Levels of disulfonated and tetrasulfonated
aluminum phthalocyanines (
AlPcS2,4) were measured in cells derived from FsaR
tumors (murine
fibrosarcoma) using a fluorescence-activated cell sorter (FACS). The
tumors were excised from animals injected with the sensitizer 24 h earlier and enzymatically dissociated. Before flow cytometry, the cells were stained with
fluorescein isothiocyanate-conjugated anti-mouse
monoclonal antibodies to specific immune cell membrane markers (Mac1,
Fc receptor (FcR) or CD45). Staining to FcR and CD45 was combined with
a DNA stain Hoechst 33342. This enabled concomitant discrimination to be made by the FACS between different populations of
tumor-infiltrating host cells and malignant cells. The results showed on average 1.49 times higher
AlPcS2 levels and 1.16 times higher
AlPcS4 levels in Mac1-positive (Mac1+) compared with Mac1-negative (Mac1-)
tumor cell populations. The same type of experiments performed with SCCVII
tumor (
squamous cell carcinoma) gave average Mac1+/Mac1- ratios of 1.75 and 1.45 for
AlPcS2 and
AlPcS4 respectively. The data using other
antibodies and
DNA staining are consistent with the conclusion that, based on average per cell content, elevated levels of
AlPcS2, and to a lesser extent
AlPcS4, are retained in tumor-associated macrophages (TAM). The levels of these
photosensitizers in other leukocytes and in non-immune host cells were not substantially different from those in malignant
tumor cells. It is also shown that elevated levels of
AlPcS2 and
AlPcS4 are not localized in all TAM, but rather in a fraction of this cell population characterized by extremely high
photosensitizer content.