Covalent
Bruton tyrosine kinase (BTK) inhibitors, such as
ibrutinib, have proven to be highly beneficial in the treatment of
chronic lymphocytic leukemia (CLL). Interestingly, the off-target inhibition of
IL-2-inducible T-cell kinase (ITK) by
ibrutinib may also play a role in modulating the tumor microenvironment, potentially enhancing the treatment benefit. However, resistance to covalently binding BTK inhibitors can develop as the result of a mutation in
cysteine 481 of BTK (C481S), which prevents irreversible binding of the drugs. In the present study we performed preclinical characterization of
vecabrutinib, a next-generation noncovalent BTK inhibitor that has ITK-inhibitory properties similar to those of
ibrutinib. Unlike
ibrutinib and other covalent BTK inhibitors,
vecabrutinib showed retention of the inhibitory effect on C481S BTK mutants in vitro, similar to that of wild-type BTK. In the murine Eμ-TCL1 adoptive transfer model,
vecabrutinib reduced
tumor burden and significantly improved survival.
Vecabrutinib treatment led to a decrease in CD8+ effector and memory T-cell populations, whereas the naive populations were increased. Of importance,
vecabrutinib treatment significantly reduced the frequency of regulatory CD4+ T cells in vivo. Unlike
ibrutinib,
vecabrutinib treatment showed minimal adverse impact on the activation and proliferation of isolated T cells. Lastly, combination treatment with
vecabrutinib and
venetoclax augmented treatment efficacy, significantly improved survival, and led to favorable reprogramming of the microenvironment in the murine Eμ-TCL1 model. Thus, noncovalent BTK/ITK inhibitors, such as
vecabrutinib, may be efficacious in C481S BTK mutant CLL while preserving the T-cell immunomodulatory function of
ibrutinib.