Continuous Monitoring of Therapeutic Monoclonal Antibody Using Regenerable Aptamer Based Electrochemical Sensor
Authors: Nagata Madoka , Ikebukuro Kazunori , Asanuma Hiroyuki , Murayama Keiji , Sode Koji 
Published: December 2024

Therapeutic humanized monoclonal antibodies (mAbs) are focused on as effective medicine owing to their high specificity and efficacy compared with conventional small-molecule pharmaceuticals. To avoid side effects and improve the treatment efficacy, controlling the dose of therapeutic mAbs for the patient is the most crucial. However, the monitoring of their concentrations demands highly specific discrimination from human immunoglobulin G (IgG), since most therapeutic mAbs are designed based on IgG, which is naturally present in large quantities in human blood and differs only in residues at the complementarity determining region (CDR).

Previously, we developed the therapeutic mAbs aptamer sensor utilizing an anti-idiotype aptamer, that recognizes the complementarity determining region, CDR, of a target therapeutic antibody, Bevacizumab [1,2]. This sensor can distinguish the target antibody and other human natural antibodies and succeed in detecting the bevacizumab from artificial serum that contains a high concentration of human natural IgG. Since this sensor does not require a chemical reaction nor a free redox probe in the solution, they are very suitable for in vivo continuous monitoring. However, due to the high binding constant (~nM-pM) of aptamer, binding site regeneration is only possible by denaturing both the target protein and aptamer structures with guanidine hydrochloride. Currently, the most challenging task for future therapeutic mAb sensors employing aptamers with a high binding constant to realize in vivo continuous monitoring is the development of versatile methods and technologies suitable for the in situ regeneration of aptamer binding sites.

To tackle this challenging task, we have been engaged in the designing of engineered aptamers which can be modulated in their binding constant by external signals. Azobenzene is an ideal photoresponsive molecule, which reversibly changes its cis/trans forms, by UV or visible light irradiation and this structure change drives aptamer structure change and releases the target [3,4]. In this study, we designed an azobenzene-inserted anti-idiotype bevacizumab aptamer and developed an electrochemical sensor that can regenerate its binding site by light irradiation.

To design the photo-regenerated anti-idiotype bevacizumab aptamer, we investigated the appropriate position to insert azobenzene without affecting the binding ability. After the confirmation of binding ability, we applied these aptamers to electrochemical measurement. Azobenzene-inserted anti-bevacizumab idiotype aptamers were immobilized on the planar electrode. Electrochemical measurements were carried out using a constructed aptamer electrode as a working electrode. After the confirmation of target binding on the electrode, we tried to regenerate the aptamer-immobilized electrode by UV light irradiation. The release of the target antibody was confirmed electrochemically.

We will present the characterization of the photo-regenerated anti-idiotype aptamer, focusing on the change in binding toward the target therapeutic mAb, bevacizumab in UV and visible light irradiated conditions. Finally, we will show repeated detection of bevacizumab using this novel-engineered aptamer combined with electrochemical detection such as an extended gate FET-based sensor toward the continuous monitoring of a therapeutic mAb, bevacizumab.

[1] Saito et al., Biosensors and Bioelectronics, 2022,203,114027

[2] Nagata et al., Int. J. Mol. Sci., 2023, 24(6) 5277

[3] Liang et al., JACS, 2003, 125, 16408

[4] Liang et al., Small, 2009, 5(5) 1761]