DAMAGE TO TUMOR-CELLS AFTER PHOTODYNAMIC THERAPY

Photodynamic therapy (PDT) is a new, promising method in the treatment of cancer. To gain insights into PDT-mediated tumour destruction we s tudied the influence of treatment with Photofrin(R) and laser light on changes in cell volume and cell viability. A-Mel-3 tumour cells were subjected to Photofrin(R) or illumination with laser light, or a combi nation of both (PDT). Cell volume was measured by flow cytometry and c ell viability by the trypan blue exclusion test for up to 60 min after PDT and the respective controls. In addition, scanning and transmissi on electron microscopy were performed. Tumour cells incubated in conce ntrations of 0.75, 1,5 and 3.0 mug Photofrin(R)/ml revealed a rapid in crease in cell volume to 117%, 207% and 235% 30 min after PDT and to 1 47%,210% and 199% 60 min after PDT. Celt viability with 1.5 and 3.0 mu g Photofrin(R)/ml and laser light was reduced to 83% and 44% at 30 min after PDT and to 38% and 17% 60 min after PDT. At Photofrin(R) concen trations of 1.5 mug/ml and exposure to laser light scanning electron m icroscopy revealed extreme loss of microvilli and formation of blebs o n the cellular surface. Transmission electron microscopy showed swolle n mitochondria and ruptures of the cell membrane. This study demonstra tes that PDT induces a significant time-dependent and dose-related inc rease in tumour cell volume. We suggest that the PDT-induced swelling of tumour cells contributes to the increase of interstitial fluid pres sure and to impairment of microvascular perfusion of tumours.