The Discovery Of C6-Celastrol Derivatives As Anticancer Agents And Design Of Novel Branched Linker Activated By Cathepsin B

PART I:Celastrol, a quinone methide triterpene extracted from Traditional Chinese Medicine’Thunder of God Vine’and’Celastrus orbiculatus Thunb’ (Tripterygium wilfordii Hook F.), has a lot of bioactivities. Abundant research has indicated that celastrol can inhibit tumor growth and induce apoptosis by the interaction of several novel molecular targets, such as NF-κB, Hsp90, VEGFR1, VEGFR2. Based on SAR, the quinone methyl structure of celastrol is the key pharmacophore for cytotoxic activity, which correlated with the cysteine sulfhydryl group by the Michael addition reaction.The quinone methyl structure is a Michael addition acceptor. We use retro-Michael addition for design prodrugs. The thiols were use as the nucleophilie for introduction to the celastrol C (6)-position, and afford the celastrol C (6)-sulfonated analogues, and then, was acetylated for enhance the stability. Celastrol C(6)-sulfonated (NSTOO1A), as a prodrug of celastrol release the NST001 by deacetylation in esterase introduced, and then celastrol was release by the reto-Michael addition for the NST001. Compound NST001 A displayed good anti-tumor activity with reduced adverse effect and improved the solubility for injection drug delivery. The results reveal that the quinone methyl structure of celastrol was a good Michael addition substrate and the celastrol C(6)-position can be used as a reconstruction site for prodrug design.In order to further understand the mechanism of the celastrol, and inspect the relationship of antitumor activity and the quinone methyl structure, a kind of stable celastrol C(6)-indole derivative compounds of series IV were designed. Celastrol analogs without quinone methyl structures (series IV) are more stable. They couldn’t release celastrol and react with the N-acetyl cysteine. Interestingly, compounds of the series IV retain the antitumor activity, and compounds 4c,4f,4h exhibited better cytotoxicity against Bel7402 than celastrol. The results indicated that the quinone methyl structure was critical for its cytotoxicity, but was not responsible for its chemical chaperone activity. The compounds of the series IV lost the quinone methyl structure, and the toxicity may be lower than celastrol. Therefore, design and application of the celastrol C (6)-indole derivatives might be a potential strategy for the celatrol.PART II:The second part of this work is the design and synthesis of a novel branched linker with is activated by cathepsin B (CB). Based on the linear linker p-aminobenzyl alcohol(PABC), propynyloxymethyl was introduced to the PABC afforded the branched linker L4 ((4-amino-2-propynyloxymethyl)phenyl)methanol. Different from the PABC, the branched linker L4 was a trifunctional liner, and the trigger group N-Cbz-L-valine-citrulline is placed in the 4-amino through a amide bond, whereas the drug is placed in the hydroxyl, and a bridge (N1,N2-dimethylethane-1,2-diamine) was placed between the linker and SN38 through carbomate bond. mPEG was introduced into the branched terminal alkyne by Click reaction, and compound 18a and 18b were obtained. The in vitro biological evaluation indicated that the branched linker can quickly release the active drug SN38, and the terminal alkyne introduced the mPEG increased the solubility of the drug, and the conjugate seemed to form the nanoparticles, which may improve drug targeting, and increased cells uptake, reduce drug efflux from the intracellular. The branched linker may form the basis for a combinatorial development of carrier-bound drugs in the future.