RNAi screen identifies essential regulators of human brain metastasis-initiating cells

Abstract

Brain metastases (BM) are the most common brain tumor in adults and are a leading cause of cancer mortality. Metastatic lesions contain subclones derived from their primary lesion, yet their functional characterization is limited by a paucity of preclinical models accurately recapitulating the metastatic cascade, emphasizing the need for a novel approach to BM and their treatment. We identified a unique subset of stem-like cells from primary human patient brain metastases, termed brain metastasis-initiating cells (BMICs). We now establish a BMIC patient-derived xenotransplantation (PDXT) model as an investigative tool to comprehensively interrogate human BM. Using both in vitro and in vivo RNA interference screens of these BMIC models, we identified SPOCK1 and TWIST2 as essential BMIC regulators. SPOCK1 in particular is a novel regulator of BMIC self-renewal, modulating tumor initiation and metastasis from the lung to the brain. A prospective cohort of primary lung cancer specimens showed that SPOCK1 was overexpressed only in patients who ultimately developed BM. Protein–protein interaction network mapping between SPOCK1 and TWIST2 identified novel pathway interactors with significant prognostic value in lung cancer patients. Of these genes, INHBA, a TGF-β ligand found mutated in lung adenocarcinoma, showed reduced expression in BMICs with knockdown of SPOCK1. In conclusion, we have developed a useful preclinical model of BM, which has served to identify novel putative BMIC regulators, presenting potential therapeutic targets that block the metastatic process, and transform a uniformly fatal systemic disease into a locally controlled and eminently more treatable one.

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Acknowledgements

This work was supported by funds from the Department of Surgery at McMaster University, Ontario Institute for Cancer Research Cancer Stem Cell Program, a Canadian Cancer Society Research Institute Innovation Grant and The Boris Family Fund for Brain Metastasis Research for Dr. Sheila Singh; Brain Canada PhD Studentship for Mohini Singh; Ontario Research Fund (GL2-01-030), McLaughlin Centre Accelerator grant (#MC-2013-05), Canada Research Chair Program (CRC #225404), and Canada Foundation for Innovation (CFI #12301, #203373, #29272, #225404, #30865) supported Dr. Igor Jurisica.

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Conceptualization and design: MS, CV, SS. Methodology: MS, CV, NM, SM, DB, PV, MQ, TV, MD, KD, AT. Data analysis and interpretation: MS, CV, TT, KB, RH, JM, IJ, DK, SS. Writing, review, and/or revision of the manuscript: MS, CV, NM, SM, DB, PV, MQ, BM, JM, IJ, DSS. Supervision, JAH, JM, IJ, SS

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Correspondence to Sheila K. Singh.

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Singh, M., Venugopal, C., Tokar, T. et al. RNAi screen identifies essential regulators of human brain metastasis-initiating cells. Acta Neuropathol 134, 923–940 (2017). https://doi.org/10.1007/s00401-017-1757-z

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Keywords

  • Brain metastasis
  • Brain metastasis-initiating cell
  • BMIC
  • BMIC regulators
  • TWIST2
  • SPOCK1
  • Patient-derived xenotransplant
  • Non-small cell lung cancer