RNA-based therapies: A cog in the wheel of lung cancer defense

Abstract

Lung cancer (LC) is a heterogeneous disease consisting mainly of two subtypes, non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC), and remains the leading cause of death worldwide. Despite recent advances in therapies, the overall 5-year survival rate of LC remains less than 20%. The efficacy of current therapeutic approaches is compromised by inherent or acquired drug-resistance and severe off-target effects. Therefore, the identification and development of innovative and effective therapeutic approaches are critically desired for LC. The development of RNA-mediated gene inhibition technologies was a turning point in the field of RNA biology. 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. The identification of antisense sequences, short interfering RNAs (siRNAs), microRNAs (miRNAs or miRs), anti-miRs, and mRNA-based platforms holds great promise in preclinical and early clinical evaluation against LC. In the last decade, RNA-based therapies have substantially expanded and tested in clinical trials for multiple malignancies, including LC. This article describes the current understanding of various aspects of RNA-based therapeutics, including modern platforms, modifications, and combinations with chemo-/immunotherapies that have translational potential for LC therapies.

Keywords: Antisense oligonucleotides; Lung cancer; RNA interference; anti-miRs; mRNA-vaccine.

Fig. 1

Different mechanisms of action for antisense oligonucleotide mediated gene silencing. Based on post-hybridization events, antisense oligonucleotides can modulate the expression of target gene through two different mechanisms 1) Occupancy-only mechanisms 2) RNA degradation mechanisms. In occupancy-only mechanisms, ASOs binding with target RNAs does not result in RNA degradation. It modulates the gene expression in several ways: splicing modulation using splice switch ASOs to perform exon-skipping or exon inclusion; inhibition of mRNA polyadenylation; translational modulation through non-DNA-like ASOs that base pair with mRNA, either to inhibit translation, for example, steric blocks or to activate translation by binding to inhibitory elements like upstream open reading frames (uORF). For the inhibition of miRNA-related function, these ASOs can also modulate miRNA either by base pairing with miRNA (anti-miRs) or by occupying miRNA-responsive elements (MRE) on target mRNA to nullify the effect of a particular miRNA. On the other hand, the ASOs in RNA degradation pathways trigger the target mRNA cleavage either by RNase H1 or siRNA-mediated AGO2 RISC complex and ribozymes mediated cleavage

Fig. 2

Common chemical modifications in antisense oligonucleotides and RNA oligonucleotides. Different types of RNA modifications or RNA analogs have been identified and evaluated in antisense mechanisms. A representative structure of dinucleotide is shown with marked positions where oligonucleotides are commonly modified. Commonly used modifications in ASOs consist of sugar modifications, base modifications, phosphate modifications, internucleoside linkage modifications, and conjugates of small or large molecules (as shown in the upper panel). Along with the structural modifications, the therapeutic properties of several key modifications are also highlighted. Specific internal RNA modifications are shown in the lower panel of figure (uridine-to-pseudo uridine and adenosine to-inosine transition are also presented). cEt BNA: (S)-constrained ethyl bicyclic nucleic acid

Fig. 3

Schematic illustrations for siRNA/miRNA biogenesis and, the mRNA inhibition via siRNA and miRNA-mediated mechanisms

Fig. 4

Schematic illustrations for mRNA-based LC vaccine development. The aim of mRNA vaccine development was started with a comparative analysis of exome of LC tissue and normal tissue to identify potential tumor-specific antigen(s). The detailed analysis coupled with high throughput methods enables the verification of identified antigen(s)/neoantigen(s) specific to LC. The mRNA sequence(s) specific to tumor antigens will then be synthesized, modified, and cloned into appropriate plasmids for the mRNA transcription. The liposome formulations (or other appropriate vehicles) of the final, optimized mRNA(s) encoding LC-specific antigens will be injected into LC patients to elicit a prominent anticancer immune response for the destruction of LC tumors