Design,Synthesis And Application Of A Novel Small Molecule Inhibitor Targeting Transcription Factor STAT3 In Cancer

Mutations or deregulation of transcription factors result in abnormal gene expression,leading to aberrant cell growth and differentiation,and contribute to the development and progression of cancer.As a member of transcription factors,transcriptional regulation of STAT3 plays an important role in physiological and pathological processes in vivo.STAT3 is activated rapidly and transiently in normal physiological conditions.However,clinical data show that STAT3 is persistently activated and highly expressed in multiple tumor cells in pathological conditions.The constitutive activation of STAT3 regulates multiple periods of tumor including growth,metastasis,resistance,and escape from the immune system.Inhibiting the phosphorylation of STAT3 is capable of suppressing tumor growth and metastasis,and is associated with drug resistance.In addition,collected data have demonstrated that STAT3 overexpression is also significantly associated with poor prognosis.Therefore,STAT3 has become a key target in the field of cancer therapy.Treatment of diseases associated with STAT3 is greatly aided by developing effective STAT3 inhibitors.There have been many significant breakthroughs with STAT3 inhibitors over the years,none of these STAT3 inhibitors has been approved by the U.S.FDA to date.Multiple methods have been reported to inhibit STAT3,including small molecule inhibitors targeting the SH2 domain of STAT3,allosteric inhibitors designed against allosteric sites on the surface of STAT3 protein,and STAT3 degraders designed and developed through PROTAC technology.Current STAT3 inhibitors or degraders also present certain problems,potential off-target effects resulting from poor selectivity.In the absence of a powerful inhibitor of STAT3,it is impossible to effectively inhibit STAT3’s transcriptional regulation function.The physicochemical properties and druggability of most STAT3 inhibitors are poor.The small molecule STAT3 inhibitors in clinical trials are mostly targeting the SH2 domain due to their importance in the function of STAT3.However,the antiproliferative activities of these STAT3 inhibitors are at the micromolar level,and their physicochemical properties are weak,so there is still a lot of room for improvement.Our group designed and synthesized a series of compounds targeting the SH2 domain of STAT3.Representative compound WB-436 C binds to STAT3 with a strong binding affinity(KD)of 0.95 μM by SPR,and the binding energy of WB-436 C to STAT3 protein is-6.7 kcal/mol in Autodock Vina.WB-436 C inhibits the phosphorylation of STAT3 at a concentration of 1 μM and its antiproliferative activity is 532.40 ± 24.89 n M.However,WB-436 C still needs to be improved due to its poor water solubility(Aqueous solubility: < 0.78 μM),and oral bioavailability after administration in rats is only 0.75%.WB-436 C was used as a lead compound for a series of investigations,the properties of the targeted compounds were improved after the exploration following structure-based drug design and molecular docking.Among them,compound 6s(IC50= 16.97 ± 0.38 n M)was almost 30-fold higher than WB-436 C.Compound 7f inhibited the phosphorylation of STAT3 at a concentration of 0.03 μM,more effective than WB-436 C.compound 7h(IC50 = 69.23 ± 7.44 n M)was almost 8-fold higher than WB-436 C,the binding energy of 7h to STAT3 protein was-7.5 kcal/mol,which is improved compared to WB-436 C.The most worth thing was that the aqueous solubility of compound 8j(Aqueous solubility: 172.3 μM)is nearly a hundred times higher than that of WB-436 C.The results of this study provide a solid foundation for further optimization.In summary,through molecular docking,structure-based drug design,and virtual screening,combined with in vitro biological activity evaluation,targeted compounds with antiproliferative activities at a nanomolar level were obtained.The targeted compounds effectively inhibited the phosphorylation of STAT3,and its physicochemical properties were relatively improved.Targeted compounds have laid a solid foundation for us to successfully develop STAT3 inhibitors for the treatment of related diseases.