Synthesis and evaluation of new 5-aminolevulinic acid derivatives as prodrugs of protoporphyrin for photodynamic therapy

Protoporphyrin IX (PpIX) is used as a photosensitizer in the photodynamic diagnosis (PDD) and photodynamic therapy (PDT) of cancer and is synthesized intracellularly from 5-aminolevulinic acid (5-ALA) precursors. Thirteen novel 5-ALA derivatives were designed and synthesized appropriately with tailored hydrophilicity and lipophilicity. The generation of PpIX was detected and their antitumor activity in vitro and in vivo was also investigated. It was shown that compounds 9b–c, 11b–c and 13a displayed a characteristic long wavelength absorption peak at 593 nm after 5 h incubation in mice fibrosarcoma S180 cells. After being exposed to 600 nm laser light irradiation, these compounds can inhibit cell proliferation in S180 cells in vitro. The growth of S180 cell tumors in Kunming mice was significantly inhibited by these compounds in vivo. Among these compounds, 13a has low dark toxicity and high phototoxicity, which makes it an effective and promising prodrug for PDT.