Clinical Research

• Richard Cheney, MD
• Marcelle Grassi, MD
• Cornelie Jones, MD
• Ilene Rothman, MD
• Howard L. Stoll, Jr., MD
• Nathalie C. Zeitouni, MD

 

Laboratory Research

Sandra Gollnick, PhD

Role of the Immune System in Photodynamic Therapy

The tumor response to PDT involves a complex interplay between direct cytotoxicity of the tumor cells and alterations of the microvasculature, as well as secondary effects mediated by PDT-induced inflammatory and immune responses. Studies in immunocompromised animal models (nude and scid) have shown that effective tumor cure by PDT requires a functional immune system. The main focus of this laboratory is to examine the effect of PDT on the immune system at a molecular and cellular level.

The effect of PDT on the immune system is dichotomous and depends on the nature of application. This laboratory is interested in the regulatory elements behind the diverse effects of PDT on the immune system and, in collaboration with Dr. Barbara Henderson of the PDT Center at Roswell Park, mechanistic studies have begun in an effort to understand the molecular events behind the dichotomous effect of PDT on the immune system. Tumor-directed PDT has been shown in this laboratory and others to result in a tumor specific enhanced immune response, which appears to contribute to the long-term survival of PDT-treated animals. This enhanced immune response appears to be due to an increase in the release of tumor antigens as a result of direct tumor cell kill by PDT. This laboratory has demonstrated that PDT causes the release of tumor-associated antigens and that the released antigens are engulfed by antigen presenting cells in the tumor bed, which migrate to the lymph node. Once in the lymph node these cells stimulate the host immune response against the tumor. An increase in tumor specific CTL activity following PDT also has been demonstrated.

Whether there are changes in the cytokine profile in the tumor bed following PDT has been examined. Cytokines are mediators of the immune response and the type cytokines produced during an immune response determines the nature and extent of the immune reaction. Tumor-directed PDT has been found to results in an increase in IL-6 expression. IL-6 is an inflammatory cytokine shown to increase the activity of cytotoxic T cells. The role of IL-6 and other cytokines in the PDT tumor destruction is being explored.

In contrast to an enhanced antitumor immunity following directed-PDT, large surface area PDT results in systemic immunosuppression as defined by a suppression of the contact hypersensitivity (CHS) response. Together with Dr. David Musser, it has been shown that PDT-induced suppression can be correlated with the increased systemic expression of IL-10. IL-10 is a key immunoregulatory cytokine that suppresses cellular immunity. IL-10 mRNA and protein expression have been shown to be increased in PDT-treated keratinocytes. This increase in suppression is due to an increase in IL-10 gene promoter activity resulting from activation of the redox regulated AP-I transcription factor and to a prolongation of IL-10 mRNA half-life by PDT. It has been shown that the effects of PDT on the CHS response can be reversed by administration of IL-12.

 

Janet Morgan, PhD

Intracellular Photodynamic Damage Sites / Mitochondrial Biology

Research is aimed at identifying subcellular sites where photosensitizers interact and determining whether certain of these sites are critical for efficient photodynamic therapy. In particular, the peripheral benzodiazepine receptor (PBR) located on the outer mitochondrial membrane is a strong candidate for a critical binding site. First, certain types of photosensitizers bind to the PBR with affinities that may be related to their antitumor effectiveness. Second, the PBR appears to be expressed at a high level in many types of cancer cells, thus providing multiple intracellular targets. Third, the PBR occurs at contact points between the inner and outer mitochondrial membranes that are abundant in proteins critical for maintaining homeostasis and that also may be sensitive to photo-oxidation. To elucidate the mechanisms of photodamage, the biochemical events that occur in mitochondria after photoirradiation are being examined on molecular and functional levels. Information provided by this work could aid in the design of better photosensitizing drugs for clinical use and also could help identify tumors that are particularly sensitive or resistant to PDT.

 

David Musser, PhD

Immunosuppressive Effects of PDT

In murine models, low-dose PDT can cause systemic antigen-specific immunosuppression of contact hypersensitivity to new antigens. The suppression is cell-mediated and can be adoptively transferred to naﶥ animals. This suppression may have therapeutic use, but also could be problematic in cases in which there is prolonged retention of low levels of photosensitizer in the skin. Research is directed at: (1) Determining parameters such as drug and light doses, and anatomic sites of irradiation, which elicit immunosuppression. (2) Characterizing the duration and antigen specificity of the effect. (3) Elucidating the cell type(s) responsible. (4) Determining the roles of immunosuppressive cytokines and/or chemokines.

 

Allan R. Oseroff, MD, PhD

• Photomedicine
• Mechanisms of PDT
• New Photosensitizers
• Molecular Responses
• Effects of ALA-PDT on T Lymphocytes and Antigen Presenting Cells
• Electroporation
• Imaging

The laboratory investigates uses of light-activated reactions for therapy and diagnosis. The principal focus is on photodynamic therapy (PDT). PDT increases therapeutic selectivity by employing light absorbing molecules (photosensitizers [PS]) which accumulate in target cells, but which are relatively innocuous in the absence of light. On illumination, the PS initiates photochemical reactions, which damage or kill the cell. The specificity of light-induced damage permits killing of tumor cells with relative sparing of overlying and adjacent normal tissues.

This laboratory is pursuing two approaches to maximizing the selectivity of PDT. One employs positively charged (cationic) PS, which have been found to preferentially accumulate in malignant cells. The other uses topical 5-aminolevulinic acid (ALA), a precursor to a naturally occurring PS, protoporphyrin IX. The precursor is preferentially absorbed through abnormal skin, and is then biosynthetically converted to the active PS within the carcinoma cells.

Work extends from chemical synthesis to biophysics, cellular and molecular biology, to in vivo studies, and to clinical trials. The effects of PDT on cell function are being characterized at biochemical and molecular levels, with a particular emphasis on mitochondrial function and the roles of the transferrin receptor. For ALA-PDT, function and survival of specific components of the immune system are being examined to better understand the mechanisms and potential for immunomodulation. In animal models, pharmacokinetics, sites of PS accumulation, and efficacy and specificity of photochemical damage are being studied. Preclinical experiments underlie the studies in patients and also are guided by the clinical results. In addition to the clinical studies, a unique National Cancer Institute-funded program has been established to examine underlying biological mechanisms of the therapeutic effects. Particularly with ALA, PDT appears to have great potential as an immunomodulator and treatment for immune cell-mediated disease. Using technology developed at RPCI, the use of photosensitizer fluorescence for non-invasive detection of malignancies is being explored.

In collaboration with the Department of Molecular & Cellular Biophysics, electroporation as a technique to deliver drugs (including photosensitizers) and biological agents through the barrier layers in the skin is being examined, with promising preliminary results. Unique DNA adducts caused by light and photosensitizers also are being defined.