Hetero-bivalent agents targeting FAP and PSMA

Area of Science:

• Radiopharmaceutical chemistry
• Molecular imaging
• Cancer theranostics

Background:

• Fibroblast activation protein alpha (FAP) and prostate-specific membrane antigen (PSMA) are key proteases overexpressed in the tumor microenvironment (TME) and in certain tumor epithelia.
• Targeting these proteases offers a strategy for broader cancer imaging and therapy.
• Developing theranostic agents that engage both FAP and PSMA is crucial for managing heterogeneous tumors.

Purpose of the Study:

• To develop and evaluate a novel theranostic radiopharmaceutical targeting both FAP and PSMA for broader cancer applications.
• To synthesize and characterize ⁶⁴Cu-labeled compounds (FP-L1 and FP-L2) with optimized linker constructs.
• To assess the in vitro and in vivo performance of these agents for imaging FAP- and PSMA-expressing tumors.

Main Methods:

• Synthesis of FP-L1 and FP-L2 using small-molecule FAP and PSMA-targeting moieties conjugated via optimized linkers.
• In vitro determination of inhibition constants (K_i) for FAP and PSMA.
• Cell uptake assays, flow cytometry, quantitative positron emission tomography/computed tomography (PET/CT), and tissue biodistribution studies in various cancer models (glioma, melanoma, prostate, renal, pancreatic).

Main Results:

• High radiochemical yields (>98%) and molar activities (>19 MBq/nmol) achieved for ⁶⁴Cu-FP-L1 and ⁶⁴Cu-FP-L2.
• Nanomolar K_i values confirmed potent inhibition of both FAP and PSMA.
• PET/CT and biodistribution studies demonstrated high and specific tumor targeting, with ⁶⁴Cu-FP-L1 showing favorable pharmacokinetics and high retention in FAP/PSMA-expressing tumors.

Conclusions:

• ⁶⁴Cu-FP-L1 exhibits high and specific tumor targeting of both FAP and PSMA.
• This dual-targeting agent enables imaging of lesions expressing FAP, PSMA, or both.
• FP-L1 holds significant potential for conversion into a theranostic agent for managing heterogeneous tumors.