Perspective and challenges of organoid-based high-throughput peptide screening platforms
According to the methods of organoid-based small molecule drug screening platforms, we believe that organoids can also be applied in the high-throughput screening of peptides. This section presents the perspective and challenges of applying organoids in peptide screens based on their characteristics.
Owing to their remarkable binding affinity and specificity, peptides are suitable for transporting cytotoxic drugs to disease lesions138-140. However, there is still a wide gap between research and clinical application of peptide drugs. For example, the discovery of organ-specific targeted peptides may further decrease the side effect of this treatment modality. Given that peptides can be rapidly synthesized and easily modified, researchers can generate peptide libraries and perform high-throughput screening of the optimal candidates using organoid models, which is a promising direction for developing more effective peptide-based drugs3. Moreover, for peptides that deliver drugs in vivo, although the interactions are present on the cell surface, they may not alter the cell phenotype and cause a therapeutical effect. In RPT, the “cold” radionuclides without radioactivity are often used to label the peptide and prescreen the peptides with high binding affinity to reduce the experimental cost. The commonly used method, CellTiter-Glo assay, determines drug efficacy by measuring cell viability, which is not suitable for assessing the binding affinity of peptide candidates. Multiple approaches are used for traditional specific peptide discovery, such as using fluorescent labeled peptides. The future direction is to modify the existing methods and develop appropriate assays that match the high-throughput organoid culture technology, for direct assessment of peptide affinity. In addition, due to the difference in the emission range of radionuclides141-143, the peptide-radionuclide conjugates not bound to the cell surface but located near the cells should be investigated to determine whether they can kill the targeted cells, which may cause false-positive results during screening.
Peptides hold high biological and chemical diversity; and most targeting peptides exhibit therapeutic effects on diseases5. For example, the expression of immune checkpoint proteins (PD-1 and PD-L1) can be suppressed by targeted peptides for increasing the immune response to kill tumor cells 144-148. However, the high diversity of nature product peptides poses a challenge to the identification of the above-mentioned tumor neoantigens and bioactive peptides derived from venoms, which are produced by many kinds of organisms, such as plants, snakes, spiders and insects, and are found to interact with tumors and modulate the proliferation, migration, immune response of tumor cells, suggesting potential therapeutic agents for cancers149-155. Therapeutic peptides are promising candidates for treating various diseases, and more effective peptide drugs are required to address clinical demands. Thus, high-throughput screening of therapeutic peptides using organoid technology may significantly improve the efficiency for identifying and uncovering the optimal peptides with high binding affinity and ideal therapeutic effects. Furthermore, although peptides are low-cytotoxic drugs compared to small molecules and antibodies, healthy organoid models can also be used to examine their side effects on normal cells, which is one of the advantages of organoid technology.