Aptamers and antisense therapy MCQs With Answer

Aptamers and antisense therapy MCQs With Answer

This blog provides a focused set of multiple-choice questions designed for M.Pharm students studying Molecular Pharmaceutics and Nucleic Acid Therapeutics. The questions cover fundamental and advanced concepts in aptamer technology and antisense oligonucleotide (ASO) therapeutics, including selection methods (SELEX variants), chemical modifications for stability and affinity, mechanisms of action (RNase H, steric-blocking, splice modulation), delivery strategies, pharmacokinetics, safety concerns and analytical evaluation. Each question tests application-level understanding expected at the postgraduate level and includes concise correct answers to help revise critical concepts for examinations and practical formulation development in nucleic acid therapeutics.

Q1. Which step in the classical SELEX process is primarily responsible for enriching high-affinity aptamer sequences?

• Reverse transcription of selected sequences
• Iterative binding and partitioning against the target
• High-throughput sequencing of the starting library
• Polymerase chain amplification of the entire library

Correct Answer: Iterative binding and partitioning against the target

Q2. Which chemical modification is most commonly used to increase nuclease resistance of RNA aptamers without dramatically altering base-pairing?

• 2′-O-methyl and 2′-fluoro substitutions on the ribose
• Phosphodiester backbone replacement with peptide backbone
• Introduction of deoxyuridine at every uridine position
• Complete replacement with L-DNA (Spiegelmer)

Correct Answer: 2′-O-methyl and 2′-fluoro substitutions on the ribose

Q3. Spiegelmers differ from regular aptamers because they are composed of which stereochemical form, conferring resistance to nucleases?

• D-ribonucleotides
• L-nucleotides (mirror-image)
• Phosphorothioate nucleotides
• Peptide nucleic acids (PNA)

Correct Answer: L-nucleotides (mirror-image)

Q4. Which mechanism best describes how a gapmer antisense oligonucleotide reduces target mRNA levels?

• Blocking ribosome binding without degrading mRNA
• Recruiting RNase H to cleave the RNA strand of RNA–DNA duplexes
• Inducing RNA interference via RISC complex loading
• Altering chromatin structure to reduce transcription

Correct Answer: Recruiting RNase H to cleave the RNA strand of RNA–DNA duplexes

Q5. Which of the following aptamer therapeutic attributes is most directly improved by PEGylation?

• Affinity (Kd) for the molecular target
• Sequence specificity for target recognition
• Circulatory half-life by reducing renal clearance
• Intrinsic catalytic activity of the aptamer

Correct Answer: Circulatory half-life by reducing renal clearance

Q6. What primary advantage do locked nucleic acids (LNA) provide when incorporated into antisense oligonucleotides?

• They completely block immune recognition by TLRs
• They markedly increase thermal stability and binding affinity to RNA
• They convert ASOs into siRNA-like duplexes
• They render ASOs biodegradable into nucleosides

Correct Answer: They markedly increase thermal stability and binding affinity to RNA

Q7. Which antisense chemistry acts by steric blockade and is commonly used for splice modulation without engaging RNase H?

• Phosphorothioate gapmers
• 2′-O-methoxyethyl (2′-MOE) gapmers
• Morpholino oligomers (PMO)
• siRNA duplexes

Correct Answer: Morpholino oligomers (PMO)

Q8. Which assay is most appropriate for determining equilibrium dissociation constant (Kd) of an aptamer-target interaction?

• Gel electrophoresis mobility shift assay (EMSA)
• Surface plasmon resonance (SPR)
• qPCR quantification of aptamer sequence
• Mass spectrometry peptide mapping

Correct Answer: Surface plasmon resonance (SPR)

Q9. A major safety concern with phosphorothioate-modified antisense oligonucleotides is:

• Complete lack of plasma protein binding
• Activation of complement and pro-inflammatory effects due to nonspecific protein interactions
• Spontaneous conversion to siRNA in plasma
• Uncontrolled enzymatic ligation into genomic DNA

Correct Answer: Activation of complement and pro-inflammatory effects due to nonspecific protein interactions

Q10. In cell-SELEX, what is the main advantage compared to purified-protein SELEX?

