Internalization-Dependent EGFR-Targeted Photoactivation by Cetuximab-I21 Conjugates.

Area of Science:

• Oncology
• Immunology
• Bioconjugation Chemistry

Background:

• Antibody-photosensitizer conjugates offer tumor-selective phototoxicity via receptor targeting and light activation.
• IR700-based near-infrared photoimmunotherapy is a clinical standard, but alternative photosensitizers are sought.

Purpose of the Study:

• To develop and characterize novel cetuximab-I21 conjugates targeting epidermal growth factor receptor (EGFR)-expressing tumors.
• To evaluate the phototoxicity, selectivity, cellular trafficking, and in vivo efficacy of these conjugates.

Main Methods:

• Synthesis and photophysical characterization of cetuximab-I21 conjugates.
• In vitro cytotoxicity assays on EGFR-positive and EGFR-low cells.
• Mechanistic studies involving cellular uptake, trafficking, and apoptosis induction.
• In vivo fluorescence imaging and tumor growth inhibition studies in xenograft models.

Main Results:

• Cetuximab-I21 conjugates demonstrated high drug-to-antibody ratios and potent, light-dependent cytotoxicity in EGFR-positive cells with minimal dark toxicity.
• Selective targeting and uptake in EGFR-expressing cells were confirmed, with >400-fold reduced sensitivity in EGFR-low cells.
• Mechanistic studies showed receptor-mediated endolysosomal trafficking, mitochondrial depolarization, and apoptosis.
• In vivo imaging confirmed tumor-specific accumulation, and cetuximab-I21-3 achieved significant tumor growth inhibition in xenografts.

Conclusions:

• Cetuximab-I21 conjugates represent a promising light-activated, EGFR-targeted antibody-photosensitizer strategy.
• The mechanism of action differs from IR700-based photoimmunotherapy, offering an alternative therapeutic approach.
• Further studies on comparative efficacy, immune response, safety, and light-dose optimization are needed for clinical translation.