Our previous study has revealed 4-(4-(4-chlorophenyl)-1,4-diazepan-1-yl)-1-(4fluorophenyl)butan-1-one-2HCI (SYA013) 1 as a sigma ligand with moderate selectivity for the sigma-2 receptor. Given the overexpression of sigma receptors in solid tumors and reports of sigma ligands with anticancer activities, we selected 1 for evaluation in several solid tumor cell lines. In addition, we have synthesized new analogs of 1 and now report that several of them bind preferentially at the sigma-2 receptor and have shown inhibition of several cancer cell lines including MDA-MB-231, MDA-MB-486, A549, PC-3, MIA PaCa-2 and Panc-1 cells. In particular, compounds 1 and 12 have demonstrated sub-micromolar activity against the Panc-1 cell line. It has also been observed that several of these compounds demonstrate selective toxicity toward cancer cells, when compared to normal cells.

Triple-negative breast cancer (TNBC) is one of the most malignant cancers associated with early metastasis, poor clinical prognosis, and high recurrence rate. TNBC is a distinct subtype of breast cancer that lacks estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor 2 receptors (HER2). Development of effective TNBC therapies has been limited partially due to the lack of specific molecular targets and chemotherapy involving different cytotoxic drugs suffers from significant side effects and drug-resistance development. Therefore, there is an unmet need for the development of novel and efficient therapeutic drugs with reduced side effects to treat TNBC. We have previously reported that certain analogues of haloperidol (a typical antipsychotic drug used for treating mental/mood disorders such as schizophrenia and bipolar disorder) suppress the viability of a variety of solid tumor cell lines, and we have identified 4-(4-(4-chlorophenyl)-1,4-diazepan-1-yl)-1-(4-fluoro-phenyl)­butan-1-one (SYA013) with such antiproliferative properties. Interestingly, unlike haloperidol, SYA013 shows moderate selectivity toward σ2 receptors. In this study, we explored the potential of SYA013 in modulating the important biological events associated with cell survival and progression as well as the mechanistic aspects of apoptosis in a representative TNBC cell line (MDA-MB-231). Our results indicate that SYA013 inhibits the proliferation of MDA-MB-231 cells in a concentration-dependent manner and suppresses cell migration and invasion. Apoptotic studies were also conducted in MDA-MB-468 cells (cells derived from a 51-year old Black female with metastatic adenocarcinoma of the breast.). In addition, we have demonstrated that SYA013 induces MDA-MB-231 cell death through the intrinsic apoptotic pathway and may suppress tumor progression and metastasis. Taken together, our study presents a mechanistic pathway of the anticancer properties of SYA013 against TNBC cell lines and suggests a potential for exploring SYA013 as a lead agent for development against TNBC.

Several lines of evidence suggest that selective sigma-2 (σ 2) ligands might be useful for the treatment of solid tumors. However, very few selective σ 2 ligands have been identified. This study was aimed at identifying new selective σ 2 receptor ligands using a previously identified agent, SYA 013 as a lead. Four groups, homopiperazine, piperazine, tropane and selected oxime analogs of the homopiperazines were identified, synthesized and subsequently screened at the σ 1 and σ 2 receptors. The results demonstrate that these scaffolds can be modified to obtain selective σ 2 receptor ligands. 1-(5-Chloropyridin-2-yl)-4-(3-((4-fluorophenyl)thio)propyl)-1,4-diazepane, 7 and 3-(4-chlorophenyl)-8-(3-((2-fluorophenyl)thio)propyl)-8-azabicyclo[3.2.1]octan-3-ol, 21 were identified as the highest binding affinity ligands (σ 2 Ki=2.2 nM) and (4-(4-(5-chloropyridin-2yl)-1,4-diazepan-1-yl)-1-(4-fluorophenyl)-butan-1-one oxime, 22 as a high affinity and the most selective ligand for the σ 2 receptor (σ 1 Ki/σ 2 Ki = 41.8).

