Spectrometric characteristics and tumor-affinity of a novel photosensitizer: mono- l-aspartyl aurochlorin e6 (Au-NPe6)

• Published in: Photodiagnosis and photodynamic therapy Vol. 1; no. 4; pp. 295 - 301
• Main Authors: Ishizumi, Taichiro, Aizawa, Katsuo, Tsuchida, Takaaki, Okunaka, Tetsuya, Kato, Harubumi
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.12.2004
• Subjects: Absorption spectrum; Photodiagnosis; Photosensitizer; Photodiagnosis; Photosensitizer; Absorption spectrum
• ISSN: 1572-1000; 1873-1597
• DOI: 10.1016/S1572-1000(05)00002-5

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.