Specific visualization of tumor cells using upconversion nanophosphors.

The development of targeted constructs on the basis of photoluminescent nanoparticles with a high photo- and chemical stability and absorption/emission spectra in the "transparency window" of biological tissues is an important focus area of present-day medical diagnostics. In this work, a targeted two-component construct on the basis of upconversion nanophosphors (UCNPs) and anti-tumor 4D5 scFv was developed for selective labeling of tumor cells overexpressing the HER2 tumor marker characteristic of a number of human malignant tumors. A high affinity barnase : barstar (Bn : Bs) protein pair, which exhibits high stability in a wide range of pH and temperatures, was exploited as a molecular adapter providing self-assembly of the two-com- ponent construct. High selectivity for the binding of the two-component 4D5 scFv-Bn : UCNP-Bs construct to human breast adenocarcinoma SK-BR-3 cells overexpressing HER2 was demonstrated. This approach provides an opportunity to produce similar constructs for the visualization of different specific markers in pathogenic tissues, including malignant tumors. k E y WORDS upconversion nanophosphors; biomarker imaging; anti-tumor antibodies; self-assembly; HER2. ABBREVIATIONS EDC - 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide; HER2 - human epidermal growth factor receptor 2; PBS - phosphate buffered saline; scFv - single chain variable antibody fragment; sulfo-NHS - N-hydroxysulfosuccinimide; Bn - barnase; Bs - barstar; BSA - bovine serum albumin; UCNPs - upconversion nanophosphors; PAAG - polyacrylamide gel; PMAO - poly(maleic anhydride-alt-1-octadecene) amphiphilic polymer; TEM - transmission electron microscopy.