Triple negative breast cancer (TNBC) is a type of breast cancer associated with early metastasis, poor prognosis, high relapse rates, and mortality. Previously, we demonstrated that SYA013, a selective σ2RL, could inhibit cell proliferation, suppress migration, reduce invasion, and induce mitochondria-mediated apoptosis in MDA-MB-231 cell lines, although we were unable to demonstrate the direct involvement of sigma receptors. This study aimed to determine the anticancer properties and mechanisms of action of SYA014, [4-(4-(4-chlorophenyl)-1,4-diazepan-1-yl)-1-(4-fluorophenyl)butan-1-one oxime], an oxime analogue of SYA013, the contribution of its sigma-2 receptor (σ2R) binding, and its possible synergistic use with cisplatin to improve anticancer properties in two TNBC cell lines, MDA-MB-231 (Caucasian) and MDA-MB-468 (Black). In the present investigation, we have shown that SYA014 displays anticancer properties against cell proliferation, survival, metastasis and apoptosis in the two TNBC cell lines. Furthermore, a mechanistic investigation was conducted to identify the apoptotic pathway by which SYA014 induces cell death in MDA-MB-231 cells. Since SYA014 has a higher binding affinity for σ2R compared to σ1R, we tested the role of σ2R on the antiproliferative property of SYA014 with a σ2R blockade. We also attempted to evaluate the combination effect of SYA014 with cisplatin in TNBC cells.

Introduction: Despite the reduction in mortality from breast cancer achieved in the last 30 years due to more effective targeted therapies, the survival rate for patients with triple negative breast cancer (TNBC) is poor and has virtually plateaued. Due to the absence of estrogen, progesterone, and human epidermal growth factor receptors 2, no targeted treatment options are currently available for TNBC. Moreover, the current standard systemic treatments are known to cause tremendous side effects. Thus, there is an urgent need to identify novel strategies for treating TNBC. Several reports have revealed that sigma-2 receptors are over-expressed in all solid tumors including TNBC, making it a plausible biomarker to explore for TNBC treatment. In this study, we investigated the effects of novel sigma-2 receptor ligands (XYZ-XI-14 and XYZ-VII-69) synthesized in our lab on the viability and survival of the TNBC, MDA-MB-231. Methods: MDA-MB-231 cells were treated for 48 h with XYZ-XI-14 and XYZ-VII-69, cell viability and proliferation were assessed using resazurin cell titre assay and cell count methods respectively. The effects of the ligands on spheroids formation, cell cycle, and mode of cell death were also investigated. Results: XYZ-XI-14 and XYZ-VII-69 decreased cell viability of MDA-MB-231 cells in a concentration-dependent manner. The EC50 for XYZ-XI-14 and XYZ-VII-69 were 12 and 13 µM respectively; and at 5 µM, the ligands inhibited cell proliferation, induced apoptosis, and arrested MDA-MB-231 cells at the G0/G1 phase of cell cycle. Additionally, concentrations of the ligand as low as 1 µM prevented the formation of spheroids as evidenced by the lack of compact spheroids, and caused the disintegration of preformed spheroids. Conclusion: This study indicates that targeting sigma-2 receptors with novel sigma-2 ligands (XYZ-XII-14 and XYZ-VII-69) effectively inhibits TNBC cancer cell growth by inducing apoptosis and cell cycle arrest, thus presenting a unique and effective pathway for treating TNBC. Additionally, the sigma-2 receptor ligands (XYZ-XI-14 and XYZ-VII-69) have the potential to halt tumor growth and prevent tumor relapse, as seen in our 3D culture assays. Thus, the sigma-2 receptor has the potential to be a valuable target for the development of novel agents for the treatment of TNBC. Citation Format: Gladys Asong, Felix Amissah, Olufisayo Salako, Rosemary Poku, Elizabeth Ntantie, Augustine Nkembo, Nazarius Lamango, Seth Ablordeppey. Sigma-2 receptor ligands induce apoptosis and inhibit proliferation in breast cancer cell line mda-mb-231 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 2308. doi:10.1158/1538-7445.AM2017-2308