From adaptive licensing to adaptive pathways: delivering a flexible life-span approach to bring new drugs to patients.

The concept of adaptive licensing (AL) has met with considerable interest. Yet some remain skeptical about its feasibility. Others argue that the focus and name of AL should be broadened. Against this background of ongoing debate, we examine the environmental changes that will likely make adaptive pathways the preferred approach in the future. The key drivers include: growing patient demand for timely access to promising therapies, emerging science leading to fragmentation of treatment populations, rising payer influence on product accessibility, and pressure on pharma/investors to ensure sustainability of drug development. We also discuss a number of environmental changes that will enable an adaptive paradigm. A life-span approach to bringing innovation to patients is expected to help address the perceived access vs. evidence trade-off, help de-risk drug development, and lead to better outcomes for patients.

Systemic thrombin inhibition by Hirulog does not alter medial smooth muscle cell proliferation and inflammatory activation after vascular injury in the rabbit.

The study evaluated the role of thrombin in activation of vascular smooth muscle cells early after vascular injury. The direct thrombin inhibitor Hirulog (10 mg/kg SQ tid) or vehicle was administered to rabbits over 3 days following balloon injury to the abdominal aorta and the right iliac artery. Hirulog treatment yielded marked systemic anticoagulation as evidenced by an about 3.5-fold prolongation of quantitative thrombin time one hour after an injection, but with a reduction to almost baseline levels at the end of the dosing interval. After 3 days, proliferating cells in the right iliac artery were enumerated. The expression of intercellular adhesion molecule 1, macrophage-colony stimulating factor, tumor necrosis factor alpha, and interleukin-1beta as markers for inflammatory activation of the vessel wall was examined by immunohistochemistry and graded semiquantitatively. Mitotic indices did not differ between control and Hirulog-treated animals. There was also no difference in the expression of markers of inflammatory activation between both groups. In conclusion, thrombin inhibition by Hirulog administration does not reduce acutely (within 3 days) vascular smooth muscle cell proliferation or inflammatory activation after angioplasty. Thrombin inhibitors may therefore limit restenosis in the rabbit by acting later or via other, unknown pathways. The lack of effect of the thrombin inhibitor on the cellular events during the early phase of the response to balloon injury may explain the failure of such strategies to reduce restenosis in recent clinical trials despite effects towards acute thrombotic complications. Together, these results suggest that acute thrombin generation is not a crucial stimulus for early smooth muscle cell proliferation and inflammatory activation after vascular injury.

Randomized, double-blind comparison of hirulog versus heparin in patients receiving streptokinase and aspirin for acute myocardial infarction (HERO). Hirulog Early Reperfusion/Occlusion (HERO) Trial Investigators.

BACKGROUND: Thrombolytic therapy improves survival after myocardial infarction through reperfusion of the infarct-related artery. Thrombin generated during thrombolytic administration may reduce the efficacy of thrombolysis. A direct thrombin inhibitor may improve early patency rates. METHODS AND RESULTS: Four hundred twelve patients presenting within 12 hours with ST-segment elevation were given aspirin and streptokinase and randomized in a double-blind manner to receive up to 60 hours of either heparin (5000 U bolus followed by 1000 to 1200 U/h), low-dose hirulog (0.125 mg/kg bolus followed by 0.25 mg x kg(-1) x h(-1) for 12 hours then 0.125 mg x kg(-1) x h(-1)), or high-dose hirulog (0.25 mg/kg bolus followed by 0.5 mg x kg(-1) x h(-1) for 12 hours then 0.25 mg x kg(-1) x h(-1)). The primary outcome was Thrombolysis In Myocardial Infarction trial (TIMI) grade 3 flow of the infarct-related artery at 90 to 120 minutes. TIMI 3 flow was 35% (95% CI, 28% to 44%) with heparin, 46% (95% CI, 38% to 55%) with low-dose hirulog, and 48% (95% CI, 40% to 57%) with high-dose hirulog (heparin versus hirulog, P=.023; heparin versus high-dose hirulog, P=.03). At 48 hours, reocclusion had occurred in 7% of heparin, 5% of low-dose hirulog, and 1% of high-dose hirulog patients (P=NS). By 35 days, death, cardiogenic shock, or reinfarction had occurred in 25 heparin (17.9%), 19 low-dose hirulog (14%), and 17 high-dose hirulog patients (12.5%) (P=NS). Two strokes occurred with heparin, none with low-dose hirulog, and two with high-dose hirulog. Major bleeding (40% from the groin site) occurred in 28% of heparin, 14% of low-dose hirulog, and 19% of high-dose hirulog patients (heparin versus low-dose hirulog, P<.01). CONCLUSIONS: Hirulog was more effective than heparin in producing early patency in patients treated with aspirin and streptokinase without increasing the risk of major bleeding. Direct thrombin inhibition may improve clinical outcome.

