Abstract 2612: BET-protein bromodomain antagonist-based combinations against ibrutinb-sensitive or resistant human Mantle Cell Lymphoma cells
Authors: Sun Baohua , Shah Bhavin , Fiskus Warren , Qi Jun , Devaraj Santhana G. T. , Iyer Swaminathan P. , Sharma Sunil , Bradner James E. , Zu Youli , Bhalla Kapil N. 
Published: August 2015

Mantle Cell Lymphoma (MCL) cells demonstrate genetic alterations involving cyclin D1, CDK4, CDKN2A, MYC, BCL2, as well as in the Toll-like receptor, B-cell receptor (BCR) and NFkB signaling genes. Increased BCR signaling and transcriptional activity of NFkB is documented in MCL cells. Ibrutinib (IB) is an inhibitor of Bruton's tyrosine kinase (BTK) clinically effective against MCL, but long-term durable remissions and cure following IB treatment remains uncertain. We have previously reported that treatment with the BET protein bromodomain antagonist (BA) JQ1 disrupts the binding of the BET-protein BRD4 to the enhancers and promoters and inhibits the mRNA and protein levels of the oncogenes MYC, BCL-2 and CDK4/6 in MCL cells. BRD4 has also been shown to be essential for NFkB activity. Consistent with this, here, we determined that treatment with JQ1 (250 to 2000 nM) reduced the nuclear localization of RelA and attenuated the expression of the NFkB target genes, including TNFα, TNFAIP3 (A20), c-FLIP, cIAP2, XIAP and Bcl-xL in the cultured MCL Mino and MO2058 cells. Notably, JQ1 treatment also reduced the mRNA and protein levels of BTK, along with inhibition of the levels of p-BTK, p-PLCγ2 and p-AKT levels in the MCL cells. Concomitantly, JQ1 dose-dependently inhibited cell growth and exerted lethal activity against cultured (MO2058 and Mino, Z138 and JeKo-1) and patient-derived, primary MCL (pMCL) cells, while relatively sparing normal CD19+ B cells and CD34+ bone marrow progenitor cells. Importantly, co-treatment with JQ1 and IB also markedly inhibited the nuclear RelA levels and attenuated the levels of p-BTK and BTK and reduced NFkB target gene expressions. Co-treatment with JQ1 and IB also synergistically induced apoptosis of the cultured and pMCL cells (CI values &lt; 1.0 by isobologram analysis). Following tail-vein infusion and engraftment of the Mino cells in the bone marrow and spleen of NOD/SCID mice, co-treatment with JQ1 (50 mg/kg/day, IP) and IB (25 mg/kg/day IP) versus treatment with each agent alone significantly improved the median survival of the mice (p &lt; 0.01). We isolated in vitro IB-resistant Mino/IR cells (&gt; 20-fold resistant), following continuous exposure to IB. As compared to the parental control Mino, Mino/IR cells expressed markedly higher levels of AKT, CDK6, BCL2, Bcl-xL, and XIAP. JQ1 treatment (1.0 μM) was able to inhibit the growth and induce apoptosis of Mino/IR cells. Notably, co-treatment with JQ1 and panobinostat (pan-histone deacetylase inhibitor) or palbociclib (CDK4/6 inhibitor) or ABT199 (BCL2 antagonist), or carfilzomib (CZ) (proteasome inhibitor) synergistically induced apoptosis of not only Mino but also Mino/IR cells. Taken together, these findings identify BA-based rational combinations that need to be further evaluated for their in vivo efficacy against IB-sensitive and IB-resistant MCL.

Citation Format: Baohua Sun, Bhavin Shah, Warren Fiskus, Jun Qi, Santhana G. T. Devaraj, Swaminathan P. Iyer, Sunil Sharma, James E. Bradner, Youli Zu, Kapil N. Bhalla. BET-protein bromodomain antagonist-based combinations against ibrutinb-sensitive or resistant human Mantle Cell Lymphoma cells. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2612. doi:10.1158/1538-7445.AM2015-2612