Hydrosilylated porous silicon particles function as an intravitreal drug delivery system for daunorubicin

Abstract

Purpose: To evaluate in vivo ocular safety of an intravitreal hydrosilylated porous silicon (pSi) drug delivery system along with the payload of daunorubicin (DNR).

Methods: pSi microparticles were prepared from the electrochemical etching of highly doped, p-type Si wafers and an organic linker was attached to the Si-H terminated inner surface of the particles by thermal hydrosilylation of undecylenic acid. DNR was bound to the carboxy terminus of the linker as a drug-loading strategy. DNR release from hydrosilylated pSi particles was confirmed in the excised rabbit vitreous using liquid chromatography-electrospray ionization-multistage mass spectrometry. Both empty and DNR-loaded hydrosilylated pSi particles were injected into the rabbit vitreous and the degradation and safety were studied for 6 months.

Results: The mean pSi particle size was 30×46×15 μm with an average pore size of 15 nm. Drug loading was determined as 22 μg per 1 mg of pSi particles. An ex vivo drug release study showed that intact DNR was detected in the rabbit vitreous. An in vivo ocular toxicity study did not reveal clinical or pathological evidence of any toxicity during a 6-month observation. Hydrosilylated pSi particles, either empty or loaded with DNR, demonstrated a slow elimination kinetics from the rabbit vitreous without ocular toxicity.

Conclusions: Hydrosilylated pSi particles can host a large quantity of DNR by a covalent loading strategy and DNR can be slowly released into the vitreous without ocular toxicity, which would appear if an equivalent quantity of free drug was injected.

FIG. 1.

Scanning electron microscope image of porous silicon (pSi) microparticles (A), close-up scanning electron microscopic view of one of the microparticles, revealing the mesoporous structure (B).

FIG. 2.

Fourier-Transform-Infrared (FTIR) spectra of empty and daunorubicin (DNR)-loaded porous silicon (pSi) microparticles. Conjugation of the drug molecule generates bands in the FTIR spectrum indicative of the formation of a linkage through amide bond (arrows).

FIG. 3.

Thermogravimetric analysis curves of pSi particles hydrosilylated with undecylenic acid (empty pSi) and pSi particles containing DNR covalently attached to the pore walls as described in the text (DNR-loaded pSi). Weight percent is reported relative to the initial weight of sample, before heating. A weight increase was observed due to the oxidation of pSi to porous silica (pSiO₂). The weight difference between empty pSi and DNR-loaded pSi accounts for the organic matter corresponding to the drug loaded into the particles.

FIG. 4.

Selected reaction monitoring liquid chromatography–electrospray ionization–multistage mass spectrometry of DNR released from DNR-loaded pSi microparticles in upper vitreous fluid taken at 24 h (a), 120 h (b), and 192 h (c). Pure vitreous showed as a control (d). Doxorubicin (DOX) was used as an internal standard.

FIG. 5.

Fundus photographs of DNR-loaded hydrosilylated pSi particles (A, B) and empty hydrosilylated pSi particles (C, D) in the rabbit eyes. Focus of the images was on the particles instead of on the retina. The photograph (A) shows DNR-loaded particles in the vitreous 1 week after intravitreal injection (arrow), (B) demonstrates a reduction in the amount of particles after 3 months in the same eye, but the color was barely changed (arrow), indicating simultaneous particle degradation and drug release. (C) shows the typical bright vivid color of empty pSi (arrow) taken at 2 months with a major change of amount and color after 6 months (D) and the degraded pSi looked whitish and dull (arrow). Color images available online at www.liebertpub.com/jop

FIG. 6.

Retinal cross sections imaged by light microscopy of the eyes harvested from a rabbit 3 months (R83) and another rabbit 6 months (R32) after intravitreal injection of DNR-loaded hydrosilylated porous Si particles (taken at 62.5×magnification). Images show a normal retina and choroid in pairs of 2 eyes of the same rabbit. The left eyes (OS) were the control eyes and the right eyes (OD) were the study eyes injected with DNR-loaded pSi particles.