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 (PK/PD) 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. PK/PD data suggests 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) 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.

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.

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.

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 pY^1234/1235MET/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 pY^1234/1235MET/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.

Comparative Metabolism of Batracylin (NSC 320846) and N-acetylbatracylin (NSC 611001) Using Human, Dog, and Rat Preparations In Vitro

BACKGROUND

Batracylin is a heterocyclic arylamine topoisomerase inhibitor with preclinical anticancer activity. Marked species differences in sensitivity to the toxicity of batracylin were observed and attributed to differential formation of N-acetylbatracylin by N-acetyltransferase. A Phase I trial of batracylin in cancer patients with slow acetylator genotypes identified a dose-limiting toxicity of hemorrhagic cystitis. To further explore the metabolism of batracylin and N-acetylbatracylin across species, detailed studies using human, rat, and dog liver microsomal and hepatocyte preparations were conducted.

METHODS

Batracylin or N-acetylbatracylin was incubated with microsomes and hepatocytes from human, rat, and dog liver and with CYP-expressing human and rat microsomes. Substrates and metabolites were analyzed by HPLC with diode array, fluorescence, radiochemical, or mass spectrometric detection. Covalent binding of radiolabeled batracylin and N-acetylbatracylin to protein and DNA was measured in 3-methylcholanthrene-induced rat, human, and dog liver microsomes, and with recombinant human cytochromes P450.

RESULTS

In microsomal preparations, loss of batracylin was accompanied by formation of one hydroxylated metabolite in human liver microsomes and five hydroxylated metabolites in rat liver microsomes. Six mono- or di-hydroxy-N-acetylbatracylin metabolites were found in incubations of this compound with 3MC rat liver microsomes. Hydroxylation sites were identified for some of the metabolites using deuterated substrates. Incubation with recombinant cytochromes P450 identified rCYP1A1, rCYP1A2, hCYP1A1 and hCYP1B1 as the major CYP isoforms that metabolize batracylin and N-acetylbatracylin. Glucuronide conjugates of batracylin were also identified in hepatocyte incubations. NADPH-dependent covalent binding to protein and DNA was detected in all batracylin and most N-acetylbatracylin preparations evaluated.

CONCLUSIONS

Microsomal metabolism of batracylin and N-acetylbatracylin results in multiple hydroxylated products (including possible hydroxylamines) and glutathione conjugates. Incubation of batracylin with hepatocytes resulted in production primarily of glucuronides and other conjugates. There was no clear distinction in the metabolism of batracylin and N-acetylbatracylin across species that would explain the differential toxicity.

Clinical and pharmacologic evaluation of two dosing schedules of indotecan (LMP400), a novel indenoisoquinoline, in patients with advanced solid tumors

PURPOSE

Indenoisoquinolines are non-camptothecin topoisomerase I (TopI) inhibitors that overcome the limitations of camptothecins: chemical instability and camptothecin resistance. Two dosing schedules of the novel indenoisoquinoline, indotecan (LMP400), were evaluated in patients with advanced solid tumors.

METHODS

The maximum tolerated dose (MTD), toxicities, and pharmacokinetics of two indotecan drug administration schedules (daily for 5 days or weekly) were investigated. Modulation of TopI and the phosphorylation of histone H2AX (γH2AX) were assayed in tumor biopsies; γH2AX levels were also evaluated in circulating tumor cells (CTCs) and hair follicles to assess DNA damage response.

RESULTS

An MTD of 60 mg/m(2)/day was established for the daily regimen, compared to 90 mg/m(2) for the weekly regimen. The TopI response to drug showed target engagement in a subset of tumor biopsies. Pharmacokinetics profiles demonstrated a prolonged terminal half-life and tissue accumulation compared to topotecan. Dose-dependent decreases in total CTCs were measured in seven patients. Formation of γH2AX-positive foci in CTCs (day 3) and hair follicles (4-6 h) was observed following treatment.

CONCLUSIONS

We established the MTD of two dosing schedules for a novel TopI inhibitor, indotecan. Target engagement was demonstrated as Top1 downregulation and γH2AX response. No objective responses were observed on either schedule in this small patient cohort. The principal toxicity of both schedules was myelosuppression; no significant gastrointestinal problems were observed. Increased DNA damage response was observed in CTCs, hair follicles, and a subset of tumor biopsies.

Preclinical Pharmacokinetics Study of R- and S-Enantiomers of the Histone Deacetylase Inhibitor, AR-42 (NSC 731438), in Rodents

AR-42, a new orally bioavailable, potent, hydroxamate-tethered phenylbutyrate class I/IIB histone deacetylase inhibitor currently is under evaluation in phase 1 and 2 clinical trials and has demonstrated activity in both hematologic and solid tumor malignancies. This report focuses on the preclinical characterization of the pharmacokinetics of AR-42 in mice and rats. A high-performance liquid chromatography-tandem mass spectrometry assay has been developed and applied to the pharmacokinetic study of the more active stereoisomer, S-AR-42, when administered via intravenous and oral routes in rodents, including plasma, bone marrow, and spleen pharmacokinetics (PK) in CD2F1 mice and plasma PK in F344 rats. Oral bioavailability was estimated to be 26 and 100% in mice and rats, respectively. R-AR-42 was also evaluated intravenously in rats and was shown to display different pharmacokinetics with a much shorter terminal half-life compared to that of S-AR-42. Renal clearance was a minor elimination pathway for parental S-AR-42. Oral administration of S-AR-42 to tumor-bearing mice demonstrated high uptake and exposure of the parent drug in the lymphoid tissues, spleen, and bone marrow. This is the first report of the pharmacokinetics of this novel agent, which is now in early phase clinical trials.

Oral and intravenous pharmacokinetics of 5-fluoro-2'-deoxycytidine and THU in cynomolgus monkeys and humans

INTRODUCTION

5-Fluoro-2'-deoxycytidine (FdCyd; NSC48006), a fluoropyrimidine nucleoside inhibitor of DNA methylation, is degraded by cytidine deaminase (CD). Pharmacokinetic evaluation was carried out in cynomolgus monkeys in support of an ongoing phase I study of the PO combination of FdCyd and the CD inhibitor tetrahydrouridine (THU; NSC112907).

METHODS

Animals were dosed intravenously (IV) or per os (PO). Plasma samples were analyzed by LC-MS/MS for FdCyd, metabolites, and THU. Clinical chemistry and hematology were performed at various times after dosing. A pilot pharmacokinetic study was performed in humans to assess FdCyd bioavailability.

RESULTS

After IV FdCyd and THU administration, FdCyd C(max) and AUC increased with dose. FdCyd half-life ranged between 22 and 56 min, and clearance was approximately 15 mL/min/kg. FdCyd PO bioavailability after THU ranged between 9 and 25 % and increased with increasing THU dose. PO bioavailability of THU was less than 5 %, but did result in plasma concentrations associated with inhibition of its target CD. Human pilot studies showed comparable bioavailability for FdCyd (10 %) and THU (4.1 %).

CONCLUSION

Administration of THU with FdCyd increased the exposure to FdCyd and improved PO FdCyd bioavailability from <1 to 24 %. Concentrations of THU and FdCyd achieved after PO administration are associated with CD inhibition and hypomethylation, respectively. The schedule currently studied in phase I studies of PO FdCyd and THU is daily times three at the beginning of the first and second weeks of a 28-day cycle.

Abstract 4517: Plasma and tumor pharmacokinetics of IV LMP744, a novel indenoisoquinoline topoisomerase I inhibitor, in a canine phase I study

Introduction: LMP744 (NSC706744) is one of 3 indenoisoquinolines being evaluated in pet dogs with lymphoma to define their safety, pharmacokinetics, and pharmacodynamic modulation (COTC007b). LMP744 forms stable DNA-topoisomerase I (Top1) cleavage complexes and induces unique DNA cleavage sites relative to approved Top1 poisons; LMP744 is not a substrate for ABC transporters and does not have the stability issues inherent to camptothecins. Here we report the plasma and tumor pharmacokinetics of LMP744 administered IV daily x 5 to patient dogs.

Methods: Eligibility included: dogs &gt;15 kg with histologically confirmed non-Hodgkin's lymphoma with nodal presentation (stage 2 or greater) and minimal nodes size for biopsy of 3 cm in the longest dimension, performance status of Grade 0 or 1 and informed owner consent. Dose levels (DL) explored were 25, 50, 75, 100, and 125 mg/m2/day through a 3+3 dose escalation study design. LMP744 was administered over 1 h IV daily x 5, Q28D. LMP744 was quantitated with a validated LC-MS/MS assay, and plasma pharmacokinetic parameters determined non-compartmentally with PK Solutions and plasma and tumor parameters compartmentally with ADAPT5 through iterated two stage (ITS) and maximum likelihood solution with the expectation maximization algorithm (MLEM).

