A goal of our laboratory is to accurately define the parameters of light dose and drug dose that contribute to tissue destruction after Photodynamic therapy (PDT). Using Photofrin as sensitizer, we examined a range of drug doses, various intervals between injection and light treatment, and various fluence rates. The effect of Photofrin photosensitizer encapsulated in liposomal delivery vehicle was also studied. Three liposome delivery vehicles were chosen to deliver the photosensitizer in vivo: DPPC/cholesterol, DMPC/HPC and stealth liposomes. Tumor response and microvessel behaviour were examined in tumor and surrounding skin in a mouse model.
Under these conditions, better selectivity of tissue damage was seen using some of the treatment. These data might be used to design better clinical protocols for patient care. In memory of Dr. Victor Fingar (Supported by R01 CA51771).
Bacteriopheophorbide molecules are second-generation photosensitizers with promise for PHotodynamic Therapy applications due largely to their absorption peaks in the near-Infrared region. Palladium bcteriopheophorbide, also called TOOKAD, has been successfully evaluated in several pre-clinical animal models. In this study the effect on tumor and normal vasculature was evaluated using an intravital vascular model on mouse cremaster muscle implanted with the RIF tumor. For tumor response studies, the same RIF tumor was implanted intradermally on the right flank and regression was evaluated for 42 days or until the tumor reached a 12 mm diameter.
A light dose 300 J/cm2 were delivered at 763 nm with power density of 100 mW/cm2. Photosensitizer dose was 4 mg/kg body weight. Mice were treated immediately, 10 minutes, 30 minutes, or 24 hours after injection. Only the higher light dose (300 J/cm2) delivered 10 minutes after injection produced a reproducible and complete vascular and tumor response after PDT in these animals. In the cremaster-tumor model, arterioles and venules partially shutdown as early as 40 minutes after the beginning of treatment, while tumor neovasculature was irreversibly closed within 20 minutes of treatment. Tumor response studies demonstrated that the magnitude of vascular stasis correlates with tumor regression studies. Further studies using this photosensitizer are warranted, given its short clearance time and its near-Infrared activation wavelength.
The phototoxicity of PDT in cell culture can be promoted by the relatively hydrophilic bile acid UDCA (ursodeoxycholic
acid). This was attributed to a conformational change in the anti-apoptotic protein Bcl-2, leading to an enhanced sensitivity
to photodamage by sensitizers that target sites of Bcl-2 localization. UDCA also promoted the binding and inactivation of
Bcl-2 by the non-peptidic antagonist HA14- 1, suggesting that UDCA may also be useful for promoting chemotherapy
designed to target Bcl-2. In tumor-bearing animals, addition of UDCA to a PDT protocol involving the tin etiopurpurin
SnET2 resulted in enhanced cancer control, but there was no effect on the extent of PDT-induced vascular shut-down.
These results are consistent with the propo proposal that UDCA only promotes direct tumor cell kill. In this report, we have
sal summarized recent research relating to mode of action of UDCA as it effects the on the efficacy of photodynamic therapy
where Bcl-2 is among the PDT targets, and discuss the implications of the results.
Photodynamic therapy, PDT, has mainly been done clinically using laser systems. The use of lasers to treat cutaneous lesions is not necessary. In order to provide a more efficient and cost effective light source for the PDT treatment of cutaneous lesions, a clinical based light emitting diode (LED) system has been developed. The system include a tight density packing of AlGaAs high-brightness LEDs to produce incident irradiance values up to 200 MW/cm2. Initial systems have wavelengths of 665 nm and exhibit a bandwidth of 25 nm, FWHM. Other wavelengths are also possible. The system includes on-line dosimetry through an isotropic probe to permit the use to simply choose a dose, J/cm2. the system has been tested against a KTP/dye laser for the photosensitizer SnET2 to determine its equivalence to a monochromatic source.
The detection and quantification of the concentration of exogenous chromophores in-vivo by their fluorescence is complicated by many physical and geometrical parameters. Measurement of such signals is advantageous in determining the pharmacokinetics of photosensitizers such as those used in photodynamic therapy (PDT) or to assist in the diagnosis of tissue histological state. To overcome these difficulties a ratio based fiber optic contact fluorometer has been developed. This fluorescence detection system (FDS) uses the ratio of the fluorescence emission peak of the exogenous chromophore to that of endogenous chromophores, i.e. autofluorescence, to correct for a variety of parameters affecting the magnitude of the measured signals. By doing so it also minimizes the range of baseline measurements prior to exogenous drug injection, for various tissue types. Design of the FDS and results of its testing in animals and patients using the second generation photosensitizer Tin ethyletiopurpurin (SnET2) are presented. These results support the feasibility and usefulness of the Ratio FDS system.
AlGaInP diode lasers generate optical output in a range of the spectrum suitable for the activation of several second=generation photosensitizers including tin ethyl etiopurpurin, SnET2. The development of a system suitable for this application entails coupling the output of multiple highly divergent and astigmatic sources into a single optical fiber for most applications. Various methods of fulfilling this requirement will be discussed along with the advantages and drawbacks of each method. The incorporation into the clinical laser system of on-line dosimetry control of the light delivery parameters will be described along with the results of biological equivalency studies.
For a number of well-defined reasons, research into the development of alternative photosensitizers to PhotofrinTM, for use in Photodynamic Therapy, continues. The efforts described in this paper cover the study of a number of sensitizers absorbing at different wavelengths, which may have selective applications in the field of photomedicine. In one approach, the use of tetraazoporphyrins (porphyrazines) as sensitizers is studied. Although related tetramacrocyclic systems such as porphyrins and phthalocyanines have been, and continue to be, well studied in this field, porphyrazines have, to-date, received little attention. In a second study, purpurins are examined as possible alternatives to PhotofrinTM. In a recent study, tissue distribution properties of tin etiopurpurin dichloride, as a function of time, were examined. Results indicate that this purpurin continues to show promise for applications in PDT.
The majority of second generation sensitizers being proposed as possible alternatives to
hematoporphyrin derivative, in photodynamic therapy, are hydrophobic in nature. Consequently,
specific carrier systems have to be developed for in vivo administration. As an attempt to understand
the interactions of these delivery systems in vivo, plasma binding properties of the sensitizer SnET2
complexed with liposomes, emulsions or cyclodextrins have been studied. Additional studies have
investigated the effect of the carrier system on the cytotoxicity of SnET2 on transplantable tumors.
Preliminary data suggest that tumor response may be mediated by the choice of carrier system.
Further studies appear to be necessary before the optimum thug/carrier system complex can be
defined.
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