Novel Siglec-15-Sia axis inhibitor leads to colorectal cancer cell death by targeting miR-6715b-3p and oncogenes

Description

Siglecs are well known immunotherapeutic targets in cancer. Current checkpoint inhibitors have exhibited limited efficacy, prompting a need for novel therapeutics for targets such as Siglec-15. Presently, small molecule inhibitors targeting Siglec-15 are not explored alongside characterised regulatory mechanisms involving microRNAs in CRC progression. Therefore, a small molecule inhibitor to target Siglec-15 was elucidated in vitro and microRNA mediated inhibitor effects were investigated. Our research findings demonstrated that the SHG-8 molecule exerted significant cytotoxicity on cell viability, migration, and colony formation, with an IC50 value of approximately 20µM. SHG-8 significantly reduced the SIGLEC15 expression at the gene and protein levels. Notably, miR-6715b-3p was the most upregulated miRNA in high-throughput sequencing, which was also validated via RT-qPCR. MiR-6715b-3p may regulate PTTG1IP, a potential oncogene which was validated via RT-qPCR and in silico analysis. Additionally, molecular docking studies revealed SHG-8 interactions with the Siglec-15 binding pocket with the binding affinity of -5.4 kcal/mol, highlighting its role as a small molecule inhibitor. Importantly, Siglec-15 and PD-L1 are expressed on mutually exclusive cancer cell populations, suggesting the potential for combination therapies with PD-L1 antagonists.

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To determine the differential expression of miRNAs treated with SHG-8, sRNA-seq was outsourced to Biomarker Technologies (Biomarker Technologies, Inc., CA, USA). SW480 cells were subjected to 24hrs SHG-8 treatment prior to total RNA extraction via TRIzol reagent method. The purity and quantity of each RNA sample was processed using a Nanodrop ND-1000 spectrophotometer UV-Vis Nanogen Inc. (Marshall Scientific, Hampton, USA) and 4150 TapeStation System (Agilent Technologies, California, USA). All samples were recorded with RIN numbers >7.0. The resulting data was subjected to Kyoto Encyclopedia of Genes and Genomes (KEGG), Gene Set Enrichment Analysis (GSEA) and Gene Ontology (GO) to identify enriched pathways, biological processes, molecular function, and cellular components in relation to CRC.

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