RNA-targeting low-molecular-weight fluorophores for nucleoli staining: synthesis, in silico modelling and cellular imaging

Herein we present our work on the synthesis, investigation of the photophysical properties, interactions with nucleic acids, molecular docking, and imaging application of three carbocyanine dyes. The described low-molecular-weight compounds were found to exhibit high resistance against photobleaching and showed promising optical properties as fluorescent labeling agents for ribonucleic acids. They form strong biocomplexes (log K-s = 6.11-7.84) and revealed remarkable sensitivity towards RNA, reaching up to a 379 times increase of the emission signal when bound to AU-rich sequences. According to the score values obtained from the molecular docking studies, the compounds show strong binding affinity towards RNA macromolecules. All fluorophores exhibit significant cell tolerance since they were found to be 16 to 60 times less toxic against MRC5 cells (healthy human fibroblasts) compared to the conventional Thiazole Orange - TO. The IC50 concentrations for the compounds were calculated up to 40 mu M in human fibroblasts MRC5, A549 adenocarcinomic human alveolar basal epithelial cells, the HCT116 human colon cancer cell line, and MDA-MB-231 adenocarcinoma cells. Analyzing the dyes for preferential cytotoxicity towards cancer cell lines in comparison to the normal human fibroblasts, we found a candidate exhibiting promising anticancer potential. Based on the selectivity (Si) towards cancer cells and more specifically against difficult to treat colon HCT116 carcinoma, we can suggest these small molecules as an interesting platform for further development. We have also demonstrated the efficiency of the carbocyanines as staining agents for in vivo labeling of human cells as well as microbial and eukaryotic cells.