# Patent

## Title
DNA origami devices

## Abstract

Provided herein are DNA origami devices useful in the targeted delivery of biologically active entities to specific cell populations.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This Application is a 35 U.S.C. §371 National Phase Entry Application of International Application No. PCT/US2011/059352 filed Nov. 4, 2011, which designates the U.S., and which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 61/410,102, filed Nov. 4, 2010, which is hereby incorporated herein by reference, including the computer program listing appended to its disclosure. The computer program listing includes the file programlisting.txt which includes a listing for robot.json.


SEQUENCE LISTING
The instant application contains a Sequence Listing which has been submitted in ASCII format via EFS-Web and is hereby incorporated by reference in its entirety. Said ASCII copy, created on Apr. 30, 2013, is named 002806-073572-US SequenceListing and is 67,040 bytes in size.
BACKGROUND
One of the long-standing challenges in medicine is the targeted delivery of therapeutic molecules to appropriate cells. For example, drugs that have a beneficial therapeutic effect if delivered to the proper cell population will often cause severe side-effects if delivered elsewhere. Unfortunately, the specific targeting of a particular cell type is often not possible with existing drug delivery technologies. Thus, there exists a great need for novel compositions and methods useful in the selective delivery of therapeutic agents.



BRIEF DESCRIPTION OF THE DRAWINGS
FIGS. 1A-1G show schematic and transmission electron microscopy images of an exemplary DNA origami device.
FIG. 2 shows the scaffold sequence of an exemplary DNA origami device.
FIG. 3 shows the sequences of the staple strands of an exemplary DNA origami device.
FIGS. 4A-4G show the effects of exemplary aptamer-encoded latch schemes on the interactions between a DNA origami device and cell populations.
FIGS. 5A-5F show the selective targeting and manipulation of cells by exemplary DNA origami devices.
FIG. 6A shows a schematic view of a DNA origami device, and FIG. 6B shows latch sequences (SEQ ID NO:229 through SEQ ID NO:234, respectively, from top to bottom) in which different numbers of latch nucleotides are replaced with thymine.
FIG. 7 shows the activation-rate dependence on latch duplex length for exemplary DNA origami devices at an antigen (PDGF) concentration of 10 nM.
FIG. 8 shows the activation-rate dependence on latch duplex length for exemplary DNA origami devices at an antigen (PDGF) concentration of 0.1 nM.
FIG. 9 shows the probability per second (p) that exemplary DNA origami devices having varying latch duplex lengths will open at a given antigen (key) concentration.
FIG. 10 shows the activation of NK leukemia cells by different concentrations of exemplary DNA origami devices that have varying latch duplex lengths.
FIG. 11 shows the percentage of exemplary DNA origami devices with different latch (lock) duplex lengths that are open in the absence of activating ligand and the concentration of antigen (ligand) that was required for DNA origami device activation.



DETAILED DESCRIPTION
Provided herein are DNA origami devices useful in, for example, the targeted delivery of therapeutic agents particular cell populations. Such devices are able to sequester potentially biologically active moieties within the interior of the device, thereby sterically preventing them from interacting with inappropriate cell populations.
In some embodiments, the DNA origami device is held in a closed configuration by a molecular latch that is capable of interacting with an antigen. When the molecular latch is contacted by the antigen, the DNA origami device transitions to an open configuration. When the DNA origami device is in an open configuration, the previously sequestered biologically active moieties are able to interact with cells proximal to the DNA origami device. Thus, by designing the molecular latch to interact with a particular antigen, the DNA origami device can be targeted to deliver biologically active moieties to certain cell populations that express the antigen, while preventing the moieties from interacting with other cell populations.
In some embodiments, the DNA origami device may be introduced into a subject to act as a scavenger. In such embodiments, the DNA origami device is able to bind to and sequester specific moieties that it encounters in the subject. Applications include, for example, detecting antigens or antibodies for diagnostic purposes, sequestering undesired moieties for clearance, and artificial antigen-presenting cells, among others.
DNA Origami
DNA origami structures incorporate DNA as a building material to make nanoscale shapes. In general, the DNA origami process involves the folding of one or more long, “scaffold” DNA strands into a particular shape using a plurality of rationally designed “staple” DNA strands. The sequences of the staple strands are designed such that they hybridize to particular portions of the scaffold strands and, in doing so, force the scaffold strands into a particular shape. Methods useful in the making of DNA origami structures can be found, for example, in Rothemund, P. W., Nature 440:297-302 (2006); Douglas et al., Nature 459:414-418 (2009); Dietz et al., Science 325:725-730 (2009); and U.S. Pat. App. Pub. Nos. 2007/0117109, 2008/0287668, 2010/0069621 and 2010/0216978, each of which is incorporated by reference in its entirety. Staple design can be facilitated using, for example, CADnano software, available at http://www.cadnano.org.
Thus, in some embodiments, the DNA origami device (or “robot” or “DNA robot” or “DNA nanorobot”) may include a scaffold strand and a plurality of rationally designed staple strands. The scaffold strand can have any sufficiently non-repetitive sequence. For example, in certain embodiments, the scaffold strand has an M13-derived sequence, such as the M13mp18-derived sequence provided in FIG. 2.
