A new Chlorin formulation promotes efficient photodynamic action in choriocapillaris of rabbit's eyes

Age-related macular degeneration (AMD) as well as other choroidal diseases, demand novel therapeutic methods. Photodynamic therapy (PDT), which uses light and photosensitizer (PS) to cause specific vascular occlusion in the macula, is an interesting alternative. The only drug approved for the PDT treatment of AMD (Verteporfin) has a natural tendency to aggregate, demanding an expensive separation procedure during purification. We report a novel and affordable PS that is intrinsically protected against aggregation, the Monomeric Chlorin at High Concentration (MCHC-Chlorin), whose liposomal formulation was developed to provoke effective photodynamic action on the choroidal vasculature. Our report starts by stablishing the conditions to allow the efficient synthesis of MCHC-Chlorin in high yields (92%). We then tested the light stimulated occlusion of choriocapillary vessels in rabbit's eyes induced by the two MCHC-Chlorin isomers, which are directly obtained from the synthetic route. The PS formulation was infused in the rabbit's ear vein and eyes were immediately irradiated at 650 nm. Indirect ophthalmoscopy, fundus photography, fluorescein angiography and histopathological evaluations were used to evaluate levels of photo-thrombosis and collateral damage. Choriocapillary occlusion was achieved in all treated rabbits' eyes, while retina and sclera were completely preserved. There was no photochemical reaction in none of the eyes that received LASER without PS. Both MCHC-Chlorin isomers were separately tested and exhibited similar positive results with no systemic toxicity. Therefore, PDT occurred equally well in all treated eyes and none of the controls showed any effect in the ophthalmological exams. MCHC-Chlorin offers great potential and should be further studied as an alternative drug for choroidal diseases.