Investigation of the threshold photodynamic dose for HPPH-sensitized PDT of Panc-1 pancreatic cancer cells

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Patel, Pooja M
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Our research group at the College of Charleston has been working in collaboration with physicians at Mayo Clinic to develop a method of drug and light dosimetry for photodynamic therapy (PDT). We are studying Panc-1 pancreatic cancer cells with the photosensitizer 2-[1-Hexyloxyethyl]-2-devinyl Pyrophenophorbide-a (HPPH) and 670-nm light. Our aim is to improve the result of photodynamic therapy (PDT) for the treatment of pancreatic cancer. The first part of the project involved quantifying the photosensitizer using an optical dosimetry method. A “ratio method” was used in which the ratio of the integrated dye fluroesence was divided by the autofluorescence for various amounts of HPPH in a tissue phantom. While dye extraction is likely to overestimate the amount of dye that is therapeutically available in vivo, the ratio method reports optically active photosensitizer content. The second goal of this project was to determine whether there is a threshold of absorbed light for irreversible destruction of photosensitized Panc-1 pancreatic cancer cells. A preliminary experiment compared red and green light sources at an energy dose of 1 Joules/cm2. For the remainder of this project red light was used as it would not limit the depth of the treatment thus, it can penetrate deeper into the tissue to kill the pancreatic cancer cells. The cells were loaded with 1 mg/kg of HPPH and 670-nm light was applied at the range of 0.025-3.0 J/cm2. Clonal assays were used to determine the cell viability, accounting for cell death by both necrosis and apoptosis. After plotting the light absorption dose against cell viability, the LD-50 light dose (light dose that kills 50% of the cells) for HPPH-mediated PDT was determined. The LD50 light dose for panc-1 cells incubated with 1mg/m2 HPPH was 0.15 J/cm2. The dosimetry calculations gave a result of 3.5 x 1010 per cell, yielding an LD-50 dose in terms of photons of 1.11 x 1019 photons per gram of tissue.
Photodynamic Therapy on PANC-1 Cells