Targeting endoplasmic reticulum protein transport: a novel strategy to kill malignant B cells and overcome fludarabine resistance in CLL.

Previous studies showed that chronic lymphocytic leukemia (CLL) cells exhibit certain mitochondrial abnormalities including mtDNA mutations, increased superoxide generation, and aberrant mitochondrial biogenesis, which are associated with impaired apoptosis and reduced sensitivity to fludarabine. Here we report that CLL cells and multiple myeloma cells are highly sensitive to brefeldin A, an inhibitor of endoplasmic reticulum (ER) to Golgi protein transport currently being developed as a novel anticancer agent in a prodrug formulation. Of importance, brefeldin A effectively induced apoptosis in fludarabine-refractory CLL cells. Disruption of protein trafficking by brefeldin A caused the sequestration of the prosurvival factors APRIL and VEGF in the ER, leading to abnormal ER swelling and a decrease in VEGF secretion. Such ER stress and blockage of secretory protein traffic eventually resulted in Golgi collapse, activation of caspases, and cell death. Notably, the cellular sensitivity to this compound appeared to be independent of p53 status. Taken together, these findings suggest that malignant B cells may be highly dependent on ER-Golgi protein transport and that targeting this process may be a promising therapeutic strategy for B-cell malignancies, especially for those that respond poorly to conventional treatments.