Summary Tecarfarin is a vitamin K antagonist (VKA) with reduced propensity for drug interactions. To evaluate the pharmacokinetic (PK), pharmacodynamic (PD), and safety of tecarfarin, we performed single ascending dose (SAD) (n=66), multiple ascending dose (MAD) (n=43), and tecarfarin versus warfarin (n=28) studies in human volunteers. In the SAD, tecarfarin was administered to 5 of 6 subjects (1 received placebo) in each of 11 cohorts. AUC0-∞ exhibited linearity and dose proportionality. Elimination T1/2 ranged from 87–136 hours (h) across all doses. In the MAD, tecarfarin was administered to 5 of 6 volunteers in each of 7 cohorts. The starting dose was continued until the subject’s INR reached the target range (TR) of 1.7 to 2.0. Dosing was down-titrated if the TR was achieved. Elimination T1/2 ranged from 107–140 h. Doses <10 mg had insignificant effect on INR. Higher doses raised INRs and required down-titration to maintain the TR. Steady state INR dosing was 10–20 mg. INR declined promptly after discontinuation. In the comparative study, subjects received tecarfarin or warfarin and dose titrated to a TR of 1.5–2.0. Mean dose after TR was achieved was 13.9 mg (range 10.0–25.5 mg) for tecarfarin and 5.3 mg (range 2.5–9.0 mg) for warfarin. At similar INR levels, the concentration of coagulation factors II, VII, IX, and X were similar for tecarfarin and warfarin. Tecarfarin was tolerated well without serious adverse events in all three studies. Supplementary Material to this article is available online at www.thrombosis-online.com.

The absorption and disposition of the serotonin 5-HT(4) receptor agonist, naronapride (6-[(3S,4R)-4-(4-amino-5-chloro-2-methoxy-benzoylamino)-3-methoxy-piperidin-1-yl]-hexanoic acid 1-aza-bicyclo[2,2,2]oct-(R)-3-yl ester dihydrochloride; ATI-7505), were evaluated in healthy males given a single 120-mg oral dose of (14)C-labeled compound. Serial blood samples and complete urine and feces were collected up to 552 h postdose. Naronapride was extensively metabolized, undergoing rapid hydrolysis to 6-[(3S,4R)-4-(4-amino-5-chloro-2-methoxy-benzoylamino)-3-methoxy-piperidin-1-yl]-hexanoic acid (ATI-7500) with stoichiometric loss of quinuclidinol. ATI-7500 was either N-glucuronidated on the phenyl ring or its hexanoic acid side chain underwent two-carbon cleavage, probably through a β-oxidation metabolic pathway, to form 4-[(3S,4R)-4-(4-amino-5-chloro-2-methoxy-benzoylamino)-3-methoxy-piperidin-1-yl]-butanoic acid (ATI-7400). ATI-7400 underwent further side-chain oxidation to form 2-[(3S,4R)-4-(4-amino-5-chloro-2-methoxy-benzoylamino)-3-methoxy-piperidin-1-yl]-acetic acid (ATI-7100). Quinuclidinol, ATI-7500, ATI-7400, and ATI-7100 were the major metabolites, with plasma area under the curve values approximately 72-, 17-, 8-, and 2.6-fold that of naronapride. Naronapride, ATI-7500, ATI-7400, and ATI-7100 accounted for 32.32, 36.56, 16.28, and 1.58%, respectively, of the dose recovered in urine and feces. ATI-7400 was the most abundant radioactive urinary metabolite (7.77%), and ATI-7500 was the most abundant metabolite in feces (35.62%). Fecal excretion was the major route of elimination. Approximately 32% of the dose was excreted unchanged in feces. Naronapride, ATI-7500, and quinuclidinol reached peak plasma levels within 1 h postdose. Peak ATI-7400 and ATI-7100 concentrations were reached within 1.7 h, suggesting rapid ATI-7500 metabolism. Naronapride plasma terminal half-life was 5.36 h, and half-lives of the major metabolites ranged from 17.69 to 33.03 h. Naronapride plasma protein binding was 30 to 40%. The mean blood/plasma radioactivity ratio indicated minimal partitioning of (14)C into red blood cells.