Results: All 18 dogs had useable pharmacokinetic data. Non-compartmental analysis suggested linear relationships between plasma Cmax and tumor C2h vs. dose. LMP744 distributed extensively to tumor tissue and mean tumor concentrations were at least 2 orders of magnitude higher than plasma concentrations at equivalent time points of 2, 6 and 120 h. Compartmental modeling with a 3 compartment linear model resulted in a good fit to the plasma data. The parameters and%CVs respectively for Clt, Vc, Cld1, Vp1, Cld2, Vp2 were 57.5 L/h/m2 (29%), 136 L/m2 (24%), 234 L/h/m2 (24%), 1180 L/m2 (27%), 30.8 L/h/m2 (63%), 5140 L/m2 (67%). Sequential plasma half-lives were 16.5 min, 13 h, and 183 (31%) h, respectively. In line with the long t1/2, plasma accumulation was observed on this daily times-5 schedule.

Conclusion: The plasma pharmacokinetics of LMP744 in dogs display triphasic behavior, a relatively high total body clearance at 57.5 L/h/m2, and a terminal half-life of 183 h. The favorable biodistribution to tumor may be a valuable distinction to consider in the translation of this novel indenoisoquinoline to the clinic.

Support: N01-CM-2011-00015, N01-CM-42202 and P30-CA-47904

Note: This abstract was not presented at the meeting.

Citation Format: Julie L. Eiseman, Julianne Holleran, David L. McCormick, Miguel Muzzio, Joseph M. Covey, Chand Khanna, Christina Mazcko, Yves Pommier, Melissa Paolini, Amy Leblanc, Jenna H. Burton, James H. Doroshow, Joseph E. Tomaszewski, Jan H. Beumer. Plasma and tumor pharmacokinetics of IV LMP744, a novel indenoisoquinoline topoisomerase I inhibitor, in a canine phase I study. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4517. doi:10.1158/1538-7445.AM2015-4517

Abstract 3691: Met target inhibition-guided efficacy in preclinical models

Background: A direct comparison of drug efficacy for the multiple agents currently in clinical development targeting MET-driven cancers would be useful for the selection of optimal treatment options. Previously, we utilized validated MET pharmacodynamic (PD) assays to compare the time course of phosphorylated-MET (pMET) suppression for five MET inhibitors (ASCO 2013). In the current study, we selected three candidates that demonstrated potent MET inhibition to compare anti-tumor efficacy.

Methods: PD time course and tumor PK data were utilized to simulate a dosing schedule anticipated to produce &gt;90% pMET suppression in a SNU5 gastric cancer xenograft model. From these data, dosing schedules of 44 mg/kg (Q12H) cabozantinib, 12.5 mg/kg (Q12H) EMD1214063, and 16.5 mg/kg (QD) foretinib were chosen to achieve necessary tumor exposure to suppress pMET. Once tumors reached a 150±50 mm3 size, drugs were administered continuously for 21 days and tumor volumes were measured intermittently for 62 days. To measure pMET suppression, tumor quadrants were collected at 4, 12, and 24 hrs from all treatment groups after dose 1 (day 1) and on day 8 (after dose 8 of foretinib or dose 14 of cabozantinib and EMD1214063).

Results: Intact MET levels (pM/μg protein) were approximately 70% lower than vehicle controls at all day 8 collection points for all three drugs. The pY1234/35MET/MET ratios were 89%-99% (p&lt;0.001) lower than vehicle controls on day 8 at 4 and 12 hrs post-dose for all three drugs. Compared to pretreatment levels, tumor volumes were reduced by 80-90% for all three drugs within 10-15 days post therapy and remained regressed until 13-20 days after treatment was stopped. Tumors then slowly regrew, but remained approximately 80% smaller than the vehicle group on day 62 (end of study).

Conclusions: These studies demonstrate that PD response-guided regimens delivered drug doses that were lower than efficacious doses described previously (except cabozantinib), but effectively reduced tumor volume in SNU5 xenografts. The three MET inhibitors showed comparable anti-tumor efficacy when accompanied by equivalent pMET inhibition. Our data also affirms the utility of the MET PD assays to guide dose ranging studies. Funded by NCI Contract No HHSN261200800001E.

Citation Format: Apurva K. Srivastava, Melinda G. Hollingshead, Jeevan P. Govindharajulu, Joseph M. Covey, Dane Liston, James Peggins, Donald P. Bottaro, John J. Wright, Robert J. Kinders, Joseph E. Tomaszewski, James H. Doroshow, Ralph E. Parchment. Met target inhibition-guided efficacy in preclinical models. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3691. doi:10.1158/1538-7445.AM2014-3691

Abstract 4689: Pre-clinical investigation of the wee1 inhibitor MK-1775 using pharmacodynamic and mechanistic markers in diverse cancer models in vivo

Wee1 kinase is a critical regulator of the G2/M checkpoint by initiating inhibitory phosphorylation of the conserved tyrosine-15 residue of cdk1/cdc2. Wee1 also phosphorylates tyrosine 15 of cdk2 and plays a crucial role in maintaining genome integrity during S-phase. MK1775 (NSC 754352) is a small molecule selective inhibitor of Wee1 kinase that is currently under clinical evaluation. We have developed a quantitative immunofluorescence assay to measure inhibition of Wee1 by detection of pY15 of cyclin-dependent kinases. A full analysis of the pharmacodynamic (PD) effects of Wee1 inhibition by MK1775, as well as the downstream mechanistic consequences of Wee1 inhibition on DNA repair, apoptosis, and premature mitotic entry markers was performed using two xenograft models: A673 Ewing sarcoma and U87-MG glioblastoma. Four DNA repair markers (pNbs1, γH2AX, Rad51, and pATR) were examined as well as the mitotic marker pHistone H3. Advanced quantitative image analysis was performed using Definiens software to measure changes in PD markers by two approaches: total nuclear area measurements and foci per nucleus. Definiens software enables enhanced analysis of the markers by enumeration of the nuclei in the imaged xenograft tissues over an entire data set with high-content capacity. Our data demonstrate greater than 80% inhibition of pY15-cdk in vivo at the clinically relevant dose of 60 mg/kg (180 mg/m2) MK1775 in two xenograft models. In addition, γH2AX induction was observed after multiple doses of MK1775 as a single agent. A PD biomarker time course was determined for MK1775 and gemcitabine (NSC 750927) as single agents to develop a drug administration schedule for combination studies in a Ewing sarcoma model. The time point at which the DNA damage response peaked following administration of the maximum tolerated dose of gemcitabine in the mouse was determined. This study elucidates a broad profile of PD marker response, as well as the corresponding levels of MK1775 in the xenografts. Funded by NCI Contract No. HHSN261200800001E.

Citation Format: Deborah F. Wilsker, Allison M. Marrero, Melinda Hollingshead, Scott M. Lawrence, Alice Chen, Shivaani Kummar, Joseph M. Covey, Ralph E. Parchment, Robert J. Kinders, Joseph E. Tomaszewski, James H. Doroshow. Pre-clinical investigation of the wee1 inhibitor MK-1775 using pharmacodynamic and mechanistic markers in diverse cancer models in vivo. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4689. doi:10.1158/1538-7445.AM2014-4689

Abstract 4632: Plasma and tumor pharmacokinetics of IV LMP400, a novel indenoisoquinoline topoisomerase I inhibitor, in a canine phase I study

Introduction: LMP400 is one of 3 indenoisoquinolines that are being evaluated in pet dogs with lymphoma to define their safety, pharmacokinetics, and pharmacodynamic modulation (COTC007b). LMP400 forms stable DNA-topoisomerase I (Top1) cleavable complexes and induces unique DNA cleavage sites relative to approved Top1 poisons; LMP400 is not a substrate for ABC transporters and does not have the stability issues that most camptothecin analogs do. Here we report the plasma and uncoupled tumor pharmacokinetics of LMP400 administered IV daily x 5 to patient dogs.

Methods: Eligibility included: dogs &gt;15 kg with histologically confirmed non-Hodgkin's lymphoma with nodal presentation (stage 2 or greater) and minimal nodes size for biopsy of 3 cm in the longest dimension, performance status of Grade 0 or 1 and informed owner consent. Dose levels (DL) explored were 8, 16, 24, and 40 mg/m2/day through a 3+3 dose escalation study design. LMP400 was administered over 1 h IV daily x 5, Q28D. LMP400 was quantitated with a validated LC-MS/MS assay (PMID: 20236781), and plasma pharmacokinetic parameters determined non-compartmentally with PK Solutions and plasma and tumor parameters compartmentally with ADAPT5 through iterated two stage (ITS) and maximum likelihood solution with the expectation maximization algorithm (MLEM).

