Abstract
Previous studies have shown that the novel microtubule poison, JG-03-14, which binds to the colchicine binding site of tubulin, has the capacity to kill breast tumor cells primarily through the promotion of autophagy. The current work was designed to determine whether autophagy was, in fact, the primary mode of action as well as susceptibility to JG-03-14 in two additional tumor cell models, the B16/F10 murine melanoma cell line and the HCT-116 human colon cancer cell line.
Drug cytotoxicity was monitored based on viable cell number and clonogenic survival. Apoptosis was assessed by DAPI staining, the TUNEL assay and/or FACS analysis. Autophagy was monitored based on staining with acridine orange, redistribution and punctuation of RFP-LC3 and electron microscopy as well as p62 degradation. Senescence was evaluated based on beta-galactosidase staining and alterations in cell morphology. Drug effects were also evaluated in a murine model of B16/F10 cells that localizes to the lungs while peripheral neuropathy was assessed by three complementary behavioral assays.
Both HCT-116 colon cancer cells and B16/F10 melanoma cells were sensitive to JG-03-14 in that the drug demonstrated tumor cell killing. However, there was minimal induction of apoptosis. In contrast, there was clear evidence for autophagy and autophagic flux while the residual surviving cells appeared to be in a state of irreversible senescence. Inhibition of drug-induced autophagy in either the melanoma cells or the colon carcinoma cells was only slightly protective as the cells instead died by apoptosis. JG-03-14 reduced the size of tumor nodules in mice lungs; furthermore, the drug did not promote peripheral neuropathy.
Taken together with evidence for its actions as a vascular disrupting agent, these observations support the potential utility of JG-03-14 to effectively treat malignancies that might be resistant to conventional chemotherapy through evasion of apoptosis.