Nanobodies for Medical Imaging: About Ready for Prime Time?

Abstract

Recent advances in medical treatments have been revolutionary in shaping the management and treatment landscape of patients, notably cancer patients. Over the last decade, patients with diverse forms of locally advanced or metastatic cancer, such as melanoma, lung cancers, and many blood-borne malignancies, have seen their life expectancies increasing significantly. Notwithstanding these encouraging results, the present-day struggle with these treatments concerns patients who remain largely unresponsive, as well as those who experience severely toxic side effects. Gaining deeper insight into the cellular and molecular mechanisms underlying these variable responses will bring us closer to developing more effective therapeutics. To assess these mechanisms, non-invasive imaging techniques provide valuable whole-body information with precise targeting. An example of such is immuno-PET (Positron Emission Tomography), which employs radiolabeled antibodies to detect specific molecules of interest. Nanobodies, as the smallest derived antibody fragments, boast ideal characteristics for this purpose and have thus been used extensively in preclinical models and, more recently, in clinical early-stage studies as well. Their merit stems from their high affinity and specificity towards a target, among other factors. Furthermore, their small size (~14 kDa) allows them to easily disperse through the bloodstream and reach tissues in a reliable and uniform manner. In this review, we will discuss the powerful imaging potential of nanobodies, primarily through the lens of imaging malignant tumors but also touching upon their capability to image a broader variety of nonmalignant diseases.

Generation and diversification of recombinant monoclonal antibodies

“…For some cell biological and biomedical applications, antibody fragments, generated by either proteolysis or genetic engineering, offer advantages over the use of intact, bivalent antibodies. For example, their smaller size allows more efficient penetration of tissue samples and may provide better access to ‘buried’ epitopes; they are able to bind targets without inducing cross-linking; they reduce steric effects (compared with intact antibodies) when monitoring an antigen in living cells, and they have reduced immunogenicity, which may be desirable for therapeutic applications ( Hayashi-Takanaka et al, 2011 ; Cheloha et al, 2020 ; Zhao et al, 2019 ; Xenaki et al, 2017 ; Berland et al, 2021 ; Ries et al, 2012 ; Morisaki et al, 2016 ; Yan et al, 2016 ; Wang et al, 2016 ; Stasevich et al, 2014 ). Another advantage is that single chain antibody fragments can be fused to a fluorescent protein and genetically encoded for expression in living cells for the purpose of real-time antigen tracking.…”

[99mTc]Tc-Labeled Plectin-Targeting Peptide as a Novel SPECT Probe for Tumor Imaging

“…As a result, an increasing number of receptors have been explored in this field, such as fibroblast activation proteins, prostate-specific membrane antigens, and somatostatin receptors [ 2 ]. In addition, several types of targeting molecules have been investigated for their receptors [ 4 , 5 , 6 , 7 , 8 , 9 ]. Because of their attractive advantages in constructing molecular imaging probes, including high affinity and specificity, fast blood clearance, low immunogenicity, and easy modification, many peptides have been labeled with radionuclides for tumor receptor imaging, and some are being widely used in clinics [ 12 ].…”

“…Molecular imaging can reflect biological events at the cellular and molecular levels during the occurrence and progression of diseases and has been widely applied for cancer diagnosis [ 1 , 2 , 3 ]. Because of the overexpression or activation of specific receptors in the tumorigenesis process, various tumor-targeting ligands, including antibodies, affibodies, nanobodies, peptides, and small-molecule compounds, have been labeled with appropriate radionuclides in the past several decades to develop molecular imaging probes for positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging [ 4 , 5 , 6 , 7 , 8 , 9 ]. Among them, radiolabeled peptides are the best candidates for clinical translation.…”

Nanobodies in the limelight: Multifunctional tools in the fight against viruses

“…An important parameter that must be considered in clinical application is that nanobody size is below the glomerular filtration threshold (50-60 kDa), resulting in rapid renal clearance and a very short half-life (10-30 min [79]). Although this might be beneficial for many applications, including diagnostic imaging and cancer treatment (reviewed in [80,81]), an increased half-life may be beneficial and preferred for prophylactic therapy or treatment of viral (and other) diseases. Methods to increase the half-life of nanobodies include multimerization, PEGylation [82], serum albumin fusion, or fusion to another nanobody specific for serum albumin [14,31,83], and genetic fusion to an Fc domain [84].…”