Non-invasive Fluorescence Imaging of Breast Cancer Metastasis to the Brain in an Orthotopic Nude-mouse Model With Very-narrow-band-width Laser Excitation of Red Fluorescent Protein Resulting in an Ultra-bright Signal Without Skin Autofluorescence

Abstract

Background/aim: Breast-cancer metastasis to the brain is an intractable disease. To discover improved therapy for this disease, we developed a precise non-invasively-imageable orthotopic nude-mouse model, using very-narrow-band-width laser fluorescence excitation.

Materials and methods: Female nu/nu nude mice, aged 4-8 weeks, were inoculated through the midline of the skull with triple-negative human MDA-MB-231 breast cancer cells (5×10⁵) expressing red fluorescent protein (RFP). The mice were imaged with the Analytik Jena UVP Biospectrum Advanced at 520 nm excitation with peak emission at 605 nm.

Results: Three weeks after injection of MDA-MB-231-RFP cells in the brain, non-invasive fluorescence images of the breast tumor growing on the brain were obtained. The images of the tumor were very bright, with well-defined margins with no detectable skin autofluorescence background. Images obtained at various angles showed that the extent of the tumor margins could be precisely measured. A skin flap over the skull confirmed that the tumor was growing on the surface of the brain which is a frequent occurrence in breast cancer.

Conclusion: A precise orthotopic model of RFP-expressing breast-cancer metastasis to the brain was developed that could be non-invasively imaged with very-narrow-band-width laser excitation, resulting in an ultra-bright, ultra-low-background signal. The model will be useful in discovering improved therapeutics for this recalcitrant disease.

Keywords: Breast cancer; brain metastasis; excitation; laser; low background; non-invasive imaging; nude mouse; orthotopic; red fluorescent protein.