STAT3 is well corroborated preclinically as a cancer therapeutic target but tractable translational strategies for its blockade by small molecule inhibitors have remained elusive. treat ovarian cancer and other solid tumors where STAT3 is widely upregulated. Introduction The toxic side effects that standard anticancer drugs exert on healthy tissues and normal cells present obstacles in cancer treatment. These effects lead to dose reductions treatment delays and even the discontinuation of therapy. “Targeted therapy” is a relatively modern term commonly used to describe new agents including small molecules and monoclonal antibodies specifically designed to take advantage molecular pathways involved in the pathophysiology to be treated. A secondary goal of such developments is to limit the negative side effects these Chlorin E6 molecules exert on normal tissues. Unfortunately even new therapeutics cause significant adverse effects on normal tissues leading to toxicity. Thus development of safe and targeted anticancer therapies that selectively kill cancer cells while sparing the surrounding healthy tissues is essential. We identified a novel class of bifunctional compounds based on a diarylidenyl-piperidone (DAP) backbone conjugated to an test and ANOVA as appropriate. The significance level was set at ≤ 0.05. Prism Graph Pad was used for all statistical calculations. Results DAPs target STAT3 A new class of DAP compounds was synthesized by linking two diarylidene groups with a piperidone group; an antioxidant-promoting docking simulations suggested that the compounds interact with the DNA-binding domain of STAT3 we evaluated this < 0.05; Fig. 2A and B). Figure 2 Selective cytotoxicity of HO-3867 toward to cancer cells. A clonogenic assay: SKOV3 and CHO cells were treated with 10 μmol/L of H-4073 or HO-3867 for 24 hours FLJ12761 after which the drug was removed and cells were observed for 72 hours for colony-forming … Successful transfection of the A2780 and CHO cells with GFP-Histone 2B fusion protein was confirmed by fluorescence-activated cell sorting (FACS; Supplementary Fig. S3). Transfected cells were treated with 10 μmol/L of HO-3867 or H-4073 for up to 24 hours followed by immunofluorescence microscopy. In Chlorin E6 Fig. 2C red arrows indicate individual cells that underwent abortive mitosis with transient chromatin condensation or apoptosis. Quantification of chromosomal aberration at different time points (means ± SEM = 100 cells/data point) confirms the differential action of HO-3867 on normal versus cancer cells < 0.0001 (Fig. 2D). Using flow cytometry apoptosis was quantified in A2780 hOSE CHO and H9c2 cells treated with 10 μmol/L of HO-3867 or H-4073 for 24 hours. HO-3867 induced less apoptosis in hOSE CHO and H9c2 Chlorin E6 cells when compared with A2780 cells (12.3% vs. 55.8% < 0.0001) respectively whereas H-4073 induces apoptosis in both cell types (63.6% vs. 48.5% < 0.0001; Supplementary Table S1 and Fig. S4A and S4B). When compared with other STAT3 inhibitors HO-3867 show similar toxicity to cancer cells but decreased toxicity to normal cells (Supplementary Fig. S5). Furthermore we evaluated oxidative stress in the cells using 8-hydroxyguanosine (8OHdG) after treating cells with HO-3867 or H-4073 for 6 hours. After treatment with H-4073 both cell lines showed similar of levels of 8OHdG. Conversely HO-3867 treatment resulted in elevated 8OHdG staining in cancer cells relative to normal cells (Fig. 2E). Based on our previous report (2) which showed that DAP compounds induce apoptosis via activation of caspase-3 in cancer cells we examined the expression level of caspase-3 activity in both hOSE and A2780 cells treated with 10 μmol/L of HO-3867 or H-4073. An increase in caspase-3 activity expression was found in HO-3867-treated ovarian cancer cells when compared with HO-3867-treated normal cells and untreated controls but no difference was observed after H-4073 treatment (Fig. 2F). This suggests a differential involvement of caspase-3 in HO-3867-induced apoptosis. It is clear that although HO-3867 and H-4073 show similar toxicity toward cancer Chlorin E6 cells H-4073 is significantly more toxic toward normal cell types. Differential bioabsorption of DAPs in ovarian cancer cells versus normal cells To evaluate the mechanism behind the differential toxicity exhibited by the 2 2 compounds Chlorin E6 we used EPR spectroscopy UV/Vis spectrophotometry and liquid chromatography/mass spectrometry (LC/MS) with both CHO or hOSE cells and A2780 cells (3). For the EPR study hOSE Chlorin E6 and A2780 cells were treated with HO-3867 at 10 μmol/L for 3 hours and then collected for analysis. The metabolism studies were completed. In both A2780 and.