Abstract B052: The role of LMO2 in DNA damage repair pathway choice in metastatic breast cancer

Abstract

Abstract Introduction: Previously we discovered that a novel metastasis-initiating cell (MIC) population is marked by LMO2, a transcriptional adaptor protein in hematopoietic stem cells, and a T-cell oncogene. Knocking down LMO2 did not affect the growth of primary tumors, but did significantly reduce the number of circulating tumor cells and lung metastases. Transcriptional analysis of LMO2 knockdown shows the HALLMARK_DNA_REPAIR pathway is upregulated, suggesting that LMO2 is involved in regulating DNA repair in breast cancer cells. Interestingly, a previous study reported that in diffuse large B-cell lymphoma high LMO2 expression results in defective repair of double-stranded DNA breaks (Parvin et al., Cancer Cell, 36, 3 [2019]). We hypothesize that in breast cancer LMO2 expression is regulating the choice between homology-directed repair (HDR), an error-free method of DNA repair, and non-homologous end-joining (NHEJ), a more error-prone method. Cells that use NHEJ to repair DNA are dependent on poly (ADP-ribose) polymerase (PARP) and can be targeted with PARP inhibitors. LMO2 could thus be used as a new biomarker for benefit from PARP inhibition. Methods: LMO2 was identified using single-cell RNAseq data from human breast cancer patients. In vitro and in vivo assays using breast cancer cell lines and patient-derived xenografts were used to characterize the effect of LMO2 on metastasis. To study the role of LMO2 in the DNA damage response, we used MDA-MB-468 and HCC1806 cells with control and 2 independent shRNAs targeting LMO2. Immunofluorescent staining for γH2AX, 53BP1, and RAD51 was performed to measure changes in DNA damage and repair markers. Control and LMO2 knockdown cells were treated with olaparib, with cellular proliferation measured with a WST-1 assay and colony formation measured with crystal violet staining. Results and Conclusion: Knocking down LMO2 expression results in decreased NHEJ and increased HDR in MDA-MB-468 and HCC1806 cells. There is no significant difference in DNA damage overall as measured by γH2AX foci/nucleus. LMO2 knockdown in MDA-MB-468 cells reduces sensitivity to PARP inhibition with olaparib, as measured by an increase in the IC50 values. Our preliminary data suggest that LMO2 expression likely regulates the choice between NHEJ and HDR. LMO2 expression introduces a bias towards NHEJ, which sensitizes cells to PARP inhibition. This suggests that LMO2+ cells could be targeted with PARP inhibition, which could thus be used to target metastasis-initiating cells. Citation Format: Isobel Fetter, Veronica Haro-Acosta, Shaheen Sikandar. The role of LMO2 in DNA damage repair pathway choice in metastatic breast cancer [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Advances in Breast Cancer Research; 2023 Oct 19-22; San Diego, California. Philadelphia (PA): AACR; Cancer Res 2024;84(3 Suppl_1):Abstract nr B052.