Targeting integrins and beyond: synthesis and biological evaluation of multifunctional peptidomimetics in tumor therapy

Abstract

The work described in this PhD thesis concerns the design and synthesis of small molecular ligands targeting some subtypes of the integrin receptor family, in particular αVβ3 and α4β1 integrins. One major effort, which is described in Chapter 1a, is focused on the synthesis of dual small molecule conjugates as potential tools to impair tumor-associated angiogenesis. These constructs are formed by the covalent conjugation of a RGD unit, which is able to selectively bind to the extracellular segment of the αVβ3 integrin receptor, with a sunitinib-like moiety, a proven tyrosine kinase inhibitor (TKI) able to interact with the cytoplasmic domain of VEGFR2. Given the strict crosstalk between the VEGFR2 and αVβ3 receptors in both activated endothelial cells (ECs) and some cancer cell types, the blockage of the αVβ3/VEGFR2 couple may assume high anti-angiogenic and anti-tumor potential. On these bases, three dual conjugates were designed, synthesized and fully characterized, and subsequently tested in vitro to assess their properties as αVβ3 binders and VEGFR2 kinase inhibitors. All the conjugated compounds showed interesting anti-angiogenesis properties in vitro and one of them demonstrated a significant angiogenesis impairment in vivo, which proved superior to the action of the single RGD or sunitinib modules and their simple combinations. In Chapter 1b the work done during my period abroad is described. The coordination of platinum to DNA is an area of intense research that allowed the development of valuable platinum-based chemotherapeutics such as cisplatin and carboplatin. Besides DNA, platinum(II) is able to coordinate other biomolecules such as proteins, and this binding ability was exploited in bioconjugation reactions. In particular, extensive research in this area showed that some N-heteroaryl and S-donor groups in the side chains of suitable amino acids are preferential coordination sites for platinum in proteins. My work focused on the exploitation of the binding properties of Pt(II) versus suitable amino acids in order to synthesize cyclic peptides. In particular, four new cyclopeptides were prepared, where the central Pt(II) metal ion coordinates to different bidentate amine ligands and diverse RGD-based peptide sequences embedding suitable N-heteroaryl and S-donor groups. This coordination-based approach testifies that the platinum(II) ion may exert a double function: i) to favour peptide cyclization by exploiting its coordinative ability; and ii) to furnish peptide-Pt(II) complexes, which could be valuable tools for anti-cancer and anti-angiogenic interventions. As a further therapeutic target of interest, another integrin receptor, α4β1, was considered, given its primary role in mediating chronic inflammation, autoimmune diseases and cancer-related inflammation. In Chapter 2, our efforts in this field are described. In particular, the design and synthesis of seven new cyclic peptidomimetics are reported, all of which containing an aminoproline core scaffold grafted into key α4β1-recognizing peptide sequences. This work constitutes a first step towards further studies aiming at the evaluation of these small molecules as effective and selective α4β1 binders, with the final goal of gaining insights about the structural and functional aspects of this important biological target.