Small Molecule Inhibition of IFN‐γ‐Induced Major Histocompatibility Complex Class II Expression by Thyroid Cells

Major histocompatibility complex (MHC) molecules are cell surface receptors involved in host immune response. Several lines of evidence suggest that increased expression of MHC class I (MHC I) and aberrant expression of MHC class II (MHC II) on non‐immune cells contributes to autoimmune disease, including the autoimmune thyroid disease termed Graves' disease. Graves' disease is often treated, especially in Europe, by methimazole (MMI). Previous work has shown that MMI decreases constitutive MHC I expression on the Fisher rat thyroid cell line 5 (FRTL‐5), a non‐transformed cell line often used to gain insights into human thyroid pathology. Further, MMI decreases interferon‐gamma (IFN‐γ) induction of MHC II in FRTL‐5 cells. Our labs, as well as others, have demonstrated that a phenyl‐derivative of MMI, termed C10, is more potent than MMI in a variety of cell models of disease including the FRTL‐5 model described above. Additionally, we have an ongoing molecular screening program that seeks to identify compounds that are more efficacious than MMI and C10. Thus, we initially sought to screen three novel compounds from our library in the FRTL‐5 model. Two of these compounds (COB‐204, COB‐214) were more effective than C10 in other cell models and the third (COB‐187) appears to be a highly specific inhibitor of glycogen synthase kinase ‐3 (GSK‐3). We first investigated the effect of the compounds on basal expression of MHC I. FRTL‐5 cells were treated with each compound for 24 hours and the level of MHC Class I determined via flow cytometric analysis. In each case, no significant effect on MHC Class I was observed at the levels of compound tested (50 μM for COB‐204 and COB‐214 and 20 μM for COB‐187). We next investigated the effect of the compounds on inhibition of IFN‐γ induction of MHC II. In this case, FRTL‐5 cells were treated for 24 hours with 100 U/ml IFN‐γ in the presence of the compounds or carrier control (DMSO) and MHC II expression determined by flow cytometry. 50 μM COB‐214 caused a slight (19%) inhibition, 50 μM COB‐204 caused a marked (54%) inhibition and 20 μM COB‐187 caused a fairly dramatic (80%) inhibition of IFN‐γ induced MHC II expression. Based on these results, we decided to investigate COB‐187 further and also test the effects of two other known GSK‐3 inhibitors, namely Tideglusib and AR‐A014418. All three compounds appeared to inhibit IFN‐γ induction of MHC II albeit with varying potencies. The IC 50 for AR‐A014418 was 4.8 μM, for COB‐187 9.6 μM and for Tideglusib > 80 μM. The MHC II inhibition did not appear to be due to non‐specific toxicity since an MTS assay revealed the 24 hour TC 50 to be 50 μM for AR‐A014418, and > 80 μM for COB‐187 and Tideglusib. Combined, these results suggest a connection between GSK‐3 and IFN‐γ induced aberrant expression of MHC II on FRTL‐5 cells and provides a possible avenue for the development of molecular therapeutics for Graves' disease. Support or Funding Information NIH R15GM110602 This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .