The Small RNA Landscape in NSCLC: Current Therapeutic Applications and Progresses

Abstract

Non-small-cell lung cancer (NSCLC) is the second most diagnosed type of malignancy and the first cause of cancer death worldwide. Despite recent advances, the treatment of choice for NSCLC patients remains to be chemotherapy, often showing very limited effectiveness with the frequent occurrence of drug-resistant phenotype and the lack of selectivity for tumor cells. Therefore, new effective and targeted therapeutics are needed. In this context, short RNA-based therapeutics, including Antisense Oligonucleotides (ASOs), microRNAs (miRNAs), short interfering (siRNA) and aptamers, represent a promising class of molecules. ASOs, miRNAs and siRNAs act by targeting and inhibiting specific mRNAs, thus showing an improved specificity compared to traditional anti-cancer drugs. Nucleic acid aptamers target and inhibit specific cancer-associated proteins, such as "nucleic acid antibodies". Aptamers are also able of receptor-mediated cell internalization, and therefore, they can be used as carriers of secondary agents giving the possibility of producing very highly specific and effective therapeutics. This review provides an overview of the proposed applications of small RNAs for NSCLC treatment, highlighting their advantageous features and recent advancements in the field.

Keywords: ASO; NSCLC; RNAi; aptamer; targeted therapy.

Figure 1

RNA-based therapeutics general mechanism of action. Scheme of the main mechanism of action of small RNA-based therapeutics: ASOs, miRNAs, and siRNAs bind to mRNA preventing proteins translation; aptamers bind their target protein by folding into complex tridimensional shapes.

Figure 2

Main mechanisms of action of ASOs. Schematic representation of the different mechanisms of action of ASOs. ASOs can block protein expression by binding to the mRNA and leading to: (i) the RNase H-mediated mRNA degradation; (ii) the steric block of the correct ribosomal assembly; (iii) the alteration of the normal splicing causing exon skipping or inclusion. Alternatively, they can sequestrate miRNAs avoiding their binding to target mRNAs.

Figure 3

microRNA biogenesis. Main steps of microRNA processing. Briefly, miRNA transcripts (pri-miRNAs) are produced and cleaved by Drosha into pre-miRNAs. The pre-miRNAs are then exported into the cytoplasm by exportin-5–Ran-GTP and further processed into mature miRNA duplexes. The functional strand of the mature miRNA is thus guided by the RISC complex to the target mRNA permitting translational repression or mRNA cleavage.

Figure 4

Schematic representation of aptamer-based complexes applied to NSCLC therapy. Aptamer complexes developed for the targeting of NSCLC were generated by: (a) direct drug intercalation within the aptamer structure; (b) aptamer covalent conjugation to miRNAs in which the aptamer sequence is extended with one of the miRNA strand and then annealed with the other miRNA strand; (c) aptamer non-covalent conjugation to miRNAs through a stick-based strategy in which the aptamer and miRNA passenger strand are extended with complementary stick sequences to allow their annealing; (d) nanosystem decoration with a targeting aptamer.