Ames, Matthew M.

Abstract Background: ABT-888 is an inhibitor of poly(ADP-ribose) polymerase1 (PARP1) and PARP2, two highly conserved enzymes implicated in DNA repair, maintenance of genomic stability, and regulation of transcription. Topotecan (TPT) is a water soluble camptothecin derivative with antitumor activity against ovarian tumors. The combination of ABT-888 with TPT is under investigation in phase I trials because PARP inhibition sensitizes tumors cells to TPT in vitro and in vivo. In those trials, the pharmacokinetics of TPT and ABT-888 are being studied to determine if ABT-888 levels are sufficient to modulate PARP activity and to investigate the potential interaction between TPT and ABT-888. Methods: Advanced cancer patients with ECOG performance scores 0-2, adequate hematological, renal and hepatic function were treated with ABT-888 on days 1-3, 8-10, and 15-17 every 28 days. Topotecan was administered on days 2, 9 and 16 every 28 days. DLTs were defined as grade 4 neutropenia, grade 4 thrombocytopenia, grade 4 anemia or ≥ grade 3 non-hematologic toxicities despite maximal supportive care. ABT-888 and Toptoecan pharmacokinetics were characterized in all patients. Analysis of urinary recovery is ongoing. Results: In this ongoing Phase I trial, 13 female patients with ovarian (n=12) or breast (n=1) cancer have been enrolled to date and pharmacokinetic data is available for 12 of those patients. ABT-888/TPT dose levels are: Level 1- 10 mg/ 2 mg/m2, Level 2- 20 mg/2 mg/m2, Level 3- 10 mg/3 mg/m2, and Level 4- 20 mg/3 mg/m2. The combination of ABT-888 with topotecan has been tolerable, with no dose limiting toxicity, and dose escalation continues at dose level 5. Topotecan t1/2 and clearance values were 3.0 ± 0.5 hrs and 9.50 ± 1.51 L/hr/m2 when administered alone, and were not affected by administration with ABT-888. When administered alone, ABT-888 t1/2, Cmax, AUC0-∞ values after the 10 mg dose were 8.2 ± 2.4 hrs, 432 ± 217 nM, and 2568 ± 1300 nM*hr, respectively. ABT-888 t1/2, Cmax, AUC values after the 20 mg dose were 5.7 ± 3.1 hrs, 600 ± 165 nM, and 3870± 934 respectively. When administered with TPT, ABT-888 t1/2, Cmax, AUC values after the 10 mg dose were 7.2 ± 2.1 hrs, 412 ± 283 nM, and 2705± 1089 nM*hr are: nM*hr respectively. ABT-888 t1/2, Cmax and AUC values after the 20 mg dose combined with TPT were 5.8 ± 2.2 hrs, 664 ± 97.6 nM, and 4283± 936 nM*hr respectively. Conclusions: Plasma clearance of TPT and ABT-888 does not appear to be altered when they are administered together. The effect of co-administration of these agents on renal clearance is presently under investigation and those results will be presented. This work was supported by NIH grants R25 GM75148-04, U01CA069912-16S and MM01-RR00585. 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 1301. doi:10.1158/1538-7445.AM2011-1301

AbstractPurpose: To determine the response rate to oral capsular fenretinide in children with recurrent or biopsy proven refractory high-risk neuroblastoma.Experimental Design: Patients received 7 days of fenretinide: 2,475 mg/m2/d divided TID (<18 years) or 1,800 mg/m2/d divided BID (≥18 years) every 21 days for a maximum of 30 courses. Patients with stable or responding disease after course 30 could request additional compassionate courses. Best response by course 8 was evaluated in stratum 1 (measurable disease on CT/MRI ± bone marrow and/or MIBG avid sites) and stratum 2 (bone marrow and/or MIBG avid sites only).Results: Sixty-two eligible patients, median age 5 years (range 0.6–19.9), were treated in stratum 1 (n = 38) and stratum 2 (n = 24). One partial response (PR) was seen in stratum 2 (n = 24 evaluable). No responses were seen in stratum 1 (n = 35 evaluable). Prolonged stable disease (SD) was seen in 7 patients in stratum 1 and 6 patients in stratum 2 for 4 to 45+ (median 15) courses. Median time to progression was 40 days (range 17–506) for stratum 1 and 48 days (range 17–892) for stratum 2. Mean 4-HPR steady-state trough plasma concentrations were 7.25 μmol/L (coefficient of variation 40–56%) at day 7 course 1. Toxicities were mild and reversible.Conclusions: Although neither stratum met protocol criteria for efficacy, 1 PR + 13 prolonged SD occurred in 14/59 (24%) of evaluable patients. Low bioavailability may have limited fenretinide activity. Novel fenretinide formulations with improved bioavailability are currently in pediatric phase I studies. Clin Cancer Res; 17(21); 6858–66. ©2011 AACR.