The sequences of the staple strands are selected such that the DNA origami device has at least one shape in which biologically active moieties can be sequestered. In some embodiments, the DNA origami can be of any shape that has at least one inner surface and at least one outer surface. In general, an inner surface is any surface area of the DNA origami device that is sterically precluded from interacting with the surface of a cell, while an outer surface is any surface area of the DNA origami device that is not sterically precluded from interacting with the surface of a cell. In some embodiments, the DNA origami device has one or more openings (e.g., two openings), such that an inner surface of the DNA origami device can be accessed by sub-cellular sized particles. For example, in certain embodiments the DNA origami device has one or more openings that allow particles smaller than 10 μm, 5 μm, 1 μm, 500 nm, 400 nm, 300 nm, 250 nm, 200 nm, 150 nm, 100 nm, 75 nm, 50 nm, 45 nm or 40 nm to contact an inner surface of the DNA origami device.
In certain embodiments, the DNA origami device is able to change shape (conformation) in response to one or more certain environmental stimuli. Thus, in some embodiments, an area of the DNA origami device may be an inner surface of the device when the device takes on some conformations, but may be an outer surface of the device when the device takes on other conformations. In some embodiments, the DNA origami device can respond to certain environmental stimulus by taking on a conformation in which it has little or no inner surface.
In some embodiments, the staple strands of the DNA origami device are selected such that the DNA origami device is substantially barrel- or tube-shaped. In such embodiments, the inner surface of the DNA origami device is the surface on the inside of the barrel, while the outer surface of the DNA origami device is the outside of the barrel. In such embodiments, the staples of the DNA origami device can be selected such that the barrel shape is closed at both ends or is open at one or both ends, thereby permitting sub-cellular sized particles to enter the interior of the barrel and access its inner surface. In certain embodiments, the barrel shape of the DNA origami device is a substantially hexagonal tube.
In some embodiments, the staple strands of the DNA origami device are selected such that the DNA origami device has a first domain and a second domain, wherein the first end of the first domain is attached to the first end of the second domain by one or more single-stranded DNA hinges, and the second end of the first domain is attached to the second domain of the second domain by the one or more molecular latches, as described below. In certain embodiments, the plurality of staples are selected such that the second end of the first domain becomes unattached to the second end of the second domain if all of the molecular latches are contacted by their respective external stimuli, as described herein.
Handle Domains
In certain embodiments, the DNA origami device includes elements bound to a surface of its DNA origami structure (e.g. molecular latches, handles, tethered moieties, etc.). Such elements can be precisely positioned on the DNA origami device through the use of extended staple strands that include a domain having a sequence that does not hybridize to the scaffold strand. The additional elements can be directly or indirectly attached to such staples. As used herein, the term “directly bound” refers to a nucleic acid that is covalently bonded an entity. In contrast, the term “indirectly bound” refers to a nucleic acid that is attached to an entity through one or more non-covalent interactions.
In some embodiments, the DNA origami device includes a staple having extensions capable of binding to a moiety (termed a “handle” domain). In such embodiments, such staples can be synthesized to have at least two domains, a staple domain and a handle domain. The staple domain is a sequence of the staple that hybridizes to the scaffold strand to contribute to the formation and stability of the DNA origami structure. The handle domain contains additional nucleic acid sequence that is not necessary for the creation of the DNA origami structure.
In some embodiments, the handle domain can be directly bound to a moiety. For example, the staple can be synthesized with a particular moiety attached, or covalently bonded to a moiety prior to or following its incorporation into the DNA origami structure.
In some embodiments, the handle domain can be indirectly bound to a moiety. For example, before, during or after the formation of the DNA origami structure, the handle sequences can available to be hybridized by oligonucleotides having a complementary DNA sequence. Thus, such staples can be indirectly bound by hybridizing the handle domain to another nucleic acid that has a nucleic acid sequence complementary to the handle and that is itself either directly or indirectly bound to a particular moiety.
The staples of a DNA origami device can be selected such that a handle domain is positioned on any surface of the device, including inner surfaces and outer surfaces. In certain embodiments, the staples are selected such that a handle domain is positioned on an inner surface of the DNA origami device. Handle positioned on an inner surface of the DNA origami device and moieties bound by such handles are sequestered, and therefore sterically precluded from interacting with the surface of cells. Inner surface positioned handles are useful, for example, for preventing bound biologically active moieties from interacting with inappropriate cell populations and thereby inducing potentially harmful effects.
In certain embodiments, the staples are selected such that a handle domain is positioned on an outer surface of the DNA origami device. Such handles can be bound by, for example, molecular entities useful for delivery, detection or recapture of the DNA origami device. In some embodiments, for example, such outer handles can be bound by polyethylene glycol (PEG), carrier proteins, or other moieties capable of protecting the DNA origami device from a physiological environment. In certain embodiments, such outer handles can be bound by a detectable moiety, such as a fluorophore or a quantum dot. In certain embodiments, such outer handles can themselves facilitate the recapture of the DNA origami device, or can be bound by moieties that facilitate the device's recapture, such as antibodies, epitope tags, biotin or streptavidin.
As discussed herein, in certain embodiments the DNA origami device is able to undergo a transition from a first conformation to a second conformation in response to an environmental stimulus. In certain embodiments, a handle that was positioned on an inner surface of the DNA origami device prior to the conformational change may become located on an outer surface of the DNA origami device after the conformational change. In some embodiments, a handle that was positioned on an outer surface of the DNA origami device prior to the conformational change may become located on an inner surface of the device following the conformational change. An “open configuration” is one in which a moiety of interest (or its handle) is located on an outer surface. A “closed configuration” is one in which a moiety of interest (or its handle) is located on an inner surface. Thus, a device when adopting a particular conformation may simultaneously have an open configuration as to one moiety and a closed configuration as to another.
