Targeted Inhibition of BTK with ACP-196: Enhancing Specificity in B-Cell Malignancies

The study focuses on the development and evaluation of ACP-196, a second-generation BTK inhibitor, which is crucial in B-cell receptor signaling and a key target for treating B-cell malignancies like chronic lymphocytic leukemia (CLL). ACP-196 has shown superior target specificity and potency compared to ibrutinib, with an IC50 of 3 nM against BTK and an EC50 of 8 nM in a human B-cell activation assay. It has been found to be significantly more selective over other TEC kinase family members and does not affect EGFR, which is important for avoiding adverse events associated with EGFR inhibition.

Methods used in the research include phospho-protein immunoblotting to assess pathway activation in CLL patient samples, helper T-cell skewing assays with purified CD4+ T-cells from various mouse models, cytolytic activity assays for CD8+ T-cells, and chromium release assays to evaluate NK-cell function. Additionally, the impact of ACP-196 on EGFR signaling was evaluated through immunoblotting of lung cancer cells.

Results indicate that ACP-196 treatment of primary human CLL cells led to a dose-dependent decrease in phosphorylation of BTK and downstream effectors without affecting total protein levels, confirming its inhibitory effect on BTK autophosphorylation and BCR signaling. ACP-196 did not inhibit T-cell receptor signaling molecules and had no impact on the differentiation of Th subsets or regulatory T cells, unlike ibrutinib. Furthermore, it did not affect CD8+ T-cell viability or cytotoxicity and did not influence NK cell function or EGFR signaling in lung epithelial cells.

The study concludes that ACP-196 selectively inhibits BTK and BCR signaling without off-target effects on T-cells, NK-cells, and lung epithelial cells and is currently in Phase 3 trials for CLL treatment. The research was supported by the NIH NCI and Acerta Pharma, with several authors disclosing affiliations or financial interests with Acerta Pharma.