Scouting Sigma Receptor Ligands As New Tools For The Treatment Of Neurodegenerative Diseases And Cancer

Sigma receptors (Rs) are nowadays recognized as an unique class of membrane receptors divided into two subtypes, R and R. Rs regulate a number of physiological functions and their role has been evaluated in many disorders. Deficits in R are associated with neurodegeneration while their activation may represent a valuable strategy for the treatment of a number of neurodegenerative disorders. Moreover, R is overexpressed in a variety of cancer cells and selective R antagonists are reported to modulate cancer cell viability.1 R are also highly expressed proliferating tumors. R agonists are giving promising results in preclinical studies for the treatment of resistant or hardly treatable tumors and R ligands have been proposed as biomarkers for tumors proliferation.2 However, the identification of potent and selective ligands and the comprehension of the chemical features behind agonism/antagonism still remain a primary challenge in this field. With this aim, following a ligand-based approach, a library of over 120 ligands have been designed and synthesized over the years, by combining different substituted five-membered heterocyclic rings with appropriate R pharmacophoric amines. Compounds were tested for R and R affinity showing Ki values in the micromolar / sub-nanomolar range, with a selectivity mainly shifted toward the R. A detailed SAR, supported by molecular modelling, was drawn up. The intrinsic activity was determined in vivo for the most promising molecules. According to their profile, R agonists were tested for neuroprotection, whereas R antagonists / R agonists for anticancer activity. Preliminary results in SH-SY5Y neuroblastoma cells showed the ability of some compounds to protect neuronal cells from death induced by four toxicity models. Cell viability assays were performed on different cancer cell lines to assess the anti-proliferative potential of selected molecules. In particular, dose and time dependent treatments were done on prostate cancer cells, which express higher levels of both R and R compared to normal samples. Similarly, we assessed the effect of the compounds on melanoma cells: BS148, a potent and selective R agonist, showed anti-proliferative activity on immortalized and PDX (metastatic melanoma patient-derived xenografts) cell lines.3 Confocal microscopy studies with BS148 fluorescent probe revealed the internalization of BS148 within melanoma cells, with a cytoplasmatic localization, mostly in the perinuclear region, according to R distribution. Finally, to verify whether TMEM97 / R mediates BS148-antiproliferative activity, we stably overexpressed the TMEM97 gene in HeLa cells: TMEM97-Hela were more sensitive to BS148 anti-proliferative activity compared to control cells, which express endogenous R levels. Taken together, these results support the idea that R is an innovative target in cancer, paving the way for improved tools for cancer diagnosis, monitoring and therapy.