A promising development in photodynamic therapy (PDT) is the use of two-photon excitation (TPE). The confinement of the excitation volume leads to the possibility of subcellular PDT. Thus, in order to design a treatment protocol, one must be aware of where a photosensitizer localizes in a cell and the individual differences, both between cellular localization sites and individual cells. One way to determine the subcellular location is to observe photobleaching dynamics in cells and compare the rate constants to those observed in solvents which have been chosen to model different characteristics of environments, such as polarity. We have observed the photobleaching behaviour of Verteporfm (VP) in a variety of solvents and single cells and have been able to correlate subcellular position with environmental polarity.
Drugs used in disease treatment can cause damage to both malignant and normal tissue. This toxicity limits the maximum therapeutic dose. Drug targeting is of high interest to increase the therapeutic efficacy of the drug without increasing systemic toxicity. Certain tissue abnormalities, disease processes, cancers, and infections are characterized by high levels of activity of specific extracellular and/or intracellular proteases. Abnormally high activity levels of specific proteases are present at sites of physical or chemical trauma, blood clots, malignant tumors, rheumatoid arthritis, inflammatory bowel disease, gingival disease, glomerulonerphritis, and acute pancreatitis. Abnormal protease activity is suspected in development of liver thrombosis, pulmonary emphysema, atherosclerosis, and muscular dystrophy. Inactiviating disease-associated proteases by the administration of appropriate protease inhibitors has had limited success. Instead, one could use such proteases to target drugs to treat the condition. Protease mediated drug delivery offers such a possibility. Solubilizing groups are attached to insoluble drugs via a polypeptide chain which is specifically cleavable by certian proteases. When the solubilized drug enounters the protease, the solubilizing moieties are cleaved, and the drug precipitates at the disease location. Thus, a smaller systemic dosage could result in a therapeutic drug concentration at the treatment site with less systemic toxicity.
The spectroscopy and photochemistry of protoporphyrin IX (PpIX) in ethanol and in Triton X-100 micelle solution and Verteporfin in methanol and Triton X-100 micelle solution have been examined using nea infrared two-photon excitation (TPE). TPE will allow photodynamic therapy with highly localized light dosage. For PpIX, we have determined that the photochemistry subsequent to TPE is very similar to that found for one-photon excitation. Moreover, the photoproducts observed possess very intense two-photon excitation fluorescence spectra, which allows their detection at low relative concentrations. Verteporfin displays photodynamic behavior in methanol similar to that of PpIX in ethanol. However, in micelle solution Verteporfin exhibits photodynamic behavior indicative of two sensitizer populations, excimers and monomers. Photochemical models are presented.