Molecular Latches
In some embodiments, the staples of the DNA origami devices are selected such that the DNA origami device is held in a particular conformation by a molecular latch. In general, such latches are formed from two or more staple stands, including at least one staple strand having at least one stimulus-binding domain that is able to bind to an external stimulus, such as a nucleic acid, a lipid or a protein, and at least one other staple strand having at least one latch domain that binds to the stimulus binding domain. The binding of the stimulus-binding domain to the latch domain supports the stability of a first conformation of the DNA origami device. The contacting of one or more of the stimulus-binding domains by an external stimulus to which it can bind displaces the latch domain from the stimulus-binding domain. This disruption of the molecular latch weakens the stability of the first conformation and may cause the DNA origami device to transition to a second conformation. In certain embodiments, this conformational change may result in previously sequestered moieties becoming externally presented and thereby rendering them capable of exerting a biological effect upon proximal cells.
In certain embodiments, the staple strands of a DNA origami device are selected such that the DNA origami device includes multiple molecular latches. For example, in certain embodiments, the DNA origami device includes two molecular latches. In some embodiments the various molecular latches may recognize different external stimuli, while in certain embodiments they recognize the same external stimuli. In certain embodiments, multiple external-stimuli binding domains and/or latch domains may be present on a single staple strand. In some embodiments, a stimuli-binding domain or a latch domain may span multiple staple strands which come together when the stimulus binds. In some embodiments, a stimuli-binding domain may bind multiple latch domains, or multiple stimuli-binding domains may bind a single latch domain.
The external stimulus to which the stimulus-binding domain can be any type of molecule including, but not limited to, a protein, a nucleic acid, a lipid, a carbohydrate and a small molecule. In certain embodiments, the external stimulus is preferentially expressed by a particular population of cells to be targeted by the DNA origami device. In such embodiments, the external stimulus may be present on or near the surface of the targeted cell population. For example, in certain embodiments the external stimulus is a cancer cell-specific antigen. In some embodiments the external stimulus is a molecule that is able to specifically bind to a particular population of cells. For example, the external stimulus can be a moiety bound to an antibody specific for an antigen expressed by a particular population of cells (e.g. a cancer cell-specific antigen).
The stimulus-binding domain is capable of forming a bond with a latch domain that is displaced upon the binding of an external stimulus. In certain embodiments, the stimulus binding domain binds to the external stimulus with a higher affinity than it binds to the latch domain.
In certain embodiments, the stimulus-binding domain is an aptamer domain. Aptamer domains have one or more aptamer sequences that are capable of binding to a particular antigen (e.g., a particular protein, a peptide, a lipid, a carbohydrate or a small molecule). Aptamers can be designed to target essentially any antigen of interest using methods known in the art. For example, methods of designing aptamers specific for a target of interest can be found in U.S. Pat. Nos. 5,582,981, 5,756,291, 5,840,867, 7,745,607 and Tang et al., Anal. Chem. 79:4900-4907 (2007), each of which are incorporated by reference in their entirety.
In embodiments where the stimulus-binding domain is an aptamer domain, the latch domain to which it binds will have a nucleotide sequence able to hybridize to at least a portion of the aptamer domain. In certain embodiments, the latch domain may include a sequence that is perfectly complementary to the aptamer domain or a portion of the aptamer domain (i.e. that is able to base pair at every nucleotide with at least a portion of the aptamer domain sequence). In some embodiments, however, the sequence of the latch domain is less than perfectly complementary to the aptamer domain sequence but is still able to hybridize to an aptamer domain sequence acid under certain conditions. Thus, in certain embodiments the sequence of the latch domain is at least 10%, 20%, 30%, 40%, 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% complementary to a sequence of the aptamer domain. In some embodiments, the sequence of the latch domain is selected such that the aptamer domain binds to it with a lower affinity than the aptamer domain binds to its antigen.
In certain embodiments, the external stimulus is a nucleic acid. In such embodiments, the stimulus-binding domain can have a nucleic acid sequence that is able to hybridize to at least a portion of the external stimulus. In certain embodiments, the stimulus-binding domain may include a sequence that is perfectly complementary to the sequence of the external stimulus or a portion of the sequence of the external stimulus. In some embodiments, however, the sequence of the stimulus-binding domain is less than perfectly complementary to the sequence of the external stimulus, but is still able to hybridize to a sequence of the external stimulus under certain conditions. Thus, in certain embodiments the sequence of the stimulus-binding domain is at least 10%, 20%, 30%, 40%, 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% complementary to a sequence of the external stimulus.
In embodiments where the stimulus-binding domain binds to a nucleic acid stimulus, the latch domain to which it binds will have a nucleotide sequence able to hybridize to at least a portion of the stimulus-binding domain. In certain embodiments, the latch domain may include a sequence that is perfectly complementary to the sequence of the stimulus-binding domain or a portion of the sequence of the stimulus-binding domain. In some embodiments, however, the sequence of the latch domain is less than perfectly complementary to the stimulus-binding domain sequence but is still able to hybridize to a stimulus-binding domain sequence acid under certain conditions. Thus, in certain embodiments the sequence of the latch domain is at least 10%, 20%, 30%, 40%, 50%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or 95% complementary to a sequence of the stimulus-binding domain. In some embodiments, the sequence of the latch domain is selected such that the stimulus-binding domain binds to it with a lower affinity than the stimulus-binding domain binds to the external stimulus. In certain embodiments, the latch domain is designed such that its sequence is not perfectly complementary to the sequence of the stimulus-binding domain in order to improve the sensitivity of the molecular latch. In certain embodiments, the latch domain contains at least 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32 or 33 nucleotides that are not complementary to the sequence of the stimulus-binding domain. The latch domain may contain more than 33 nucleotides that are not complementary to the sequences of the stimulus-binding domain. In some embodiments, the stimulus-binding domain further comprises a single-stranded toehold when bound to the latch domain.
