HCE6-mediated photodynamic therapy induces hepatocellular carcinoma cell death via inhibition of autophagic flux.

Porphyrin derivatives are potential candidates for photodynamic therapy against cancer. In this study, hydrophilic chlorin e6 trisodium salt (HCE6) was selected for treatment of hepatocellular carcinoma (HCC). SK-hep1 cells and a xenograft mouse model were used to investigate the antitumor efficacy and the autophagic mechanism of cell death. Time and concentration dependent cellular uptake of HCE6 indicated that HCE6-PDT can significantly induce death of SK-hep1 cells without notable toxicity. In addition, the treatment suppressed cell migration and colony formation and arrested cell cycle progression, thus promoting apoptosis. HCE6-PDT induced severe mitochondrial damage due to HCE6 gathering on mitochondria, which was confirmed by disrupted cristae, loss of membrane potential, calcium dyshomeostasis, and elevated reactive oxygen species (ROS). Mitochondrial changes and ROS burst induced TOM20 and AMPK expression, indicating mitophagy activation in cells. Furthermore, increased LC3-II levels and their enhanced co-localization with P62 suggested autophagic flux blockade. HCE6-PDT significantly inhibited tumor growth in vivo, and the pathological and immunohistochemical findings were consistent with the in vitro study. HCE6 exhibited strong photo-induced cytotoxicity and robust antitumor efficacy. Mechanistically, it appears to induce mitochondrial dysfunction, trigger autophagy, and subsequently impair autophagic flux, ultimately resulting in cell death.