TEMPORAL AND ILLUMINATION-INDUCED VARIATIONS IN THE IN-VIVO LIGHT TRANSMISSION SPECTRA OF 4 PHOTOSENSITIZERS IN EMT6 ED MURINE TUMORS/

Temporal and illumination-induced variations in the in vivo light tran smission spectrum of the photosensitizer will influence light dosimetr y for photodynamic therapy (PDT). The present authors have studied the in vivo spectra of four photosensitizers in the EMT6/Ed murine tumour model in Balb/c mice. The following photosensitizers were used: bis(d imethylthexylsiloxy)silicon 2,3-naphthalocyanine (SiNc 8), benzoporphy rin-derivative monoacid ring A (BPD Verteporfin), Photofrin and ethano lamined hypocrellin B (HBEA-R2). Spectra were measured non-invasively in the EMT6/Ed murine tumour model in the spectral range 600-840 nm, u sing a diode laser, a dye laser and a Ti:sapphire laser. Red-shift and broadening of the SiNc 8 absorption band was observed at 790 nm, and a slight red-shift was observed in the BPD, HBEA-R2 and Photofrin in v ivo absorption spectrum. Exposure to 300 J of light at the peak absorp tion wavelength caused complete photobleaching of BPD at 690 nm, and a reduced absorption by SiNc 8 at 780 nm, Photofrin at 626 nm, and HBEA -R2 at 656 nm.