Inhibition by hirulog-1 of generation of plasminogen activator inhibitor-1 from vascular smooth-muscle cells induced by thrombin.

Hirulog-1 effectively prevents thrombosis in coronary artery disease and is associated with a low incidence of bleeding complications. Our study characterized the effect of Hirulog-1 on thrombin-induced production of plasminogen activator inhibitor-1 (PAI-1) in cultured baboon aortic smooth-muscle cells (BASMCs). Thrombin increased the steady-state levels of PAI-1 messenger RNA (mRNA) and the release of PAI-1 antigen from BASMCs. Treatments with 10-20 mg/L of Hirulog-1 inhibited >80% of thrombin-induced PAI-1 generation from BASMCs. Hirulog-1 alone did not significantly alter PAI-1 production in the absence of thrombin. Significant reduction of thrombin-induced PAI-1 release was observed in cultures treated with Hirulog-1 for 1 h. The maximal effect of Hirulog-1 on thrombin-induced PAI-1 release was achieved in cultures treated with thrombin plus Hirulog-1 for 3 to 6 h, associated with the normalization of PAI-1 mRNA levels induced by thrombin treatment. Strong inhibition by Hirulog-1 on thrombin-induced PAI-1 release remained in cultures with 8 h of the treatment, but the effect was attenuated 16 h after a single addition of the inhibitor. Our study demonstrates that Hirulog-1 effectively inhibited thrombin-induced PAI-1 production in cultured vascular SMCs at mRNA and protein levels. Vascular SMCs may be exposed to high concentrations of thrombin when endothelium is injured. The information generated from this study suggests that Hirulog-1 potentially prevents intravascular thrombogenesis through inhibiting thrombin-induced PAI-1 production in vascular SMCs, especially when hypercoagulation and endothelial injury occurs.

Effectiveness of hirulog in reducing restenosis after balloon angioplasty of atherosclerotic femoral arteries in rabbits.

BACKGROUND: Thrombin may play an important role in restenosis after balloon angioplasty (BA). Angiographic and pathologic restenosis have been shown to be reduced after BA in an atherosclerotic rabbit model using recombinant desulfatohirudin, a selective and direct thrombin inhibitor. We hypothesized that potent and specific thrombin inhibition with the synthetic peptide hirulog given intravenously at the time of angioplasty would reduce restenosis in rabbits, confirming a specific role of thrombin in restenosis. METHODS AND RESULTS: Focal femoral atherosclerosis was induced in 27 rabbits by air desiccation endothelial injury followed by a 2% cholesterol diet for 1 month. Rabbits received either heparin (150 units/kg bolus, n = 14) or hirulog (5 mg/kg bolus followed by 5 mg/kg/h for 2 h, n = 13) at the time of BA (2.5-mm balloon with three 60-second, 10-atm inflations 60 s apart). Angiograms performed before and after BA and before sacrifice were analyzed quantitatively. Rabbits were sacrificed 28 days after BA for quantitative histopathologic analysis. Minimum luminal diameter (mm) did not differ between treatment groups before (1.1 +/- 0.2 vs. 1.2 +/- 0.1 mm) or after (1.5 +/- 0.2 vs. 1.6 +/- 0.1) BA in arteries from heparin-versus hirulog-treated rabbits, respectively. At 28 days, however, minimum luminal diameter was significantly less (1.0 +/- 0.4 vs. 1.5 +/- 0.2, p = 0.0001) and percent stenosis was greater (0.46 +/- 0.25 vs. 0.22 +/- 0.08, p = 0.0002) in arteries from heparin- versus hirulog-treated rabbits, respectively. Similarly, quantitative histopathology showed less cross-sectional area narrowing by plaque in the hirulog group (56 +/- 24 vs. 42 +/- 21%, p = 0.04). CONCLUSION: A 2-hour infusion of hirulog at the time of angioplasty improved late angiographic luminal dimensions and reduced cross-sectional area narrowing by plaque in rabbits compared with heparin controls. Together with previous studies, this confirms a specific role for thrombin in restenosis after angioplasty.

