Oncogenic MET as an Effective Therapeutic Target in Non-Small Cell Lung Cancer Resistant to EGFR Inhibitors: The Rise of the Phoenix

The Latest Battles Between EGFR Monoclonal Antibodies and Resistant Tumor Cells

Epidermal growth factor receptor (EGFR) is a tyrosine kinase receptor involved in homeostatic regulation of normal cells and carcinogenesis of epithelial malignancies. With rapid development of the precision medicine era, a series of new therapies targeting EGFR are underway. Four EGFR monoclonal antibody drugs (cetuximab, panitumumab, nimotuzumab, and necitumumab) are already on the market, and a dozen other EGFR monoclonal antibodies are in clinical trials. Here, we comprehensively review the newly identified biological properties and anti-tumor mechanisms of EGFR monoclonal antibodies. We summarize recently completed and ongoing clinical trials of the classic and new EGFR monoclonal antibodies. More importantly, according to our new standard, we re-classify the complex evolving tumor cell resistance mechanisms, including those involving exosomes, non-coding RNA and the tumor microenvironment, against EGFR monoclonal antibodies. Finally, we analyzed the limitations of EGFR monoclonal antibody therapy, and discussed the current strategies overcoming EGFR related drug resistance. This review will help us better understand the latest battles between EGFR monoclonal antibodies and resistant tumor cells, and the future directions to develop anti-tumor EGFR monoclonal antibodies with durable effects.

High Expression of Long Noncoding RNA PCNA-AS1 Promotes Non-Small-Cell Lung Cancer Cell Proliferation and Oncogenic Activity via Upregulating CCND1

Accumulating evidences showed that aberrantly expressed long noncoding RNAs (lncRNAs) have critical roles in many cancers. However, the expression and roles of a poorly studied lncRNA PCNA-AS1 in non-small-cell lung cancer (NSCLC) remain unknown. In this study, we investigated the expression, clinical significance, biological roles, and functional mechanism of PCNA-AS1 in NSCLC. Our results showed that PCNA-AS1 was upregulated in NSCLC tissues and cell lines, and correlated with TNM stages. Functional experiments showed that overexpression of PCNA-AS1 promoted NSCLC cell proliferation and cell cycle progression. Depletion of PCNA-AS1 inhibited NSCLC cell proliferation and cell cycle progression, and also inhibited NSCLC tumor growth in vivo. Mechanistically, we found that PCNA-AS1 upregulated CCND1 expression. The expression of PCNA-AS1 was positively correlated with that of CCND1 in NSCLC tissues. Moreover, depletion of CCND1 abrogated the oncogenic roles of PCNA-AS1 in NSCLC. In conclusion, highly expressed PCNA-AS1 promotes NSCLC cell proliferation and oncogenic activity via upregulating CCND1. Our results imply that PCNA-AS1 might serve as a therapeutic target for NSCLC.

Brain Metastases from Lung Cancer: Is MET an Actionable Target?

The process of metastatic dissemination begins when malignant cells start to migrate and leave the primary mass. It is now known that neoplastic progression is associated with a combination of genetic and epigenetic events. Cancer is a genetic disease and this pathogenic concept is the basis for a new classification of tumours, based precisely on the presence of definite genetic lesions to which the clones are addicted. Regarding the scatter factor receptors MET and Recepteur d'Origin Nantais (RON), it is recognised that MET is an oncogene necessary for a narrow subset of tumours (MET-addicted) while it works as an adjuvant metastogene for many others. This notion highlights that the anti-MET therapy can be effective as the first line of intervention in only a few MET-addicted cases, while it is certainly more relevant to block MET in cases of advanced neoplasia that exploit the activation of the invasive growth program to promote dissemination in other body parts. Few data are instead related to the role played by RON, a receptor homologous to MET. We have already demonstrated an implication of MET and RON genes in brain metastases from lung cancer. On this basis, the aim of this work is to recapitulate and dissect the molecular basis of metastatic brain dissemination from lung cancer. The latter is among the big killers and frequently gives rise to brain metastases, most often discovered at diagnosis. Molecular mechanisms leading to tumour spread to the brain are mostly unknown and in turn these tragic cases are still lacking effective therapies. Based on previously published data from our group, we aim to summarise and analyse the pathogenic mechanisms leading to activation of the scatter factor receptor in brain metastatic lesions of lung primaries, from the point of view of replacing the currently used empirical treatment with a more targeted approach.

HGF-mediated crosstalk between cancer-associated fibroblasts and MET-unamplified gastric cancer cells activates coordinated tumorigenesis and metastasis

Cancer-associated fibroblasts (CAFs) are important components of tumor stroma and play a key role in tumor progression. CAFs involve in crosstalk with tumor cells through various kinds of cytokines. In the present study, we screened hepatocyte growth factor (HGF) as a cytokine predominantly originating from CAFs. CAFs-derived HGF was found to promote MET-unamplified gastric cancer (GC) proliferation, migration, and invasion through the activation of HGF/c-Met/STAT3/twist1 pathway. It also activated interleukin (IL)-6/IL-6R/JAK2/STAT3/twist1 pathway by up-regulating IL-6R expression. As IL-6 was also found to upregulate c-Met expression, we identified the cooperation of HGF and IL-6 in enhancing the characteristics of CAFs. In vivo experiments revealed that CAFs-derived HGF promoted tumorigenesis and metastasis of MET-unamplified GC. Gene set enrichment analysis (GSEA) was performed to confirm our findings. Our study found that the increased expression of HGF in CAFs induced by MET-unamplified GC contributed to the malignant phenotype of both MET-unamplified GC and CAFs in tumor microenvironment.

