Abstract 65: Anti-apoptotic proteins BCL-XL and MCL-1 are crucial for nasopharyngeal carcinoma (NPC) cell survival
Authors: Rahman Siti Fairus Abdul , Muniandy Kalaivani , Azzam Ghows , Kumaran Nethia Mohana 
Published: September 2020

Abstract
Patients diagnosed with Nasopharyngeal carcinoma (NPC) initially respond well to chemo- and radiotherapy but eventually develop resistance to these treatments. Hence, novel and improved treatment strategies are needed for NPC. The BCL-2 family proteins are critical regulators of the intrinsic apoptosis pathway. These proteins are up-regulated in many cancers hence they have become attractive therapeutic targets. Given that different cell population rely on different anti-apoptotic proteins for survival, it is crucial to determine which proteins are important for NPC survival. A human apoptosis RT2 Profiler PCR Array was first employed to profile the anti-apoptotic gene expressions in both the NPC cell lines. The HK1 cells expressed all the anti-apoptotic genes (MCL-1, BFL-1, BCL-2, BCL-XL, and BCL-w). On the other hand, C666-1 expressed all except for BFL-1 (undetectable level). Given that there are no specific BFL-1 inhibitors, the role of BFL-1 in NPC cell survival was determined by deleting the gene using the CRISPR/Cas9 technique. The BFL-1 single guide RNAs were cloned into the PX459 plasmid (pSpCas9(BB)-2A-Puro) and transfected into the NPC cells to establish BFL-1 knock-out cells. Parallel to this experiment, the contributions of the other anti-apoptotic proteins in NPC survival was determined by treating NPC cell lines HK1, C666-1 and C17 with BH3 mimetics ABT-199, A-1331852 and S63845 which inhibit BCL-2, BCL-XL and MCL-1, respectively, alone and in combination, in both 2D and 3D cell culture models. The HK1 and C666-1 cells were resistant to single agent treatment of all three drugs, suggesting that none of these anti-apoptotic proteins singly mediate survival of the cells. The NPC C17 cells however were sensitive to single agent treatment of S63845 indicating that these cells rely on MCL-1 for survival. Co-inhibition of BCL-XL and MCL-1 with A1331852 and S63845 significantly inhibited cell proliferation in all three cell lines. Similar data were obtained with 3-dimensional spheroid cell culture models. Treatment with a combination of A1331852 and S63845 resulted in inhibition of growth and invasion of the 3D spheroids generated from the HK1 cells. Co-inhibition of BCL-2 and MCL-1 with ABT-199 and S63845, also inhibited cell proliferation of the NPC cell lines. However, the effect of the combination was not as pronounced as combination of A1331852 and S63845. Collectively, our data demonstrate that BCL-XL and MCL-1 are crucial for NPC survival and targeting these proteins with selective inhibitors may be potentially useful as treatment strategies for the management of NPC.
Citation Format: Siti Fairus Abdul Rahman, Kalaivani Muniandy, Ghows Azzam, Nethia Mohana Kumaran. Anti-apoptotic proteins BCL-XL and MCL-1 are crucial for nasopharyngeal carcinoma (NPC) cell survival [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 65.