Background: The third-generation epidermal growth factor receptor (EGFR) inhibitor, Osimertinib, is used to treat non-small cell lung cancer (NSCLC) patients with tyrosine kinase inhibitor (TKI) resistance caused by acquired EGFR T790M mutation. However, patients eventually develop resistance against Osimertinib with mechanisms not yet fully clarified. Activated alternative survival pathways within the tumor cells and cancer-associated fibroblasts (CAFs) have been proposed to contribute to Osimertinib resistance. MET and MEK inhibitors may overcome EGFR-independent resistance. Another acquired resistance mechanism of EGFR-TKI is the up-regulation of the RAS/RAF/MEK/ERK signaling pathway, which is the key to cell survival and proliferation; this may occur downstream of various other signaling pathways. In this report, we reveal the possible regulatory mechanism and inhibitory effect of the MEK inhibitor trametinib applied to MEK/ERK/miR-21 axis and PDCD4 in Osimertinib resistance. We found a possible regulatory role of PDCD4 in ERK signaling. PDCD4 is a new type of tumor suppressor that has multiple functions of inhibiting cell growth, tumor invasion, metastasis, and inducing apoptosis. Previous bioinformatics analysis has confirmed that PDCD4 contains the binding site of miR-21 and acts as a tumor suppressor in the regulation of various processes associated with the development of cancer, including cell proliferation, invasion, metastasis, and neoplastic transformation. Based on the above analysis, we hypothesized that the tumor suppressor PDCD4 is one of the effective inhibitory targets of miR-21-5p. Methods: The expression between EGFR and ERK2 in lung adenocarcinoma was evaluated from the TCGA database. Osimertinib-sensitive and resistant NSCLC cells obtained from patients were used to co-culture with human lung fibroblasts (HLFs) to generate CAF cells (termed CAF_R1 and CAF_S1), and the functional roles of these CAF cells plus the regulatory mechanisms were further explored. Then, MEK inhibitor Trametinib with or without Osimertinib was applied in xenograft model derived from patients to validate the effects on growth inhibition of Osimertinib-resistant NSCLC tumors. Result: ERK2 expression correlated with EGFR expression and higher ERK2 level was associated with worse prognosis of patients and Osimertinib resistance. CAFs derived from Osimertinib-resistant cells secreted more IL-6, IL-8, and hepatocyte growth factor (HGF), expressed stronger CAF markers including α-smooth muscle actin (α-SMA), fibroblast activation protein (FAP) plus platelet-derived growth factor receptor (PDGFR), and enhanced stemness and Osimertinib resistance in NSCLC cells. Meanwhile, increased MEK/ERK/miR-21 expressions were found in both CAFs and NSCLC cells. MEK inhibitor Trametinib significantly abrogated the abovementioned effects by modulating β-catenin, STAT3, and ERK. The xenograft model showed combining Osimertinib and Trametinib resulted in the most prominent growth inhibition of Osimertinib-resistant NSCLC tumors. Conclusions: Our results suggested that MEK/ERK/miR-21 signaling is critical in Osimertinib resistance and CAF transformation of NSCLC cells, and MEK inhibitor Trametinib significantly suppressed Osimertinib-resistant NSCLC tumor growth by abolishing both processes.

Background: Recently we demonstrated that Astragalus polysaccharide (PG2), the active ingredient in dried roots of astragalus membranaceus, ameliorates cancer symptom clusters and improve quality of life (QoL) in patients with metastatic disease by modulating inflammatory cascade, against the background that inflammatory cells including macrophages, dendritic cells (DCs), and cytotoxic T lymphocytes (CTLs) in tumor initiation, metastasis, and progression. Nevertheless, the role of PG2 in the modulation of anticancer immunogenicity and therapeutic response remains relatively underexplored and unclear. Purpose: The present study investigates how and to what extent PG2 modulates cellular and biochemical components of the inflammatory cascade, enhance anticancer immunity, and the therapeutic implication of same in patients with lung cancer. Methods and Results: Herein, we demonstrated that PG2 significantly increased the M1/M2 macrophage polarization ratio in non-small cell carcinoma (NSCLC) H441 and H1299 cells. This PG2-induced preferential pharmacologic up-regulation of tumoral M1 population in vitro, positively correlated with the downregulation of tumor-promoting IL-6 and IL-10 expression in NSCLC cell-conditioned medium, with concomitant marked inhibition of cell proliferation, clonogenicity and tumorsphere formation. Our ex vivo results, using clinical sample from our NSCLC cohort, demonstrated that PG2 also promoted the functional maturation of DCs with consequent enhancement of T cell-mediated anticancer immune responses. Consistent with the in vitro and ex vivo results, our in vivo studies showed that mice treated with PG2 exhibited significant time-dependent depletion of the tumor-associated M2 population, synergistically enhanced the anti-M2-based anticancer effect of cisplatin, and inhibition of xenograft tumor growth in the NSCLC mice models. Moreover, in the presence of PG2, cisplatin-associated dyscresia and weight-loss was markedly suppressed. Conclusion: These results do indicate a therapeutically-relevant role for PG2 in modulating the M1/M2 macrophage pool, facilitating DC maturation, and synergistically enhancing the anticancer effect of conventional chemotherapeutic agent, cisplatin; thus laying the foundation for further exploration of the curative relevance of PG2 as surrogate immunotherapy and/or clinical feasibility of its use for maintenance therapy in patients with lung cancer.

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