Rheumatoid arthritis (RA) is a debilitating inflammatory autoimmune disease with no known cure. Recently, we identified the immunomodulatory enzyme indoleamine-2,3-dioxygenase 2 (IDO2) as an essential mediator of autoreactive B and T cell responses driving RA. However, therapeutically targeting IDO2 has been challenging given the lack of small molecules that specifically inhibit IDO2 without also affecting the closely related IDO1. In this study, we develop a novel monoclonal antibody (mAb)-based approach to therapeutically target IDO2. Treatment with IDO2-specific mAb alleviated arthritis in two independent preclinical arthritis models, reducing autoreactive T and B cell activation and recapitulating the strong anti-arthritic effect of genetic IDO2 deficiency. Mechanistic investigations identified FcγRIIb as necessary for mAb internalization, allowing targeting of an intracellular antigen traditionally considered inaccessible to mAb therapy. Taken together, our results offer preclinical proof of concept for antibody-mediated targeting of IDO2 as a new therapeutic strategy to treat RA and other autoantibody-mediated diseases.

During the development of autoimmune disease, a switch occurs in the antibody repertoire of B cells so that the production of pathogenic rather than non-pathogenic autoantibodies is enabled. However, there is limited knowledge concerning how this pivotal step occurs. Here, we present genetic and pharmacological evidence of a positive modifier function for the vesicular small GTPase RhoB in specifically mediating the generation of pathogenic autoantibodies and disease progression in the K/BxN preclinical mouse model of inflammatory arthritis. Genetic deletion of RhoB abolished the production of pathogenic autoantibodies and ablated joint inflammation in the model. Similarly, administration of a novel RhoB-targeted monoclonal antibody was sufficient to ablate autoantibody production and joint inflammation. In the MRL/lpr mouse model of systemic lupus erythematosus (SLE), another established preclinical model of autoimmune disease associated with autoantibody production, administration of the anti-RhoB antibody also reduced serum levels of anti-dsDNA antibodies. Notably, the therapeutic effects of RhoB blockade reflected a selective deficiency in response to self-antigens, insofar as RhoB-deficient mice and mice treated with anti-RhoB immunoglobulin (Ig) both mounted comparable productive antibody responses after immunization with a model foreign antigen. Overall, our results highlight a newly identified function for RhoB in supporting the specific production of pathogenic autoantibodies, and offer a preclinical proof of concept for use of anti-RhoB Ig as a disease-selective therapy to treat autoimmune disorders driven by pathogenic autoantibodies.

Meglumine is a methylamino derivative of sorbitol that is an approved drug excipient. Recent preclinical studies suggest that administration of high-dose oral meglumine can exert beneficial medicinal effects to treat diabetes, obesity, and fatty liver disease (NAFLD/nonalcoholic steatohepatitis [NASH]). Here we address gaps in knowledge about the pharmacology and toxicology of this substance administered at high concentrations to explore its medicinal potential. We observed that high-dose meglumine limited secretion of proinflammatory cytokines and cell adhesion molecules from activated human THP-1 or murine RAW264.7 monocytes. Preclinical pharmacokinetic analysis in Swiss mice confirmed that meglumine was orally available. Informed by this data, oral doses of 18 to 75 mM meglumine were administered ad libitum in the drinking water of Sprague-Dawley rats and two cohorts of C57BL/6 mice housed in different vivariums. In a 32-week study, urinary isoprostane levels trended lower in subjects consistent with the possibility of antiinflammatory effects. In full lifespan studies, there was no detrimental effect on longevity. Heart function evaluated in C57BL/6 mice using an established noninvasive cardiac imaging system showed no detrimental effects on ejection fraction, fractional shortening, left ventricle function or volume, and cardiac output in mice up to 15-month old, with a potential positive trend in heart function noted in elderly mice consistent with earlier reported benefits on muscle stamina. Finally, in a transgenic model of inflammation-associated skin carcinogenesis, the incidence, number, and growth of skin tumors trended lower in subjects receiving meglumine. Overall, the evidence obtained illustrating the long-range safety of high-dose oral meglumine support the rationale for its evaluation as a low-cost modality to limit diabetes, hypertriglyceridemia, and NAFLD/NASH. K E Y W O R D Sdrug discovery, preclinical pharmacology, preclinical toxicology

The tryptophan catabolizing enzymes indoleamine 2,3-dioxygenase (IDO) 1 and 2 lie at the interface between metabolism and immunity. Recently, we identified a unique functional role for IDO2 in modulating the initiation and severity of autoimmune arthritis in a murine model of disease. We find that IDO2, but not its better-studied counterpart IDO1, acts as a pro-inflammatory mediator affecting autoantibody production and T helper cell function in the KRN preclinical model of arthritis. Reciprocal adoptive transfer experiments demonstrate that IDO2 acts by a B-cell intrinsic mechanism to regulate inflammation. IDO2 function in B cells was contingent on a cognate, antigen-specific interaction to exert its immunomodulatory effects on arthritis development. Alterations in costimulatory molecules and associated cytokines involved in cross-talk between B and T cells suggest that IDO2 acts at the T:B cell interface to modulate the potency of T cell help needed to promote autoantibody production. Given the paucity of novel therapies for rheumatoid arthritis and related autoimmune disorders, IDO2 should be considered as a potential novel therapeutic target for modulating disease pathways leading to autoimmunity. However, therapeutically targeting IDO2 has been challenging due to the lack of small molecules that specifically inhibit IDO2 without also affecting the closely related IDO1. To this end, we have recently begun development and characterization of approaches that ameliorate disease by specifically targeting IDO2. We find that we are able to recapitulate the reduction in arthritis seen in genetic knockouts with IDO2-targeted therapies in preclinical models of disease.