[Novel approach for management of age-related macular degeneration--antiangiogenic therapy and retinal regenerative therapy].

Age-related macular degeneration (AMD) is a leading cause of legal blindness in developed countries. Even with the recent advent of several treatment options, treatment of exudative AMD, characterized by choroidal neovascularization (CNV), remains difficult. Thus, in this review article, we report on the investigation of novel approaches for the management of AMD, antiangiogenic therapy for CNV, and retinal regenerative therapy. Polyion complex(PIC) micelles have a range in size of several tens of nanometers formed through an electrostatic interaction, and accumulate in solid tumors through an enhanced permeability and retention(EPR) effect. In this study, we examined the distribution of the PIC micelles which encapsulate fluorescein isothiocyanate-labeled poly-L-lysine{FITC-P(Lys)} in experimental CNV in rats, to investigate whether PIC micelles can be used for the treatment of CNV. We demonstrated that PIC micelles accumulate in the CNV lesions and are retained in the lesions for as long as 168 hours after intravenous administration. These results raise the possibility that PIC micelles can be used for achieving an effective drug delivery system against CNV. Although photodynamic therapy (PDT) is a very promising treatment for AMD, most patients require repeated treatments. For effective PDT against AMD, the selective delivery of a photosensitizer to the CNV lesions and an effective photochemical reaction at the CNV site are necessary. The characteristic dendritic structure of the photosensitizer prevents aggregation of its core sensitizer, thereby inducing a highly effective photochemical reaction. We present an effective PDT for AMD employing a supramolecular nanomedical device, i.e., a novel dendritic photosensitizer encapsulated in a polymeric micelle formulation. With its highly selective accumulation in CNV lesions, this treatment resulted in a remarkably efficacious CNV occlusion with minimal unfavorable phototoxicity. Our results will provide a basis for an effective approach to PDT for AMD. Spatial control of gene transfection in the body is a core issue in the gene therapy for ocular diseases including AMD. Photochemical internalization (PCI) is a technology that effects light-induced delivery of DNA directly inside cells. PCI usually requires that a photosensitizer be added to the drug-delivery system to photochemically destabilize the endosomal membrane. We have developed a ternary complex composed of a core containing DNA packaged with cationic peptides and enveloped in the anionic dendrimer, phthalocyanine, which provides the photosensitizing action. Subconjunctival injection of the ternary complex followed by laser irradiation resulted in transgene expression only in the laser-irradiated site in rats. This PCI-mediated gene delivery system is potentially useful in gene therapy for ophthalmic diseases. Accumulation of lipofuscin is related to an increased risk of AMD. We report that a major lipofuscin component, A2E(N-retinyledin-N-retinylethanolamin), activates the retinoic acid receptor (RAR). In vivo experiments suggest that A2E accumulation results in the pro-angiogenic conversion of retinal pigment epithelial(RPE) cell phenotype. This physiological consequence of A2E accumulation may be related to a novel potential therapeutic target for CNV. To recover visual function damaged by AMD, retinal regenerative therapy is essential. We investigated whether subretinal transplantation of bone marrow mesenchymal stem cells(MSCs) promotes photoreceptor survival in a rat model of retinal degeneration. Morphological and functional studies in vivo, including histological analysis and electrophysiological studies, indicate that the subretinal transplantation of MSCs delays retinal degeneration and preserves retinal function. These results suggest that MSC is a useful cell source for cell-transplantation therapy for retinal degeneration. In order to elucidate the molecular mechanisms of development of the fovea, which is composed mainly of cone photoreceptors and is susceptible to injury from AMD, we performed a comparative gene expression analysis between the central and peripheral regions of the monkey retina using monkey (rhesus macaque) genome microarray chips. We then selected the clones which were expressed at significantly higher levels in the central region and confirmed their expression in the monkey retina by section in situ hybridization. This study sheds light on the mechanisms of foveal development and may lead to the development of regenerative medicine for cone photoreceptors.