Despite recent advances in medicine, mortality from all forms of epithelial cancers remains unexpectedly high, highlighting the need for improved treatment strategies. Recent developments in the understanding of the molecular pathogenesis of cancer have aided in formulating both preventive and/or therapeutic strategies. Accumulating evidence indicates that the development and progression of many malignancies, including breast and colorectal cancer are associated with constitutive activation of multiple signaling including those induced through activation of Src and EGFR and its family members (EGFRs). The current investigation was under taken to determine the therapeutic effectiveness of simultaneous targeting of multiple pathways. In pursuit of this goal, we initially utilized dasatinib, a Src family kinase inhibitor as a primary agent. Dasatinib has been shown to exert anti-proliferative activity in different hematological as well as solid cancers. However, in breast cancer cells dasatinib caused a modest 20-40% growth inhibition. In order to augment the inhibitory properties of this agent, we included a novel 55 kDa protein referred to as ErbB I nhibitory P rotein (EBIP) that represents a modified ectodomain of human EGFR and targets EGFR and its family members (pan-ErbB inhibitor). Indeed, dasatinib together with EBIP caused a much greater inhibition of growth of breast cancer cells than either agent alone. Calsusyn analysis revealed a synergistic interaction between the two agents in breast cancer cells expressing varying levels of EGFRs. Since MDA-MB-468 is a triple negative breast cancer with known resistance to known EGFR targeted therapies, we utilized this cell line for further investigations. The combination therapy of EBIP and dasatinib was highly effective in inhibiting growth, cell cycle arrest and inducing apoptosis through caspases -8 and -9. The combined therapy was also more effective in inhibiting the aggressive behavior of cancer cells, as evidenced by decreased colony formation and extracellular invasion. Additionally, the processes of angiogenesis, as determined by tubule formation by endothelial cells, were greatly inhibited. In vivo studies further demonstrated the synergy between EBIP and dasatinib in inhibiting the growth of breast cancer derived xenografts. Like EBIP, curcumin, a dietary ingredient, has also been shown to inhibit activation of EGFR and its family members, suggesting a pan-ErbB inhibitory role of this agent. To determine whether the combination of dasatinib and curcumin could be a potential therapeutic strategy for epithelial cancers the next set of experiments were conducted in colon cancer cells. The combined therapy of curcumin and dasatinib was found to be synergistic and highly effective in inhibiting cell growth and diminish the aggressive behavior of colon cancers cells. These changes were associated with inhibition of multiple signaling pathways that included EGFRs, IGF-1R and c-Src, leading to attenuation of NFκB activity. Based on our observations, we conclude that simultaneous inhibition of multiple signaling pathways is a better therapeutic strategy for epithelial cancers with particular reference to breast and colon.
