Alternative non-antibody protein scaffolds for molecular imaging of cancer
Graphical abstract
Introduction
Molecular imaging can provide critical clinical information regarding the presence, concentration, and localization of cancer biomarkers in vivo. The data, which can be obtained dynamically or longitudinally if desired, empowers early detection, patient stratification, and treatment monitoring. A major challenge in this field is the development of high affinity, specific ligands for the multitude of important biomarkers. Directed evolution and other strategies position engineered proteins to offer a robust, high throughput means for ligand generation (Figure 1). Many of these engineered proteins have shown promising results in preclinical evaluation as well as early clinical results. While antibodies and their fragments have been explored [1], their large size and slow clearance are not ideal due to the functional requirement of reduced background signal necessary for imaging contrast; moreover, for targeting of poorly vascularized tumors, such as those in early formation, large size slows extravasation and delivery [2•]. For these reasons, as well as benefits in stability, production, and chemical conjugation, alternative protein topologies have been studied as scaffolds for molecular imaging. Short linear and cyclic peptides have exhibited significant success as molecular imaging agents [3], although their robustness in engineering high affinity toward novel targets is limited. Thus, this review will focus on advances in molecular imaging of cancer, particularly positron emission tomography (PET), single-photon emission computed tomography (SPECT), and gamma-camera imaging using engineered, folded, non-antibody proteins (Figure 2 and Table 1). The majority of the research has been performed using subcutaneous xenografted tumors in mice. There are exceptions to these experimental systems, including clinical data, which will be noted.
Section snippets
Affibody
The affibody is a 58 amino acid, three helical bundle [4]. Typically, randomization of 13 amino acids on the surface of helices 1 and 2 is used to generate novel binding ligands. The most extensively studied class of affibodies is those targeting human epidermal growth factor receptor 2 (HER2). The second generation HER2-binding affibody, ZHER2:342, was engineered to bind with 22 pm affinity [5•], and has successfully imaged HER2-expressing tumor xenografts in mice when labeled with 125I [5•],
Designing delivery
It is evident that disparate protein topologies can be engineered for in vivo molecular recognition and delivery of radioisotopes to tumors. As the field continues to mature, we should strive to identify the ideal molecule for the application of interest, to maximize tumor uptake, minimize off-target retention, and tune kinetics for efficacy, logistics, and patient safety. Quantitative design rules would be tremendously useful to optimize performance. Select studies have been performed that
References and recommended reading
Papers of particular interest, published within the period of review, have been highlighted as:
• of special interest
Acknowledgements
This work was funded by the National Institutes of General Medical Science Biotechnology Training Grant (L.A.S.) and the University of Minnesota.
References (63)
- et al.
Engineering of affibody molecules for therapy and diagnostics
Methods Mol Biol
(2012) - et al.
Direct comparison of 111In-labelled two-helix and three-helix Affibody molecules for in vivo molecular imaging
Eur J Nucl Med Mol Imaging
(2011) - et al.
Evaluation of a (64)Cu-labeled cystine-knot peptide based on agouti-related protein for PET of tumors expressing alphavbeta3 integrin
J Nucl Med
(2010) - et al.
Iodine-123-vascular endothelial growth factor-165 (123I-VEGF165). Biodistribution, safety and radiation dosimetry in patients with pancreatic carcinoma
Q J Nucl Med Mol Imaging
(2004) - et al.
ScVEGF-PEG-HBED-CC and scVEGF-PEG-NOTA conjugates: comparison of easy-to-label recombinant proteins for [68Ga]PET imaging of VEGF receptors in angiogenic vasculature
Nucl Med Biol
(2010) - et al.
Influence of valency and labelling chemistry on in vivo targeting using radioiodinated HER2-binding Affibody molecules
Eur J Nucl Med Mol Imaging
(2009) - et al.
Advances in immuno-positron emission tomography: antibodies for molecular imaging in oncology
J Clin Oncol
(2012) - et al.
A modeling analysis of the effects of molecular size and binding affinity on tumor targeting
Mol Cancer Ther
(2009) - et al.
Molecular imaging targeting peptide receptors
Methods
(2009) - et al.
Tumor imaging using a picomolar affinity HER2 binding affibody molecule
Cancer Res
(2006)
Pre-clinical evaluation of [111In]-benzyl-DOTA-Z(HER2:342), a potential agent for imaging of HER2 expression in malignant tumors
Int J Mol Med
Tc-99m-maEEE-Z(HER2:342), an affibody molecule-based tracer for the detection of HER2 expression in malignant tumors
Bioconjug Chem
[18F]FBEM-ZHER2:342 — affibody molecule — a new molecular tracer for in vivo monitoring of HER2 expression by positron emission tomography
Eur J Nucl Med Mol Imaging
Evaluation of [(111/114m)In]CHX-A″-DTPA-ZHER2:342, an affibody ligand coniugate for targeting of HER2-expressing malignant tumors
Q J Nucl Med Mol Imaging
On the selection of a tracer for PET imaging of HER2-expressing tumors: direct comparison of a 124-labeled affibody molecule and trastuzumab in a murine xenograft model
J Nucl Med
(68)Ga-DOTA-affibody molecule for in vivo assessment of HER2/neu expression with PET
Eur J Nucl Med Mol Imaging
HER2-positive tumors imaged within 1 hour using a site-specifically 11C-labeled Sel-tagged affibody molecule
J Nucl Med
Molecular imaging of HER2-expressing malignant tumors in breast cancer patients using synthetic 111In- or 68Ga-labeled affibody molecules
J Nucl Med
Affibody molecules for epidermal growth factor receptor targeting in vivo: aspects of dimerization and labeling chemistry
J Nucl Med
Imaging of EGFR expression in murine xenografts using site-specifically labelled anti-EGFR 111In-DOTA-Z EGFR:2377 Affibody molecule: aspect of the injected tracer amount
Eur J Nucl Med Mol Imaging
In vivo and in vitro uptake of 111In, delivered with the affibody molecule (ZEGFR:955)2, in EGFR expressing tumour cells
Oncol Rep
Small-animal PET imaging of human epidermal growth factor receptor positive tumor with a 64Cu labeled affibody protein
Bioconjug Chem
PET of EGFR expression with an 18F-labeled affibody molecule
J Nucl Med
Imaging of insulinlike growth factor type 1 receptor in prostate cancer xenografts using the affibody molecule 111In-DOTA-ZIGF1R:4551
J Nucl Med
[99mTc(CO)3]+-(HE)3-ZIGF1R:4551, a new Affibody conjugate for visualization of insulin-like growth factor-1 receptor expression in malignant tumours
Eur J Nucl Med Mol Imaging
Evaluation of backbone-cyclized HER2-binding 2-helix Affibody molecule for in vivo molecular imaging
Nucl Med Biol
Engineered two-helix small proteins for molecular recognition
ChemBioChem
A 2-helix small protein labeled with 68Ga for PET imaging of HER2 expression
J Nucl Med
A novel 18F-labeled two-helix scaffold protein for PET imaging of HER2-positive tumor
Eur J Nucl Med Mol Imaging
Engineering knottins as novel binding agents
Methods Enzymol
Engineered knottin peptides: a new class of agents for imaging integrin expression in living subjects
Cancer Res
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