Arthritis & Rheumatism, Volume 63,
November 2011 Abstract Supplement

Abstracts of the American College of
Rheumatology/Association of Rheumatology Health Professionals
Annual Scientific Meeting
Chicago, Illinois November 4-9, 2011.


A Bruton's Tyrosine Kinase Inhibitor Prevents Antigen-Driven B Cell Activation In Vivo.

Benson1,  Micah, Rodriguez1,  Varenka A., Andreyeva1,  Tatyana, Keegan1,  Sean, Springer2,  John R., Schnute2,  Mark E., Dunussi-Joannopoulos1,  Kyri

Pfizer, Cambridge, MA
Pfizer, Inc, Cambridge, MA

Background/Purpose:

Therapeutic targeting of B cells has proven effective for a multitude of human autoimmune indications. Most investigative and approved therapies are injected monoclonal antibodies that either deplete or inactivate B cells by targeting B cell surface moieties directly or by inactivating B cell modulating cytokines, with orally-available B cell modulating treatments currently lacking. Proximal to the intracellular signaling components of the B cell receptor (BCR) resides a network of adaptor proteins and protein tyrosine kinases that include the Tec family kinase Bruton's Tyrosine Kinase (BTK). The kinase activity of BTK is critical for transmitting signals received through the BCR to downstream signaling pathways that direct B cell activation. In this study, we assessed the ability of an orally-accessible BTK inhibitor to prevent antigen-driven B cell activation in vivo.

Methods:

C57BL/6 mice were dosed orally with either vehicle alone or vehicle with BTK inhibitor at 10, 3, 1, or 0.3 mgs/kg as indicated. For the anti-IgD model, either 100mg of agonistic anti-CD40 (clone 1C10) or 200ml of goat-anti-mouse anti-IgD antisera (Ebioscience) were injected intraperitoneally (i.p) two hours after dosing. Mice were sacrificed between 4–18 hours later and splenic B cells analyzed. For mRNA transcript analysis, mature B220+CD23+ B cells were enriched to >93% purity by B cell negative selection followed by CD23 positive selection by antibody-coupled microbeads. Purified RNA was analyzed for mRNA transcript levels. To analyze the induction of B cell surface activation markers, B220+ B cells were analyzed by FACS for CD86 expression levels. For the NP-Ficoll model, 100mg of NP-Ficoll were injected i.p. the day after dosing with either vehicle alone or vehicle with BTK inhibitor. BTK inhibitor was dosed daily for the duration of the experiment until day 7, whereupon anti-NP serum IgM and IgG3 titers were quantified by ELISA.

Results:

We report that dosing with a BTK inhibitor suppressed, in a dose dependent manner, both anti-IgD driven B cell activation and NP-Ficoll elicited anti-NP IgM and IgG3 antibody titers in vivo. The suppression of anti-IgD driven B cell activation was manifested by suppression of the surface activation markers CD86 as well as suppression of mRNA transcripts (e.g. c-Myc, Bcl-xL, CCL3, CD98, EBI2, EGR1, EGR2 and IRF4), all markers otherwise rapidly induced upon engagement of the BCR with antigen. BTK inhibition had no impact on agonistic anti-CD40 driven B cell activation, indicating the specificity of the BTK inhibitor used in this study for the BCR signaling pathway. Lastly, inhibition of BTK prevented, in a dose-dependent manner, the generation of anti-NP IgM and IgG3antibodies upon immunization with NP-Ficoll.

Conclusion:

Our results provide mechanistic insight into the role of BTK inhibition in a mouse model of in vivo BCR-driven B cell activation and support the concept that BTK kinase inhibitors represent a promising therapeutic approach for patients with B cell-dependent autoimmune disorders.

To cite this abstract, please use the following information:
Benson, Micah, Rodriguez, Varenka A., Andreyeva, Tatyana, Keegan, Sean, Springer, John R., Schnute, Mark E., et al; A Bruton's Tyrosine Kinase Inhibitor Prevents Antigen-Driven B Cell Activation In Vivo. [abstract]. Arthritis Rheum 2011;63 Suppl 10 :1758
DOI:

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