We wanted to make a structure that would have precise and compartmentalized drug delivery in reaction to its surroundings. In this way, we could target more than one key places on the cell.
How we started thinking about it
We started with the idea of having a structure resembling a shell that could open and close to release some sort of particle. Then we thought, what if we could create one device with two compartments that would open via different stimuli?
We also wanted a clever structure, so we drew out a house-shaped box that had four pentagons as sides and a square floor. The "attic" and "ground floor" would open in response to different stimuli and release different kinds of particles of our choice.
How it would work
We wanted to construct a delivery particle composed of several bonded monomeric structures that will respond to external stimuli such as light activation and/or pH activation.
The “roof” of the house is initially closed , but opens in response to a pH change via an I-switch. The I-switch is made out of DNA and has a conformational change in response to pH. It also functions as a pH sensor and reporter through a FRET signal, functional inside cells. It is composed of three oligonucleotides. The oligonucleotides on the edges have single-stranded cytosine-rich overhangs. At a low pH, these overhangs attract protons and come together, causing the whole structure to fold and thus release the parts of the box that it is bound to.
Mechanism of I-switch (Reference 11)
While a response to a pH change is a consequence of a conformational change in the DNA itself, light activation will require an additional factor. To confer this light sensitivity, the structure will include several azobenzene-linked staple strands.
The “ground floor” is attached via azobenzene to the “walls,” and detaches in the presence of light. Azobenzene is an intercalating molecule that can adopt two forms: the trans form, which allows for inter-helix binding, and the cis form, which is not involved in binding. Light stimulus affects this conformation change of azobenzene and allows for strands to release their hold of one another, thereby conferring a shape change to the macro structure. As it switches conformations, the floor detaches from the house, causing it to open and drug particles to be released. This floor is linked to the rest of the house by flexible strands so that it will reform after the release of the drug. The floor can either stay attached by a hinge and swing open, or it can detach around the edges completely but be held by spring-like linkers that attach to the inside of the box and the floor.
Left: Azobenzene in its trans conformation. Right: Azobenzene in its cis conformation
Ideally, the device will have two different compartments and will be able to respond to two different stimuli at either the same time or different times, and from different directions. In our video, we present a case study in which the “house” has the ability to respond to both light and pH, but in a non-compartmentalized way, for visual simplicity. Conferring the ability to respond to different stimuli would prove invaluable in the targeted delivery of small molecules, making it highly applicable to drug delivery.