Development of non-stimuli and stimuli-responsive ion carriers and their biological applications

Abstract

The transport of ions is an essential biological process that helps to maintain healthy biological processes such as ion homeostasis, pH gradients, and membrane polarization. In a natural system, this vital function is performed by ion channels and ion carriers. The dysfunction of these transport proteins results in life-threatening diseases such as barter syndrome, cystic fibrosis, dents diseases, etc. In the last few decades, there have been tremendous studies in supramolecular research that mimic the function of natural ion transporters and known to cause apoptotic cell death. However, application of sugar derived systems in ion transport field is less explored. Therefore, to address the selective ion recognition, we have taken advantage of oligo-(1→6)-D glucosamine-based derivatives which exhibit polar cavity. We have designed a 3-amino 3-deoxyallose and 4-amino 4-deoxygalactose-based macrocycle having an amino group at the axial position. To improve anion recognition amino group is attached to different aromatic tails for the contribution of anion binding. The synthesis of these cyclic saccharides-based macrocycles was done in collaboration with Dr. Yuri Tsvetkov, N. D. Zelinsky Institute of Organic Chemistry, Moscow. A series of 12 3-amino-3-deoxyallose and 11 4-amino 4-deoxygalactose core systems with various side chains were screened for ion transport activity. Two systems with pyrrole and indole side chains in the deoxyallose series and four systems with pyrrole, indole, para-substituted methyl and bromo side chains in deoxygalactose series were identified to exhibit good ion transport activity. The ion selectivity data shows that transport activity is anion-dependent and cation independent. Biological studies could not be performed due to precipitation at of the compounds in cell culture media. Due to the difficulty associated with the synthesis and precipitation of these cyclic carbohydrate systems, owing to their complexity of structure, it was decided to make the test system structurally simpler. Prodigiosin is naturally occurring tripyrrolic transporter capable of promoting H/Cl symport or Cl/HCO3 antiport due to which it shows promising potential therapeutic activity. Inspired by the structure of prodigiosin many pyrrole-based ion transporters have been reported. However, indole is not much explored for ion recognition even though indole NH is more acidic compared to pyrrole NH. Therefore, we have designed and synthesised novel bis-indole-based ion transporters. The ion transport activity demonstrated most active compound is anion selective and the mechanism of transport is antiport. The MTT assay shows that compounds are cytotoxic towards cancerous cells over non-cancerous cells. The apoptotic cancer cell death was confirmed by disturbance of mitochondrial membrane polarization (MMP), generation of reactive oxygen species (ROS), and cell cycle study. The major limitation of synthetic ion transporters from biological perspective is its non-specificity and uncontrolled transport activity. Recently, photoactivated approach have attracted attention in drug delivery research field due to its specificity and precise control. Therefore, we have integrated the concept of photoactivated approach and ion transporter to get procarrier (inactive form of active carrier). We have designed and synthesised an indole-2-carboxamide receptor as an efficient membrane chloride carrier while the corresponding o-nitrobenzyl-linked derivative is a procarrier of the ion. Photoirradiation of the procarrier in liposomes results in the release of the active carrier displaying up to 90% transport efficiency. Such photorelease of the carrier also works within cancer cells resulting in efficient cell death. All in all, such photocleavable procarriers have great potential as a photodynamic therapy to combat various types of cancers.