Tumor vascular shutdown following photodynamic therapy based on polyhematoporphyrin or 5-aminolevulinic Acid

The effects of photodynamic therapy (PDT) based on polyhaematoporphyrin (PHP) or 5-aminolaevulinic acid (ALA) on the tumour vascular perfusion (TVP) of a rat fibrosarcoma were examined using an (RbCl)-Rb-86 extraction technique. Both forms of therapy induced large and highly significant reductions in TVP, countering the previous suggestion that ALA-PDT has no vascular effects. Ultrasensitive digital imaging fluorescence microscopy indicated that ALA-induced PpIX was distributed relatively evenly throughout the tumour. Use of Hoechst 33342 as a vascular marker revealed that PpIX was also present in cells lining the tumour microvascular spaces, contrary to previous findings.