Effects of modified bioactive pectins on colon cancer cells in vitro

Pectin is a complex structural polysaccharide present in the cell walls of terrestrial plants, fruit and vegetables. Modified pectin (MP), pectin treated with pH, heat or enzymes, has been shown to have anti-cancer activity in several cancer cell lines. The galactan chains of MP are postulated to be essential for bioactivity due to their ability to bind and inhibit the pro-metastatic protein galectin-3 (Gal3) on cancer cells. However, the structural requirements for bioactive MP, as well as interactions with Gal3 in vitro, have rarely been addressed. In this study several pectins from citrus, sugar beet and potato were screened for their biological effects on colon cancer cells, their structures characterised in detail to assess the structure-function relationship and the molecular mechanisms of action investigated. Alkali-treated sugar beet pectin (SSBA) reduced viability of HT29 cells via induction of apoptosis. The enzymatic removal of galactan side chains abolished activity indicating their importance for anti-proliferative action. Additionally, potato rhamnogalacturonan I (P-RGI) reduced viability of DLD1 cells and the homogalacturonan backbone, not the galactan side chains, was shown to be essential for bioactivity. siRNA-mediated knockdown of Gal3 expression in cells showed that bioactivities of SSBA and P-RGI are independent of Gal3, prompting an investigation into alternative mechanisms of action. Expression of the adhesion molecule ICAM1 was shown to be significantly reduced by P-RGI, suggesting a novel potential mode of action. Results presented in this thesis suggest that MPs of varying structures can exert anti-proliferative activity in colon cancer cells via Gal3-independent mechanisms and in a cell-specific manner. This study is also the first to report the anti-cancer activity of sugar beet pectin. The structural complexity of pectin makes it a potential multi-functional therapeutic agent, and results highlight the need for extensive structural characterisation of bioactive pectins as well as further exploration of Gal3-independent mechanisms of action.

Name dc:type.qualificationname

phd

Level dc:type.qualificationlevel

doctoral

Grantor dc:publisher.institution

University of East Anglia

Year dc:date.issued

2014

Author dc:creator

• Maxwell, Ellen

Language dc:language

en