5-Aminolevulinic Acid-Induced Protoporphyrin IX Fluorescence Imaging for Tumor Detection: Recent Advances and Challenges

Abstract

5-Aminolevulinic acid (5-ALA) is a natural amino acid and a precursor of heme and chlorophyll. Exogenously administered 5-ALA is metabolized into protoporphyrin IX (PpIX). PpIX accumulates in cancer cells because of the low activity of ferrochelatase, an enzyme that metabolizes PpIX to heme. High expression of 5-ALA influx transporters, such as peptide transporters 1/2, in cancer cells also enhances PpIX production. Because PpIX radiates red fluorescence when excited with blue/violet light, 5-ALA has been used for the visualization of various tumors. 5-ALA photodynamic diagnosis (PDD) has been shown to improve the tumor removal rate in high-grade gliomas and non-muscular invasive bladder cancers. However, 5-ALA PDD remains a challenge as a diagnostic method because tissue autofluorescence interferes with PpIX signals in cases where tumors emit only weak signals, and non-tumorous lesions, such as inflammatory sites, tend to emit PpIX fluorescence. Here, we review the current outline of 5-ALA PDD and strategies for improving its diagnostic applicability for tumor detection, focusing on optical techniques and 5-ALA metabolic pathways in both viable and necrotic tumor tissues.

Adverse Effect of Blue Light on DNA Integrity Is Accelerated by 5-Aminolevulinic Acid in HaCaT Human Keratinocyte Cells and B16F1 Murine Melanoma Cells

“…Additionally, 5-ALA enhances the activity of oxidative stress-related genes, such as nuclear factor erythroid 2-related factor 2 (Nrf2) and heme oxygenase-1 (HO-1), and protects bovine mammary epithelial cells from heat stress [ 8 ]. In cancer cells, PPIX tends to accumulate in the cells because of the low ferrochelatase activity, which converts PPIX into heme [ 9 ]. Thus, 5-ALA has been used for photodynamic therapy (PDT).…”

The impact of heme biosynthesis regulation on glioma aggressiveness: Correlations with diagnostic molecular markers

“…Furthermore, there is increasing evidence that the presence of clinically observable 5-ALA induced fluorescence is also associated with poor patient survival ( Jaber et al, 2019 ; Hosmann et al, 2021 ). Since tumor visualization relies on the metabolization of non-fluorescent 5-ALA to Protoporphyrin IX within the heme biosynthesis pathway, an association between metabolically active heme biosynthesis protein levels and patient survival seems likely ( Pustogarov et al, 2017 ; Harada et al, 2022 ; Mischkulnig et al, 2022 ). Since prognostic effects can therefore be established for the mRNA expression signature as well as 5-ALA induced fluorescence that is highly likely to be facilitated by heme biosynthesis upregulation on protein level, the presence of a complex association between both expression levels seems plausible.…”

Photodynamic Therapy for Bladder Cancers, A Focused Review†

“…5‐ALA, a common precursor of hemoglobin and chlorophyll, produces protoporphyrin IX (PpIX) in the mitochondria through the biosynthetic pathway (61). Along with other cancers, bladder cancer experiences abnormal activity of ABCG2, a porphyrin transporter that is upregulated in hypoxia, and porphyrin synthetic enzymes (coproporphyrinogen III), which promote PpIX production and inhibit its catabolism (reduced ferrochelatase activity in cancer) (62–66).…”