Superiority of YM598 over atrasentan as a selective endothelin ETA receptor antagonist

Bosentan: a review of its use in the management of mildly symptomatic pulmonary arterial hypertension

Bosentan (Tracleer) is an orally administered dual endothelin-1 (ET-1) receptor antagonist approved for use in patients with WHO class II (mildly symptomatic) pulmonary arterial hypertension (PAH). Oral bosentan therapy was beneficial and generally well tolerated in patients with mildly symptomatic PAH. In a well designed, placebo-controlled trial in adolescents and adults with mildly symptomatic PAH, pulmonary vascular resistance was significantly reduced with bosentan relative to placebo, but the 6-minute walk distance did not increase significantly. Similarly, pediatric patients (most of whom had mildly symptomatic PAH) in a small uncontrolled trial experienced some improvement in hemodynamic variables with bosentan, but did not experience a significant increase in exercise capacity. Adverse events associated with bosentan were consistent with those seen in other indications, with major concerns being the potential for teratogenicity and hepatotoxicity, for which regular liver function monitoring is recommended. Overall, considering the progressive nature of PAH, bosentan extends the treatment options available to patients with mildly symptomatic PAH.

Bosentan: a review of its use in the management of digital ulcers associated with systemic sclerosis

Bosentan (Tracleer) is an orally administered dual endothelin-1 (ET-1) receptor antagonist approved in the EU for reducing the number of new digital ulcers in patients with systemic sclerosis and ongoing digital ulcer disease. Oral bosentan therapy was beneficial and generally well tolerated in patients with digital ulcers associated with systemic sclerosis. In well designed, placebo-controlled trials, bosentan treatment significantly reduced the number of new ulcers, but had no effect on ulcer healing, in patients with digital ulcers. Adverse events associated with bosentan were consistent with those seen during treatment for other indications, with major concerns being the potential for teratogenicity and hepatotoxicity, for which regular liver function monitoring is recommended. Overall, considering the large unmet need for therapeutic options in patients with digital ulcers, bosentan extends the treatment options available to patients with systemic sclerosis-associated digital ulcers.

Endothelin-1-mediated wave-like [Ca2+]i oscillations in intact rabbit inferior vena cava

Endothelin-1 (ET1) is an endogenous vasoconstrictor released by the vascular system to regulate the contractility of vascular smooth muscle cells (VSMC). It is implicated in the pathogenesis of hypertension and diabetic vasculopathy. In rabbit inferior vena cava (IVC), 10 nM ET1 induces tonic contraction mainly via type A endothelin receptor activation. Using confocal imaging of Fluo-3 loaded in thein situ VSMC within the intact IVC, we found that ET1 elicited [Ca2+]i oscillations with an average frequency of 0.31 +/- 0.01 Hz. These [Ca2+]i oscillations occurred as repetitive Ca2+ waves traveling along the longitudinal axis of the cells with an average velocity of 29 +/- 3 microm/s. The Ca2+ waves were not synchronized between neighboring VSMC nor were they propagated between them. Nifedipine (10 microM) inhibited the tonic contraction by 27.0 +/- 5.0% while SKF96365 (50 microM) abolished the remaining contraction. In a parallel Ca2+ study, nifedipine reduced the frequency of the oscillations to 0.22 +/- 0.01 Hz while SKF96365 abolished the remaining [Ca2+]i oscillations. Subsequent application of 25 mM caffeine elicited no further Ca2+ signal. Thus, we conclude that ET1 stimulates tonic contraction in the rabbit IVC by inducing [Ca2+]i oscillations and that stimulated Ca2+ entry through both the L-type voltage-gated Ca2+ channels and a nifedipine-resistant and SKF96365-sensitive pathway is crucial for the maintenance of [Ca2+]i oscillations and tonic contraction.

New Targets in the Management of Prostate Cancer

Our understanding of growth factors and growth-factor receptors, signal transduction pathways, cellular survival pathways, angiogenesis, and their potential roles in prostate-cancer tumorigenesis remains a work in progress. Novel agents targeting these key mechanisms are showing promise in clinical trials. Many more agents, including those not discussed in this article, such as radio-pharmaceuticals, bisphosphonates, nutriceuticals, immunotherapy, and newer generation chemotherapy, are also showing promise as emerging treatments for prostate cancer. It is important to recognize when designing clinical trials of novel agents that traditional endpoints of disease response may not be applicable in measuring success of biologic compounds. Especially in a disease where tumor marker levels are critical for both patient and physician, additional biomarkers are necessary to better assess response. Halting drug development due to lack of response in serum PSA may lead to an unnecessary demise of an active agent.As expected, the combination of biologic agent with cytotoxic chemotherapy has a higher traditional response rate compared with biologic agent alone. The challenge of combination trials is to determine if the combination of agents will produce a higher traditional response rate compared with chemotherapy alone. For several of the agents discussed, the clinical benefit derived from a combination of biologic agent and cytotoxic chemotherapy may not justify additional drug toxicity. Efficient trial design, appropriate selection of correlative markers,and close toxicity monitoring will help improve our ability to identify promising novel agents.

