THE VALUE OF SERUM ALPHA-N-ACETYL GALACTOSAMINIDASE MEASUREMENT FOR THE ASSESSMENT OF TUMOR RESPONSE TO RADIODYNAMIC AND PHOTODYNAMIC THERAPY

Serum activity of alpha-N-acetylgalactosaminidase (NaGalase), the extr acellular matrix-degrading enzyme that appears to be produced exclusiv ely by cancer cells, was measured in mice bearing SCCVII tumours (squa mous cell carcinoma). The NaGalase levels in these mice increased with time of tumour growth and were directly proportional to tumour burden . After exposure of SCCVII tumours to a single X-ray dose of 20 Gy, th e serum NaGalase levels gradually decreased during the first 10 days a fter treatment (to approximately one-third of the initial value) and t hen began to increase. The decrease in serum NaGalase activity was mor e rapid after the treatment of SCCVII and EMT6 tumours by photodynamic therapy (PDT) and was dependent on the PDT dose. The treatments (base d on photosensitizers Photofrin or mTHPC) that were fully curative res ulted in the reduction of NaGalase activity to background levels withi n 2 or 3 days after PDT. A slower decrease in NaGalase activity was fo und after PDT treatments that attain an initial tumour ablation but ar e not fully curative. The regrowth of PDT-treated SCCVII tumours was p receded by an increase in serum NaGalase levels, which was detected as early as 8 days before the visible tumour reappearance. These finding s ascertain the validity of serum NaGalase measurement for the assessm ent of tumour response to different treatments and support the concept that the NaGalase measurement could serve as a diagnostic and prognos tic index that might allow oncologists to design the dosage or nature of treatment.