PEG₄-Modified FAP-CAIX Heterodimeric Radioligand for Precision Imaging and Radiotherapy

Area of Science:

• Oncology
• Radiopharmaceutical Therapy
• Molecular Imaging

Background:

• Tumor heterogeneity poses a significant challenge to the effectiveness of single-targeted radiopharmaceuticals.
• Fibroblast Activation Protein (FAP) and Carbonic Anhydrase IX (CAIX) are key biomarkers frequently overexpressed in various tumors and their microenvironments.
• Developing dual-targeting agents can potentially overcome limitations associated with targeting single biomarkers.

Purpose of the Study:

• To design and evaluate a novel heterodimeric radioligand, FC, for the simultaneous targeting of FAP and CAIX.
• To assess the binding affinity, tumor uptake, pharmacokinetic properties, and therapeutic efficacy of the dual-targeting agent.
• To investigate the potential of [68Ga]Ga/ [177Lu]Lu-FC as a theranostic agent for FAP-positive malignancies.

Main Methods:

• A PEG4-modified heterodimeric radioligand (FC) was synthesized for dual targeting of FAP and CAIX.
• Binding affinity to FAP was determined using IC50 assays.
• [68Ga]Ga-FC and [177Lu]Lu-FC were evaluated in FAP- or CAIX-positive tumor models using micro-SPECT imaging.
• Pharmacokinetic properties, including tumor retention and in vivo stability, were assessed.
• Therapeutic efficacy and organ toxicity of [177Lu]Lu-FC were evaluated in a preclinical mouse model.

Main Results:

• The heterodimeric radioligand FC demonstrated high binding affinity for FAP (IC50 = 18.2 ± 0.23 nM).
• [68Ga]Ga-FC showed significantly enhanced tumor uptake compared to monomeric tracers in relevant tumor models at 120 minutes post-injection.
• PEG4 modification improved hydrophilicity, tumor retention, and in vivo stability of the radioligand.
• Micro-SPECT imaging revealed substantial tumor accumulation of [177Lu]Lu-FC for up to 168 hours.
• A single dose of [177Lu]Lu-FC resulted in complete tumor suppression in mice bearing HEK293-FAP tumors without observable organ toxicity.

Conclusions:

• The PEG4-modified heterodimeric radioligand FC effectively targets both FAP and CAIX.
• Dual targeting with [68Ga]Ga/[177Lu]Lu-FC offers superior tumor uptake and retention compared to single-targeted agents.
• [177Lu]Lu-FC exhibits potent therapeutic efficacy with a favorable safety profile, establishing it as a promising theranostic agent for FAP-positive cancers.