ATI 9242 is a dibenzo(b,f)(1,4)oxazepine derivative designed with the goal of developing an oral drug that is effective for neuropsychiatric disorders with an improved side effect profile.The in vitro receptor profiling demonstrated that ATI 9242 has high affinity for 5‐HT2A and D2 receptor and submicromolar affinity for other dopamine (D1, D3, D4 and D5), serotonin (5‐HT1A, 5‐HT1B, 5‐HT1D, 5‐HT2B, 5‐HT2C, 5‐HT6 and 5‐HT7), histamine (H1) and alpha‐adrenergic (α1B and α2C) receptors.In cell‐based functional assays, ATI 9242 (10 μM) had no measurable agonist activity at dopamine (D1, D2S), histamine (H1), alpha‐adrenergic and serotonin (5‐HT2A, 5‐HT2B, 5‐HT2C, 5‐HT6 and 5‐HT7) receptors. At the 5‐HT1A receptor, ATI 9242 appeared to be a partial agonist (Ki=147 nM).ATI‐9242 prevented 5‐HT2A receptor‐mediated rat aortic ring contractions in a concentration‐dependent manner (ED50 = 3 nM), data consistent with the receptor binding results.In vivo, ATI 9242 exhibited an atypical antipsychotic‐like activity against apomorphine‐induced disruption of swimming in mice, but also in models of prepulse inhibition (PPI), without cataleptic effect (up to 30mg/kg IP), sedation (up to 10mg/kg IP), nor motor coordination impairment.Overall, the data presented herein indicate that ATI‐9242 is a novel atypical antipsychotic designed for multi‐target interactions with reduced side effects.

Tecarfarin is a novel vitamin K epoxide reductase (VKOR) inhibitor being developed for oral anticoagulation therapy for the prophylaxis and treatment of thromboembolic complications associated with atrial fibrillation and other coagulation disorders. It is metabolized to a single inactive metabolite, ATI‐5900, by human microsomal esterases, a CYP450‐independent pathway. We characterized the pharmacokinetics, tissue distribution, and mass balance of tecarfarin after IV and oral administration to Sprague‐Dawley rats. IV administration of tecarfarin was associated with a moderately rapid clearance and a low volume of distribution (Vss). Hydrolysis to ATI‐5900 was moderately fast, with Tmax of the metabolite occurring within 1 hour after that of the parent. Plasma exposure to the metabolite (AUClast) was approximately 30–50% that of the parent. Elimination half‐life (t1/2) of the parent ranged from 2.98 – 6.26 hr. Tecarfarin was well absorbed after oral administration, with oral bioavailability ranging from 80 – 90%. Following oral administration of 14C‐tecarfarin, most of the drug‐derived radioactivity was eliminated within 48 hrs, with 57% being eliminated in the feces, and 33% in the urine. In addition, tissue accumulation was low as most tissues had lower concentration of radioactivity than plasma. These results suggest that the metabolism of tecarfarin is dependent on various esterases in vivo.

The antithrombotic activity of tecarfarin, a novel orally active vitamin K epoxide reductase inhibitor, was assessed in canine and rabbit thrombosis models. In dogs, once-daily oral doses of 0.5mg/kg tecarfarin selectively reduced the levels of the vitamin K-dependent coagulation factors (factors II, VII, IX, and X) and prolonged the prothrombin time (PT). A 4 to 7day course of oral tecarfarin (0.05 - 0.5mg/kg) prolonged the PT by 3 to 5-fold and reduced thrombus formation in arterial and venous segments subjected to a combination of electrical injury and flow-limiting constriction. To compare the effects of tecarfarin with those of warfarin, rabbits were given once-daily oral doses of 1mg/kg tecarfarin, 1.5mg/kg warfarin, or saline for 2days. After verifying increases in the PT with tecarfarin and warfarin, blood loss from standardized ear incisions was measured to assess hemorrhagic potential. Then, after intravenous injection of (125)I-labeled rabbit fibrinogen, thrombosis was induced in an isolated jugular vein segment by a combination of balloon catheter-induced endothelial denudation and venous occlusion. Compared with the saline control, both tecarfarin and warfarin prolonged the PT, increased blood loss from the ear incisions, and attenuated thrombus formation. Thus, like warfarin, tecarfarin attenuates venous and arterial thrombus formation in animal models by reducing the levels of the vitamin K-dependent coagulation factors.

