naphthoquinones and Carcinoma--Merkel-Cell

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

Merkel cell polyomavirus (MCV) causes ~80% of primary and metastatic Merkel cell carcinomas (MCCs). By comparing digital transcriptome subtraction deep-sequencing profiles, we found that transcripts of the cellular survivin oncoprotein [BIRC5a (baculoviral inhibitor of apoptosis repeat-containing 5)] were up-regulated sevenfold in virus-positive compared to virus-negative MCC tumors. Knockdown of MCV large T antigen in MCV-positive MCC cell lines decreased survivin mRNA and protein expression. Exogenously expressed MCV large T antigen increased survivin protein expression in non-MCC primary cells. This required an intact retinoblastoma protein-targeting domain that activated survivin gene transcription as well as expression of other G(1)-S-phase proteins including E2F1 and cyclin E. Survivin expression is critical to the survival of MCV-positive MCC cells. A small-molecule survivin inhibitor, YM155, potently and selectively initiates irreversible, nonapoptotic, programmed MCV-positive MCC cell death. Of 1360 other chemotherapeutic and pharmacologically active compounds screened in vitro, only bortezomib (Velcade) was found to be similarly potent, but was not selective in killing MCV-positive MCC cells. YM155 halted the growth of MCV-positive MCC xenograft tumors and was nontoxic in mice, whereas bortezomib was not active in vivo and mice displayed serious morbidity. Xenograft tumors resumed growth once YM155 treatment was stopped, suggesting that YM155 may be cytostatic rather than cytotoxic in vivo. Identifying the cellular pathways, such as those involving survivin, that are targeted by tumor viruses can lead to rapid and rational identification of drug candidates for treating virus-induced cancers.

Topics: Animals; Antigens, Viral, Tumor; Antineoplastic Agents; Base Sequence; Boronic Acids; Bortezomib; Carcinoma, Merkel Cell; Cell Line, Tumor; Female; Gene Expression Profiling; Humans; Imidazoles; Inhibitor of Apoptosis Proteins; Merkel cell polyomavirus; Mice; Mice, Inbred NOD; Mice, SCID; Naphthoquinones; Polyomavirus Infections; Pyrazines; RNA, Messenger; RNA, Neoplasm; Survivin; Translational Research, Biomedical; Tumor Virus Infections; Xenograft Model Antitumor Assays