Collagen II antibody-induced arthritis in Tg1278TNFko mice: optimization of a novel model to assess treatments targeting human TNFα in rheumatoid arthritis.

BACKGROUND: Novel molecules that specifically target human TNFα in rheumatoid arthritis pose problems for preclinical assessment of efficacy. In this study collagen antibody-induced arthritis (CAIA) has been induced in human TNFα transgenic mice to provide a novel model that has been optimised for the evaluation of molecules targeting human TNFα. METHODS: Tg1278TNFko mice lack murine TNFα and are heterozygous for multiple copies of the human TNFα transgene that is expressed under normal physiological control. To establish CAIA, a collagen II monoclonal antibody cocktail (CAb) at 2, 4 or 8 mg was injected i.p. on Day 0 followed by a lipopolysaccharide (LPS) boost (10 or 100 µg) i.p. on Day 1 or Day 4. Animals were assessed for arthritis symptoms using a clinical score, cytokine levels (human TNFα, IL-1ß and IL-6) in sera and joints, and histopathology. The dependence of the model on human TNFα was determined by dosing animals with etanercept. RESULTS: Tg1278TNFko animals treated with 2, 4 or 8 mg CAb on Day 0, with 100 µg LPS on Day 4, had more severe arthritis and earlier symptoms than wild type animals at all doses of CAb tested. Subsequently it was found that the transgenic model did not require LPS at all for arthritis development but a lower dose of LPS (10 µg) was found necessary for reproducible and robust disease (close to 100% incidence, well-synchronised, with high arthritis scores). Furthermore the LPS challenge could be brought forward to Day 1 so that its' actions to facilitate disease could be separated temporally from the arthritis phase (beginning about Day 4). Etanercept, administered immediately after the serum spike of cytokines associated with LPS had subsided, was able to dose-dependently inhibit arthritis development and this was associated with a marked protection of the joints histologically on Day 14. Etanercept was also able to reverse the signs of arthritis when given therapeutically allowing animals to be matched for disease burden before dosing begins. CONCLUSIONS: The features of CAIA in Tg1278TNFko animals make the model well-suited to testing the next generation of therapeutics that will target human TNFα in rheumatoid arthritis.

Dampening of the bone formation response following repeat dosing with sclerostin antibody in mice is associated with up-regulation of Wnt antagonists.

Administration of antibodies to sclerostin (Scl-Ab) has been shown to increase bone mass, bone mineral density (BMD) and bone strength by increasing bone formation and decreasing bone resorption in both animal studies and human clinical trials. In these studies, the magnitude and rate of increase in bone formation markers is attenuated upon repeat dosing with Scl-Ab despite a continuous and progressive increase in BMD. Here, we investigated whether the attenuation in the bone formation response following repeated administration of Scl-Ab was associated with increased expression of secreted antagonists of Wnt signalling and determined how the circulating marker of bone formation, P1NP, responded to single, or multiple doses, of Scl-Ab four days post-dosing. Female Balb/c mice were treated with Scl-Ab and we demonstrated that the large increase in serum P1NP observed following the first dose was reduced following administration of multiple doses of Scl-Ab. This dampening of the P1NP response was not due to a change in the kinetics of the bone formation marker response, or differences in exposure to the drug. The abundance of transcripts encoding several secreted Wnt antagonists was determined in femurs collected from mice following one or six doses of Scl-Ab, or vehicle treatment. Compared with vehicle controls, expression of SOST, SOST-DC1, DKK1, DKK2, SFRP1, SFRP2, FRZB, SFRP4 and WIF1 transcripts was significantly increased (approximately 1.5-4.2 fold) following a single dose of Scl-Ab. With the exception of SFRP1, these changes were maintained or further increased following six doses of Scl-Ab and the abundance of SFRP5 was also increased. Up-regulation of these Wnt antagonists may exert a negative feedback to increased Wnt signalling induced by repeated administration of Scl-Ab and could contribute to self-regulation of the bone formation response over time. After an antibody-free period of four weeks or more, the P1NP response was comparable to the naïve response, and a second phase of treatment with Scl-Ab following an antibody-free period elicited additional gains in BMD. Together, these data demonstrate that the rapid dampening of the bone formation response in the immediate post-dose period which occurs after repeat dosing of Scl-Ab is associated with increased expression of Wnt antagonists, and a treatment-free period can restore the full bone formation response to Scl-Ab.