The DAC Inhibitor, LBH589, Is Highly Effective in Both Rituximab-Sensitive and Rituximab-Resistant Lymphomas and Enhances the Anti-Tumor Activity of Bortezomib, Other Chemotherapy Agents, and Anti-CD20 Monoclonal Antibodies.

Abstract 2715 Poster Board II-691 Deacetylases (DACs) are enzymes that remove the acetyl groups from target proteins [histones (class I) and non-histones (class II)], leading to regulation of gene transcription and other cellular processes. LBH589 is a novel and potent DAC class I and II inhibitor undergoing pre-clinical and clinical testing. In order to better characterize the role of DAC inhibitors in the treatment of refractory/resistant B-cell lymphomas we studied the anti-tumor effect that LBH589 had when used with chemotherapy agents and anti-CD20 monoclonal antibodies against a panel of rituximab-[chemotherapy]-sensitive cell lines (RSCL), rituximab-[chemotherapy]-resistant cell lines (RRCL), and primary lymphoma cells isolated from patients with treatment-naive or refractory/relapsed B-cell lymphoma. Non-Hodgkin9s lymphoma (NHL) cell lines were exposed to the following chemotherapy agents or monoclonal antibodies: CDDP, doxorubicin, vincristine, bortezomib versus rituximab or veltuzumab (or isotype control), alone or in combination with LBH589. In dose-sequence studies the treatment with LBH589 preceded or followed in vitro exposure to the chemotherapy agent or the monoclonal antibody by 24 hrs. Changes in mitochondrial potential were determined by alamar blue reduction using a kinetic assay. Patient-derived primary tumor cells (N=25) were exposed to either LBH589 (2-25uM), bortezomib (1 to 10nM) or both. Changes in ATP content were determined by cell titer glow assay. RNA was isolated from NHL cell lines exposed to LBH859 or bortezomib and changes in gene expression of the Bcl-2 family members were determined by qualitative polymerase chain reaction (PCR). LBH589 was active as a single agent against RSCL, RRCL or patient-derived primary tumor cells. In addition, Bcl-XL gene down-regulation was observed following exposure to LBH859. On the other hand, upregulation of Bak and downregulation of Mcl-1 were observed following proteasome inhibition. Synergistic activity was observed by combining LBH589 and chemotherapy agents, bortezomib or either of the two anti-CD20 mAbs studied. In tumor-derived primary cells from lymphoma patients, the combination of LBH589 and bortezomib resulted in significant anti-tumor activity in follicular, Hodgkin and diffuse large B-cell lymphoma. The sequence of administration impacted the degree of antitumor activity observed (ie in general, exposure of tumors cells initially to LBH589, followed by exposure to chemo/mAbs was associated with the greatest degree of anti-tumor activity). Our data suggests that LBH589 is active against various RSCL, RRCL and patient-derived primary tumor cells. Our findings strongly suggest that LBH589 added to anti-CD20 and/or chemotherapy results in a novel and potent treatment strategy against B-cell lymphoma. Research, in part, supported as part of a subproject on NIH PO1 grant CA103985-1 awarded to the Garden State Cancer Center, Belleville, NJ and NHI R-01 grant R01 CA136907-01A1 awarded to Roswell Park Cancer Institute Disclosures: No relevant conflicts of interest to declare.