Acalabrutinib is a second generation Bruton’s tyrosine kinase (BTK) inhibitor that targets the B-cell receptor signaling and is considered a prime target for the treatment of CLL. Acalabrutinib inhibits BTK activity preventing the activation of the B-cell antigen receptor pathway, and leads to CLL cell death. Recently at the 2016 ASCO annual meeting researchers presented preliminary results from an ongoing phase 1-2 study using acalabrutinib to treat patients with previously untreated CLL. Of the 74 patients enrolled in the trial 72 were evaluable for response. Acalabrutinib was well tolerated, with 72 of 74 patients remaining on treatment at time of analysis and evaluable for response. Neither of the two patients discontinued treatment for drug related adverse events.
The most common side effects were headaches, diarrhea, arthralgia, contusion, nausea, and weight increase, all characterized as mild. Treatment related lymphocytosis occurred in 53% of patients and was resolved in 97% of the affected patients at a median of 7 weeks. Patients who took acalabrutinib experienced a 96% overall response rate (PR=86%, PR-L=10%) with the median time to response being 2-8 months. For patients with untreated CLL the initial safety profile and high response rates are promising. Based on these results a phase 3 trial of acalabrutinib versus ibrutinib has commenced to further study the use of acalabrutinib in the treatment of patients with CLL.