Effects of bromelain and N-acetylcysteine on mucin-expressing human gastrointestinal carcinoma cells and their peritoneal spread: towards development of novel locoregional approaches to peritoneal surface malignancies and pathological mucin synthesis

Abstract

Gastrointestinal cancers account for more than one third of all deaths from cancer. Peritoneal dissemination is considered as an advanced stage in the natural history of these malignancies and a frequent finding in the recurrent condition. As a curative approach to peritoneal surface malignancies confined to the peritoneal cavity, cytoreductive surgery (CRS) combined with hyperthermic intraperitoneal chemotherapy (HIPEC) has brought about long-term benefits in selected patients with peritoneal carcinomatosis (PC) of gastrointestinal origin and pseudomyxoma peritonei (PMP) syndrome. However, HIPEC fails to maintain the surgical complete response in a proportion of patients. Furthermore, tumor-secreted mucin makes a major contribution to tumor cell growth and survival, resistance to chemotherapy, evasion of immune surveillance, and formation of mucinous ascites, and is a key player in the pathogenesis of PMP and mucinous carcinomatosis. In order to discover novel locoregional approaches to gastrointestinal PC and PMP, the present project aimed to develop a novel formulation capable of enhancing microscopic cytoreduction and eliminating mucin. To this end, I investigated growth-inhibitory and mucin-depleting effects of bromelain (BR) and N-acetylcysteine (NAC), two natural agents with good safety profile, in experimental models of gastrointestinal cancers. Using a panel of human cancer cell lines, I observed that BR and NAC, on their own and more potently in combination, significantly inhibited proliferation and survival of cancer cells and reduced the expression of the characteristic mucins, in vitro. Mechanistically, apoptosis was found to mediate inhibitory effects of BR/NAC, with likely contribution of cell cycle arrest and autophagy. BR/NAC was also shown to sensitize cancer cells to cytotoxic agents. In vivo, I developed and treated nude mice models of PC and PMP-like syndromes with intraperitoneal administration of BR and NAC, individually and in combination. My results indicated that BR/NAC significantly inhibited peritoneal tumor growth in both models. Specific immunohistochemical staining of tumor sections revealed a significant decrease in the expression of the tumor-secreted MUC2 and MUC5AC. Taken together, this novel formulation with dual effects on gastrointestinal cancer cells and their mucin product holds promise for locoregional therapies targeting residual disease and mucin barrier in peritoneal malignancies.