Effect of YM598, a selective endothelin ETA receptor antagonist, on endothelin-1-induced bone formation

We investigated the effect of endothelin-1 on bone formation in vitro and in vivo, and the effect of YM598, a novel selective endothelin ET(A) receptor antagonist, on endothelin-1-induced responses. In in vitro studies, the effect of endothelin-1 on cellular responses was investigated by measuring intracellular Ca(2+) levels, cell growth and alkaline phosphatase activity in the mouse osteoblast-like cell line MC3T3-E1. In in vivo studies, the effect of endothelin-1 on bone morphogenetic protein-2-induced ectopic bone formation in rats was investigated. A carrier containing bone morphogenetic protein-2 with or without endothelin-1 was subcutaneously implanted over the thorax, and the tissue (carrier) calcium content 3 weeks after implantation was evaluated. The inhibitory effect of YM598 on these responses was also investigated. In the in vitro studies, endothelin-1 (10(-13) to 10(-6) M) significantly increased intracellular Ca(2+) concentration, DNA synthesis and cell number in a concentration-dependent manner, while significantly decreasing alkaline phosphatase activity. YM598 (10(-12) to 10(-4) M) significantly inhibited these increases, as well as the decrease in alkaline phosphatase activity, in a concentration-dependent manner. In the in vivo studies, the tissue calcium content 3 weeks after carrier implantation was significantly higher in the group that received both bone morphogenetic protein-2 and endothelin-1 than in the group receiving bone morphogenetic protein-2 alone. Chronically administered YM598 (1 mg/kg/day) marginally inhibited this endothelin-1-potentiated ectopic bone formation. These results suggest that endothelin-1 may induce bone formation via endothelin ET(A) receptors in vitro and in vivo.

Targeted therapies for prostate cancer

The development of targeted therapies for prostate cancer has exploited various elements of prostate biology. The androgen-dependence of prostate cancer continues to be the focus for the development of new drugs and the analysis of details of the intermolecular interactions of the androgen receptor. Importantly, new applications of androgen ablation therapy have proven to have the greatest effect on cause-specific and overall survival during the last decade. Prostate epithelial cells express a number of tissue-specific proteins that have been the target either for antibody-directed therapies, in the case of prostate-specific membrane antigen, or target-activated therapies in the case of prostate-specific antigen, a serine protease. Prostate-specific proteins have also been targeted by the development of vaccines that have entered clinical trials. Humanized monoclonal antibodies and small molecules designed to inhibit oncogenic signalling pathways have been subjected to clinical trials in prostate cancer with limited success. The application of pathway inhibitors to prostate cancer therapy has been limited because no common dominant oncogenic mutation affecting signal kinase activation in prostate cancer has yet been identified. The interaction of signal kinase inhibitors with androgen ablation and with cytotoxic chemotherapy remains to be explored.

Ambrisentan, a Non-peptide Endothelin Receptor Antagonist

Increasing numbers of experimental investigations and recently also of clinical trials strongly suggest an integral involvement of the endothelin (ET)-system in the pathophysiology of a variety of disease states, mainly of the cardiovascular system. Ambrisentan (LU 208075), a selective ET(A)-receptor antagonist, is an orally active diphenyl propionic acid derivative. It has been shown to have a very promising efficacy to safety ratio in the initial clinical trials. Phase II and Phase III trials with ambrisentan in pulmonary arterial hypertension have been performed. The pharmacological properties and data from the experimental investigations suggest additional possible uses of ambrisentan in the prevention of reperfusion injury after organ transplantation and in restenosis following coronary artery dilatation. Furthermore, the pharmacological profile of ambrisentan indicates that this drug may also be suitable in the treatment of cerebrovascular disorders. In the present article basic investigations, animal studies and clinical trials with ambrisentan are reviewed. This review may help to define pathophysiological conditions, in which ambrisentan could be indicated and further evaluated in appropriate preclinical and clinical trials.