MITOPHAGY-MEDIATED NOVEL CELL DEATH INDUCED BY FOLATE-APPENDED METHYL-β-CYCLODEXTRIN

Keiichi Motoyama

Department of Physical Pharmaceutics, Graduate School of Pharmaceutical Science, Kumamoto University, Kurokami Chuo-ku Kumamoto, Japan

Abstract

In cancer chemotherapy to obtain the maximum treatment efficacy of anticancer agents, the drug delivery technique is extremely important. To confer an active targeting-ability, the chemical modification of tumor-specific ligands to a drug carrier is known. Recently, folic acid (FA) has emerged as a prominent targeting moiety capable of specific interaction with cells expressing the folate receptor (FR). FR is overexpressed in many human tumor cells, and has little expression in normal tissues. Therefore, FR is one of the potent candidates for an attractive marker and a target molecule for diagnosis and therapy of cancer, respectively.

Cyclodextrins (CyDs) have been reported to interact with cell membrane constituents such as cholesterol and phospholipids. Recently, we demonstrated that 2,6-di-O-methyl-b-cyclodextrin (DM-b-CyD) induced apoptosis through the inhibition of PI3K-Akt-Bad pathway, leading to cholesterol depletion from lipid rafts in NR8383 cells, a rat alveolar macrophage cell line [1]. Notably, Grosse et al. reported that the intraperitoneal administration of M-b-CyD had antitumor activity in the human tumor xenografted athymic nude mice [2]. However, the cytotoxic reaction of M-b-CyD has a lack of a tumor cell-selectivity.

Therefore, in the present study to confer a tumor cell-selectivity on M-b-CyD, we newly synthesized folate-appended M-b-CyD (FA-M-b-CyD), and evaluated its potential as a novel anticancer agent in vitro and in vivo. Potent antitumor activity and cellular association of FA-M-b-CyD were higher than those of M-b-CyD in KB cells, FR-positive cells [3]. In addition, FR-overexpressing cell-selective cytotoxic activity of FA-M-b-CyD was found to be mediated by the regulation of autophagy, rather than the induction of apoptosis [4]. Notably, FA-M-b-CyD drastically elevated a mitochondrial transmembrane potential and promoted ROS production from mitochondria in KB cells. In addition, FA-M-b-CyD augmented the PINK1 expression, a specific mitophagy marker. Actually, the mitochondrial DNA in KB cells was significantly decreased after treatment with FA-M-b-CyD [5]. From the in vivo studies, FA-M-b-CyD drastically inhibited the tumor growth after an intravenous injection to KB cells-xenografted mice⁵. FA-M-b-CyD was rapidly eliminated from blood after an intravenous administration to KB cells-xenografted mice. Meanwhile, FA-M-b-CyD significantly accumulated in tumor tissues rather than in other organs. Importantly, an intravenous administration of FA-M-b-CyD to tumor-bearing mice showed the only slight change in blood chemistry values. These findings strongly indicate that FA-M-b-CyD provides the potent antitumor efficacy in vivo, through an accumulation in tumor tissue and induction of mitophagy-mediated cell death.

Keywords: Cyclodextrins, tumor, mitophagy, antitumor, chemotherapy.

REFERENCES

[1] Motoyama, K. et al., Eur. J. Pharm. Sci., 2009, 38, 249-261.
[2] Grosse, P.Y. et al., Brit. J. Cancer, 1998, 78, 1165-1169.
[3] Onodera, R. et al., Sci. Rep., 2013, 3, 1104, 1-9.
[4] Onodera, R. et al., Sci. Rep., 2014, 4, 4417, 1-8.
[5] Kameyama, K. et al., Int. J. Nanomedicine, in press.