BTK and B-cell chronic lymphocytic leukemia: In contrast to RL cells, single kinase inhibitors were not sufficient to fully reverse PDCD4 down-regulation in CLL cells in all samples (Fig. 4) and we therefore investigated the effects of combining either mTORC1 or MEK1/2 inhibition (using rapamycin or U0126, respectively) with the BTK inhibitor ibrutinib.