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Sequential Transcription Factor Targeting for Diffuse Large B-Cell Lymphomas

Departments of ¹ Developmental and Molecular Biology and ² Pathology, Albert Einstein College of Medicine, Bronx, New York; ³ Department of Pathology, British Columbia Cancer Agency, Vancouver, British Columbia, Canada; and ⁴ Howard Hughes Medical Institute and Department of Cellular and Molecular Medicine, University of California at San Diego School of Medicine, La Jolla, California

Requests for reprints: Ari Melnick, Department of Developmental and Molecular Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461. Phone: 718-430-4238; Fax: 718-430-8567; E-mail: amelnick{at}aecom.yu.edu.

Key Words: BCL6 • p53 • Transcription factors

Transcription factors play a central role in malignant transformation by activating or repressing waves of downstream target genes. Therapeutic targeting of transcription factors can reprogram cancer cells to lose their advantages in growth and survival. The BCL6 transcriptional repressor plays a central role in the pathogenesis of diffuse large B-cell lymphomas (DLBCL) and controls downstream checkpoints, including the p53 tumor suppressor gene. We report that a specific inhibitor of BCL6 called BPI can trigger a p53 response in DLBCL cells. This was partially due to induction of p53 activity and partially due to relief of direct repression by BCL6 of p53 target genes. BPI could thus induce a p53-like response even in the presence of mutant p53. Moreover, sequential BCL6 peptide inhibitors followed by p53 peptide or small-molecule activators provided a more powerful antilymphoma effect than either treatment alone by maximally restoring p53 target gene expression. Therefore, tandem targeting of the overlapping BCL6 and p53 transcriptional programs can correct aberrant survival pathways in DLBCL and might provide an effective therapeutic approach to lymphoma therapy. [Cancer Res 2008;68(9):3361–9]