Apoptosis Mechanisms Related to the Increased Sensitivity of Jurkat T-cells vs A431 Epidermoid Cells to Photodynamic Therapy with the Phthalocyanine Pc 4 †‡ Malcolm S. Ke 1 , Liang-yan Xue 2 , Denise K. Feyes 1,2 , Kashif Azizuddin 2 , Elma D. Baron 1,3,4,5 , Thomas S. McCormick 1,3,4 , Hasan Mukhtar 1,3,4§ , Ashok Panneerselvam 6 , Mark D. Schluchter 4,6 , Kevin D. Cooper 1,3,4,5 , Nancy L. Oleinick* 2,3,4 and Seth R. Stevens 1,3,4,5– 1 Department of Dermatology, University Hospitals Case Medical Center and Case Western Reserve University, Cleveland, OH 2 Department of Radiation Oncology, University Hospitals Case Medical Center and Case Western Reserve University, Cleveland, OH 3 Skin Diseases Research Center, University Hospitals Case Medical Center and Case Western Reserve University, Cleveland, OH 4 Case Comprehensive Cancer Center, University Hospitals Case Medical Center and Case Western Reserve University, Cleveland, OH 5 Dermatology Service, Louis Stokes Department of Veterans Affairs Medical Center, Cleveland, OH 6 Department of Epidemiology and Biostatistics, University Hospitals Case Medical Center and Case Western Reserve University, Cleveland, OH Received 27 October 2007, accepted 4 December 2007, DOI: 10.1111/j.1751-1097.2007.00278.x ABSTRACT To examine the clinical applicability of Pc 4, a promising second-generation photosensitizer, for the photodynamic treat- ment of lymphocyte-mediated skin diseases, we studied the A431 and Jurkat cell lines, commonly used as surrogates for human keratinocyte-derived carcinomas and lymphocytes, respectively. As revealed by ethyl acetate extraction and absorption spectro- photometry, uptake of Pc 4 into the two cell lines was linear with Pc 4 concentration and similar on a per cell basis but greater in Jurkat cells on a per mass basis. Flow cytometry showed that uptake was linear at low doses; variations in the dose–response for uptake measured by fluorescence supported differential aggregation of Pc 4 in the two cell types. As detected by confocal microscopy, Pc 4 localized to mitochondria and endoplasmic reticulum in both cell lines. Jurkat cells were much more sensitive to the lethal effects of phthalocyanine photody- namic therapy (Pc 4-PDT) than were A431 cells, as measured by a tetrazolium dye reduction assay, and more readily underwent morphological apoptosis. In a search for molecular factors to explain the greater photosensitivity of Jurkat cells, the fate of important Bcl-2 family members was monitored. Jurkat cells were more sensitive to the induction of immediate photodamage to Bcl-2, but the difference was insufficient to account fully for their greater sensitivity. The antiapoptotic protein Mcl-1 was extensively cleaved in a dose- and caspase-dependent manner in Jurkat, but not in A431, cells exposed to Pc 4-PDT. Thus, the greater killing by Pc 4-PDT in Jurkat compared with A431 cells correlated with greater Bcl-2 photodamage and more strongly to the more extensive Mcl-1 degradation. Pc 4-PDT may offer therapeutic advantages in targeting inflammatory cells over normal keratinocytes in the treatment of T-cell-mediated skin diseases, such as cutaneous lymphomas, dermatitis, lichenoid tissue reactions and psoriasis, and it will be instructive to evaluate the role of Bcl-2 family proteins, especially Mcl-1, in the therapeutic response. INTRODUCTION Photodynamic therapy (PDT) has been gathering acclaim as an effective mode of treatment for a variety of diseases outside of those already accepted by the United States Food and Drug Administration (FDA). Approved for the treatment of esoph- ageal and lung carcinomas in the United States, PDT has been evaluated to treat other neoplasms, including transitional cell carcinomas of the bladder, head and neck tumors and brain lesions as adjuvant therapy (1–3). Along with malignant neoplasms, PDT has been approved for premalignant (actinic keratosis and Barrett’s esophagus) and nonmalignant (age- related macular degeneration) conditions, and tested for others, such as benign prostatic hypertrophy, atherosclerosis and arthritis (1,4–8). Results have been favorable, and it seems only a matter of time before approval for other treatments is gained. Approved in Canada for the prophylactic treatment of papillary bladder tumors in 1993, PDT has already been accepted in other countries for the treatment of a variety of diseases (1–3,5,9,10). †This paper is part of a special issue dedicated to Professor Hasan Mukhtar on the occasion of his 60th birthday. ‡Presented in part at the Society for Investigative Dermatology, May 15–18, 2002, Los Angeles, CA, USA. §Current address: Hasan Mukhtar, Department of Dermatology, University of Wisconsin, Madison, WI, USA. –Current address: Seth R. Stevens, Amgen, Incorporated, Thousand Oaks, CA, USA. *Corresponding author email: nlo@case.edu (Nancy L. Oleinick) Ó 2008 The Authors. Journal Compilation. The American Society of Photobiology 0031-8655/08 Photochemistry and Photobiology, 2008, 84: 407–414 407