Radioactive (90Y) upconversion nanoparticles conjugated with recombinant targeted toxin for synergistic nanotheranostics of cancer.

We report combined therapy using upconversion nanoparticles (UCNP) coupled to two therapeutic agents: beta-emitting radionuclide yttrium-90 (90Y) fractionally substituting yttrium in UCNP, and a fragment of the exotoxin A derived from Pseudomonas aeruginosa genetically fused with a targeting designed ankyrin repeat protein (DARPin) specific to HER2 receptors. The resultant hybrid complex UCNP-R-T was tested using human breast adenocarcinoma cells SK-BR-3 overexpressing HER2 receptors and immunodeficient mice, bearing HER2-positive xenograft tumors. The photophysical properties of UCNPs enabled background-free imaging of the UCNP-R-T distribution in cells and animals. Specific binding and uptake of UCNP complexes in SK-BR-3 cells was observed, with separate 90Y- and PE40-induced cytotoxic effects characterized by IC50 140 µg/mL (UCNP-R) and 5.2 µg/mL (UCNP-T), respectively. When both therapeutic agents were combined into UCNP-R-T, the synergetic effect increased markedly, ∼2200-fold, resulting in IC50 = 0.0024 µg/mL. The combined therapy with UCNP-R-T was demonstrated in vivo.