Antioxidant, Antibacterial and Cytotoxic Activity of the Dillenia suffruticosa Leaves against the Lung (A549) and Cervical (CaSki) Cancer Cell Lines

Background: Dillenia suffruticosa (Griff.) Mart. has been traditionally used to promote wound healing, relieve rheumatism, fever and some cancerous growths. The leaves of the local variety of D. suffruticosa lack scientific studies on its biological applications in the context of antibacterial, antioxidant and cytotoxic activities. Objective: The objective of this study is to evaluate the antioxidant, antibacterial and cytotoxic properties of the leaves of D. suffruticosa from Brunei Darussalam. Methods: The leaves were extracted using 80% (v/v) methanol, 80% (v/v) ethanol and aqueous. The antioxidant capacities were determined using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging, 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging and ferric ion reducing antioxidant power (FRAP) assays. The Folin-Ciocalteu and aluminium chloride colorimetric assays were also used to evaluate the total phenolic and flavonoid contents. The antibacterial and cytotoxic activities of the extracts were determined using the Kirby-Bauer disc diffusion and MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) cell proliferation assays. Results: The methanolic extract of the D. suffruticosa leaves displayed the highest antioxidant activity despite having comparable phenol content when extracted using the ethanol extraction solvent. The methanolic extract also demonstrated antibacterial activity on Staphylococcus aureus at a concentration of 50 mg/mL or above. The cytotoxicity of the methanolic extract was higher against the CaSki cell line than the A549 lung cancer cell line in the first 24 h but became more cytotoxic against A549 than CaSki at 48 h and 72 h. Conclusion: Our findings suggest that the methanolic extract of the leaves of D. suffruticosa from Brunei Darussalam has significant antioxidant and antibacterial activity against S. aureus and moderate cytotoxicity against A549 and CaSki cell lines.