Results: All fifteen dogs had useable pharmacokinetic data. Non-compartmental analysis suggested linear relationships between plasma Cmax and AUC vs. dose and tumor C2h vs. dose. Plasma terminal half-life was 11.9 ± 5.0 h and the CL was 26.7 L/h/m2. In line with the t1/2, slight plasma accumulation was observed on this daily times 5 schedule. Compartmental modeling with a 2 compartment linear model resulted in a good fit to the data. The parameters and %CVs respectively for Ke, Vc, Kcp, Kpc, Kct and Ktc were 0.181 h-1 (42.6%), 108 L/m2 (32.7%), 0.250 h-1 (30.1%), 0.0602 h-1 (67%), 0.0632 h-1 (3.65%), and 0.649 h-1 (42.2%). Plasma compartmental CL and half-life were 19.5 L/h/m2 and 29.7 h.

Conclusion: The plasma pharmacokinetics of LMP400 in dogs display biphasic behavior, a relatively high total body clearance at 19.5 L/h/m2, and a terminal half-life of 29.7 h. LMP400 distributed to the tumors and mean tumor concentrations were at least 10-fold higher than plasma concentrations at equivalent time points of 2, 6 and 120 h. This favorable biodistribution to tumor (lymph node) may be a valuable distinction to consider in the translation of this novel indenoisoquinoline to the clinic.

Support: N01-CM-2011-00015, N01-CM-42202 and P30-CA-47904

Citation Format: Julie L. Eiseman, Julianne Holleran, David L. McCormick, Miguel Muzzio, Joseph M. Covey, Chand Khanna, Christina Mazcko, Yves Pommier, Melissa Paoloni, James D. Doroshow, Joseph E. Tomaszewski, Jan H. Beumer. Plasma and tumor pharmacokinetics of IV LMP400, a novel indenoisoquinoline topoisomerase I inhibitor, in a canine phase I study. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4632. doi:10.1158/1538-7445.AM2014-4632

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 β-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.

Application of MET pharmacodynamic assays to compare effectiveness of five MET inhibitors to engage target in tumor tissue

11103

Background: Several MET inhibitors are currently being developed that block aberrant HGF/MET signaling in different cancers. We utilized validated MET pharmacodynamic (PD) assays to compare time course, magnitude, and reversal of MET suppression by 5 MET inhibitors in preclinical models. Methods: Immunoassays (total MET, pY1234/35MET, and pY1356MET) were developed and validated to measure modulation of MET by 5 MET inhibitors (crizotinib, tivantinib, cabozantinib, foretinib, and EMD1214063). The comparison was implemented in 3 sequential stages: 1) establish time course and magnitude of MET inhibition after single drug administration of 4 different doses; 2) determine dose(s) and schedule for sustained MET inhibition and downstream signaling at optimal levels; and 3) compare efficacy of MET inhibitors at MTD and equal MET inhibition. The preclinical models include an autophosphorylation gastric tumor (SNU5) model and a paracrine MET activation model in hHGF knock-in mice. Plasma and tumor exposures were measured using LC-MS/MS to correlate with PD effects. Results: We completed phase one in the SNU5 model and determined inhibition of pY1234/35MET and total MET in tumor tissues after single administration of MET inhibitors. Time course and magnitude of pY1234/35MET inhibition varied considerably among MET inhibitors, with the most rapid (>80% suppression in 30 min) and sustained inhibition (up to 48 h) observed with EMD1214063 at a dose of 30 mg/kg. The maximal inhibition of pY1234/35MET and time taken for biomarker recovery were wide-ranging among MET inhibitors. Tumor drug exposures were concomitantly higher than plasma for all drugs and correlated inversely with pY1234/35MET, except for tivantinib which, unlike other drugs, is not ATP competitive inhibitor. Conclusions: We applied validated PD assays to directly compare similarities and differences in extent and duration of MET inhibition by 5 MET inhibitors. Our results provide important foundation for head-to-head comparison of efficacies of MET inhibitors at MTD and equal MET inhibition. Funded by NCI Contract No HHSN261200800001E.

Abstract 2462: Pharmacokinetics and in vivo metabolism of the naphthofuran NSC373981 in male nu/nu mice

NSC 373981 is 1-ethanol, 2-nitro-naphtho[2,1-b]furan that has demonstrated activity in the NCI60 anticancer screen and in the mouse hollow-fiber assay. Growth inhibitory activity was also observed in several xenograft models. There is some evidence that antitumor activity is greater in vivo than would be predicted by the in vitro results, suggesting the possibility of activating metabolism. While the mechanism of anticancer activity is unknown, naphthofurans have been reported to modulate certain nuclear receptors. The purpose of this study was to characterize the plasma pharmacokinetics of NSC 373981 following i.v. and i.p. administration to athymic nude mice and to characterize potential metabolites of this compound in plasma, urine, and bile. We developed and validated suitable positive ionization LC/MS/MS methodology for measuring NSC 373981 that utilized liquid extraction with 1-chlorobutane and MS/MS detection with the 258&gt;212 and 244&gt;169 transitions, respectively, for NSC 373981 and NSC 329226, an analog that was used as the internal standard. Baseline separations were achieved on a Polaris C18 column under a mobile phase consisting of 70:30 methanol:water containing 0.1% formic acid. Standard curves were linear over the concentration range 2.5-1000 ng/mL with a lower limit of detection of 2.5 ng/mL. NSC 373981 was stable under acidic, neutral and basic conditions, as well as human and mouse plasma during 24-hr incubation at 37°C. NSC 373981 pharmacokinetics were characterized in male nu/nu mice after a 37.5 mg/kg i.v. dose or a 150 mg/kg i.p. dose. Plasma, bile, urine and feces were collected for 24-hr after drug administration. Following i.v. administration, the peak concentration was &gt; 5.9 μg/mL and the terminal elimination half-life was 1.2 hours. Volume of distribution and plasma clearance values were 694 ml and 390 mL/hr, respectively. Following i.p. administration, NSC373981 reached a peak concentration of 2.1 μg/mL at 15 minutes and the terminal elimination half-life was 36.8 hours. The i.p. bioavailability of NSC373981 was 58%. In vivo metabolite profiles were characterized in plasma, urine, feces, and bile. We detected several Phase I metabolites in these samples including those produced by reduction of the aromatic nitro group, oxidation of the primary alcohol moiety on the reduced metabolite, oxidation of the primary alcohol moiety, benzylic hydroxylation, hydroxylation and dihydrodiol formation on the naphthalene moiety, and Phase II metabolites including glucuronidation of the carboxylic acids and a glutathione metabolite of hydroxylated NSC 373981. Supported by NCI contract N01-CM-2011-00014.

Citation Format: Joel M. Reid, Sarah A. Buhrow, Renee M. McGovern, Joseph M. Covey, Matthew M. Ames. Pharmacokinetics and in vivo metabolism of the naphthofuran NSC373981 in male nu/nu mice. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2462. doi:10.1158/1538-7445.AM2013-2462

LC-MS/MS quantification of a neuropeptide fragment kisspeptin-10 (NSC 741805) and characterization of its decomposition product and pharmacokinetics in rats

The kisspeptins are critical regulators of mammalian reproduction. Kisspeptin-10 ((45)YNWNSFGLRF-NH2(54), kisspeptin-112-121 or metastin 45-54, NSC 741805), an active fragment of kisspeptin, has been shown to be a potent stimulator of gonadotropin-releasing hormone and secretion of luteinizing hormone in both rodents and primates. This shorter peptide fragment may have clinical utility potential and it is important to characterize its pharmacokinetic property. Recently, the pharmacokinetics of both kisspeptin-54 and kisspeptin-10 were characterized in humans using a radioimmunoassay (RIA), which measures only the immunoreactive kisspeptin (kisspeptin-IR). In this study, a highly sensitive and specific LC-MS/MS assay was developed to quantify kisspeptin-10 levels in rat plasma. The lower limit of quantitation (LLOQ) was 0.5 ng/mL, the within-day and between-day coefficient of variations (CVs) ranged from 5.2 to 15.4% and 1.3 to 14.2%, and the accuracy values ranged from 98 to 114% and 99 to 105%, respectively. With this method, stability studies demonstrated that kisspeptin-10 degraded rapidly with decomposition half-lives of 6.8 min, 2.9 min and 1.7 min at 4 °C, 25 °C, and 37 °C, respectively. The principal decomposition product was characterized as the N-terminal tyrosine deleted kisspeptin-10 (46)NWDSFGLRF-NH2(54). Pharmacokinetic study in rats showed that low ng/mL kisspeptin-10 was detected in the first few minutes, and eliminated rapidly and became undetectable 30 min after intravenous (i.v.) bolus administration of 1.0 mg/kg kisspeptin-10.

