Comparison between amine-terminated phthalocyanines and their chlorambucil conjugates: Synthesis, spectroscopic properties, and in vitro anticancer activity

•Two novel phthalocyanine-CLB conjugates (5 and 7) have been synthetized.•The structure-activity relationships of these compounds have been discussed.•6 and 7 show weaker singlet oxygen generation efficiency than that of 4 and 5.•Compound 6 shows the highest photocytotoxicity against HepG2 cells (IC50 = 9 nM).

Two amine-terminated phthalocyanines, including mono-α-substituted zinc phthalocyanine (ZnPc) 4 and axially di-substituted silicon phthalocyanine (SiPc) 6, as well as their chlorambucil (CLB) conjugates (5 and 7) have been prepared. Both 4 and 6 show very high photocytotoxicities against HepG2 cells with IC50 values down to 31 nM and 9 nM, respectively. However, after conjugating with CLB, the anticancer activities of both conjugates, ZnPc-CLB 5 (IC50 = 0.20 μM) and SiPc-CLB 7 (IC50 = 17.47 μM), are greatly reduced as a result of their lower efficiency in fluorescence emission and singlet oxygen generation in aqueous solution. Moreover, both conjugates show significantly lower cellular uptake than their precursors, 4 and 6. Synergetic chemo-photodynamic therapy could not be observed on the two conjugates.

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