Researchers have developed innovative nonsymmetrical near-infrared (NIR) rhodamine-based fluorophores to improve tumor imaging and PDT. These new compounds feature large Stokes shifts and tunable emission wavelengths. Consequently, they overcome the optical limitations of traditional fluorophores in biomedical applications.

Improving Tumor Imaging and PDT with Phenothiazine Auxochromes

The team engineered these fluorophores by introducing varying phenothiazine moieties as auxochromes. Specifically, rhodamine incorporated with phenoselenazine shows significantly red-shifted profiles and high reactive oxygen species production. Furthermore, they created a new activatable probe for carboxylesterase (CE) by caging a secondary amine group. This probe remains in a predominantly spirolactone state until CE-catalyzed hydrolysis triggers its transition to an open zwitterion form. Therefore, clinicians can achieve highly specific imaging of enzyme activity and induce apoptosis in CE-positive cells.

Theranostic Potential and In Vivo Applications

Moreover, the study highlights a PEG-modified version of the probe for systemic administration. This refined probe allows for the specific imaging and ablation of tumors in living models. Since the probe targets specific enzyme activity, it significantly reduces potential off-target effects. Thus, these nonsymmetrical NIR rhodamine-based fluorophores offer a promising platform for advanced theranostic interventions in modern oncology.

Frequently Asked Questions

Why is carboxylesterase a good target for tumor imaging and PDT?

Carboxylesterase is often overexpressed in various tumor types. Consequently, using it as a biological trigger ensures that the imaging signal and therapeutic effects activate only within the cancer microenvironment.

What are the benefits of near-infrared wavelengths in cancer therapy?

NIR wavelengths provide deeper tissue penetration and lower background interference from natural tissue fluorescence. Therefore, they are ideal for high-resolution imaging and effective photodynamic treatment of deep-seated tumors.

Disclaimer: This content is for informational and educational purposes only and does not constitute medical advice or a professional recommendation. Always consult with a qualified healthcare provider for diagnosis and treatment. Refer to the latest local and national guidelines for clinical practice.

References

Zhou S et al. Nonsymmetrical Near-Infrared Rhodamines for Carboxylesterase-Activatable Tumor Imaging and Photodynamic Therapy. Anal Chem. 2026 Mar 17. doi: 10.1021/acs.analchem.5c06782. PMID: 41844510.