Pharmacodynamics and proteomic analysis of acalabrutinib therapy: similarity of on-target effects to ibrutinib and rationale for combination therapy.

Acalabrutinib, a highly selective Bruton's tyrosine kinase inhibitor, is associated with high overall response rates and durable remission in previously treated chronic lymphocytic leukemia (CLL); however, complete remissions were limited. To elucidate on-target and pharmacodynamic effects of acalabrutinib, we evaluated several laboratory endpoints, including proteomic changes, chemokine modulation and impact on cell migration. Pharmacological profiling of samples from acalabrutinib-treated CLL patients was used to identify strategies for achieving deeper responses, and to identify additive/synergistic combination regimens. Peripheral blood samples from 21 patients with relapsed/refractory CLL in acalabrutinib phase I (100-400 mg/day) and II (100 mg BID) clinical trials were collected prior to and on days 8 and 28 after treatment initiation and evaluated for plasma chemokines, reverse phase protein array, immunoblotting and pseudoemperipolesis. The on-target pharmacodynamic profile of acalabrutinib in CLL lymphocytes was comparable to ibrutinib in measures of acalabrutinib-mediated changes in CCL3/CCL4 chemokine production, migration assays and changes in B-cell receptor signaling pathway proteins and other downstream survival proteins. Among several CLL-targeted agents, venetoclax, when combined with acalabrutinib, showed optimal complementary activity in vitro, ex vivo and in vivo in TCL-1 adoptive transfer mouse model system of CLL. These findings support selective targeting and combinatorial potential of acalabrutinib.