Perspectives for the combined use of photodynamic therapy and hyperthermia in cancer patient

Evaluation of novel nonlaser light source for endometrial ablation using 5-aminolevulinic acid

BACKGROUND AND OBJECTIVE

This research evaluated the effectiveness of a new nonlaser prototype short-arc lamp to achieve photodynamic ablation of endometrium in a rat.

STUDY DESIGN/MATERIALS AND METHODS

Thirty female Sprague-Dawley rats were divided into two groups. 5-Aminolevulinic acid (ALA), the precursor to the photosensitizer protoporphyrin IX, was injected into the left uterine horn and vehicle alone (Hyskon) was injected into the right horn of 23 rats (group 1). An additional seven rats received vehicle only into both uterine horns (group 2). Three hours later, a cylindrical diffusing optical fiber was inserted into the lumen of the uterine horns, and light treatment was delivered from either a laser or a nonlaser light source. Rats in group 1 received either 1 hour (n = 15) or 10 minutes (n = 8) of light treatment into both uterine horns. In rats in group 2, the left horn was exposed to 1 hour of light treatment. Uterine tissues were examined histologically 4 days after light treatment.

RESULTS

One hour of light exposure to the uterine horns injected with ALA produced extensive necrosis of the rat uterine wall. No difference in the magnitude of destruction was seen between the groups treated with the laser and nonlaser light sources. Ten minutes of light exposure resulted in endometrial ablation that was comparable in both the laser- and the prototype-treated groups, but the destruction of the deepest layers of the uterine wall was more consistent in the group treated with the nonlaser prototype. One hour of light treatment from either light source did not result in any histological changes in the uterine horns not exposed to ALA.

CONCLUSION

The extent of endometrial ablation in the rat uterine horn achieved with the nonlaser prototype was comparable to that achieved with the laser. Thus, the nonlaser prototype may provide a less expensive approach to photodynamic endometrial ablation.

Interstitial photodynamic therapy with the second-generation photosensitizer bacteriochlorin a in a rat model for liver metastases

Bacteriochlorin a (BCA) is a second-generation photosensitizer that is effective in tumour destruction upon illumination with light of a wavelength of 760 nm. Tissue penetration by light at this wavelength is greater compared with wavelengths at which commonly used photosensitizers are illuminated, making it possible to treat larger tumours. In a model of experimental liver metastases in rats, we measured lesion sizes after interstitial illumination of tumours at different times after intravenous administration of BCA (10 mg kg(-1) bodyweight), as well as BCA concentrations in liver and tumour tissue. In both, BCA concentrations showed a rapid decline within the first 4 h, followed by a slow decrease over the next 20 h, suggesting biphasic pharmacokinetics. No selective uptake in tumour tissue was observed. A near-linear relationship was found between lesion sizes and liver and tumour BCA concentrations, suggesting that optimal results with photodynamic therapy (PDT) could be obtained by illumination within a short time interval after administration, when tissue concentrations are highest. No severe liver toxicity was observed as indicated by serum ALAT levels. However, in all tumours evaluated, islands of vital-looking cells were present leading to tumour regrowth within 35 days. In view of the obtained lesion diameters of approximately 13 mm after BCA-PDT and the rapid clearance rate of BCA, the concept of a near-infrared absorbing photosensitizer for PDT of liver tumours is a potential interesting strategy.

Clinical and preclinical photodynamic therapy

Photodynamic therapy (PDT) is a treatment modality that utilizes a photosensitizing drug activated by laser generated light, and is proving effective for oncologic and nononcologic applications. This report provides an overview of photosensitizers, photochemistry, photobiology, and the lasers involved in photodynamic therapy. Clinical and preclinical PDT studies involving Photofrin and various second generation photosensitizers are reviewed.