PAR4 (Protease-Activated Receptor 4) Antagonism With BMS-986120 Inhibits Human Ex Vivo Thrombus Formation.

OBJECTIVE: BMS-986120 is a novel first-in-class oral PAR4 (protease-activated receptor 4) antagonist with potent and selective antiplatelet effects. We sought to determine for the first time, the effect of BMS-986120 on human ex vivo thrombus formation. APPROACH AND RESULTS: Forty healthy volunteers completed a phase 1 parallel-group PROBE trial (Prospective Randomized Open-Label Blinded End Point). Ex vivo platelet activation, platelet aggregation, and thrombus formation were measured at 0, 2, and 24 hours after (1) oral BMS-986120 (60 mg) or (2) oral aspirin (600 mg) followed at 18 hours with oral aspirin (600 mg) and oral clopidogrel (600 mg). BMS-986120 demonstrated highly selective and reversible inhibition of PAR4 agonist peptide (100 µM)-stimulated P-selectin expression, platelet-monocyte aggregates, and platelet aggregation (P<0.001 for all). Compared with pretreatment, total thrombus area (µm2/mm) at high shear was reduced by 29.2% (95% confidence interval, 18.3%-38.7%; P<0.001) at 2 hours and by 21.4% (9.3%-32.0%; P=0.002) at 24 hours. Reductions in thrombus formation were driven by a decrease in platelet-rich thrombus deposition: 34.8% (19.3%-47.3%; P<0.001) at 2 hours and 23.3% (5.1%-38.0%; P=0.016) at 24 hours. In contrast to aspirin alone, or in combination with clopidogrel, BMS-986120 had no effect on thrombus formation at low shear (P=nonsignificant). BMS-986120 administration was not associated with an increase in coagulation times or serious adverse events. CONCLUSIONS: BMS-986120 is a highly selective and reversible oral PAR4 antagonist that substantially reduces platelet-rich thrombus formation under conditions of high shear stress. Our results suggest PAR4 antagonism has major potential as a therapeutic antiplatelet strategy. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT02439190.

First-in-human study of milvexian, an oral, direct, small molecule factor XIa inhibitor.

Milvexian (BMS-986177/JNJ-70033093) is a small molecule, active-site inhibitor of factor XIa (FXIa) being developed to prevent and treat thrombotic events. The safety, tolerability, pharmacokinetics (PKs), and pharmacodynamics (PDs) of milvexian were assessed in a two-part, double-blind, placebo-controlled, sequential single ascending dose (SAD) and multiple ascending dose (MAD) study in healthy adults. Participants in SAD panels (6 panels of 8 participants; n = 48) were randomized (3:1) to receive milvexian (4, 20, 60, 200, 300, or 500 mg) or placebo. The 200- and 500-mg panels investigated the pharmacokinetic impact of a high-fat meal. Participants in MAD panels (7 panels of 8 participants; n = 56) were randomized (3:1) to receive milvexian (once- or twice-daily) or placebo for 14 days. All milvexian dosing regimens were safe and well-tolerated, with only mild treatment-emergent adverse events and no clinically significant bleeding events. In SAD panels, maximum milvexian plasma concentration occurred 3 h postdose in all fasted panels. The terminal half-life (T1/2 ) ranged from 8.3 to 13.8 h. In fasted panels from 20 to 200 mg, absorption was dose-proportional; results at higher doses (300 and 500 mg) were consistent with saturable absorption. Food increased milvexian bioavailability in a dose-dependent fashion. In MAD panels, steady-state milvexian plasma concentration was reached within 3 and 6 dosing days with once- and twice-daily dosing, respectively. Renal excretion was less than 20% in all panels. Prolongation of activated partial thromboplastin time was observed and was directly related to drug exposure. These results suggest that the safety, tolerability, PK, and PD properties of milvexian are suitable for further clinical development.

Enhancement of in vitro and in vivo tumor cell radiosensitivity by the DNA methylation inhibitor zebularine.

