Iminosugar C-glycosides as new NAMPT inhibitors and anti-cancer agents

Overview & Synopsis

Nicotinamide phosphoribosyltransferase (NAMPT) is the rate-limiting enzyme for the synthesis of nicotinamide adenine dinucleotide (NAD+). NAD+ is a cofactor in multiple redox reactions related to cellular energy production and is also used as a substrate by enzymes involved in regulating important functions, including energy metabolism, DNA repair, apoptosis, inflammation, and gene expression. NAMPT is a glycosyltransferase involved in the first step reaction of the so-called salvage pathway, where nicotinamide (NAM) generates NAD+. NAD+ biosynthesis is dependent on different metabolic pathways, but the salvage pathway represents the major route to NAD+ biosynthesis. Moreover, NAMPT is frequently up-regulated in cancer where it contributes to cancer cell metabolism. Overall, since many cancer cells are highly dependent on NAMPT activity for proliferation, NAMPT represents an attractive target in cancer research. Over the last years, several compounds were identified as potent NAMPT inhibitors with strong anti-cancer activity. The NAMPT inhibitors (FK866 and CHS828), discovered in the early 2000s, have exhibited anticancer activity by depleting NAD+ and ATP levels and have reached phase II and phase I clinical trials, respectively. Unfortunately, these trials were stopped due to limited antitumor activity and to toxicity problems, mainly thrombocytopenia and gastrointestinal toxicity. Over the past 20 years, many inhibitors have been designed based on a unique pharmacophore model.This PhD dissertation aims at finding out a “next generation” of NAMPT inhibitors which present a better solubility profile and a chemical design that differs from those previously proposed. We focused on the design of new inhibitors of NAMPT with the aim of mimicking the transition state formed in the rate-determining step of the glycosylation process catalysed by the enzyme. As a new potential inhibitor of NAMPT we designed and synthesised C-iminofuranosides linked through the anomeric carbon to a moiety closely related to FK866. The iminofuranoside should mimic the ribosyl moiety, the natural substrate for the enzyme. Moreover, the conjugation with a highly hydrophilic structure as an iminosugar, could improve the solubility and pharmacokinetics properties of these potential inhibitors. We prepared 10 novel aryl β-D-iminoribitol derivatives using an enantioselective and diastereoselective L-proline catalysed method. To compare whether the iminosugar provided an advantage in inhibiting NAMPT, the corresponding molecules without the iminosugar attached were also synthesized. In parallel, we performed the synthesis of 14 NAMPT inhibitors that follow the pharmacophore model. For all the compounds, the inhibitory activity in vitro has been assessed by conducting enzymatic tests with NAMPT and biological assays in a human pancreatic cancer cell line, MiaPaca-2.We found that 3 products featuring the iminosugar moiety have moderate inhibitory activity (micromolar range) towards both enzyme and cells. From the comparison with the corresponding molecules without the attached iminosugar, we concluded that its presence does not negatively influence the activity and, in some cases, it slightly improves it. Furthermore, one of the compounds following the pharmacophore model was identified to have strong enzymatic and cellular inhibition activity, comparable to that observed for FK866.