Combined antiproliferative effects of the aminoalkylindole WIN55,212-2 and radiation in breast cancer cells.

The potential antitumor activity of cannabinoid receptor agonists, such as the aminoalklylindole WIN55,212-2 (WIN2), has been studied extensively, but their potential interaction with conventional cancer therapies, such as radiation, remains unknown. In the present work, the influence of WIN2 on the antiproliferative activity of radiation in human (MCF-7 and MDA-MB231) and murine (4T1) breast cancer cells was investigated. The antiproliferative effects produced by combination of WIN2 and radiation were more effective than either agent alone. The stereoisomer of WIN2, WIN55,212-3 (WIN3), failed to inhibit growth or potentiate the growth-inhibitory effects of radiation, indicative of stereospecificity. Two other aminoalkylindoles, pravadoline and JWH-015 [(2-methyl-1-propyl-1H-indol-3-yl)-1-naphthalenyl-methanone], also enhanced the antiproliferative effects of radiation, but other synthetic cannabinoids (i.e., nabilone, CP55,940 [(+)-rel-5-(1,1-dimethylheptyl)-2-[(1R,2R,5R)-5-hydroxy-2-(3-hydroxypropyl)cyclohexyl]-phenol], and methanandamide) or phytocannabinoids [i.e., Δ9-tetrahydrocannabinol (THC) and cannabidiol] did not. The combination treatment of WIN2 + radiation promoted both autophagy and senescence but not apoptosis or necrosis. WIN2 also failed to alter radiation-induced DNA damage or the apparent rate of DNA repair. Although the antiproliferative actions of WIN2 were mediated through noncannabinoid receptor-mediated pathways, the observation that WIN2 interfered with growth stimulation by sphingosine-1-phosphate (S1P) implicates the potential involvement of S1P/ceramide signaling pathways. In addition to demonstrating that aminoalkylindole compounds could potentially augment the effectiveness of radiation treatment in breast cancer, the present study suggests that THC and nabilone are unlikely to interfere with the effectiveness of radiation therapy, which is of particular relevance to patients using cannabinoid-based drugs to ameliorate the toxicity of cancer therapies.

Autophagy inhibition for chemosensitization and radiosensitization in cancer: do the preclinical data support this therapeutic strategy?

Recognition of the cytoprotective functions of autophagy that occur in tumor cells exposed to various forms of chemotherapy or radiation has generated intense interest in the possibility that pharmacological interference with autophagy could provide a clinical strategy for overcoming therapeutic resistance. Multiple clinical trials are currently in progress to evaluate the antimalarial agent chloroquine (generally in its clinical formulation as hydroxychloroquine) and its impact on various forms of cancer therapy. In this commentary/review, we focus on the relatively limited number of studies in the literature where chloroquine has been tested in combination with chemotherapy or radiation in experimental tumor-bearing animal models. We also present recent data from our own laboratories, in cell culture experiments as well as in vivo studies, which demonstrate that neither chloroquine nor silencing of an autophagy regulatory gene was effective in conferring radiation sensitivity in an experimental model of breast cancer. The capacity for sensitization by chloroquine appears to be quite wide-ranging, with dramatic effects for some drugs/tumor models and modest or minimal effects in others. One possible caveat is that, with only a few exceptions, experiments have generally been performed in xenograft models, thereby eliminating the involvement of the immune system, which might ultimately be proven to play a central role in determining the effectiveness of autophagy inhibition in chemosensitization or radiosensitization. Nevertheless, a careful review of the current literature suggests that caution is likely to be warranted in translating preclinical findings relating to autophagy inhibition as an adjunctive therapeutic strategy.

Autophagy, cell death and sustained senescence arrest in B16/F10 melanoma cells and HCT-116 colon carcinoma cells in response to the novel microtubule poison, JG-03-14.

PURPOSE: 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. METHODS: 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 ß-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. RESULTS: 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. CONCLUSIONS: 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.