Abstract Background: Controversy exists regarding the association between CYP2D6 enzyme activity and tamoxifen effectiveness in the adjuvant treatment of invasive breast cancer; however, this association in the primary prevention of breast cancer is unknown. Methods: We conducted a nested case–control study in the context of the NSABP P1 and P2 prevention trials to determine the impact of CYP2D6 genotype, CYP2D6 inhibitor use, and metabolizer status (CYP2D6 genotype combined with CYP2D6 inhibitor use), on breast cancer events. Women who developed breast cancer (both noninvasive and invasive) while on 5 years of selective estrogen receptor modulators therapy (cases) were matched to controls free of breast cancer. Comprehensive CYP2D6 genotyping was conducted for alleles associated with absent (*3, *4, *5, and *6), reduced (*10, *17, and *41), and increased (*1XN and *2XN) enzyme activity. Information regarding the use of CYP2D6 inhibitors was recorded. Results: A total of 591 cases were matched to 1,126 controls and DNA was genotyped in more than 97%. In patients treated with tamoxifen, there was no association of CYP2D6 genotype [OR (extensive/poor metabolizer): 0.90; 95% CI: 0.46–1.74, P = 0.74), use of a potent CYP2D6 inhibitor (OR 0.92; 95% CI: 0.575–1.486), or CYP2D6 metabolizer status (OR 1.03; 95% CI: 0.669–1.607) with breast cancer occurrence. Likewise, there was no association between any CYP2D6 metabolism parameter with breast cancer events in raloxifene-treated patients. Conclusion: In the NSABP P1 and P2 clinical trials, alterations in CYP2D6 metabolism are not associated with either tamoxifen or raloxifene efficacy. Clin Cancer Res; 17(21); 6944–51. ©2011 AACR.

Abstract A phase I trial of ABT-888 (veliparib), a PARP inhibitor, in combination with topotecan, a topoisomerase I–targeted agent, was carried out to determine maximum tolerated dose (MTD), safety, pharmacokinetics, and pharmacodynamics of the combination in patients with refractory solid tumors and lymphomas. Varying schedules and doses of intravenous topotecan in combination with ABT-888 (10 mg) administered orally twice a day (BID) were evaluated. Plasma and urine pharmacokinetics were assessed and levels of poly(ADP-ribose) (PAR) and the DNA damage marker γH2AX were measured in tumor and peripheral blood mononuclear cells (PBMC). Twenty-four patients were enrolled. Significant myelosuppression limited the ability to coadminister ABT-888 with standard doses of topotecan, necessitating dose reductions. Preclinical studies using athymic mice carrying human tumor xenografts also informed schedule changes. The MTD was established as topotecan 0.6 mg/m2/d and ABT-888 10 mg BID on days one to five of 21-day cycles. Topotecan did not alter the pharmacokinetics of ABT-888. A more than 75% reduction in PAR levels was observed in 3 paired tumor biopsy samples; a greater than 50% reduction was observed in PBMCs from 19 of 23 patients with measurable levels. Increases in γH2AX response in circulating tumor cells (CTC) and PBMCs were observed in patients receiving ABT-888 with topotecan. We show a mechanistic interaction of a PARP inhibitor, ABT-888, with a topoisomerase I inhibitor, topotecan, in PBMCs, tumor, and CTCs. Results of this trial reveal that PARP inhibition can modulate the capacity to repair topoisomerase I–mediated DNA damage in the clinic. Cancer Res; 71(17); 5626–34. ©2011 AACR.