Hirulog: a direct thrombin inhibitor for management of acute coronary syndromes.

Hirulog therapy has been studied extensively in numerous settings including prevention of DVT, treatment of unstable angina, treatment of acute myocardial infarction during thrombolysis, and prevention of acute complications of PTCA. Being one of the first direct thrombin inhibitors in clinical development, it has had to 'test the waters', so to speak, of the relationship between pathophysiology and clinical trial design: what are the correct indications, patient entry criteria, endopoints, frequency and duration of dosing, and so on? Our findings validate a role for thrombin in treating arterial thromboembolism and demonstrate clinical activity and tolerability of Hirulog.

Thrombin functions as an inflammatory mediator through activation of its receptor.

A rat model of inflammation was used to investigate the biological effects of thrombin. The thrombin-specific inhibitor Hirulog markedly attentuated the carrageenin-induced edema of the paw of the rat. Injection of thrombin into the paw also produced edema. The effect of thrombin was due to activation of its receptor; a thrombin receptor activating peptide (TRAP) reproduced the effects of thrombin in causing edema. TRAP also increased vascular permeability as demonstrated by extravasation of Evans blue and 125I-labeled serum albumin. The release of bioactive amines played an important role in mediating the TRAP-induced edema; the serotonin/histamine antagonist cryproheptadine and the histamine H2 receptor antagonist cimetidine reduced significantly the edema caused by TRAP. Treatment of rats with the mast cell degranulator 48/80 to deplete these cells of their stores of histamine and serotonin abolished completely the ability of TRAP to produce edema. Histochemical examination confirmed that TRAP treatment led to mast cell degranulation. Thus, it has been possible to demonstrate that thrombin acts as an inflammatory mediator in vivo by activating its receptor, which in turn leads to release of vasoactive amines from mast cells.

Treatment with bivalirudin (Hirulog) as compared with heparin during coronary angioplasty for unstable or postinfarction angina. Hirulog Angioplasty Study Investigators.

BACKGROUND: Heparin is often administered during and after coronary angioplasty to prevent closure of the dilated vessel. However, ischemic or hemorrhagic complications occur in 5 to 10 percent of treated patients. We studied whether these complications could be prevented when the direct thrombin inhibitor bivalirudin (Hirulog) was used in place of heparin. METHODS: We performed a double-blind, randomized trial in 4098 patients undergoing angioplasty for unstable or postinfarction angina. Patients were assigned to receive either heparin or bivalirudin immediately before angioplasty. The primary end point were death in the hospital, myocardial infarction, abrupt vessel closure, or rapid clinical deterioration of cardiac origin. RESULTS: In the total study group, bivalirudin did not significantly reduce the incidence of the primary end point (11.4 percent, vs. 12.2 percent for heparin) but did result in a lower incidence of bleeding (3.8 percent vs. 9.8 percent, P < 0.001). In the prospectively stratified subgroup of 704 patients with postinfarction angina, bivalirudin therapy resulted in a lower incidence of the primary end point (9.1 percent vs. 14.2 percent, P = 0.04) and a lower incidence of bleeding (3.0 percent vs. 11.1 percent, P < 0.001), but in a similar cumulative rate of death, myocardial infarction, and repeated revascularization in the six months after angioplasty (20.5 percent vs. 25.1 percent, P = 0.17). CONCLUSIONS: Bivalirudin was at least as effective as high-dose heparin in preventing ischemic complications in patients who underwent angioplasty for unstable angina, and it carried a lower risk of bleeding. Bivalirudin, as compared with heparin, reduced the risk of immediate ischemic complications in patients with postinfarction angina, but this difference was no longer apparent after six months.

