Use of Hepatic Gene Expression Analysis to Investigate Iron Accumulation in Rats Treated with an RGMc Antagonist Monoclonal Antibody

As the development processes mature for large molecule biologics, additional technologies to assess potential safety issues would be favorable, especially as related to target engagement. ABT‐207 is a humanized antibody that inhibits repulsive guidance molecule C (RGMc). The antibody has possible application to treat anemia of chronic disease. In this study, we used an affinity maturated variant of ABT‐207 (PR‐1285929; h5F9‐AM8) to examine the toxicological effects of RGMc inhibition. We applied hepatic whole genome transcriptomic profiling using the Affymetrix platform to investigate the effects of PR‐1285929 and to examine whether there were toxicologically relevant pathway perturbations. Female Sprague Dawley rats were treated for 3 weeks (i.v.) with PR‐1285929 at doses of 0.02, 0.20, 2.0, or 20.0 mg/kg/week. At the end of the dosing period, the rats were sacrificed, and liver was collected for histology and gene expression analysis (rat RAE230 2.0 array). Histological examination showed mild to moderate dose dependent accumulation of hepatic iron as determined by Prussian blue staining. This effect was histopathologically assessed as non‐adverse since no other effects (e.g. inflammation or degeneration) were observed. Global gene expression profiling revealed a relatively minor impact on the hepatic transcriptome. Levels of hepatic hepcidin (Hamp) mRNA, the main regulator of serum iron homeostasis, declined in excess of 20‐fold in a dose dependent manner. This finding was also reflected in liver Hamp mRNA expression as measured using RT‐PCR and decreased serum hepcidin protein levels. Interestingly, RGMc is a main regulator of hepcidin, and thus, its inhibition is likely associated with the reduced Hamp. At the transcript level, a minor oxidative stress response induction, mostly related to glutathione metabolism, was apparent at the highest dose (20 mg/kg), but lower doses revealed few consistent changes in these genes. Only minor modulations were apparent with respect to select BMPs and ferroportin. No other toxicologically relevant pathways were consistently up‐ or down‐regulated. This experimental example shows the potential utility of transcriptomic profiling to investigate plausible mechanisms of cellular changes mediated by biologic therapies and can serve as a method for risk mitigation in the development of protein pharmaceuticals.Support or Funding InformationAuthor Disclosures: All authors are employees of AbbVie. The design, study conduct, and financial support for this research was provided by AbbVie. AbbVie participated in the interpretation of data, review, and approval of the publication.