Abstract SR13668, an orally active Akt pathway inhibitor, has demonstrated cancer chemopreventive potential in preclinical studies. To accelerate the clinical development of this promising agent, we designed and conducted the first-ever phase 0 chemoprevention trial to evaluate and compare the effects of food and formulation on SR13668 bioavailability. Healthy adult volunteers were randomly assigned to receive a single, 38-mg oral dose of SR13668 in one of five different formulations, with or without food. On the basis of existing animal data, SR13668 in a PEG400/Labrasol oral solution was defined as the reference formulation. Blood samples were obtained pre- and post-agent administration for pharmacokinetic analyses. Area under the plasma concentration–time curve (AUC0–∞) was defined as the primary endpoint. Data were analyzed and compared using established statistical methods for phase 0 trials with a limited sample size. Participants (n = 20) were rapidly accrued over a 5-month period. Complete pharmacokinetic data were available for 18 randomized participants. AUC0–∞ values were highest in the fed state (range = 122–439 ng/mL × hours) and were statistically significantly different across formulations (P = 0.007), with Solutol HS15 providing the highest bioavailability. SR13668 time to peak plasma concentration (3 hours; range, 2–6 hours) and half-life were (11.2 ± 3.1 hours) were not formulation-dependent. Using a novel, highly efficient study design, we rapidly identified a lead formulation of SR13668 for further clinical testing. Our findings support application of the phase 0 trial paradigm to accelerate chemoprevention agent development. Cancer Prev Res; 4(3); 347–53. ©2011 AACR.

Abstract The diazeniumdiolate O2-(2,4-dinitrophenyl)-1-[(4-ethoxycarbonyl)piperazin-1-yl]diazen-1-ium-1,2diolate (JS-K, NSC 724771) is a nitric oxide (NO)-donating prodrug that was designed to release NO upon reaction with glutathione-S-transferase which is overexpressed in some tumors. We demonstrated that JS-K reacts with nucleophiles in biological fluids and has an extremely short half-life in mice. The purpose of the study was to test the hypothesis that liposomal encapsulation improves the in vivo half-life, tissue distribution and acute toxicity profile of JS-K. We investigated the pharmacokinetics of [3H]JS-K in CD mice administered the drug in DMSO or DMPC (dimyristoylphosphatidylcholine) liposomes (20:1 molar ratio of DMPC: JS-K) and in tumor-bearing athymic nu/nu NCr mice administered the radiolabeled drug in DMPC liposomes. The terminal elimination half-life of total radioactivity (2 hours) was similar for both formulations. We did not detect [3H]JS-K in any plasma or red blood cell samples from mice administered 6 mg/kg JS-K in DMSO and only trace amounts of [3H]JS-K were detected in samples collected at the earliest time-points from mice administered 6 mg/kg JS-K in DMPC liposomes. Small amounts of radioactivity, presumably associated with JS-K metabolites, were detected at the solvent front of HPLC chromatograms. Very little radioactivity and no JS-K was detected in tumor samples. Finally, we developed an LC/MS/MS assay to investigate formation of JS-K metabolites in biological samples and used that method to measure concentrations of JS-K and its metabolites in plasma, red blood cells, liver tissue and tumor tissue collected from tumor-bearing mice administered 3 mg/kg or 6 mg/kg JS-K in DMPC liposomes. We confirmed extremely rapid in vivo degradation of JS-K in the systemic circulation following intravenous administration and rapid formation of several expected metabolites including high concentrations of the glutathione conjugate of the dinitrophenol moiety and piperazine. Supported by NCI Contract NO1-CM-52206. 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 2662.

