Novel sigma binding site ligands as inhibitors of cell proliferation in breast cancer

Sigma receptors, namely sigma(1) and sigma(2), have been shown to be expressed in a variety of human cell lines playing a role in cell growth. In the human breast, they are absent in normal mammary tissue but expressed in tumors, particularly in the proliferating stage. The study presented here concerns nine newly synthesized ligands for sigma receptors. The compounds are of general structure consisting of: five (1alpha/1beta-arylalkyl)quinolizidines including two thioisosteres and four spiro-[3,4-dihydro-1,2,4-benzotriazino-3,4'-(1'-substituted) piperidines]. These compounds exhibited varying degrees of affinity for sigma receptors and were able to inhibit the growth of MCF-7 and MDA-MB 231 human breast cancer cell lines, in vitro. Good to moderate binding to sigma(1) receptors occurred with all tested ligands. However, affinity for sigma(2) appeared more evident with compounds FN/C-2 and FN/C-4 (spiro-[3,4-dihydro-1,2,4-benzotriazino-3,4'-(1'-substituted) piperidines] derivatives). In addition, higher cytotoxic activity of FN/C-2 and FN/C-4 with IC50 values below 100 muM in MCF-7 and lower than 40 muM in MDA-MB 231 was revealed. The data from the current study show that these novel sigma receptor ligands exhibit interesting cytotoxic activity and suggest their potential for development as antitumor agents.