Although great changes have taken place in cancer diagnosis methods and treatment strategies in the past decades, the prognosis of ESCC patients is still poor. Additionally, because of tumor heterogeneity, TNM stage cannot fully reflect the molecular characteristics of ESCC patients[20], and often the same TNM staging has different prognosis. Therefore, it is urgent to find new biomarkers. Previous studies have found that anoikis is crucial for tumor metastasis. Cells shed from the original site will activate anoikis to maintain tissue homeostasis[21]. However, since cancer cells have lost their sensitivity to anoikis, they can continue to proliferate without adhering to ECM and metastasize to other organs[22]. Overcoming the resistance of cancer cells to anoikis may become a new therapeutic direction.
In this study, we identified key anoikis-related genes through LASSO regression and SVM-RFE machine learning algorithms and constructed prognosis-related ARGS, including CLDN1, EGFR, PLK1, SATB1 and TNFSF10. The expression of these five genes in ESCC and normal tissues was significantly different, which was confirmed by qRT-PCR. CLDN1 is a membrane protein that constitutes the tight junction of cells and participates in the invasion and metastasis of cancer. The expression of CLDN1 in advanced and metastatic colon cancer lesions was significantly higher than that in normal cells[23]. In ESCC, EGFR is overexpressed in about half of the patients[24]. Cetuximab, which targets EGFR overexpression in ESCC, was carrying out several related studies. Although it has not significantly improved the prognosis of ESCC patients, the study of the population with significant expression of this molecular target will eventually bring dawn to ESCC patients[25]. PLK1 is a serine/threonine kinase that regulates cell cycle and is highly expressed in many cancers. PLK1 inhibitors combined with other chemotherapy drugs have been proven to reduce drug resistance[26]. High expression of SATB1 promotes the occurrence and metastasis of multiple cancers by affecting cell apoptosis and the EMT process[27]. However, in this study, SATB1 was low expressed in ESCC compared with normal tissues, while qRT-PCR showed the opposite result. The possible reason was that the sample size was too small. TNFSF10 enhances tumor metastasis by promoting EMT. In vitro experiments showed that knockout of TNFSF10 can reduce ESCC cell migration[28].
ESCC was divided into two subgroups according to ARGS, and there was significant discrepancy in biological function and pathways between the two groups. The ARGS-high group was mainly related to immune-related pathways, and ssGSEA analysis also confirmed this result. The infiltration of immune cells in the TME is closely related to the potential response to immunotherapy[29]. Therefore, we can speculate that there is a positive correlation between immune cell infiltration and the effect of immunotherapy. EMT plays a key role in promoting tumor metastasis, and it is also a necessary process for tumor cells to obtain anti-anoikis property[30]. The results of GSEA indicated that the ARGS-low group was mainly related to the negative regulation of cell aging and negative regulation of EMT, which may be the main reasons for the better prognosis of such patients.
Given the correlation between ARGS and immune pathways, we further predicted immunotherapy efficacy based on ARGS. It is found that the ARGS-low group has higher the TIDE score and T cell exclusion score. Higher TIDE score means a greater likelihood of immune escape of immunotherapy. Many chemotherapy drugs inhibit tumor growth by inducing apoptosis, and tumor cells will increase their drug resistance due to resistance to anoikis[31]. We analyzed IC50 of multiple chemotherapy drugs and found that the ARGS-low group was more sensitive to multiple chemotherapy drugs. These results may provide more appropriate diagnosis and treatment strategies for ESCC patients.
This study has some limitations. First of all, the transcriptome data in this study was from public databases, and its credibility still needs to be verified by real world data. In addition, the effects of key anoikis-related genes alone or in combination need to be further analyzed through in vitro and in vivo experiments.