Abstract LB-318: SMARCA4-inactivating mutations increase sensitivity to Aurora kinase A-targeted therapies in non-small cell lung cancers (NSCLCs)
Authors: Tagal Vural , Wei Shuguang , Zhang Wei , Brekken Rolf A. , Posner Bruce A. , Gazdar Adi F. , Roth Michael G. 
Published: July 2016

Purpose: Here, we sought to identify critical genes, whose depletion and inhibition caused differential cytotoxicity in SMARCA4-mutant non-small cell lung cancers (NSCLCs).

Background: The SWI/SNF complex is a master regulator of gene expression, affecting at least 10% of the transcriptome. Because of its crucial role in controlling cell cycle, development and differentiation, the SWI/SNF complex components function as tumor suppressor genes. Therefore, not surprisingly, the ATPases SMARCA2 and SMARCA4 are frequently down-regulated in cancers and mutations of SMARCA4 are frequently present in many cancer types including lung cancers. However, currently, no single therapeutic agent has been identified as synthetically lethal with SMARCA4 loss.

To identify SMARCA4-inactivating mutation related targetable gene products, we developed and applied a high throughput cell-based one-well/one-gene screening platform with a genome-wide synthetic library of chemically synthesized small interfering RNAs. Using this approach, we have identified a molecular target (SMARCA4) frequently present in lung cancer cells, whose loss leads to increased sensitivity to a class of Aurora kinase A inhibitors.

Materials, Methods and Results: SMARCA4-mutant NSCLC line NCI-H1819 was screened with a genome-wide library of ∼22,000 pools of 4 siRNA oligonucleotides, identifying 38 pools that were 50% more toxic than the median toxicity in the screen, and were not toxic for wild-type SMARCA4-expressing HBEC30-KT cells. Among our high-priority toxic siRNAs, a number of targeted genes encode proteins important for the cell cycle, including RAN and TPX2. RAN is required for TPX2 to function in mitosis and TPX2 binds to microtubules and activates Aurora kinase A. Individual siRNAs targeting these “hits” in the primary screen, as well as siRNA to Aurora kinase A, were tested and shown to inhibit the growth of NCI-H1819, but not HBECs. In addition, NCI-H1819 cells were hyper-sensitive to VX-680, an inhibitor of Aurora kinases.

We then tested a panel of other NSCLC cell lines that either expressed or did not express wild-type SMARCA4 for sensitivity to siRNA targeting Aurora kinase A, or VX-680. The cell lines with loss of SMARCA4 were more sensitive to loss of AURKA or to VX-680 than NSCLC or HBEC cells expressing SMARCA4. Our observations were further expanded and validated with xenograft mouse models.

Next, we explored why AURKA-targeted therapy causes differential toxicity to the NSCLCs with SMARCA4 loss and identified centrosomal impairments in SMARCA4-null NSCLC cells that create defective mitotic spindle assembly machinery.

Conclusions: SMARCA4-inactivating mutations make cells dependent to RAN/TPX2-mediated mitotic spindle assembly machinery and create targetable mitotic vulnerabilities in NSCLCs.

SMARCA4-mutant NSCLCs are sensitive to Aurora kinase A-targeted treatments due to its crucial role on RAN/TPX2-dependent mitotic spindle formation.

Our data suggest that wild-type SMARCA4-expressing cells tolerate the inhibition of AURKA due to properly regulated and, therefore, functionally normal centrosomes whereas SMARCA4 loss leads to centrosomal defects.

Citation Format: Vural Tagal, Shuguang Wei, Wei Zhang, Rolf A. Brekken, Bruce A. Posner, Adi F. Gazdar, Michael G. Roth. SMARCA4-inactivating mutations increase sensitivity to Aurora kinase A-targeted therapies in non-small cell lung cancers (NSCLCs). [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr LB-318.