Exploring the anti-cancer and anti-inflammatory properties of isothiocyanates

Isothiocyanates are a class of phytochemicals responsible for the characteristic tastes and odours of cruciferous vegetables. Epidemiological evidence indicates that increased consumption of isothiocyanates is associated with improved outcomes in a number of diseases, including inflammation and cancer. While many biological activities of isothiocyanates have been observed in vitro and in vivo, the detailed mechanisms that underlie isothiocyanate action are largely unknown. In this thesis, a library of structurally diverse isothiocyanates were examined for their ability to inhibit the pro- inflammatory cytokine macrophage migration inhibitory factor (MIF), and to trigger apoptosis. Isothiocyanates are known to covalently modify the N-terminal proline residue of MIF, inhibiting its tautomerase activity. The isothiocyanate library was tested for its ability to inhibit recombinant human MIF and also MIF activity in a human T-cell line. Structural differences in isothiocyanates were shown to influence their inhibitory capacity, with several compounds exhibiting low micromolar IC50 values in both systems. Inhibition of tautomerase activity was associated with a loss in the biological function of MIF in two physiological models. While MIF is known to have anti-apoptotic activity, there was no correlation between the ability of isothiocyanates to inhibit MIF tautomerase activity and their ability to trigger apoptosis. This suggests two independent pathways. It also indicates that isothiocyanates can be developed as MIF inhibitors that are not directly cytotoxic. Isothiocyanate-induced cytotoxicity was examined in more detail by investigating the role of the Bcl-2 family of pro- and anti-apoptotic proteins. Phenethyl isothiocyanate (PEITC) induced apoptosis via a classical apoptosis pathway involving Bax and Bak, and required the BH3-only proteins Bim and Bid. Intriguingly, however, the anti- apoptotic protein Bcl-2 could not protect the cells from phenethyl isothiocyanate (PEITC). Indeed, the Bcl-2 overexpressing cells were more sensitive to PEITC. The isothiocyanate has a greater effect on mitochondrial metabolic activity in the Bcl-2 overexpressing cells than wild-type cells. This suggests that isothiocyanates bypass the action of Bcl-2 by acting directly on mitochondria, and this information could be valuable for designing novel isothiocyanates that target Bcl-2 overexpressing cancer cells