Design,Synthesis And Anticancer Mechanism Of Novel Curcumin Analogues

As a polyphenolic natural product,curcumin possesses extensive biological activities such as antitumor,antioxidant,anti-inflammatory,and antiviral properties.The previous research showed that curcumin had little or no adverse effects and systemic toxicity as well as broad-spectrum anti-tumor activity,and it can treat and prevent cancer.In this paper,we focused largely on the antitumor mechanism and the structure-activity relationships(SARs)of curcumin.Poor selectivity,low water solubility and instability in vitro and in vivo resulted the low antitumor activity of curcumin.Therefore,on the basis of preliminary studies in our laboratory,several aspects of the structural modification were carried out from curcumin and its analogues in antipication of improved water solubility or/and anti-tumor activity in vitro and in vivo,and in-depth study SAR.Firstly,30 novel curcumin derivatives bearing O-aminoalkyl moieties of Series Ⅰ(EM-1～EM-6,PM-1～PM-8,EB-1～EB-8 和 PB-1～PB-8)were designed and sythesized from curcumin via dialkylation at the carbon atom of the active methylene,and introduction of the alkyl side chains of different lengths to the phenolic hydroxy groups and addition of the terminal hydrophilic amino groups in the side chains.Secondly,by dialkylation at the carbon atom of the active methylene and introduction of the hydrophilic amino groups to two benzene ring using Mannich reaction,11 new Mannich base derivatives of curcumin of Series Ⅱ(MB-1～MB-11)were obtained from demethoxy curcumin(DMC).Finally,Since the conjugatedα,β-unsaturated diketone moiety in curcumin skeleton is believed to play an important role in mediating the antitumor activity,in ordeto further investigation of the effects of α,β-unsaturated ketone moiety,8 novel tetrahydrocurcumin derivatives of Series Ⅲ and Ⅳ(MH-1,MH-2 and HPB-1～HPB-6)were achived via hydrogenation of α,β-unsaturated ketone moiety of some curcumin analogues.The structures of all the target compounds were confirmed by 1H-NMR and HR-MS spectra.The growth inhibitory effects of 49 curcumin analogues and 9 intermediates were evaluated by MTT assay in ten human carcinoma cell lines including HeLa,MCF-7,HepG2,HCT116,A549,A375-S2,HT-1080,U-937,HL-60 and K562,and curcumin was used as controls.The pharmacological results showed that Most of them possessed moderate to excellent growth inhibitory activity against one or more cell lines.Compound PB-3,PB-4 and HPB-6 showed dramatically increased antiproliferative effects in all tested cell lines as compared with curcumin.The most promising compound HPB-6,possessing a α,β-saturated ketone moiety,showed strong anti-tumor activity against eight of the ten carcinoma cell lines,and the IC50 values were below 1μM,which was 9-to 81-fold more potent than curcumin.In addition,compound EB-4 displayed remarkable selective anti-proliferative activity against non-solid tumor cells.In general,the target compounds of EB and PB with 4,4-dibenzyl substitution were more potent than the target compounds of EM and PM with 4,4-dimethyl substitution.The potential antitumor mechanism of the representative compound PB-3 was explored.The proliferation of A375-S2 cells was monitored by the MTT cell viability assay,while the nuclear morphology of apoptotic cells was assessed by AO/EB staining.Flow cytometry was performed to analyze the apoptotic progression of propidium iodide(PI)-stained A375-S2 cells.Western blotting was used to examine the expression of molecular chaperone protein Hsp90,and the apoptosis-regulated proteins including cytochrome c,pro-caspase 9,ICAD and cleaved-caspase 3.The MTT assay demonstrated that PB-3(1～16 μM)could induce significant dose-and time-dependent inhibition of A375-S2 cell proliferation.Following PB-3 treatment for 24 h,its IC50 value was 3.1 μM,while curcumin was 22.0 μM.Marked morphological changes,AO/EB staining and PI flow cytometry were used,and at the centration of 3 μM,PB-3 resulted in significant apotosis and the apoptosis-inducing activity is much more potent than that of curcuimn(20μM).The result of Western blot assay showed that PB-3 could down-regulate the expression of Hsp90 protein in time-dependent manner,and Hsp90 may be the target of PB-3.PB-3 treatment also resulted in elevation of cytoplasmic cytochrome c,degradationg of procaspase-9 and activation of caspase-3.These data indicated that PB-3 which target may be Hsp90 could act as an inhibitor of proliferation in A375-S2 cells by inducing mitochondria-dependent apoptosis.The S ARs of these compounds were discussed,which would provide useful information for further study in this field.