P5.10 - Bromelain and N-acetylcysteine inhibit proliferation and survival of gastrointestinal cancer cells: significance of combination therapy

Abstract

ABSTRACT Bromelain and N-acetylcysteine (NAC) are two natural, sulfhydryl-containing compounds with good safety profiles which have been investigated for their benefits and application in health and disease. In the present study, the efficacy of bromelain and NAC in single agent and combination treatment of human gastrointestinal carcinoma cells was evaluated in vitro and underlying mechanisms of effect were explored. The growth-inhibitory effects of bromelain and NAC, on their own and in combination, on a panel of human gastrointestinal carcinoma cell lines, including MKN45, KATO-III, HT29-5F12 & -5M21 and LS174T, were assessed by SRB. Moreover, the influence of the treatment on the expression of a range of regulators of cell cycle and survival was investigated by Western blot. The presence of apoptosis was also examined by TUNEL assay. Bromelain and NAC significantly inhibited cell proliferation, more potently in combination therapy. Drug-drug interaction in combination therapy was predominantly synergistic or additive. Mechanistically, apoptotic bodies were detected in treated cells by TUNEL assay. Western blot analysis revealed diminution of cyclins A, B and D, the emergence of immunoreactive subunits of caspases 3, 7, 8 and cleaved PARP, withering or cleavage of procaspase-9, overexpression of cytochrome c, reduced expression of anti-apoptotic Bcl-2 and pro-survival phospho-Akt, the emergence of the autophagosomal marker LC3-II and deregulation of other autophagy-related proteins, including Atg3, 5, 7, 12 and Beclin 1. These results were more prominent in combination therapy. We report for the first time growth-inhibitory and cytotoxic effects of bromelain and NAC, in particular in combination, on gastrointestinal cancer cell lines with different phenotypes and characteristics. These effects apparently resulted from cell cycle arrest, apoptosis and autophagy. Towards the development of novel strategies for the enhancement of microscopic cytoreduction, our results lay the basis for further evaluation of this formulation in locoregional approaches to peritoneal surface malignancies and carcinomatosis.