Abstract 3782: Plasma pharmacokinetics of fluorodeoxycytidine, downstream metabolites, and tetrahydrouridine after combined administration to cynomolgus monkeys

Introduction: 5-Fluoro-2′-deoxycytidine (FdCyd; NSC48006) is a fluoropyrimidine nucleoside inhibitor of DNA methylation that is degraded by cytidine deaminase (CD) and has better aqueous stability than decitabine or azacytidine. A toxicokinetic study was carried out to support a phase I study of the PO combination of FdCyd and the CD inhibitor tetrahydrouridine (THU; NSC112907). We examined the pharmacokinetics of THU, FdCyd, and its downstream metabolites in cynomolgus monkeys. Methods: Monkeys were treated and plasma samples, collected between 15 min and 24 h after FdCyd administration, were analyzed. For IV administration, 20% of the THU dose was administered as a bolus followed by FdCyd (4, 8 or 16 mg/kg to two monkeys each) concomitantly with 80% of the THU dose of 30 mg/kg as a 3 h infusion. For PO administration, FdCyd was administered at 10 mg/kg as a single agent and at 10, 15 or 20 mg/kg 1 h after administration of 150 mg/kg THU or at 0.1, 1.0 or 10 mg/kg 1h after a dose of 500 mg/kg THU (2 monkeys/sex/group). The concentrations of FdCyd, and its downstream metabolites, fluorodeoxyuridine (FdUrd) and fluorouracil (FU), and THU were quantitated by validated LC-MS/MS assays. Data were modeled non-compartmentally using PK Solutions. Results: When FdCyd and THU were administered IV, FdCyd Cmax and AUC increased with dose, while the latter appeared more than dose-proportional. The half-life of FdCyd ranged between 22 and 56 min and the AUC0-inf increased from 0.28 to 2.99 mg·min/L after doses of 4 to 16 mg/kg. FdUrd/FdCyd Cmax and AUC0-infratios were less than 13% suggesting inhibition of CD at 30 mg/kg IV THU. In monkeys receiving 0.1 or 10 mg/kg FdCyd alone PO, no FdCyd nor any downstream metabolites were detectable. When FdCyd was administered 1 h after 150 or 500 mg/kg THU, PO FdCyd concentrations increased with doses of FdCyd. FdCyd PO bioavailability after THU appeared to range between 12 and 30% and did not clearly increase with increasing THU dose. FdUrd/FdCyd Cmax and AUC0-inf ratios after PO administration were higher than after IV administration and much more variable between monkeys. THU Cmax and AUC0-inf were proportional with THU dose and were not affected by FdCyd dose. PO bioavailability of THU was approximately 3.5%, but did result in plasma concentrations associated with inhibition of its target cytidine deaminase. Conclusion: Administration of THU with FdCyd increased the exposure to FdCyd and improved PO FdCyd bioavailability from &lt;1% to &gt;12%. Concentrations of THU and FdCyd achieved after PO administration are associated with inhibition of CD and hypomethylation, respectively. The phase I study of PO FdCyd and THU is under development. Support: N01-CM-52202, N01-CM-42202, U01-CA099168, P30-CA47904

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3782. doi:1538-7445.AM2012-3782

Characterization of silvestrol pharmacokinetics in mice using liquid chromatography-tandem mass spectrometry

A sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for the quantification of the plant natural product silvestrol in mice, using ansamitocin P-3 as the internal standard. The method was validated in plasma with a lower limit of quantification of 1 ng/mL, accuracy ranging from 87 to 114%, and precision (coefficient of variation) below 15%. The validated method was used to characterize pharmacokinetics in C57BL/6 mice and metabolism in mouse, human and rat plasma, and liver microsomes. Mice were dosed with silvestrol formulated in hydroxypropyl-β-cyclodextrin via intravenous, intraperitoneal, and oral routes followed by blood sampling up to 24 h. Intraperitoneal systemic availability was 100%, but oral administration resulted in only 1.7% bioavailability. Gradual degradation of silvestrol was observed in mouse and human plasma, with approximately 60% of the parent drug remaining after 6 h. In rat plasma, however, silvestrol was completely converted to silvestric acid (SA) within 10 min. Evaluation in microsomes provided further evidence that the main metabolite formed was SA, which subsequently showed no cytotoxic or cytostatic activity in a silvestrol-sensitive lymphoblastic cell line. The ability of the analytical assay to measure tissue levels of silvestrol was evaluated in liver, brain, kidney, and spleen. Results indicated the method was capable of accurately measuring tissue levels of silvestrol and suggested it has a relatively low distribution to brain. Together, these data suggest an overall favorable pharmacokinetic profile of silvestrol in mice and provide crucial information for its continued development toward potential clinical testing.

Abstract 1303: Characterization of the metabolite profile for batracylin and N-acetylbatracylin in rat and human models of invitro and in vivo metabolism: Elucidation of pathways that might contribute to batracylin toxicity

Batracylin (NSC 320846, BAT) is a heterocyclic arylamine and topoisomerase II inhibitor that was shown to be active in several murine tumor models. Pharmacology and toxicology studies demonstrated marked species differences in sensitivity to the toxic effects of BAT attributed to metabolism to N-acetylbatracylin (NacBAT) by N-acetyltransferase (NAT). It was subsequently shown that BAT is a preferential substrate for human NAT2; thus production of NacBAT is likely subject to population variability as a function of known NAT2 polymorphisms. A phase I clinical trial of BAT in patients with advanced cancer and slow acetylator NAT2 genotypes to reduce the risk of toxicity due to NacBAT is ongoing and a potentially dose-limiting toxicity of cystitis/hemorrhagic cystitis was observed in several patients. In order to determine if this toxicity is due to BAT, NacBAT, and/or other metabolites, we investigated the in vitro metabolism of BAT and NacBAT in human (h) and rat (r) liver microsomes (LM) and hepatocytes, and the in vivo metabolism of BAT and NacBAT in rats. 14C-BAT and differentially deuterated (d3- and d4-) BAT were provided to facilitate metabolic profiling. d3- and d4- NacBAT were generated in situ. BAT, NacBAT and their metabolites were detected and quantified by HPLC with diode array, fluorescence, radiochemical and mass spectrometry as appropriate. The goals of these investigations were to obtain a detailed metabolic profile for BAT in rats and humans and to elucidate pathways that might contribute to BAT toxicity. In NADPH-fortified microsomal preparations, loss of BAT was accompanied by formation of one hydroxylated metabolite in hLM and three hydroxylated metabolites in rLM. The single hydroxylated metabolite found in incubations of NacBAT with hLM was attributed to deacetylation by microsomal carboxlesterase. Six mono- and di- hydroxy NacBAT metabolites were found in incubations of NacBAT with rLM. Hydroxylation sites were identified with deuterated BAT and NacBAT. Incubation with recombinant cytochomes P450 (CYPs) identified rCYP1A1, rCYP1A2, hCYP1A1 and hCYP1B1 as the major CYP isoforms that metabolize BAT and NacBAT. Glucuronide conjugates of BAT and NacBAT were identified in rat and human hepatocyte incubations. NacBAT, hydroxylated BAT and NacBAT, and glucuronide conjugates were detected in in vivo metabolism and pharmacokinetic studies with BAT and NacBAT in rats. Finally, thiol-containing adducts, consistent with metabolic activation of BAT, were identified in kidney and urine samples from in vivo metabolism and pharmacokinetic studies with rats. In conclusion, we characterized the in vitro and in vivo metabolism of BAT and identified a pathway for metabolic activation of BAT to potential toxic metabolites. Supported by NCI Contract N01-CM-52206.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1303. doi:10.1158/1538-7445.AM2011-1303

Plasma pharmacokinetics and oral bioavailability of the 3,4,5,6-tetrahydrouridine (THU) prodrug, triacetyl-THU (taTHU), in mice

PURPOSE

Cytidine drugs, such as gemcitabine, undergo rapid catabolism and inactivation by cytidine deaminase (CD). 3,4,5,6-tetrahydrouridine (THU), a potent CD inhibitor, has been applied preclinically and clinically as a modulator of cytidine analogue metabolism. However, THU is only 20% orally bioavailable, which limits its preclinical evaluation and clinical use. Therefore, we characterized THU pharmacokinetics after the administration to mice of the more lipophilic pro-drug triacetyl-THU (taTHU).

METHODS

Mice were dosed with 150 mg/kg taTHU i.v. or p.o. Plasma and urine THU concentrations were quantitated with a validated LC-MS/MS assay. Plasma and urine pharmacokinetic parameters were calculated non-compartmentally and compartmentally.

