Photodiagnosis and
photodynamic therapy with
photosensitizers can be indicated only for
tumors of the superficial type, because these approaches utilizing visible light are limited by said light penetrability. To overcome this disadvantage, we innovated a novel
photosensitizer, mono-l-aspartyl aurochlorin e6 (Au-NPe6), by incorporating a
gold atom in the center of
tetrapyrrole ring of
NPe6 with a coordination bond. The
gold atom in Au-NPe6 plays a role as an X-ray
interceptor to detect deeply sited
tumors. In this study, the absorption spectrum of novel Au-NPe6 in the diagnosis of deeply sited
tumors was investigated, and the results were compared with the parent
photosensitizer NPe6. Furthermore, the
tumor-affinity of Au-NPe6 was evaluated using atomic absorption spectrometry. Despite the fact that both
photosensitizers display a difference in the absorption spectrum, waveform changes of either
photosensitizer with
human serum albumin established a saturation point at a molar ratio of 1:1. The results indicate that it is highly possible that Au-NPe6 bound with
albumin at a molar ratio (1:1) similar to
NPe6. The accumulation rate of
gold in
tumor tissues was always significantly (p<0.05) higher than that in normal muscle tissues during the observation terms. Moreover, absorption spectra of
tumor-tissue homogenates obtained from
tumor-bearing mice after Au-NPe6 administration revealed a common peak with a wavelength equivalent to that of
albumin-bond Au-NPe. This result suggests that the
gold atom and
NPe6 probably remained bonded even when Au-NPe6 was incorporated in
tumor tissues.