Lung cancer (LC), non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) is a heterogeneous disease that mainly includes two subtypes and remains the leading cause of death worldwide. Despite recent advances in treatments, the 5-year overall survival rate of LC remains below 20%. The efficacy of current therapeutic approaches is compromised by natural or acquired drug resistance and serious off-target effects. Therefore, identifying and developing innovative and effective therapeutic approaches holds critical promise for LC. A turning point in the field of RNA biology is the development of RNA-mediated gene inhibition technologies.
The critical regulatory role of different RNAs in multiple cancer pathways makes them a rich source of targets and innovative tools for developing anticancer therapies. Identification of antisense sequences, short intrusive RNAs (siRNAs), microRNAs (miRNAs or miRs), anti-miRs and mRNA-based platforms, great hope in pre-clinical and early clinical evaluation against LC promises. RNA-based treatments have expanded and tested significantly in clinical trials for multiple malignancies, including LC, in recent years.
Studies on RNA therapy have suggested that these molecules have enormous potential to regulate multiple cellular pathways by inhibiting a variety of genes. The ease of targeting multiple pathways simultaneously provides an advantage in an RNA-based therapeutic platform to target different aspects of cancer such as tumor growth, metastasis, and drug resistance. Since most tumors exhibit mutational diversity, current cancer treatment methods, including surgery and chemotherapy, are far from ideal approaches, especially for advanced stage tumors. These mutational heterogeneities play an important role in cancer progression, chemo resistance, and immune escape. Therefore, RNA-based treatment strategies are potentially superior to traditional targeted therapies (containing protein as drug target) because they have a diverse target range with drug-like properties developed for cancer treatments.
Various approaches have been used to modulate gene function at the RNA level in cancer cells, including base editing, small molecules targeting RNA, the use of synthetic antisense oligonucleotides (ASOs), and exogenously expressed mRNAs. Promise of RNA-based therapeutic modalities, successful results of mRNA vaccine approach in treating disease caused by SARS-CoV-2 virus (COVID-19), U.S. Food and Drug Administration (FDA) approval by Patisiran (first RNAi-based therapy for hereditary transthyretin amyloidosis), Givosiran (RNAi drug for acute intermittent porphyria) and provides a strong rationale for discovering RNA fragments as a novel therapeutic strategy for cancer. Recent advances in time, safety, pharmacokinetics, and potency provide further support for the search for RNA toolbox to develop potential anticancer therapies.
RNAi Treatments in LC
RNAi groups effectively suppress target genes by inducing mRNA degradation or inhibiting the binding regions of the translation mechanism. Cyclooxygenase-2 (COX-2) is an important drug target that regulates cancer progression, metastasis, metabolism and tumor immunity in the LC. However, current COX-2 inhibitors have failed to show clinical efficacy. Instead of direct COX-2 inhibition, elimination of delta-5-desaturase (D5D) offers a unique approach that limits the formation of arachidonic acid (a substrate for COX-2) and promotes peroxidation of dihomo-linolenic acid. Pang et al. Incorporated D5D siRNA with epithelial cell adhesion molecule (EpCAM) aptamers into three-way junction RNA nanoparticles exhibiting target-specific accumulation, D5D knockdown, and 8-HOA formation in lung cancer cell lines and mouse models. These D5D siRNA loaded nanoparticles inhibited the proliferation of lung cancer cells and induced apoptosis by suppressing the YAP1 / TAZ axis.
Single nucleotide polymorphism (SNPs) and lncRNAs play an important role in LC. Analysis of SNPs and lncRNAs associated with LC risk identified serine-rich 1 antisense RNA1 (OSER-AS1), susceptible to oxidative stress, as a prognostic biomarker and therapeutic target. Down-regulation of OSER1-AS1 in tumor tissues is associated with poor OS in NSCLC patients. Myc suppresses the OSER-AS1 promoter, which is also targeted by the RNA binding protein ELAVL, like 1 (ELAVL1) and hsa-miR-17-5p at the 3′-end. OSER1-AS1 served as a decoy for ELAVL1 and prevented its interaction with the target mRNA. Treatment with OSER1-AS1 resulted in inhibition of growth and metastasis of xenograft LC tumors.
