Abstract 1426: Blinding the CYCLOPS - Cancer vulnerabilities unveiled by genomic loss

Abstract Background: Heterozygous deletions within distal 1p are observed in 30% of neuroblastomas. So far, several potential 1p tumor suppressor genes have been identified. However, in this study we are focussing on 1p genes whose inactivation is not necessarily linked to tumor development but which mediate cell-essential functions, rendering cells with copy number loss vulnerable to further impairment. These genes are candidate therapeutic targets according to the concept of CYCLOPS (copy number alterations yielding cancer liabilities owing to partial loss). Methods: To identify a subset of 1p genes for which heterozygous loss may be tolerated but further reduction leads to cell death, we performed siRNA screens mediating the systematic knock-down of distal 1p genes in five 1p-deleted versus five non-1p-deleted neuroblastoma cell lines. We used 3 different siRNAs per gene in a liquid forward approach. After 96h Hoechst stained nuclei were count. Among others, a neuron-related candidate gene has been identified as a potential CYCLOPS. The candidate gene was validated by viability assays, immunocytochemistry and cell cycle analysis via FACS. Results: We identified many potential CYCLOPS genes mapping on the distal end of chromosome arm 1p. One of these genes is involved in neuronal and embryonic development and has been further validated. Knock-down of the gene impaired cell viability in 1p-deleted cell lines but did not in 1p-non-deleted cells. G1/G0 phase arrest with corresponding S phase decrease was observed in both 1p-deleted and 1p-non-deleted cells. Additionally, neurite-like outgrowth could be observed in 1p-non-deleted cells indicating an induction of differentiation. Conclusion: This study identified a candidate CYCLOPS gene in neuroblastoma. Heterozygous deletions of chromosome arm 1p are also frequently observed in other cancers including melanoma, colorectal and breast cancer. We hypothesize that this proof-of-principle opens a new therapeutic window for tumors harbouring a heterozygous deletion of our candidate gene or other cell essential genes on chromosome arm 1p. Citation Format: Alica Torkov, Kai-Oliver Henrich, Chunxuan Shao, Moritz Gartlgruber, Frank Westermann. Blinding the CYCLOPS - Cancer vulnerabilities unveiled by genomic loss [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1426. doi:10.1158/1538-7445.AM2017-1426