In vitro cytotoxic properties of crude polar extracts of plants sourced from Australia

Background Numerous commercial pharmaceuticals – including anticancer, antiviral, and antidiabetic drugs have been developed from traditional plant-derived medicines. There are approximately 25,000 species of flora occurring in Australia, which are adapted to a range of harsh environments, and hence a plethora of novel compounds are still awaiting research in the context of their medicinal properties. Objective The current study therefore aimed to develop a systematic protocol for screening plants with potential cytotoxicity. Many studies have found polar compounds such as to be the bioactive components responsible for the therapeutic effects. Methods The total phenolic content (TPC) and antioxidant capacity (FRAP) of methanolic extracts of selected plants was first determined. A high correlation between the TPC values and FRAP values of the plant polar extracts were evident. Cell viability of the cancer cell lines were assessed using the MTS assay. Results Cells subjected to Pittosporum angustifolium Lodd. Extracts at concentration of 250 µg/mL showed no viable cells, comparable to cisplatin (a chemotherapy medication) used as a positive control (10 µg/mL). Some promising inhibitory effects were also seen with Murrya koenigii flower and leaves at concentration of 250 µg/mL, with only 43.46% and 63.88% cell viability, respectively. In contrast, extracts of Citrus hystrix (leaves) and Sygyzium australe (stamen) showed higher percentage cell viabilities (around 82-93%) at same concentrations. The phenolic profile of P. angustifolium B extracts demonstrating greater peak intensity and dominant peaks were tentatively identified as chlorogenic acid, p-coumaric acid, caffeic acid, t-ferulic acid and rutin. Conclusion The Australian species P. angustifolium extract was the most cytotoxic against HeLa and HT29 cells comparing to the other plant extracts tested. A HPLC profile of the P. angustifolium extract also showed an array of promising therapeutic phenolic compounds. Future work will aim to fractionate and isolate novel compounds from this species and test their bioactivity.