Pharicin a, a Novel Natural Compound That Induces Mitotic Arrest and Catastrophe of Cancer Cells by Perturbing Microtubule Dynamics and the Spindle Checkpoint

Microtubule poisons such as taxol represent a potent and effective class of anticancer compounds. In the past decades, great efforts have been directed to identify novel natural products with a mode of action similar to taxol but with a minimal side effect. In this study, we report the functional characterization of a new ent-kaurene diterpenoid termed pharicin A, which was originally isolated from Isodon pharicus leaves, a perennial shrub frequently used in Chinese folk medicine for tumor treatment. Pharicin A induces mitotic arrest in Jurkat, Raji and HeLa based on their morphology, DNA content, histone H3 serine-10 phosphorylation, and mitotic marker protein analyses. Pharicin A stabilizes the formation of mitotic spindles, which is coupled with a rapid accumulation of Cdc20 as well as an increased phosphorylation of Cdc27 and BubR1. Pharicin A treatment also results in an enhanced interaction between Cdc20 and spindle checkpoint components including Mad2 and BubR1. Moreover, pharicin A-induced mitotic arrest in HeLa cells is tightly associated with the presence of lagging/missegregated chromosomes at spindle pole regions, which are highly enriched in BubR1, CENP-E and Sgo1. Although pharicin A stabilizes microtubules both in vitro and in vivo, it induces mitotic arrest in taxol-resistant Jurkat cells. Combined, our study strongly suggests that pharicin A represents a novel class of small molecule compounds capable of perturbing microtubule dynamics and the spindle checkpoint in tumor cells, which merits further preclinical and clinical investigations for cancer drug development.