Research paper Silk hydrogels for sustained ocular delivery of anti-vascular endothelial growth factor (anti-VEGF) therapeutics Michael L. Lovett a,b , Xiaoqin Wang a , Tuna Yucel a,b , Lyndsey York a , Marc Keirstead a , Linda Haggerty a , David L. Kaplan a,⇑ a Tufts University, Department of Biomedical Engineering, Medford, MA, USA b Ekteino Laboratories, Waltham, MA, USA article info Article history: Received 21 September 2014 Accepted in revised form 22 December 2014 Available online xxxx Keywords: Silk fibroin Sustained drug delivery Hydrogel Bevacizumab Controlled release Biodegradation abstract Silk hydrogels were formulated with anti-vascular endothelial growth factor (anti-VEGF) therapeutics for sustained ocular drug delivery. Using silk fibroin as a vehicle for delivery, bevacizumab-loaded hydrogel formulations demonstrated sustained release of 3 months or greater in experiments in vitro as well as in vivo using an intravitreal injection model in Dutch-belted rabbits. Using both standard dose (1.25 mg bevacizumab/50 lL injection) and high dose (5.0 mg bevacizumab/50 lL injection) hydrogel formulations, release concentrations were achieved at day 90 that were equivalent or greater than those achieved at day 30 with the positive standard dose control (single injection (50 lL) of 1.25 mg bevacizumab solution), which is estimated to be the therapeutic threshold based on the current dosage administration schedule of 1 injection/month. These gels also demonstrated signs of biodegradation after 3 months, suggesting that repeated injections may be possible (e.g., one injection every 3–6 months or longer). Due to its pharmacokinetic and biodegradation profiles, this delivery system may be used to reduce the frequency of dosing for patients currently enduring treatment using bevacizumab or other anti-VEGF therapeutics. Ó 2015 Elsevier B.V. All rights reserved. 1. Introduction Age-related macular degeneration (AMD) is an eye condition characterized by the loss of central vision and is a leading cause of blindness and visual impairment worldwide [1]. Early and inter- mediate signs of AMD include pigment disruption and extracellular deposits called drusen, generally resulting in minimal visual impairment. During the advanced stages of AMD, however, vision loss occurs via two processes: geographic atrophy (late dry form), characterized by degradation of retinal photoreceptors and the ret- inal pigment epithelium, or neovascular AMD (wet form), charac- terized by the presence of fluid and blood in the back of the eye due to abnormal blood vessel formation [2–4]. Due to its broad impact on an aging population, the development of more effective treatments for AMD and comparison between treatments remain active fields of research. To date, therapeutic approaches have mainly focused on the more severe, wet form of AMD, and include photodynamic therapy as well as anti-VEGF therapeutics. In 2000, the light-activated drug verteporfin (Visudyne Ò , Novartis/Valeant Pharmaceuticals) was approved by the Food and Drug Administration (FDA) for the treatment of wet AMD. During treatment, verteporfin is infused intravenously before applying laser treatment in the eye to activate the drug, resulting in damage to the local endothelium and vessel occlusion [3]. This therapy typically requires several treatments (repeated every 3 months) and necessitates that the patient avoids exposure to light for at least 48 h post-treatment [5]. Over time, this photodynamic approach has largely been replaced by intravitreal injections of anti-VEGF therapeutics as the current standard of care [6]. The first drug to be approved by the FDA in 2004, pegaptanib sodium (Macugen Ò , Eyetech/Valeant Pharmaceuticals) is a PEGylated aptamer which selectively binds to VEGF-A 165 , prevent- ing it from binding to its endothelial cell receptor, and thus inhibit- ing blood vessel formation [3,4,7]. It is administered by intravitreal injection (0.3 mg/dose) every 6 weeks [3]. Another VEGF inhibitor, ranibizumab (Lucentis Ò , Genentech) was approved by the FDA in 2006 and is derived from the Fab fragment of bevacizumab (Avastin Ò , Genentech), a recombinant, humanized monoclonal anti- body that binds all isoforms of VEGF-A and is currently approved for treatment of metastatic colorectal cancer [7]. As the parent antibody http://dx.doi.org/10.1016/j.ejpb.2014.12.029 0939-6411/Ó 2015 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tufts University, Department of Biomedical Engineering, 4 Colby Street, Medford, MA 02155, USA. Tel.: +1 617 627 3251; fax: +1 617 627 3231. E-mail address: David.Kaplan@tufts.edu (D.L. Kaplan). European Journal of Pharmaceutics and Biopharmaceutics xxx (2015) xxx–xxx Contents lists available at ScienceDirect European Journal of Pharmaceutics and Biopharmaceutics journal homepage: www.elsevier.com/locate/ejpb Please cite this article in press as: M.L. Lovett et al., Silk hydrogels for sustained ocular delivery of anti-vascular endothelial growth factor (anti-VEGF) ther- apeutics, Eur. J. Pharm. Biopharm. (2015), http://dx.doi.org/10.1016/j.ejpb.2014.12.029