Synthesis of new nampt inhibitors as potential anti-cancer drugs. An approach to antibody-drug conjugates

Abstract

Nicotinamide phosphoribosyltransferase (NAMPT) catalyzes the rate-limiting step in the biosynthesis of Nicotinamide Adenine Dinucleotide (NAD+), a cofactor essential for several cellular processes. NAD+ is involved in important biological processes such as energy metabolism, sirtuin function, DNA repair machinery and intracellular oxidative stress. Cancer cells are highly dependent on NAMPT activity for proliferation due to an increased metabolism and a high activity of NAD+-consuming enzymes. NAMPT represents an interesting target for the development of anticancer drugs given that this enzyme is overexpressed in different types of tumours and that NAMPT expression appears to be related with tumour progression. In this thesis, we present the synthesis and biological evaluation of a library of new NAMPT inhibitors. The compounds showed excellent in vitro anticancer activity in MIA PaCa-2 pancreatic cancer cells and in several haematological cancer cell lines (in the picomolar range). Some candidates exhibited a much higher cytotoxicity than that showed by reference compound FK866. However, when the lead compounds were assayed in in vivo xenograft mouse models, unfortunately, there was not a good correlation between the in vitro results and the in vivo activity. For that reason, we accomplished structural modifications of the most promising candidates to provide these molecules with a chemical function that could act as a handle for the preparation of antibody-drug-conjugates (ADCs). An ADC consists of a potent cytotoxic compound (payload) that is bioconjugated to a tumour-targeted antibody by a chemical linker. This type of conjugates can deliver the cytotoxic payload directly to tumour cells while sparing healthy cells. Two different approaches have been followed: (1) preparation of ADCs using classical peptide linkers; (2) development of a new strategy of drug-release based on the chemistry of oxanorbornadienes (ONDs) that could be used for the preparation of novel ADCs. The first approach allowed the preparation of six new ADCs, by combination of the new modified NAMPT inhibitors with several classical enzymatically cleavable linkers. Finally, in order to validate the strategy of glutathione-triggered release of cytotoxic drugs in OND systems, we explored the reactivity of simple models of oxanorbornadienic thiovinylsulfones. We have demonstrated that these OND systems can suffer a fragmentation reaction via a two-reaction sequence and therefore, could be used as innovative linkers in drug delivery strategies.