Tumor stem cells fuse with monocytes to form highly invasive tumor-hybrid cells

ABSTRACT

The ‘cancer cell fusion’ theory is controversial due to the lack of methods available to identify hybrid cells and to follow the phenomenon in patients. However, it seems to be one of the best explanations for both the origin and metastasis of primary tumors. Herein, we co-cultured lung cancer stem cells with human monocytes and analyzed the dynamics and properties of tumor-hybrid cells (THC), as well as the molecular mechanisms beneath this fusion process by several techniques: electron-microscopy, karyotyping, CRISPR-Cas9, RNA-seq, immunostaining, signaling blockage, among others. Moreover, mice models were assessed for in vivo characterization of hybrids colonization and invasiveness. Then, the presence of THCs in bloodstream and samples from primary and metastatic lesions were detected by FACS and immunofluorescence protocols, and their correlations with TNM stages established. Our data indicate that the generation of THCs depends on the expression of CD36 on tumor stem cells and the oxidative state and polarization of monocytes, the latter being strongly influenced by microenvironmental fluctuations. Highly oxidized M2-like monocytes show the strongest affinity to fuse with tumor stem cells. THCs are able to proliferate, colonize and invade organs. THC-specific cell surface signature CD36⁺CD14⁺PANK⁺ allows identifying them in matched primary tumor tissues and metastases as well as in bloodstream from patients with lung cancer, thus functioning as a biomarker. THCs levels in circulation correlate with TNM classification. Our results suggest that THCs are involved in both origin and spread of metastatic cells. Furthermore, they might set the bases for future therapies to avoid or eradicate lung cancer metastasis.

KEYWORDS:

• Cancer stem cells
• CD36
• lung cancer
• metastasis
• monocytes/macrophages

Acknowledgments

We thank Arturo Martínez-Arroyo for exosomes characterisation; Covadonga Aguado and Francisco Rafael Urbano for electron-microscopyy technical assistance; José Luis Martín-Ventura for LDL reagents; Daniel Pando for Transfectosome® technology; Ismael Morales-Flores for informatics support; María Elena Mansilla for karyotype assistance; Jose Casas, Aníbal Varela and Aurora Muñoz for technical assistance.

Disclosure of potential conflicts of interest

No potential conflicts of interest were disclosed.

Ethics approval and consent to participate

This study was approved by the Committee for Human Subjects of La Paz University Hospital (HULP: PI-3521) and the Clinical Research Ethics Committees of the Hospitals of Madrid (17.10.1125-GHM). Written informed consent was obtained from all participants. All animal studies were approved by the Ethics Committee for Animal Research from La Paz University Hospital (CSIC: 733/2018).

Supplementary material

Supplemental data for this article can be accessed on the publisher’s website.

Additional information

Funding

Research in the laboratory of EL-C was supported by “Fundación para la Investigación Biomédica La Paz Hospital” ((FIBHULP) and “Fundación Familia Alonso”.