Synthesis and SAR Analysis of a Family of STAT3 Inhibitors

Abstract

Inhibiting STAT3 dimerization and the interaction of STAT3 with the DNA-binding domain is important for preventing the progression of malignant transformations in glioma, breast, prostate, ovarian and other cancers. The Tius group has designed STAT3 inhibitors that disrupt STAT3 dimerization/DNA-binding. However, for these STAT3 inhibitors to be developed into effective anti-cancer drugs, the potency and physicochemical properties of these molecules needs to be improved. Previous SAR analysis was performed to improve the potency and physicochemical properties of the STAT3 inhibitors and from this analysis a general scaffold was developed (Chapter 1, Figure 7). It was determined that pyridine or pyrazine structural motifs in region 2 (R2) produced the most potent compounds compared to analogs with different heterocycles. To resolve which heteroarene, pyridine or pyrazine, produces the most potent compounds more analogs containing these functional groups were needed for comparison. It was also shown that one compound with difluorocyanobenzenesulfonamide in region 3 (R3) had improved potency over its pentafluorobenzenesulfonamide analog. To confirm that the difluorocyanobenzenesulfonamide fragment generally improves compound potency, more analogs needed to be examined. Furthermore, it was discovered that compounds containing a carboxyl or hydroxamic acid functional group in region 4 (R4) have good potency, but poor permeability. Functionalities in R4 needed to be varied to improve both potency and permeability. In an attempt to optimize R2, R3, and R4 in terms of potency and physicochemical properties 12 small molecule STAT3 inhibitors were prepared. These compounds were designed and synthesized using convergent routes containing 7-15 synthetic steps. The synthetic route employed had broad functional group tolerance that easily enabled the development of a small molecule library for biological screening. Each molecule prepared was tested for STAT3 DNA-binding inhibitory activity using the EMSA assay. The physicochemical properties of lead inhibitory agents will be tested in the near future. SAR analysis on R2 was inconclusive; more analogs comparing pyridine and pyrazine need to be explored to resolve which heterocycle leads to the most potent compounds. Replacing the pentafluorobenzenesulfonamide functional group with difluorocyanobenzenesulfonamide increased potency in three out of the four analog comparisons suggesting that compounds with R3 = difluorocyanobenzenesulfonamide have better potency compared to analogs with R3 = pentafluorobenzenesulfonamide. Compounds with R4 = N-methylsalicylamide, N,N-dimethylsalicylamide, meta-difluoromethylbenzene, or meta-fluorobenzene had similar or lower STAT3 inhibitory activity than the parent compounds with R4 = salicylic acid. However, replacing the salicylic acid functionality with benzene enhanced potency. This suggests that functional groups on the benzene ring in R4 are not necessary for enhancing potency.