New guidelines and definitions for type I photodynamic therapy

Area of Science:

• Photochemical technologies
• Photodynamic therapy (PDT)
• Cancer treatment

Background:

• Type II PDT requires high oxygen, limiting its use in hypoxic tumors.
• Type I PDT is effective in low-oxygen conditions, making it suitable for solid tumors.
• Recent research has focused on type I photosensitizers (PSs) and their diverse applications.

Purpose of the Study:

• To provide a comprehensive review of type I PDT.
• To establish standardized definitions, mechanisms, molecular designs, detection techniques, and clinical applications.
• To foster a deeper understanding and inspire future innovations in type I PDT for cancer treatment.

Main Methods:

• Review of research on type I photosensitizers and their applications.
• Analysis of the "partial oxygen-recyclable mechanism" for overcoming PDT hypoxia resistance.
• Synthesis of existing knowledge on type I PDT mechanisms, design, detection, and clinical use.

Main Results:

• Type I PDT utilizes reactive oxygen species (ROS) and is effective in hypoxic tumor microenvironments.
• A "partial oxygen-recyclable mechanism" involving O2˙− explains type I PDT's efficacy in low-oxygen conditions.
• Significant advancements have been made in type I PS development and applications.

Conclusions:

• Type I PDT presents a viable strategy for cancer therapy, particularly in challenging hypoxic conditions.
• Standardization of definitions and methodologies is crucial for advancing the field.
• This review aims to guide future research towards more effective and clinically relevant type I PDT treatments.