In vitro cytotoxic and apoptotic activity of the Mauritian marine sponge <i>Neopetrosia exigua</i>

Abstract

Marine sponges belonging to the genus Neopetrosia represent a quasi-inexhaustible source of novel cytotoxic compounds. Yet studies delineating their molecular mechanisms of action in cancer cells remain scarce. We investigated the cytotoxic and apoptosis inducing potential of the Mauritian marine sponge Neopetrosia exigua derived crude extract, hexane and ethyl acetate fraction. Their cytotoxic activity was screened against four cancer cell lines and two non-malignant cell lines via the Alamar Blue metabolic assay. The level of intracellular reactive oxygen species (ROS) production, endogenous antioxidant enzyme activity (catalase and superoxide dismutase) and mitochondrial membrane potential were determined. The ability of the active extract to induce apoptosis in cancer cells and modulate the expression levels of apoptotic markers (caspases and polyADP-ribose polymerase (PARP)) was further evaluated via western blot. The ethyl acetate fraction (NEEAF) displayed the highest inhibitory effect with an IC₅₀ of 6.87 μg/mL against the liver hepatocellular carcinoma cell line (HepG2). Mechanistically, NEEAF induced
morphological hallmarks characteristic of apoptosis, increased ROS production, decreased catalase and superoxide dismutase activity and mitochondrial membrane depolarisation in a concentration-dependent
manner compared to the control (p<0.05). In addition, NEEAF induced the activation of caspase-9, -7, -3 and cleavage of PARP. Overall, this study provides biochemical evidence for oxidative stress-mediated cytotoxicity and apoptosis in HepG2 cells by NEEAF. Further in-depth investigations are needed to isolate the active constituents, which may potentially lead to the development of novel anticancer therapeutics.

Significance:
• Marine sponges represent an untapped goldmine of structurally unique compounds with interesting anticancer properties.
• This important initial investigative work will set the stage for more in-depth mechanistic studies and chemical characterisation of potentially novel bioactive compounds from the genus Neopetrosia.
• This work will also help to strengthen frameworks oriented towards the conservation of Neopetrosia species in the Western Indian Ocean region.