Aberrant DNA hypermethylation is a frequent finding in tumor cells, which has suggested that inhibition of DNA methylation may be an effective cancer treatment strategy. Because DNA methylation affects gene expression and chromatin structure, parameters considered to influence radioresponse, we investigated the effects of the DNA methylation inhibitor zebularine on the radiosensitivity of human tumor cells. Three human tumor cell lines were used in this study (MiaPaCa, DU145, and U251) and the methylation status of three genes frequently hypermethylated in tumor cells (RASSF1A, HIC-1, and 14-3-3sigma) was determined as a function of zebularine exposure. Zebularine resulted in DNA demethylation in a time-dependent manner, with the maximum loss of methylation detected by 48 hours. Treatment of cells with zebularine for 48 hours also resulted in an increase in radiosensitivity with dose enhancement factors of >1.5. As a measure of radiation-induced DNA damage, gammaH2AX expression was determined. Whereas zebularine had no effect on radiation-induced gammaH2AX foci at 1 hour, the number of gammaH2AX foci per cell was significantly greater in the zebularine-treated cells at 24 hours after irradiation, suggesting the presence of unrepaired DNA damage. Zebularine administration to mice reactivated gene expression in U251 xenografts; irradiation of U251 tumors in mice treated with zebularine resulted in an increase in radiation-induced tumor growth delay. These results indicate that zebularine can enhance tumor cell radiosensitivity in vitro and in vivo and suggest that this effect may involve an inhibition of DNA repair.

Gleevec-mediated inhibition of Rad51 expression and enhancement of tumor cell radiosensitivity.

Rad51 is an essential component of the homologous DNA repair pathway and has been implicated as a determinant of cellular radiosensitivity. Gleevec is a relatively specific inhibitor of c-Abl, a tyrosine kinase that can play a role in the regulation Rad51. The aim of this study was to determine the effects of Gleevec on Rad51 levels and the radiosensitivity of two human glioma cell lines and a nonimmortalized normal human fibroblast cell line. Exposure of both glioma cell lines to radiation resulted in an increase in Rad51 expression; Gleevec treatment alone reduced Rad51 expression. When glioma cells were pretreated with Gleevec, radiation-induced Rad51 expression and nuclear foci formation were reduced. Accordingly, pretreatment of the glioma cells with Gleevec resulted in an enhancement in their radiosensitivity. These data indicate that Gleevec enhances radiation-induced tumor cell killing and suggest that the mechanism involves the reduction in Rad51 levels. In contrast to the glioma cell lines, radiation or Gleevec treatments had no effect on Rad51 expression or foci formation in the normal fibroblast cells. Consistent with these observations, Gleevec did not modify the radiosensitivity of the normal cell line. These results suggest that Rad51 expression is subject to different regulatory processes in the glioma and normal cell lines and further suggest that Rad51 may be an appropriate target for selectively enhancing the radiosensitivity of brain tumor cells.

Enhanced radiation-induced cell killing and prolongation of gammaH2AX foci expression by the histone deacetylase inhibitor MS-275.

Histone deacetylase (HDAC) inhibitors are undergoing clinical evaluation for cancer therapy. Because HDAC modulates chromatin structure and gene expression, parameters considered to influence radioresponse, we have investigated the effects of the HDAC inhibitor MS-275 on the radiosensitivity of two human tumor cell lines (DU145 prostate carcinoma and U251 glioma). Acetylation status of histones H3 and H4 was determined as a function of time after MS-275 addition to and removal from culture medium. Histone acetylation increased by 6 h after MS-275 addition, reaching a maximum between 24 and 48 h of exposure; providing fresh drug-free medium then resulted in a decrease in histone acetylation that began by 6 h and approached untreated levels by 16 h. Treatment of cells with MS-275 for 48 h followed by irradiation had little or no effect on radiation-induced cell death. However, exposure to MS-275 before and after irradiation resulted in an increase in radiosensitivity with dose enhancement factors of 1.9 and 1.3 for DU145 and U251 cells, respectively. This MS-275 treatment protocol did not result in a redistribution of the cells into a more radiosensitive phase of the cell cycle or in an increase in apoptosis. However, MS-275 did modify the time course of gammaH2AX expression in irradiated cells. Whereas there was no significant difference in radiation-induced gammaH2AX foci at 6 h, the number of cells expressing gammaH2AX foci was significantly greater in the MS-275-treated cells at 24 h after irradiation. These results indicate that MS-275 can enhance radiosensitivity and suggest that this effect may involve an inhibition of DNA repair.

Enhanced tumor cell radiosensitivity and abrogation of G2 and S phase arrest by the Hsp90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin.

