Efficacy of the DAC inhibitor LBH589 in both rituximab-sensitive and rituximab-resistant lymphomas and effect on the antitumor activity of chemotherapy agents, monoclonal antibodies, and bortezomib

Abstract

8576 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 develop therapeutic options for refractory/resistant B-cell lymphomas we studied the effects of LBH589 in the anti-tumor activity of chemotherapy agents and monoclonal antibodies in a panel of rituximab-sensitive cell lines (RSCL), rituximab-resistant cell lines (RRCL), and in lymphoma cells isolated from patients with treatment-naïve or refractory/relapsed B-cell lymphomas by negative selection using magnetic beads. NHL cells lines were exposed to the following chemotherapy agents or monoclonal antibodies: CDDP, doxorubicin, vincristine, bortezomib or rituximab, veltuzumab, or isotype, 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 tumor cells were exposed to either LBH589, bortezomib or both. Changes in ATP content were determined by cell titer glow assay. RNA was isolated from NHL cell lines exposed to LBH859 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 tumor cells. In addition, Bcl-XL gene down-regulation was observed following exposure to LBH859. Synergistic activity was observed by combining LBH589 and chemotherapy agents, bortezomib or either of the two anti-CD20 mAbs studied. The sequence of administration impacted the degree of antitumor activity observed. Our data suggests that LBH589 is active against various RSCL, RRCL and patient-derived tumor cells. Findings suggest that LBH589 added to systemic anti-CD20 and/or chemotherapy could result in a novel and potent treatment strategy against B-cell lymphomas. No significant financial relationships to disclose.