BENZOPHENOTHIAZINE AND BENZOPORPHYRIN DERIVATIVE COMBINATION PHOTOTHERAPY EFFECTIVELY ERADICATES LARGE MURINE SARCOMAS

The tumoricidal effects of photochemotherapy with two photosensitizers , 5-ethylamino-9-diethylaminobenzo[a] phenothiazinium chloride (EtNBS) and benzoporphyrin derivative monoacid ring A (BPD-MA), were evaluate d separately and in combination against the EMT-6 fibrosarcoma implant ed subcutaneously in BALB/c mice. Animals carrying tumors 8-10 mm in d iameter were divided into eight different groups (similar to 20/group) and subjected to various photoirradiation and drug conditions. The tu mor response to photodynamic therapy (PDT) was measured as the mean tu mor wet weight 2 weeks post-PDT. The combination treatment with 5.25 m g/kg EtNBS and 2.5 mg/kg BPD-MA followed by photoirradiation with 100 J/cm(2) at 652 mn and then by 100 J/cm(2) at 690 nm resulted in a 95% reduction in the average tumor weights compared to controls (no light, no drugs) with 76% of the mice being tumor free 2 weeks post-PDT. Bec ause treatment with EtNBS or BPD-MA at twice the light dose and drug c oncentration resulted in either no significant reduction in tumor weig hts or increased the lethality of treatment, respectively, the data su ggest that the enhanced PDT effect observed with the combination of dr ugs is synergistic rather than additive. Histology of tumors 24 h post -PDT with the combination of drugs showed nearly complete destruction of the tumor mass with little or no damage to the vasculature and no e xtravasation of red blood cells. There was no damage to the normal ski n adjacent to the tumor. Fluorescence microscopy of EMT-6 cells incuba ted in vitro with the two photosensitizers revealed that they were loc alized to different intracellular compartments, The fluorescence patte rn from frozen tumor tissue slices following the in vivo administratio n of the photosensitizers indicated a greater intracellular localizati on for EtNBS vs BPD-MA.