SYNTHESIS OF NEW RGD PEPTIDOMIMETIC-DRUG CONJUGATES TARGETING ΑVΒ3 INTEGRIN

Abstract Nowadays, systemic administration of cytotoxic agents is one of the main keystones of modern anticancer chemotherapy. However, many drugs do not selectively localize into solid tumors, as they normally accumulate also in healthy organs (e.g. liver and kidney). As a result, severe side effects are caused by the suboptimal biodistribution profile, in combination with the non-specific mode of action of cytotoxic agents, preventing the drug administration at therapeutic doses. The targeted delivery of anticancer agents into solid tumors is emerging as encouraging approach to overcome the intrinsic drawbacks of cytotoxic drugs. For example, some antibodies with high affinity for accessible tumor markers have been used as vehicles for the targeted drug delivery (Antibody-Drug Conjugates, ADCs). Since they may have limitations due to their high molecular weight, to their possible immunogenicity and to their high production costs, the development of smaller ligands (e.g. vitamins, peptides and peptidomimetics) capable of binding efficiently to tumor-overexpressed receptors, may show some significant therapeutic advantages. Peptides and peptidomimetics with the Arg-Gly-Asp tripeptide (RGD) are known to bind integrin αvβ3, a heterodimeric transmembrane receptor which shows low expression on healthy tissues, while being upregulated in a variety of cancer cells. For these reasons, integrin ligands have been widely explored as homing devices for the selective delivery of anticancer agents. In this PhD thesis, the synthesis and the biological evaluation of new small molecule-drug conjugates (SMDCs) targeting αvβ3 integrin are described. This work started with the preparation of a SMDC for the integrin-targeted delivery of Camptothecin, containing a disulfide linker and a naphtalimide moiety for the real-time monitoring of the cellular uptake (Chapter II). While the design of this complex molecular structure was carried out to reproduce literature data, the biological evaluation of this compound revealed a complex scenario. For this reason, the biological properties of all the three moieties (ligand, drug and linker) have been deeply investigated individually. Firstly, in Chapter III we established the role and the behavior of the ligand, trying to understand its action mechanism. Moreover, modifications of the ligand unit have been carried out to deface the affinity for the receptor and to unambiguously evaluate the capability of the original ligand to selectively target cancer cells that (over)express αvβ3. Later on, linker-related structural features (e.g. stability, linker cleavage experiments, kinetics of drug release, etc.) have been studied and improved (Chapter IV). Finally, the development of other integrin-targeted SMDC products featuring peptide linkers (with their biological evaluation) is reported in Chapter V. In Chapter VII, all the experimental details of synthetic and biological procedures are included, together with spectroscopic data and HPLC profiles of the newly synthesized compounds.