Abstract
Therapeutic resistance of cerebral secondary tumours largely depends on unique aspects linked to the neurovascular unit, especially cerebral endothelial cells and astrocytes. By using advanced microscopy techniques, here we explored novel mechanisms related to the neurovascular unit during extravasation and proliferation of triple negative breast cancer cells in the brain. Metastatic mammary carcinoma cells arrested and elongated within one hour in cerebral microvessels, but their number decreased by almost 80% in the first two days. Interestingly, malignant cells induced vasoconstriction and development of intraluminal endothelial plugs, which isolated invading cells from the circulation. During diapedesis – which usually took place on day four and five after inoculation of the tumour cells – continuity of cerebral endothelial tight junctions remained intact, indicating migration of cancer cells through the transcellular pathway. In addition, metastatic cells induced formation of multiluminal vessels and claudin-5-positive endothelial blebs. However, even severe endothelial blebbing could be reversed and the vessel morphology was restored shortly after the tumour cells completed transendothelial migration. Similar to neuro-inflammatory leukocytes, tumour cells migrated not only through the endothelial layer, but through the glia limitans perivascularis as well. Nevertheless, along with the growth of metastatic lesions by co-option of pre-existing capillaries, astrocytes and astrocyte end-feet were gradually expelled from the vessels to the border of the tumour. Taken together, we identified previously unknown mechanisms involved in the reaction of brain resident cells to invading breast cancer cells. Our results contribute to a better understanding of the complex cross-talk between tumour cells and host cells in the brain, which is essential for the identification of new therapeutic targets in this devastating disease.
Highlights
Brain metastases, most often originating from lung cancer, breast cancer and melanoma, have a dismal prognosis
By monitoring the same brain regions in living mice using intravital two-photon microscopy, we explored the number of tumour cells/cell clusters disappearing, changing position and remaining in resting phase in the first 48 h after inoculation of triple negative, tdTomato-expressing 4T1 breast cancer cells
We found that 33.09 ± 26.97% of the cells adhered in the first hour, 31.33 ± 30.23% arrested between 1 h and 5 h and the remaining 35.58 ± 28.18% of the cells attached to the luminal side of the endothelium between 5 h and 24 h, and remained in the same location by 48 h post-inoculation (Fig. 1b)
Summary
Most often originating from lung cancer, breast cancer and melanoma, have a dismal prognosis. Cells of the neurovascular unit (NVU) have a decisive role in the fate of brain metastatic tumour cells [40]. The concept of the NVU emerged to emphasize the unique intimate relationship between brain cells and the cerebral vasculature [12]. Regulated by input from pericytes, glial cells and neurons, cerebral endothelial cells (CECs) take the centre stage of the NVU to form and maintain the BBB. In contrast to peripheral endothelial cells, CECs are connected to each other by continuous tight junctions (TJs), formed by transmembrane proteins like claudin-5 or occludin and a cytoplasmic plaque. Brain metastatic cells have to take up the challenge of opening or overcoming this tight endothelial barrier before diapedesis through brain microvessels. Tumour cells spend several days arrested in the lumen of cerebral capillaries before
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
