Inhibition of BCL6 as a Mechanism To Target Therapy-Resistant Malignant Cells.
Kristy Wolniak, Nisha Mohindra, Timothy Lax, Leondro Cerchietti, Ari Melnick, Jonathan Licht. Northwestern University, Chicago, IL; Children's Memorial Hospital, Chicago, IL; Weill Cornell Medical College, New York, NY
Background: B-cell lymphoma 6 (BCL6) is a transcriptional repressor expressed at high levels in germinal center B cells and promotes genomic instability by repressing genes involved in sensing DNA damage. Overexpression of BCL6 plays a clear role in diffuse large B cell lymphoma. Previous studies have also demonstrated an upregulation of BCL6 in response to kinase inhibitor therapy in myeloid hematopoietic malignancy. In this study, we hypothesize that increased expression of BCL6 in response to kinase therapy in both hematopoietic and non-hematopoietic malignant cells may serve as a putative escape mechanism which could be overcome by inhibition of BCL6.
Design: Human erythroleukemia (HEL), KMS11 myeloma, and MV-411 acute leukemia cell lines were treated with a dose range of kinase inhibitors and expression of BCL6 was assessed by real-time PCR and western blot. A BCL6 peptide inhibitor (Retro-inverso BCL6-peptide inhibitor, RI-BPI) was added at 10μM to the cell cultures to evaluate for an effect of BCL6 inhibition on sensitivity of cell growth effects by kinase inhibitors. Additionally, the small cell lung cancer A549 cell line was treated with gefitimib with or without RI-BPI to assess for increased sensitivity to therapy. To evaluate potential toxicity of RIBPI on non-malignant cells, CD34+ hematopoietic cells from orthopedic bone marrow samples were treated with RI-BPI in maintenance culture.
Results: All cell lines tested demonstrated an increase in BCL6 mRNA (2 to 89-fold increase) and protein following kinase inhibitor therapy. HEL cells demonstrated an increase in cell growth inhibition by JAK kinase inhibitor with the addition of RI-BPI (19% increase). KMS11, MV-411, and A549 cells also all demonstrated an increase in growth inhibition by kinase inhibitor therapy with RI-BPI (25%-54% increased inhibition). A modest inhibition of cell growth occurred in all malignant cell lines tested with RI-BPI alone. Normal CD34+ hematopoietic cell growth and survival in maintenance culture was unaffected by treatment with 10μM RI-BPI.
Conclusions: Both hematopoietic and non-hematopoietic malignant cells demonstrate an increase in BCL6 expression following kinase inhibitor therapy. This increase may serve as an anti-apoptotic escape mechanism for tumor cells, and blocking this pathway enhances the effectiveness of kinase inhibitors.
Monday, February 28, 2011 9:30 AM
Poster Session I Stowell-Orbison/Surgical Pathology/Autopsy Awards Poster Session # 178, Monday Morning