PMN-MDSCs Enhance CTC Metastatic Properties through Reciprocal Interactions via ROS/Notch/Nodal Signaling

Int J Mol Sci. 2019 Apr 18;20(8):1916. doi: 10.3390/ijms20081916.

Abstract

Intratumoral infiltration of myeloid-derived suppressor cells (MDSCs) is known to promote neoplastic growth by inhibiting the tumoricidal activity of T cells. However, direct interactions between patient-derived MDSCs and circulating tumors cells (CTCs) within the microenvironment of blood remain unexplored. Dissecting interplays between CTCs and circulatory MDSCs by heterotypic CTC/MDSC clustering is critical as a key mechanism to promote CTC survival and sustain the metastatic process. We characterized CTCs and polymorphonuclear-MDSCs (PMN-MDSCs) isolated in parallel from peripheral blood of metastatic melanoma and breast cancer patients by multi-parametric flow cytometry. Transplantation of both cell populations in the systemic circulation of mice revealed significantly enhanced dissemination and metastasis in mice co-injected with CTCs and PMN-MDSCs compared to mice injected with CTCs or MDSCs alone. Notably, CTC/PMN-MDSC clusters were detected in vitro and in vivo either in patients' blood or by longitudinal monitoring of blood from animals. This was coupled with in vitro co-culturing of cell populations, demonstrating that CTCs formed physical clusters with PMN-MDSCs; and induced their pro-tumorigenic differentiation through paracrine Nodal signaling, augmenting the production of reactive oxygen species (ROS) by PMN-MDSCs. These findings were validated by detecting significantly higher Nodal and ROS levels in blood of cancer patients in the presence of naïve, heterotypic CTC/PMN-MDSC clusters. Augmented PMN-MDSC ROS upregulated Notch1 receptor expression in CTCs through the ROS-NRF2-ARE axis, thus priming CTCs to respond to ligand-mediated (Jagged1) Notch activation. Jagged1-expressing PMN-MDSCs contributed to enhanced Notch activation in CTCs by engagement of Notch1 receptor. The reciprocity of CTC/PMN-MDSC bi-directional paracrine interactions and signaling was functionally validated in inhibitor-based analyses, demonstrating that combined Nodal and ROS inhibition abrogated CTC/PMN-MDSC interactions and led to a reduction of CTC survival and proliferation. This study provides seminal evidence showing that PMN-MDSCs, additive to their immuno-suppressive roles, directly interact with CTCs and promote their dissemination and metastatic potency. Targeting CTC/PMN-MDSC heterotypic clusters and associated crosstalks can therefore represent a novel therapeutic avenue for limiting hematogenous spread of metastatic disease.

Keywords: Heterotypic CTC clusters; biomarkers and signaling pathways; breast cancer; circulating tumor cells (CTCs); melanoma; mutual CTC/PMN-MDSC activation cycle; polymorphonuclear-myeloid derived suppressor cells (PMN-MDSCs).

MeSH terms

  • Adult
  • Aged
  • Animals
  • Breast Neoplasms / blood*
  • Breast Neoplasms / genetics
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology
  • Carcinogenesis / genetics*
  • Cell Transplantation / methods
  • Female
  • Flow Cytometry
  • Gene Expression Regulation, Neoplastic
  • Humans
  • Male
  • Melanoma / blood*
  • Melanoma / genetics
  • Melanoma / metabolism
  • Melanoma / pathology
  • Mice
  • Middle Aged
  • Myeloid-Derived Suppressor Cells / metabolism*
  • Myeloid-Derived Suppressor Cells / pathology
  • NF-E2-Related Factor 2 / genetics
  • Neoplasm Metastasis
  • Neoplastic Cells, Circulating / metabolism
  • Neoplastic Cells, Circulating / pathology
  • Reactive Oxygen Species / metabolism
  • Receptor, Notch1 / genetics
  • Vesicular Transport Proteins / genetics

Substances

  • NF-E2-Related Factor 2
  • NFE2L2 protein, human
  • Reactive Oxygen Species
  • Receptor, Notch1
  • VPS52 protein, human
  • Vesicular Transport Proteins