Active Targeting to Osteosarcoma Cells and Apoptotic Cell Death Induction by the Novel Lectin Eucheuma serra Agglutinin Isolated from a Marine Red Alga.

Previously, we demonstrated that the novel lectin Eucheuma serra agglutinin from a marine red alga (ESA) induces apoptotic cell death in carcinoma. We now find that ESA induces apoptosis also in the case of sarcoma cells. First, propidium iodide assays with OST cells and LM8 cells showed a decrease in cell viability after addition of ESA. With 50 µg/ml ESA, the viabilities after 24 hours decreased to 54.7 ± 11.4% in the case of OST cells and to 41.7 ± 12.3% for LM8 cells. Second, using fluorescently labeled ESA and flow cytometric and fluorescence microscopic measurements, it could be shown that ESA does not bind to cells that were treated with glycosidases, indicating importance of the carbohydrate chains on the surface of the cells for efficient ESA-cell interactions. Third, Span 80 vesicles with surface-bound ESA as active targeting ligand were shown to display sarcoma cell binding activity, leading to apoptosis and complete OST cell death after 48 hours at 2 µg/ml ESA. The findings indicate that Span 80 vesicles with surface-bound ESA are a potentially useful drug delivery system not only for the treatment of carcinoma but also for the treatment of osteosarcoma.

In vitro and in vivo anti-tumor effects of novel Span 80 vesicles containing immobilized Eucheuma serra agglutinin.

The lectin Eucheuma serra agglutinin (ESA) is known from previous studies to specifically bind to high-mannose type N-glycans and to induce apoptotic cancer cell death in vitro. In this study, Span 80 vesicles, with an average diameter between about 200 and 400 nm, containing immobilized ESA were prepared from the nonionic surfactant Span 80, also known as sorbitan monooleate. The vesicles were investigated in vitro and in vivo to evaluate the vesicles's potential applicability as novel drug delivery system. The results obtained are promising since the following was observed: (i) vesicular ESA had the same hemagglutinating activity as free ESA, demonstrating its biological activity when bound to the vesicles; (ii) vesicles containing immobilized ESA decreased the viability of Colo201 cancer cells in vitro while the growth of normal cells was not affected; (iii) the vesicles showed binding to Colo201 cells in vitro and caused inhibition of cancer cell growth in nude mice to which the vesicle-treated cells were added; (iv) the vesicles diminished tumor growth after intravenous administration to nude mice which contained an implanted Colo201 tumor; (v) the vesicles showed a tendency to accumulate at the site of the tumor 6h after i.v. administration to nude mice. Thus, all measurements carried out indicate that this type of Span 80 vesicle can be considered as promising alternatives to conventional phospholipid-based vesicles.

The anti-tumor effect of Euchema serra agglutinin on colon cancer cells in vitro and in vivo.

Eucheuma serra agglutinin (ESA) is a lectin derived from a marine red alga E. serra and binds specifically to mannose-rich sugar chains. Previous reports have indicated that ESA associates with several cancer cells via sugar chains on cell surfaces and induces apoptotic cell death. In this study, we investigated the effect of ESA on Colon26 mouse colon adenocarcinoma cells both in vitro and in vivo. ESA induced cell death against Colon26 cells in vitro, and the expression of caspase-3 and the translocation of phosphatidylserine in ESA-treated Colon26 cells suggested that this cell death was induced through apoptosis. An intravenous injection of ESA significantly inhibited the growth of Colon26 tumors in BALB/c mice; moreover, DNA fragmentation was detected in tumor cells following ESA treatment. These results indicated that ESA is effective as an anti-cancer drug not only in vitro but also in vivo. The side-effects of ESA were not considered to be serious because the decrease in body weight of the mice injected with it was negligible. These observations suggest that ESA has the potential to be an effective anti-tumor drug.