Discovery of thalicthuberine as a novel antimitotic agent from nature that disrupts microtubule dynamics and induces apoptosis in prostate cancer cells

ABSTRACT

We report for the first time the mechanism of action of the natural product thalicthuberine (TH) in prostate and cervical cancer cells. TH induced a strong accumulation of LNCaP cells in mitosis, severe mitotic spindle defects, and asymmetric cell divisions, ultimately leading to mitotic catastrophe accompanied by cell death through apoptosis. However, unlike microtubule-binding drugs (vinblastine and paclitaxel), TH did not directly inhibit tubulin polymerization when tested in a cell-free system, whereas it reduced cellular microtubule polymer mass in LNCaP cells. This suggests that TH indirectly targets microtubule dynamics through inhibition of a critical regulator or tubulin-associated protein. Furthermore, TH is not a major substrate for P-glycoprotein (Pgp), which is responsible for multidrug resistance in numerous cancers, providing a rationale to further study TH in cancers with Pgp-mediated treatment resistance. The identification of TH's molecular target in future studies will be of great value to the development of TH as potential treatment of multidrug-resistant tumors.

KEYWORDS:

• Thalicthuberine
• mitotic inhibitor
• microtubule dynamics
• tubulin polymerization
• prostate cancer

Abbreviations

LCMS	=	liquid chromatography/mass spectrometry
MT	=	microtubule
NMR	=	nuclear magnetic resonance
TH	=	thalicthuberine

Disclosure of potential conflicts of interest

No potential conflicts of interest were disclosed.

Acknowledgments

The authors would like to thank Associate Professor Derek Richard for kindly allowing us to use his DeltaVision microscope. We gratefully acknowledge access to the NatureBank (Hernandia albiflora plant sample) housed at the Griffith Institute for Drug Discovery.

Author contributions

Conception and design: Claire Levrier, Martin C. Sadowski, Maria Kavallaris, Rohan A. Davis, Colleen C. Nelson

Development of methodology: Claire Levrier, Martin C. Sadowski

Acquisition of data: Claire Levrier, Martin C. Sadowski, Anja Rockstroh

Analysis and interpretation of data: Claire Levrier, Martin C. Sadowski, Anja Rockstroh, Brian Gabrielli, Melanie Lehman

Writing, review, and/or revision of the manuscript: Claire Levrier, Martin C. Sadowski, Brian Gabrielli, Maria Kavallaris, Rohan A. Davis, Colleen C. Nelson

Administrative, technical, or material support: Martin C. Sadowski

Study supervision: Martin C. Sadowski, Rohan A. Davis, Colleen C. Nelson

Other [Supply of compound (TH)]: Claire Levrier, Rohan A. Davis

Additional information

Funding

The authors acknowledge the National Health and Medical Research Council (NHMRC) for financial support (Grant APP1024314 to R.A.D.). This work was supported by funding from the Australian Government Department of Health and The Movember Foundation and the Prostate Cancer Foundation of Australia through a Movember Revolutionary Team Award (M.C.S., C.C.N). B.G. was supported by an NHMRC Senior Research Fellowship. M.K. is funded by the Australian Research Council Center of Excellence in Convergent Bio-Nano Science and Technology (CE140100036), NHMRC Program Grant (APP1091261) and NHMRC Senior Research Fellowship (APP1058299). C.L would like to thank Griffith University for a Ph.D. scholarship (GUIPRS) and CTx for a PhD Top up scholarship. The Translational Research Institute is supported by a grant from the Australian Government.