A clinical problem in the treatment of colorectal cancer is the high rate of local tumor recurrence. Adjuvant therapy methods are necessary to receive a better clinical outcome in minimizing local tumor relapse. Adjuvant intraoperative photodynamic therapy (AIOPDT) seems to be a promising alternative therapy in the treatment of malignant colorectal diseases. IN experimental settings the success of AIOPDT depends on the accumulation of the photosensitizer (PS) in tumor tissue and may be jeopardized by high mortality rates, due to inadequate energy doses. Our study evaluated mortality rates of nude mice after AIOPDT with ALA, Photofrin II and mTHPC using the following various light doses: ALA/Photofrin II: 100J, 50J, 25J; mTHPC: 30J, 15J, 5J generated by an Argon-Dye-laser system. There was a close correlation between laser energy applied for AIOPDT and postoperative mortality rate. Initial high mortality rates were lowered by stepwise reduction of the energy dose. Mortality rates reached a maximum 24 hours after AIOPDT in all groups.
The effectiveness of PDT as an adjuvant alternative therapy method for diverse malignant tumors has been investigated in numerous studies. The therapeutic benefit and extent of side effects is mainly determined by the applied photoactive substance. The second generation photosensitizer (PS) mTHPC is capable of causing selective tumor cell death in colon carcinoma when combined with laser irradiation of a PS specific wavelength. Our study revealed PDT with mTHPC as an efficient adjuvant intraoperative modality after R1/R2 resection of a subcutaneously implanted colon tumor. There was a significant increase of postoperative recurrence-free survival time using PDT compared to a control group in a colon cancer model in nude mice. The accumulation of the PS determined by point spectrometry showed a high tumor-selectivity in the tumor, tumor bed, and overlying skin compared to muscle tissue as reference parameter.
Accurate staging can be a major problem in therapeutic planning of advanced abdominal malignancies. We experimentally combined conventional staging laparoscopy with aminolevulinic acid (ALA) induced fluorescence diagnosis (FD) to improve the detection of disseminated peritoneal tumors. Using different photosensitization times and ALA concentrations we evaluated the optimal fluorescence parameters for laparoscopic fluorescence diagnosis of intra abdominal tumor spread. In a rat tumor model we performed conventional and fluorescence laparoscopy to determine the increase of sensitivity gained by FD in terms of additionally detected lesions. After laparoscopic examination, the fluorescence emission from the tumors was spectrometically analyzed. Serum levels of ALA and PpIX were measured by HPLC to determine their systemic metabolism. Fluorescence staging laparoscopy was able to visualize even macroscopically occult neoplasms. Using 1.5 percent ALA solution and a photosensitization time of 4 hours as favorable parameters the diagnostic value of conventional staging laparoscopy was significantly improved: 35 percent of all malignant lesions were detected only by FD. Therefore, fluorescence laparoscopy suggest to be a highly promising preoperative staging tool requiring minimal technical and clinical expenditure. It provides the laparoscopist with a rapid and accurate technique to assess more thoroughly the full extent of malignant tumor growth in the abdominal cavity.
In the presented study, the intracellular PDT efficiency of a new poly-ethylene glycol (PEG) derivative of meso-tetra- chlorin (mTHPC) was tested in a cell culture model and the PDT dose-efficiency dependence determined using mTHPC as a reference. Squamous cell carcinoma cells incubated with mTHPC or mTHPC-PEG in 96-well microplates were irradiated with laser light. Cell viability was determined at several timepoints after irradiation by an MTS cell proliferation assay. Equal products of irradiant energy and applied doses of mTHPC-PEG, or mTHPC respectively, yielded identical PDT effects on the cells. PDT efficiency depended in a threshold-like manner on the applied light and sensitizer doses for either compound. For mTHPC-PEG, below 250 (ng/ml)*(J/cm2) no effect could be detected; with 1250 (ng/ml)*(J/cm2) and more, all cells were killed. mTHPC was 20 fold more effective than mTHPC-PEG. Since mTHPC-PEG shows higher tumor accumulation rates in several animal models than mTHPC, appropriate parameters and clinical applications should be found where the pegylation further enhances the potential of mTHPC PDT< although mTHPC-PEG is less effective than the free compound in vitro. In conclusion, the new mTHPC-PEG conjugate as a macromolecular and water-soluble variation of mTHPC shows intracellular PDT efficiency and therefore holds the potential for an improved mTHPC PDT.