In some embodiments, the stimulus-binding domain comprises a non-nucleic acid moiety that is able to bind to an external stimulus. For example, in certain embodiments the stimulus-binding domain comprises an antibody, an antibody fragment, a protein or a peptide that is able to bind to an antigen or ligand present on or near the surface of a targeted cell. In such embodiments, the latch domain would comprise a moiety (such as an antibody, an antibody fragment, a protein or a peptide) that is also able to bind to the stimulus-binding domain. As with the aptamer domains, the binding of the stimulus to the stimulus-binding domain causes the displacement of the latch domain from the stimulus-binding domain. This displacement can either be a direct displacement (e.g., the stimulus and the latch domain bind the same epitope of the stimulus-binding domain), or can be indirect displacement (e.g. the binding of the stimulus to the stimulus-binding domain causes a conformational change in the stimulus-binding domain such that the latch domain is no longer able to bind).
In some embodiments, the DNA origami device may further include a “locking” or “support” staple having a single-stranded toehold domain. The locking staple is selected such that the presence of the locking staple on the DNA origami device prevents its transition from a first conformation to a second conformation (e.g. from a closed configuration to an open configuration). Such a locking staple may, for example, improve the proper self-assembly of the DNA origami device in the first conformation. In some embodiments, the DNA origami device may include a plurality of locking staples. For example, in some embodiments the DNA origami device will include 2, 3, 4, 5, 6, 7, 8 or more locking staples. Contacting a locking staple with an oligonucleotide having a complementary sequence displaces the locking staple for the DNA origami device, thereby “unlocking” the device and permitting it to transition to the second conformation if provided with the appropriate external stimulus. In certain embodiments, the single-stranded toehold domain of the locking staple extends from the inner surface of the DNA origami device. In some embodiments, the single-stranded toehold domain of the locking staple extends from the outer surface of the DNA origami device.
In some embodiments, the staples of the DNA origami device are selected such that the device emits one or more different detectable signals depending upon its conformation. For example, the DNA origami device may include at least one staple bound to a fluorophore (a “signal staple”) and at least one staple bound to a quencher (a “quencher staple”). The binding of staples to fluorophores or quenchers can be either direct or indirect. The staple strands of the DNA origami device can be selected such that the transition from one conformation (e.g., an open configuration) to a second conformation (e.g., a closed configuration) changes the distance between at least one fluorophore and at least one quencher, thereby changing a signal output of the device.
Bound Moieties
In certain embodiments, staple strands of the DNA origami device are selected such that one or more handle domains are positioned on the inner surface of the DNA origami device. In certain embodiments, at least some of those handle domains are bound by a moiety. Such a moiety can be attached to the handle domain using any method known in the art. For example, the moiety can be covalently bonded to handle domain. The moiety can also be indirectly attached to the handle domain by, for example, hybridizing to the handle domain of a staple strand, as described above.
In certain embodiments, the DNA origami device includes a plurality of internally positioned handle domains. In such embodiments, the handle domains can all bind to a single type of moiety, or can bind to a plurality of distinct moieties. In some embodiments, the handle domains bind to a plurality of distinct moieties in a predefined a stoichiometric ratio. In certain embodiments, the moieties are bound to handles of the DNA origami device at predetermined positions. Such stoichiometric and spatial control of moiety binding is useful in, for example, the synergistic delivery of multiple biologically active moieties for combinational drug therapy.
Any type of moiety can be bound to the handle domains of the DNA origami device. For example, in certain embodiments the moiety includes at least one of: an antibody, an antibody fragment, a cell surface receptor ligand, a biologically active fragment of a cell surface receptor ligand, a small molecule, a nucleic acid, a DNAzyme, an aptamer, a lipid, a glycan, a glycoprotein, a glycolipid, a proteoglycan, a nanoparticle, a quantum dot, a fluorophore, and a nanocrystal. In some embodiments the moiety includes a fusion of one or more of the above moiety types.
In certain embodiments, the moiety bound to the handle of the DNA origami device may include an antibody. As used herein, the term “antibody” includes full-length antibodies and any antigen binding fragment (i.e., “antigen-binding portion”) or single chain thereof. The term “antibody” includes, but is not limited to, a glycoprotein comprising at least two heavy (H) chains and two light (L) chains inter-connected by disulfide bonds, or an antigen binding portion thereof. Antibodies may be polyclonal or monoclonal; xenogeneic, allogeneic, or syngeneic; or modified forms thereof (e.g., humanized, chimeric).
As used herein, the phrase “antigen-binding portion” of an antibody, refers to one or more fragments of an antibody that retain the ability to specifically bind to an antigen. The antigen-binding function of an antibody can be performed by fragments of a full-length antibody. Examples of binding fragments encompassed within the term “antigen-binding portion” of an antibody include (i) a Fab fragment, a monovalent fragment consisting of the VH, VL, CL and CH1 domains; (ii) a F(ab′)2 fragment, a bivalent fragment comprising two Fab fragments linked by a disulfide bridge at the hinge region; (iii) a Fd fragment consisting of the VH and CH1 domains; (iv) a Fv fragment consisting of the VH and VL domains of a single arm of an antibody, (v) a dAb fragment (Ward et al., (1989) Nature 341:544 546), which consists of a VH domain; and (vi) an isolated complementarity determining region (CDR) or (vii) a combination of two or more isolated CDRs which may optionally be joined by a synthetic linker. Furthermore, although the two domains of the Fv fragment, VH and VL, are coded for by separate genes, they can be joined, using recombinant methods, by a synthetic linker that enables them to be made as a single protein chain in which the VH and VL regions pair to form monovalent molecules (known as single chain Fv (scFv); see e.g., Bird et al. (1988) Science 242:423 426; and Huston et al. (1988) Proc. Natl. Acad. Sci. USA 85:5879 5883). Such single chain antibodies are also intended to be encompassed within the term “antigen-binding portion” of an antibody. These antibody fragments are obtained using conventional techniques known to those with skill in the art, and the fragments are screened for utility in the same manner as are intact antibodies.
