Pharmacological characterization of FE 202158, a novel, potent, selective, and short-acting peptidic vasopressin V1a receptor full agonist for the treatment of vasodilatory hypotension.

FE 202158, ([Phe(2),Ile(3),Hgn(4),Orn(iPr)(8)]vasopressin, where Hgn is homoglutamine and iPr is isopropyl), a peptidic analog of the vasoconstrictor hormone [Arg(8)]vasopressin (AVP), was designed to be a potent, selective, and short-acting vasopressin type 1a receptor (V(1a)R) agonist. In functional reporter gene assays, FE 202158 was a potent and selective human V(1a)R agonist [EC(50) = 2.4 nM; selectivity ratio of 1:142:1107:440 versus human vasopressin type 1b receptor, vasopressin type 2 receptor (V(2)R), and oxytocin receptor, respectively] contrasting with AVP's lack of selectivity, especially versus the V(2)R (selectivity ratio of 1:18:0.2:92; human V(1a)R EC(50) = 0.24 nM). This activity and selectivity profile was confirmed in radioligand binding assays. FE 202158 was a potent vasoconstrictor in the isolated rat common iliac artery ex vivo (EC(50) = 3.6 nM versus 0.8 nM for AVP) and reduced rat ear skin blood flow after intravenous infusion in vivo (ED(50) = 4.0 versus 3.4 pmol/kg/min for AVP). The duration of its vasopressor effect by intravenous bolus in rats was as short as AVP at submaximally effective doses. FE 202158 had no V(2)R-mediated antidiuretic activity in rats by intravenous infusion at its ED(50) for reduction of ear skin blood flow, in contrast with the pronounced antidiuretic effect of AVP. Thus, FE 202158 seems suitable for treatment of conditions where V(1a)R activity is desirable but V(2)R activity is potentially deleterious, such as vasodilatory hypotension in septic shock. In addition to the desirable selectivity profile, its short-acting nature should allow dose titration with rapid onset and offset of action to optimize vasoconstriction efficacy and safety.

A uniquely selective inhibitor of the mammalian fetal neuromuscular nicotinic acetylcholine receptor.

We have purified and characterized a novel conotoxin from the venom of Conus obscurus, which has the unique property of selectively and potently inhibiting the fetal form of the mammalian neuromuscular nicotinic acetylcholine receptor (nAChR) (alpha1beta1gammadelta-subunits). Although this conotoxin, alphaA-conotoxin OIVB (alphaA-OIVB), is a high-affinity antagonist (IC50 of 56 nm) of the fetal muscle nAChR, it has >1800-fold lower affinity for the adult muscle nAChR (alpha1beta1epsilondelta-subunits) and virtually no inhibitory activity at a high concentration on various neuronal nAChRs (IC50 > 100 microm in all cases). The peptide (amino acid sequence, CCGVONAACPOCVCNKTCG), with three disulfide bonds, has been chemically synthesized in a biologically active form. Although the neuromuscular nAChRs are perhaps the most extensively characterized of the receptors/ion channels of the nervous system, the precise physiological roles of the fetal form of the muscle nAChR are essentially unknown.alphaA-OIVB is a potentially important tool for delineating the functional roles ofalpha1beta1gammadelta receptors in normal development, as well as in various adult tissues and in pathological states. In addition to its potential as a research tool, alphaA-OIVB may have some direct biomedical applications.

AlphaA-Conotoxin OIVA defines a new alphaA-conotoxin subfamily of nicotinic acetylcholine receptor inhibitors.

The venoms of cone snails are rich in multiply disulfide-crosslinked peptides, the conotoxins. Conotoxins are grouped into families on the basis of shared cysteine patterns and homologous molecular targets. For example, both the kappaA- and alphaA-conotoxin families share the same Class IV Cys pattern (-CC-C-C-C-C-), but differ in their molecular targets. The kappaA-conotoxins are excitatory toxins that purportedly block potassium channels, while the alphaA-conotoxins are paralytic conotoxins that inhibit nicotinic acetylcholine receptors (nAChRs). In this work, we describe the isolation and characterization of a novel Conus peptide from venom milked from Hawaiian specimens of Conus obscurus. This peptide shares the Class IV Cys pattern but differs from both previously characterized alphaA- and kappaA-conotoxins in the spacing of amino acids between Cys resides. However, the peptide is similar to previously characterized alphaA-conotoxins in its paralytic effects on fish and its antagonist activity on the neuromuscular nAChR. Unexpectedly, the peptide differs in its disulfide bonding from alphaA-conotoxin PIVA. We have named this unique peptide alphaA-conotoxin OIVA, and we consider it the defining member of a subfamily of alphaA-conotoxins that we designate the alphaA(1-3)-conotoxins to identify them by their unique disulfide bonding framework. These results indicate that the alphaA-conotoxin family is both more structurally diverse and broadly distributed than previously believed.