THE ANTIPROLIFERA TIVE AND APOPTOTIC EFFECTS OF ANNONA MURICATA EXTRACT ON PROSTATE CANCER CELLS

Abstract

Annona muricata (AM), a tropical evergreen tree, also known as graviola, guanabana or soursop, belongs to the custard apple tree family known as the Annonaceae. It has become known as a "cancer killer" due to its ability to reduce the proliferation of 12 different types of tumors, including breast, prostate, lung, colon and pancreatic cancers. The major phytochemical compounds that have been identified in AM are cyclic hexapeptides and annonaceous acetogenins (AAGs). The AAGs have been reported to have promising anticancer activities in multidrug resistant cancers (MOR). 10• 11 The structures of AA Gs are comprised of adjacent tetrahydrofuranic rings flanked by hydroxyl groups and tetrahydropyranic rings or epoxides. In previous studies AA Gs have been demonstrated to inhibit the ubiquinone-linked NADH oxidase that is constitutively overexpressed in the membranes of cancer cells, but which is only transiently expressed in normal cells. This event could potentially activate the apoptotic cascade. The purpose of this study was to evaluate the antiproliferative and apoptotic effects of the AM extracts on prostate cancer cells (PC3). The PC3 cells were treated with methanol extract (ME), aqueous fraction (WF), and ethyl acetate fraction (EAF) of AM (l-100 μg/mL). A cell viability assay utilizing 3-( 4, 5-dimethylthiazol-2-yl)-5- (3-carboxymethoxyphenyl)-2-( 4-sulfophenyl)-2H-tetrazolium (MTS) was performed to evaluate the antiproliferative effects. The results demonstrated that EAF results in a significant reduction in cell viability after 24 h (ICso 14.02 ± 1.14 μg/mL). Caspase 3/7 activities were also tested to verify activation of caspases. The activities of caspase 3/7 were significantly elevated 3 h after treatment with IO μg/mL of EAF. Furthermore, PC3 cells exposed to EAF were tested for Bcl-2 and Bax, the regulatory proteins involved in apoptosis, by Western Blot. EAF caused a significant reduction in the expression of the antiapoptotic protein Bcl-2 but had no effect on the expression of the proapoptotic protein Bax. Moreover, the Bax/Bcl-2 ratio was significantly increased after PC3 cells were treated with 30 μg/mL of EAF. These results suggested that the EAF reduces cell proliferation and/or causes cell death in PC3 cells by the induction of apoptosis. Further studies will confirm the application of these plant constituents in cancer therapy.