Revisiting Lung Cancer Metastasis: Insight From the Functions of Long Non-coding RNAs

Globally, lung cancer is the most common cause of cancer-related deaths. After diagnosis at all stages, <7% of patients survive for 10 years. Thus, diagnosis at later stages and the lack of effective and personalized drugs reflect a significant need to better understand the mechanisms underpinning lung cancer progression. Metastasis should be responsible for the high lethality and recurrence rates seen in lung cancer. Metastasis depends on multiple crucial steps, including epithelial–mesenchymal transition, vascular remodeling, and colonization. Therefore, in-depth investigations of metastatic molecular mechanisms can provide valuable insights for lung cancer treatment. Recently, long noncoding RNAs (lncRNAs) have attracted considerable attention owing to their complex roles in cancer progression. In lung cancer, multiple lncRNAs have been reported to regulate metastasis. In this review, we highlight the major molecular mechanisms underlying lncRNA-mediated regulation of lung cancer metastasis, including (1) lncRNAs acting as competing endogenous RNAs, (2) lncRNAs regulating the transduction of several signal pathways, and (3) lncRNA coordination with enhancer of zeste homolog 2. Thus, lncRNAs appear to execute their functions on lung cancer metastasis by regulating angiogenesis, autophagy, aerobic glycolysis, and immune escape. However, more comprehensive studies are required to characterize these lncRNA regulatory networks in lung cancer metastasis, which can provide promising and innovative novel therapeutic strategies to combat this disease.

MicroRNAs in cancer metastasis and angiogenesis

Cancer metastasis is a malignant process by which tumor cells migrate from their primary site of origin to other organs. It is the main cause of poor prognosis in cancer patients. Angiogenesis is the process of generating new blood capillaries from pre-existing vasculature. It plays a vital role in primary tumor growth and distant metastasis. MicroRNAs are small non-coding RNAs involved in regulating normal physiological processes as well as cancer pathogenesis. They suppress gene expression by specifically binding to the 3′-untranslated region (3′-UTR) of their target genes. They can thus act as oncogenes or tumor suppressors depending on the function of their target genes. MicroRNAs have shown great promise for use in anti-metastatic cancer therapy. In this article, we review the roles of various miRNAs in cancer angiogenesis and metastasis and highlight their potential for use in future therapies against metastatic cancer.

[Cancer cell plasticity and metastatic dissemination]

Metastatic dissemination consists of a sequence of events resulting in the invasion by cancer cells of tissues located away from the primary tumour. This process is highly inefficient, since each event represents an obstacle that only a limited number of cells can overcome. However, two biological phenomena intrinsically linked with tumour development facilitate the dissemination of cancer cells throughout the body and promote the formation of metastases, namely the genetic diversity of cancer cells within a given tumour, which arises from their genetic instability and from successive clonal expansions, and cellular plasticity conveyed to the cells by micro-environmental signals. Genetic diversity increases the probability of selecting cells that are intrinsically resistant to biological and physical constraints encountered during metastatic dissemination, whereas cellular plasticity provides cells with the capacity to adapt to stressful conditions and to changes in the microenvironment. The epithelial-mesenchymal transition, an embryonic trans-differentiation process frequently reactivated during tumour development, plays an important role in that context by endowing tumor cells with a unique capacity of motility, survival and adaptability to the novel environments and stresses encountered during the invasion-metastasis cascade.

[Resistance to anti-angiogenic therapy: a clinical and scientific current issue]

Although the use of anti-angiogenic agents has been considered a promising strategy to block tumor growth and improve the bioavailability of drugs into the tumor, the use of most of them in clinical trials is limited. The development of resistance to some anti-angiogenic agents and their high toxicity are currently under investigations. However, the approach is still valid since this therapeutic tool has lengthened survival of patients with colon, breast, kidney, lungs and liver cancers. The identification of biomarkers in response to this family of drugs is an important area of investigation.