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

Background/Aim: Breast-cancer metastasis to the brain is an intractable disease. To discover improved therapy for this disease, we developed a precise non-invasivelyimageable orthotopic nude-mouse model, using very-narrowband-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 (5x105) 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, noninvasive 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.