Abstract
Background: Immunotherapy can now be considered as game changer of cancer treatment. So far, numerous monoclonal antibodies (mAbs) and their derivatives, such as antibody-drug conjugates (ADCs), have been approved by regulatory agencies for medical use. This implies that the recombinant or chemical conjugation of mAbs to cytotoxic agents can be regarded as a potential cancer treatment modality. Objectives: This study aimed to design an antibody conjugate through the recombinant conjugation of a humanized CD19-specific single-chain variable fragment (scFv), named HuFMC63, to granzyme B (GrB) using precise in silico approaches. Methods: Four different linker peptides were used for the conjugation of HuFMC63 to GrB, and the 3D structure of these antibody conjugates were predicted using GalaxyWEB. The antibody conjugate whose linker peptide had the least impact on the structural conformation of HuFMC63 and GrB was subsequently selected. Additionally, the solubility and melting temperature of the selected conjugate was compared with those of HuFMC6 and GrB, and its physicochemical properties and flexibility were also assessed. Ultimately, the binding capacity and the dissociation constant (Kd) of the selected conjugate to CD19 were compared with those of HuFMC63 (concisely referred to as Hu63), and then the residues that contributed to antigen binding were identified using LigPlot+ software. Results: The Hu63-(G4S)3-GrB conjugate, which is constructed using the (G4S)3 linker, was selected as the best conjugate. The solubility of Hu63-(G4S)3-GrB was predicted to be higher than HuFMC63 and GrB (from 60% in the unconjugated to 98% in the conjugated format). Moreover, it was elucidated that Hu63-(G4S)3-GrB binds CD19 in the same orientation as that of HuFMC63 and with the same Kd of 17 and 33 nM at 25.0°C and 37.0°C, respectively. Conclusions: In silico techniques, such as those employed in this study, could be utilized for the early development of immune-based therapeutics. Moreover, Hu63-(G4S)3-GrB could be introduced as a potent therapeutic for the elimination of CD19-positive malignant cells after careful preclinical and clinical evaluations.