Background/Purpose:

Bruton tyrosine kinase (Btk) is a Tec family kinase that participates in B cell receptor (BCR), Toll-like Receptor (TLR) and chemokine receptor signaling. It is expressed in all cell lineages of the hematopoietic system, except for T cells, and it plays a critical role in B cell development and function. We have recently reported a potent and highly selective competitive inhibitor of Btk RN486, which blocks the Btk kinase activity with an IC50 of 4.0 nM. This compound inhibits BCR and FcR-mediated signaling and is efficacious in murine models of arthritis. Here we tested RN486 in the NZB/NZBW model of lupus.

Methods:

Animals were randomized into two groups based on the serum anti-dsDNA antibody levels and proteinuria measured at 30 weeks of age. Beginning at 32 weeks of age one group of mice was fed chow formulated with 30mg/kg of RN486 equivalent to 0.225 mg/g of chow, while the other group received regular chow ad libitum for 8 weeks.  

Results:

Treatment of NZB/W F1 mice with RN486 completely prevented the progression of proteinuria in 32 week-old mice. In contrast, a normal progression of the proteinuria scores until the termination of the study at 40 weeks of age was observed in animals fed with regular chow. This effect was associated with decreased IgG antibody deposition and decreased glomerular nephritis at the histological level. At the cellular level, there was a dramatic inhibition of B cell activation upon BCR crosslinking in vitro in peripheral blood B cells, as determined by the induction of CD69 by flow cytometry which is used as a pharmacodynamic marker. The IgG anti-dsDNA antibody secretion was almost completely abolished in the treated group as determined by ELISA and total splenocyte ELISpot. In contrast, the anti-dsDNA antibody secretion from bone-marrow derived plasma cells was not significantly inhibited, suggesting that similarly to other B-cell depleting therapies, the main target population corresponds to short-lived plasma cells in the spleen. This hypothesis was confirmed by flow cytometry data demonstrating complete depletion of a CD138hi population of cells in the spleen that was not detectable in the bone marrow. Interestingly, the compound inhibited IgG but not IgM anti-dsDNA secretion suggesting that pharmacological blockade of Btk resembles the previously reported transgenic expression of low endogenous Btk levels in B cells.  Finally, we studied the effect of our compound in acute TLR9-mediated responses in vivo and found a dose-dependent inhibition of CpG-induced IL-12 secretion. In line with this result, the animals treated with RN486 for eight weeks had lower levels of IL-12 in the serum.

Conclusion:

Our results demonstrate that Btk selective inhibition is efficacious in an animal model of lupus via plasma cell depletion and inhibition of BCR and TLR9-dependent stimulation.

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« Back to 2012 ACR/ARHP Annual Meeting

ACR Meeting Abstracts - https://acrabstracts.org/abstract/suppression-of-glomerulonephritis-in-nzbw-f1-mice-by-a-selective-inhibitor-of-brutons-tyrosine-kinase-rn486/