Granzyme B-Targeting Quenched Activity-Based Probes for Assessing Tumor Response to Immunotherapy

Area of Science:

• Biomedical Engineering
• Molecular Imaging
• Immunology

Background:

• Molecular imaging of immune activation is crucial for developing new immunotherapies.
• Detecting immune responses before tumor size changes can guide early therapeutic strategies.

Purpose of the Study:

• To develop a chemical probe for detecting granzyme B as a biomarker of antitumor immunity.
• To enable early assessment of immune response using noninvasive optical imaging.

Main Methods:

• Designed and optimized a quenched activity-based optical imaging probe (Cy5-IEPCyaPhP-QSY21) targeting granzyme B.
• Evaluated probe specificity, sensitivity, and background signal in complex proteomes.
• Assessed in vivo and ex vivo fluorescence signals in mouse tumor models.

Main Results:

• The probe selectively labels active granzyme B at substoichiometric concentrations.
• In vivo imaging revealed granzyme B-induced near-infrared fluorescence signals in tumors shortly after injection.
• Fluorescence signals correlated with granzyme B activity, CD8+ cell populations, and immunotherapy response.

Conclusions:

• The developed probe is a valuable chemical tool for assessing immune-mediated anticancer activity.
• Noninvasive optical imaging of granzyme B can track tumor response to immunotherapy.
• This approach facilitates early detection of immune activation in cancer treatment.