Constitutive activation of the signal transducer and activator of transcription-3 (STAT3) protein in cancer cells is thought to promote cell proliferation and angiogenesis, inhibit apoptosis, and drive genes important for invasion and metastasis. Therefore inhibition of STAT3 represents a rational approach to cancer therapy for a large proportion of malignancies. One promising lead compound for STAT3 inhibition is the natural product, curcumin. Curcumin has anti-cancer properties in numerous models and has been shown to inhibit a variety of cellular targets including STAT3. The molecular structure of curcumin indicates that the molecule exists in two distinct tautomeric forms: 1) a diketone form (-keto) and 2) an keto-enol (-enol) form. Computational chemistry and structure-activity-relationship preliminary studies conducted by our group have predicted that the diketo- tautomer but not the enol-tautomer of curcumin can inhibit STAT3 dimerization. Therefore, we have designed novel curcumin analogs locked into the diketo form with the goal of enhancing the specificity for STAT3 as a molecular target. Preliminary data contained within this proposal demonstrate that early generation analogs are highly specific for STAT3, and induce potent pro-apoptotic effects in vitro. We hypothesize that the diketo- tautomer form of curcumin can be manipulated to produce enhanced pro-apoptotic activity on melanoma cells by inhibiting STAT3 phosphorylation and dimerization. To test this hypothesis, we propose to develop soluble, metabolically stable, small molecule curcumin analogs that specifically inhibit STAT3 SH2 phosphorylation and dimerization (Aim 1). The pro-apoptotic effects of the resulting STAT3-inhibitory curcumin analogs will subsequently be evaluated in vitro (Aim 2). For these studies, melanoma cells will be used as a model as it represents a highly chemo-resistant tumor in which STAT3 is thought to play a major role. Finally, we will determine if STAT3 inhibition with curcumin or its resulting analogs can serve to augment the direct anti-tumor actions of Type I and Type II interferons on melanoma cells (Aim 3). The data derived from these studies will support the development of complementary approaches to cancer care by investigating a novel, targeted agent derived from a natural compound. The studies proposed in Aim 3 will extend our focus on testing whether STAT3-targeted inhibitors derived from curcumin could also be used to augment the anti-tumor effects of conventional melanoma therapy with cytokines (e.g. the interferons). Ultimately, knowledge gained from these studies will guide future translational research to devise novel therapeutic strategies for melanoma and any other cancer in which STAT3 plays a role. PUBLIC HEALTH RELEVANCE: Curcumin is a natural product derived from the dietary spice 'turmeric'that has been shown to kill cancer cells in culture. Preliminary experiments performed by our research group have shown that the chemical structure of curcumin can be modified to make it more specific for a protein named STAT3 that is highly active in cancer cells. We propose to further modify this chemical structure to more effectively kill melanoma skin cancer cells. We will also determine if this modified derivative of curcumin can enhance the ability of standard drugs (called interferons) to kill cancer cells.