Detection of cancer cells using SapC-DOPS nanovesicles

Abstract

Unlike normal cells, cancer cells express high levels of phosphatidylserine on the extracellular leaflet of their cell membrane. Exploiting this characteristic, our lab developed a therapeutic agent that consists of the fusogenic protein, saposin C (SapC) which is embedded in dioleoylphosphatidylserine (DOPS) vesicles. These nanovesicles selectively target cancer cells and induce apoptosis. Here we review the data supporting use of SapC-DOPS to locate tumors for surgical resection or for treatment. In addition, there is important evidence suggesting that SapC-DOPS may also prove to be an effective novel cancer therapeutic reagent. Given that SapC-DOPS is easily labeled with lipophilic dyes, it has been combined with the far-red fluorescent dye, CellVue Maroon (CVM), for tumor targeting studies. We also have used contrast agents incorporated in the SapC-DOPS nanovesicles for computed tomography and magnetic resonance imaging, and review that data here. Administered intravenously, the fluorescently labeled SapC-DOPS traversed the blood–brain tumor barrier enabling identification of brain tumors. SapC-DOPS-CVM also detected a variety of other mouse tumors in vivo, rendering them observable by optical imaging using IVIS and multi-angle rotational optical imaging. Dye is detected within 30 min and remains within tumor for at least 7 days, whereas non-tumor tissues were unstained (some dye observed in the liver was transient, likely representing degradation products). Additionally, labeled SapC-DOPS ex vivo delineated tumors in human histological specimens. SapC-DOPS can also be labeled with contrast reagents for computed tomography or magnetic resonance imaging. In conclusion, labeled SapC-DOPS provides a convenient, specific, and nontoxic method for detecting tumors while concurrently offering a therapeutic benefit.

SapC-DOPS – a Phosphatidylserine-targeted Nanovesicle for selective Cancer therapy

“…PS is normally distributed asymmetrically in the plasma membrane where it is predominantly found in the inner leaflet of the membrane bilayer. This occurs, in part, through the action of flippase complexes, which selectively translocate PS inwards [1][2][3]. However, in cancer cells, PS is often expressed at high levels on the outer leaflet of the plasma membrane [4][5][6][7].…”

“…Decreased flippase activity associated with increased influx of Ca 2+ into cells and oxidative stress, chemotherapy and radiotherapy have all been shown to increase PS expression in the surface of cancer cells [6,[8][9][10]. The overexpression of PS on the surface of cancer cells has presented an opportunity for selective therapeutic targeting of cancer cells without effecting healthy cells with low surface PS [2,11]. PS can be used for identification and killing of cancer cells [2,7,[12][13][14][15][16][17].…”

“…The overexpression of PS on the surface of cancer cells has presented an opportunity for selective therapeutic targeting of cancer cells without effecting healthy cells with low surface PS [2,11]. PS can be used for identification and killing of cancer cells [2,7,[12][13][14][15][16][17]. Strategies for achieving this therapeutic effect have included the use of PStargeting antibodies that block PS-mediated immunosuppression by binding to PS on tumor cells and vasculature; annexins which inhibit tumor angiogenesis by binding to PS on tumor cells; and PS-targeting synthetic peptides which enhance membrane poration through binding to PS leading to increased cell death [18][19][20][21].…”

“…The focus of this review will be PS-targeting nanovesicles which have emerged as a strategy for selective targeting of high surface PS cancer cells [17]. These nanovesicles target cancer cells based on their binding affinities to PS, allowing them to deliver therapeutic drugs via binding to PS to induce cancer cell death while leaving healthy cells unaffected [2,11,17]. Specifically, our lab has focused on the development of SapC-DOPS, a PS-targeting nanovesicle comprised of saposin C (SapC; a lysosomal protein) and dioleylphosphatidylserine (DOPS) [2,10,12,15,17,22,23].…”

“…These nanovesicles target cancer cells based on their binding affinities to PS, allowing them to deliver therapeutic drugs via binding to PS to induce cancer cell death while leaving healthy cells unaffected [2,11,17]. Specifically, our lab has focused on the development of SapC-DOPS, a PS-targeting nanovesicle comprised of saposin C (SapC; a lysosomal protein) and dioleylphosphatidylserine (DOPS) [2,10,12,15,17,22,23]. The unique appeal of SapC-DOPS as a cancer therapy include its consistent selective targeting and killing of cancer cells while being tolerated in healthy cellsthis phenomenon has been reflected in results of phase I clinical trials where SapC-DOPS showed a strong safety profile [24,25].…”