 for the Treatment of Cancer.

Neomorphic mutations in isocitrate dehydrogenase 1 (IDH1) are oncogenic for a number of malignancies, primarily low-grade gliomas and acute myeloid leukemia. We report a medicinal chemistry campaign around a 7,7-dimethyl-7,8-dihydro-2H-1λ2-quinoline-2,5(6H)-dione screening hit against the R132H and R132C mutant forms of isocitrate dehydrogenase (IDH1). Systematic SAR efforts produced a series of potent pyrid-2-one mIDH1 inhibitors, including the atropisomer (+)-119 (NCATS-SM5637, NSC 791985). In an engineered mIDH1-U87-xenograft mouse model, after a single oral dose of 30 mg/kg, 16 h post dose, between 16 and 48 h, (+)-119 showed higher tumoral concentrations that corresponded to lower 2-HG concentrations, when compared with the approved drug AG-120 (ivosidenib).

Intravenous 5-fluoro-2'-deoxycytidine administered with tetrahydrouridine increases the proportion of p16-expressing circulating tumor cells in patients with advanced solid tumors.

PURPOSE: Following promising responses to the DNA methyltransferase (DNMT) inhibitor 5-fluoro-2'-deoxycytidine (FdCyd) combined with tetrahydrouridine (THU) in phase 1 testing, we initiated a non-randomized phase 2 study to assess response to this combination in patients with advanced solid tumor types for which tumor suppressor gene methylation is potentially prognostic. To obtain pharmacodynamic evidence for DNMT inhibition by FdCyd, we developed a novel method for detecting expression of tumor suppressor protein p16/INK4A in circulating tumor cells (CTCs). METHODS: Patients in histology-specific strata (breast, head and neck [H&N], or non-small cell lung cancers [NSCLC] or urothelial transitional cell carcinoma) were administered FdCyd (100 mg/m2) and THU (350 mg/m2) intravenously 5 days/week for 2 weeks, in 28-day cycles, and progression-free survival (PFS) rate and objective response rate (ORR) were evaluated. Blood specimens were collected for CTC analysis. RESULTS: Ninety-three eligible patients were enrolled (29 breast, 21 H&N, 25 NSCLC, and 18 urothelial). There were three partial responses. All strata were terminated early due to insufficient responses (H&N, NSCLC) or slow accrual (breast, urothelial). However, the preliminary 4-month PFS rate (42%) in the urothelial stratum exceeded the predefined goal-though the ORR (5.6%) did not. An increase in the proportion of p16-expressing cytokeratin-positive CTCs was detected in 69% of patients evaluable for clinical and CTC response, but was not significantly associated with clinical response. CONCLUSION: Further study of FdCyd + THU is potentially warranted in urothelial carcinoma but not NSCLC or breast or H&N cancer. Increase in the proportion of p16-expressing cytokeratin-positive CTCs is a pharmacodynamic marker of FdCyd target engagement.

Modulation of gemcitabine (2',2'-difluoro-2'-deoxycytidine) pharmacokinetics, metabolism, and bioavailability in mice by 3,4,5,6-tetrahydrouridine.

PURPOSE: In vivo, 2',2'-difluoro-2'-deoxycytidine (dFdC) is rapidly inactivated by gut and liver cytidine deaminase (CD) to 2',2'-difluoro-2'-deoxyuridine (dFdU). Consequently, dFdC has poor oral bioavailability and is administered i.v., with associated costs and limitations in administration schedules. 3,4,5,6-Tetrahydrouridine (THU) is a potent CD inhibitor with a 20% oral bioavailability. We investigated the ability of THU to decrease elimination and first-pass effect by CD, thereby enabling oral dosing of dFdC. EXPERIMENTAL DESIGN: A liquid chromatography-tandem mass spectrometry assay was developed for plasma dFdC and dFdU. Mice were dosed with 100 mg/kg dFdC i.v. or orally with or without 100 mg/kg THU i.v. or orally. At specified times between 5 and 1,440 min, mice (n = 3) were euthanized. dFdC, dFdU, and THU concentrations were quantitated in plasma and urine. RESULTS: THU i.v. and orally produced concentrations >4 microg/mL for 3 and 2 h, respectively, whereas concentrations of >1 microg/mL have been associated with near-complete inhibition of CD in vitro. THU i.v. decreased plasma dFdU concentrations but had no effect on dFdC plasma area under the plasma concentration versus time curve after i.v. dFdC dosing. Both THU i.v. and orally substantially increased oral bioavailability of dFdC. Absorption of dFdC orally was 59%, but only 10% passed liver and gut CD and eventually reached the systemic circulation. Coadministration of THU orally increased dFdC oral bioavailability from 10% to 40%. CONCLUSIONS: Coadministration of THU enables oral dosing of dFdC and warrants clinical testing. Oral dFdC treatment would be easier and cheaper, potentially prolong dFdC exposure, and enable exploration of administration schedules considered impractical by the i.v. route.

