Use of a soft-agar colony-forming assay to determine the photosensitizing effects of several components of hematoporphyrin derivative.

The photosensitizing/cytotoxic effects of four porphyrin compounds derived from hematoporphyrin were compared using two human tumor cell lines with a soft-agar colony-forming assay. Reproducible dose- and time-dependent increases in reproductive cell death were observed for each porphyrin tested. Two fractions derived from hematoporphyrin derivative (HPD) were found to be better photosensitizers than HPD itself, indicating the potential value of this in vitro assay for detecting the most active component from a heterogeneous mixture.