Galleria Mellonella As an Invertebrate Screening Model for Biocompatibility and in Vivo Functionality Testing of Imaging Contrast Agents.

The preclinical evaluation of novel imaging agents, such as contrast agents for computed tomography (CT), still largely relies on rodent models or simplified in vitro systems, each carrying limitations with regard to ethical burden, physiological relevance or translational value. To address this gap, we propose Galleria mellonella larvae as a scalable, ethically favourable and physiologically relevant in vivo model for use in the early-stage screening of novel CT contrast agents. We established a standardised imaging protocol utilising isoflurane-based sedation and longitudinal micro-CT scanning, and used it to evaluate three commercially available contrast agents: one clinically approved molecular agent and two nanoparticulate formulations that are used for preclinical studies. All agents were systemically distributed, well-tolerated and enabled consistent visualisation of internal anatomy over eight days. While differences in clearance kinetics and route related to particle size or formulation were less pronounced compared to vertebrate models, this larval system reliably reflected biodistribution trends and allowed non-invasive tracking of agent functionality and safety. The use of G. mellonella in this context enables early elimination of less promising candidates and reduces reliance on vertebrates in downstream (pre)clinical development, aligning with the Three Rs principles. Our findings support the use of G. mellonella as a practical intermediate model, bridging in vitro cell-based assays and in vivo rodent studies in the development of next-generation CT and imaging contrast agents.