Effects of combined thromboxane synthetase inhibition/thromboxane receptor antagonism in two models of sudden cardiac death in the canine: limited role for thromboxane

BCL2A1 is a lineage-specific antiapoptotic melanoma oncogene that confers resistance to BRAF inhibition

Although targeting oncogenic mutations in the BRAF serine/threonine kinase with small molecule inhibitors can lead to significant clinical responses in melanoma, it fails to eradicate tumors in nearly all patients. Successful therapy will be aided by identification of intrinsic mechanisms that protect tumor cells from death. Here, we used a bioinformatics approach to identify drug-able, "driver" oncogenes restricted to tumor versus normal tissues. Applying this method to 88 short-term melanoma cell cultures, we show that the antiapoptotic BCL2 family member BCL2A1 is recurrently amplified in ∼30% of melanomas and is necessary for melanoma growth. BCL2A1 overexpression also promotes melanomagenesis of BRAF-immortalized melanocytes. We find that high-level expression of BCL2A1 is restricted to melanoma due to direct transcriptional control by the melanoma oncogene MITF. Although BRAF inhibitors lead to cell cycle arrest and modest apoptosis, we find that apoptosis is significantly enhanced by suppression of BCL2A1 in melanomas with BCL2A1 or MITF amplification. Moreover, we find that BCL2A1 expression is associated with poorer clinical responses to BRAF pathway inhibitors in melanoma patients. Cotreatment of melanomas with BRAF inhibitors and obatoclax, an inhibitor of BCL2A1 and other BCL2 family members, overcomes intrinsic resistance to BRAF inhibitors in BCL2A1-amplified cells in vitro and in vivo. These studies identify MITF-BCL2A1 as a lineage-specific oncogenic pathway in melanoma and underscore its role for improved response to BRAF-directed therapy.

Effects of a thromboxane A2-receptor antagonist, a thromboxane synthetase inhibitor and aspirin on prostaglandin I2 production in endothelium-intact and -injured aorta of guinea pigs

We examined the effects of KW-3635, a thromboxane (TX) A2-receptor antagonist, and OKY-046, a TX synthetase inhibitor, on the prostaglandin (PG) I2 production in endothelium-intact and -injured guinea pig aorta and compared them with those of aspirin. In the endothelium-intact aorta, both the low (3 mg/kg) and the high (100 mg/kg) dose of aspirin similarly reduced the PGI2 production, as measured ex vivo 1 hr after the injury. In contrast, neither KW-3635 (10 mg/kg) nor OKY-046 (30 mg/kg) inhibited the PGI2 production. The endothelial injury, induced by balloon catheterization, caused a reduction of PGI2 production in the aorta and decline of plasma PGI2/TXA2 ratio. In the endothelium-injured animals, the high dose of aspirin further reduced the PGI2 production in the aorta, whereas KW-3635 and OKY-046 did not affect it. KW-3635 and OKY-046 also ameliorated the reduced ratio of PGI2/TXA2 in the plasma. The present results demonstrate that aspirin, but not KW-3635 or OKY-046, reduces the PGI2 production in the aorta either in the endothelium-intact or -injured state. It is thus suggested that the TXA2-receptor antagonist and the TX synthetase inhibitor have some advantages over aspirin when used for the prevention of acute thrombosis after percutaneous transluminal angioplasty.

Antiarrhythmic versus antifibrillatory actions: inference from experimental studies

Pathophysiology of the coronary circulation is a major contributor to altering the myocardial substrate, rendering the heart susceptible to the onset of arrhythmias associated with sudden cardiac death. Antiarrhythmic drug therapy for the prevention of sudden cardiac death has been provided primarily on the basis of trial and error and in some instances based on ill-suited preclinical evaluations. The findings of the Cardiac Arrhythmia Suppression Trial (CAST) requires a reexamination of the manner in which antiarrhythmic drugs are developed before entering into clinical testing. The major deficiency in this area of experimental investigation has been the lack of animal models that would permit preclinical studies to identify potentially useful or deleterious therapeutic agents. Further, CAST has emphasized the need to distinguish between pharmacologic interventions that suppresses nonlethal disturbances of cardiac rhythm as opposed to those agents capable of preventing lethal ventricular tachycardia or ventricular fibrillation. Preclinical models for the testing of antifibrillatory agents must consider the fact that the superimposition of transient ischemic events on an underlying pathophysiologic substrate makes the heart susceptible to lethal arrhythmias. Proarrhythmic events, not observed in the normal heart, may become manifest only when the myocardial substrate has been altered. We describe a model of sudden cardiac death that may more closely simulate the clinical state in humans who are at risk. The experimental results show a good correlation with clinical data regarding agents known to reduce the incidence of lethal arrhythmias as well as those showing proarrhythmic actions.

Potentiation of phosphodiesterase inhibitor antithrombotic activity with alpha-2 adrenergic blockade

The antithrombotic activity of pelrinone, a phosphodiesterase III inhibitor was examined in a canine model of coronary thrombosis that uses electrical current to injure the coronary endothelium. Ninety percent of vehicle treated animals developed complete coronary occlusion and thrombus mass was 32.0 +/- 5.8 mg. In a group of animals treated with zomepirac, 10 mg/kg i.v., included as a positive control, thrombus mass was decreased to 10.3 +/- 3.3 mg and incidence of occlusion was reduced to 37.5%. Pelrinone, 5.0 mg/kg i.v. decreased the incidence of occlusion to 50%, thrombus mass to 21.3 +/- 8.3 mg and inhibited platelet aggregation to collagen, ADP and arachidonic acid by 80%, 54% and 87% of baseline, respectively. When yohimbine, an alpha 2-adrenergic antagonist, was co-administered (2.0 mg/kg at the beginning of the experiment +0.5 mg/kg halfway through the experiment) with the same dose of pelrinone, thrombus mass was decreased to 1.0 +/- 0.5 mg and none of the animals developed coronary occlusion. Yohimbine administration by itself at 2.0-3.0 mg/kg showed no evidence of antithrombotic activity (thrombus mass = 32.8 +/- 8.0 mg, incidence of occlusion = 100%). This dose of yohimbine inhibited significantly ADP-induced aggregation in the presence of epinephrine. These results demonstrate that, even though this dose of pelrinone elicited near maximal inhibition of platelet aggregation, the concurrent administration of an alpha 2-adrenergic antagonist was able to potentiate markedly the phosphodiesterase inhibitor antithrombotic activity.