CDK4 and B-cell chronic lymphocytic leukemia: Consequently we observed that treatment with triptolide resulted in the partial depletion of kinase clients of HSP90 such as BTK, c-RAF and CDK4 in cultured and primary CLL cells (Figure 3C), with no decrease in the levels of non-HSP90 client kinases, ERK1/2 and CHK2 (Figure 3D).