Brain penetration of WEB 2086 (Apafant) and dantrolene in Mdr1a (P-glycoprotein) and Bcrp knockout rats.

Transporter gene knockout rat models are attracting increasing interest for mechanistic studies of new drugs as transporter substrates or inhibitors in vivo. However, limited data are available on the functional validity of such models at the blood-brain barrier. Therefore, the present study evaluated Mdr1a [P-glycoprotein (P-gp)], Bcrp, and combined Mdr1a/Bcrp knockout rat strains for the influence of P-gp and breast cancer resistance protein (BCRP) transport proteins on brain penetration of the selective test substrates [(14)C]WEB 2086 (3-[4-(2-chlorophenyl)-9-methyl-6H-thieno[3,2-f][1,2,4]triazolo-[4,3-a][1,4]-diazepin-2-yl]-1-(4-morpholinyl)-1-propanon) for P-gp and dantrolene for BCRP. Brain-to-plasma concentration ratios (BPR) were measured after intravenous coinfusions of 5.5 µmol/kg per hour [(14)C]WEB 2086 and 2 µmol/kg per hour dantrolene for 2 hours in groups of knockout or wild-type rats. Compared with wild-type controls, mean BPR of [(14)C]WEB 2086 increased 8-fold in Mdr1a knockouts, 9.5-fold in double Mdr1a/Bcrp knockouts, and 7.3-fold in zosuquidar-treated wild-type rats, but was unchanged in Bcrp knockout rats. Mean BPR of dantrolene increased 3.3-fold in Bcrp knockouts and 3.9-fold in double Mdr1a/Bcrp knockouts compared with wild type, but was unchanged in the Mdr1a knockouts. The human intestinal CaCo-2 cell bidirectional transport system in vitro confirmed the in vivo finding that [(14)C]WEB 2086 is a substrate of P-gp but not of BCRP. Therefore, Mdr1a, Bcrp, and combined Mdr1a/Bcrp knockout rats provide functional absence of these efflux transporters at the blood-brain barrier and are a suitable model for mechanistic studies on the brain penetration of drug candidates.

Pharmacokinetics and pharmacodynamics of terbogrel, a combined thromboxane A2 receptor and synthase inhibitor, in healthy subjects.

AIMS: To characterize the pharmacokinetics of terbogrel, a new combined thromboxane A2 (TxA2) receptor and synthase inhibitor, in healthy human subjects after single or multiple oral administration. METHODS: Forty-eight healthy male subjects received a single oral dose (10, 25, 50, 100, 150 or 200 mg) of terbogrel or placebo and 32 different subjects received one of the following treatments twice daily for 7 days: 50, 100 or 150 mg terbogrel, placebo, or once-a-day 330 mg acetylsalicylic acid. RESULTS: Terbogrel was well tolerated without obvious adverse effects following either a single oral dose or administration over 7 days. Plasma drug concentrations were dose-linear and there was no accumulation over 7 days. There was a dose-dependent blockade of TxA2 receptors and of inhibition of thromboxane synthase activity with values for IC50 of 12 ng ml(-1) and 6.7 ng ml(-1), respectively. At the highest dose tested (150 mg) there was almost complete inhibition of thomboxane synthase and thromboxane receptor occupancy. Even at trough concentrations, receptor occupancy remained above 80% and thromboxane synthase was still completely inhibited. These two activities were associated with a dose-dependent inhibition of platelet aggregation (>80% at the 150 mg dose of terbogrel) and enhanced prostacyclin production. CONCLUSIONS: Terbogrel is a potent agent having two distinct, complimentary pharmacodynamic actions, namely inhibition of thromboxane synthase and antagonism of the TxA2 receptor. The antithrombotic effect of terbogrel was dose-dependent and was associated with enhanced prostacyclin production. Terbogrel is an attractive candidate for long-term antithrombotic therapy.

A Phase I dose-escalation study of sibrotuzumab in patients with advanced or metastatic fibroblast activation protein-positive cancer.

