DNA-gated liposomes represent a sophisticated class of stimuli-responsive drug delivery systems that leverage the programmability of nucleic acids for precise payload release. Among these, hairpin-gated liposomes stand out due to their ability to respond to specific mRNA triggers, such as tumor-associated microRNAs, through toehold-mediated strand displacement mechanisms. These systems offer high specificity in recognizing disease biomarkers, making them particularly valuable in precision oncology and autoimmune disease treatment.

The core design of DNA hairpin-gated liposomes involves anchoring a hairpin-structured DNA sequence to the liposomal surface. This hairpin acts as a gatekeeper, preventing the encapsulated therapeutic agents from leaking prematurely. The hairpin is engineered to include a toehold region—a short, single-stranded segment that facilitates binding to a complementary mRNA trigger. Upon encountering the target mRNA, the toehold initiates strand displacement, unraveling the hairpin and opening pores in the liposomal membrane. This allows the controlled release of the payload exclusively in cells expressing the trigger mRNA.

Toehold-mediated strand displacement is critical for ensuring both specificity and kinetics of release. The toehold length typically ranges from 4 to 8 nucleotides, balancing binding affinity and dissociation rates. Longer toeholds increase binding stability but may also raise the risk of off-target interactions. Studies have demonstrated that a 6-nucleotide toehold provides an optimal trade-off, enabling rapid displacement in the presence of the target while minimizing unintended activation. The displacement process follows a predictable, step-wise unwinding of the hairpin, ensuring that release occurs only when the correct mRNA is present.

Leakage control is a major challenge in liposomal drug delivery, as premature payload release reduces therapeutic efficacy. DNA hairpin-gated systems address this through structural stability. The hairpin’s double-stranded stem region resists spontaneous opening under physiological conditions, while the loop region adds further kinetic barriers to unintended unfolding. Additionally, chemical modifications such as phosphorothioate backbones or locked nucleic acids (LNAs) can be incorporated to enhance nuclease resistance, prolonging circulation time and reducing false triggers.

Applications in precision oncology exploit tumor-specific microRNA signatures. For example, miR-21 is overexpressed in many cancers and can serve as a trigger for hairpin-gated liposomes carrying chemotherapeutics like doxorubicin. Upon entering cancer cells, the miR-21 binds the toehold, displaces the hairpin, and releases the drug directly within the tumor, sparing healthy tissues. Similarly, in autoimmune diseases, liposomes can be designed to respond to inflammation-associated mRNAs, such as TNF-α mRNA, enabling localized immunosuppression.

A key advantage of DNA-gated liposomes over pH-sensitive alternatives is their reliance on nucleic acid recognition rather than environmental acidity. pH-sensitive liposomes release their payload in acidic environments like endosomes or tumor extracellular spaces, but they lack mRNA-level specificity. This can lead to off-target effects in normal tissues with similar pH gradients. In contrast, DNA hairpin systems respond only to the exact complementary mRNA sequence, drastically improving targeting precision.

However, DNA-gated liposomes face challenges such as potential immune recognition and degradation by serum nucleases. Advances in stealth coatings, like PEGylation, and the use of chemically modified nucleic acids have mitigated these issues. Furthermore, optimizing liposomal composition—such as incorporating cholesterol for membrane stability—enhances in vivo performance.

In summary, DNA hairpin-gated liposomes exemplify the convergence of nanotechnology and molecular biology for precision medicine. Their ability to decode cellular mRNA signatures and release therapeutics on demand positions them as promising tools for oncology and autoimmune therapy, offering a level of specificity unattainable with conventional pH-sensitive systems. Future refinements in toehold design, leakage control, and biocompatibility will further solidify their role in next-generation drug delivery.