Hirulog effect in rat endotoxin shock.

Hirulog is a thrombin catalytic site inhibitor which exhibits specificity for the anionic binding exosite of alpha thrombin. Here, we have evaluated the effect of Hirulog (1, 5 and 10 mg/kg, 30 min pretreatment) in a rat model of endotoxemia. Intravenous injection of lipopolysaccharide from E. coli (25 mg/kg; serotype 0127:B8) caused decreases in blood pressure which were significantly reduced (about 60%) in animals pretreated with Hirulog. Rat survival to endotoxin was significantly increased in Hirulog pretreated group (5 and 10 mg/kg) up to 24 hours. Hirulog at the dose of 10 mg/kg inhibited both endotoxin-induced leukopenia at 30 and 60 minute points and thrombocytopenia at 30 minute point but not at 90 and 120 minute points. Fibrinogen levels were significantly reduced after 2 hours following endotoxin administration. Pretreatment with Hirulog (5-10 mg/kg i.v.) 30 min prior to administration of endotoxin prevented changes in fibrinogen plasma levels. These results demonstrate that Hirulog-induced inhibition of thrombin is effective in reducing toxic and lethal effects of endotoxin.

Kinetic mechanism for the interaction of Hirulog with thrombin.

Hirulog (D-FPRPGGGGDGDFEEIPEEYL) is a bivalent inhibitor of thrombin consisting of a moiety (D-FPRP) that binds to the active-site cleft and a hirudin-like C-terminal region (DGDFEEIPEEYL) that binds to the positively charged surface groove of thrombin known as the anion-binding exosite. The formation of the thrombin-Hirulog complex was studied using steady-state and rapid kinetics at 37 degrees C. The inhibition constant for Hirulog was found to be 1.9 nM. Hirulog was slowly degraded by thrombin with a kcat value of 0.01 s-1. The formation of the complex resulted in an enhancement of 44% in the intrinsic fluorescence of thrombin. The kinetics of the increase in thrombin fluorescence were described by a double-exponential decay. The dependence of the rate constant for the fast phase on the concentration of Hirulog could be described by the Michaelis-Menten equation with Km and kmax values of 0.75 +/- 0.12 microM and 325 +/- 17 s-1. The data were consistent with a mechanism in which the C-terminal region of Hirulog binds to the anion-binding exosite with a dissociation constant of 0.75 microM in the first step, followed by two intramolecular steps with rate constants of about 300 and 30 s-1. A C-terminal fragment of hirudin was found to compete in the first step confirming that this process corresponded to the binding of the hirudin-like C-terminus of Hirulog to the anion-binding exosite.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects on thrombin generation of single injections of Hirulog in patients with calf vein thrombosis.

STUDY OBJECTIVE: To determine whether single injections of Hirulog, a direct thrombin inhibitor, can inhibit thrombin generation in patients with calf vein thrombosis and, if so, if the inhibition is sustained. DESIGN: Phase II open label cohort study. SETTING: Tertiary-care referral centres, university affiliated hospitals. PATIENTS: 10 patients with venographically-demonstrated calf vein thrombosis. INTERVENTION: Patients received a single injection of Hirulog, either 1.0 mg/kg subcutaneously or 0.6 mg/kg as a 15 min intravenous infusion. Prothrombin fragment (F1++2) levels, as an index of thrombin generation, were measured before as well as 6 h post- and 24 h post-Hirulog administration. Patients were followed with non-invasive tests to detect thrombus extension into the proximal veins. RESULTS: There was a significant reduction in the levels of F1+2 with both regimens, 6 h after Hirulog. The F1+2 levels 24 h post-Hirulog showed a significant increase relative to the 6 h post-Hirulog results. One patient developed thrombus extension into the popliteal vein and was treated with conventional anticoagulants. CONCLUSION: The single injections of Hirulog used in the study produced incomplete and temporary suppression of F1+2. Complete and permanent inhibition of thrombin generation with Hirulog in patients with calf vein thrombosis may require higher doses, multiple subcutaneous injections and/or prolonged intravenous infusion.

