Abstract 4419: Cancer exosomal microRNAs promote global mRNA 3' end shortening, multidrug chemoresistance, and cancer stemness

Abstract Background and Aim: Multidrug resistance (MDR) is a major cause of failure in cancer chemotherapy. It is commonly caused by efflux of anticancer drugs by ABC transporters including ABCG2. ABCG2 is also a cancer stem cell survival factor to drive cancer recurrence. Preferential production of mRNA isoforms with shortened 3’untranslated region (3’UTR) in cancer is associated with poor drug response. We previously reported that mRNA 3’UTR shortening could trigger ABCG2 overexpression in MDR cancer. Exosomes are cell-derived vesicles that are present in various biological fluids. Tumor-derived exosomes are emerging as important cell-to-cell couriers of oncogenic materials to mediate tumorigenesis. This study investigated the enrichment of specific microRNAs in MDR colon cancer derived exosomes to promote global mRNA 3’UTR shortening and spread chemoresistance. Method: Exosomes were isolated from a sensitive (S1) or resistant (S1M1-80) colon cancer cell lines conditioned medium by differential centrifugation, denoted as exo/S and exo/R, respectively. The transfer of microRNAs from exo/S or exo/R to a few sensitive colon cancer cell lines was evaluated. The shortening of ABCG2 mRNA 3’UTR in the exosome-donor and -recipient cancer cells was investigated by 3’RACE assay. MicroRNA microarray was conducted to identify differentially expressed microRNAs in drug sensitive cells after incubation with exo/R. Western blot and qPCR analysis were conducted to measure relevant protein and transcript expressions. Result: By 3’RACE assay, the shortening of ABCG2 3’UTR observed in the exosome donor resistant cells was also detected in the exosome recipient sensitive cells. MicroRNA profiling was conducted on 3 drug-sensitive and ABCG2low colon cancer cell lines (HCT116, SW480, and SW620) incubated with exo/S or exo/R. MiR-1260b was found to be remarkably upregulated in all 3 sensitive cell lines after incubation with exo/R. Intriguingly, the polyadenylation factor PABPN1 was found to be remarkably downregulated in exo/R-treated cells, which was accompanied by higher expression of ABCG2 and a few cancer stem cell markers (DCLK1, LGR5 and BMI1), and shortening of their mRNA 3’UTR. PABPN1 was subsequently confirmed to be a miR-1260b target. MiR-1260b inhibitor was able to reverse the downregulation of PABPN1 in HCT116 cells treated with exo/R, which subsequently suppressed ABCG2 level and reversed the MDR phenotype. Furthermore, while exo/R treated HCT116 form tumorspheres readily in vitro, miR-1260b inhibitor effectively reduced tumorsphere formation. Conclusion: MDR cells-derived exosomes may spread chemoresistance by transferring a miR-1260b/PABPN1/ABCG2 regulatory machinery to sensitive cells. We will set the stage to develop novel therapies aimed at interfering with the master regulators that mediate the microRNA sorting into exosome and mRNA 3’UTR shortening during MDR development. Citation Format: Kenneth K.W. To. Cancer exosomal microRNAs promote global mRNA 3' end shortening, multidrug chemoresistance, and cancer stemness [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4419.