The present DNA origami devices permit use of thermally labile moieties as payload, provided that the origami structure assembled in the closed orientation includes an opening large enough for the moiety to enter the device and become bound. Assembly normally requires a temperature high enough to denature DNA; denaturation can start at temperatures as low as 60° C. and is typically carried out at a temperature in the range of 60-95° C., frequently at 95° C. Many potentially useful moieties cannot retain biological activity following exposure to such temperatures. But because the device may be fully assembled (i.e., by a thermal annealing process) in the closed orientation yet leave the handle domains accessible to the moiety, the moiety need not be included in the annealing mixture; it can instead be added later, once the reaction has cooled.
Methods of Use
A method of delivering one or more moieties to a cell having an external stimulus (e.g. an antigen) on or near its surface may include contacting the cell with a latched DNA origami device that is carrying the moiety, thereby allowing the external stimulus to displace a latch domain from an stimulus-binding domain, and allowing the moiety to contact the cell.
As described above, in certain embodiments, contacting a DNA origami device with an external stimulus present on the surface of a cell causes the DNA origami device to transition from a closed configuration to an open configuration. In such embodiments, this conformational change will cause previously internal handle domains to become external handle domains, thereby allowing their bound moieties to interact with the cell. In certain embodiments, the moieties remain bound to the handle domains after the transition to an open configuration. Thus, in certain embodiments a method of treating a disease or disorder in a subject may include administering to the subject a DNA origami device as disclosed herein that delivers an effective amount of a therapeutic moiety to one or more targeted cell in the subject. Multi-drug therapy may be delivered by these methods by attaching different drug moieties to various handles. The relative amounts of moieties may be precisely controlled in this manner, because each handle can be made receptive to specific moieties. So, for example, if three moieties A, B, and C are to be delivered in a stoichiometric ratio of 2:1:3, a DNA origami device can be made with staple strands having domains such that there are two handles specific for moiety A, and three handles specific for moiety C, for every handle that is specific for moiety B.
A wide variety of diseases and disorders are susceptible to treatment by these methods. Diseases or disorders characterized by the absence of a tangible mass that can be physically targeted may be especially well-suited to the present methods of treatment. Examples include blood-borne illnesses, such as a blood-borne cancer (e.g. a leukemia) or an autoimmune disease.
In some embodiments, the transition to the open configuration or the interaction with the cell causes the moiety to be released by the handle domain. For example, the handle domain can include an aptamer sequence specific for an antigen present on the surface of the cell. In such embodiments, the binding of the antigen to the handle domain displaces the moiety from the handle domain. Thus, in these embodiments, the DNA origami device not only delivers the therapeutic moiety to a cell, it can achieve a high local concentration of the therapeutic moiety around intended targets while sparing unintended targets from undesirable side-effects. The released therapeutic moiety will also be freer to interact with the cell, possibly being internalized for therapeutic effect.
In certain embodiments, a method of sequestering a particle smaller than the inner cross-section of the DNA origami device in size may include contacting the particle with a DNA origami device that includes an internally-bound moiety capable of specifically binding to the particle and wherein the structure of the DNA origami device has one or more openings that allow the particle to contact the internally bound moiety. Such methods are useful, for example, for sequestering potentially harmful molecules in a subject, thereby reducing the amount such molecules interact with cells. It is not necessary that such scavenger DNA origami devices have the ability to undergo a conformational change to an open state. A scavenging device may be used without a moiety pre-loaded; in this case, the handles may include aptamer domains or chemical modifications that bind particles of interest. Alternatively (or in addition), a scavenging device may be preloaded with a moiety that itself binds a particle of interest.
In certain embodiments, the DNA origami device can then deliver scavenged particles to targeted cells. For example, in some embodiments, scavenged particles are sequestered, as described above, in DNA origami devices. The devices then encounter a target cell bearing the appropriate stimulus to open the latch(es), thereby causing the device to open and deliver the scavenged particle to the target cell. In this way, the DNA origami device can act, for example, as an artificial antigen presenting cell, presenting scavenged, moiety-bound antigens to T cells or B cells in conjunction with additional biologically active moieties. By selecting the amount of antigen presented and the nature of the additional biologically active moieties, such DNA origami devices can, for example, induce the targeted immune cell to undergo apoptosis, to become activated, to become tolerized, or to differentiate into a particular sub-type of immune cell. Such DNA origami devices are useful, for example, in the induction of an immune response against a cancer or pathogenic agent (e.g. a virus or bacterium), or in the inhibition of an allergic or autoimmune response.
In certain embodiments, a method of detecting a particle smaller than the inner cross-section of the DNA origami device in size may include contacting the particle with a DNA origami device that includes an internally-bound moiety capable of specifically binding to the particle and wherein the structure of the DNA origami device has one or more openings that allow the particle to contact the internally bound moiety. In such embodiments, a DNA origami device previously introduced into a subject may be retrieved from a subject and the presence of sequestered particles detected using methods known in the art. For example, the DNA origami device can be induced to transition into an open state by contacting it with an external stimulus that displaces a latch domain from a stimulus-detecting domain and the particle detected using a probe (e.g., an antibody or antibody fragment). In some embodiments, the presence of the particle in the DNA origami device is detected while the particle remains sequestered. In some embodiments, the DNA origami device is bound to a solid support prior to or during the detection of the particle. In certain embodiments, the solid support includes an external stimulus capable of displacing a latch domain from a stimulus-detecting domain, thereby opening the DNA origami device on the support.
