5-N-Acetylardeemin

An efficient and versatile synthesis of 5-N-acetylardeemin (1a) and sixteen 2-, 3- and 13-substituted derivatives 1b-q was achieved through Ugi three-component reaction of 3,3a,8,8a-tetrahydropyrrolo[2,3-b]indole and cyclization/epimerization. Their inhibitory activity on the drug efflux of breast cancer resistance protein (ABCG2) was evaluated by flow cytometric analysis of accumulation of Hoechst 33342 stain in Flp-In-293/ABCG2 cells. Most of the derivatives exhibited a stronger ABCG2 inhibitory effect compared with natural product 1a. The derivative 1m with a 4-tolyl substituent at the C-13 position exhibited the most potent ABCG2 inhibition. This preliminary structure-activity relationship study indicates that an electron-rich aryl moiety as the 13-substituent is key to increasing the inhibitory activity.

Objective: To explore the reversal effect of (- )-5-N-acetylardeemin on adriamycin resistance in multidrug-resistant cancer cells including human breast cancer cells MCF-7/Adr and human non-small cell lung cancer cells A549/Adr in vitro. Methods: The multidrug-resistant cancer cells MCF-7/Adr, A549/Adr and their respective parental cells were treated with different concentrations of (- )-5-N-acetylardeemin and adriamycin individually or in combination. Cell death was detected based on the release of lactate dehydrogenase (LDH) using a cytotoxicity detection kit. Intracellular accumulation of adriamycin was measured by the detection of fluorescence intensity of cell lysates using microplate reader. The expression of P-glycoprotein (P-gp) was evaluated by Western blot. Results: (-)-5-N-acetylardeemin significantly reversed the adriamycin resistance in MCF-7/Adr and A549/ Adr in a dose-dependent manner, and the reversal folds were 10. 8 in MCF-7/Adr cells and 20.1 in A549/Adr cells with the treatment of 10 μmol/L (-)-5-N acetylardeemin. (- )-5-N-acetylardeemin also enhanced the sensitivity of parental MCF-7 and A549 cells to adriamycin. The fluorescence intensity in both MCF-7/Adr and A549/Adr cells, which reflected the intracellular accumulation of adriamycin, were significantly enhanced by ( -)5-N- acetylardeemin in a dose-dependent manner. The expressions of P-gp in MCF-7/Adr and A549/Adr cells were significantly inhibited by (- )-5-N-acetylardeemin. Conclusion: (- )5-N-acetylardeemin could reverse the multidrug resistance in cancer cells through inhibiting the expression of P-gp and enhancing the intracellular accumulation of cytotoxic drug.

Four ardeemin derivatives, 5-N-acetylardeemin (1), 5-N-acetyl-15bβ-hydroxyardeemin (2), 5-N-acetyl-15b-didehydroardeemin (3), and 5-N-acetyl-16α-hydroxyardeemin (4), were isolated from the fermentation broth of an endophytic Aspergillus fumigatus SPS-02 associated with Artemisia annua L. The structures of these metabolites were elucidated by a combination of spectroscopic data, including 1D-, 2D-NMR and MS. In vitro chemosensitization assay indicated that these ardeemins had different activities of reversing the multidrug-resistant (MDR) phenotype in three cancer cell lines, leukemia doxorubicin resistant cell K562/DOX, human lung adenocarcinoma cis-platin-resistant cell A549/DDP, and ovarian cancer cisplatin-resistant cell SK-OV-S/DDP. Compound 4 exhibited the strongest MDR reversing effect at 5 μM concentration in K562/DOX and A549/DDP cell lines 5.2±0.18-fold, 8.2±0.23-fold, respectively, while compound 2 had the highest reversal capacity in SK-OV-S/DDP cell line with 10.8±0.28 fold. Preliminary investigation of their structureactivity relationship suggested that a OH group at C(15b) or C(16) in ardeemin plays a key role in reversing the MDR effect. It is the first report on ardeemin analogs from endophytic A. fumigatus with reversal effects on MDR cancer cell lines K562/DOX, A549/DDP and SK-OV-S/DDP.