Fig. 2
From: Therapy-resistant nature of cancer stem cells in view of iron metabolism
The current limitations and new therapeutic strategies of 5-ALA-based PDD/PDT to detect CSCs for cancer eradication. CSCs exhibit lower PpIX accumulation in 5-ALA-based PDD/PDT, potentially due to PpIX efflux by ABCG2 transporter, accelerated iron usage to convert PpIX to heme and the increased expression of HO-1 to accelerate PpIX-heme metabolism. The combination of 5-ALA-PDD/PDT with targeted proteins in heme/iron metabolism might establish the novel therapeutic strategies to eradicate CSCs. ABCG2, ATP-binding cassette sub-family G member 2; 5-ALA, 5-aminolevulinic acid; FPN1, ferroportin1; PDD, photodynamic diagnosis; PDT, photodynamic therapy; PpIX, protoporphyrin IX; TFR1, transferrin receptor 1; HO-1, heme oxygenase-1