RESULTS

taTHU did not inhibit CD. THU, after 150 mg/kg taTHU i.v., had a 235-min terminal half-life and produced plasma THU concentrations >1 μg/mL, the concentration shown to inhibit CD, for 10 h. Renal excretion accounted for 40-55% of the i.v. taTHU dose, 6-12% of the p.o. taTHU dose. A two-compartment model of taTHU generating THU fitted the i.v. taTHU data best. taTHU, at 150 mg/kg p.o., produced a concentration versus time profile with a plateau of approximately 10 μg/mL from 0.5-2 h, followed by a decline with a 122-min half-life. Approximately 68% of i.v. taTHU is converted to THU. Approximately 30% of p.o. taTHU reaches the systemic circulation as THU.

CONCLUSIONS

The availability of THU after p.o. taTHU is 30%, when compared to the 20% achieved with p.o. THU. These data will support the clinical studies of taTHU.

Abstract 4549: Plasma pharmacokinetics and oral bioavailability of the 3,4,5,6-tetrahydrouridine (THU) prodrug, triacetyl-THU (taTHU), in mice

Introduction

Cytidine drugs, such as gemcitabine, undergo rapid, inactivating catabolism by cytidine deaminase (CD). 3,4,5,6-tetrahydrouridine (THU), a potent CD inhibitor, has been applied preclinically and clinically as a modulator of cytidine drug metabolism. However, p.o. THU is at most 20% bioavailable (Beumer et al.), which limits its preclinical evaluation and clinical use. Therefore, the more lipophilic prodrug triacetyl THU (taTHU) was developed. We characterized THU pharmacokinetics after administration of taTHU to mice.

Methods

Mice were dosed 150 mg/kg taTHU i.v. or p.o. Plasma and urine THU concentrations were quantitated with a validated LC-MS/MS assay. Plasma and urine pharmacokinetic parameters and p.o. bioavailability were calculated non-compartmentally and compartmentally. We assessed taTHU inhibition of metabolism of gemcitabine by recombinant CD.

ResultsTHU parameterstaTHU i.v. 150 mg/kgtaTHU p.o. 150 mg/kgCmax (µg/mL)10611.8Tmax (min)560Half-life (min)235122AUC0-inf (mg/mL*min)7.553.36Vd/F (L/kg)4.495.26Cl/F (mL/min/kg)13.229.8F-THUi.v. (%)68.030.3% dose in 0-16 h urine405.6% dose in 0-24 h urine5512

THU, after 150 mg/kg taTHU i.v., had a 235 min terminal half-life and produced plasma THU concentrations &gt;1 µg/mL, the concentration shown to inhibit CD, for 10 h. A multi-compartment model fit the data best. 150 mg/kg p.o. taTHU produced a concentration versus time profile with a plateau of approximately 10 µg/mL from 0.5-2 h, followed by a decline with a 122 min half-life. Approximately 68% of i.v. taTHU was converted to THU. Approximately 30% of p.o. taTHU reached the systemic circulation as THU. After i.v dosing, renal excretion accounted for 40-55% of the taTHU dose, 26-35% as THU and an additional 14-19% as acetylated forms of THU. After p.o. dosing, the renal excretion percentages were 6-12%, 5.2-11%, and 0.42-0.71%, respectively. taTHU did not inhibit recombinant CD.

Conclusion

The availability of THU after p.o. taTHU in mice is 30%, as compared to the 20% achieved after p.o. THU. Clinical studies are warranted to evaluate availability of THU from taTHU in humans.

Support: N01-CM07106, N01-CM52202, P30-CA47904 from the NCI and P41-EB001978.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4549.

Liquid chromatography-tandem mass spectrometric assay for the quantitation in human plasma of the novel indenoisoquinoline topoisomerase I inhibitors, NSC 743400 and NSC 725776

Topoisomerase I (Topo I) is a recognized target for ovarian, lung, and colorectal cancer therapy. The FDA-approved camptothecin (CPT) Topo I inhibitors, topotecan and irinotecan are labile and their effects are rapidly reversible. The indenoisoquinoline topoisomerase I inhibitors, NSC 743400 and NSC 725776, have been developed as a new generation of Topo I inhibitors and are being advanced to clinical evaluation. To support the clinical development of NSC 743400 and NSC 725776, we developed and validated, according to FDA guidelines, LC-MS/MS assays for the sensitive, accurate and precise quantitation of NSC 743400 and NSC 725776 in 0.2 mL human plasma. After ethyl acetate extraction, separation was achieved with a Synergi Polar RP column and a gradient of 0.1% formic acid in acetonitrile:water. NSC 743400 and NSC 725776 eluted at approximately 3 min, and the total run time was 14 min. Detection consisted of electrospray, positive-mode ionization mass spectrometry. Between 3 and 1000 ng/mL, accuracy was 96.9-108.2% for NSC 743400 and 95.1-106.7% for NSC 725776, and precision was <11.4% for NSC 743400 and <5.9% for NSC 725776. Extraction recovery was >80% for both analytes, and ion suppression ranged from -46.7 to 5.7%. The use of isotopically labeled internal standards and a wash phase at the end of the run were necessary to achieve adequate assay performance. Protein binding in human plasma as assessed by equilibrium dialysis showed both indenoisoquinolines to be more than 98% protein bound.

Metabolism of a sulfur-containing heteroarotionoid antitumor agent, SHetA2, using liquid chromatography/tandem mass spectrometry

SHetA2 {[(4-nitrophenyl)amino][2,2,4,4-tetramethylthiochroman-6-yl)amino]methanethione], NSC 726189}, a sulfur-containing heteroarotinoid, selectively inhibits cancer cell growth and induces apoptosis without activation of nuclear retinoic acid receptors (RARs). The objective of this study was to investigate its in vitro metabolism in rat and human liver microsomes and in vivo metabolism in the mouse and rat using liquid chromatography-ultraviolet/multi-stage mass spectrometry (LC-UV/MS(n)) on an ion-trap mass spectrometer coupled with a photo-diode array (PDA) detector. In vitro, in the absence of glutathione (GSH), oxidation of the four aliphatic methyl groups of SHetA2 yielded one mono-, two di-, and one tri-hydroxylated SHetA2 metabolites, which were identified based on their UV and multi-stage mass spectra. In the presence of GSH, in addition to these primary oxidative metabolites, four GSH adducts of SHetA2 and a novel rare form thioether GSH adduct was detected and characterized. In vivo, the monohydroxylated SHetA2 metabolites were also detected in mouse and rat plasma and two GSH adducts were detected in rat liver following intravenous (i.v.) bolus administration of SHetA2 at 40 mg/kg.

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.

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.

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.

Quantitative determination of the cytidine deaminase inhibitor tetrahydrouridine (THU) in mouse plasma by liquid chromatography/electrospray ionization tandem mass spectrometry

A number of anticancer drugs are cytidine analogues that undergo metabolic deactivation catalyzed by cytidine deaminase (CD). 3,4,5,6-Tetrahydrouridine (THU) is a potent inhibitor of CD, by acting as a transition-state analogue of its natural substrate cytidine. However, to date its pharmacokinetic properties have not been fully characterized, which has impaired its optimal preclinical evaluation and clinical use. We report a liquid chromatography/tandem mass spectrometry (LC/MS/MS) assay for the sensitive, accurate and precise quantitation of THU in mouse plasma. Validation was performed according to FDA guidelines. The assay employed deuterated THU as the internal standard and an acetonitrile protein precipitation step. Separation, based on hydrophilic interaction chromatography, was achieved with an amino column and an isocratic mobile phase of 0.1% formic acid in acetonitrile and water followed by a wash. Chromatographic separation was followed by positive-mode electrospray ionization MS/MS detection in the multiple reaction monitoring (MRM) mode. The assay was accurate (92.5-109.9%) and precise (2.1-9.0%) in the concentration range of 0.2-50 microg/mL. Recovery from plasma was near-complete (92.9-119.3%) and ion suppression was negligible (-17.5 to -0.2%). Plasma freeze/thaw stability (93.1-102.1%), stability for 3 months at -80 degrees C (99.5-110.9%), and stability for 4 h at room temperature (92.1-102.4%) were all in order. This assay is currently being used to quantitate THU in ongoing pharmacokinetic studies. In addition, the assay is expected to be a useful tool in any future studies involving co-administration of THU with cytidine analogues.

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.

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.