Tecarfarin is a novel compound being developed for oral anticoagulation therapy for the prophylaxis and treatment of thromboembolic complications associated with atrial fibrillation and other cardiac disorders. Like warfarin, tecarfarin inhibits vitamin K epoxide reductase and is equipotent to warfarin at inhibiting this enzyme. It is metabolized to a single inactive metabolite, ATI‐5900, by human esterases. We compared the biotransformation of tecarfarin in cryopreserved hepatocytes isolated from male rats, dogs and humans and assessed the formation of ATI‐5900. We also scanned for, but did not quantify, several potential Phase I and Phase II metabolites for which chemical standards were not available. In dog and human hepatocytes, metabolism of tecarfarin was much slower than in rat hepatocytes, with less than 20% converted to ATI‐5900 at the end of 6 hours. We did not detect the formation of Phase II metabolites in any of the hepatocyte preparations. These results were supported by experiments where tecarfarin was incubated with rat, dog and human liver microsomes. It is well known that the metabolism of warfarin is dependent on CYP2C9 which is associated with various polymorphisms and, as a consequence, variable elimination. In contrast, the metabolism of tecarfarin is dependent on the ubiquitous esterase enzyme superfamily and therefore, its elimination should be more predictable in vivo.

Background and purpose:Tecarfarin (ATI-5923) is a novel vitamin K epoxide reductase inhibitor that is metabolized by esterase (mainly human carboxylesterase 2) to a single major metabolite, ATI-5900, in rats, dogs and humans. Tecarfarin is not significantly metabolized by CYP450 enzymes. The objective of this study was to test and compare the efficacy of tecarfarin with that of warfarin, when administered either intravenously or once a day orally, to produce stable anticoagulation in beagle dogs.Experimental approach:Effects on coagulation were assessed by measuring the activity levels of Factor VII and Factor X and thromboplastin-induced coagulation times, reported as prothrombin time (PT).Key results:Continuous intravenous infusions and oral administration of tecarfarin and warfarin caused a dose-dependent decrease in activity of Factor VII and Factor X, and associated increase in PT. Intravenous fresh frozen canine plasma or subcutaneous vitamin K-1 treatment reversed the anticoagulant effects of orally administered tecarfarin. Consistent with the inhibitory effects of amiodarone on CYP2C9, co-administration of amiodarone significantly increased the anticoagulation effect of warfarin and plasma warfarin concentrations. In contrast, amiodarone had no effect on the anticoagulation induced by tecarfarin or tecarfarin plasma concentrations in this model.Conclusions and implications:Overall, the data presented herein indicate that tecarfarin, via a vitamin K-dependent mechanism, causes changes in key parameters of haemostasis in beagle dogs that are consistent with effective anticoagulation. Compared to warfarin it has a decreased potential to interact metabolically with drugs that inhibit CYP450 enzymes and, therefore, may offer an improved safety profile for patients.

ATI‐5923 is a novel oral anticoagulant and like warfarin, is a vitamin K epoxide reductase inhibitor. Unlike warfarin, which is metabolized by CYP2C9 and CYP3A4, ATI‐5923 is metabolized by carboxylesterases. These studies compared the efficacy of ATI‐5923 to that of warfarin, when administered either intravenously (IV) or once a day orally, to produce stable anticoagulation in beagle dogs. The drug‐drug interaction potential was assessed using co‐administration with amiodarone, an inhibitor of CYP3A4 and CYP2C9, with either ATI‐5923 or warfarin. Effects on coagulation were assessed by measuring Factor VII and X levels and prothrombin times (PT). Continuous IV infusions and oral administration of ATI‐5923 or warfarin caused a dose‐dependent decrease in plasma concentrations of Factor VII and Factor X, and an associated increase in PT. On a dose basis, ATI‐5923 was a more potent anticoagulant than warfarin. Intravenous fresh frozen canine plasma or subcutaneous vitamin K1 treatment reversed the anticoagulant effects of orally‐administered ATI‐5923 in beagle dogs. Co‐administration of amiodarone (40mg/kg for 2 days, 20mg/kg for 6 days) significantly increased the plasma levels and anticoagulation effect of warfarin (0.25mg/kg) in beagle dogs, as measured by an increase in PT and decrease in factor VII and X. In contrast, amiodarone had no effect on the anticoagulation parameters and plasma levels of ATI‐5923 (0.3mg/kg). We conclude that ATI‐5923, via a vitamin K‐dependent mechanism, causes changes in key parameters of hemostasis in beagle dogs that are consistent with effective anticoagulation without the important drug‐drug interaction commonly observed with amiodarone in warfarin‐treated patients.

