Evaluation of a novel type of imaging probe based on a recombinant bivalent mini-antibody construct for detection of CD44v6-expressing squamous cell carcinoma

Abstract

We have developed the CD44v6-targeting human bivalent antibody fragment AbD19384, an engineered recombinant human bivalent Fab antibody formed via dimerization of dHLX (synthetic double helix loop helix motif) domains, for potential use in antibody-based molecular imaging of squamous cell carcinoma in the head and neck region. This is a unique construct that has, to the best of our knowledge, never been assessed for molecular imaging in vivo before. The objective of the present study was to evaluate for the first time the in vitro and in vivo binding properties of radio-iodinated AbD19384, and to assess its utility as a targeting agent for molecular imaging of CD44v6-expressing tumors. Antigen specificity and binding properties were assessed in vitro. In vivo specificity and biodistribution of 125I-AbD19384 were next evaluated in tumor-bearing mice using a dual-tumor setup. Finally, AbD19384 was labeled with 124I, and its imaging properties were assessed by small animal PET/CT in tumor bearing mice, and compared with 2-deoxy-2-[18F]fluoro-D-glucose (18F-FDG). In vitro studies demonstrated CD44v6-specific binding with slow off-rate for AbD19384. A favorable biodis-tribution profile was seen in vivo, with tumor-specific uptake. Small animal PET/CT images of 124I-AbD19384 supported the results through clearly visible high CD44v6-expressing tumors and faintly visible low expressing tumors, with superior imaging properties compared to 18F-FDG. Tumor-to-blood ratios increased with time for the conjugate (assessed up to 72 h p.i.), although 48 h p.i. proved best for imaging. Biodistribution and small-animal PET studies demonstrated that the recombinant Fab-dHLX construct AbD19384 is a promising tracer for imaging of CD44v6 antigen expression in vivo, with the future aim to be used for individualized diagnosis and early detection of squamous cell carcinomas in the head and neck region. Furthermore, this proof-of-concept research established the feasibility of using recombinant Fab-dHLX constructs for in vivo imaging of tumor biomarkers.

Standardization of Preclinical PET/CT Imaging to Improve Quantitative Accuracy, Precision, and Reproducibility: A Multicenter Study

“…This recognition mainly stemmed from multicenter trials focused on quantifying and tracking changes in malignant tumors as well as prognosis and treatment evaluations. Today preclinical PET/CT is a pivotal quantitative imaging research tool supporting innovative research in areas such as disease diagnosis and prognosis and in the development of novel radiotracers and pharmaceuticals (5)(6)(7)(8)(9)(10)). Yet, standardization in preclinical PET/CT imaging remains essentially nonexistent.…”

A promising cancer diagnosis and treatment strategy: targeted cancer therapy and imaging based on antibody fragment

“…Antibody that specifically binds to overexpressed antigen on the surface of the tumour can be combined with radionuclide, fluorescent substance or microbubble into complex for cancer imaging [41][42][43]. When mAb is involved in tumour imaging, long half-life mAb requires longer imaging time and can only obtain background blurred imaging results [44].…”

CD44v6-Targeted Imaging of Head and Neck Squamous Cell Carcinoma: Antibody-Based Approaches

“…This was demonstrated for AbD15179 using different squamous cell carcinoma cell lines [ 91 ] and highlights the importance of functional assessment of the radioimmunoconjugate. Reformatting AbD15179 into a bivalent construct followed by radiolabeling resulted in a tracer ( 124 I-AbD19384) with slower target dissociation that displayed more favorable tumor imaging properties when compared to 18 F-FDG PET ( Figure 3 ) [ 92 ]. Similar results speaking in favor of a smaller bivalent antibody fragment were obtained when a Fab, a bivalent F(ab′) 2 , and a full-length version of mAb U36 were compared side by side in vitro and in mice carrying CD44v6-expressing xenografts [ 63 ].…”

“…The smaller size of scFvs versus, for example, F(ab′) 2 combined with high affinity monovalent binding yielded advantageous tumor to organ ratios already at 24 h p.i. (Haylock et al [ 8 ]), which is half the time required to reach similar ratios for the F(ab′) 2 fragment [ 92 ]. For imaging, the contrast between tumor and surrounding tissue is more important than the total tumor uptake and a high affinity is generally advantageous for radioimmunodiagnostic applications [ 25 ].…”