Determination of desoxyepothilone B in nude mice plasma by liquid–liquid extraction and reversed-phase high-performance liquid chromatography

A novel reversed-phase high-performance liquid chromatographic (HPLC) method has been established for the determination of a newly developed anti-cancer agent desoxyepothilone B (dEpo B) in nude mice plasma. The sample preparation involved deproteination of 200 microl of plasma sample first, followed by liquid-liquid extraction of the resultant supernatant with chloroform. The compound taxol was used as the internal standard. Chromatographic separations were carried out on a 250 mm x 4.6 mm Zorbax SB-phenyl column with acetonitrile-0.25% orthophosphoric acid (50/50, v/v) as mobile phase and UV detection at 250 nm. For dEpo B and taxol at the concentration level of 10 microg/ml in nude mice plasma, the absolute extraction recoveries were 85.3 and 87.2%, respectively. The linear quantification range of the method was 0.1-100 microg/ml in nude mice plasma with linear correlation coefficients greater than 0.999. The within-day and between-day relative standard deviations (R.S.D.s) for dEpo B at 0.5, 2.5 and 10 microg/ml levels in nude mice plasma fell in the range of 2.8-4.8 and 1.5-4.6%, and the within-day and between-day recoveries were in the range of 96.5-101.7 and 97.7-101.2%, respectively.

LC–MS/MS assay and dog pharmacokinetics of the dimeric pyrrolobenzodiazepine SJG-136 (NSC 694501)

The dimeric pyrrolobenzodiazepine SJG-136 (NSC 694501) has potent in vitro cytotoxicity and in vivo antitumor activity. SJG-136 binds in the minor groove of DNA and produces G-G interstrand cross-links via reactive N(10)-C(11)/N(10')-C(ll') imine/carbinolamine moieties. We have developed a sensitive, specific liquid chromatography tandem mass spectrometry (LC/MS/MS) method for the quantitative determination of SJG-136 in plasma. SJG-136 was isolated by solid phase extraction through a C8 column, reverse-phase HPLC separation was accomplished on a C18 column with isocratic elution and MS/MS detection, monitoring the m/z 557-m/z 476 transition after electrospray ionization. The linear range and lower limit of quantitation from plasma standard curves were 2.8-1800 nM, and 5 nM, respectively. SJG-136 plasma protein binding was species-dependent. Values of the unbound fraction in human, rat and mouse were 25%, 16.2% and <1%, respectively. Protein binding was saturable in dog plasma where the unbound fraction increased from 10.8% to 22.3% over a 22-720 nM concentration range. SJG-136 pharmacokinetics after a single intravenous dose were best fit to a two-compartment open model with elimination half-life and plasma clearance values of 97 min and 6.1 mL/min/kg, respectively. SJG-136 did not accumulate in plasma following intravenous administration of 1.0 microg/kg doses for five consecutive days.

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.

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.

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.

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.

Preclinical toxicity of a geldanamycin analog, 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG), in rats and dogs: potential clinical relevance

PURPOSE

17-DMAG is a hydrophilic derivative of the molecular chaperone inhibitor 17-(allylamino)-17-demethoxygeldanamycin (17-AAG; NSC-330507), which is currently being evaluated for the treatment of cancer in clinical trials. 17-DMAG offers a potential advantage over 17-AAG because its aqueous solubility eliminates the need for complicated formulations that are currently used for administration of 17-AAG. In addition, 17-DMAG undergoes only limited metabolism compared to 17-AAG. The present results are from preclinical toxicity studies evaluating 17-DMAG in rats and dogs.

METHODS

Doses of 0, 2.4, 12 and 24 mg/m2 per day were administered to rats, while dogs received doses of 0, 8 or 16 mg/m2 per day. In both species, 17-DMAG was administered i.v. (slow bolus for rats; 1-h infusion for dogs) daily for 5 days. An additional cohort of dogs received 16 mg/m2 per day orally for 5 days. Clinical observations were noted, and standard hematology and clinical chemistry parameters were monitored. Selected tissues were evaluated microscopically for drug-related lesions. Tissue and plasma 17-DMAG concentrations were measured by HPLC/MS at selected time-points on days 1 and 5.

RESULTS

Daily i.v. administration of 17-DMAG at doses of 24 mg/m2 per day in rats or 16 mg/m2 per day in dogs produced lethality on day 6, approximately 24 h following the last dose. Body weight loss was common in rats and dogs. Drug-related gastrointestinal, bone marrow and hepatic toxicities were also common in rats and dogs. Dogs also exhibited signs of renal and gallbladder toxicity. Plasma concentrations of 17-DMAG increased proportionately with dose in rats and disproportionately with dose in dogs. In rat tissues, however, only fourfold to sixfold increases in 17-DMAG concentrations were observed with a tenfold increase in dose. The highest concentrations of 17-DMAG were found in the liver of rats, with progressively lower concentrations in the spleen, lung, kidney and plasma. Regardless of the route of administration, higher drug concentrations were present in plasma (rat and dog) and tissue (rat) samples obtained on day 5 compared to those obtained on day 1. Although plasma concentrations decreased with time, 17-DMAG was still detected in dog plasma for at least 24 h after drug administration.

CONCLUSIONS

With the recent approval of 17-DMAG for clinical use, the data generated from these preclinical studies will provide guidance to clinicians as they administer this drug to their patients. The MTD of 17-DMAG was 12 mg/m2 per day in rats and 8 mg/m2 per day in dogs; therefore, the recommended starting dose for phase I trial is 1.3 mg/m2 per day for 5 days. Gastrointestinal and bone marrow toxicity were dose-limiting in rats, and gastrointestinal, renal, gallbladder and bone marrow toxicity were dose-limiting in dogs. All adverse effects were fully reversible in surviving animals after treatment was complete.

Preclinical pharmacology of 2-methoxyantimycin A compounds as novel antitumor agents

PURPOSE

The present study was designed to determine pharmacological and biochemical properties of 2-methoxyantimycin A analogs (OMe-A1, OMe-A2, OMe-A3, and OMe-A5), which are novel antitumor compounds, and provide a basis for future pharmaceutical development, preclinical evaluation, and clinical trials.

METHODS

A high-performance liquid chromatography (HPLC) method was established and employed to assess the biostability of these analogs and to determine their pharmacokinetic properties in mice and rats.

RESULTS

In vitro biostability of the 2-methoxyantimycin analogs was esterase-dependent, compound-dependent, and species-dependent. In the absence of esterase inhibitors, all of the analogs were relatively unstable. Stability was greater, however, in human and dog plasma than in rat and mouse plasma. In the presence of esterase inhibitors, OMe-A1 was stable at 37 degrees C for 60 min in mouse and rat plasma, moderately stable in human plasma, and unstable in dog plasma. OMe-A2 was generally stable in all types of plasma. OMe-A3 was stable in dog and rat plasma, but not in human or mouse plasma. OMe-A5 was stable in human and dog plasma, but not in mouse or rat plasma. Each of these analogs was highly bound to plasma proteins. Of S9 fractions from four species, human S9 was least efficient in metabolizing OMe-A3. Following an intravenous dose of OMe-A1 in mice, plasma levels decreased rapidly, with an initial half-life of 2.7 min and a terminal half life of 34 min. Following an intraperitoneal dose in mice, plasma levels decreased less rapidly with a terminal half-life of 215 min. Following an intravenous dose of OMe-A1 or OMe-A3 in rats, plasma levels decreased more rapidly with initial half-lives of about 1.0 min. At an equivalent dose, OMe-A3 had a faster clearance than OMe-A1.

CONCLUSIONS

For 2-methoxyantimycin A analogs, species differences in biostability, metabolism, and pharmacokinetics may be pertinent in assessing their pharmacological and toxicological profiles and antitumor activity in humans.

Preclinical pharmacology of epothilone D, a novel tubulin-stabilizing antitumor agent

PURPOSE

To determine, for various species, the pharmacological and biochemical properties of epothilone D (EpoD) that are relevant in establishing an appropriate animal model for further evaluation of this promising antitumor agent.

METHODS

A method involving high-performance liquid chromatography (HPLC) was developed and used to assess the stability and protein binding of EpoD in plasma from various species, its metabolism by various S9 fractions, and its pharmacokinetics in mice.

RESULTS

EpoD was stable in dog and human plasma. In plasma from other species, stability decreased in the order: hamster > mouse > guinea pig > rat. EpoD was highly bound to proteins in dog and human plasma. In an evaluation of S9 fractions from mouse, rat, guinea pig, dog, and human, mouse S9 was most efficient in metabolizing EpoD. Following administration to CD2F1 mice, the initial half-lives for plasma elimination of EpoD were <5 min for an intravenous dose and <20 min for an intraperitoneal dose.

CONCLUSIONS

The species differences in EpoD biostability and metabolism may have implications in assessing its antitumor activity and pharmacologic and toxicologic profiles in humans. Relative to humans, the mouse is not a good model for disposition of EpoD; the dog would be more appropriate.

