Innovative nanomedical application of CKSTHDLC peptide: from targeting of arthritic joints to a precise cancer theranostic approach

The development of nanomedical applications requires to take an increasing attention to a variety of different factors, in order to selectively address a specific pathological site maintaining safe conditions. The nanoparticle formulation, surface modifications to reach a specific target, and the biocompatibility of nanoformulations are just a few examples of the amount of data required in preclinical settings, both in vitro and in vivo, to develop a diagnostic, therapeutic or, better, theranostic approach based on the peculiar characteristics of nanomaterials. In this context, we initially focused on the characterization of a specific targeting peptide that have already been demonstrated able to address inflamed synovial tissues and to specifically drive both therapeutic molecules and theranostic nanoparticles in this pathological site. The precise analysis of the binding capability of this targeting peptide and, most importantly, of its cell surface interactions, required cellular, protein and computer-based molecular simulations; collected data allowed to demonstrate that the CKSTHDLC cyclic peptide binds the calcium-activated potassium channel subunit alpha-1 (BKα1). It has been previously demonstrated that BK channels expression and function are perturbed in fibroblast-like synoviocytes, causing an increased proliferation, invasion, and inflammatory cytokines production. Moreover, literature and database analysis report an over-expression of this transmembrane molecule in several cancer cells and its role as a poor prognostic factor in breast and prostate cancers. These results prompted us the possibility to extend the use of targeting molecule in different tumor microenvironments. A chitosan-based formulation with a core of perfluopentane for US-imaging, labelled with fluorescent dyes and coated with the targeting molecule, has been produced and then studied in vitro and in vivo as a novel potential therapeutic and early diagnostic approach, not only for rheumatoid arthritis, but also against high surface expressing BKα1 cells in cancer microenvironment, including cancer cells but also endothelial cells of neo-formed vessels. Targeted nanobubbles resulted stable over time and their biocompatibility was guaranteed analyzing protein corona composition, formed after incubation in human serum, but also evaluating their low interactions with both the complement and coagulation systems. The particle internalization was demonstrated, allowing the intracellular drug delivery, and supported by the absence of cytotoxicity valuated against a variety of cell lines and erythrocytes. Moreover, the in vivo biodistribution study performed in zebrafish embryos, showed an in vivo biocompatibility, and as expected, an accumulation of these nanostructures in macrophages-rich tissues. The pivotal role of the targeting molecule on nanobubbles surface was demonstrated, both in vitro and in vivo, using breast and prostate cancer cells, and xenograft zebrafish embryos as cellular and animal models, respectively. In particular, after their in vivo injection in tumor-bearing animals, targeted nanobubbles showed their ability to distribute in different tissues, but especially, to accumulate in cancer microenvironment. Altogether, these results pointed out the basis for the development of targeted chitosan-based nanobubbles as a theranostic material useful in the management of patients affected by a chronic inflammatory disease, like rheumatoid arthritis, but also, of patients with different solid tumors, both characterized by the over-expression of the BKα1 protein channel.