Plasma pharmacokinetics and oral bioavailability of 3,4,5,6-tetrahydrouridine, a cytidine deaminase inhibitor, in mice.

Cytidine analogues such as cytosine arabinoside, gemcitabine, decitabine, 5-azacytidine, 5-fluoro-2'-deoxycytidine and 5-chloro-2'-deoxycytidine undergo rapid catabolism by cytidine deaminase (CD). 3,4,5,6-tetrahydrouridine (THU) is a potent CD inhibitor that has been applied preclinically and clinically as a modulator of cytidine analogue metabolism. However, THU pharmacokinetics has not been fully characterized, which has impaired the optimal preclinical evaluation and clinical use of THU. Therefore, we characterized the THU pharmacokinetics and bioavailability in mice. Mice were dosed with THU iv (100 mg/kg) or po (30, 100, or 300 mg/kg). Plasma and urine THU concentrations were quantitated with a validated LC-MS/MS assay. Plasma pharmacokinetic parameters were calculated compartmentally and non-compartmentally. THU, at 100 mg/kg iv had a 73 min terminal half-life and produced plasma THU concentrations >1 microg/ml, the concentration shown to effectively block deamination, for 4 h. Clearance was 9.1 ml/min/kg, and the distribution volume was 0.95 l/kg. Renal excretion accounted for 36-55% of the THU dose. A three-compartment model fit the iv THU data best. THU, at 100 mg/kg po, produced a concentration versus time profile with a plateau of approximately 10 mug/ml from 0.5-3 h, followed by a decline with an 85 min half-life. The oral bioavailability of THU was approximately 20%. The 20% oral bioavailability of THU is sufficient to produce and sustain, for several hours, plasma concentrations that inhibit CD. This suggests the feasibility of using THU to decrease elimination and first-pass metabolism of cytidine analogues by CD. THU pharmacokinetics are now being evaluated in humans.

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.

Molecular Pharmacodynamics-Guided Scheduling of Biologically Effective Doses: A Drug Development Paradigm Applied to MET Tyrosine Kinase Inhibitors.

The development of molecularly targeted agents has benefited from use of pharmacodynamic markers to identify "biologically effective doses" (BED) below MTDs, yet this knowledge remains underutilized in selecting dosage regimens and in comparing the effectiveness of targeted agents within a class. We sought to establish preclinical proof-of-concept for such pharmacodynamics-based BED regimens and effectiveness comparisons using MET kinase small-molecule inhibitors. Utilizing pharmacodynamic biomarker measurements of MET signaling (tumor pY1234/1235MET/total MET ratio) in a phase 0-like preclinical setting, we developed optimal dosage regimens for several MET kinase inhibitors and compared their antitumor efficacy in a MET-amplified gastric cancer xenograft model (SNU-5). Reductions in tumor pY1234/1235MET/total MET of 95%-99% were achievable with tolerable doses of EMD1214063/MSC2156119J (tepotinib), XL184 (cabozantinib), and XL880/GSK1363089 (foretinib), but not ARQ197 (tivantinib), which did not alter the pharmacodynamic biomarker. Duration of kinase suppression and rate of kinase recovery were specific to each agent, emphasizing the importance of developing customized dosage regimens to achieve continuous suppression of the pharmacodynamic biomarker at the required level (here, ≥90% MET kinase suppression). The customized dosage regimen of each inhibitor yielded substantial and sustained tumor regression; the equivalent effectiveness of customized dosage regimens that achieve the same level of continuous molecular target control represents preclinical proof-of-concept and illustrates the importance of proper scheduling of targeted agent BEDs. Pharmacodynamics-guided biologically effective dosage regimens (PD-BEDR) potentially offer a superior alternative to pharmacokinetic guidance (e.g., drug concentrations in surrogate tissues) for developing and making head-to-head comparisons of targeted agents. Mol Cancer Ther; 17(3); 698-709. ©2018 AACR.