• It guarantees higher thermal stability of aptamers
• It selects aptamers recognizing native cell-surface conformations and post-translational modifications
• It eliminates the need for iterative PCR amplification
• It ensures aptamers are resistant to denaturation by organic solvents

Correct Answer: It selects aptamers recognizing native cell-surface conformations and post-translational modifications

Q11. Which delivery system has been successfully used to enhance intracellular delivery of antisense oligonucleotides and siRNAs in clinical formulations?

• Lipidoid/lipid nanoparticles (LNPs)
• Unformulated naked DNA plasmids only
• Hydrophobic organic solvents like DMSO for infusion
• Free oligos administered orally without carriers

Correct Answer: Lipidoid/lipid nanoparticles (LNPs)

Q12. For an antisense oligonucleotide targeting pre-mRNA splice sites to induce exon skipping, which design feature is most critical?

• High RNase H recruitment potential
• Sequence complementarity spanning the splice junction or regulatory elements
• Complete phosphodiester backbone to enable rapid degradation
• Inclusion of immunostimulatory CpG motifs to boost potency

Correct Answer: Sequence complementarity spanning the splice junction or regulatory elements

Q13. Which structural motif is frequently observed in G-rich DNA or RNA aptamers and contributes to high-affinity binding?

• Alpha helix
• G-quadruplex
• Z-DNA helix
• Beta-sheet

Correct Answer: G-quadruplex

Q14. A primary pharmacokinetic determinant causing rapid renal clearance of short oligonucleotides is:

• Their high affinity for plasma albumin
• Their small hydrodynamic radius and molecular weight below glomerular filtration cutoff
• Strong binding to lipoproteins leading to hepatic sequestration
• Incorporation into red blood cells

Correct Answer: Their small hydrodynamic radius and molecular weight below glomerular filtration cutoff

Q15. Which modification to an antisense oligonucleotide backbone increases resistance to exonucleases while retaining RNase H activity in a gapmer design?

• Uniform replacement of all nucleotides with 2′-O-methyl
• Phosphorothioate backbone in the flanking wings with a central DNA gap
• Full morpholino backbone across entire sequence
• Substitution with peptide nucleic acid for the central gap

Correct Answer: Phosphorothioate backbone in the flanking wings with a central DNA gap

Q16. Which immune receptor is most commonly implicated in oligonucleotide-mediated innate immune activation when unmethylated CpG motifs are present?

• Toll-like receptor 9 (TLR9)
• TLR4 on endothelial cells
• MHC class I molecules
• NOD-like receptor NLRP3 exclusively

Correct Answer: Toll-like receptor 9 (TLR9)

Q17. Compared to siRNA, antisense oligonucleotides (ASOs) have which key difference in mechanism or use?

• ASOs always require RISC loading to function
• ASOs can modulate splicing and act in the nucleus more readily than siRNAs
• ASOs are double-stranded RNAs of ~21 bp
• ASOs cannot recruit RNase H under any circumstances

Correct Answer: ASOs can modulate splicing and act in the nucleus more readily than siRNAs

Q18. Which analytical technique can be used to monitor sequence integrity and metabolites of an administered antisense oligonucleotide in plasma?

• Northern blotting exclusively
• LC-MS/MS (liquid chromatography–tandem mass spectrometry)
• Colorimetric protein assay
• Fluorescent protein gel electrophoresis

Correct Answer: LC-MS/MS (liquid chromatography–tandem mass spectrometry)

Q19. A therapeutic aptamer that binds and inhibits a circulating protein target is most likely to be administered by which route for systemic action?

• Topical application to the skin
• Intravenous or subcutaneous injection
• Oral administration without formulation
• Nasal spray without delivery enhancers

Correct Answer: Intravenous or subcutaneous injection

Q20. Toggle-SELEX or cross-species SELEX is designed primarily to achieve which objective for aptamer development?

• Amplify only human-specific aptamers ignoring animal models
• Select aptamers that bind conserved epitopes across species for preclinical translation
• Remove all secondary structures from selected aptamers
• Ensure aptamers are fully resistant to all nucleases in vivo

Correct Answer: Select aptamers that bind conserved epitopes across species for preclinical translation

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