bryostatin-1 and Lymphoma--Mantle-Cell

In spite of potent first-line therapies for chronic lymphocytic leukemia, treatment remains palliative and all patients frequently relapse. Treatment options for these patients are more limited. BL22 is a recombinant protein composed of the variable region of a monoclonal antibody that binds to CD22 and of PE38, a truncated Pseudomonas exotoxin. BL22 is a very potent drug already used in patients with hairy cell leukemia, whereas in chronic lymphocytic leukemia its cytotoxicity is limited by a lower expression of CD22. Here we demonstrate that this limitation can be overcome by pre-activation of chronic lymphocytic leukemia cells with bryostatin 1.. Primary malignant B cells from chronic lymphocytic leukemia and mantle cell lymphoma patients were used in vitro to assess the therapeutic impact of drug combinations using BL22 and bryostatin 1.. We demonstrate that bryostatin 1 sensitizes chronic lymphocytic leukemia cells for the cytotoxic effects of BL22 through activation of protein kinase C and subsequently increased CD22 surface expression. Dose and time response analysis reveals that activation of protein kinase C further activates an autocrine feedback loop degrading protein kinase C-βII protein. Depletion of protein kinase C-βII and upregulation of CD22 persist for several days following pre-stimulation with bryostatin 1. Therefore, our data provide a rationale for the sequential administration of BL22 following bryostatin 1 treatment. In addition to primary chronic lymphocytic leukemia cells, bryostatin 1 also sensitizes diffuse large B-cell lymphoma and mantle cell lymphoma cells to BL22 induced apoptosis.. Our data suggest that the combination of bryostatin 1 with antibodies directed against CD22 is a potent drug combination for the treatment of low- and high-grade B-cell lymphoma.

Topics: Antibodies; Antineoplastic Agents; Apoptosis; Bryostatins; Enterotoxins; Humans; Immunotoxins; Leukemia, Lymphocytic, Chronic, B-Cell; Lymphoma, B-Cell; Lymphoma, Mantle-Cell; Protein Kinase C; Protein Kinase C beta; Sialic Acid Binding Ig-like Lectin 2; Tumor Cells, Cultured; Up-Regulation

The anti-cancer effects of bryostatin-1, a potent diacylglycerol analogue, have traditionally been attributed to its action on protein kinase C. However, we previously documented apoptosis in a B non-Hodgkin lymphoma cell line involving diacylglycerol analogue stimulation of Ras guanyl-releasing protein, a Ras activator, and Bim, a proapoptotic Bcl-2 family protein. To further explore the role of Bim, we examined several Bim-deficient B non-Hodgkin lymphoma cells for their responses to pico, a synthetic bryostatin-1-like compound. The Bim(-) mantle cell lymphoma cell lines Jeko-1, Mino, Sp53, UPN1, and Z138 and the Bim(+) cell line Rec-1, as well as the Burkitt lymphoma cells lines BL2 (Bim(-)) and Daudi (Bim(+)), were examined for their response to pico using assays for proliferation and apoptosis as well as biochemical methods for Ras guanyl-releasing proteins and Bcl-2 family members. With the exception of UPN1, mantle cell lymphoma cell lines underwent pico-induced apoptosis, as did BL2. In some cases, hallmarks of apoptosis were substantially diminished in the presence of mitogen-activated protein kinase kinase inhibitors. Pico treatment generally led to increased expression of proapoptotic Bik, although the absolute levels of Bik varied considerably between cell lines. A pico-resistant variant of Z138 exhibited decreased Bik induction compared to parental Z138 cells. Pico also generally decreased expression of anti-apoptotic Bcl-XL and Mcl1. Although, these changes in Bcl-2 family members seem unlikely to fully account for the differential behavior of the cell lines, our demonstration of a potent apoptotic process in most cell lines derived from mantle cell lymphoma encourages a re-examination of diacylglycerol analogues in the treatment of this subset of B non-Hodgkin lymphoma cases.

Topics: Antineoplastic Agents; Apoptosis; Apoptosis Regulatory Proteins; Bcl-2-Like Protein 11; bcl-X Protein; Bryostatins; Cell Line, Tumor; DNA-Binding Proteins; Extracellular Signal-Regulated MAP Kinases; Guanine Nucleotide Exchange Factors; Humans; Lymphoma, Mantle-Cell; Membrane Proteins; Proto-Oncogene Proteins; Proto-Oncogene Proteins c-bcl-2