Actinomycin D is a competitive and selective antagonist at NK2 tachykinin receptors

The ability of actinomycin D, a known antineoplastic agent, to affect NK1 NK2 and NK3 tachykinin (TK) receptor types was assessed on several in vitro bioassays. Actinomycin D was completely ineffective as a TK antagonist in the guinea-pig ileum longitudinal muscle (GPI) and on the rat portal vein (RPV) (two issues containing NK1, and NK3 TK receptors, respectively) while it was a weak competitive antagonist in the endothelium-denuded rabbit pulmonary artery (RPA) and in the hamster trachea (HT) (tissues containing the NK2A and NK2B receptor subtypes, respectively). Furthermore actinomycin D was able to displace [125I]-His-NKA from NK2 receptor sites of the rat small intestine smooth muscle membranes. Although actinomycin D is about 3 orders of magnitude weaker as an NK2 antagonist as compared to the most effective ligands available, it could represent a starting point in the development of non-peptidic NK2 receptor antagonists.