Multiple Means by Which Nitric Oxide can Antagonize Photodynamic Therapy

Area of Science:

• Oncology
• Biochemistry
• Photomedicine

Background:

• Photodynamic therapy (PDT) utilizes photosensitizing agents, light, and oxygen to generate reactive oxygen species for tumor eradication.
• Endogenous nitric oxide (NO) has been shown to reduce PDT efficacy in preclinical models.
• Recent findings suggest NO produced by photostressed tumor cells contributes to anti-PDT effects.

Purpose of the Study:

• To investigate the role of inducible nitric oxide synthase (iNOS) and NO in PDT resistance and cancer cell aggressiveness.
• To explore the potential of iNOS inhibitors as adjuvants to enhance PDT effectiveness.

Main Methods:

• Utilized 5-aminolevulinic acid (ALA)-induced protoporphyrin-IX sensitization followed by visible light irradiation in cancer cell lines (COH-BR1, PC3).
• Employed iNOS inhibitors and NO scavengers to assess the impact of NO on PDT-induced apoptosis and cell behavior.
• Investigated NO translocation from targeted to non-targeted bystander cells.

Main Results:

• Upregulation of iNOS and subsequent NO production were observed in photostressed cancer cells, conferring resistance to apoptotic photokilling.
• Surviving cells exhibited increased proliferation, migration, and invasion in an iNOS/NO-dependent manner.
• Induced NO in targeted cells promoted aggressiveness in non-targeted bystander cells.

Conclusions:

• NO plays a critical role in mediating PDT resistance and enhancing the aggressiveness of surviving cancer cells.
• Targeting iNOS with inhibitors could be a viable strategy to overcome NO-mediated suppression of PDT and prevent tumor promotion.