Roles of Annexin A1 Expression in Small Cell Lung Cancer

Background/Objectives: Small cell lung cancer (SCLC) is one of the malignancies with the worst prognosis, and there have been no major breakthroughs in its treatment for a long time. The majority of patients are diagnosed at the extensive stage, where the only option is chemotherapy, and even the addition of immune checkpoint inhibitors results in only modest benefits. The characterization of the molecular mechanisms behind therapy resistance has relevance in finding novel therapeutic approaches. Previous studies showed the possibility of annexin A1’s (ANXA1) involvement in the immunosuppressive tumor microenvironment in SCLC, and there are studies showing the direct effects of ANXA1 modulation on cancer cell aggressiveness. Methods: We aimed to characterize the roles of ANXA1 expression using publicly available transcriptomic data, the RNA-seq-based predictive algorithms EPIC and ESTIMATE, and immunohistochemistry on patient samples. For the in vitro studies, we silenced ANXA1 expression with short hairpin RNA in three SCLC cell lines, measured the growth rate with the trypan blue exclusion assay, assessed the chemosensitivity to cisplatin and etoposide with the Presto BlueTM viability assay, and performed Western blots to assess changes in the levels of metabolic and mesenchymal markers and transcriptional drivers. Results: ANXA1-high tumors are associated with significantly increased immune infiltrates, stromality, and tumor-associated macrophages (TAMs). The ANXA1 protein is expressed on tumor cells and TAMs at the tissue level. ANXA1 silencing in H841 cells did not affect the growth rate; in SW1271 cells, shANXA1 cells grew significantly slower than shCTRL cells. Meanwhile, in H1048 cells, proliferation was significantly faster. Despite the different growth rates of the tested cell lines, ANXA1 silencing decreased the chemosensitivity to both cisplatin and etoposide in all three cell lines. Gene expression changes in mesenchymal markers, metabolic markers, dominant transcriptional drivers, and immune-relevant molecules were also characterized. Conclusions: This is the first comprehensive characterization of ANXA1 in SCLC to reveal its role in the tumor’s cell biology and the TME, aiming to boost further research in the field.