Drug Delivery Carriers: The PhotoTarget™ System
RetinaPharma is developing a proprietary approach to precision drug delivery by utilizing a combination of proven technologies in a novel treatment method. Termed the PhotoTarget™ drug delivery system, its primary emphasis has been on delivery of drugs and dyes to the back of the eye.
The key advance is the development of materials and methods for Light-Targeted Delivery (‘LTD’) of drugs and diagnostic imaging dyes to the vasculature of the retina. The approach involves intravenous administration of heat-sensitive liposomal encapsulated drugs or dyes. The contents of the liposomes are released by administration of a short, low-intensity pulse of light delivered through the pupil to the back of the eye. The light causes a noninvasive, gentle warming of the drug carriers and the local target tissue (retinal or choroidal blood vessels). This results in release of a small bolus of drug or dye from circulating liposomes. The intensity of the light alone is insufficient to damage either the targeted or the surrounding tissues.
The technology utilizes a combination of proven technologies in a novel treatment method, with the potential to redefine the standard in ophthalmic posterior chamber drug delivery (ophthalmic photodynamic therapy, angiogenesis-inhibitors, siRNA, etc).
Liposome (artificial lipid spheres) with its encapsulated drug (left) releases its contents through mild, non-damaging heat (right). This targeted method permits very precise control over affected tissues.
The PhotoTarget drug delivery system incorporates the application of a second-generation liposome technology that allows for the release of a drug precisely at the time and location desired, with limited release elsewhere in the body. The liposome vesicles are microscopic hollow spheres made of artificial phospholipids. They encapsulate active substances including water soluble drug or dye. The encapsulated drug or dye is then injected intravenously into the bloodstream. Upon intentional rupture of the lipid vesicles the drug or dye is released. The release of drug is controlled by gentle heating, with a source of light precisely focused at the required site. The result is disruption of drug-containing liposomes that have been specially formulated to be heat-labile at 41°C (105.8°F). The heat is generated for a brief moment, and unlike laser-based photocoagulation therapies currently used, does not result in any damage to tissue.
RetinaPharma is presently commercializing two PhotoTarget compounds. One compound is for Light-Targeted Occlusion (LTO) using photodynamic drugs. The second compound uses a fluorescent dye for diagnostic angiography. It is referred to as Light-Targeted Angiography.
In Detail
LTA and LTO:
A Complementary Combination
LTA and LTO are very complementary techniques and could be used in combination to offer benefits beyond LTA or LTO alone:
- LTA allows for more precise LTD targeting of CNV feeder vessels.
- Therapy could proceed immediately after completion of diagnostic angiography.
- Use of dye and drug together could allow for repeated sequences of visualization and treatment, until full occlusion of target CNV is effected.