DEVELOPMENT OF A RADIOIMMUNOASSAY FOR THE NOVEL N-TYPE CALCIUM-CHANNEL BLOCKER, SNX-111 (CI-1009)

Compounds that selectively target the N-type neuronal voltage-sensitiv e calcium channels (N-VSCC) offer the possibility of producing effecti ve neuroprotection through a novel mode of action when compared to exi sting therapies, SNX-111 (CI-1009) has a high in vitro affinity, selec tivity, and specificity for the N-VSCC and crosses the blood-brain bar rier when administered intravenously, SNX-111 is a 25-amino acid pepti de containing three disulfide bonds, presently manufactured by solid-p hase peptide synthesis, and is identical in chemical structure and bio logical activity to omega-Conotoxin M VIIA obtained from the marine co ne snail, The principal therapeutic property of SNX-111 is its ability to induce significant neuroprotection following an episode of global brain ischemia, even when administered 24 hours after the original isc hemic event, Because of the extremely low circulating plasma concentra tions that resulted from efficacious and therapeutic doses of SNX-111 in preclinical studies, HPLC was not a feasible analytical method, Con sequently, a radioimmunoassay (RIA) was developed by conjugating SNX-1 11 to bovine serum albumin to generate rabbit antibody which was used with a radioiodinated SNX-111 derivative, The assay was validated in h uman plasma, with two types of anticoagulants, using 100 mu L of sampl e with a resulting limit of quantitation of 9.77 pg/mL.