EXAMPLES
Example 1
Design and Synthesis of a DNA Origami Device
Described herein is the design and synthesis of a DNA origami device capable of selectively interfacing with cells to manipulate their biology. A DNA origami device in the form of a hexagonal pod with dimensions of approximately 35×35×45 nm3 in size was designed using CADnano, a computer-aided design tool for DNA origami. FIG. 1A is a schematic front view of an exemplary DNA origami device loaded with proteins. The pod is made of a single 7308-base M13mp18-derived scaffold strand hybridized to a plurality of rationally-designed staple strands. The pod structure includes two domains that are covalently attached in the rear by single-stranded DNA hinges and can be non-covalently fastened in the front by DNA-aptamer-based latches. Design blueprints are provided in the computer program listing submitted with U.S. provisional application Ser. No. 61/410,102, which provides the “robot.json” file containing the structure of the illustrated device for use with CADnano. The sequence of the M13mp18-derived scaffold strand is provided in FIG. 2. The sequences of the staple strands are provided in FIG. 3. (Abbreviations within the sequences indicating chemical modifications follow the nomenclature used by Integrated DNA Technologies, Inc.: /5BioTEG/ indicates 5′ Biotin-TEG (tetra-ethyleneglycol); /5AmMC6/ indicates 5′ Amino Modifier C6 (6-(4-Monomethoxytritylamino)hexyl-(2-cyanoethyl)-(N,N-diisopropyl)-phosphoramidite); /5ThioMC6-D/ indicates 5′ Thiol Modifier C6 S—S (1-O-Dimethoxytrityl-hexyl-disulfide,1′-[(2-cyanoethyl)-(N,N-diisopropyl)]-phosphoramidite); /5DTPA/ indicates 5′ Dithiol; /36-FAM/ indicates 3′ 6-FAMTM (6-carboxyfluorescein); /5IAbFQ/ indicates 5′ Iowa Black® FQ; /5TYE665/ indicates 5′ TYETM 665; and /3IAbRQSp/ indicates 3′ Iowa Black® RQ-Sp.) Staples 179-190 include handle domains. The handle domain sequence is GTGCTACTCCAGTTC (SEQ ID NO: 228), and it is separated from the staple domain by a 2-base TT spacer. Staples 219-222 are typical linker strands, which are chemically attached to a moiety. The linker strands include an anti-handle domain, GAACTGGAGTAGCAC (SEQ ID NO: 220), which is complementary to the handle domain. In this example, all the handle domains are the same; in practice, distinct handle domains can be used in order to load more than one type of moiety.
To modify the device such that it emits a detectable signal upon opening, staples 175-178 can be replaced by staples 223-226. If such a substitution is made, staples 223 and 226 bind to the top domain of the device, while staples 224 and 225 bind to the bottom domain of the device (as the device is illustrated in FIG. 1A). As indicated in FIG. 3, staples 223 and 225 are modified with fluorophores, while staples 224 and 226 are modified with quenchers. The staples are positioned such that, when the device is closed the 3′ end of staple 223 is less than 2 nm away from the 5′ end of staple 224, while the 3′ end of staple 225 is less than 2 nm away from the 5′ end of staple 226. At this distance, the fluorescent signals produced by the fluorophores bound to staples 223 and 225 are quenched by the quenchers bound to staples 224 and 226. When the device is in an open configuration, the fluorophores bound to staples 223 and 225 move apart from the quenchers bound to staples 224 and 226, respectively, increasing the signal output of the device.
Initial self-assembly of the DNA origami device was performed using in a one-pot reaction, in which 196 oligonucleotide staple strands directed the scaffold strand into its target shape during a thermal-annealing ramp of rapid heating followed by slow cooling. Two support staples that span the top and bottom domains were incorporated adjacent to the latch sites, and were found to increase the folding yield to 97.5% of the devices in the closed state, as compared to 48% closed when folded without support staples. The support staples included 8-base toehold overhangs and were removed after folding and purification through the addition of fully complementary strands to the mixture (FIG. 1C).
In order to operate the device in response to a wide array of input types, including proteins, a DNA-aptamer-based latch mechanism was designed that opens in response to binding antigen keys. FIG. 1B is a schematic diagram of an exemplary aptamer latch mechanism that includes a DNA aptamer domain and its complementary latch domain. In the presence of its cognate antigen, the two strands dissociate. A DNA duplex having an aptamer strand and its complementary latch strand were designed such that the two strands can be separated via intramolecular displacement by the aptamer strand's cognate antigen. Aptamer-complement duplexes were incorporated on the left and right sides of the front of the device, such that the aptamer strands are attached to the top domain and the complement strands are attached to the bottom domain (FIG. 1A). Similar to a combination lock, the pod is able to open only upon disassembly of both latches, driven by each aptamer recognizing its own cognate target. FIG. 1D depicts an exemplary DNA origami device in its open configuration. In such a configuration, the two halves of the device remain connected by scaffold hinges in the rear. A number of different aptamer sequences were used to make DNA origami devices, including aptamers previously described as binding to platelet-derived growth factor (PDGF), Ramos and CCRF-CEM cell-surface antigens.
