Organoids are three-dimensional cell aggregates with near-physiologic cell behaviors and can undergo long-term expansion in vitro. They are amenable to high-throughput drug screening processes, which renders them a viable preclinical model for drug development. The procedure of organoid-based high-throughput screening has been extensively employed to discover small molecule drugs, encompassing the steps of generating organoids, examining efficient drugs in organoid cultures, and data assessment. Compared to small molecules, peptides are more straightforward to synthesize, can be modified chemically, and demonstrate a high degree of target specificity and low cytotoxicity. Therefore, they have emerged as promising carriers to deliver drugs to disease-associated targets, and could be efficient therapeutic drugs for various diseases. To date, organoids have been used to evaluate the efficacy of certain peptide agents; however, no organoid-based high-throughput screening of peptide drugs has been reported. Given the advantages of peptide drugs, there is an urgent need to establish organoid-based peptide high-throughput screening platforms. In this review, we discuss the typical approach of screening small-molecular drugs with the use of organoid cultures, as well as provide an overview of the studies that have incorporated organoids in peptide research. Drawing on the knowledge gained from small molecular screens, we explore the difficulties and potential avenues for creating new platforms to identify peptide agents using organoid models.

Background and Purpose: Opioids are widely used in the treatment of moderate and severe pain. Nociceptive stimulation and classical opioids have been reported to potentially promote microglial activation and neuroinflammation, which also reduces the analgesic effect of opioid drugs and causes chronic pain sensitization. The aim of this study was to demonstrate whether the novel opioid agonist MEL-0614 could inhibit activated microglia and neuroinflammation while facilitating recovery from persistent pain. Experimental approach: Mice were administered lipopolysaccharide and formalin to induce allodynia. Von Frey test was used to detect the anti-allodynia effect of MEL-0614 before and after LPS and formalin injection. In the spinal cord, the levels of proinflammatory cytokines and microglial activation were determined after MEL-0614 administration. BV2 and primary microglia were cultured to further explore the effect of MEL-0614 on LPS-induced microglial activation and key signalling pathways involved. Key results: MEL-0614 prevented and reversed allodynia induced by LPS and formalin in vivo, which was not inhibited by the μ opioid receptor antagonist CTAP. MEL-0614 also downregulated the activation of microglia and related proinflammatory cytokines in the spinal cord. Additionally, in BV2 and primary microglia, MEL-0614 inhibited the LPS-induced upregulation of proinflammatory factors, which was unaffected by CTAP. The NOD-like receptor protein 3-related signalling pathway may be involved in the interaction between MEL-0614 and microglia. Conclusion and Implications: The opioid agonist MEL-0614 inhibited the activation of microglia and the subsequent upregulation of proinflammatory factors both in vivo and in vitro. Notably, this effect is not mediated by the opioid receptors.