The disruption of protein-protein interactions (PPIs) is emerging as a new paradigm for the control of intercellular contacts and signaling in a number of biological
scenarios. This approach poses a whole new set of challenges to chemists for the design and synthesis of new effector molecules with the potential of being evolved in therapeutic and diagnostic tools. In this project, we have collected a pool of different expertise to take up some of these challenges, focusing on a selected group of related and well-characterized cases relevant in the oncologic field, that can be addressed using peptidomimetics or foldamers.
The strategy builds on previous knowledge, created in the course of earlier PRIN projects, on the design, synthesis and characterization of peptidomimetics capable of reproducing short peptide pharmacophoric fragments representing “hot spots” of PPIs (e.g. the RGD tripeptide and related sequences), and of foldamers able to imitate elements of secondary structure, typically alpha-helices, known to promote the selective formation of relevant PP complexes.
A fundamental aspect in cancer therapy is the control of tumor cells proliferation, which is partly regulated by the activity of receptors of growth factors (GFR) and by
integrins, through the formation of specific protein-protein complexes. Hence, integrins and GFR will be one of our major targets. Since integrins are overexpressed by tumor cells, integrin-targeted multifunctional systems can selectively deliver to neoplastic cells imaging biomarkers or anti-tumor cargos (e.g. cytotoxic agents, kinase inhibitors, pro-apoptotic molecules). This represents a particularly promising area of research that may improve the efficacy of diagnostic tools and decrease the toxic side effects associated with systemic delivery of chemotherapy. Thus, peptidomimetic integrin ligands obtained in the previous PRIN project and endowed with high potency and selectivity will be exploited as tumor-targeting devices to generate hybrid entities - either covalently linked or non-covalently assembled in nanoscale devices - of potential efficacy for molecular targeting in cancer therapy and diagnosis.
A second interesting feature of such integrin-targeted multifunctional systems is the potential of inhibiting multiple cancer-related pathways, which generally results
in an improvement of clinical outcome. With a similar approach, dual-function molecular constructs (covalently or non-covalently linked) will be generated and used as probes to interrogate the signaling pathways downstream of integrins and their cross-talk with GFR. Growing evidence supports a central role for cooperative
signaling between integrins and growth factor receptors, particularly the vascular endothelial GFR (VEGFR), in many aspects of tumor progression. Therefore
simultaneous blocking of selected integrins and VEGFR function will be studied. Helical foldamers mimicking the N-terminal sequence of VEGF will be used to
engage VEGFR.
Selective delivery of multifunctional constructs to tumor cells will also be sought exploiting molecularly imprinted polymeric vectors, able to specifically recognize
the template protein used during their preparation in nano-sized vescicular compartments. In principle, this approach can be applied to many if not all membrane protein templates, and can find an application in the recognition of a wide variety of tumor-related receptors.
The potential of interactions developed at the surface of protein structures is being harnessed also in promising new approaches in cancer therapy, that are based on the selective cell homing of host defense peptides (HDP). HDP are effector molecules of innate immunity that were found to specifically target and kill cancer cells while showing negligible toxicity against normal cells. Their mechanism of action is believed to depend on the specific recognition of tumor cell membranes, which differ in many ways from normal cell. Helical peptide foldamers will be designed, prepared, and tested for the ability to kill neoplastic cell models and to perturb membrane permeability. Interestingly, recent studies showed that peptides mimicking the peptaibol HDPs, i.e. natural helical peptides rich in Aib, have a strong tendency to bind to cells of the innate immune system, such as monocytes or macrophages. Since these pro-inflammatory cells are considered key regulators of tumor progression, the identification of the features allowing these peptides to selectively bind to a specific leukocyte type will provide an additional way to control tumor growth.
Collectively, the activities and ambitious aims of this multidisciplinary proposal are well within the scope and objectives identified by Horizon 2020 (Excellent
Science, Industrial Leadership and Societal Challenges sections) and will possibly establish a major contribution of chemical knowledge in the development of novel,
less toxic, therapeutic strategies.