The exemplary DNA origami device had twelve staple strands positioned inside of its DNA origami structure that had single-stranded 3′ extensions capable of serving as “handles” for the loading of molecular payloads. The attachment points were arranged in an inward-facing ring inside the pod (FIG. 1A). These handles were able to be loaded molecular payloads covalently attached to the 5′ end of a 15-base single-stranded DNA oligonucleotide linkers having sequence complementarity to the oligonucleotide handles (FIG. 1E). Two types of cargo were loaded into the robot: 5-nm gold nanoparticles (Sigma) covalently attached to 5′-thiol-modified linkers, and various Fab′ antibody fragments that were covalently attached to 5′-amine modified linkers.
FIG. 1F is a schematic illustration depicting the function of an exemplary DNA origami device. Following initial self-assembly, the DNA origami device is “unlocked” by treating the device with nucleic acid strands that are complementary to the device's support staples, which causes the support staples to disassociate from the device. Binding of the device's aptamer strands to its cognate antigen causes the device to undergo a conformational change and expose its molecular payload.
Negative-stain transmission electron microscopy (TEM) was used to analyze exemplary devices (FIG. 1G). The left column of micrographs depicts unloaded devices, the center column depicts devices loaded with 5 nm gold-nanoparticles and the right column depicts devices loaded with Fab′ fragments.
Example 2
Use of a DNA Origami Device for Target-Specific Signal Delivery
When the input antigen keys do not correspond to the antigen recognized by the aptamer locks, the DNA origami device remains inactive. As depicted in FIG. 4A, FITC-labeled antibody fragments are loaded as payload into DNA origami devices. Unlocked devices readily allow cell binding and result in a significant shift in the histogram peak on flow-cytometry (FIG. 4A, top). When locked devices are mixed with cell types that do not bear the cognate antigen to both aptamer locks, the device remains inactive, sequestering the dye-labeled cargo. When analyzed by flow-cytometry, cells that do not bind active robots only display baseline fluorescence (FIG. 4A, middle). Cells that are able to activate and bind to both aptamers of the DNA origami device display a significant shift in the histogram peak (FIG. 4A, bottom). Thus, the aptamer-encoded locks can be conceptualized as an AND gate responding to molecular inputs expressed by cells (FIG. 4B). As depicted in FIG. 4C, six versions of the robot with different aptamer lock combinations were combined with various cell lines. The contacted cells displayed varying states of activation depending on the cell type and aptamer lock pair.
By use of targeted, controlled transport, the DNA origami device can be used to skew cell-cell communication and signaling events. As an example, growth factor signaling was manipulated in a target cell population using monoclonal antibodies as a payload. Monoclonal anti-human CD33 and anti-human CDw328 were selected due to their reported ability to suppress leukemic cell growth. A DNA origami device able to target NKL, a cell line isolated from a patient with aggressive NK cell leukemia was designed and synthesized as described above. NKL cells over-express platelet-derived growth factor (PDGF)-ββ. Thus, the aptamer latch was of the DNA origami device was designed using an aptamer able to bind to PDGF-BB. NKL and Jurkat cells were mixed, labeled with FITC-anti human CD3ε and incubated with devices loaded with APC-anti human HLA A/B/C Fab′ for 30 minutes. Devices locked with stabilizing staples did not react with the cell surface molecules, while latching the device with an aptamer latch alone enabled the device to discriminate NKL cells from a mixed population (FIGS. 4D-4F).
To test the ability of the DNA origami devices to distinguish NKL cells from healthy whole blood, the DNA origami device described above was added to a solution containing a mixture of healthy human blood cells and NKL leukemia cells. As depicted in FIG. 4G, the DNA origami devices were able to distinguish NKL cells from healthy whole blood with high precision.
The DNA origami device/cell interface was investigated in two different contexts. First, devices loaded with a combination of anti-human CD33 and anti-human CDw328 Fab′ fragments and guided by the same buffer were used to treat NKL cells at various concentrations (FIG. 5A). As depicted in FIGS. 5B-5C, the DNA origami devices suppressed Akt/Protein Kinase B and Jun N-terminal Kinase (JNK) signaling and induced growth arrest in NKL cells in a time- and dose-dependent fashion.
As depicted in the schematics of FIGS. 5D-5E, one possible use of the DNA origami devices is as artificial antigen presenting cells for the activation of T cells. As depicted in FIG. 5F, incubation for 1 hour with devices loaded with anti-human CD3ε Fab′ successfully activated Jurkat T cells, as indicated by expression of phosphorylated Syk/ZAP-70 by intracellular flow cytometry. These findings demonstrate that the DNA origami devices can induce a variety of significant and tunable changes in cell behavior and direct it towards a desired outcome.
Example 3
Aptamer-Latch Optimization
To determine the effect of aptamer-complement duplex length on DNA origami device function, a series of DNA origami devices having different numbers of mismatches between their aptamer and latch domains were designed and synthesized. To avoid compromising antigen-binding by the aptamer domain, the mismatches were created by varying latch domain sequences by replacing several bases with thymines without changing the sequence of the aptamer domain. Complement strands were designed with 0, 7, 14, 21 and 28 replacement thymine bases. FIG. 6A shows a schematic orthographic view of the devices, in which helices are replaced as circles, along with aptamer based locks (lines). FIG. 6B shows detail of the latch shown on the right side of FIG. 6A, including the sequences of the latch domains and the various complement strands with thymine replacements.
A microbead-based assay coupled with quantitative flow cytometry (qFCM) was performed to determine the rate of opening for the various versions of the DNA origami devices, as well as the probability for a given device to open per unit of time. Cy3-labeled devices were constructed and then loaded with payload oligos modified with 5′ BioTEG. Devices that opened in response to aptamer/antigen binding expose their biotinylated payload and are able to label the microbeads, which are then analyzed by qFCM. Acquisition was made at precalibrated photomultiplier tube voltages so that median fluorescence values represent molecular equivalent of soluble fluorochrome (MESF).
