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Purpose: Melanoma is the most invasive and deadly form of skin cancer. Few agents are available for treating advanced disease to enable long-term patient survival, which is driving the search for new compounds inhibiting deregulated pathways causing melanoma. Akt3 is an important target in melanomas because its activity is increased in f70% of tumors, decreasing apoptosis in order to promote tumorigenesis. Experimental Design: Because naturally occurring products can be effective anticancer agents, a library was screened to identifyAkt3 pathway inhibitors. Isothiocyanates were identified as candidates, but low potency requiring high concentrations for therapeutic efficacy made them unsuitable. Therefore, more potent analogs called isoselenocyanates were created using the isothiocyanate backbone but increasing the alkyl chain length and replacing sulfur with selenium. Efficacy was measured on cultured cells and tumors by quantifying proliferation, apoptosis, toxicity, and Akt3 pathway inhibition. Results: Isoselenocyanates significantly decreased Akt3 signaling in cultured melanoma cells and tumors. Compounds having 4 to 6 carbon alkyl side chains with selenium substituted for sulfur, called ISC-4 and ISC-6, respectively, decreased tumor development by f60% compared with the corresponding isothiocyanates, which had no effect. No changes in animal body weight or in blood parameters indicative of liver-, kidney-, or cardiac-related toxicity were observed with isoselenocyanates. Mechanistically, isoselenocyanates ISC-4 and ISC-6 decreased melanoma tumorigenesis by causing an f3-fold increase in apoptosis. Conclusions: Synthetic isoselenocyanates are therapeutically effective for inhibiting melanoma tumor development by targeting Akt3 signaling to increase apoptosis in melanoma cells with negligible associated systemic toxicity.

Malignant melanoma has a high propensity for metastatic spread, making it the most deadly form of skin cancer. B-RAF has been identified as the most mutated gene in these invasive cells and therefore an attractive therapeutic target. However, for uncertain reasons, chemotherapy inhibiting B-Raf has not been clinically effective. This has raised questions whether this pathway is important in melanoma metastasis or whether targeting a protein other than B-Raf in the signaling cascade could more effectively inhibit this pathway to reduce lung metastases. Here, we investigated the role played by V600E B-Raf in melanoma metastasis and showed that targeting this signaling cascade significantly reduces lung metastases. Small interfering RNA (siRNA)-mediated inhibition was used in mice to reduce expression (activity) of each member of the signaling cascade and effects on metastasis development were measured. Targeting any member of the signaling cascade reduced metastasis but inhibition of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (Mek) 1 and Mek 2 almost completely prevented lung tumor development. Mechanistically, metastatic inhibition was mediated through reduction of melanoma cell extravasation through the endothelium and decreased proliferative capacity. Targeting B-Raf with the pharmacologic inhibitor BAY 43-9006, which was found ineffective in clinical trials and seems to act primarily as an angiogenesis inhibitor, did not decrease metastasis, whereas inhibition of Mek using U0126 decreased cellular proliferative capacity, thereby effectively reducing number and size of lung metastases. In summary, this study provides a mechanistic basis for targeting Mek and not B-Raf in the mutant V600E B-Raf signaling cascade to inhibit melanoma metastases. (Cancer Res 2006; 66(16): 8200-9)

Synthesis and identification of novel phenylalkyl isoselenocyanates (ISCs), isosteric selenium analogs of naturally occurring phenylalkyl isothiocyanates (ITCs), as effective cytotoxic and anti-tumor agents is described. The structure-activity relationship comparison of ISCs with ITCs and effect of the increasing alkyl chain length in inhibiting cancer cell growth was evaluated on melanoma, prostate, breast, glioblastoma, sarcoma, and colon cancer cell lines. IC50 values for ISC compounds were generally lower than their corresponding ITC analogs. Similarly, in UACC 903 human melanoma cells, the inhibition of cell proliferation and induction of apoptosis were more pronounced with ISCs as compared to ITCs. Further, ISCs and ITCs effectively inhibited melanoma tumor growth in mice following intraperitoneal xenograft. A similar reduction in tumor size was observed at three times lower doses of ISCs as compared to corresponding ITCs.