Abstract 6116: Ablation of mitotic checkpoint kinase BUB1 sensitizes lung adenocarcinoma to different classes of chemotherapy, radiation, and chemo-radiation
Authors: Thoidingjam Shivani , Sriramulu Sushmitha , Siddiqui Farzan , Movsas Benjamin , Gadgeel Shirish , Nyati Shyam 
Published: June 2023

Abstract
Lung cancer causes the most cancer associated deaths worldwide. About 80 percent patients with inoperable non-small cell lung cancer (NSCLC) develop local recurrence and about 60 percent distant metastasis. NSCLC subtype, lung adenocarcinoma (LUAD) accounts for about 40% of all lung cancers. Recently, targeted therapy with chemotherapy combination has shown to enhance the pathologic complete response rate in a subgroup of NSCLC patients, but most patients do not benefit from therapy due to development of resistance. Thus, identifying molecular drivers of primary and adaptive chemotherapy resistance that can be effectively targeted represents a critical unmet clinical need. Here we aim to evaluate BUB1 (a mitotic checkpoint kinase) as a viable molecular target for increasing the effectiveness of radiotherapy and chemotherapy in LUAD. Bioinformatic analyses were conducted to evaluate BUB1 expression across lung cancer and normal tissues. BUB1 was found to be overexpressed in LUAD compared to normal tissues and BUB1 expression also correlated with cancer stage and tumor grade. LUAD cell lines A549, H1975 and H2030 were used to study the effect of BUB1 inhibition on chemo-radiosensitization. MTT cell proliferation and clonogenic cell survival studies were conducted with pharmacological (BAY1816032) and genomic (CRISPR) BUB1 ablation in combination with Platinum (Cisplatin), Taxol (Paclitaxel) or a PARP inhibitor (Olaparib) without/with radiation. BUB1 inhibition showed cytotoxicity in LUAD cell lines at micromolar concentration and enhanced the radiation mediated cell killing at nanomolar concentration. Moreover, BUB1 inhibition sensitized LUAD cell lines to Cisplatin, Paclitaxel and Olaparib in double or triple chemotherapy combinations. Additionally, BUB1 inhibition significantly increased LUAD cell death when combined with different classes of chemotherapies with radiation (chemo-radiation). Our preliminary mechanistic studies revealed prolonged presence of γH2AX foci, an indicator of DNA double stand breaks. BLRR DNA damage reporter assay indicated that the non-homologous end joining (NHEJ) pathway was inhibited upon BUB1 ablation. Detailed mechanistic studies combining BUB1 ablation with chemo-radiation are underway to delineate signaling cascades involved in BUB1 driven chemo-radiation sensitization. Our data provides evidence that BUB1 inhibition sensitizes lung adenocarcinoma to radiotherapy, different classes of chemotherapy and chemo-radiation through DNA-double strand break repair pathways and provides rationale for clinical trials that combine BUB1 inhibition with chemo-radiation in NSCLC.
Citation Format: Shivani Thoidingjam, Sushmitha Sriramulu, Farzan Siddiqui, Benjamin Movsas, Shirish Gadgeel, Shyam Nyati. Ablation of mitotic checkpoint kinase BUB1 sensitizes lung adenocarcinoma to different classes of chemotherapy, radiation, and chemo-radiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6116.