BRYOSTATIN 1 INDUCES APOPTOSIS AND AUGMENTS INHIBITORY EFFECTS OF VINCRISTINE IN HUMAN DIFFUSE LARGE-CELL LYMPHOMA

Bryostatin 1 (Bryo1), a macrocyclic lactone and a protein kinase C act ivator, is isolated from the marine bryozoan Bugula neritina. In this study we describe its effect, alone or after sequential use with vincr istine (VCR), on the human diffuse large cell lymphoma cell line WSU-D LCL2. Our results show that both Bryo1 and VCR induced apoptosis as de monstrated by morphological examination, DNA flow cytometry (FCM), and DNA fragmentation on agarose gel electrophoresis. Cells pretreated fo r 24 h with Bryo1 and then exposed to VCR showed an increase in apopto sis compared to cells that were exposed to Bryo1 or VCR alone. We also studied the effects of Bryo1, VCR and their combination on cell growt h, bcl-2 and p53 expression, and inhibition of cell proliferation as m easured by [H-3]-thymidine incorporation. Cell analysis showed signifi cant growth inhibition of WSU-DLCL2 cells by the Bryo1/VCR combination as compared to either agent alone. Immunocytochemistry (ICC) revealed that relative bcl-2 oncoprotein expression was decreased in cells tre ated with Bryo1, or VCR separately and was abolished by combining both drugs. When examined by ICC, WSU-DLCL2 cells were initially negative for the p53 protein. However, upon treatment with the above agents, th e relative expression of p53 was moderate on Bryo1-or VCR-treated cell s and strong on cells treated with the Bryo1/VCR combination. Cell pro liferation as measured by [H-3]-thymidine incorporation revealed signi ficant inhibition of tumor growth by exposure to the agents when compa red to the control. in contrast, Bryo1, VCR and their combination did not show any inhibition of normal bone marrow growth. These findings t aken together, suggest that the exposure of WSU-DLCL2 cells to Bryo1 p rior to treatment with VCR enhances apoptosis, a phenomenon which migh t be exploited for future therapies.