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.

A mass balance and disposition study of the DNA methyltransferase inhibitor zebularine (NSC 309132) and three of its metabolites in mice.

PURPOSE: To elucidate the in vivo metabolic fate of zebularine (NSC 309132), a DNA methyltransferase inhibitor proposed for clinical evaluation in the treatment of cancer. EXPERIMENTAL DESIGN: Male, CD(2)F(1) mice were dosed i.v. with 100 mg/kg 2-[(14)C]zebularine. At specified times between 5 and 1,440 minutes, mice were euthanized. Plasma, organs, carcass, urine, and feces were collected and assayed for total radioactivity. Plasma and urine were also analyzed for zebularine and its metabolites with a previously validated high-pressure liquid chromatography assay. A similar experiment was done with 2-[(14)C]uridine, the proposed primary metabolite of zebularine. RESULTS: Maximum plasma concentrations were 462, 306, 33.6, 21.7, and 11.5 mumol/L for total radioactivity, zebularine, uridine, uracil (each at 5 minutes), and dihydrouracil (at 15 minutes), respectively. Total radioactivity, zebularine, uridine, uracil, and dihydrouracil were rapidly eliminated from plasma, and after 45 minutes, none of the individual compounds could be quantitated by high-pressure liquid chromatography. Plasma data were consistent with sequential conversion of zebularine to uridine, uracil, and dihydrouracil. 2-Pyrimidinone was not observed. Prolonged retention of radioactivity, at concentrations higher than in plasma, was observed in tissues. Recovery of given radioactivity in urine (30.3% of dose), feces (0.4% of dose), cage wash (7.9% of dose), and tissues and carcass (6.1% of dose) after 24 hours implied that up to 55% of radioactivity was expired as (14)CO(2). Comparison of zebularine and uridine pharmacokinetic data indicated that approximately 40% of the zebularine dose was converted to uridine. CONCLUSIONS: Zebularine is extensively and rapidly metabolized into endogenous compounds that are unlikely to have effects at the concentrations observed.

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.

High performance liquid chromatographic analysis and preclinical pharmacokinetics of the heteroarotinoid antitumor agent, SHetA2.

BACKGROUND: SHetA2 {[(4-nitrophenyl)amino][2,2,4,4-tetramethylthiochroman-6-yl)amino]methane-thione], NSC 726189} is a sulfur-containing heteroarotinoid, which selectively inhibits cancer cell growth and induces apoptosis without activation of nuclear retinoic acid receptors (RARs). The objective was to develop and validate a HPLC/UV method for the determination of SHetA2, and study the pharmacokinetics of SHetA2 in the mouse. METHODS: SHetA2 and the internal standard, methylated XK469 (MeXK469) were isolated from 0.2 ml of mouse plasma by solid phase extraction. The analytes were separated on a narrow-bore C18 column, with the mobile phase consisting of 60% acetonitrile in water at a flow rate of 0.2 ml/min. UV detection was set at 341 nm. Pharmacokinetic studies of SHetA2 were carried out in mice following i.v. bolus dose at 20 mg/kg and oral administrations at 20 and 60 mg/kg. RESULTS: The standard curves were linear between 25 and 2,500 nM and the lower limit of quantification (LLOQ) was 25 nM. The within-run coefficients of variation (CVs) were 11.1% at 10, 9.4% at 100, and 5.2% at 2,500 nM and the respective between-run CVs were 10.9, 3.1, and 1.5% (all n=5). The recovery was 85.8% for SHetA2 and 80.6% for MeXK469. Following i.v. bolus dose, plasma concentrations of approximately 10 microM were achieved at 5 min in mice and declined biexponentially with detectable levels at 60 h. The data were fitted with a two-compartment model, which gave a mean initial t1/2 of 40 min and terminal t1/2 of 11.4 h (n=6). The total body clearance was approximately 1.81 l/h/kg. The volume of distribution at steady state (Vdss) was 20.8 l/kg. Plasma protein binding was found to be 99.3-99.5% at low micromolar concentrations. Plasma concentration data for the i.v. and p.o. doses were also fitted interactively to a two-compartment deconvolution model. From this result, oral bioavailability values of 15% at 20 mg/kg and 19% at 60 mg/kg were obtained. CONCLUSIONS: A highly sensitive HPLC/UV method for the quantification of SHetA2 in plasma has been developed to support pharmacokinetics of SHetA2 in the mouse. Pharmacokinetic behaviors of this drug appear to be favorable for future development.

