In-vivo Penetration of WST11 to the Corneal Stroma using Dextran with Various Molecular Weights

Abstract

Purpose : To evaluate the in-vivo corneal penetration depth of the photosensitizer WST11 in saline and with dextran of different molecular weights following different impregnation times. We have demonstrated previously that WST11 followed by near infrared (NIR) light can induce ex-vivo and in-vivo corneal stiffening. Its penetration in the cornea determines its tissue effect and safety.

Methods : Eyes of anesthetized rabbits were incubated after corneal deepithelization with 2.5 mg/mL WST11 in saline or in 20% dextran of 6kD, 70kDa and 500kDa molecular weight for 10 and 30 minutes. After euthanization, corneal sagittal slices were prepared using cryomicrotome. Fluorescence microscopy detected corneal stromal WST11 penetration depth. In eyes incubated with WST11 in 20% dextran 500kDa (WST11-D500) anterior chamber humor was drawn after incubation and WST11 concentration was assessed spectroscopically and by Inductively coupled plasma mass spectrometry (ICP-MS).

Results : WST11 in saline crossed ~0.7 of the corneal stromal depth within 10 minutes of incubation and the entire stromal depth after 30 minutes of incubation. The addition of dextran attenuated the stromal penetration according to dextran’s molecular weight. The 10 minutes penetration of WST11 formulated with 6kD, 70kDa and 500kDa dextran was ~0.7, ~0.5 and ~0.5 of stromal depth, respectively. After 30 minutes of incubation with WST11 formulated with 6kD, 70kDa and 500kDa dextran the stromal penetration reached ~0.85, ~0.7 and ~0.7 respectively. With the heavier 500kDa dextran, even after 30 minutes of incubation, there was a sharp decline in the intensity of the fluorescence levels at 0.5-0.6 of the corneal stromal depth. No detectable levels of WST11 were observed in the anterior chamber by spectroscopy and ICP-MS.

Conclusions : We demonstrated in-vivo that the addition of high molecular weight dextran to WST11 limits its penetration into the deepithelized corneal stroma. This feature increases the safety of the treatment by confinement of the photodynamic effect away from the endothelium. This newly described phenomenon may be applied to other drugs or tissues.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.