Current Drug Targets - Cardiovascular & Hematological Disorders - Volume 2, Issue 1, 2002

Ca2+ is an important secondary messenger and any alteration to intracellular Ca2+ signaling pathways or components of these pathways can have a profound physiological effect on any cell, particularly cardiomyocytes. Early approaches to investigate heart disease focused on many muscle proteins, however recent findings indicate that molecules considered as “non-muscle” proteins may be equally important players in etiology of many cardiac pathologies. Many of these “non-muscle” proteins play a role in Ca2+ cycling or Ca2+-dependent signaling pathways in the heart. In this review we focus on Ca2+ -dependent pathways in normal, growing, and diseased hearts. Understanding of these unique signaling pathways may hold answers to many cardiac pathologies in children and adults.

In patients with acute coronary syndromes, inhibition of platelet aggregation with parenteral αIIb / βIII antagonists has proven effective at preventing nonfatal myocardial infarction and repeat percutaneous coronary interventions. Paradoxically, the efficacy observed for acute indications and parenteral agents has not extended to oral agents and chronic prevention of secondary thrombotic events, despite robust antithrombotic properties in preclinical thrombosis models.This report documents the preclinical data of Lotrafiban, an oral αIIb / βIII antagonist that recently failed in a phase III clinical trial (BRAVO) for the prevention of secondary thrombosis. Lotrafiban was characterized in a dog circumflex artery electrical injury model, and a cyclic flow reduction model (“Folts”). The data demonstrate that both oral (1.0-50.0 mg / kg) and intravenous (0.1-0.8ug / kg / min) administration of lotrafiban produced dose-related inhibition (45%-95%) of ex vivo platelet aggregation. In the electrical injury model, the doserelated inhibition correlated with a significant reduction in the frequency of coronary occlusion, size of the developing thrombus, and the extent of left ventricular ischemic damage. Effects on blood flow and bleeding time were also dose related. The combination of low dose lotrafiban (0.1ug / kg / min) and aspirin (5.0 mg / kg) generated additive antithrombotic effects, approximating the antithrombotic efficacy of a 2-4 fold higher dose of lotrafiban while only modestly prolonging the bleeding time. For purposes of comparison, the ADP receptor antagonist clopidogrel was also assessed in the electrical injury model. Clopidogrel (5.0-10.0 mg / kg, iv.) significantly reduced the resulting left ventricular infarct areas, but lacked the overall efficacy of lotrafiban. In the “Folts” model, lotrafiban inhibited cyclic blood flow reductions (CFR's) by 100% in animals insensitive to the antithrombotic effects of aspirin. Overall, the preclinical data demonstrated that αIIb / βIII antagonism with lotrafiban was a well tolerated and effective strategy for attenuating acute arterial thrombosis. The lack of a correlation between these preclinical data and the outcome of the clinical trial BRAVO are unexplained. However, the combined evidence suggests that these acute canine thrombosis studies may not completely capture the pathology reflected in chronic human atherothrombotic disease.

Proteolytic degradation of fibrin (fibrinolysis) is mediated by plasminogen and its activators, tissue-type plasminogen activator (tPA1) and urokinase (uPA). Fibrinolysis is critical for preventing thrombus growth and restoring blood flow following thrombotic vascular occlusion. Plasminogen activator inhibitor-1 (PAI-1), a member of the serine protease inhibitor (serpin) superfamily, is the principal inhibitor of tPA and uPA in the fibrinolytic system. High levels of circulating PAI-1 are associated with a number of thrombotic diseases. In animal studies, transgenic mice overexpressing human PAI-1 develop spontaneous thrombosis, whereas PAI-1-deficient mice are more resistant to venous or arterial thrombosis. Furthermore, inhibition of PAI-1 activity prevents thrombus formation in animal models. The antithrombotic effects of PAI-1 inhibition are achieved by enhancing endogenous fibrinolytic activity without directly affecting blood coagulation and platelet function. Phenotypic analysis of PAI-1 deficiency in both human and mouse suggests that inhibition of PAI-1 will not lead to severe bleeding or other major adverse effects. Thus, PAI-1 inhibitors represent a new class of antithrombotic drugs with a possible wider therapeutic index than conventional antiplatelet and anticoagulant agents. This review summarizes the role of PAI-1 in thrombotic diseases and recent progress in the development of small molecule PAI-1 inhibitors.

Chagas' disease affects about 18 million people and 25% of the population of Latin America is at risk of acquiring Chagas' disease. The chemotherapy of Chagas'disease is still an open field and remains as an unsolved problem. Nifurtimox and benznidazole are currently used to treat this disease, however, both drugs have high toxicity and are mutagenic with the result that the patients frequently fail to follow treatment.T. cruzi enzimes such as trypanothione reductase, represent potential drug targets because they play an essential role in the life of this organism. This enzyme has been isolated, purified and studied by X ray crystallography. Phenothiazines and related compounds inhibit trypanothione reductase and a specially favoured fit is a phenothiazine with a 2- substitued with 2- chloro and 2- trifluoromethyl with a remote hydrophobic patch. The essential phenothiazine nucleus can adopt more than one inhibitory orientation in its binding site.Phenothiazines and related compounds are drugs used in psychiatric treatments. These anti-depressants inhibit trypanothione reductase through the peroxidase / H2O2 / system, and also exert other trypanocidal effects upon epimastigotes and tripomastigotes forms: clomipramine through an anticalmodulin action; trifluopherazine and thioridazine induced disruption of mitochondria and prometazine provoked serious cell membrane disorganization. Clomipramine and thioridazine were also effective in treatment of mice with experimental Chagas' disease, significantly modifying the natural evolution of the infection; cardiac function and survival of infected and treated animals were not different from non infected animals. Phenothiazines and related compounds are promising trypanocidal agents for treatment of Chagas' disease.Other trypanocidal agents as nifurtimox, benznidazol,Allopurinol, cystein protease inhibitors and others, are also discussed.