Development of Novel Self-Immolative Linkers based on Fragmentation and Cyclisation Reactions for Targeted Therapeutic Applications stars

Abstract

Targeted-drug delivery has emerged within the last years as one of the most promising approaches to treat cancer. These systems consist of a molecule, with a high affinity and selectivity for a target present in cancer cells, conjugated to cytotoxic payloads. In this sense, antibody-drug conjugates have been the gold standard of targeted therapy and have been widely studied in the past years. Indeed, to date there are 11 ADCs approved by the US FDA for their use in cancer patients. An ADC is formed by a monoclonal antibody and a payload joined by a linker. Nevertheless, despite the selectivity of ADCs and the progress made in their development in the last years, they present several drawbacks. To this end, conjugates featuring different targeting ligands such as peptide-drug conjugates (PDCs) have emerged as a viable alternative to the use of ADCs, where a peptide plays the recognition function of the targeted drug delivery system. Linkers play a crucial role in targeted drug delivery systems and their design and properties largely determine their stability and efficiency for their use in cancer treatment. Therefore, within this thesis we have focused on the development of novel self-immolative spacers, which trigger the release of drugs upon the action of enzymes such as proteases and glycosidases, overexpressed in tumour cells and their connection to peptides to develop PDCs. Specifically, within the scope of this thesis we have focused on the development of two self-immolative linkers, based either on the Grob fragmentation or on intramolecular cyclisation reactions and we have proved that both reactions occur spontaneously at physiological conditions. First, in Chapter 4, we have studied a self-immolative linker based on the Grob fragmentation and we have proved that this reaction takes place inside living cells both with a linker carrying a fluorophore as the dansyl group and with one with a cytotoxic payload such as a Crizotinib derivative. Additionally, in Chapter 5, we have explored the potential of intramolecular cyclisation reactions for the development of self-immolative linkers. Thus, we have rationally designed and screened a library that allowed us to identify suitable candidates in which the intramolecular cyclisation reaction occurred spontaneously under physiological conditions. In order to control the release in living cells, these linkers have been applied to the development of a PDC that included a dipeptide moiety targeted by lysosomal proteases, and it has been studied in vitro in a HER2 positive cell line. Finally, we have explored the introduction of carbohydrate moieties susceptible to be cleaved by lysosomal glycosidases for the controlled activation of these novel self-immolative linkers.