Inhibition of Type IV Secretion Activity and Growth of Helicobacter pylori by Cisplatin and Other Platinum Complexes

Abstract

Type IV secretion systems are protein secretion machineries that are frequently used by pathogenic bacteria to inject their virulence factors into target cells of their respective hosts. In the case of the human gastric pathogen Helicobacter pylori, the cytotoxin-associated gene (Cag) type IV secretion system is considered a major cause for severe disease, such as gastric cancer, and thus constitutes an attractive target for specific treatment options against H. pylori infections. Here, we have used a Cag type IV secretion reporter assay for screening a repurposing compound library for inhibitors targeting this system. We found that the antitumor agent cisplatin, a platinum coordination complex that kills target cells by formation of DNA crosslinks, is a potent inhibitor of the Cag type IV secretion system. Strikingly, we found that this inhibitory activity of cisplatin depends on a ligand exchange reaction which incorporates a solvent molecule (dimethylsulfoxide) into the complex, a modification which is known to be deleterious for DNA crosslinking, and for its anticancer activity. We extended our analysis to several analogous platinum complexes containing N-heterocyclic carbene, as well as DMSO or other ligands, and found varying inhibitory activities toward the Cag system which were not congruent with their DNA-binding properties, suggesting that protein interactions may cause the inhibitory effect. Inhibition experiments under varying conditions revealed effects on adherence and bacterial viability as well, and showed that the type IV secretion-inhibitory capacity of platinum complexes can be inactivated by sulfur-containing reagents and in complex bacterial growth media. Taken together, our results demonstrate DNA binding-independent inhibitory effects of cisplatin and other platinum complexes against different H. pylori processes including type IV secretion.

Culture media, DMSO and efflux affect the antibacterial activity of cisplatin and oxaliplatin

“…We expect that the sulphur present in cysteine and methionine react with one of the cisplatin's platinum atoms, leading to its inability to bind to DNA, akin to DMSO (Hall et al 2014). Our results also correspond to the antagonistic role of methionine and cysteine on the antibacterial activity of cisplatin shown previously in Helicobacter pylori (Lettl et al 2020). We suspect that the same observations will be reproduced in other Gram-negative and Gram-positive organisms, as the reduction in cisplatin's antibacterial activity is a consequence of the choice of growth media.…”

Kinetics of CagA type IV secretion by Helicobacter pylori and the requirement for substrate unfolding

“…Interestingly, however, administration of erythromycin resulted in a rapid decrease in bacterial viability (Figure S3b). In contrast, adding the anticancer drug cisplatin, which interferes with CagA translocation and with H. pylori viability by yet unknown mechanisms (Lettl et al, 2020), resulted in an almost immediate reduction of the CagA translocation rate (Figure 3d), but not in rapid killing of the bacteria (Figure S3b), supporting the previous conclusion that cisplatin acts rapidly and directly on the type IV secretion process.…”

Culture media, DMSO and efflux affect the antibacterial activity of cisplatin and oxaliplatin

“…2014). Our results also correspond to the antagonistic role of methionine and cysteine on the antibacterial activity of cisplatin shown previously in Helicobacter pylori (Lettl et al . 2020).…”

“…We expect that the sulphur present in cysteine and methionine react with one of cisplatin's platinum atoms, leading to its inability to bind to DNA, akin to DMSO (Hall et al 2014). Our results also correspond to the antagonistic role of methionine and cysteine on the antibacterial activity of cisplatin shown previously in Helicobacter pylori (Lettl et al 2020). We also show that the reduction in antibacterial activity in MHBII is not specific to cisplatin.…”