Abstract 664: Galiximab (anti-CD80 mAb) sensitizes TRAIL-resistant B-lymphoma to TRAIL-induced apoptosis via inhibition of the transcription repressor Yin Yang 1 (YY1)

Abstract

Abstract Treatment of B-lymphomas with rituximab, alone or in combination with chemotherapy, resulted in significant clinical responses and prolongation of survival. However, a significant subset relapses or does not respond to initial treatments. Therefore, there is an urgent need to identify new targets and develop therapies to reverse resistance. CD80 is expressed on APCs and normal B cells and most B-lymphomas express CD80 on the surface. A primatized anti-CD80 mAb, galiximab, was developed and shown to inhibit tumor cell proliferation and mediates ADCC. A phase I/II clinical study with galiximab in patients with refractory B lymphomas demonstrated its safety TRAIL is a death-inducing ligand that is not toxic to normal cells but selectively cytotoxic to sensitive tumor cells and is currently in clinical trails in patients with a variety of cancers. The objective of this study was to investigate whether galiximab can sensitize TRAIL-resistant B lymphoma to TRAIL-induced apoptosis. We hypothesized that galiximab-induced inhibition of cell proliferation must have triggered the cells and inhibited constitutively activated survival pathways, such as NF-κB, and downstream anti-apoptotic gene products, thus, reducing the threshold of resistance and facilitating TRAIL to mediate apoptosis. This hypothesis was tested in vitro using CD80+ Raji cells as model and recombinant TRAIL. Galiximab was obtained from Biogen Idec. Treatment of Raji with galiximab (5-40 μg/ml) for 18h and followed by treatment with TRAIL (2.5-10 ng/ml) resulted in significant apoptosis as assessed by activation of Caspase 3. Galiximab treatment of Raji inhibited the NF-κB pathway and its DNA-binding activity as assessed by western and EMSA, respectively. The direct role of NF-κB-induced inhibition by galiximab in sensitization was corroborated by the use of the NF-κB inhibitor DHMEQ. We have reported that the TRAIL receptor DR5 transcription repressor YY1 regulates tumor-cell sensitivity to TRAIL. We have found that galiximab inhibits YY1 expression and DNA-binding activity in Raji in parallel with upregulation of DR5. The direct role of YY1-induced inhibition by galiximab in TRAIL sensitization was corroborated in cells transfected with siRNA YY1 and which were sensitive to TRAIL apoptosis. Sensitization by galiximab was due, in part; to activation of the type II mitochondrial pathway for apoptosis. Galiximab-induced inhibition of anti-apoptotic Bcl-2 family, such as Bcl-2 and Bcl-XL, in sensitization was verified by the use of the specific Bcl-2 inhibitor, 2 MAM-A3. Altogether, these findings established that galiximab is capable to sensitize TRAIL-resistant B lymphomas to TRAIL apoptosis. The findings also suggest the potential therapeutic application of the combination of galiximab and TRAIL or agonist DR4/DR5 antibodies in the treatment of resistant B lymphomas. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 664.