In Vitro Evaluation of the Cytotoxicity of Streptomyces MCH11 Extract Isolated from Lebanese Soil on A549 Lung Cancer Cells

Abstract

Bacterial extracts possess many therapeutic attributes such as antibacterial, antifungal, antiviral, antioxidant, and anticancer activities. Streptomyces is the largest genus of Actinobacteria that provides various compounds with different activities, including anticancer.

Our study aims to explore the cancer-suppressive activity of extract from Streptomyces MCH11, which was isolated from soil in Machghara, a city in Lebanon’s West Bekaa, on A549 lung cancer cells, to investigate the molecular mechanisms of cell death, and to identify the bioactive compounds in this extract.

Our results suggest a potential anticancer activity of the extract cultured in medium C on A549 cells. MTT assay showed that the extract significantly reduced the viability of A549 cells. In addition, it induced the apoptosis of cells as determined via the Annexin V-PI assay and confirmed by the demonstration of cleaved PARP-1 and cleaved caspase-9 by western blot. Thus, the extract may act by activating the intrinsic apoptotic pathway. The involvement of caspase-8 and the extrinsic pathway could not be verified. Furthermore, the scratch assay showed that the extract inhibited the metastatic potential of A549 cells after treatment with the specific dose of 0.03 mg/ml and that was accompanied with a downregulation in the protein expression of β-catenin by western blot.

Our bio-guided fractionation and sub-fractionation (using thin-layer chromatography and flash chromatography) revealed that the observed cytotoxic effect of the extract was related to the ethyl acetate fraction and probably to the sub-fraction B of the ethyl acetate fraction. Upon confirmation of the sub-fractionation analysis, the bioactive compound/s will be isolated, and the structure of this compound/s will be identified by Liquid Chromatography-Mass Spectrometry (LC-MS) and Nuclear Magnetic Resonance (NMR). This would pave the way for evaluating these compounds in the treatment of lung cancer.