The natural product Aristolactam AIIIa as a new ligand targeting the polo-box domain of polo-like kinase 1 potently inhibits cancer cell proliferation.

AIM: To search for novel inhibitors of human polo-like kinase 1 (Plk1), which plays important roles in various aspects of mitotic progression and is believed as a promising anti-cancer drug target, and further investigate the potential inhibition mechanism of active compounds against Plk1, thus developing potent anti-tumor lead compounds. METHODS: Surface plasmon resonance (SPR) technology-based assay and enzymatic inhibition assay were used to screen Plk1 inhibitors. Sulphorhodamine B (SRB)-based assay, flow cytometry, confocal microscopy and Western blotting were used to further identify the potent Plk1 inhibitor. To investigate the inhibitory mechanism of the active compound against Plk1, enzymatic inhibition assay, SPR and yeast two-hybrid technology-based assays were used. RESULTS: Aristolactam AIIIa was identified as a new type of Plk1 inhibitors, targeting the Polo Box domain (PBD) which is another efficient tactic for exploring Plk1 inhibitors. Further studies indicated that it could block the proliferations of HeLa, A549, HGC and the HCT-8/V cells (clinical Navelbine-resistant cancer cell), induce mitotic arrest of HeLa cells at G2/M phase with spindle abnormalities and promote apoptosis in HeLa cells. The results from SPR and yeast two-hybrid technology-based assays suggested that it could target both the catalytic domain of Plk1 (CD) and PBD and enhance the CD/PBD interaction. CONCLUSION: Our current work is expected to shed light on the potential anti-tumor mechanism of Aristolactam AIIIa, and this natural product might be possibly used as a lead compound for further developing anti-tumor drugs.

7-Chloroarctinone-b as a new selective PPARgamma antagonist potently blocks adipocyte differentiation.

AIM: Peroxisome proliferator-activated receptor gamma (PPARgamma) is a therapeutic target for obesity, cancer and diabetes mellitus. In order to develop potent lead compounds for obesity treatment, we screened a natural product library for novel PPARgamma antagonists with inhibitory effects on adipocyte differentiation. METHODS: Surface plasmon resonance (SPR) technology and cell-based transactivation assay were used to screen for PPARgamma antagonists. To investigate the antagonistic mechanism of the active compound, we measured its effect on PPARgamma/RXRalpha heterodimerization and PPARgamma co-activator recruitment using yeast two-hybrid assay, Gal4/UAS cell-based assay and SPR based assay. The 3T3-L1 cell differentiation assay was used to evaluate the effect of the active compound on adipocyte differentiation. RESULTS: A new thiophene-acetylene type of natural product, 7-chloroarctinone-b (CAB), isolated from the roots of Rhaponticum uniflorum, was discovered as a novel PPARgamma antagonist capable of inhibiting rosiglitazone-induced PPARgamma transcriptional activity. SPR analysis suggested that CAB bound tightly to PPARgamma and considerably antagonized the potent PPARgamma agonist rosiglitazone-stimulated PPARgamma-LBD/RXRalpha-LBD binding. Gal4/UAS and yeast two-hybrid assays were used to evaluate the antagonistic activity of CAB on rosiglitazone-induced recruitment of the coactivator for PPARgamma. CAB could efficiently antagonize both hormone and rosiglitazone-induced adipocyte differentiation in cell culture. CONCLUSION: CAB shows antagonistic activity to PPARgamma and can block the adipocyte differentiation, indicating it may be of potential use as a lead therapeutic compound for obesity.