Reversal of human multi-drug resistance leukaemic cells by stemofoline derivatives via inhibition of P-glycoprotein function.

Our previous study reported multi-drug resistance (MDR) reversing properties of synthetic stemofoline derivatives (STFD), OH-A1, NH-B6 and NH-D6 on P-glycoprotein (P-gp) overexpressing leukaemic cells (K562/Adr); however, the mechanism was unclear. In this study, we further investigated whether the STFD reverse MDR through either the inhibition of P-gp function or expression in K562/Adr cells, or both. The P-gp functional studies showed that the STFD increased the accumulation of calcein-AM, rhodamine 123 and [(14) C]-doxorubicin in K562/Adr cells, while the effects have not been seen in their parental sensitive cancer cell line (K562). Further, the STFD did not alter the P-gp expression as determined by Western blotting. This study concludes that the STFD reverse MDR via the inhibition of P-gp function. The efficacy of the STFD to inhibit P-gp function followed the order: NH-B6 > OH-A1 > NH-D6. These compounds could be introduced as candidate molecules for treating cancers exhibiting P-gp-mediated MDR.

Inhibition of P-glycoprotein mediated multidrug resistance by stemofoline derivatives.

Resistance to chemotherapy in cancer patients has been correlated to the overexpression of the ATP-binding cassette (ABC) drug transporters including P-glycoprotein (P-gp) that actively efflux chemotherapeutic drugs from cancer cells. We examined the multidrug resistance reversing property of stemofoline derivatives in drug-resistance human cervical carcinoma (KB-V1) and human leukemic (K562/Adr) cell lines that overexpress P-gp. Didehydrostemofoline and eleven of its derivatives were synthesized and the cytotoxicity and their effect on doxorubicin, vinblastine and paclitaxel sensitivity in drug resistant (KB-V1 and K562/Adr) and drug sensitive (KB-3-1 and K562) cell lines by a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay were determined. We found that three out of the twelve stemofoline derivatives including OH-A1, NH-B6 and NH-D6 showed commitment efficiency to increase sensitivity to doxorubicin, vinblastine and paclitaxel in KB-V1 cells and increase sensitivity to doxorubicin, and paclitaxel in K562/Adr cells whereas the effects have not been seen in their parental sensitive cancer cell lines (KB-3-1 and K562). These results indicate that stemofoline derivatives reversed P-gp-mediated multidrug resistance in vitro, and thus could be developed as effective chemosensitizers to treat multidrug-resistant cancers. The molecular mechanism of modulation of P-gp would be further determined.

Semisynthesis and acetylcholinesterase inhibitory activity of stemofoline alkaloids and analogues.

Semisynthesis of the known Stemona alkaloids oxystemofoline (7) and methoxystemofoline (8) has been achieved starting from (11Z)-1',2'-didehydrostemofoline (6), which confirmed their structures and absolute configurations. The synthesis of (1'R)-hydroxystemofoline (9) helped establish this compound as a natural product from Stemona aphylla. (1'S)-Hydroxystemofoline (10) and a number of related analogues were also prepared. In a TLC bioautographic assay, 9 was found to be the most active acetylcholinesterase inhibitor, but it was not as active as galanthamine.

Structural revision of stemoburkilline from an E-alkene to a Z-alkene.

Semisynthesis studies starting from (11Z)-1',2'-didehydrostemofoline (4) indicated that the known Stemona alkaloid stemoburkilline is the Z-isomer and not the E-isomer as initially reported. The semisynthesis involved conversion of (11Z)-1',2'-didehydrostemofoline (4) to 11(S),12(S)-dihydrostemofoline (3) followed by a stereoselective base-catalyzed ring-opening reaction to give (Z)-stemoburkilline (8). The same product was obtained using a similar synthetic protocol starting from isostemofoline (6) via a based-catalyzed ring-opening reaction of 11(S),12(R)-dihydrostemofoline (1). A re-examination of the crude root extracts of Stemona burkillii Prain and further NOE studies established stemoburkilline as the Z-isomer (8).