A new class of 7-deazaguanine agents targeting autoimmune diseases: dramatic reduction of synovial fibroblast IL-6 production from human rheumatoid arthritis patients and improved performance against murine experimental autoimmune encephalomyelitis.

A simple in vitro assay involving the measurement of IL-6 production in human synovial fibroblasts from rheumatoid arthritis patients has been utilised to select candidates from a targeted library of queuine tRNA ribosyltransferase (QTRT) substrates for subsequent in vivo screening in murine experimental autoimmune encephalomyelitis (EAE - a model of multiple sclerosis). The in vitro activity assay discriminated between poor and excellent 7-deazaguanine QTRT substrates and allowed the identification of several structures which subsequently outperformed the previous lead in EAE. Two molecules were of significant promise: one rigidified analogue of the lead, and another considerably simpler structure incorporating an oxime motif which differs structurally from the lead to a considerable extent. These studies provide data from human cells for the first time and have expanded both the chemical space and current understanding of the structure-activity relationship underpinning the remarkable potential of 7-deazguanines in a Multiple Sclerosis disease model.

Queuine Analogues Incorporating the 7-Aminomethyl-7-deazaguanine Core: Structure-Activity Relationships in the Treatment of Experimental Autoimmune Encephalomyelitis.

A library of queuine analogues targeting the modification of tRNA isoacceptors for Asp, Asn, His and Tyr catalysed by queuine tRNA ribosyltransferase (QTRT, also known as TGT) was evaluated in the treatment of a chronic multiple sclerosis model: murine experimental autoimmune encephalomyelitis. Several active 7-deazaguanines emerged, together with a structure-activity relationship involving the necessity for a flexible alkyl chain of fixed length.

The human tRNA-guanine transglycosylase displays promiscuous nucleobase preference but strict tRNA specificity.

Base-modification can occur throughout a transfer RNA molecule; however, elaboration is particularly prevalent at position 34 of the anticodon loop (the wobble position), where it functions to influence protein translation. Previously, we demonstrated that the queuosine modification at position 34 can be substituted with an artificial analogue via the queuine tRNA ribosyltransferase enzyme to induce disease recovery in an animal model of multiple sclerosis. Here, we demonstrate that the human enzyme can recognize a very broad range of artificial 7-deazaguanine derivatives for transfer RNA incorporation. By contrast, the enzyme displays strict specificity for transfer RNA species decoding the dual synonymous NAU/C codons, determined using a novel enzyme-RNA capture-release method. Our data highlight the broad scope and therapeutic potential of exploiting the queuosine incorporation pathway to intentionally engineer chemical diversity into the transfer RNA anticodon.

In vivo modification of tRNA with an artificial nucleobase leads to full disease remission in an animal model of multiple sclerosis.

Queuine is a modified pyrrolopyrimidine nucleobase derived exclusively from bacteria. It post-transcriptionally replaces guanine 34 in transfer RNA isoacceptors for Asp, Asn, His and Tyr, in almost all eukaryotic organisms, through the activity of the ancient tRNA guanine transglycosylase (TGT) enzyme. tRNA hypomodification with queuine is a characteristic of rapidly-proliferating, non-differentiated cells. Autoimmune diseases, including multiple sclerosis, are characterised by the rapid expansion of T cells directed to self-antigens. Here, we demonstrate the potential medicinal relevance of targeting the modification of tRNA in the treatment of a chronic multiple sclerosis model­murine experimental autoimmune encephalomyelitis. Administration of a de novo designed eukaryotic TGT substrate (NPPDAG) led to an unprecedented complete reversal of clinical symptoms and a dramatic reduction of markers associated with immune hyperactivation and neuronal damage after five daily doses. TGT is essential for the therapeutic effect, since animals deficient in TGT activity were refractory to therapy. The data suggest that exploitation of the eukaryotic TGT enzyme is a promising approach for the treatment of multiple sclerosis.

Synthesis and characterisation of a mesocyclic tripodal triamine ligand.

Meso- and macrocyclic polydentate amine ligands have been widely explored in oxidation catalysis and for the stabilization of unstable metal-superoxide, -peroxide, and -oxo intermediates. Herein we report on the design and synthesis of a novel mesocyclic, tripodal, triamine ligand that we believe will be an excellent addition to this field. We explored a number of synthetic procedures towards the mesocyclic asymmetric tetraalkylated ligand 1. We expect that 1 will bind metals in a facially capping manner, yielding complexes that display pseudo-tetrahedral geometry, potentially providing access to unprecedented late transition metal-oxo complexes (metal = Co, Ni, Cu). We describe the preparation of a library of mesocyclic polyamine synthons (8, 16, 17, 18, 19) that are precursors in the synthesis of 1. These synthons will be used to tailor the electronic properties of metal complexes of 1 and derivatives thereof. The X-ray crystal structures of 19 and mono- and di-protonated forms of 1b show that the triamine crystalises in a boat­chair conformation which is undesirable for metal coordination. However, solution (1)H NMR studies show that in solution both 19 and the tetraalkylated derivative 1b are remarkably flexible. 1b reacted with [CuI(NCCH3)4](OTf) yielding a 1:1 copper(I) complex [CuI(NCCH3)(1b)](+).