PKC412, a Small Molecule Tyrosine Kinase Inhibitor, Regulates Survival and Proliferation Pathways in Waldenström Macroglobulinemia

Background: Waldenström’s Macroglobulinemia (WM) is an incurable lymphoplasmacytic lymphoma with limited options of therapy. Protein kinase C (PKC) is a multigene family that that plays an important role in the regulation of cell growth and tumor progression. PKC412, a derivate of staurosporine, is a competitive inhibitor of ATP binding to PKC subtypes. This PKC inhibitor was used to examine its role in WM.

Methods: WM cell lines (BCWM1 and WSU-WM) and IgM secreting low-grade lymphoma cell lines (MEC1, RL) were used. Bone marrow primary CD19+ cells and bone marrow stromal cells (BMSC) were obtained from patients with WM after informed consent. Cytotoxicity and DNA synthesis were measured by MTT assay and thymidine uptake assay. Cell signaling of HSP response, VEGF signaling and AKT pathways were determined by Western Blot analysis. Cell cycle and apoptosis analysis were obtained through flow cytometry.

Results: We showed that PKC412 induced cytotoxicity in WM cell lines tested (IC50 of 1uM) with no cytotoxic effect on healthy donor peripheral blood mononuclear cells at concentrations as high as 5uM. Cell proliferation and apoptosis analysis showed similar results, in a time independent manner. A G2/M arrest was observed upon cell cycle analysis, suggesting a possible mechanism for apoptosis. Similarly, the Akt pathway was investigated and was found to show a decrease in its activity in a dose dependent manner. Finally, PKC412 regulated VEGF levels in WM samples indicating an anti-angiogenic activity.

Conclusion: PKC412 has a significant effect on the survival and proliferation of WM cells, including regulation of angiogenesis. These studies provide the framework for clinical evaluation of this novel PKC inhibitor in Waldenström Macroglobulinemia.