Characterization of silkworm chlorophyll metabolites as an active photosensitizer for photodynamic therapy.

Silkworm excreta containing chlorophyll metabolites have long been used for their medicinal activities in the Far East. The major chlorophyll derivative (CpD) fraction in the Me2CO extract from the silkworm excreta exhibits strong photodynamic action on mice and human tumor cells in vitro. The main CpD component was isolated, purified, and subjected to extensive structural and characterization studies to assess its photodynamic therapeutic activity. According to the spectral analyses, the structure of the major unknown CpD was determined to be 10-hydroxypheophytin a [1]. The CpD component possessed a high quantum efficiency (50%) for the photosensitized production of singlet molecular oxygen, thus providing a molecular basis for its photodynamic therapeutic efficiency. A further advantage is that the "photooxidation/degradation" product(s) from this CpD retains all the characteristics of a photodynamic sensitizer.