In vitro and ex vivo characterization of sigma-1 and sigma-2 receptors: agonists and antagonists in biological assays

Methods for addressing sigma receptor affinity and activity have been explored and although several protocols have been employed, only few procedures resulted reliable. Sigma-1 receptor affinity protocol using guinea-pig brain and (+)-[(3)H]-pentazocine and sigma-2 receptor affinity protocol employing rat liver and [(3)H]-DTG are usually reported by authors as standard procedures. By contrast, the intrinsic activity evaluation of sigma ligands has been performed in several manners: tumor cell lines, isolated organ bath, in vivo animal model. The last is not considered in the present paper because this method studied the physiological role of sigma receptors. The studies carried out in tumor cell lines involved the role of sigma receptors in tumors progression while, although isolated organ bath experiment employed physiological samples, the pharmacokinetic properties of ligands, a strictly requirement for the in vivo assays, did not affect the pharmacodynamic properties of tested compounds. The advances in the above mentioned assays have been reported.