PURPOSE: The purpose of this research was to determine the safety, immunogenicity, pharmacokinetics, biodistribution, and tumor uptake of repeat infusions of a complementarity-determining region grafted humanized antibody (sibrotuzumab) directed against human fibroblast activation protein (FAP). EXPERIMENTAL DESIGN: A Phase I open-label dose escalation study was conducted in patients with cancers epidemiologically known to be FAP positive. Patients were entered into one of four dosage tiers of 5, 10, 25, or 50 mg/m(2) sibrotuzumab, administered weekly for 12 weeks, with trace labeling with 8-10 mCi of (131)I in weeks 1, 5, and 9. RESULTS: A total of 26 patients were entered into the trial (15 males and 11 females; mean age, 59.9 years; age range, 41-81 years). Twenty patients had colorectal carcinoma, and 6 patients had non-small cell lung cancer. A total of 218 infusions of sibrotuzumab were administered during the first 12 weeks of the study, with 24 patients being evaluable. One patient received an additional 96 infusions on continued-use phase for a total of 108 infusions over a 2-year period, and 1 patient received an additional 6 infusions on continued use. There were no objective tumor responses. Only one episode of dose-limiting toxicity was observed. Therefore, a maximum tolerated dose was not reached. Treatment-related adverse events were observed in 6 patients during the infusional monitoring period. Four of the 6 patients, 3 of whom had associated positive serum human antihuman antibody, were removed from the study because of clinical immune responses. Gamma camera images of [(131)I]sibrotuzumab demonstrated no normal organ uptake of sibrotuzumab, with tumor uptake evident within 24-48 h after infusion. Analysis of pharmacokinetics demonstrated a similar mean terminal t(1/2) of 1.4-2.6 days at the 5, 10, and 25 mg/m(2) dose levels, and with a longer mean t(1/2) of 4.9 days at the 50 mg/m(2) dose level. CONCLUSION: Repeat infusions of the humanized anti-FAP antibody sibrotuzumab can be administered safely to patients with advanced FAP-positive cancer.

Pharmacokinetics and pharmacodynamics of tenecteplase in fibrinolytic therapy of acute myocardial infarction.

Tenecteplase is a novel fibrinolytic protein bioengineered from human tissue plasminogen activator (alteplase) for the therapy of acute ST-segment elevation myocardial infarction. Specific mutations at three sites in the alteplase molecule result in 15-fold higher fibrin specificity, 80-fold reduced binding affinity to the physiological plasminogen activator inhibitor PAI-1 and 6-fold prolonged plasma half-life (22 vs 3.5 minutes). Consequently, tenecteplase can be administered as a single intravenous bolus of 30-50mg (0.53 mg/kg bodyweight) over 5-10 seconds, in contrast to the 90-minute accelerated infusion regimen of alteplase. Tenecteplase plasma concentration-time profiles have been obtained from a total of 179 patients with acute myocardial infarction. Tenecteplase exhibited biphasic disposition; the initial disposition phase was predominant with a mean half-life of 17-24 minutes, and the mean terminal half-life was 65-132 min. Over the clinically relevant dose range of 30-50mg, mean clearance (CL) was 105 ml/min. The mean initial volume of distribution V(1) was 4.2-6.3L, approximating plasma volume, and volume of distribution at steady state was 6.1-9.9L, suggesting limited extravascular distribution or binding. Bodyweight and age were found to influence significantly both CL and V(1). Total bodyweight explained 19% of the variability in CL and 11% of the variability in V(1), and a 10kg increase in total bodyweight resulted in a 9.6 ml/min increase in CL. This relationship aided the development of a rationale for the weight-adjusted dose regimen for tenecteplase. Age explained only a further 11% of the variability in CL. The percentage of patients who achieved normal coronary blood flow was clearly related to AUC. More than 75% of patients achieved normal flow at 90 minutes after administration when their partial AUC(2-90) exceeded 320 microg.min/ml, corresponding to an average plasma concentration of 3.6 microg/ml. Systemic exposure to tenecteplase at all times after bolus administration of 30-50mg was higher than for alteplase 100mg. Tenecteplase has demonstrated equivalent efficacy and improved safety compared with the current gold standard alteplase in a large mortality trial (ASSENT-2). This suggests that the reduced clearance, greater fibrin specificity and higher PAI-1 resistance of tenecteplase allow higher plasma concentrations and thus a more rapid restoration of coronary patency to be attained, while providing a reduction in major non-cerebral bleeding events.