Abstract
Pterocellin A is a novel bioactive alkaloid isolated from the New Zealand marine bryozoan Pterocella vesiculosa. It exhibits potent antitumour activity towards the P388 (murine leukaemia) cell line in vitro and is selectively sensitive towards certain non-small cell lung, melanoma, and breast cancer cell lines, however, the biological mode of action of pterocellin A is unknown. Using the human cervical cancer cell line HeLa, we show that pterocellin A exhibited cytotoxicity against HeLa cells with an IC50 of 886 ng/mL. Time-course MTT and LDH assays were carried out and the results showed only a low level of cytosolic LDH was detected in the supernatant after all the cells have died from pterocellin A treatment at 2000 ng/mL. This indicated the cells maintained membrane integrity upon cell death which suggested apoptotic cell death. Additionally, morphological changes were observed under the microscope after 6 h of treatment. Cell shrinkage and nucleus condensation were observed, as well as apparent membrane blebbing, a key feature of apoptosis. The MTT data was also indicative of mitochondria impairment which could suggest that pterocellin A targets the mitochondria. This idea was supported by the observed changes in the morphology and location of the mitochondria after exposure to pterocellin A. Furthermore, the level of activated caspase-3 in HeLa cells increased after treatment with pterocellin A; activated caspase-3 can only be detected after a series of signalling events following the induction of apoptosis. These data support the notion that pterocellin A is an inducer of apoptosis in HeLa cells possibly via mitochondria related processes.
Highlights
Natural products, known as secondary metabolites, are organic compounds produced by living organisms
We investigated to see if pterocellin A was cytotoxic to the human cervical cancer cell line HeLa via apoptotic cell death processes
After 24 h incubation, HeLa cells treated with pterocellin A had an IC50 value of 886 ng/mL, which was within the same order of magnitude as the IC50 of pterocellin A with the P388 cell line noted in a previous study (Yao et al 2003)
Summary
Known as secondary metabolites, are organic compounds produced by living organisms. Unlike primary metabolites such as carbohydrates and amino acids, secondary metabolites are considered non-essential to life and have no apparent function within the organism (Williams et al 1989) These compounds attract research interest because they can exert physiological effects on other organisms, often playing an ecological role in regulating a wide range of chemical interactions. The rate of discovery of novel bioactive compounds from terrestrial organisms has decreased in recent years, due to an increased frequency of rediscovery (Dias et al 2012). This led to the search being extended to unexplored habitats in marine environments.
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