Chemically-defined camelid antibody bioconjugate for the magnetic resonance imaging of Alzheimer's disease

Abstract

Today, molecular imaging of neurodegenerative diseases is mainly based on small molecule probes. Alternatively, antibodies are versatile tools that may be developed as new imaging agents. Indeed, they can be readily obtained to specifically target any antigen of interest and their scaffold can be functionalized. One of the critical issues involved in translating antibody-based probes to the clinic is the design and synthesis of perfectly-defined conjugates. Camelid single-domain antibody-fragments (VHHs) are very small and stable antibodies that are able to diffuse in tissues and potentially cross the blood brain barrier (BBB). Here, we selected a VHH (R3VQ) specifically targeting one of the main lesions of Alzheimer's disease (AD), namely the amyloid-beta (Aß) deposits. It was used as a scaffold for the design of imaging probes for magnetic resonance imaging (MRI) and labeled with the contrastophore gadolinium using either a random or site-specific approach. In contrast to the random strategy, the site-specific conjugation to a single reduced cysteine in the C-terminal part of the R3VQ generates a well-defined bioconjugate in a high yield process. This new imaging probe is able to cross the BBB and label Aß deposits after intravenous injection. Also, it displays improved r1 and r2 relaxivities, up to 30 times higher than a widely used clinical contrast agent, and it allows MRI detection of amyloid deposits in post mortem brain tissue of a mouse model of AD. The ability to produce chemically-defined VHH conjugates that cross the BBB opens the way for future development of tailored imaging probes targeting intracerebral antigens.

Brain Delivery of Single-Domain Antibodies: A Focus on VHH and VNAR

“…VHH R3VQ recognizing amyloid plaques has been coupled to gadolinium, a magnetic resonance imaging (MRI) contrast agent. Immunohistochemistry showed positive staining of amyloid plaques validating the BBB passage [ 90 ]. Even if MRI visualization of amyloid plaques was obtained in vitro, no labeling of plaques was obtained in vivo on live mice, suggesting that the amount of VHH in the brain was too low.…”

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

“…These structural changes allow the nanobody to retain antigen-specific binding ability in the absence of the light chain and improve its hydrophilicity and stability. In another interesting aspect, there is evidence that small volumes of nanobodies can cross the blood-brain barrier for the treatment of brain diseases [32,33].…”

Use of camel single-domain antibodies for the diagnosis and treatment of zoonotic diseases

“…VHHs have been shown to recognize a wide range of epitope types, from small haptens [16,19] to the binding sites of enzymes [17,20], and can bind epitopes that cannot be recognized by conventional antibodies [21]. -The small size and basic isolectric point of VHHs allows them to penetrate tissues, pass through barriers, such as the blood-brain barrier [22][23][24][25][26], and bind intracellular antigens. -VHHs can be efficiently functionalized [27][28][29] and are widely used for imaging [24,26,30].…”

“…-The small size and basic isolectric point of VHHs allows them to penetrate tissues, pass through barriers, such as the blood-brain barrier [22][23][24][25][26], and bind intracellular antigens. -VHHs can be efficiently functionalized [27][28][29] and are widely used for imaging [24,26,30].…”

“…There has been an explosion in the number of publications concerning applications of VHHs that cover their use in pharmaceutical development or as biotechnological tools [26,[31][32][33][34][35]. Here, we mainly focus on the potential use of VHHs for the diagnosis and the treatment of zoonotic diseases.…”