Design,Synthesis And Biological Evaluation Of Tetrazole-Containing RXRα Ligands As Anticancer Agent And Structure-Based Virtual Screening Of Novel RXRα Ligands

Retinoid X receptor is a member of the nuclear receptor superfamily,which plays a key role in various biological processes through the formation of homodimer and heterodimer.Recently,besides its transcriptional activity,RXRa is found to exert non-genomic action.RXRa can translocate from nuclear to cytoplasm to modulating cell proliferation,survival,apoptosis and inflammation.Our group reported that sulindac and its derivatives could mediate the non-genomic action of RXRa.Sulindac could inhibit the TNFa-induced interaction between RXRa and the p85a regulatory subunit of PI3K through binding to the RXRa,resulting in the inhibition of the PI3K/AKT pathway and leading to the death of cancer cells.Our group also found a novel compound named K-8008 by introducing a bioisostere of the carboxyl in sulindac,and found that K-8008 exerts enhanced anticancer activity in animal experiments.During the three-years research,we utilized the K-8008 as a lead compound and introduced a full-scale modification,through which we have synthesized 26 new derivatives of K-8008.Firstly,we tested the new compouds with reporter assay and MTT assay and found that two new compounds(8b and 18a)showed enhanced activities.The IC50 value of the 8b compound was 1.4-fold(8.90±0.72μM)more potent than K-8008 in MDA-MB-231 cancer cell line and 1.6-fold(17.34±0.78 μM)in MCF-7 and the 18a compound was 2.5-fold(5.00±0.57 μM)more potent than K-8008 in MDA-MB-231 cancer cell line and 1.3-fold(20.77±0.78 μM)in MCF-7.We also evaluated their Structure-Activity relationship using the results of the two assays(Figure 14).Moreover,the dissociation constant(Kd)of 8b and 18a was measured to be 1.59± 0.20 μM and 1.13 ± 0.14 μM,respectively.Next,we utilized molecular docking study to predict the binding mode of compound 8b and 18a,and to explain why these two compounds exert enhanced anticancer activity.Further evaluation revealed that 8b and 18a could dose-dependently induce PARP cleavage,which could be enhanced in the presence of TNFa.Elimination of the expression of RXRa caused the compounds’ ability of inducing PARP cleavage to vanish,indicating that 8b and 18a-induced PARP cleavage was RXRa-dependent.The other part of my work involved applying the Computer-Aided Drug Discovery(CADD)method to screen for novel RXRa ligands from PubChem database.We analyzed the screening results and synthesized some of the best-scored compounds.Overall,8 compounds were synthesized based on their docking scores and binding modes.These 8 compounds were further evaluated for the biological activities.Reporter assay and western blotting showed that two compounds S3-5 and S3-8 exerted antagonism and inflammatory activities.