Our smart drug delivery platform is based on neutral phospholipid nanoliposomes. Where classic liposomes modalities have had manufacturing problems involving sizing, uniformity, loading, storage, and enhancement compatibility, we overcome these concerns by employing true nanotechnology to build our liposomes upon discrete self-assembling DNA scaffolds. How the nucleic acid based scaffold is designed and built determines the size and rigidity of the liposome both during and after assembly. Directed bilayer formation is facilitated by a ssDNA-phospholipid adduct which links to the DNA scaffold through complementary base pair binding. The rest of the bilayer includes phosphatidylcholine and cholesterol to fill in the gaps. The ssDNA-phospholipid adducts residing in the phospholipid bilayer face inward and outward when incorporated into the liposome. Outward facing ssDNA-phospholipid adducts become acceptor ends for the next phospholipid bilayer such that multiple layers can be created stepwise with varying drug content and membrane affinity.
Our liposomes are functionalized with membrane fusion peptide catalysts and aptamers that work in tandem to selectively penetrate and fuse with the required cellular membrane barriers. Since the DNA scaffold is only required for assembly and storage of liposomes, a heat-activated enzyme is added to each layer to selectively cut the scaffold DNA strands. This loosening of the DNA scaffold increases phospholipid bilayer fluidity as an activation step to promote membrane fusion catalysis at the target. A multiple layer liposome can be designed to fuse with cell membrane barriers and deposit its underlying liposome layers into the next cellular compartment. When done in series, “onion like” layers can be tailored to fuse with the cell plasma membrane, followed by the nuclear envelop outer layer, then by the inner nuclear envelop layer to deposit the final cargo into the nucleus. By this model, smart drugs of any size, including chromosome sized molecules, can be deposited into sub-cellular addresses. The same principle is useful for traversing other tissue barriers that are made up of cell bodies, such as the capillary endothelium of the blood brain barrier.
Due to the highly adaptable nature of this model, all of the parameters of the liposome can be altered to suit new applications and challenges. This is of great importance when considering the architecture of various tissue types and past difficulties in modifying single models to suit different disease treatments. For example, liposome size can be held small to allow for greater penetration within a solid tumour or increased to accommodate the components required for a complex task. Liposome rigidity is variable depending on how much or little ssDNA-phospholipid adduct is added to each bilayer. Aptamers made from ssDNA or nucleic acid analogs are designed to bind specifically to a target epitope even at the nanomolar affinity range. This type of technology can very easily be loaded onto the ssDNA-phospholipid surface scaffold by adding the required complementary binding tether to the end of the aptamer chain. The exterior surface of the liposome can be further modified with any number of existing technologies, such as polyethylene glycol or hyaluronic acid modifications, to facilitated retention within the blood stream and evasion of phagocytic cells types in the liver and spleen. Surface coating liposomes with loosely bound serum albumin has also been described as a means of immune phagocyte evasion and endosome-surface recycling.
In conclusion, our technology is useful for highly customized smart drug delivery and gene editing with broad applicability in cell and animal models. Our model’s ability to traverse multiple membrane barriers adds further utility for delivery of liposome contents through the blood brain barrier, nuclear envelope, and beyond.