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Sigma receptor content in a range of cancer cell lines Sigma receptors are becoming an area of interest for a wide range of clinical conditions. The sigma-1 receptor has been associated with cancer treatment and diagnosis, neurological conditions including depression and Alzheimer’s disease whereas the sigma-2 receptor (now thought to be the progesterone receptor membrane component-1) has been linked to cancer treatment and diagnosis. Many studies comparing these two receptors have required masking drugs to prevent interaction of ligands with both receptors. We have characterised a series of human cancer cell lines in order to establish sigma-1 and sigma-2 receptor levels in each. Radioactive ligand binding assays were performed using membranes prepared from each cell line and (+)-pentazocine which is a selective sigma-1 ligand, or 1,3-ditolyl guanidine (DTG), a pan-sigma ligand. Haloperidol was used to determine non-specific binding in all cases. Assays were performed at room temperature and stopped by rapid filtration through GF/C filters. Cells showed a variety of binding profiles (Table 1). Table 1. Sigma-receptor number as determined using saturation binding curves. Data represent mean + SEM from 3-4 experiments.
Our results show that the sigma-1 receptor is present in a variety of cancer cell lines. Our data agree with previous studies (1) showing MCF-7 cells lack sigma-1 receptors. To our knowledge, these are the only cell line yet characterised that lack sigma-1 receptors. In contrast, several cell lines lacked sigma-2 receptors; these include Flo-1, HCT116 and oe21 cells. Other cell lines expressed low levels of sigma-2 receptors, including Caco-2, HEK293 and SW480 cells. The use of these cell lines will allow us to determine the roles of these receptors in cell signalling and biology. (1) Vilner, BJ et al. (1995) Cancer Res. 55:408-13.
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