34th Annual Scientific Meeting proceedings

Objectives:

Achieving an adequate tumour-to-background ratio (TBR) is crucial during fluorescence-guided surgery (FGS). While monoclonal antibodies (mAbs) have shown potential in tumour delineation, issues such as offsite binding and high background signal persist. Preclinical imaging studies showcased the advantages of nanobodies (Nbs), small antibody fragments that offer deeper tumour penetration and faster serum clearance while maintaining high affinity and specificity. This first-ever clinical trial investigated the potential of using fluorescent anti-EGFR Nbs for FGS and the effect of mAb preloading in canine patients.

Methods:

The Ethical Committee of Veterinary Medicine and Bioengineering Sciences approved the study (EC 2022–035), which complied with the Belgian Royal Decree and EU Directive 2010/63/EU. Client-owned dogs with EGFR-positive tumours were enrolled with the owner’s informed consent, and divided into three groups. The dogs received an intravenous Nb dose, with or without anti-EGFR mAb preloading. The tumours and lymph nodes were imaged at multiple time points, including ex vivo, and then processed for histopathology and EGFR immunohistochemistry.

Results:

The second cohort showcased a high TBR; however, offsite specific binding was observed in healthy surrounding tissues. An anti-EGFR mAb preloading dose was included in the third cohort to address this issue, resulting in improved contrast. Histopathology confirmed a correlation between fluorescence intensity and EGFR expression.

Conclusions:

This study showed that the tracer accumulated in EGFR-positive tissues and that the innovative use of mAb preloading resulted in effective tumour visualisation. Furthermore, the study demonstrated that intravenous Nbs were well tolerated in dogs, advancing research and clinical translation of this probe.