Chemoresistance to Depsipeptide FK228 [(E)-(1S,4S,10S,21R)-7-[(Z)-Ethylidene]-4,21-diisopropyl-2-oxa-12,13-dithia-5,8,20,23-tetraazabicyclo[8,7,6]-tricos-16-ene-3,6,9,22-pentanone] Is Mediated by Reversible MDR1 Induction in Human Cancer Cell Lines

Histone acetylation status, an epigenetic determinant of gene transcription, is controlled by histone acetyltransferases (HATs) and histone deacetylases (HDACs). The potent HDAC inhibitor FK228 [(E)-(1S,4S,10S,21R)-7-[(Z)-ethylidene]-4,21-diisopropyl-2-oxa-12,13-dithia-5,8,20,23-tetraazabicyclo[8,7,6]-tricos-16-ene-3,6,9,22-pentanone] is a substrate for multidrug resistance protein (MDR1) and multidrug resistance-associated protein 1 (MRP1), both of which mediate FK228 resistance. To determine the mechanisms underlying acquired FK228 resistance, we developed four FK228-resistant cell lines from HCT-15, IGROV1, MCF7, and K562 cells by stepwise increases in FK228 exposure. Parent and resistant cells were characterized using a 70-oligomer cDNA microarray, real-time reverse transcription-polymerase chain reaction (RT-PCR), Western blot, and cytotoxicity assays. At both mRNA and protein levels, MDR1, but not MRP1 or other potential resistance genes, was strongly up-regulated in all resistant cell lines. HAT or HDAC activities were unaffected in resistant cells, consistent with a lack of cross-resistance to HDAC inhibitors that are not MDR1 substrates. FK228 was found to reversibly induce MDR1 expression by HDAC inhibition and subsequent histone hyperacetylation at the MDR1 promoter, as shown by real-time RT-PCR, Western blot, and chromatin immunoprecipitation. This study reveals a significant role of histone acetylation in MDR1 transcription, which seems to mediate FK228 resistance.

Liquid chromatography-electrospray tandem mass spectrometric assay suitable for quantitation of halofuginone in plasma

An LC-MS/MS method was developed to quantitate the potential antitumor agent halofuginone in plasma. The assay uses 0.2 ml of plasma; chlorohalofuginone internal standard; acetonitrile for protein precipitation; a Phenomenex SYNERGI 4 micro Polar RP 80A (4 microm, 100 mm x 2 mm) column; an isocratic mobile phase of methanol:water:formic acid (80:20:0.02, v/v/v); and positive-ion electrospray ionization with selective reaction monitoring detection. Halofuginone eluted at approximately 2.4 min, internal standard eluted at approximately 2.9 min, and no endogenous materials interfered with their measurement. The assay was accurate, precise, and linear between 0.1 and 100 ng/ml. Halofuginone could be quantitated in dog plasma for at least 24 h after an i.v. dose of 0.1mg/kg. The assay is being used in ongoing pharmacokinetic studies of halofuginone.

Pharmacokinetics and pharmacodynamics of 17-demethoxy 17-[[(2-dimethylamino)ethyl]amino]geldanamycin (17DMAG, NSC 707545) in C.B-17 SCID mice bearing MDA-MB-231 human breast cancer xenografts

PURPOSE

17-demethoxy 17-[[(2-dimethylamino)ethyl]amino]geldanamycin (17DMAG, NSC 707545) is a water-soluble analogue of 17-(allylamino)-17-demethoxygeldanamycin (17AAG), a compound currently in clinical trials. These preclinical studies: (1) characterized 17DMAG concentrations in plasma, normal tissues, and tumor after i.v. delivery to mice; and (2) correlated tumor and normal tissue 17DMAG concentrations with alterations in heat shock protein 90 (HSP90) and selected HSP90-chaperoned proteins.

METHODS

At specified times after i.v. administration of 75 mg/kg 17DMAG, SCID mice bearing s.c. MDA-MB-231 human breast xenografts were killed and plasma and tissues were retained. 17DMAG concentrations were determined by HPLC. Raf-1, heat shock protein 70 (HSP70), and HSP90 in tissues were determined by Western blotting.

RESULTS

Peak plasma 17DMAG concentration was 15.4+/-1.4 microg/ml. The area under the plasma 17DMAG concentration versus time curve was 1072 microg/ml min, corresponding to a total body clearance of 70 ml/kg/min. Peak 17DMAG concentrations in liver (118.8+/-5.7 microg/g), kidney (122.9+/-10.6 microg/g), heart (81.3+/-8.1 microg/g), and lung (110.6+/-25.4 microg/g) occurred at 5-10 min, while peak concentrations in spleen (70.6+/-9.6 microg/g) and tumor (9.0+/-1.0 microg/g) occurred at 30-45 min. At 48 h, 17DMAG was detectable in tumor but not in any normal tissue. Raf-1 in tumors of 17DMAG-treated mice killed at 4, 7, 24 and 48 h was about 20% lower than in tumors from vehicle-treated mice. HSP90 and HSP70 in tumors of 17DMAG-treated animals were significantly lower than in tumors of control animals at 4, 7, and 24 h. Hepatic Raf-1 was decreased by more than 60% at all times after 17DMAG treatment; however, hepatic HSP90 was not affected. HSP70 was undetectable in livers of vehicle-treated mice or mice killed at 2 or 4 h after 17DMAG treatment, but was detected in livers at 7, 24 and 48 h. 17DMAG did not affect renal Raf-1. In contrast, renal HSP70 and HSP90 were decreased by more than 50% at 2 and 4 h after 17DMAG treatment. Renal HSP70 increased approximately twofold above that in kidneys from vehicle-treated control mice at 7 and 24 h, while HSP90 relative protein concentration was no different from that in controls.

CONCLUSIONS

Plasma pharmacokinetics of 17DMAG in tumor-bearing mice were similar to those previously reported in nontumor-bearing mice. 17DMAG was distributed widely to tissues but was retained for longer in tumors than normal tissues. Raf-1, HSP90, and HSP70 were altered to different degrees in tumors, livers, and kidneys of 17DMAG-treated animals. These data illustrate the complex nature of the biological responses to 17DMAG.

IN VITRO METABOLISM OF THE PHOSPHATIDYLINOSITOL 3-KINASE INHIBITOR, WORTMANNIN, BY CARBONYL REDUCTASE

The phosphatidylinositol 3-kinase inhibitor, wortmannin, is extensively used in molecular signaling studies and has been proposed as a potential antineoplastic agent. The failure to detect wortmannin in mouse plasma after i.v. administration prompted in vitro studies of wortmannin metabolism. Wortmannin was incubated with mouse tissue homogenates, homogenate fractions, or purified, recombinant human carbonyl reductase in the presence of specified cofactors and inhibitors. Reaction products were characterized and quantified with liquid chromatography (LC)/mass spectrometry. Reaction rates were characterized using Michaelis-Menten kinetics. Wortmannin was metabolized to a material 2 atomic mass units greater than wortmannin. Liver homogenate had the highest metabolic activity. Some metabolism occurred in kidney and lung homogenates. Very little metabolism occurred in brain or red blood cell homogenates. Liver S9 fraction and cytosol metabolized wortmannin in the presence of NADPH and, to a much lesser extent, in the presence of NADH. Microsomal metabolism of wortmannin was minimal. Purified, recombinant human carbonyl reductase metabolized wortmannin. Quercetin, a carbonyl reductase inhibitor, greatly decreased wortmannin metabolism by S9, cytosol, and carbonyl reductase. The K(M) for wortmannin metabolism by purified, recombinant human carbonyl reductase was 119 +/- 9 microM, and the V(max) was 58 +/- 9 nmol/min/mg of protein. LC-tandem mass spectrometry spectra indicated that carbonyl reductase metabolized wortmannin to 17-OH-wortmannin. Wortmannin reduction by carbonyl reductase may partly explain why wortmannin is not detected in plasma after being administered to mice. Metabolism of wortmannin to 17-OH-wortmannin has mechanistic, and possibly toxicologic, implications because 17-OH-wortmannin is 10-fold more potent an inhibitor of phosphatidylinositol 3-kinase than is wortmannin.

Biliary excretion of 17-(allylamino)-17-demethoxygeldanamycin (NSC 330507) and metabolites by Fischer 344 rats

PURPOSE

17-(Allylamino)-17-demethoxygeldanamycin (17AAG), an analogue of the benzoquinone ansamycin geldanamycin, has been extensively studied preclinically and is being evaluated clinically. Studies were performed to define the biliary excretion of 17AAG after i.v. delivery to rats, and to characterize the metabolites of 17AAG observed in rat bile.

