The sensitivity of lung cancer to epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitors (TKIs) has been found to be associated with mutations in the tyrosine kinase domain of EGFR. However, not all mutations are sensitive to gefitinib. While CpG island methylation in the promoter region of the EGFR gene and transcriptional silencing are common in solid tumors, the role of the EGFR gene promoter methylation in affecting resistance to TKIs in non-small cell lung cancer (NSCLC) remains unknown. In this study, we examined the correlation between EGFR gene promoter methylation and the therapeutic effect of gefitinib in NSCLC cells. Three NSCLC cell lines with different EGFR mutation statuses and levels of sensitivity to EGFR-TKIs were used in this study: H1650 (del E746-A750), H1299 (wild-type EGFR) and PC-9 (del E746-A750). Cells were treated with gefitinib or 5-aza-2'-deoxy cytidine (5-aza-CdR), a methylation inhibitor, alone or in combination. Subsequently, the methylation status of the EGFR gene promoter was examined by methylation-specific PCR (MSP). Cell survival and apoptosis assays were performed using the Cell Counting Kit-8 (CCK-8) and flow cytometry. In addition, western blot analysis and quantitative real-time PCR were used to examine the expression levels of EGFR protein and mRNA. Our study showed that the promoter region of the EGFR gene in PC-9 cells was unmethylated, and that the cells were sensitive to gefitinib. By contrast, the promoter region of the EGFR gene in the H1650 and H1299 cells was methylated, and the cells were resistant to gefitinib. Of note, the combination treatment with 5-aza-CdR and gefitinib further enhanced the growth inhibitory effects and led to the induction of apoptosis, while a significant reduction in the expression of EGFR protein and mRNA was observed in the H1650 and H1299 cells. These results suggest that blockade of DNA methylation may enhance the antitumor effects of EGFR-TKIs and gefitinib in NSCLC cells. Thus, EGFR gene promoter methylation may be a potential mechanism for acquired resistance to gefitinib.
Focusing beyond the acoustic diffraction limit has always been expected, especially in acoustic imaging and ultrasonic therapy. Manipulating the acoustic waves beyond the diffraction limit offers an alternative application potential in high-resolution imaging and medical ultrasound diagnosis and treatment. Here, a two-dimensional circular meta-lens is presented, with a sub-wavelength acoustic Helmholtz resonator array to implement the super-diffraction focusing. The proposed acoustic meta-lens consists of 28 units, which possesses the ability to yield designed arbitrary phase shifts and maintain the impedance matching to provide the high sound transmission efficiency. The simulation and experimental results show that the designed acoustic meta-lens can realize subwavelength sound focusing beyond the diffraction limit. The proposed method can greatly promote the application and development of the acoustic superfocusing technology in acoustic imaging, particle manipulation, and other fields.
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