Two independent studies performed on LncRNA nicotinamide nucleotide transhydrogenase-antisense RNA1 (NNT-AS1) showed that overexpression of NNT-AS1 correlated with poor prognosis of NSCLC. NNT-AS1 upregulation decreases miR-22 by sponging, associated with increased expression of FOXM1 and YAP-1. Deactivation of NNT-AS1 reduces cell proliferation, invasion, migration, induces apoptosis, and suppresses tumor growth in vivo. Also, NNT-AS1 contributes to drug resistance in NSCLC via the MAPK-slug signal. Therefore, NNT-AS1 is a potential RNA-based therapeutic target and prognostic marker for NSCLC. Wanjun and his team reported on the analysis of non-canonical small non-coding RNAs (sncRNAs) using human peripheral blood mononuclear cells. And they analyzed small RNAs derived from rRNA (rsRNAs) and small RNAs derived from YRNA (ysRNAs), consisting of small RNAs derived from different tRNAs (tsRNAs). This TRY-RNA signature helps to distinguish between LC and pulmonary tuberculosis and thus has diagnostic implications for LC screening. A recent study demonstrated the potential of PD-L1 siRNA encapsulated gold nanoparticles for imaging and treatment of LC. These nanoparticles reduced PD-L1 expression in NSCLC cell lines and xenograft studies and acted as photothermal agents for LC photothermal therapy. Thus, it indicates the therapeutic application of siRNAs in the LC when combined with the appropriate photothermal agent. KDM3A is lysine-specific demethylase that increases DCLK1 expression by decreasing the methylation of H3K9me2. Recently, it has been shown that bone marrow mesenchymal stem cell derived extracellular vesicles (BMSC-EV) reduce LC growth by suppressing the KDM3A-DCLK1-FXYD3 axis of encapsulated let-7i miRNA. This study reported that KDM3A is a direct target of let-7i, with high expression of KDM3A and DCLK1 associated with reduced expression of let-7i. In addition, let-7i derived from BMSC-EV in vivo down-regulated KDM3A and reduced tumor growth.
In addition, extracellular miRNAs also serve as diagnostic biomarkers for LC. A study involving patients with NSCLC, patients with benign nodules, and healthy controls demonstrated that miR-520c-3p and miR-1274b are useful in identifying risk factors for NSCLC. This two-miRNA panel has the potential to differentiate between NSCLC and benign nodules. He also suggested the importance of extracellular miRNAs for diagnostic use in NSCLC. Similarly, another recent study determined the clinical significance of circulating or serum exosomal miR-let-7e as a biomarker for NSCLC metastasis. Analysis of serum exosomes and tumor tissues from NSCLC patients found that the suppressor of miR-let-7e was low, variation 3-9 homologous 2 (SUV39H2) was associated with high and low OS in NSCLC tissues. Ectopic overexpression of miR-let-7e or treatment with serum-derived exosomes (miR-let-7e is high in serum-derived exosomes) reduced cell viability, migration, invasion, and delayed tumor growth in vivo by targeting SUV39H2-LSD1. The therapeutic utility of miRNAs is also being explored for SCLC. For example, low expression of miRNA-195 was observed in SCLC. Low miRNA-195 and high Rap2C have been associated with low OS in SCLC patients. Overexpression of miRNA-195 reduced the proliferation of SCLC cells through Bax up-regulation and Bcl2 down-regulation, and this study also identified the binding site for miRNA-195 in Rap2C mRNA. Overexpression of miRNA-195 in SCLC cell lines inhibited activation of the MAPK pathway by decreasing Rap2C expression and inducing apoptosis.
Writer: Ozlem Guvenc Agaoglu