Use of Multifunctional Sigma-2 Receptor Ligand Conjugates to Trigger Cancer-Selective Cell Death Signaling

Department of Surgery, Alvin J Siteman Cancer Center, Washington University School of Medicine, St Louis, Missouri 63110, USA.
Cancer Research (Impact Factor: 9.33). 11/2011; 72(1):201-9. DOI: 10.1158/0008-5472.CAN-11-1354
Source: PubMed


One major challenge in the development of cancer therapeutics is the selective delivery of the drugs to their cellular targets. In the case of pancreatic cancer, the σ-2 receptor is a unique target that triggers apoptosis upon activation. We have previously developed a series of chemical compounds with high affinity for the σ-2 receptor and showed rapid internalization of the ligands. One particular specific ligand of the σ-2 receptor, SV119, binds to pancreatic cancer cells and induces target cell death in vitro and in vivo. In this study, we characterized the ability of SV119 to selectively deliver other death-inducing cargos to augment the cytotoxic properties of SV119 itself. When conjugated to SV119, small molecules that are known to interfere with intracellular prosurvival pathways retained their ability to induce cell death, the efficiency of which was enhanced by the combinatorial effect of SV119 delivered with its small molecule cargo. Our findings define a simple platform technology to increase the tumor-selective delivery of small molecule therapeutics via σ-2 ligands, permitting chemotherapeutic synergy that can optimize efficacy and patient benefit.

