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

Abstract

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.

Fig. 1. The QTRT-catalysed wobble-base exchange reaction involving tRNA^{His,Asp,Tyr,Asn}, the structures of queuine, guanine, NPPDAG and related analogues.

Fig. 2. Reduction in production of IL-6 by synovial fibroblasts from RA patients in the presence of NPPDAG.

Fig. 3. Reduction in production of IL-6 by synovial fibroblasts from RA patients in the presence of a library of NPPDAG derivatives.

Fig. 4. Evaluation of selected compounds in EAE. Upon reaching a clinical score of approximately 2, EAE diseased female mice were administered PBS as control or equimolar concentrations of 6 (15 mg Kg⁻¹), 17 (16 mg Kg⁻¹), 21 (16 mg Kg⁻¹) 25 (9 mg Kg⁻¹) or 26 (9 mg kg⁻¹) i.p. daily for 7 days, n = 5. Animals were monitored daily for clinical score. Data represent the mean ± S.E.M. *P < 0.05, **P < 0.01, by two-way Anova with post hoc pair-wise comparison.