Structure-Diversity Oriented Design,Synthesis And Biological Evaluation Of Novel Gossypol Derivatives And Analogs

Gossypol is a naturally occurring polyphenol which presents in members of the Malvaceae family.It was not considered to be a valuable natural product with useful biological activities due to its inherent toxicity until its outstanding anticancer and male infertility activities were discovered.Gossypol exists as two optically active forms due to the restricted rotation bond around the C2-C2' inter naphthyl.Many studies have demonstrated that(-)-gossypol was usually more potent in most biological evaluations in comparison with(+)-gossypol or racemic gossypol.AT-101((-)-gossypol),which was developed by Ascenta company,has been undergoing Phase ? clinical trials,displaying single-agent antitumor activity in patients with advanced malignancies.However,side effects such as gastrointestinal toxicities and liver damage etc.have restricted the clinical applications of gossypol.Gossypol was approved firstly as a male infertility drug in China in 1978 but stopped due to its toxicities.The development of gossypol as a therapeutic agent still remained a challenge because of a number of side effects from gossypol's two reactive aldehyde groups,the active aldehydes are easily to react with amino acids in vivo and cause toxicities.Therefore,it is significant to develop novel gossypol derivatives with enhanced biological activities and reduced toxicity.Cancer is a serious disease and a leading cause of death which threats to human life.To discover new anticancer drugs based on gossypol,we designed and synthesized a variety of structure-diversity oriented gossypol derivatives as well as analogs and evaluated their biological activities using gossypol as the lead compound.(1)Gossypol Schiff bases are aldehydes masked derivatives of gossypol with reduced toxicity.However,from known results,the reported gossypol Schiff bases decreased dramatically compared with gossypol itself in terms of antitumor activity,even the(-)-gossypol Schiff bases can't give better results.And the effects of the introduced substituents of gossypol Schiff bases were still ambiguous.As a matter of fact,an investigation of the mechanism of gossypol Schiff bases was not pursued in these previous studies.Herein,we firstly reported gossypol with hydrophobic linear esters exhibits enhanced antitumor activity.To explore the SAR,we systematically investigated many types of gossypol Schiff bases with hydrophilic,hydrophobic and steric hindrance substituents and synthesized 28 compounds.The results indicated that compound III-6-16 with a hydrophobic linear ester was the most potent compound,it showed pan antitumor activity with GI50 values of 0.1 to 1.7?M in NCI-60 human cancer cell lines,which was more potent than gossypol(GI50 = 0.8?5.1 ?M)and Bcl-2 selective inhibitor ABT-199(GI50 = 0.2?5.1 ?M).The competitive FP assays demonstrated that the active compound had high binding affinity to Bcl-2 and Mcl-1.The molecular modeling study indicated that hydrophobic groups that were introduced by linear amino acid methyl esters were responsible for the extra affinity for the potent compounds.(2)Removing the aldehyde groups on gossypol led to apogossypol.Preclinical in vivo data displayed that apogossypol has superior efficacy and maximum tolerated dose as well as markedly reduced toxicity compared to gossypol.Apogossypol also displayed superior blood concentrations over time compared to gossypol because of slower clearance.These observations indicated that apgossypol is a promising lead compound for cancer therapy.As a part of our ongoing interest of multicomponent reaction(MCRs),we applied this method for the design and synthesis of three series of N-containing heterocyclic apogossypol derivatives in combination with the concept of bioisostere(27 compounds).These synthesized apogossypol derivatives with benzo[d]imidazole core,imidazo[1,2-a]pyridine core and 1,2,3-tiazole core were then evaluated for their biological activities.The competitive FP assays results and NIH cell growth inhibitory data indicated that the three series of N-containing heterocyclic apogossypol derivatives were potent Bcl-2 antiapoptotic small molecular inhibitors and displayed strong antitumor activity to NCI-60.The optimized compounds in each series of N-containing heterocyclic apogossypol derivatives were compounds IV-22-1 and IV-22-5 in imidazo[1,2-a]pyridine core containing apogossypol derivatives,compound IV-25-6 in 1,2,3-tiazole core comprising apogossypol derivatives,and compound IV-27-1 in benzo[d]imidazole core containing apogossypol derivatives.What's more,these derivatives showed better antitumor activity than both gossypol and gossypol Schiff bases developed in our previous studies.For example,the GI50 values of compound IV-22-1 for NCI-60 was 0.08?1.05 ?M,better than optimized gossypol Schiff bases III-6-16(GI50 = 0.1?1.7 ?M for NCI-60)and gossypol.Another typical potent compound was IV-25-6,which displayed high selectivity to Bcl-2 antiapoptotic proteins,similar to Bcl-2 selective inhibitor ABT-199.The Ki value of compound ?-25-6 for Bcl-2 was less than 1 nM,which was more than 171-fold and 77-fold potent than Mcl-1 and Bcl-XL,respectively.The molecular modeling study indicated that the N-containing heterocycles were responsible for the extra affinity for the potent compounds.(3)On the basis of the previous work,we designed and synthesized 25 gossypol analogs-symmetric 2,3,4-trihydroxyl-5-sulfamoyl derivatives which mimics the scaffold of gossypol applied the scaffold hopping strategy.The 2,3,4-trihydroxyl structure mimics most binding sites between gossypol and the BH3 binding groove in Bcl-2.The competitive FP assays and molecular modeling study demonstrated that these 2,3,4-trihydroxyl-5-sulfamoyl derivatives could selectively bind to Bcl-2 and Bcl-XL,and invalid to Mcl-1.Further screening assay demonstrated that these 2,3,4-trihydroxyl-5-sulfamoyl derivatives were good IL-17A inhibitors rather than antitumor agents,and the results might be caused by the low liposolubility of these compounds.The inhibitory data showed that these 2,3,4-trihydroxyl-5-sulfamoyl derivatives could potent inhibit IL-17A,with IC50 value of 1.32 ?M.The interleukin 17A(IL-17A)is a pro-inflammatory cytokine which has a potential effect on various inflammatory conditions such as autoimmune disease,metabolic disorders,and cancer.However,synthetic molecules as ligands for IL-17A/IL-17R have not yet been found,current clinical inhibitors are all monoclonal antibodies.Therefore,these 2,3,4-trihydroxyl-5-sulfamoyl derivatives are promising IL-17A inhibitors for further study.(4)Phosphoric acid plays an important physiological role in cells.It is not only an important part of the specific binding between proteins and receptors,but also a structural component of DNA and RNA.Based on the unique naphthalene structure of gossypol,we introduced the phosphoric acid to the 1,1'-hydroxy groups on apogossypol to improve the hydrophilicity of gossypol derivatives.However,neither the FP assay nor cell growth inhibitory results showed that these compounds were good inhibitors for Bcl-2,but they were potential IL-17A inhibitors.In summary,in this thesis,we designed and synthesized a variety of structure-diversity oriented gossypol derivatives and analogs and evaluated their biological activities applying gossypol as the lead compound.The results showed that gossypol Schiff bases and N-containing heterocyclic apogossypol derivatives were potent Bcl-2 small molecule inhibitors and could be further developed for anticancer agents.While symmetric 2,3,4-trihydroxyl-5-sulfamoyl derivatives which are scaffold hopping analogs of gossyol and the novel binol-like apogossypol phosphine derivatives are good IL-17A inhibitors rather than antitumor agents.Thus,the work in this thesis enriched the species of gossypol derivatives,and promoted the development of anticancer drugs.