濱 進

Intraperitoneal administration of anticancer nanoparticles is a rational strategy for preventing peritoneal dissemination of colon cancer due to the prolonged retention of nanoparticles in the abdominal cavity. However, instability of nanoparticles in body fluids causes inefficient retention, reducing its anticancer effects. We have previously developed anticancer nanoparticles containing tocopheryl succinate, which showed high in vivo stability and multifunctional anticancer effects. In the present study, we have demonstrated that peritoneal dissemination derived from colon cancer was prevented by intraperitoneal administration of tocopheryl succinate nanoparticles. The biodistribution of tocopheryl succinate nanoparticles was evaluated using inductively coupled plasma mass spectroscopy and imaging analysis in mice administered quantum dot encapsulated tocopheryl succinate nanoparticles. Intraperitoneal administration of tocopheryl succinate nanoparticles showed longer retention in the abdominal cavity than by its intravenous (i.v.) administration. Moreover, due to effective biodistribution, tumor growth was prevented by intraperitoneal administration of tocopheryl succinate nanoparticles. Furthermore, the anticancer effect was attributed to the inhibition of cancer cell proliferation and improvement of the intraperitoneal microenvironment, such as decrease in the levels of vascular endothelial growth factor A, interleukin 10, and M2-like phenotype of tumor-associated macrophages. Collectively, intraperitoneal administration of tocopheryl succinate nanoparticles is expected to have multifaceted antitumor effects against colon cancer with peritoneal dissemination.

α-Tocopheryl succinate (TS) is a tocopherol derivative and has multifaceted anti-cancer effects; TS not only causes cancer cell-specific apoptosis but also inhibits tumor angiogenesis. Although TS has the potential to be used as a well-tolerated anti-angiogenic drug, it is still unclear which step of the angiogenic process is inhibited by TS. Here, we show that TS inhibits the expression of angiopoietin (Ang)-2, which induces destabilization of vascular structure in the initial steps of the angiogenic process. In mouse melanoma cells, TS treatment decreased mRNA and extracellular protein levels of Ang-2; however, the mRNA level of Ang-1, which stabilizes the vascular structure, remained unchanged. Furthermore, aorta ring and Matrigel plug angiogenesis assays indicated that the conditioned medium from TS-treated cells (CM-TS) inhibited neovascularization and blood leakage from the existing blood vessels, respectively. Following immunohistochemical staining of the vessels treated with CM-TS, imaging studies showed that the vascular endothelial cells were highly packed with pericytes. In conclusion, we found that TS inhibits Ang-2 expression and, consequently, stabilizes the vascular structure during the initial step of tumor angiogenesis.

We previously found that antioxidative activity of liposomes co-encapsulating astaxanthin (Asx) and tocotrienols (T3s) was higher than the calculated additive activity, which results from intermolecular interactions between both antioxidants (J. Clin. Biochem. Nutr., 59, 2016, Kamezaki et al.). Herein, we conducted experiments to optimize Asx/α-T3 ratio for high antioxidative activity, and tried to elucidate details of intermolecular interaction of Asx with α-T3. Higher activity than calculated additive value was clearly observed at an Asx/α-T3 ratio of 2 : 1, despite two α-T3 would potentially interact with two terminal rings of one Asx. The synthetic Asx used in this study was a mixture of three stereoisomers, 3R,3'R-form (Asx-R), 3S,3'S-form (Asx-S) and 3R,3'S-meso form (Asx-meso). The calculated binding energy of the Asx-S/α-T3 complex was higher than those of Asx-R/α-T3 and Asx-meso/α-T3, suggesting that Asx-S and α-T3 is the most preferable combination for the intermolecular interaction. The optimal Asx-S/α-T3 ratio for antioxidation was shown to be 1 : 2. These results suggest that the Asx stereochemistry affects the intermolecular interaction of Asx/α-T3. Moreover, the absorption spectrum changes of Asx-S upon co-encapsulation with α-T3 in liposomes indicate that the electronic state of Asx-S is affected by intermolecular interactions with α-T3. Further, intermolecular interactions with α-T3 affected the electronic charges on the C9, C10 and C15 atoms in the polyene moiety of Asx-S. In conclusion, the intermolecular interaction of Asx/T3 depends on the Asx stereochemistry, and caused a change in the electronic state of the Asx polyene moiety by the presence of double bond in the T3 triene moiety.