Involvement of sigma-receptors in the increase in contraction of mouse vas deferens induced by exogenous ATP

Fenfluramine modulates the anti-amnesic effects induced by sigma-1 receptor agonists and neuro(active)steroids in vivo

Fenfluramine (N-ethyl-α-methl-3-(trifluoromethyl)phenethylamine) is an anti-seizure medication (ASM) particularly effective in patients with Dravet syndrome, a severe treatment-resistant epileptic encephalopathy. Fenfluramine acts not only as neuronal serotonin (5-HT) releaser but also as a positive modulator of the sigma-1 receptor (S1R). We here examined the modulatory activity of Fenfluramine on the S1R-mediated anti-amnesic response in mice using combination analyses. Fenfluramine and Norfenfluramine, racemate and isomers, were combined with either the S1R agonist (PRE-084) or the S1R-acting neuro(active)steroids, pregnenolone sulfate (PREGS), Dehydroepiandrosterone sulfate (DHEAS), or progesterone. We report that Fenfluramine racemate or (+)-Fenfluramine, in the 0.1-1 mg/kg dose range, attenuated the dizocilpine-induced learning deficits in spontaneous alternation and passive avoidance, and showed low-dose synergies in combination with PRE-084. These effects were blocked by the S1R antagonist NE-100. Dehydroepiandrosterone sulfate or PREGS attenuated dizocilpine-induced learning deficits in the 5-20 mg/kg dose range. Co-treatments at low dose between steroids and Fenfluramine or (+)-Fenfluramine were synergistic. Progesterone blocked Fenfluramine effect. Finally, Fenfluramine and (+)-Fenfluramine effects were prevented by the 5-HT1A receptor antagonist WAY-100635 or 5-HT2A antagonist RS-127445, but not by the 5-HT1B/1D antagonist GR 127935 or the 5-HT2C antagonist SB 242084, confirming a 5-HT1A and 5-HT2A receptor involvement in the drug effect on memory. We therefore confirmed the positive modulation of Fenfluramine racemate or dextroisomer on S1R and showed that, in physiological conditions, the drug potentiated the low dose effects of neuro(active)steroids, endogenous S1R modulators. The latter are potent modulators of the excitatory/inhibitory balance in the brain, and their levels must be considered in the antiepileptic action of Fenfluramine.

Sigma1 Pharmacology in the Context of Cancer

Sigma1 (also known as sigma-1 receptor, Sig1R, σ1 receptor) is a unique pharmacologically regulated integral membrane chaperone or scaffolding protein. The majority of publications on the subject have focused on the neuropharmacology of Sigma1. However, a number of publications have also suggested a role for Sigma1 in cancer. Although there is currently no clinically used anti-cancer drug that targets Sigma1, a growing body of evidence supports the potential of Sigma1 ligands as therapeutic agents to treat cancer. In preclinical models, compounds with affinity for Sigma1 have been reported to inhibit cancer cell proliferation and survival, cell adhesion and migration, tumor growth, to alleviate cancer-associated pain, and to have immunomodulatory properties. This review will highlight that although the literature supports a role for Sigma1 in cancer, several fundamental questions regarding drug mechanism of action and the physiological relevance of aberrant SIGMAR1 transcript and Sigma1 protein expression in certain cancers remain unanswered or only partially answered. However, emerging lines of evidence suggest that Sigma1 is a component of the cancer cell support machinery, that it facilitates protein interaction networks, that it allosterically modulates the activity of its associated proteins, and that Sigma1 is a selectively multifunctional drug target.

Small molecule antagonists of the sigma-1 receptor cause selective release of the death program in tumor and self-reliant cells and inhibit tumor growth in vitro and in vivo

The acquisition of resistance to apoptosis, the cell's intrinsic suicide program, is essential for cancers to arise and progress and is a major reason behind treatment failures. We show in this article that small molecule antagonists of the sigma-1 receptor inhibit tumor cell survival to reveal caspase-dependent apoptosis. sigma antagonist-mediated caspase activation and cell death are substantially attenuated by the prototypic sigma-1 agonists (+)-SKF10,047 and (+)-pentazocine. Although several normal cell types such as fibroblasts, epithelial cells, and even sigma receptor-rich neurons are resistant to the apoptotic effects of sigma antagonists, cells that can promote autocrine survival such as lens epithelial and microvascular endothelial cells are as susceptible as tumor cells. Cellular susceptibility appears to correlate with differences in sigma receptor coupling rather than levels of expression. In susceptible cells only, sigma antagonists evoke a rapid rise in cytosolic calcium that is inhibited by sigma-1 agonists. In at least some tumor cells, sigma antagonists cause calcium-dependent activation of phospholipase C and concomitant calcium-independent inhibition of phosphatidylinositol 3'-kinase pathway signaling. Systemic administration of sigma antagonists significantly inhibits the growth of evolving and established hormone-sensitive and hormone-insensitive mammary carcinoma xenografts, orthotopic prostate tumors, and p53-null lung carcinoma xenografts in immunocompromised mice in the absence of side effects. Release of a sigma receptor-mediated brake on apoptosis may offer a new approach to cancer treatment.

Review of the pharmacological and clinical profile of rimcazole

Rimcazole is a carbazole derivative that acts in part as a sigma receptor antagonist. Wellcome Research Laboratories introduced this compound during the 1980s when it was hypothesized to be a novel antipsychotic with an improved side effect profile. However, subsequent clinical trials demonstrated that rimcazole lacked efficacy in schizophrenic patients and it is now primarily used as an experimental tool. In addition to its actions as a sigma receptor antagonist, rimcazole also has high affinity for dopamine transporters, and in recent years it has served as a lead compound for the development of novel dopamine transporter ligands. Although rimcazole cannot be considered a selective ligand for sigma receptors, the recent development of other selective agonists and antagonists for sigma receptors have aided in clarifying the involvement of these receptors in the actions of rimcazole. Many of the physiological and behavioral effects of rimcazole can in fact be ascribed to its action as a sigma receptor antagonist, although there are exceptions. Rimcazole is likely to have a continued role in elucidating sigma receptor function in either in vitro or in vivo systems where sigma receptor-mediated effects can be studied independently of the influence of dopamine and serotonin transporters.