New fluorescently labeled isothiocyanate derivatives as a potential cancer theranostic tool

Cancer is the plague of the 20^th and 21^st centuries, affecting sick individuals, their families, and entire micro- and macro-communities. Despite the efforts of scientists to search for new diagnostic and therapeutic methods, the statistics regarding cases of illness and deaths are becoming more and more alarming. Therefore, it is extremely important to look for theranostic tools that enable the initiation of therapy during the diagnostic process. Theranostics involves the use of a tool that is one construct that simultaneously performs two functions: imaging (diagnostics) and selective cytotoxicity towards cancer cells (therapeutics). Currently, due to its low invasiveness and extremely high sensitivity, fluorescence imaging is attracting attention in the development of theranostics. Therefore, the impact of structural modifications on the biological activity of fluorescently labeled isothiocyanate (ITC) derivatives was designed, synthesized and studied. The covalent combination of a fluorescent marker enabling imaging and an isothiocyanate group responsible for biological activity, connected via a linker, allowed for obtaining constructs with high application potential, which combine diagnostic and therapeutic functions. To verify the therapeutic potential of the synthesized derivatives, the influence of the type of fluorophore and the length of the linker on the anticancer effect of ITC group was examined. Moreover, the ability of the obtained compounds to pass through the cell membrane and their retention time in the cell after penetration were monitored to verify their diagnostic potential. Model cell lines of breast cancer (T47D) and prostate cancer (PC3) were used to study the activity. Healthy dermal fibroblast cell line (HDFa) was used to test selectivity. The reference compound used was sulforaphane (SFN), one of the best-studied active ITC derivatives. During the research, it was found that all compounds have higher anti-cancer activity than the reference compound. The anticancer activity depends on both the type of fluorophore and the length of the linker. The most active compound has an IC₅₀ value that is over 30 times lower for prostate cancer cells and almost 30 times lower for breast cancer cells than SFN. Studies of the anticancer activity of the synthesized analogues allowed us to conclude that the ITC group is responsible for the activity of these compounds, while the presence of a fluorophore enhances it. Moreover, it was found that all tested compounds penetrate the cell membrane. The accumulation of the dye in the cell was visible after 5 min of treatment with compounds at low concentrations. Moreover, after removing the dye from the medium, cell fluorescence could be recorded even after 24 h at higher contrast. The research confirmed that compounds combining potential diagnostic and therapeutic functions were obtained. Therefore, fluorescently labeled ITC derivatives represent super promising theranostic tools.