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    • "Sigma-2 ligands are especially suitable for purposes of diagnostic imaging and therapeutic targeting of solid tumors due to their high selectivity for tumor cells in vivo [17,18]. Furthermore, by virtue of their rapid internalization and binding to the sigma-2 receptor [19], these ligands represent excellent candidates for selective delivery of anticancer drugs into the tumor cells [14]. Taking advantage of these two unique properties of sigma-2 ligands, we have generated dual-domain therapeutics, wherein sigma-2 ligands additionally function as targeting domains for a cancer-selective delivery of effector molecules such as pro-apoptotic peptides into the tumor cells (12). "
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    ABSTRACT: Drug resistance is a significant problem in the treatment of ovarian cancer and can be caused by multiple mechanisms. Inhibition of apoptosis by the inhibitor of apoptosis proteins (IAPs) represents one such mechanism, and can be overcome by a mitochondrial protein called second mitochondria-derived activator of caspases (SMAC). We have previously shown that the ligands of sigma-2 receptors effectively induce tumor cell death. Additionally, because sigma-2 receptors are preferentially expressed in tumor cells, their ligands provide an effective mechanism for selective anti-cancer therapy. In the current work, we have improved upon the previously described sigma-2 ligand SW43 by conjugating it to a pro-apoptotic small molecule SMAC mimetic SW IV-52, thus generating the novel cancer therapeutic SW IV-134. The new cancer drug was tested for receptor selectivity and tumor cell killing activity in vitro and in vivo. We have shown that SW IV-134 retained adequate sigma-2 receptor binding affinity in the context of the conjugate and potently induced cell death in ovarian cancer cells. The cell death induced by SW IV-134 was significantly greater than that observed with either SW43 or SW IV-52 alone and in combination. Furthermore, the intraperitoneal administration of SW IV-134 significantly reduced tumor burden and improved overall survival in a mouse xenograft model of ovarian cancer without causing significant adverse effects to normal tissues. Mechanistically, SW IV-134 induced degradation of cIAP-1 and cIAP-2 leading to NF-[cyrillic small letter ka with descender]B activation and TNFalpha-dependent cell death. Our findings suggest that coupling sigma-2 ligands to SMAC peptidomimetics enhances their effectiveness while maintaining the cancer selectivity. This encouraging proof-of-principle preclinical study supports further development of tumor-targeted small peptide mimetics via ligands to the sigma-2 receptor for future clinical applications.
    Molecular Cancer 03/2014; 13(1):50. DOI:10.1186/1476-4598-13-50 · 4.26 Impact Factor
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    • "In addition, we have previously demonstrated that the fluorescent sigma-2 receptor probe, SW 120, is rapidly internalised into cancer cells by an endocytotic pathway and localises in multiple subcellular organelles such as mitochondria and endoplasmic reticulum (Zeng et al, 2007, 2011), suggesting that sigma-2 receptor ligands are excellent candidates to deliver anticancer drugs selectively into tumours. This sigma-2 receptor-targeting strategy has shown the initial success in pancreatic tumour xenograft mouse models (Spitzer et al, 2012). Recently, our group has identified progesterone receptor membrane component 1 as the potential sigma-2 receptor (Xu et al, 2011). "
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    ABSTRACT: Background: The sigma-2 receptor has been validated as a biomarker for proliferating tumours. Second mitochondria-derived activator of caspase (Smac) is a protein released from mitochondria into the cytosol, leading to apoptosis. In this study, we investigated a sigma-2 ligand as a tumour-targeting drug delivery agent for treating ovarian cancer. Methods: A sigma-2 ligand, SW 43, was conjugated with a Smac mimetic compound (SMC), SW IV-52s, to form SW III-123. The delivery function of the sigma-2 moiety and cell killing mechanisms of SW III-123 were examined in human ovarian cancer cell lines. Results: SW III-123 internalisation into ovarian cancer cells was mediated by sigma-2 receptors. SW III-123, but not SW IV-52s or SW 43, exhibited potent cytotoxicity in human ovarian cancer cell lines SKOV-3, CaOV-3 and BG-1 after 24-h treatment, suggesting that the sigma-2 ligand successfully delivered SMC into ovarian cancer cells. SW III-123 induced rapid degradation of inhibitor of apoptosis proteins (cIAP1 and cIAP2), accumulation of NF-κB-inducing kinase (NIK) and phosphorylation of NF-κB p65, suggesting that SW III-123 activated both canonical and noncanonical NF-κB pathways in SKOV-3 cells. SW III-123 cleaved caspase-8, -9 and -3. Tumour necrosis factor alpha (TNFα) antibody markedly blocked SW III-123-induced cell death and caspase-3 activity in SKOV-3 cells, indicating that SW III-123 activated both intrinsic and extrinsic apoptotic pathways and induced TNFα-dependent cell death in SKOV-3 cells. Conclusion: Sigma-2 ligands are a promising tumour-targeting drug delivery agent. Sigma-2-conjugated SMC exemplifies a novel class of therapeutic drugs for treating ovarian cancer.
    British Journal of Cancer 10/2013; 109(9). DOI:10.1038/bjc.2013.593 · 4.84 Impact Factor
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    • "SV119 is a small molecule ligand that binds to sigma-2 receptors with high affinity and specificity.21 The tumor-targeting efficiency of SV119 has been demonstrated by conjugating SV119 with apoptosis-inducing peptides, which resulted in the selective killing of tumor cells.22 The present study explores the potential of SV119 to mediate the targeted delivery of liposomes to multiple tumor cell lines. "
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    ABSTRACT: The sigma-2 receptor is an attractive target for tumor imaging and targeted therapy because it is overexpressed in multiple types of solid tumors, including prostate cancer, breast cancer, and lung cancer. SV119 is a synthetic small molecule that binds to sigma-2 receptors with high affinity and specificity. This study investigates the utility of SV119 in mediating the selective targeting of liposomal vectors in various types of cancer cells. SV119 was covalently linked with polyethylene glycol-dioleyl amido aspartic acid conjugate (PEG-DOA) to generate a novel functional lipid, SV119-PEG-DOA. This lipid was utilized for the preparation of targeted liposomes to enhance their uptake by cancer cells. Liposomes with various SV119 densities (0, 1, 3, and 5 mole%) were prepared and their cellular uptake was investigated in several tumor cell lines. In addition, doxorubicin (DOX) was loaded into the targeted and unmodified liposomes, and the cytotoxic effect on the DU-145 cells was evaluated by MTT assay. Liposomes with or without SV119-PEG-DOA both have a mean diameter of approximately 90 nm and a neutral charge. The incorporation of SV119-PEG-DOA significantly increased the cellular uptake of liposomes by the DU-145, PC-3, A549, 201T, and MCF-7 tumor cells, which was shown by fluorescence microscopy and the quantitative measurement of fluorescence intensity. In contrast, the incorporation of SV119 did not increase the uptake of liposomes by the normal BEAS-2B cells. In a time course study, the uptake of SV119 liposomes by DU-145 cells was also significantly higher at each time point compared to the unmodified liposomes. Furthermore, the DOX-loaded SV119 liposomes showed significantly higher cytotoxicity to DU-145 cells compared to the DOX-loaded unmodified liposomes. SV119 liposomes were developed for targeted drug delivery to cancer cells. The targeting efficiency and specificity of SV119 liposomes to cancer cells was demonstrated in vitro. The results of this study suggest that SV119-modified liposomes might be a promising drug carrier for tumor-targeted delivery.
    International Journal of Nanomedicine 08/2012; 7:4473-85. DOI:10.2147/IJN.S31981 · 4.38 Impact Factor
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