A model of breast cancer heterogeneity reveals vascular mimicry as a driver of metastasis

Abstract

Cancer metastasis requires that primary tumour cells evolve the capacity to intravasate into the lymphatic system or vasculature, and extravasate into and colonize secondary sites1. Others have demonstrated that individual cells within complex populations show heterogeneity in their capacity to form secondary lesions2–5. Here we develop a polyclonal mouse model of breast tumour heterogeneity, and show that distinct clones within a mixed population display specialization, for example, dominating the primary tumour, contributing to metastatic populations, or showing tropism for entering the lymphatic or vasculature systems. We correlate these stable properties to distinct gene expression profiles. Those clones that efficiently enter the vasculature express two secreted proteins, Serpine2 and Slpi, which were necessary and sufficient to program these cells for vascular mimicry. Our data indicate that these proteins not only drive the formation of extra-vascular networks but also ensure their perfusion by acting as anticoagulants. We propose that vascular mimicry drives the ability of some breast tumour cells to contribute to distant metastases while simultaneously satisfying a critical need of the primary tumour to be fed by the vasculature. Enforced expression of SERPINE2 and SLPI in human breast cancer cell lines also programmed them for vascular mimicry, and SERPINE2 and SLPI were overexpressed preferentially in human patients that had lung-metastatic relapse. Thus, these two secreted proteins, and the phenotype they promote, may be broadly relevant as drivers of metastatic progression in human cancer.

Transposon mutagenesis identifies genes that cooperate with mutant Pten in breast cancer progression

“…Recent studies using a breast metastasis model have shown that SERPINB2 protects metastatic cells from plasminogen activator plasmin in the brain, providing a metastatic advantage (55). Another serpin family member, Serpine2, was initially discovered in a model of breast cancer metastasis to bone and later reported to facilitate tumor cells to form vascular-like networks enabling perfusion and lung metastasis (64,65). Likewise, SERPINE1 has been used as a prognostic marker of breast cancer and evaluated during chemotherapy administration (66,67).…”

Distinctive properties of metastasis-initiating cells

“…Although it is a rare and poorly studied phenomena, cancer cells can transdifferentiate into endothelial cells or pericytes to mimic components of the tumor microenvironment . Vascular mimicry has recently been reported to facilitate metastasis of 4T1 mouse mammary tumor cells (Wagenblast et al 2015). Further research is needed to explore whether transdifferentiation events can also happen at the metastatic site to enable metastasis initiation and whether transdifferentiation is one of the cellular properties of some MICs.…”

“…However, recent studies using lineage tracing, barcode sequencing, and whole-genome sequencing are shedding light on this question and have demonstrated a mostly polyclonal nature of metastasis (Fig. 5;McFadden et al 2014;Gundem et al 2015;Maddipati and Stanger 2015;Wagenblast et al 2015).…”

“…Another whole-genome sequencing study analyzed 51 tumors of 10 prostate cancer patients, including primary tumors and multiple metastases in the same patients, and revealed the coexistence of multiple clones in the metastases, including those from metastasis-to-metastasis spreads (Gundem et al 2015). Molecular barcoding offers another effective method to track clonal populations in experimental animal models of metastasis, and this approach has recently been used to analyze metastasis heterogeneity generated by the 4T1 mouse mammary tumor cell line (Wagenblast et al 2015). In this study, orthotopic injection of barcoded cells generated metastases composed of multiple, different clones in various tissues, although it cannot be ruled out that independent metastatic nodules in the same organ might be seeded monoclonally.…”

“…Gene expression analysis at the single-cell level has become a powerful tool to analyze the population dynamics of tumor cells during metastatic evolution (Lawson et al 2015). In addition, lineage tracing and barcode sequencing studies have also been applied to study the interclonal interactions and population dynamics (Maddipati and Stanger 2015;Wagenblast et al 2015). Advances in animal modeling of metastasis and detailed analysis of tumor-intrinsic pathways and tumor-stromal cross-talk further provided unprecedented insights into the molecular mechanism of metastasis initiation.…”