Initial experience with a direct antithrombin, Hirulog, in unstable angina. Anticoagulant, antithrombotic, and clinical effects.

BACKGROUND: Currently available antithrombotic therapy for unstable angina is unwieldy and occasionally ineffective. This study was designed to investigate the potential of Hirulog, a new synthetic specific antithrombin agent, for the management of this condition. METHODS AND RESULTS: A total of 55 patients in the acute phase of unstable angina received intravenous Hirulog according to one of two protocols. In an acute dose-escalating study, 0.02, 0.05, 0.1, 0.25, and 0.5 mg.kg-1 x h-1, each for 30 minutes, were infused in 15 patients. Prolongation of activated partial thromboplastin time (aPTT) (r = .95), fibrinopeptide A inhibition (r = .96), and Hirulog plasma levels (r = .91) correlated closely with the dose infused, with significant changes compared with baseline appearing at doses of 0.25 mg.kg-1 x h-1 and higher. The purposes of the second protocol were to determine whether the anticoagulant and antithrombotic effects of the drug were sustained during a 72-hour infusion and to assess whether such treatment prevented the complications of unstable angina. Based on the initial study, we planned to give a dose of 0.25 mg.kg-1 x h-1 to each patient until 2 patients failed therapy, then successively higher doses until a 95% success rate was achieved or adverse effects intervened, increasing the dose after two failures had occurred at each level. Five patients received the 0.25-mg.kg-1 x h-1 dose and 14 the 0.5-mg.kg-1 x h-1 dose before two failures occurred. Failure was observed in only one of 21 patients at the dose of 1 mg.kg-1 x h-1. aPTT (+/- SEM) levels increased to 62 +/- 5, 76 +/- 2, and 98 +/- 3 seconds at the three doses, with minimal intraindividual variation, and Hirulog plasma levels to 1050, 2100, and 4200 mg/mL, respectively. Fibrinopeptide A plasma levels decreased at all doses but more consistently at the dose of 1 mg.kg-1 x h-1. The overall clinical success rate was 87.5%: 60% (3/5) at the low dose, 86% (12/14) at the intermediate dose, and 95% (20/21) at the high dose. No deaths, myocardial infarctions, or bleeding complications occurred. CONCLUSIONS: In unstable angina patients, Hirulog infusions quickly and reproducibly yield stable, dose-dependent anticoagulant and antithrombotic effects with a favorable clinical efficacy profile.

Anticoagulant effects of hirulog, a novel thrombin inhibitor, in patients with coronary artery disease.

Selective thrombin inhibitors are a new class of antithrombotic drugs that, unlike heparin, can effectively inhibit clot-bound thrombin and escape neutralization by activated platelets. Hirulog is a 20 amino acid hirudin-based synthetic peptide that has shown promise in experimental models of thrombosis. Little information is available about the effects of hirulog in patients with coronary artery disease. Forty-five patients undergoing cardiac catheterization, who were taking aspirin, were randomized to receive either (1) hirulog, 0.05 mg/kg intravenous bolus followed by 0.2 mg/kg/hour intravenous infusion until the end of the catheterization; (2) hirulog, 0.15 mg/kg intravenous bolus followed by 0.6 mg/kg/hour intravenous infusion; or (3) heparin; 5,000 U intravenous bolus. Serial activated partial thromboplastin time (APTT), prothrombin time, activated clotting time and fibrinopeptide A were measured. Hirulog produced a dose-dependent prolongation of all coagulation parameters; the 0.6 mg/kg/hour dose prolonged the APTT to 218 +/- 50% of baseline after 2 minutes and 248 +/- 50% of baseline after 15 minutes. The half-life of the effect on APTT was 40 minutes. The hirulog blood level correlated well with the APTT, prothrombin time and activated clotting time (r = 0.77, 0.73, and 0.82 respectively, all p < 0.001). Both doses of hirulog potently suppressed the generation of fibrinopeptide A (p < 0.05). There were no major hemorrhagic, thrombotic or allergic complications in patients treated with hirulog or heparin. Thus, hirulog, a direct thrombin inhibitor, provides a predictable level of anticoagulation and appears to have a potent yet well-tolerated anticoagulant profile in patients with coronary artery disease.

