The BTK inhibitor ibrutinib potentiates ASNase-induced apoptosis. (A) Schematic overview of the experimental procedure. BCP-ALL cell lines were treated with ASNase, ibrutinib, or a combination of both for 7 days, followed by direct evaluation of apoptosis or recovery capacity in a clonogenic assay after washout of the ASNase. (B) Apoptosis induction as measured by immunoblot analysis of PARP in BCP-ALL cell lines. Nalm6, Sem, and Reh cells were treated with indicated doses of ASNase and ibrutinib. Representative of 3 independent experiments. (C-D) Clonogenic proliferation assay of Nalm6 and Sem cells. After 7 days’ treatment with indicated doses of ibrutinib and ASNase 5000 to 10 000 viable (trypan blue–negative) cells from each sample were seeded in soft agar. Recovery capacity was determined by quantification of colonies. Bars represent mean ± SEM of n = 3 replicates of 1 experiment. Representative of 3 independent experiments. ***P < .001; **P < .01; ***P < .05 (2-tailed, unpaired Student t test).