Design of a synthetic non-natural antibody (NoNabody) against GRP as a new therapy for small cell lung cancer

(a) An introductory sentence indicating the purposes of the study; Gastrin-releasing peptide (GRP) has been described as an autocrine growth factor for small cell lung carcinoma (SCLC) and the use of a monoclonal antibody (MoAb) against GRP was shown to reduce tumor growth in animal models and had a positive profile in a phase 2 clinical trial. Here we aim to develop a synthetic non-natural antibody (NoNabody) as a potential new therapeutic tool for SCLC. (b) A brief description of pertinent experimental procedures; The first step to obtain a NoNabody against GRP was to study the interaction between a well-characterized anti-GRP MoAb and the peptide itself. After obtaining the sequence of the variable binding region, ColabFold was used to predict the antibody structure and VMD, together with NAMD, were used to analyze the antibody-peptide interaction. (c) A summary of the new, unpublished data; An in silico evaluation of the interaction between the anti-GRP antibody and the peptide identified the last seven residues of GRP, including the terminal amide group, as the main target of the antibody.Throughout all the molecular dynamics simulations, the MoAb remained structurally stable, whereas the full-length GRP peptide exhibited limited stability. In contrast, simulations performed with only the last 10 or 7 amino acids of the peptide showed increased stability.A comparison of the interactions between the amidated versus the free-acid peptide with the MoAb showed that amidation greatly enhances the antibody's affinity for GRP.Analysis of the antibody-peptide interface revealed that the interaction is distributed between the heavy and light chains, with GRP positioned right in between them. CDR3 (light chain) interacts with the last three residues of GRP, whereas CDR1 and CDR2 (heavy chain) interact with residues 16-22. (d) A statement of the conclusions; NoNanobodies represent a new tool for employing antibodies in in vitro and in vivo studies. This work focuses on generating a NoNanobody against GRP. An initial in silico analysis showed that antibody-peptide binding occurs at the C-terminal amino acids and that this interaction is strengthened when GRP is amidated. This information is critical for developing new synthetic binding moieties against GRP that may improve drug performance through their small size, improved tissue penetrability and low immune responses to the small synthetic forms. This work was supported by the Science and Innovation System of the Government of La Rioja (25658-2025/0000000016).