Preclinical pharmacology of the novel antitumor agent adaphostin, a tyrphostin analog that inhibits bcr/abl.

PURPOSE: To define several pharmacological properties for the potential anticancer agent, adaphostin, in order to determine whether the compound is appropriate for clinical evaluation as an anticancer agent. METHODS: The analytical procedure involved high-performance liquid chromatography and utilized an analytical J'Sphere ODS H-80 column. RESULTS: The stability of adaphostin at two different concentrations was determined at temperatures of 37 degrees C, 4 degrees C, and -80 degrees C, in the plasma of mice, rats, dogs, and humans. The compound was most stable at the lower temperatures. At all temperatures, adaphostin was generally most stable in human plasma and least stable in dog plasma. Adaphostin bound strongly (>93%) to proteins in plasma from all four species. Following intravenous (i.v.) administration to mice (50 mg/kg; 150 mg/m(2)), plasma concentrations declined rapidly from 50 microM at 2 min to 1 microM at 2 h. Elimination was triexponential, with t (1/2) values of 1.1, 9.1, and 41.2 min. The Cl(tb) was 0.411 L/(min.m(2)), the V (dss) was 24.6 L/m(2), and the AUC was 927 microM.min. In a comparison of vehicles for intraperitoneal (i.p.) dosing, PEG 300 allowed the highest plasma concentrations of adaphostin. Bioavailability following an i.p. dose was greater than that following a subcutaneous dose, or that for a dose administered by oral gavage. For rats dosed i.v. with adaphostin (50 mg/kg; 300 mg/m(2)), plasma concentrations also decreased triexponentially, with t (1/2) values of 1.8, 10.6, and 136 min. Other pharmacokinetic values were Cl(tb) = 0.466 L/(min.m(2)), AUC = 1,161 microM.min, and V (dss)=8.0 L/m(2). Analysis of samples collected from two dogs dosed i.v. with adaphostin (7.5 mg/kg; 150 mg/m(2)) showed that plasma concentrations decreased in a biphasic manner, with individual values for t (1/2alpha) of 6.0 and 9.8 min for the distribution phase and t (1/2beta) of 40.6 and 66.2 min for the elimination phase. Other pharmacokinetic values were Cl(tb) = 0.565 and 0.852 L/(min.m(2)), AUC = 673 and 446 microM min, and V (dss) = 29.6 and 56.8 L/m(2). CONCLUSIONS: The stability of adaphostin in plasma varies with species. In mice and dogs dosed with adaphostin, plasma concentrations of the compound decreased rapidly. The clearance of adaphostin from plasma, on an m(2) basis, was equivalent for mice and rats but more rapid in dogs. These results are relevant for assessing the pharmacologic and toxicologic profiles and the antitumor activity of adaphostin in humans.

Quantitative determination of zebularine (NSC 309132), a DNA methyltransferase inhibitor, and three metabolites in murine plasma by high-performance liquid chromatography coupled with on-line radioactivity detection.

The metabolism of zebularine (NSC 309132), a novel agent that inhibits DNA methyltransferases, is still uncharacterized. To examine the in vivo metabolism of zebularine, an analytical method was developed and validated (based on FDA guidelines) to quantitate 2-[(14)C]-zebularine and its major metabolites in murine plasma. Zebularine and its metabolites uridine, uracil and dihydrouracil were baseline-separated based on hydrophilic interaction chromatography by using an amino column. The assay was accurate and precise in the concentration ranges of 5.0-100 microg/mL for zebularine, 2.5-50 microg/mL for uridine, 1.0-10 microg/mL for uracil and 0.5-5.0 microg/mL for dihydrouracil. This assay is being used to quantitate zebularine and its metabolites in ongoing pharmacokinetic studies of zebularine.