Lutetium Texaphyrin (PCI‐0123): A Near‐Infrared, Water‐Soluble Photosensitizer

Abstract

Lutetium texaphyrin, PCI‐0123, is a pure, water‐soluble photosensitizer with a large broad absorption band centered at 732 nm. The compound was tested for photodynamic therapy (PDT) effectiveness in a murine mammary cancer model. The texaphyrin macrocycle as illustrated by magnetic resonance imaging and ¹⁴C‐radiolabeled texaphyrin studies was shown to be tumor selective; a tumor‐to‐muscle ratio of 10.55 was seen after 5 h. Lutetium texaphyrin, at a drug dose of 20 μmol/kg with irradiation 5 h postinjection at 150 J/cm² and 150 mW/cm², had significant efficacy (P < 0.0001) in treating neoplasms of moderate size (40 ± 14 mm³) and also had significant efficacy (P < 0.0001) in treating larger neoplasms (147 ± 65 mm³). The PDT efficacy was correlated with the time interval between PCI‐0123 administration and light exposure. A 100% cure rate was achieved when photoirradiation took place 3 h postinjection compared to 50% for 5 h using 10 μmol/kg and 150 J/cm² at 150 mW/cm². The PDT efficacy was attributable to the selective uptakehetention of the texaphyrin photosensitizer in addition to the depth of light penetration achievable at the 732 nm laser irradiation.