ABSTRACT : Autophagy is a homeostatic degradation process that is involved in tumor development and normal
development. Autophagy is induced in cancer cells in response to chemotherapeutic agents, and inhibition of autophagy
results in enhanced cancer cell death or survival. Chloroquine (CQ), an anti-malarial drug, is a lysosomotropic agent and is
currently used as a potential anticancer agent as well as an autophagy inhibitor. Here, we evaluate the characteristics of these dual activities of CQ using human colorectal cancer cell line HCT15. The results show that CQ inhibited cell viability in dose- and time-dependent manner in the range between 20 to 80 uM, while CQ did not show any antiproliferative activity at 5 and
10 uM. Cotreatment of CQ with antitumor agent NVP-BEZ235, a dual inhibitor of PI3K/mTOR, rescued the cell viability at
low concentrations meaning that CQ acted as an autophagy inhibitor, but CQ induced the lethal effect at high concentrations.
Acridine orange staining revealed that CQ at high doses induced lysosomal membrane permeabilization (LMP). High doses of
CQ produced cellular reactive oxygen species (ROS) and cotreatment of antioxidants, such as NAC and trolox, with high
doses of CQ rescued the cell viability. These results suggest that CQ may exert its dual activities, as autophagy inhibitor or
LMP inducer, in concentration-dependent manner.
Key words : Autophagy, Chloroquine, Lysosomal membrane permeabilization (LMP), HCT15 colorectal cancer cell line,
NVP-BEZ235