naphthoquinones and Cell-Transformation--Viral

Merkel cell carcinoma (MCC) is a neuroendocrine skin cancer associated with high mortality. Merkel cell polyomavirus (MCV), discovered in 2008, is associated with ~80% of MCC. The MCV large tumor (LT) oncoprotein upregulates the cellular oncoprotein survivin through its conserved retinoblastoma protein-binding motif. We confirm here that YM155, a survivin suppressor, is cytotoxic to MCV-positive MCC cells in vitro at nanomolar levels. Mouse survival was significantly improved for NOD-Scid-Gamma mice treated with YM155 in a dose and duration dependent manner for 3 of 4 MCV-positive MCC xenografts. One MCV-positive MCC xenograft (MS-1) failed to significantly respond to YM155, which corresponds with in vitro dose-response activity. Combination treatment of YM155 with other chemotherapeutics resulted in additive but not synergistic cell killing of MCC cell lines in vitro. These results suggest that survivin targeting is a promising therapeutic approach for most but not all MCV-positive MCCs.

Topics: Animals; Antineoplastic Agents; Carcinoma, Merkel Cell; Cell Line, Tumor; Cell Survival; Cell Transformation, Viral; Disease Models, Animal; Female; Humans; Imidazoles; Inhibitor of Apoptosis Proteins; Merkel cell polyomavirus; Mice; Naphthoquinones; Neoplasm Metastasis; Polyomavirus Infections; Survivin; Tumor Burden; Tumor Virus Infections; Xenograft Model Antitumor Assays

It was found that the activities of prooxidant enzymes (NAD(P)H oxidases and NAD(P)H:cytochrome c reductases) in bovine leukemia virus-transformed calf and lamb embryo kidney fibroblasts (lines Mi-18 and FLK) were by 1.25-18 times higher when compared to corresponding nontransformed calf cells. The activity of DT-diaphorase was also increased by about one order of magnitude in transformed cells. The activities of antioxidant enzymes were almost unchanged (superoxide dismutase), decreased by 13% or 53% (catalase) or increased by 25% or 90% (glutathione reductase) in Mi-18 or FLK cells, respectively. These changes of enzyme activity increased the toxicity of simple redox-cycling quinones (duroquinone, naphthazarin) towards transformed cells, but did not affect the toxicity of daunorubicin. The latter was most probably related to the inhibition of plasma membrane NADH dehydrogenase.

Topics: Animals; Benzoquinones; Cattle; Cell Line, Transformed; Cell Survival; Cell Transformation, Viral; Embryo, Mammalian; Ferricyanides; Fibroblasts; Kidney; Leukemia Virus, Bovine; Multienzyme Complexes; NAD(P)H Dehydrogenase (Quinone); NADH Dehydrogenase; NADH, NADPH Oxidoreductases; NADPH Oxidases; NADPH-Ferrihemoprotein Reductase; Naphthoquinones; Oxidation-Reduction; Quinones; Sheep