PURPOSE: Because of the potential for affecting multiple signaling pathways, inhibition of Hsp90 may provide a strategy for enhancing tumor cell radiosensitivity. Therefore, we have investigated the effects of the orally bioavailable Hsp90 inhibitor 17-(dimethylaminoethylamino)-17-demethoxygeldanamycin (17-DMAG) on the radiosensitivity of human tumor cells in vitro and grown as tumor xenografts. EXPERIMENTAL DESIGN: The effect of 17-DMAG on the levels of three proteins (Raf-1, ErbB2, and Akt) previously implicated in the regulation of radiosensitivity was determined in three human solid tumor cell lines. A clonogenic assay was then used to evaluate cell survival after exposure to 17-DMAG followed by irradiation. For mechanistic insight, the G(2)- and S-phase checkpoints were evaluated in 17-DMAG-treated cells. Finally, the effect of in vivo administration of 17-DMAG in combination with radiation on the growth rate of xenograft tumors was determined. RESULTS: 17-DMAG exposure reduced the levels of the three radiosensitivity-associated proteins in a cell line-specific manner with ErbB2 being the most susceptible. Corresponding concentrations of 17-DMAG enhanced the radiosensitivity of each of the tumor cell lines. This sensitization seemed to be the result of a 17-DMAG-mediated abrogation of the G(2)- and S-phase cell cycle checkpoints. The oral administration of 17-DMAG to mice bearing tumor xenografts followed by irradiation resulted in a greater than additive increase in tumor growth delay. CONCLUSIONS: These data indicate that 17-DMAG enhances the in vitro and in vivo radiosensitivity of human tumor cells. The mechanism responsible seems to involve the abrogation of radiation-induced G(2)- and S-phase arrest.

Flavopiridol enhances human tumor cell radiosensitivity and prolongs expression of gammaH2AX foci.

Flavopiridol is a cyclin-dependent kinase (CDK) inhibitor, which has recently entered clinical trials. However, when administered as a single agent against solid tumors, the antitumor actions of flavopiridol have been primarily cytostatic. Given its reported effects on cell cycle regulation, transcription, and apoptosis, flavopiridol may also influence cellular radioresponse. Thus, to evaluate the potential for combining this cyclin-dependent kinase inhibitor with radiation as a cancer treatment strategy, we have investigated the effects of flavopiridol on the radiation sensitivity of two human prostate cancer cell lines (DU145 and PC3). The data presented here indicate that exposure to flavopiridol (60-90 nM) after irradiation enhanced the radiosensitivity of both DU145 and PC3 cells. This sensitization occurred in the absence of significant reductions in cell proliferation, retinoblastoma protein phosphorylation, or P-TEFb activity. Moreover, the post-irradiation addition of flavopiridol had no effect on radiation-induced apoptosis or the activation of the G2 cell cycle checkpoint. However, flavopiridol did modify the time course of gammaH2AX expression in irradiated cells. Whereas there was no significant difference in radiation-induced gammaH2AX foci at 6 h, at 24 h after irradiation, the number of cells expressing gammaH2AX foci was significantly greater in the flavopiridol-treated cells. These results indicate that flavopiridol can enhance radiosensitivity of human tumor cells and suggest that this effect may involve an inhibition of DNA repair.

Transcriptional signature of flavopiridol-induced tumor cell death.

Flavopiridol has been shown to inhibit the proliferation of a variety of human tumor cells and is currently undergoing clinical evaluation in cancer treatment. Although the antiproliferative effect of flavopiridol has been attributed to the inhibition of cyclin-dependent kinases 2 and 4, recent reports indicate that the mechanism responsible for the cell death induced by this agent is more complex. To provide insight into the molecular processes mediating flavopiridol-induced cytotoxicity and to investigate the availability of markers indicative of its activity, we have applied cDNA microarray technology. Gene expression profiles were determined for four human tumor cell lines (prostate carcinomas PC3 and DU145 and gliomas SF359 and U251) following exposure to selected concentrations of flavopiridol. Treatment of these cell lines with a concentration of flavopiridol sufficient to reduce survival to 10% resulted in the identification of a set of 209 genes, the expression of which were altered in each of the cell lines. This common set of 209 gene expression changes suggested that flavopiridol-induced cell death can be defined in terms of a specific transcriptome. The flavopiridol death transcriptome consisted primarily of down-regulated genes; however, there were also a significant number of genes with increased expression. Whereas causal relationships were not established, these data suggest molecular events/processes that may be associated with flavopiridol-induced tumor cell death. Moreover, the identification of a set of gene expression changes in four human tumor cell lines suggests that such a transcriptome may be applicable to investigations of flavopiridol pharmacodynamics.

Liver-to-plasma vaniprevir (MK-7009) concentration ratios in HCV-infected patients.

