Single-cell quantification and dose-response of cytosolic siRNA delivery

Area of Science:

• Biotechnology
• Molecular Biology
• Drug Delivery Systems

Background:

• Endosomal escape and cytosolic delivery of small interfering RNA (siRNA) therapeutics are critical but inefficient steps.
• Quantifying intracellular siRNA amounts at therapeutic doses has been a significant challenge, hindering the optimization of delivery strategies.

Purpose of the Study:

• To develop and validate a confocal microscopy-based method for quantifying cytosolic delivery of fluorescently labeled siRNA.
• To establish intracellular dose-response relationships for siRNA-mediated gene knockdown.

Main Methods:

• Utilized confocal microscopy to detect and quantify sub-nanomolar cytosolic amounts of fluorescently labeled siRNA from individual lipid-mediated delivery events.
• Incorporated measures of quantitation confidence for each detected cytosolic siRNA release event.
• Analyzed single-cell kinetics of siRNA-mediated knockdown in cells expressing destabilized enhanced green fluorescent protein (eGFP).

Main Results:

• The developed method accurately quantifies cytosolic siRNA delivery, even at sub-nanomolar concentrations.
• Demonstrated a clear dose-response relationship between cytosolic siRNA levels and gene knockdown (induction, depth, and duration).
• Identified a therapeutic range requiring several hundred to thousands of cytosolic siRNA molecules for effective knockdown.

Conclusions:

• Accurate quantification of cytosolic siRNA is achievable with the presented microscopy-based method.
• Established intracellular dose-response relationships provide critical insights into siRNA therapeutic efficacy.
• This quantification approach will significantly aid in the development and characterization of novel nucleic acid delivery strategies.