Prospects for the Use of Upconverting Nanoparticles as a Contrast Agent for Enumeration of Circulating Cells in vivo

Prospects for the Use of Upconverting Nanoparticles as a Contrast Agent for Enumeration of Circulating Cells in vivo

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Peter B Bartosik,1 Jessica E Fitzgerald,1 Mirna El Khatib,2 Mohammad A Yaseen,3 Sergei A Vinogradov,2 Mark Niedre1 1Department of Bioengineering, Northeastern University, Boston, MA, USA; 2Department of Biochemistry and Biophysics, Perelman School of Medicine and Department of Chemistry, School of Arts and Sciences, University of Pennsylvania, Philadelphia, PA, USA; 3Athinoula A.Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Charlestown, MA, USACorrespondence: Mark Niedre Email [email protected]: We recently developed a new fluorescence-based technique called “diffuse in vivo flow cytometry” (DiFC) for enumerating rare circulating tumor cells (CTCs) directly in the bloodstream.Non-specific tissue autofluorescence is a persistent problem, as it creates a background which may obscure signals from weakly-labeled CTCs.

Here we investigated the use of upconverting nanoparticles (UCNPs) as a contrast agent for DiFC, here which in principle could significantly reduce the autofluorescence background and allow more sensitive detection of rare CTCs.Methods: We built a new UCNP-compatible DiFC instrument (U-DiFC), which uses a 980 nm laser and detects upconverted luminescence in the 520, 545 and 660 nm emission bands.We used NaYF4:Yb,Er UCNPs and several covalent and non-covalent surface modification strategies to improve their biocompatibility and cell uptake.We tested U-DiFC with multiple myeloma (MM) and Lewis lung carcinoma (LLC) cells in tissue-mimicking optical flow phantoms and in nude mice.Results: U-DiFC significantly reduced the background autofluorescence signals and motion artifacts from breathing in yale law school colors mice.

Upconverted luminescence from NaYF4:Yb,Er microparticles (UμNP) and cells co-incubated with UCNPs were readily detectable with U-DiFC in phantoms, and from UCNPs in circulation in mice.However, we were unable to achieve reliable labeling of CTCs with UCNPs.Our data suggest that most (or all) of the measured U-DIFC signal in vitro and in vivo likely arose from unbound UCNPs or due to the uptake by non-CTC blood cells.Conclusion: UCNPs have a number of properties that make them attractive contrast agents for high-sensitivity detection of CTCs in the bloodstream with U-DiFC and other intravital imaging methods.More work is needed to achieve reliable and specific labeling of CTCs with UCNPs and verify long-term retention and viability of cells.

Keywords: in vivo flow cytometry, upconverting nanoparticles, phosphorescence.