BACKGROUND: Some drugs that are actively taken up into the liver exhibit greater than dose proportional increases in plasma exposure, although human liver-to-plasma concentration ratios have rarely been evaluated. Understanding these relationships has implications for drug concentrations at the target site for certain classes of compounds, such as direct-acting antivirals, targeted towards HCV. METHODS: Treatment-experienced, chronic HCV non-cirrhotic patients (n=3) received vaniprevir (600 mg or 300 mg twice daily) on days 1-3 and (600 mg or 300 mg single dose) on day 4. Core needle biopsy was performed at 6 or 12 h post-dose on day 4. Blood samples were collected pre-dose on days 1 and 4, and for 24 h post-dose on day 4. The primary study objective was the hepatic concentration of vaniprevir at 6 and 12 h post-dose. RESULTS: Vaniprevir plasma pharmacokinetic parameters increased in a greater than dose-proportional manner between the 300 mg and 600 mg doses, with approximately fivefold increases in AUC0-12 and Cmax associated with a twofold increase in dose (AUC0-12, 10.6 µM/h to 59.5 µM/h; Cmax, 2.60 µM to 13.5 µM). In the 300 mg and 600 mg dose groups, mean liver concentrations of vaniprevir were 84.6 µM and 169 µM at 6 h post-dose, and 29.4 µM and 53.7 µM at 12 h post-dose. Liver concentrations were higher than plasma with liver-to-plasma concentration ratios of approximately 20-280. CONCLUSIONS: These data confirm higher vaniprevir concentrations in human liver compared with plasma and demonstrate that measurement of human liver drug concentration using needle biopsy is feasible.

The effects of simvastatin on the pharmacokinectics of sitagliptin.

BACKGROUND: Treatment with the combination of sitagliptin (a dipeptidyl peptidase 4 inhibitor which improves glycemic control) and simvastatin (a well characterized lipid-lowering agent) may be considered an appropriate approach to management of type 2 diabetes and its associated increased risk of cardiovascular disease. OBJECTIVE: An investigation of the effects of simvastatin on the pharmacokinetics of sitagliptin was conducted. METHODS: Ten healthy men and women were enrolled into an open-label, randomized, 2-period, crossover study. Pharmacokinetics of sitagliptin were measured after a single dose of sitagliptin 100-mg alone, and after a single dose of sitagliptin 100-mg administered on Day 5 of a 7 day course of simvastatin 80-mg once daily. RESULTS: The geometric mean ratio of (sitagliptin + simvastatin) / sitagliptin and corresponding 90% confidence interval for sitagliptin AUC0-∞ and Cmax were 1.01 (0.97, 1.05), and 1.12 (1.00, 1.26), respectively. CONCLUSIONS: Simvastatin has no clinically important effect on sitagliptin pharmacokinetics. No dose adjustment for either sitagliptin or simvastatin is recommended when these drugs are coadministered.

Enhancement of in vitro and in vivo tumor cell radiosensitivity by valproic acid.

Valproic acid (VA) is a well-tolerated drug used to treat seizure disorders and has recently been shown to inhibit histone deacetylase (HDAC). Because HDAC modulates chromatin structure and gene expression, parameters considered to influence radioresponse, we investigated the effects of VA on the radiosensitivity of human brain tumor cells grown in vitro and in vivo. The human brain tumor cell lines SF539 and U251 were used in our study. Histone hyperacetylation served as an indicator of HDAC inhibition. The effects of VA on tumor cell radiosensitivity in vitro were assessed using a clonogenic survival assay and gammaH2AX expression was determined as a measure of radiation-induced DNA double strand breaks. The effect of VA on the in vivo radioresponse of brain tumor cells was evaluated according to tumor growth delay analysis carried out on U251 xenografts. Irradiation at the time of maximum VA-induced histone hyperacetylation resulted in significant increases in the radiosensitivity of both SF539 and U251 cells. The radiosensitization was accompanied by a prolonged expression of gammaH2AX. VA administration to mice resulted in a clearly detectable level of histone hyperacetylation in U251 xenografts. Irradiation of U251 tumors in mice treated with VA resulted in an increase in radiation-induced tumor growth delay. Valproic acid enhanced the radiosensitivity of both SF539 and U251 cell lines in vitro and U251 xenografts in vivo, which correlated with the induction of histone hyperacetylation. Moreover, the VA-mediated increase in radiation-induced cell killing seemed to involve the inhibition of DNA DSB repair.