Study of intermolecular interactions of antiviral agent tilorone with RNA and nucleosides

Abstract

Background: While antiviral and interferon-inducing agent tilorone is used as a reactant of a number of popular pharmacological preparations, the molecular mechanisms of its biological antiviral activity are under discussions among the specialists. That is why the molecular level model studies of interactions of tilorone with targeting biomolecules and their components are considered to be urgent and useful for understanding the molecular mechanisms of the agent biological activity. Objectives: The current model study is devoted to mechanistic examining of the intermolecular interactions of tilorone with its possible biomolecular targets which are believed to be nucleic acids and such their components as nucleosides containing purine or pyrimidine nitrogen bases. Materials and methods: The objects of the study are model systems composed of tilorone dihydrochloride (Til•2HCl) and its potential targeting biomolecules: single-stranded RNA (ssRNA) obtained from Saccharomyces cerevisiae yeast or nucleosides - adenosine (Ado), thymidine (Thd), or uridine (Urd). Dynamic light scattering (DLS) measurements aimed at observation of drug-biomolecules aggregation is applied to the system (tilorone+ssRNA) (1:10 molar ratio) in RNA-free phosphate buffered saline solution (with 10% fetal bovine serum). Electrospray ionization (ESI) mass spectrometry is used to examine the intermolecular interactions in the binary (tilorone + nucleoside) (Ado, or Thd, or Urd in 1:10 molar ratio) and triple (tilorone + Ado + Urd) (1:10:10 molar ratio) systems dissolved in polar solvent methanol. Results: The obtained DSL data demonstrate that under conditions similar to the physiological ones, introduction of tilorone into the ssRNA solution results in formation of tilorone+ssRNA aggregates which more than 10 times exceed in size the particles observed in the ssRNA solution itself. The ESI mass spectrometry experiments reveal that while the mass spectra of all studied (tilorone + nucleoside) model systems contain ions characteristic of the individual components of the mixtures, in the spectra of (tilorone + Urd) system the ions of stable ion-molecular clusters of uridine with tilorone dication Urd•Til•2H2+ are recorded. The examining of the three-component model system (tilorone + Ado + Urd) testifies to the selectivity of tilorone binding: while the peak of noncovalent complex of Urd•Til•2H2+ is detected, any peaks of the complexes of Ado with tilorone are not found in the mass spectrum. Conclusions: Formation of large-scale molecular aggregates of tilorone with ssRNA in the solutions which are similar to the physiological solution in physical and chemical characteristics is revealed in the performed DLS investigation. Creation of stable Urd•Til•2H2+ noncovalent complexes in (tilorone + nucleoside) model systems was demonstrated by ESI mass spectrometry, while the complexes of tilorone with Ado and Thd are not detected in the experiments. It testifies to the possibility of formation of stable noncovalent complexes of tilorone with ssRNA and their components in biological systems, and pointed at Urd as one of the potential centers of specific binding of RNA molecules with tilorone.

Keywords

• tilorone
• RNA
• nucleosides
• intermolecular interactions
• dynamic light scattering
• mass spectrometry