Anticoagulant activity of Hirulog, a direct thrombin inhibitor, in humans.

Hirulog (BG8967) is a direct thrombin inhibitor built by rational design using the protein hirudin as a model (Maraganore et al. [1990]; Biochemistry 29: 7095-101). In order to evaluate the therapeutic potential for hirulog in the management of thrombotic disease, the tolerability and anticoagulant activity of the agent were examined in a study of human volunteers. In a randomized, placebo-controlled study (n = .54), the intravenous infusion of hirulog over 15 min showed a rapid, dose-dependent prolongation of activated partial thromboplastin time (APTT), prothrombin time (PT), and thrombin time (TT). There was a corresponding dose-dependent increase in plasma hirulog levels. The peptide was rapidly cleared with a half-life of 36 min and a total body clearance rate for the peptide of 0.43 l kg-1 h-1. Similar activity was observed following subcutaneous injection but with sustained pharmacodynamic and pharmacokinetic behavior. There was a significant correlation between pharmacokinetic and pharmacodynamic variables for both intravenous (r = 0.8, p < 0.001) and subcutaneous administration (r = 0.7, p = 0.002). To evaluate the possible interactions of aspirin on the tolerability and anticoagulant activity of intravenous hirulog, a cross-over design was employed in eight subjects. Aspirin administration did not modify the peptide's activity. At the administered dose of 0.6 mg kg-1 h-1 for 2 h, hirulog infusion prolonged APTT from 230 to 260% baseline. The infusion of hirulog in subjects who had received aspirin was not associated with any significant changes in the template bleeding time.(ABSTRACT TRUNCATED AT 250 WORDS)

The arterial thrombotic process and emerging drugs for its control.

Unabated, the arterial thrombotic process continues to be a major challenge in the management of acute coronary artery disease. Pharmacologic and mechanical revascularization therapies, which have proliferated over the last decade, remain impeded by arterial thrombosis and its clinical sequelae. New antithrombotic drugs aimed at specific points in the arterial thrombotic process offer the potential for substantial improvements in the management of coronary artery disease. The use of these agents as a mainstay of patient care is becoming a reality as controlled clinical studies test their safety and potential benefits.

Structure of the hirulog 3-thrombin complex and nature of the S' subsites of substrates and inhibitors.

The X-ray crystallographic structure of the human alpha-thrombin complex with hirulog 3 (a potent, noncleavable hirudin-based peptide of the "hirulog" class containing a beta-homoarginine at the scissile bond), which is isomorphous with that of the hirugen-thrombin crystal structure, was solved at 2.3-A resolution by starting with a model for thrombin derived from the hirugen-thrombin complex and was refined by restrained least squares methods (R = 0.132). Residues of hirulog 3 were well-defined in the electron density, which included most of the pentaglycine linker and the C-terminal helical turn that was disordered in a related structure of thrombin with hirulog 1. The interactions of D-Phe1'-Pro2'-beta-homoArg3' with the active site of thrombin were essentially identical to those of related structures of PPACK- (D-Phe-Pro-Arg chloromethyl ketone) and hirulog 1-thrombin, with the guanidinium function of the arginyl P1 residue forming a hydrogen-bonding ion pair with Asp189 of the S1 site. A noticeable shift in the CA atom of beta-homoArg3' due to the methylene insertion displaces the scissile bond from attack by Ser195, thus imparting proteolytic stability to the beta-homoArg hirulog derivative. Resolution of the pentaglycine spacer, linking N- and C-terminal functional domains into a single oligopeptide bivalent inhibitor, permitted delineation of corresponding S' subsites of thrombin. The position of Gly4' (P1') is stabilized by three hydrogen bonds with His57, Lys60F, and Ser195, while the conformational angles maintained in a strained, nonallowed configuration for non-glycyl amino acids.(ABSTRACT TRUNCATED AT 250 WORDS)