Design and in vitro assessment of L-lactic acid-based copolymers as prodrug and carrier for intravitreal sustained L-lactate release to reverse retinal arteriolar occlusions Marieke Veurink a , Lutz Asmus a , Maren Hennig b , Béatrice Kaufmann a , Lena Bagnewski b , Arnd Heiligenhaus b , Efstratios Mendrinos c , Constantin J. Pournaras c , Robert Gurny a , Michael Möller a,⇑ a School of Pharmaceutical Sciences, University of Geneva, University of Lausanne, 1211 Geneva, Switzerland b Department of Ophthalmology, St. Franziskus Hospital, Muenster, Germany c Department of Ophthalmology, Geneva University Hospitals, 1211 Geneva, Switzerland article info Article history: Received 4 October 2012 Received in revised form 21 February 2013 Accepted 27 February 2013 Available online 14 March 2013 Keywords: L-lactate Retinal vasodilation Biocompatibility Biodegradable copolymers Sustained release Intravitreal injection abstract Ophthalmic conditions in which the retinal vasculature is obstructed generally lead to vision loss. Admin- istration of the vasodilator L-lactate might offer a treatment strategy by restoring the blood flow, but unfortunately its effect after single intravitreal injection is short-lived. This study describes a concept in which the sustained release of L-lactic acid from a biodegradable copolymer system is investigated. The 50:50 (n/n) copolymer system, composed of L-lactic acid and L,D-2-hydroxyoctanoic acid, is a viscous injectable that will form an intravitreal drug depot. Hydrolysis of the copolymer will automatically lead to the release of L-lactic acid, which will convert to L-lactate at physiological pH, thereby providing a car- rier and pro-drug in one. In vitro and ex vivo release studies demonstrate an L-lactic acid release over sev- eral weeks. Biocompatibility of the co-polymer and its degradation products is shown on a human retinal pigment epithelial cell line and on ex vivo retinal tissues. A low molecular weight copolymer (1200 g/mol) with low polydispersity has promising properties with a constant release profile, good biocompatibility and injectability. Ó 2013 Elsevier B.V. All rights reserved. 1. Introduction Many sight threatening ophthalmic conditions cause obstruc- tion of the retinal vasculature. Such posterior segment diseases might be treated by administration of vasodilative drugs, which re- store the blood flow in the obstructed vessels. The retinal vascula- ture lacks autonomic innervations (Ye et al., 1990) and therefore, retinal blood flow is most probably controlled locally through the release of vasoactive substances by the retinal tissues (Brown and Jampol, 1996). Although the exact mechanism of retinal vasodila- tion has not been fully elucidated, the endogenous compound L-lactate is involved in this mechanism because its intravenous administration results in dilation of retinal vessels (Garhöfer et al., 2003). Moreover, intravitreal injections of L-lactate in mini- pigs induce vasodilation of retinal arteries both in healthy eyes and in eyes in which acute branch retinal vein occlusion is evoked (Brazitikos et al., 1993; Mendrinos et al., 2008, 2011). Based on these observations and on the fact that L-lactate is an endogenous substance present in the eye, it is envisaged a potential drug candi- date for the treatment of posterior segment diseases in which the retinal vasculature is obstructed. However, one major disadvantage of a single intravitreal injection of an L-lactate solution is its limited duration of action of approximately 15 min (Brazitikos et al., 1993). This is due to the fact that elimination from the eye depends on the size of the molecule, resulting in short half-lives for molecules like L-lactate (Mw 89 Da) with a molar mass <500 Da. Consequently, fre- quent injections are necessary to maintain therapeutic drug levels (Trimawithana et al., 2011). In order to prolong the therapeutic ef- fect, a sustained intraocular release system is envisaged, ideally releasing L-lactate over a period of several weeks. The therapeutic benefit of such a system would be an immediate intervention to overcome the vascular obstruction, thereby preventing angiogene- sis and giving time to plan further surgery. For a suitable intraocular sustained release formulation, several challenges and limitations should be taken into account. First, the volume of injection is linearly related to the intraocular pressure (IOP) (Pallikaris et al., 2005), limiting the formulation volume that can be administered. Currently used volumes do not exceed 0.1 ml per injection (Bakri et al., 2009). Second, posterior segment diseases are difficult to treat because of the layer-like structure of the eye, which serves as protection barrier for the sensitive inner 0928-0987/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ejps.2013.02.021 ⇑ Corresponding author. Address: School of Pharmaceutical Sciences, University of Geneva, Quai Ernest-Ansermet 30, 1211 Geneva 4, Switzerland. Tel.: +41 22 379 31 32; fax: +41 22 379 65 67. E-mail address: Michael.Moeller@unige.ch (M. Möller). European Journal of Pharmaceutical Sciences 49 (2013) 233–240 Contents lists available at SciVerse ScienceDirect European Journal of Pharmaceutical Sciences journal homepage: www.elsevier.com/locate/ejps