MATERIALS AND METHODS

In vivo studies were performed in bile-duct-cannulated Fischer 344 rats given a 10 mg/kg i.v. bolus dose of 17AAG. In vitro studies were performed with cloned human CYPs and microsomal epoxide hydrolase. Biliary excretion of 17AAG and metabolites was quantified by HPLC and followed for 4 h after drug delivery. 17AAG metabolites in bile and in in vitro reaction mixtures were identified with LC/MS/MS.

RESULTS

By 15 min after i.v. delivery of 17AAG, bile contained at least 15 biotransformation products with absorbance spectra similar to that of 17AAG. Of these, metabolites eluting at 2.7, 2.9, and 8.6 min were present in sufficient concentrations to be quantified, although the lack of authentic standards resulted in their being expressed as 17AAG equivalents. Within the first 4 h after drug delivery, biliary excretion accounted for 28.9+/-6.1% of the 10-mg/kg 17AAG dose. 17AAG and 17-(amino)-17-demethoxygeldanamycin (17AG) accounted for 4.1+/-1.0% of the delivered dose, with 17AAG accounting for 2.0+/-0.5% and 17AG accounting for 2.1+/-0.5%. The metabolites eluting at 2.7, 2.9, and 8.6 min accounted for 10.6+/-2.0%, 9.8+/-1.2%, and 1.0+/-0.2%, respectively, of the administered dose. LC/MS/MS analysis of bile demonstrated major metabolites with molecular weights of 545 and 619, corresponding to 17AG and the diol previously described as resulting from metabolism of 17AAG by CYP3A and microsomal epoxide hydrolase. Of the remaining proposed metabolites, ten had a mass and MS/MS spectrum consistent with mono-oxygenated 17AAG metabolites. One of these metabolites has been identified as the epoxide previously described as resulting from CYP3A oxidation of the allyl double bond. Two other proposed metabolites had a mass and MS/MS spectrum consistent with demethylated 17AAG metabolites, and one had a mass and MS/MS spectrum consistent with a di-demethylated 17AAG metabolite. An analogous series of demethylated and oxidized metabolites was also observed for the 17AG metabolite.

CONCLUSIONS

Biliary excretion of 17AAG represents a major route of elimination, although most of the material excreted is in the form of metabolites. Bile of rats dosed with 17AAG contained a number of metabolites not previously identified in the plasma or urine of mice treated with 17AAG, but analogous to metabolites described in bile of rats treated with 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17DMAG, NSC 707545), another geldanamycin analogue undergoing preclinical evaluation in preparation for subsequent clinical trials.

Electrospray LC-MS/MS quantitation, stability, and preliminary pharmacokinetics of bradykinin antagonist polypeptide B201 (NSC 710295) in the mouse

B201 (NSC 710295), [SUIM-(Darg-Arg-Pro-Hyp-Gly-Igl-Ser-Digl-Oic-Arg)(2)], a third generation of bradykinin (BK) antagonist, has been found to possess high potency. We report the development of a highly sensitive electrospray LC-MS/MS assay method for the analysis of B201 in plasma for the first time, using an ion-trap mass spectrometer. Human or mouse plasma (0.2 ml) was spiked with B201 and the internal standard, substance P. The compounds were extracted with a preconditioned C-18 reversed-phase column and analyzed by LC-MS/MS. The analytes were separated on a 50 x 2 mm (i.d.) BetaBasic C8 column, using a gradient elution. The positive ion selected reaction monitor mode was used monitoring the transitions of ions at m/z 938.9(3+)-->816.0(2+) for B201 and 674.3(2+)-->665.7(2+) for substance P. Assay validation was performed, and the limit of quantitation (LOQ) for B201 was found to be 1 ng/ml for human plasma and 2.5 ng/ml for mouse plasma. The recovery was 78% for B201 and 88% for substance P. The assay was linear from 2.5 to 1500 ng/ml for mouse plasma monitored. Using a 0.2 ml plasma, the within-day CVs were 9.3% at 2.5 ng/ml, 6.5% at 100 ng/ml, and 3.8% at 1000 ng/ml for human plasma (n=6). For mouse plasma, the respective within-day CVs were 17.6, 9.6, and 6.2% (n=6). The between-day CVs for human plasma were 8.2, 10.9, and 2.4%, respectively, (n=3) and the respective values for mouse plasma were 11.9, 8.6 and 6.5% (n=6). Pharmacokinetics of B201 in the mouse was studied following i.v. administration at 5 mg/kg and found to conform to a two-compartment model with an initial half-life of 14 min and a terminal half-life of 44 h. Plasma B201 peak level was detected at microg/ml range and the levels were detectable for a least 24 h. Preliminary oral bioavailability was found to be about 1%. This method demonstrates that an ion trap mass spectrometer can be a powerful tool to quantify large peptides at low nanogram per milliliter with a non-isotopically labeled internal standard.

Bradykinin antagonist dimer, CU201, inhibits the growth of human lung cancer cell lines in vitro and in vivo and produces synergistic growth inhibition in combination with other antitumor agents

Small cell lung cancers (SCLCs), many non-SCLCs, and other cancers have neuroendocrine features, including paracrineand autocrine growth stimulation by various neuropeptides. Interference with this pathway is an attractive target for novel therapies. We developed a novel bradykinin antagonist dimer, CU201 (B9870), that acts as a "biased agonist" for neuropeptides by blocking G(alphaq) signaling and activating G(alpha12,13) signaling. CU201 induced apoptosis and complete growth inhibition in various lung cancer and other cancer cell lines. CU201 was 10-fold more potent than substance P derivatives and was stable in serum for >7 days. In this study, we evaluated the ability of CU201 to produce additive or synergistic growth inhibition in combination with various antitumor agents used in lung cancer therapy. We found that CU201 produced additive or synergistic growth inhibition when combined with doxorubicin, etoposide, cisplatin, vinorelbine, and paclitaxel for SCLC lines and with paclitaxel and ZD1839, an epidermal growth factor receptor tyrosine kinase inhibitor, for non-SCLC cell lines. Pharmacokinetic parameters associated with the i.v. administration of CU201 were evaluated in normal mice, and the effects of CU201 on the growth of human lung cancer xenografts were evaluated in athymic nude mice. In CD2F1 mice given an i.v. bolus infusion of 5 mg/kg, the c(max) was 5773 ng/ml (5 microM), and the decay was biexponential. When fitted to a two-compartment model, the t(1/2alpha) was 14.4 min, and the t(1/2beta) was 44.3 h, indicating a long terminal half-life consistent with the prolonged in vitro effects. CU201 inhibited the growth of human lung cancers in athymic nude mice by the intratumoral, s.c., and i.p. routes at a dose of 5 mg/kg/day. This dose is >10-fold less than the dose of substance P derivatives used to inhibit SCLC xenografts in nude mice. We conclude that CU201 should undergo further preclinical toxicology studies in its development as a novel targeted therapy for the treatment of lung cancers with neuroendocrine features. These studies are in progress through the NCI RAID mechanism.

Chiral high-performance liquid chromatographic analysis of the enantiomers of XK469, a new antitumor agent, in plasma and urine

XK469 (NSC697887), (+/-)-2-[4-(7-Chloro-2-quinoxaliny)oxy]-phenoxy propionic acid, an analog of the herbicide Assure(R), which possesses antitumor activity, especially against murine solid tumors and human xenografts, has recently been found to be the first topoisomerase II beta poison. Both R(+) and S(-) isomers are cytotoxic, although the R-isomer is more potent. A chiral high-performance liquid chromatography (HPLC) assay that utilizes Chirobiotic T column for the measurement of enantiomers of XK469 in plasma has been developed with a limit of quantitation (LOQ) of 0.2 microg/ml using a 0.2 ml plasma sample. Chloroqinoxaline sulfonamide (CQS) was used as the internal standard and the assay has been validated in rat plasma. The within-run coefficient of variations (CVs) were 5.9, 5.0, and 3.1% for the S-isomer and 8.1, 4.2, 6.4% for R(+)-XK469 at 0.2, 1, and 2 microg/ml, respectively. The between-run CVs were 10.5, 5.3, and 1.9% for S(-)- and 10.9, 6.3, and 3.6% for R(+)-XK469. Using this chiral assay, a plasma concentration time data of R(+)-,S(-)-XK469 in a Fischer 344 rat receiving i.v. dosing of S(-)XK469 at 10 mg/kg was monitored. S(-)XK469 was found to be significantly converted to the R-enantiomer in circulation even when the S-enantiomer was administered. The predominant inversion from S(-)- to R(+)-XK469 was also observed in the mouse and dog plasma. In the rat, the plasma concentration-time profiles for both isomers follow two compartmental pharmacokinetics with the t(1/2 beta) for the R-enantiomer slightly longer and the clearance of the S-enantiomer higher than the R-enantiomer.