Development of transmembrane ion transport systems for biomedical applications

Abstract

This thesis aims to advance transmembrane ion transport systems as prospective therapeutic agents for the treatment of cancer and bacterial infections by overcoming their limitation of non-specific activity. In this direction, ion transporters formulated in the prodrug form or protransporters that are selectively activable in the target via certain stimuli were explored. Initially, a cancer cell targeting protransporter was designed that could be activated by the cell-protecting, quinone-reducing enzyme, NQO1, which is overexpressed in cancer cells. Salicylamide was chosen as the transporter and shown to be capable of transmembrane H+/Cland#8722; symport. Blocking of the salicylamide OH group with NQO1 activable quinones inhibited transport activity, yielding two protransporter systems. NQO1-triggered release of the free transporter from protransporters was verified. Both transporters and protransporters were selectively toxic toward the MCF-7 breast cancer cell line over non-cancerous MEFs. Studies in MCF-7 indicated cytotoxicity to be mediated via ion homeostasis disruption triggered induction of oxidative stress, mitochondrial membrane depolarization, and lysosomal deacidification. Induction of cell death via intrinsic apoptotic pathway was also verified. Next, the utility of the salicylanilide system in the antibacterial role was assessed. Screening of a library of derivatives yielded transporters with significant antibacterial activity, and structure-activity relationships were established. The screened compounds were effective against the Gram-negative bacterial strains: Escherichia coli, Salmonella enterica (serovar Typhimurium), and Klebsiella pneumoniae. Cell surface imaging of E. coli subjected to osmotic shock following salicylanilide treatment showed extensive cell damage, indicating transporter-facilitated H+/Cland#8722; transport across the bacterial OM degrades its cell-protecting ability.