Downregulation of Cyclin B1 mediates nagilactone E-induced G2 phase cell cycle arrest in non-small cell lung cancer cells

Non-small cell lung cancer (NSCLC) is one of the most common forms and leading causes of cancer-related mortality worldwide, and discovery of new effective drugs still remains imperative to improve the survival rate. Nagilactone E (NLE) is a natural product isolated from Podocarpus nagi seeds, which has been used as raw materials for edible oil and industrial oil extraction. This study aimed to investigate the anticancer potential of NLE against NSCLC A549 and NCI-H1975 cells. MTT assay revealed that NLE inhibited the proliferation of A549 and NCI-H1975 cells with IC₅₀s of 5.18 ± 0.49 and 3.57 ± 0.29 μM, respectively. NLE treatment inhibited clone formation in both cancer cell lines. Cell cycle analysis indicated that NLE treatment effectively induced G2 phase cell cycle arrest in A549 and NCI-H1975 cells. NLE downregulated the phosphorylation of cdc2 (Tyr15) and cdc25C (Ser216) as well as the expression level of the protein kinase Wee1 in concentration- and time-dependent manners. In addition, NLE treatment decreased the protein level of Cyclin B1 as well as its nuclear localization, which might decrease the activity of the Cyclin B1/cdc2 complex and induce G2 phase arrest. Long-term NLE treatment also induced caspase-dependent cell apoptosis, as evidenced by increase in Annexin V positive cells and the cleavage of PARP. To sum, NLE inhibited proliferation, induced G2 phase arrest, and triggered caspase-dependent apoptosis in NSCLC cells, suggesting it to be a potential leading compound for cancer treatment.

The multiple paths towards MET receptor addiction in cancer

Targeted therapies against receptor tyrosine kinases (RTKs) are currently used with success on a small proportion of patients displaying clear oncogene activation. Lung cancers with a mutated EGFR provide a good illustration. The efficacy of targeted treatments relies on oncogene addiction, a situation in which the growth or survival of the cancer cells depends on a single deregulated oncogene. MET, a member of the RTK family, is a promising target because it displays many deregulations in a broad panel of cancers. Although clinical trials having evaluated MET inhibitors in large populations have yielded disappointing results, many recent case reports suggest that MET inhibition may be effective in a subset of patients with unambiguous MET activation and thus, most probably, oncogene addiction. Interestingly, preclinical studies have revealed a particularity of MET addiction: it can arise through several mechanisms, and the mechanism involved can differ according to the cancer type. The present review describes the different mechanisms of MET addiction and their consequences for diagnosis and therapeutic strategies. Although in each cancer type MET addiction affects a restricted number of patients, pooling of these patients across all cancer types yields a targetable population liable to benefit from addiction-targeting therapies.

c-Met, CREB1 and EGFR are involved in miR-493-5p inhibition of EMT via AKT/GSK-3β/Snail signaling in prostate cancer

miR-493-5p downregulation has emerged as a critical player in cancer progression yet, the underlying mechanisms of miR-493-5p expression pattern and its function in prostate cancer remains to be elucidated. Here, we illustrate that miR-493-5p is frequently downregulated in prostate cancer, at least partially due to altered DNA methylation. miR-493-5p functions as a tumor suppressor in prostate cancer cells. c-Met, CREB1 and EGFR are downstream target genes of miR-493-5p. miR-493-5p inhibits EMT via AKT/GSK-3β/Snail signaling in prostate cancer. Taken together, our study identified c-Met, CREB1, EGFR and miR-493-5p establish a regulatory loop in prostate cancer, which could prove useful in the development of effective and therapies against prostate cancer.

MET/SMAD3/SNAIL circuit mediated by miR-323a-3p is involved in regulating epithelial-mesenchymal transition progression in bladder cancer

Bladder cancer (BCa) is the one of the most common cancers with high incidence, occurrence and low 5-year survival rate. Emerging evidence indicates that DLK1-DIO3 genomic region especially the miRNA cluster in this region is involved in several pathologic processes and various cancers, and miR-323a-3p is a member of this miRNA cluster. In this study, we investigate the function and regulatory network of miR-323a-3p in BCa. miR-323a-3p is frequently downregulated in BCa tissues and three cell lines compared with adjacent non-tumorous tissues and bladder normal cell line (SV-HUC-1). Besides, downregulation of miR-323a-3p is significantly associated with poor overall survival rate of BCa. Methylation of DLK1-MEG3 intergenic DMR (IG-DMR) contributes to the reduction of miR-323a-3p. Overexpression of miR-323a-3p significantly inhibits the epithelial-mesenchymal transition (EMT) progression of BCa. Both upregulated MET and SMAD3 are direct targets of miR-323a-3p, and the knockdown of MET and SMAD3 also represses the EMT progression consistently with overexpression of miR-323a-3p. SNAIL is detected in the last targeted confocal protein of both MET and SMAD3 signaling that trigger EMT consequently. Hence, a miR-323a-3p/MET/SMAD3/SNAIL circuit is established to regulate the EMT progression of BCa. And a mutual regulatory mechanism between miR-323a-3p/miR-433/miR-409 and MET also participates in this circuit. In conclusion, our study demonstrates a novel regulatory mechanism of the miR-323a-3p/MET/SMAD3/SNAIL circuit that is involved in the EMT regulation of BCa, which may be a potential therapy target for BCa.