Inhibition of Protein Kinase C (PKC) delta with Rottlerin Induces Apoptosis in B-CLL Cells, Augments Chemotherapeutic Cytotoxicity and Inhibits Antiapoptotic Survival Signals.

Purpose: We have previously shown that PKC delta is constitutively activated in B-CLL cells. In the present study, we have analyzed the mechanism of apotosis induction as well as the effets of PKC delta in the presence of survival signal and chemotherapeutic agents.

Methods: The mitochondrial membrane potential, presence of active caspase 3, conformational status of Bax and apoptosis assays (Annexin V stain, Tunel assay) were performed using flow cytometric analysis. Expression of BCL-2 family proteins and XIAP as well as processing of caspase 8 and 9 was revealed in western blot experiments.

Results: Rottlerin at 5μM (which is not toxic for normal lymphocytes) induced apoptosis in a large amount of B-CLL samples. Rottlerin was equally effective in zap70 positive- and negative samples. Rottlerin induced apoptosis was in part caspase dependent and involved processing of caspase 3, 8 and 9. Expression of antiapoptotic proteins MCL-1 and XIAP was reduced in Rottlerin treated cells and BAX expression increased and Bax conformation changed to its proapoptotic form.IN contrast, expression of bcl-2 was not changed.

B-CL cells are likely to receive survival signals from the microenvironment and might be rescued from cell death induced by chemotherapeutic agents. Rottlerin was very effective in inhibiting survival signals like IL-4 or stromal cell contact. In addition, treatment with Rottlerin enhanced the cytotoxicity of the chemotherapeutic agents Fludarabine, Vncristine and Daunorubicine.

Conclusion: Inhibition of PKC delta might be a powerful treatment option for B-CLL given its potential to induce apoptosis, inhibit antiapoptotic survival signals and augment the cytotoxicity of chemotherapeutic agents.