Synthesis, photophysical and electrochemistry of near-IR absorbing bacteriochlorins related to bacteriochlorophyll a.

A series of new bacteriochlorins was synthesized using 13(2)-oxo-bacteriopyropheophorbide a (derived from bacteriochlorophyll a) as a starting material, which on reacting with o-phenylenediamine and 1,10-diaminonaphthalene afforded highly conjugated annulated bacteriochlorins with fused quinoxaline, benzimidazole, and perimidine rings, respectively. The absorption spectra of these novel bacteriochlorins demonstrated remarkably red-shifted intense Q(y) absorption bands observed in the range of 816-850 nm with high molar extinction coefficients (89,900-136,800). Treatment of 13(2)-oxo-bacteriopyropheophorbide a methyl ester with diazomethane resulted in the formation of bacterioverdins containing a fused six-membered methoxy-substituted cyclohexenone (verdin) as an isomeric mixture. The pure isomers which exhibit long-wavelength absorptions in the near-IR region (865-890 nm) are highly stable at room temperature with high reactivity with O(2) at the triplet photoexcited state and favorable redox potential and could be potential candidates for use as photosensitizers in photodynamic therapy (PDT).

Vascular accumulation of a novel photosensitizer, MV6401, causes selective thrombosis in tumor vessels after photodynamic therapy.

The antivascular effects of photodynamic therapy (PDT) and their mechanisms are not clearly understood. Here, we examined the effects of PDT with a novel photosensitizer MV6401 on the microvasculature in a mammary tumor (MCaIV) grown in a murine dorsal skinfold chamber and in normal tissue controls. The mice were irradiated with light 15 min after i.v. administration of MV6401 when the drug was localized only in the vascular compartment, as shown by fluorescence microscopy and immunohistochemistry. PDT with MV6401 caused a dose-dependent biphasic blood flow stasis and vascular hyperpermeability, as determined by intravital microscopy. This biphasic response was classified into two components: (a) an acute response observed immediately after PDT; and (b) a long-term response observed at times greater than 3 h after PDT. The acute temporal vascular effects were characteristic of vasoconstriction but not of thrombus formation. However, the long-term vascular shutdown was mediated by thrombus formation, as evidenced by histological evaluation and inhibition with heparin. Minimal effects were observed in normal vessels after antivascular doses used against the tumor, but there was no long-term vascular damage. In concert with the stasis, a dose-dependent tumor growth delay was observed. This study provides mechanistic insights into antitumor vascular effects of PDT and suggests novel strategies for tumor treatment with PDT.