Abstract 2774: Moesin-induced adriamycin resistance through IL-6/MSN/STAT3 axis and therapeutic efficacy of atovaquone in chemotherapy resistant triple-negative breast cancer

Abstract Introduction: Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer with a high frequency of chemotherapy resistance. Moesin (MSN) is a cytoskeleton linker discovered as a novel oncogene in our previous proteomics analysis. Here, we evaluated the molecular mechanisms of MSN and how it functions in response to chemotherapy, which remains unclear in TNBC. Method: The 178 in-house TNBC patient cohort and METABRIC data set were enrolled for clinicopathologic analysis. The multiple TNBC four-cell lines were used to establish MSN knock-down and over-expressed in vitro models using a lentiviral system. RNA sequencing was analyzed with MDA-MB-231 parent cell and MDA-MB-231/ADR12 (adriamycin resistance cell line). Invasion and migration assay was done. The drug response based on MSN gene expression was observed by cell viability assay, western blot, and AV/PI flow cytometry. Drug resistance concerning cancer stemness was confirmed with sphere formation and ALDH activity assay. Immunofluorescence and immunoprecipitation were performed. The combination index(CI), which is to define the synergism of combined treatment was calculated with the Compusyn program. Results: The cohort with METABRIC and our in-house clinical data showed concordant findings that overexpressed MSN mRNA and protein expressions have a poor prognosis in TNBC patients. The MSN protein expression in TNBC was increased compared to the protein level in both the normal human tissues and non-TNBC cell lines. Overexpressed MSN induced high cell proliferation activity, invasion, and migration ability. The apoptosis rate (AV+/PI+) along with cleaved PARP and caspase-3 expression was increased in TNBC cell lines with MSN downregulation. Further tests to determine the role of MSN in adriamycin resistance showed an increased number and size of spheres in the MSN overexpressed cell lines. Moreover, the protein and mRNA levels of MSN expression in MDA-MB-231/ADR12 were significantly higher than the level in the matched parental cell line. MSN and phospho-STAT3(T705) were increased by treatment of IL-6 in TNBC cell lines. The direct binding between MSN and STAT3, and the co-localization of MSN and pSTAT3 were consistently confirmed by co-immunoprecipitation and immunofluorescence, which were all activated by IL-6. Blocking the STAT3 pathway with atovaquone restored ADR response in MSN overexpressed tumor cells. CI value on the combined treatment of ADR and atovaquone in the MDA-MB-231/ADR12 cell line showed higher synergetic efficacy than the parental cell line. Conclusion: This research demonstrates the involvement of the MSN in doxorubicin resistance through IL-6/MSN/STAT3 pathway and provides a novel therapeutic candidate for TNBC patients. Citation Format: Cheng Hyun Lee, Da Sol Kim, Soo Young Park, Han Suk Ryu. Moesin-induced adriamycin resistance through IL-6/MSN/STAT3 axis and therapeutic efficacy of atovaquone in chemotherapy resistant triple-negative breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2774.