Annona muricata Graviola Induces Apoptosis in Two Osteosarcoma Cell Lines and Downregulates the Cytokines IL-6 and TGFβ1 Which Are Implicated in Tumour Growth and Metastasis

Background Osteosarcoma (OS) is an aggressive bone tumour which affects mostly young children. Despite advances in chemotherapy regimens there is still high fatality and cure rates remain low. Annona muricata Graviola (GR) is a tropical fruit bearing tree whose leaves, stems and fruits have indigenous medicinal properties. Studies have shown that GR has anti-tumour effects on breast, liver and prostate tumours. Objectives The aim of this study was to investigate the effect of GR on bone cancer cell lines of the OS lineage. Methods Two human OS cell lines; HOS and MG63 were cultured with GR (300 mg/mL) for 24 h at 37°C. After which supernatants and cell pellets were collected and analyzed for apoptosis by microscopy and flow cytometry, using annexin staining. Culture supernatants were analyzed for IL-6 and transforming growth beta (TGFβ) using ELISAs. Label free proteomics was used to evaluate changes in protein expression. We also investigated the effect of combining blocking antibodies to p53 and BCL-2 with GR treatment on the cell lines. The effect on TGFβ expression was then measured using flow cytometry. Results Treatment of HOS and MG63 cells with GR increased the expression of annexin compared to untreated cells. GR treatment also caused a dysregulation in the secretion of the cytokines IL-6 and TGFβ. Proteomics showed that GR induced apoptosis in OS cells through multiple pathways triggering an alteration in the expression of key proteins involved in cellular respiration, cell cycle, motility, DNA synthesis and cell death. Further, GR was shown to downregulate TGFβ through BCL-2 and p53 mediated pathways. Conclusion The data suggest GR has anti-tumour effects on OS cell lines therefore the efficacy of GR should be tested clinically in OS patients.