(S)-Warfarin, the most active enantiomer of warfarin, is metabolized by CYP2C9. Genetic variations of the CYP2C9 gene result in slower metabolism and are major contributors to inter-patient dose variability with resultant INR instability, especially in patients on multiple medications. This leads to higher hemorrhagic and thrombotic complications. ATI-5923 (ARYx therapeutics Inc.) is a novel VKOR inhibitor that undergoes metabolism by human carboxyles-terase and not by CYP2C9. We hypothesize that time in therapeutic range (TTR) based on Rosendaal method is better for ATI-5923 than for historic warfarin and that maintenance dose is independent of CYP2C9 polymorphism, but dependent on VKOR haplotype. This was a multi-center, open-label, 3 month study of 66 patients with AF treated with ATI-5923. All except two patients were on prior warfarin. Periodic INR testing occurred twice weekly for the first 3 weeks and then weekly during the maintenance phase. Genetic testing for the CYP2C9 and VKORC1 polymorphism was performed on all patients. Drug dosing was performed using a standardized nomogram. Pre-study INRs and warfarin dose data were collected for up to one year prior to study entry. 77 % of patients were in therapeutic range (INR 2–3) after 7 days and 80% had stable INR (3 consecutive INR values within range without dose adjustment) by 3 months. For the maintenance phase the mean TTR was 71.5 and 59.3% for ATI-5923 and warfarin respectively (12.2% improvement; p=0.0009). Patients with the VKOR AA haplotype required lower maintenance doses than VKOR GA or GG haplotype (8.6 vs 15.8 and 18.7mg; p < 0.0001). CYP2C9 genotype had no influence on maintenance dose. CYP2C9 variants (n=20), showed a trend toward better control compared to warfarin; 16% improvement vs. 11% for wild type CYP2C9 (n =42). ATI-5923 has better INR control than prior warfarin therapy. VKOR AA patients require a significantly lower maintenance dose. CYP2C9 variants show a trend to added improvement compared to the CYP2C9 wild type, suggesting that, unlike warfarin, ATI-5923 is not influenced by CYP2C9 genetic variations.

Warfarin (WARF) is a Vitamin K epoxide reductase (VKOR) inhibitor and oral anticoagulant widely used for prevention and/or treatment of stroke associated with atrial fibrillation. In spite of proven efficacy, WARF therapy is limited by numerous drug-drug interactions (DDIs). Of these, many involve inhibition of it’s cytochrome P450 (CYP) mediated metabolism, leading to increased drug exposure and risk of bleeding. ATI-5923 was created with the goal of producing a VKOR inhibitor that was non-oxidatively hydrolyzed by esterases to an inactive metabolite (ATI-5900) and thereby reduced likelihood of DDIs and maintain the benefits of WARF. We hypothesized that, unlike warfarin the pharmacokinetics (PK) of ATI-5923 is not subject to DDI with the CYP 2C9/3A4 inhibitor fluconazole (FCZ). Two groups (n=10/group) of healthy volunteers were randomized to receive a single equipotent oral doses of either WARF (17.5 mg) or ATI-5923 (50 mg). ATI-5923, ATI-5900, R-WARF and S-WARF concentrations were measured in serial plasma samples collected over a 7 day period and the PK parameters (AUC, C max , T max and T1/2) were determined. On day 7, subjects were given FCZ (400 mg/day) for 14 days and on day 21, subjects received a second dose of either WARF or ATI-5923 and FCZ was continued for 7 days and the PK study was repeated. Exposure (AUC)for WARF were dramatically increased by FCZ treatment, with the effects being more pronounced on the more active S-isomer: The AUC inf for S-WARF was increased more than 3 fold while this parameter was increased 2 fold for R-warf. Increased exposure appeared to result from reduced clearance: The T 1/2 increased from 48 to 104.3 hrs (R-warf) and from 31 to 87.9 hrs (S-warf). No significant effects of FCZ treatment on ATI-5923 or ATI-5900 exposures or clearance were observed. The dramatic effect of the CYP2C9/3A4 inhibitor FCZ on WARF exposure is consistent with the known CYP-mediated clearance of this drug. In the clinical setting, a corresponding increase in WARF exposures would be expected to increase anticoagulant effects and raise the risk of bleeding. In contrast, ATI-5923 which undergoes non-CYP mediated metabolism, is unaffected by FCZ treatment.