Abstract 1010: LIG1 deletion predicts chemotherapy resistance, chromosomal instability, and poor prognosis in triple negative breast cancer
Authors: Anurag Meenakshi , Jaehnig Eric , Lei Jonathan , Kim Beom-Jun , Huynh Anh Minh Tran , Dou Yongchao , Vashist Tanmayi , Bergstrom Erik , Gou Xuxu , Korchina Viktoriya , Muzny Donna Marie , Otte Kristen , Doddapaneni Harshavardhan , Dobrolecki Lacey , Echeverria Gloria Vittone , Lim Bora , Rimawi Mothaffar , Krug Karsten , Hageman Ian , Rodriguez Henry , Robles Ana I. , Hiltke Tara , Osborne Kent , Gillette Michael , Miles George , Carr Steven , Lewis Michael T , Zhang Bing , Ademuyiwa Foluso , Satpathy Shankha , Ellis Matthew J. 
Published: June 2022

Abstract
Introduction: Cytotoxic chemotherapy for sporadic Triple Negative Breast Cancer (TNBC) remains the standard of care and the recent approval for adjuvant PD1 therapy is not biomarker guided. Pathological complete response (pCR) is often not achieved and portends poor survival. Predictive markers for individual drugs have proven elusive.
Approach: Microscaled proteogenomics (MPG) was applied to snap-frozen TNBC clinical trial core needle biopsies obtained before treatment with carboplatin and docetaxel (WashU: NCT201404107 and BCM: NCT02544987). Clinical endpoints for discovery analysis were pathological complete response (pCR) and residual cancer burden (RCB). Standard non-parametric statistical tests were employed to identify proteogenomic features associated with these endpoints.
Results: Copy number aberrations (CNA) are a recurrent feature of TNBC and a potential driver of chemotherapy sensitivity. We therefore sought CNA with concordant changes at the mRNA and protein levels that also associate with pCR status. Genes located within a recurrent interstitial deletion at chromosomal location 19q13.3 were the most significantly down-regulated at mRNA and protein level in chemotherapy resistant cases. 19q13.3 encodes multiple DNA damage response (DDR) genes; however, only LIG1, a DNA ligase required for lagging strand synthesis and DNA repair, showed concordant changes at both the mRNA and protein level. In multiple independent TNBC data sets, LIG1 deletion was associated lack of pCR and poor metastasis-free survival. Additionally in the BrighTNess TNBC trial lower LIG1 mRNA levels were associated with increased chemotherapy resistance in the carboplatin containing arms (no pCR and residual cancer burden I-III; p=0.0008 and 0.003 respectively). In PDX-derived short-term cultures and PDXs treated with docetaxel or carboplatin, a specific association of carboplatin resistance with LIG1 deletion was observed. LIG1 depleted-tumors did not harbor elevated scores for homologous recombination defect signature, suggesting LIG1 loss is an orthogonal pathway for TNBC pathogenesis The high chromosomal instability index in LIG1 deletion tumors in our TNBC study was robustly reproduced in multiple datasets (including TCGA-BRCA ; Metastatic breast cancer project). LIG1 copy number deletion was also associated with poor progression free survival, and high chromosomal instability in multiple other cancers (including TCGA-​UCEC HR=2.23, TCGA-HNSC HR=1.46, TCGA-PRAD HR=2.07, TCGA- COAD HR=1.75 and TCGA-KIRP HR=4.00).
Conclusion: Deletion of LIG1 is associated with chromosomal instability in TNBC and occurs in tumors without genomic evidence for defects in homologous recombination. Other clinical features of LIG1 deleted TNBC and how LIG1 loss may cause chromosomal instability and tumorigenesis will be discussed.
Citation Format: Meenakshi Anurag, Eric Jaehnig, Jonathan Lei, Beom-Jun Kim, Anh Minh Tran Huynh, Yongchao Dou, Tanmayi Vashist, Erik Bergstrom, Xuxu Gou, Viktoriya Korchina, Donna Marie Muzny, Kristen Otte, Harshavardhan Doddapaneni, Lacey Dobrolecki, Gloria Vittone Echeverria, Bora Lim, Mothaffar Rimawi, Karsten Krug, Ian Hageman, Henry Rodriguez, Ana I. Robles, Tara Hiltke, Kent Osborne, Michael Gillette, George Miles, Steven Carr, Michael T Lewis, Bing Zhang, Foluso Ademuyiwa, Shankha Satpathy, Matthew J. Ellis. LIG1 deletion predicts chemotherapy resistance, chromosomal instability, and poor prognosis in triple negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1010.