Arginine-Tryptophan Peptides Enhancing Antibacterial and Anticancer Effects of Ruthenium(II) Polypyridyl Complex Photosensitizers

Abstract

In recent years, photodynamic therapy (PDT) has emerged as a potential antibacterial and anticancer alternative. The free radicals are generated in the presence of photosensitizers (PS) and oxygen under light irradiation of a specific wavelength, causing cytotoxic damage to the cells. Ruthenium(II) photosensitizers (Ru(PS)) are of interest due to their rich photochemical properties and potential antibacterial and anticancer activities reported in previous studies. However, the low uptake by bacterial and cancer cells has limited the clinical uses of Ru(PS). In this study, the potential of membrane-targeting peptides involving arginine-tryptophan (Arg-Trp or RW) in enhancing the uptake of the Ru(PS), namely, RuCOOH, into bacterial and cancer cells, as well as their antibacterial and anticancer efficiencies, has been studied. The minimum inhibitory concentrations (MICs) of compounds against eight bacteria, including Staphylococcus aureus (SA), Acinetobacter baumannii (AB), Pseudomonas aeruginosa (PA), and Escherichia coli (EC), both susceptible (S) and resistant (R) strains, were determined using the broth microdilution method. Anticancer activities (IC50) of the compounds against breast cancer cell lines (MCF-7, MDA-MB-231, and MDA-MB-468) were studied using the MTT assay. The cellular uptake of the compounds into bacterial and cancer cells was also studied via confocal and fluorescence imaging. Noncancerous cells MRC-5 and MCF-10A were used to compare the selectivity of the compounds to bacterial or cancer cells. RuCOOH alone demonstrated MIC values of >128 μM against all eight bacteria, whereas its Arg-Trp conjugates showed lower MIC values (2–32 μM) against all bacteria except PA(R) and AB(S). A significant 4-fold reduction in MIC values (from >128 to 2–32 μM) was observed when the conjugates were tested against EC(S) and AB(R) compared to RuCOOH alone. For anticancer activities, RuCOOH alone demonstrated IC50values of >100 μM, whereas its Arg-Trp conjugates (RuRW6, RuRW8, and RuRW9) showed lower IC50values (5.44–93.08 μM) against all three breast cancer cell lines. Cellular uptake studies demonstrated the associations of RuRW9 with bacteria and breast cancer cells, whereby a red color signal was observed in the areas presented with cells when compared to the control and RuCOOH alone. MTT assay presented that all conjugates are selective in terms of selective index (SI) values toward EC bacteria instead of MRC-5 and the MDA-MB-468 breast cancer cell line instead of MCF-10A. Arg-Trp peptides enhanced the antibacterial and anticancer activities of the Ru(PS), which highlighted the pertinence of combining the use of photosensitizers and targeting agents to fight against multidrug-resistant bacteria and breast cancer.