DenTimol as A Dendrimeric Timolol Analogue for Glaucoma Therapy: Synthesis and Preliminary Efficacy and Safety Assessment

In this work, we report the synthesis and characterization of DenTimol, a dendrimer-based polymeric timolol analog, as a glaucoma medication. A timolol precursor (S)-4-[4- (oxiranylmethoxy)-1,2,5-thiadiazol-3-yl] morpholine (OTM) was reacted with the heterobifunctional amine polyethylene glycol acetic acid (amine-PEG-acetic acid, M-n = 2000 g/mol) via a ring opening reaction of an epoxide by an amine to form the OTM-PEG conjugate. OTM-PEG was then coupled to an ethylenediamine (EDA) core polyamidoamine (PAMAM) dendrimer G3 to generate DenTimol using the N-(3-(dimethylamino)propyl)-N'-ethylcarbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) coupling reaction. MALDI mass spectrometry, H-1 NMR spectroscopy, and HPLC were applied to characterize the intermediate and final products. Ex vivo corneal permeation of DenTimol was assessed using the Franz diffusion cell system mounted with freshly extracted rabbit cornea. The cytotoxicity of DenTimol was assessed using the WST-1 assay. Our results show that DenTimol is nontoxic up to an OTM equivalent concentration of 100 mu M. DenTimol is efficient at crossing the cornea. About 8% of the dendrimeric drug permeated through the cornea in 4 h. Its IOP-lowering effect was observed in normotensive adult Brown Norway male rats. Compared to the undosed eye, an IOP reduction by an average of 7.3 mmHg (similar to 30% reduction from baseline) was observed in the eye topically treated with DenTimol (2 X 5 mu L, 0.5% w/v timolol equivalent) in less than 30 min. Daily dosing of DenTimol for a week did not cause any irritation or toxicity as confirmed by the histological examination of ocular tissues, including the cornea, ciliary body, and retina.