Abstract 1840: SapC-DOPS nanovesicles: Acidic lipid domain-targeted agents for cancer therapy

Proceedings: AACR 103rd Annual Meeting 2012‐‐ Mar 31‐Apr 4, 2012; Chicago, IL Introduction: Acidic phosphatidylserine-enriched membrane microdomains (PS-EMMs) are exposed on the membrane surface of cancer cells and tumor blood vessels. We have explored a novel PS-EMMs targeting mechanism by saposin C (SapC)-coupled dioleoylphosphatidylserine (DOPS) nanovesicles that are found to specifically target and destroy cancer and tumor-associated endothelial cells with little or no systemic toxicity (Qi et al. Clin. Cancer Res. 2009; Kaimal et al. Mol. Imaging Biol. 2011). Methods: We have developed a novel biotheragnositic agent, SapC-DOPS, which we assembled into cancer-selective nanovesicles. Surface exposed PS levels were analyzed by a flow cytometric method using fluorescently labeled annexin-V. Deparafinized tissue slides were stained using far-red fluorophore (CellVue Maroon, CVM) labeled SapC-DOPS nanovesicles, SapC-DOPS-CVM was used to determine cancer-selective targeting via PS-mediated membrane fusion in human cancer cells, patient-derived cancer tissue specimens, and preclinical animal tumor models, including brain, pancreatic, lung, and pediatric cancers. The cytotoxicity of SapC-DOPS was measured using the MTT assay. Live imaging for visualization of SapC-DOPS PS-targeting and survival curves were demonstrated in transgenic and xenograft mouse tumor models. Results: We demonstrated the specific targeting of SapC-DOPS in paraffin embedded patient-derived tumor tissue sections. Based on MTT assay and annexin-V labeled flow cytometry, we revealed that SapC-DOPS cytotoxic effects correlated to the level of surface exposed PS in a variety of human cancer cell lines. Kinetic studies indicated that SapC-DOPS fused with tumor cell membrane within a few minutes, followed by internalization into the cells. In vivo cancer cell targeting of SapC-DOPS was blocked by pretreatment with PS-specific binding proteins (Lact-C2 and beta-2 glycoprotin-1). Increased PS expression and externalization on cancer cell membrane surfaces after chemotherapy or extracellular stresses enhanced the SapC-DOPS response. SapC-DOPS showed cancer-selective targeting in numerous spontaneously formed and xenografted tumors in living mice using either a double-tracking optical or a contrast-enhanced magnetic resonance imaging system. Furthermore, we observed that tumor-bearing animals treated with intravenous SapC-DOPS had significant tumor reduction and increased survival. Tumor-free survivals were confirmed by tumor-luminescence imaging and at necropsy. Conclusion: We have demonstrated a novel biomarker for numerous human cancers that can be effectively targeted by using cancer-selective SapC-DOPS nanovesicles. The direct confirmation of tumor-targeting by SapC-DOPS provides powerful new evidence in support of our goal to develop PS-EMMs targeted nanovesicles as novel therapeutic agents for cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1840. doi:1538-7445.AM2012-1840