Zephycandidine A, the First Naturally Occurring Imidazo[1,2-f]phenanthridine Alkaloid from Zephyranthes candida, Exhibits Significant Anti-tumor and Anti-acetylcholinesterase Activities.

Guanqun Zhan,Junjun Liu,Xiaolan Qu,Qingyi Tong,Guangmin Yao,Bin Sun,Junfei Zhou

doi:10.1038/srep33990

Abstract

Zephycandidine A (1), the first naturally occurring imidazo[1,2-f]phenanthridine alkaloid, was isolated from Zephyranthes candida (Amaryllidaceae). The structure of 1 was elucidated by spectroscopic analyses and NMR calculation, and a plausible biogenetic pathway for zephycandidine A (1) was proposed. Zephycandidine A (1) exhibited significant cytotoxicity against five cancer cell lines with IC50 values ranging from 1.98 to 7.03 μM with selectivity indices as high as 10 when compared to the normal Beas-2B cell. Further studies suggested that zephycandidine A (1) induces apoptosis in leukemia cells by the activation of caspase-3, upregulation of Bax, downregulation of Bcl-2, and degradation of PARP expression. In addition, zephycandidine A (1) showed acetylcholinesterase (AChE) inhibitory activity, and the docking studies of zephycandidine A (1) and galanthamine (2) with AChE revealed that interactions with W286 and Y337 are necessary.

Highlights

Table 1. 1H (400 MHz) and 13C NMR (100 MHz) data for zephycandidine A (1) (Methanol-d4) and DFT calculation of 13C NMR for 1a and 1b
We describe the isolation, structure determination, plausible biosynthetic pathway, cytotoxicity and inducing apoptosis in leukemia cells, AChE inhibitory activity, and the docking study with AChE of zephycandidine A (1)
The molecular formula C16H10N2O2 was determined by the High-resolution electrospray ionization mass spectra (HRESIMS) ion at m/z 263.0789 [M +H]+ in conjunction with the 13C NMR data, requiring thirteen degrees of unsaturation

Summary

Results and Discussion

The treatment of VP16 (etoposide phosphate, 5 μM) leads to 83.8% apoptosis incidence (Fig. 5B) These results demonstrate that zephycandidine A (1) induced apoptosis of HL-60 cells. Zephycandidine A (1) treatment altered the expression levels of PARP and cleaved-caspase 3, it down regulated Bcl-2 and upregulated Bax. Changes of apoptosis-related protein, including Bax, Bcl-2, cleaved caspase-3 and PARP, were assessed by western blot analysis. Zephycandidine A (1) treatment altered the expression levels of PARP and cleaved-caspase 3, it down regulated Bcl-2 and upregulated Bax Taken together, these data suggest that zephycandidine A (1)-induced apoptosis in leukemia cells is mediated by the activation of caspase-3, upregulation of Bax, downregulation of Bcl-2 and degradation of PARP. In the peripheral anionic site, zephycandidine A (1) binds the enzyme primarily by the π–πstacking interaction with W286 and by two hydrogen bonds with S293 and R296, respectively

Highest index of selectivity

Methods

Author Contributions

Additional Information