Investigating the Selectivity of Putative Sigma‐2 Receptor Compounds in Human Cancer Cells Compared to Non‐Cancerous Cell Lines
Authors: Inbody Laura R. , Stang Christopher R.T. , Mohamed Ahmed H. , Hickey Mikaela C. , Orahood Cassandra B. , Dick Matt J. , Eichel Amanda M. , Zaibek Ann E. , Kinder David H. , Schneider Ryan A. 
Published: June 2021

Sigma‐2 receptors are being investigated as therapeutic targets for cancer as they have been found to be overexpressed in numerous tumor types. The selective estrogen receptor modulator, tamoxifen, has been shown to have affinity for sigma‐2 receptors. We previously presented screening data of a small library of compounds, based on tamoxifen, against estrogen receptor positive and negative cancer cell lines. The lead compounds from this library, SP‐1, SP‐5, and SP‐6, demonstrated low micromolar anticancer activity in several human cancer cell lines. Here we present screening data from a fourth analog, SP‐9, against MCF7 breast adenocarcinoma cells and A‐172 glioblastoma cells. Additionally, we present screening data of these lead compounds in normal human astrocytes (NHA) and normal human mammary epithelium (NHME).Activity of our lead compounds against A‐172 and MCF7 cells was assessed using the XTT cell viability assay to determine IC50 values. Initial screening of SP‐9 in A‐172 and MCF7 cells revealed IC50 values of 11 μM and 30 μM respectively. These calculated IC50 values are similar in potency to the most potent previously reported compound in each cell line (SP‐1 for A‐172 and SP‐5 for MCF7).To determine whether our lead compounds were selective for cancerous vs. non‐cancerous cells, we screened for cell death activity in NHA and NHME cells using the Vialight cell viability assay. In NHA cells, the lowest tested dose of 25 μM yielded viability of 10, 15, and 41% for SP‐1, SP‐5, and SP‐9 respectively. SP‐1, SP‐5, and SP‐9 treatments at 50 μM produced nearly 100% cell death. In contrast, NHA cells remained resistant to the effects of SP‐6 at 25 and 50 μM, but nearly 100% cell death was observed at 100 μM. The calculated IC50 for SP‐6 in NHA cells was 90 μM. In NHME cells, a similar pattern was observed. SP‐1, SP‐5, and SP‐9 treatments at 25 μM resulted in cell viability of 25, 53, and 29% respectively. Treatment with these compounds at 50 μM resulted in a near 100% cell death response. In contrast, NHME cells were resistant to the effects of SP‐6 at 25 and 50 μM. SP‐6 treatment at 100 μM yielded approximately 50% viability, resulting in an IC50 for SP‐6 in NHME cells of 98 μM. Using this data, the selectivity index of SP‐6 in NHA cells compared to A‐172 cells was 2.1. The selectivity index of SP‐6 in NHME cells compared to MCF7 cells was 1. We were unable to determine selectivity indices for SP‐1, SP‐5 or SP‐9 at the concentrations tested, though these compounds appear to be non‐selective. In summary, the lead compounds tested were found to be relatively non‐selective for cancerous vs. non‐cancerous cells. Despite this lack of selectivity, the potency of these compounds in breast and glioblastoma cell lines warrants further investigations to optimize the structure activity relationship of these proposed sigma‐2 analogs. Additional studies are also ongoing to investigate and compare mechanisms of cell death in these cancerous and non‐cancerous cell lines.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.