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Melanoma is the most lethal human skin cancer. If metastatic, it becomes very aggressive and resistant to standard modalities of anticancer treatment. During the last 10 years, several therapeutic strategies have been tested including the use of single and combined small drugs. Experimental results indicate that RAS and PI3K pathways are important for the development and maintenance of melanoma. In this study, we assessed thein vitroandin vivoinhibition potential of PI-103, a PI3K (p110α)/mTOR inhibitor and sorafenib, a BRAF inhibitor, as single agents and in combination in primary melanoma cell lines. Although PI-103 and sorafenib inhibited melanomain vitrocell proliferation and viability, the inhibition of RAS pathway appeared to be more effective. The combination of the two agents inin vitroshowed a synergistic effect inhibiting RAS and PI3K pathways in a cell line dependent manner. However, no cooperative effect was observed in blockingin vivotumor growth in immunocompetent mice. In contrary to the expected, the data indicate that PI-103 induced immunosuppression promotingin vivotumor growth and inhibiting apoptosis. Furthermore,in vitrostudies examining the effects of the PI3K/mTOR inhibitor in tumor derived cell lines indicated that PI-103 induced the anti-apoptotic BH3 family proteins Mcl1, Bcl2 and BclxL favoring, thein vitrosurvival of sorafenib treated melanoma cells. These data certainly makes an argument for investigating unexpected effects of rational drug combinations on immunocompetent animal models prior to conducting clinical studies.