Phototriggerable 2',7-caged paclitaxel.

Three different variants of photoactivatable caged paclitaxel (PTX) have been synthesized and their bioactivity was characterized in in vitro assays and in living cells. The caged PTXs contain the photoremovable chromophore 4,5-dimethoxy-2-nitrobenzyloxycarbonyl (Nvoc) attached to position C7, C2' and to both of these positions via a carbonate bond. Single caged PTXs remained biologically active even at low dosages. Double caging was necessary in order to fully inhibit its activity and to obtain a phototriggerable PTX that can be applied successfully at commonly used concentrations. Irradiation of solutions containing the double caged PTX allowed dose-dependent delivery of functional PTX. Light-triggered stabilization of microtubule assemblies in vitro and in vivo by controlled light exposure of tubulin solutions or cell cultures containing caged PTX was demonstrated. Short light exposure under a fluorescence microscope allowed controlled delivery of free PTX during imaging.