Photodynamic inactivation of mammalian DNA-dependent RNA polymerase by hematoporphyrin and visible light

Amino- and Hydroxytetraphenylporphyrins with Activity against the Human Immunodeficiency Virus

A series of amino- and hydroxytetraphenylporphyrin derivatives was found to have activity against the human immunodeficiency virus type 1 (HIV-1) in human peripheral blood mononuclear cells. Activity tends to be associated with increased hydrophilicity of the porphyrins for the porphyrins with one substituent on each phenyl ring but there is no clear pattern for the porphyrins with two substituents on each phenyl ring. The antiviral activity of certain porphyrins has been demonstrated in the absence of light, suggesting a non-photochemical process. Whereas only some of the porphyrins that inhibit HIV-1 in culture inhibit HIV-1 reverse transcriptase in a cell-free system, none of those tested inhibit DNA polymerase α.

Cross-resistance to photofrin-mediated photodynamic therapy and UV light and recovery from photodynamic therapy damage in Rif-8A mouse fibrosarcoma cells measured using viral capacity

Photodynamic therapy (PDT) utilizes the localized delivery of light to activate a photosensitizing drug (such as Photofrin) which is selectively retained by the tumour tissues. The intrinsic in vitro sensitivity of tumour cells to PDT is thought to be an important determinant of clinical tumour response to PDT. In this work we show the feasibility of using a viral capacity assay for adenovirus (Ad) DNA synthesis as an indicator of cellular sensitivity to and recovery from Photofrin-mediated PDT. Rif-1 mouse fibrosarcoma cells and a PDT resistant derivative, Rif-8A, as well as Chinese hamster ovary (CHO) cells and CHO-MDR multi-drug resistant mutant cells were studied. Consistent with the clonogenic survival of these cells, the capacity of PDT-treated cells for Ad DNA synthesis was greater for Rif-8A compared to Rif-1 cells and for CHO-MDR compared to CHO-N cells. Delaying infection of the Rif cells from immediately after, to 6 hours after PDT, resulted in an increased capacity for Ad DNA synthesis, which was greater for Rif-8A compared to Rif-1 cells, suggesting that the increased resistance of Rif-8A cells to PDT results from an elevated recovery and/or repair of PDT damage. The capacity of UV-irradiated cells for Ad DNA synthesis was also greater for Rif-8A compared to Rif-1 cells indicating a cross-resistance of Rif-8A cells to UV. These results suggest some overlap in the types of cellular damage induced by UV and PDT and/or overlap in the pathways for the repair of UV and PDT damage in Rif cells.

The use of porphyrins and non-ionizing radiation for treatment of cancer

Photodynamic therapy (PDT) is the treatment of malignant lesions with visible light following systemic or local administration of a photosensitizer or its precursor. Initially, hematoporphyrin derivative and a purified component called Photofrin II was used for clinical PDT. Later on interest has focused on new sensitizers with more favourable absorption as regards light transmission in tissues. Twenty years of clinical experience has revealed that PDT is best applied to early stage cancers. The present review discusses the basic components of PDT and its clinical use in treatment of cancer.

Molecular, cellular, and tissue responses following photodynamic therapy

Photodynamic therapy (PDT) is being utilized in the treatment of a wide variety of malignant tumors. Results using PDT have been encouraging, and controlled clinical trials are currently being performed. The procedure exploits both the tumor-localizing and -photosensitizing properties of hematoporphyrin derivative or its purified component, Photofrin II. When this porphyrin mixture is administered systemically, it is retained preferentially in tumor tissue as compared to surrounding normal tissue. Localized tumor destruction induced by PDT results from the photochemical generation of cytotoxic oxygen species within the tumor. This review will provide a summary of historical and current research pertaining to molecular, cellular, and tissue responses induced by PDT. Emphasis is placed on information related to the chemistry of current photosensitizers, subcellular targets, preclinical treatment parameters, and clinical responses following PDT.

Phototherapy of bladder cancer: dose/effect relationships

Hematoporphyrin derivative photodynamic therapy has very important clinical applicability in the diagnosis and treatment of transitional cell carcinoma of the bladder, but many aspects of the photodynamic process are yet to be elucidated. This paper investigates the role of dihematoporphyrin ether (DHE) concentration, the duration of light exposure, and the initial size of the tumors in the treatment of a transplantable murine transitional cell tumor system. The best results were noted in tumors less than six mm. in diameter when treated with 15 mg./kg. DHE and exposed to 100 to 180 minutes of visible light. Animals with small initial tumor size combined with higher DHE concentration and longer light exposure time were most likely to show tumor response.

Photodynamic effects of hematoporphyrin-derivative on transmembrane transport systems of murine L929 fibroblasts

Photodynamic treatment of murine L929 fibroblasts with hematoporphyrin-derivative causes deterioration of various membrane functions. Most sensitive to photodynamic inactivation are the energy-coupled transport systems for aminoisobutyric acid and for Rb+. The facilitated diffusion system for 2-deoxy-D-glucose is slightly less sensitive. After longer illumination periods also the membrane barrier function is impaired, as reflected by K+ leakage and increased passive Rb+ uptake. After still longer illumination periods intermolecular protein crosslinking can be observed. This makes it unlikely that intermolecular protein crosslinking is causally involved in the deterioration of these membrane functions.