Molecular Interplay between Dormant Bone Marrow-Resident Cells (BMRCs) and CTCs in Breast Cancer.

Debasish Boral,Dario Marchetti,S Ray Kenney,Haowen N Liu

doi:10.3390/cancers12061626

Debasish Boral, Dario Marchetti + Show 2 more

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https://doi.org/10.3390/cancers12061626

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Abstract

Despite widespread knowledge that bone marrow-resident breast cancer cells (BMRCs) affect tumor progression, signaling mechanisms of BMRCs implicated in maintaining long-term dormancy have not been characterized. To overcome these hurdles, we developed a new experimental model of clinical dormancy employing patient-isolated Circulating Tumor Cells (de novo CTCs) and their injection in xenografts with subsequent tumor monitoring and CTC characterization (ex vivo CTCs). We hypothesized that significant distinctions exist between signaling pathways of bone marrow-homing vs metastasis-competent CTCs upon transplantation in xenografts. Comparative transcriptomic analyses of ex vivo vs de novo CTCs identified increased mTOR signaling—a critical pathway frequently dysregulated in breast cancer and implicated in cell survival and dormancy—with contrasting actions by its two complementary arms (mTORC2/mTORC1). Heightened mTORC2 downstream targets augmented quiescent CTCs (Ki67−/RBL2+ cells) in paired breast cancer tissues, along with high mTORC2 activity in solitary BMRCs and tissue-resident CTCs. Further, shRNA mediated the knockdown of RICTOR, an essential component of mTORC2, and augmented Ki67/PCNA biomarker expression and proliferation. Collectively, these findings suggest that the balance between mTORC1 vs mTORC2 signaling regulates CTC-associated mitotic and/or dormancy characteristics.

Highlights

Patients with metastatic breast cancer have a 5-year survival rate of only 28% compared to99% in patients with non-metastatic cancer [1]
Since the bone marrow serves as the foremost reservoir for these circulating tumor cells (CTCs), we developed a the bone marrow serves as the foremost reservoir for these CTCs, we developed a preclinical model preclinical model employing a three-tiered enrichment strategy (FACS - in vivo selection for 4–8 employing a three-tiered enrichment strategy (FACS - in vivo selection for 4–8 months - FACS) for months - FACS) for isolating ex vivo BMRCs using metastatic breast cancer (mBC) patient-derived CTCs (Figure 1)
We considered a three-way comparison between transcriptomes of de novo CTCs (GSE99394) ex vivo BMRCs, and ex vivo CTCs to reflect differences in signaling mechanisms acquired during the bone-homing vs. organ colonization and selection in vivo

Summary

Introduction

Patients with metastatic breast cancer (mBC) have a 5-year survival rate of only 28% compared to. 99% in patients with non-metastatic cancer [1]. The pathogenesis of metastatic dissemination starts early in the carcinogenic process, in a step referred to as ‘metastatic seeding’, when BC cells invade through the basement membrane and intravasate into blood as circulating tumor cells (CTCs) [2,3,4,5]. While the overwhelming majority of these CTCs die in the circulation, some CTCs are able to survive. These CTCs persist in distant organs as clinically undetectable micro-metastases, either as quiescent (G0 ) single cells or as dormant foci where the total number of cells undergoing proliferation is balanced by cells undergoing apoptosis [6,7,8]. It is likely that at least a sub-population of BC cells home to, and reside in, the bone marrow (BM) where they accumulate genomic instability over time, gradually acquiring the ability to colonize additional organs [11,12,13]

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