Aspertaichamide B, a new anti-tumor prenylated indole alkaloid from the fungus Aspergillus japonicus TE-739D

Abstract

Prenylated indole alkaloids, which are mainly produced by genera Aspergillus and Penicillium, are a class of structurally intriguing specialized metabolites with remarkable biomedical interests. In this study, chemically guided isolation of the Nicotiana tabacum-derived endophytic fungus Aspergillus japonicus TE-739D yielded eight structurally diverse prenylated indole alkaloids, including an undescribed compound, namely aspertaichamide B (ATB, 1), together with seven previously discovered derivatives (compounds 2 - 8). Their chemical structures as well as the stereochemical features were determined by integrated spectroscopic analyses, including HRESIMS, NMR, NMR calculations with DP4 + probability analysis, and a comparison of the experimental ECD data with computed DFT-based quantum chemical calculations. In vitro cytotoxic effects against the gastric cancer MFC cells revealed that the new compound ATB demonstrated considerable activity. Further studies found that ATB suppressed the viability, colony formation, and migration ability of MFC cells, and induced MFC cells apoptosis in a concentration-dependent way. Moreover, ATB stimulated ROS production in MFC cells and inhibited the tumor growth in the MFC-sourced subcutaneous tumor model while not significantly reducing the weight of mice. The pharmacological results suggested that the newly discovered ATB may be a promising anti-tumor lead compound. KEY POINTS: • Eight structurally diverse prenylated indole alkaloids including a new aspertaichamide B (ATB) were isolated from the fungus Aspergillus japonicus TE-739D. • The structure of ATB was elucidated by HRESIMS, NMR, NMR calculations with DP4 + probability analysis, and ECD calculations. • ATB inhibited cell proliferation, promoted apoptosis, and increased ROS production in gastric cancer cells, and exhibited inhibitory effects on tumor growth in vivo.

Keywords: Aspergillus japonicus; Anti-tumor activity; Endophytic fungus; Prenylated indole alkaloids; Specialized metabolites.

Fig. 1

Chemical structures of 1–8

Fig. 2

A Morphology of A. japonicus TE-739D on different culture media (PDA, potato dextrose agar; MEA, malt extract ager; SDA, Sabouraud dextrose agar) and B neighbor-joining tree based on ITS nucleotide sequences

Fig. 3

COSY and HMBC correlations for 1

Fig. 4

Experimental and calculated ECD spectra of 1

Fig. 5

Key MOs in the important transitions regarding ECD spectra

Fig. 6

ATB inhibited the MFC cells proliferation and migration. A MFC cells were conducted with the indicated concentrations of ATB for indicated times. B ATB inhibited colony formation in MFC cells. C The wound healing assay in MFC cells with ATB for 24 h. *P < 0.05; **P < 0.01

Fig. 7

ATB induced apoptosis in MFC cells. A MFC cells with ATB for 24 h and the detection of apoptosis. B The percentages of apoptotic cells. *P < 0.05; **P < 0.01

Fig. 8

ATB promoted induction of ROS in MFC cells. A Fluorescent images taken by a fluorescence microscope with DCFH-DA staining in MCF cells at indicated concentrations of ATB. B DCF fluorescence distribution of cells with ATB. C ROS levels at indicated concentrations of ATB. *P < 0.05; **P < 0.01

Fig. 9

ATB inhibited tumor growth. A ATB inhibited tumor growth in the MFC-derived subcutaneous mouse model. B The tumor volume of mice. C The tumor mass in ATB-treated mice. D The body weights of MFC-derived subcutaneous mouse model with ATB. *P < 0.05; **P < 0.01