Preparation and in vitro photodynamic activities of folate-conjugated distyryl boron dipyrromethene based photosensitizers.

Two folate-conjugated diiododistyryl boron dipyrromethenes have been prepared and characterized with various spectroscopic methods. These conjugates exhibit higher photocytotoxicity toward the KB human nasopharyngeal carcinoma cells, which have high expression of folate receptors when compared with the MCF-7 human breast adenocarcinoma cells, which have low expression of folate receptors. The difference in photocytotoxicity for these two cell lines is particularly large for the conjugate with a shorter oligoethylene glycol linker (compound 11a) as a result of its higher cellular uptake and slightly lower aggregation tendency. Its IC50 value toward KB cells (0.06 μM) is 43-fold lower than that for MCF-7 cells, while the difference is only 6-fold for the analogue with a longer linker (compound 11b). The length of the spacer also affects their subcellular localization. While compound 11a shows high affinity toward the endoplasmic reticulum of KB cells, conjugate 11b is mainly localized in the lysosomes.