Harnessing subcellular-resolved organ distribution of cationic copolymer-functionalized fluorescent nanodiamonds for optimal delivery of therapeutic siRNA to a xenografted tumor in mice

TL;DR

This study introduces a high-resolution imaging method to quantify fluorescent nanodiamonds in mouse tissues, demonstrating their potential for targeted siRNA delivery to inhibit tumor oncogenes effectively.

Contribution

The paper presents a novel automated quantification technique using time-delayed fluorescence microscopy for nanodiamond biodistribution analysis in vivo.

Findings

Nanodiamonds can be accurately quantified in tissues with subcellular resolution.

Systemic injection results in low nanodiamond accumulation in tumors.

Direct tumor injection of nanodiamonds achieves significant oncogene inhibition.

Abstract

Diamond nanoparticles (nanodiamonds) can transport active drugs in cultured cells as well as in vivo. However, in the latter case, methods allowing to determine their bioavailability accurately are still lacking. Nanodiamond can be made fluorescent with a perfectly stable emission and a lifetime ten times longer than the one of tissue autofluorescence. Taking advantage of these properties, we present an automated quantification method of fluorescent nanodiamonds (FND) in histological sections of mouse organs and tumor, after systemic injection. We use a home-made time-delayed fluorescence microscope comprising a custom pulsed laser source synchronized on the master clock of a gated intensified array detector. This setup allows to obtain ultra-high-resolution images 120 Mpixels of whole mouse organs sections, with subcellular resolution and single-particle sensitivity. As a proof-of-principle experiment, we quantified the biodistribution and aggregation state of new cationic FNDs able to transport small interfering RNA inhibiting the oncogene responsible for Ewing sarcoma. Image analysis showed a low yield of nanodiamonds in the tumor after intravenous injection. Thus, for the in vivo efficacy assay we injected the nanomedicine into the tumor. We achieved a 28-fold inhibition of the oncogene. This method can readily be applied to other nanoemitters with $\approx$100 ns lifetime.