Perylene derivatives are compounds used in a variety of industrial applications for decades, especially in the dye-sensitized solar cells, organic light-emitting diodes, semiconductors and organic thin film transistors, as well as in chemical oxidations as photosensitizers (1–3). The most commonly analyzed perylene derivatives were from hypericin (1,3,4,6,8,13-hexahydroxy-10,11-dimethylphenanthro[1,10,9,8-opqra]perylene-7,14-dione), which is the most potent, naturally occurring pro-oxidant that facilitate, or induce, the apoptosis and necrosis in a wide spectrum of cancer cell types (4). Moreover, these compounds have shown some antiviral, antidepressant, and antibacterial activities, and still in use as part of natural food supplements available in the markets (4–6). The current use of hypericin and other perylene derivatives in biomedical applications is usually based on their capacity to produce free radicals or reactive oxygen species (ROS) upon radiation, so-called photodynamic therapy (7). Here, the nontoxic compound, administered systemically, locally, or topically, acts as photosensitizer and during the tissue irradiation becomes active and generate ROS. Eventually, the increased ROS levels cause cytotoxicity on tumor cells leading to death and tissue destruction (8).The toxicity of non-radiated photosensitizer is a critical issue for these applications, because the administered compound directly interacts with metabolic detoxification system enzymes, and upon irradiation, the resulting product may become less effective or more toxic to the organism. As a defense mechanism, the detoxification system enzymes are evolved and can be induced to protect the organism against toxic effects of chemicals that may be harmful to their survival (9). Among these enzymes, mammalian glutathione transferase (GST, EC 188.8.131.52) is one of the most important detoxification enzymes that catalyze the nucleophilic addition of glutathione to diverse electrophilic molecules (10) and solubilize them to facilitate the transport of toxic substances from cells. On the other hand, GSTs have emerged as promising therapeutic targets because the specific isozymes are either overexpressed, or overactivated, in a wide variety of diseases, including cancer. Furthermore, current evidence showed the role of GSTs in signal transduction events is fundamental for cellular functioning (10–12) through the protein tyrosine kinase (PTK)–mediated GST activation and signaling from cell membrane to nucleus (13–17).Signal transduction is under tight control, provided by signaling components, such as kinases, and also by detoxification system enzymes, which are mostly the GSTs. For therapeutic purposes, the use of small molecules interfering with signaling components was shown to induce drug resistance as a result of GST-mediated detoxification reactions or signaling events. Therefore, in this context, a series of perylenediimides has been evaluated for their ability to bind DNA and their potential to induce cytotoxic effects on multiple cancer cell lines (18–22). However, such studies, searching the biological effects, were focused mainly on cytotoxic effects of perylene derivatives on cell viability, without mentioning the signaling components that contribute to the therapeutic effectiveness of compounds. In signal transduction from extracellular stimuli through cell membrane to cytoplasm, and to the nucleus, Src kinase (Src), among the PTKs, emerges as a fundamental constituent with essential roles in diverse signaling mechanisms (23). Therefore, the deregulations in its activity have been associated with various pathologic conditions, including cancer. In this context, studies with hypericin in photodynamic therapy applications revealed its association with GST and various members of PTK, where the enhanced photodynamic response was reported with GST inhibition at low nanomolar ranges of compound administered, and related with the decreased GST-dependent resistance (19–22).
Perylenediimides are known for their photo- and chemical stability. However, they do not have absorptions in the red end of the visible spectrum to be suitable for photodynamic applications. Our previous efforts to design and develop novel perylenediimide derivatives resulted in compounds with potential efficacy in photodynamic therapy (24–26). Recently, green perylenediimides with dialkylamino substituents on the perylene core was reported as an alternative photosensitizer for photodynamic therapy (27). Previously, we synthesized water-soluble green perylenediimide dyes with absorption peaks beyond 650 nm as an alternative photosensitizer for photodynamic therapy (24). With these compounds, we demonstrated that the cytotoxicity of derivatives on red-light excitation was more significant compared to non-excited compounds. These preliminary in vitro experiments, hence, verified their potential utility in photodynamic therapy. Consistent with these efforts, in this current study, we report the design and synthesis of novel perylenediimides (Scheme 1: panel A) with amino acid substitutions (Scheme 1: panel B) and their inhibitory characteristics against two critical enzyme targets. To reveal their potential to minimize tissue resistance while improving anticancer effectiveness, the structure-activity relationships were assessed by dose–response studies.