Abstract PO4-13-08: Mechanical conditioning (MeCo) score is higher in circulating tumor cells (CTCs) compared to primary tumors in early-stage breast cancer and even higher in metastases compared to CTCs in metastatic breast cancer
Authors: Mouneimne Gus , Watson Adam , Grant Adam , Campo Daniel , Ring Alexander , Bains Pushpinder , Lang Julie 
Published: May 2024

Background: The mechanical conditioning (MeCo) score is a gene expression signature that is acquired early by cancer cells in the primary breast tumor and is reflective of their responsiveness to matrix stiffness (fibrotic-like matrix rigidity). Further, chromatin remodeling in response to stiffness allows cancer cells to retain their aggressive features even in the absence of mechanical stimulation by the primary tumor microenvironment, for instance, during their dissemination through the circulation in metastasis. Importantly, patients who have high MeCo score tumors are at higher risk of developing metastatic breast cancer, compared to low MeCo scores (p&lt; 0.0001; HR=2.2, 95%CI 1.7-2.7; Watson et al 2021, PMID: 34192535). Moreover, circulating tumor cells (CTCs) are associated with higher rate of metastatic dissemination, making CTC detection in the circulation of breast cancer patients a significant prognostic biomarker for breast cancer metastasis. Beyond their enumeration per blood volume units, specific prognostic features of CTCs are not fully explored. We sought to determine whether, compared to primary tumors, CTCs retain high MeCo scores and whether these scores are maintained during late-stage breast cancer in the metastatic sites.

Methods: CTCs were isolated from peripheral blood of two patient cohorts: stage II-III breast cancer patients using immunomagnetic enrichment/FACS methodology (Lang et al 2018, PMID: 29868978) and of metastatic breast cancer patients using ANGLE Parsortix microfluidics system (Ring et al 2022, PMID: 35000083). Gene expression profiling using RNA-seq was performed in CTCs and in matching primary tumors (PT) and metastases (MET) for the early-stage and late-stage cohorts, respectively. A quantile normalization approach was used to allow comparison across cohorts. MeCo scores were computed for all samples as per Watson et al 2021. Wilcoxon matched-pairs signed rank test was performed for comparison of MeCo scores from matching samples within each cohort; Mann-Whitney unpaired test was used to compared MeCo scores of CTCs across cohorts.

Results: In 12 pairs of early-stage breast cancer patient CTCs and PT, MeCo scores of CTCs were significantly higher than their matched PTs (p=0.026). Furthermore, in 26 pairs of metastatic patient’s CTCs and MET, MeCo scores of METs were significantly higher than matching CTCs (p=0.0004). MeCo scores of CTCs were similar between early- and late-stage breast cancer despite differing CTC isolation strategies (epitope-dependent and microfluidics size gradient). 98% of genes in the MeCo score were present in the evaluable CTC, MET and PT samples.

Conclusions: Our results show that the MeCo score is higher in CTCs compared to PTs and in METs compared to CTCs in early- and late-stage breast cancer, respectively. Therefore, the MeCo score is progressively higher throughout the metastatic cascade in breast cancer. These findings demonstrate that mechanical conditioning is retained during metastatic progression, even as cancer cells transition through the circulation where the initial induction by matrix stiffness is lost. Further, these findings support that cancer cells with higher MeCo scores are more competent with–and potentially selected for by–metastatic progression. Importantly, these findings provide a novel feature of CTCs, mechanical conditioning (MeCo), which is associated with higher capacity for metastasis. Further, since the CTC MeCo score is elevated even in early-stage breast cancer, it could provide, in addition to CTC enumeration, a potential prognostic tool to predict metastatic risk in breast cancer patients.

Citation Format: Gus Mouneimne, Adam Watson, Adam Grant, Daniel Campo, Alexander Ring, Pushpinder Bains, Julie Lang. Mechanical conditioning (MeCo) score is higher in circulating tumor cells (CTCs) compared to primary tumors in early-stage breast cancer and even higher in metastases compared to CTCs in metastatic breast cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO4-13-08.