Cellular differentiation as a means to enhance photodynamic therapy
Investigators: Drs. Anand, Sato, Gasbarre, Mack, Maytin
Collaborator: Dr. T. Hasan
Photodynamic therapy (PDT) is an approach to treating cancer that requires visible light, a photoactivatable drug, and oxygen. We are studying one form of PDT in which an inactive precursor molecule called aminolevulinic acid (ALA) is taken up by tumor cells and converted into a photosensitizing molecule (protoporphyrin, PpIX) by enzymes within the cells. The protoporphyrin can then absorb light, release free radicals, and kill the cells. We have found that the effectiveness of this form of PDT can be greatly enhanced by preconditioning cells with hormones (androgens, vitamin D, or methotrexate) that alter the state of differentiation of the cells, allowing higher levels of the protoporphyrin to build up. We are investigating the mechanism of this effect.
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Figure 1. Pink fluorescence, from porphryins (PpIX) within cells, delineates this basal cell cancer. |
In addition to basic research involving cultured cells and tumor models in animals, the project includes a clinical pilot study to test whether a topical Vitamin D analog will alter levels of the protoporphyrin in basal cell carcinoma. We have already shown that Vitamin D can increase the production of PpIX in an artificial skin model (Fig. 2). Patients will rub a Vitamin D cream onto their skin cancer daily for 2 weeks, then come in for their regularly-scheduled surgical excision. A small biopsy from the tumor will be examined by confocal microscopy to see if Vitamin D has increased the amount of PpIX. This is translational research, applying molecular and cellular approaches to the clinical problem of how to improve cancer therapy.
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Figure 2. Vitamin D, administered to keratinocyte raft cultures over days, enhances keratinocyte differentiation and PpIX accumulation. (A-E) Fluorescent images of PpIX from frozen sections taken with a Leica confocal microscope.. (F) Integrated fluorescent intensities within the living layers of the REK epidermis were measured using an image processing program. Ref: Sato et al, 2007 |
Reference
Sato N, Moore B, Keevey S, Drazba J, Hasan T, Maytin EV. Vitamin D enhances ALA-mediated protoporphyrin IX production and photodynamic cell death in 3-D organotypic cultures of keratinocytes. J Invest Dermatol 127:925-934, 2007.
Maytin EV, Anand S, Sato N, Mack J, Ortel BJ. Harnessing cellular differentiation to improve ALA-based photodynamic therapy in an artificial skin model. Proceedings of the International Society for Optical Engineering (SPIE). 2005; Progress in Biomedical Optics and Imaging, Vol 6, No. 4. Optical Methods for Tumor Treatment and Detection: Mechanisms and Techniques in Photodynamic Therapy XIV, volume 5689, pp. 318-329.