Abstract Endoxifen (END), the active metabolite of tamoxifen (TAM), is currently being developed as a drug for the treatment of estrogen receptor positive breast cancer based on recent in vitro and clinical data demonstrating that TAM drug effect is substantially related to circulating plasma concentrations of END, a secondary metabolite produced by human CYP2D6 metabolism. Women with deficient CYP2D6 metabolism have lower END concentrations and a higher risk of breast cancer recurrence. We characterized the pharmacokinetics and oral bioavailability of END in female rats and dogs. We further compared END exposure following equivalent doses of END and TAM. Rats were administered 2 mg/kg i.v. END, 20 − 200 mg/kg oral END or 80 mg/kg oral TAM. Fasted dogs were administered 0.5 mg/kg i.v. END, 15 − 100 mg/kg oral END or 30 mg/kg oral TAM. Plasma END concentrations were also measured in rats or dogs after oral dosing once per day for 4 consecutive days. Plasma samples were analyzed using a validated reverse-phase HPLC method with fluorescence detection. In the single-dose administration study, terminal elimination half-life and plasma clearance values in rats given 2 mg/kg i.v. END were 6.3 h and 2.4 L/h/kg, respectively. Plasma concentrations above 0.1 µM and 1 µM END were achieved with 20 mg/kg and 200 mg/kg doses, respectively, and those concentrations were maintained for longer than 24 h. Oral absorption of END was linear over the range of 20 − 140 mg/kg with a bioavailability greater than 67%. END exposure in rats following 80 mg/kg oral END was 100-fold greater than END exposure following 80-mg/kg oral TAM. Following 0.5 mg/kg i.v. END to dogs, terminal elimination half-life and plasma clearance values were 9.2 h and 0.4 L/h/kg, respectively. Plasma concentrations above 1 µM and 10 µM were achieved with the 15 mg/kg dose and 100 mg/kg, respectively, and those concentrations were maintained for longer than 24 h. Absorption was linear over the range of 15 − 100 mg/kg with a bioavailability greater than 50%. END exposure in dogs following 30 mg/kg oral END was 10-fold greater than END exposure following 30-mg/kg oral TAM. In the repeated-dose administration study, the day 4 END peak plasma concentration in rats increased from 1 to 9 µM as the daily END dose was increased from 20 to 200 mg/kg. The day 4 END peak plasma concentration in dogs exceeded 20 µM and plasma concentrations remained above 2 µM for 24 hours following 4 daily doses of 30 mg/kg END. Based on these data, we conclude that END has high oral bioavailability; high concentrations may be maintained after repeated dosing in dogs and rats; and substantially higher END concentrations are achievable following an oral dose of END in comparison to a similar dose of TAM. Supported by NCI contract N01-CM-52206. 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 2607.

Abstract 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 >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.

Abstract In collaboration with NCI, we are developing endoxifen (END), the active metabolite of tamoxifen (TAM), as a drug for the treatment of estrogen receptor positive breast cancer. Tamoxifen treated women with reduced or absent CYP2D6 enzyme activity have significantly lower END plasma concentrations. In a retrospective analysis of two different prospective tamoxifen trials (NCCTG and ABCSG), we have demonstrated that genetic or drug-induced reductions in CYP2D6 metabolism are associated with a higher risk of breast cancer recurrence in Tam treated ER positive breast cancer. To test the hypothesis that clinically relevant concentrations and exposures of END are achieved following oral administration of END, we characterized the pharmacokinetics of i.v. and oral END and oral TAM in female mice. Endoxifen was synthesized and provided by NCI/DTP. Plasma samples were analyzed using a validated reverse-phase HPLC method with fluorescence detection. Following i.v. administration of a 1 mg/kg dose, peak plasma concentration, terminal elimination half-life and plasma clearance values were 0.26 µM, 6.5 h and 11.8 L/h/kg, respectively. Oral pharmacokinetics and bioavailability were determined following doses of 50 and 200 mg/kg. Peak plasma concentrations of 0.76 µM were achieved with a 50 mg/kg dose and plasma concentrations above 0.1 µM were maintained for longer than 8 h. Peak plasma concentrations of 8 µM were achieved with a 200 mg/kg dose and plasma concentrations above 2 µM were maintained for 24 h. Bioavailability was 50% and greater than 100% following the 50 mg/kg and 200 mg/kg doses, respectively. Based on pharmacokinetic data for oral END and TAM normalized to a 50 mg/kg oral dose, END plasma concentrations and total exposure were 20-fold greater following oral END as compared to oral TAM. In conclusion, END has high oral bioavailability in mice and substantial plasma concentrations are achieved and maintained after a single oral END dose. Compared to an equivalent oral dose of Tam, substantially higher END concentrations are achieved following oral END. These data suggest that the primary administration of End may overcome the limitations related to human CYP2D6 metabolism, and support the ongoing development of endoxifen as a primary therapy for ER breast cancer. Supported by the Mayo Comprehensive Cancer Center Grant (CA15083) and the Mayo Clinic Breast Cancer SPORE (CA 116201; MMA, JMR, MPG). 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 3603.