The binding of a population of unlocked devices were first measured in order to determine baseline parameters for the assay. Open devices saturated the microbeads after 30 minutes, with a binding capacity of approximately 100,000 devices per microbead. To examine how lock design affected test activation rate, the various device versions were incubated with 10 nM antigen (PDGF) for 24 hours and the fraction of open devices were determined at various time points using the microbead assay. As depicted in FIG. 7, devices with more latch mismatches were able to open faster than those with fewer mismatches. A similar result was obtained when a lower antigen (key) concentration of 0.1 nM was used (FIG. 8). Based on these results, the probability per second (p) that any given device will open was calculated. This value for each device version, expressed as mean log(p), is depicted in FIG. 9.
A functional assay was performed to determine how the different lock versions affected device function (FIG. 10). Devices with 16, 23, 30, 37 and 34 bp lock duplex lengths were loaded with anti-CD33 and anti-CD232a Fab′ antibody fragments and their signaling phosphorylation of the p42/44 kinase ERK was compared. Each device version was tested at varying concentrations (0-10 nM) for its ability to stimulate cell signaling in aggressive NK leukemia cells. Signaling levels were determined by intracellular flow cytometry by measuring phosphorylation levels of the p42/44 kinase ERK. Locks with 0 or 7 thymine replacements exhibited similar profiles (possibly indicating that the first 7 base pairs of the molecular latch are typically unzipped). As depicted in FIG. 10, devices with weaker locks (more mismatches) were able to stimulate cell signaling at lower device concentrations.
In designing a lock system, it may be desirable to balance device sensitivity against device leakiness. Fluorescently labeled devices with anti-PDGF aptamer-latch locks (duplex lengths of 16, 23, 30, 37 and 44 bp) were loaded with biotinylated cargo and incubated with streptavidin-coated beads and then analyzed by flow cytometry. A positive control of 100% open devices was used to establish a baseline fluorescence value, which was used to determine the percentage of each locked device that was initially open. The same device versions were also tested for the minimum concentration of ligand that was required to achieve a measurable activation response. Each version of the device was incubated with streptavidin-coated beads in the presence of increasing concentrations of PDGF, and then tested for activation by flow cytometry. As depicted in FIG. 11, by optimizing the lock strength by introducing mismatches between the aptamer domain and the latch domain, a 100 fold improvement in device sensitivity was achieved by tuning the duplex strength.
Equivalents
Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents of the specific embodiments of the subject matter described herein. Such equivalents are intended to be encompassed by the following claims.
INCORPORATION BY REFERENCE
All publications, patents, and patent applications cited in this specification are herein incorporated by reference to the same extent as if each individual publication or patent application was specifically and individually indicated to be incorporated by reference.

## Claims

1. A DNA origami device comprising a scaffold strand and a plurality of staple strands,
one of the staple strands comprises an aptamer domain capable of binding to an antigen;
another of the staple strands comprises a latch domain hybridized to the aptamer domain, the latch domain sequence selected such that the aptamer domain is capable of binding to the antigen such that the antigen displaces the latch domain;
the aptamer domain and the latch domain, when hybridized to one another, hold the device in a closed configuration; and
the device transitions to an open configuration when the aptamer domain and the latch domain are not hybridized to one another, the DNA origami device has a shape that (a) allows a particle smaller than the inner cross-section of the DNA origami device to access an inner surface of the DNA origami device, and (b) sterically precludes a particle larger than the inner cross-section of the DNA origami device from accessing an inner surface of the device.

2. A DNA origami device comprising a scaffold strand and a plurality of staple strands, wherein:
one of the staple strands comprises a first aptamer domain capable of binding to a first antigen;
another of the staple strands comprises a second aptamer domain capable of binding to a second antigen;
yet another of the staple strands comprises a first latch domain hybridized to the first aptamer domain, the first latch domain sequence selected such that the first aptamer domain is capable of binding to the first antigen such that the first antigen displaces the first latch domain;
still another of the staple strands comprises a second latch domain hybridized to the second aptamer domain, the second latch domain sequence selected such that the second aptamer domain is capable of binding to the second antigen with a greater affinity than it is capable of binding to the second latch domain;
the first aptamer domain hybridized to the first latch domain, and the second aptamer domain hybridized to the second latch domain, hold the device in a closed configuration; and
the device transitions to an open configuration when the first aptamer domain is not hybridized to the first latch domain and the second aptamer domain is not hybridized to the second latch domain, the DNA origami device has a shape that (a) allows a particle smaller than the inner cross-section of the DNA origami device to access an inner surface of the DNA origami device, and (b) sterically precludes a particle larger than the inner cross-section of the DNA origami device from accessing an inner surface of the device.

3. The DNA origami device of claim 1, wherein the device is biased to the open configuration.

4. The DNA origami device of claim 1, wherein one of the staple strands comprises a handle domain capable of binding to a moiety.

5. The DNA origami device of claim 4, wherein multiple staple strands comprise a handle domain capable of binding a plurality of moieties at a stoichiometrically predetermined ratio.

6. The DNA origami device of claim 4, wherein the plurality of staple strands are selected such that:
a moiety bound by the handle domain is positioned on an inner surface of the DNA origami device when the device is in the closed configuration; and
the transition to the open configuration causes a moiety bound by the handle domain to be positioned on an outer surface of the DNA origami device.

7. The DNA origami device of claim 6, wherein the handle domain is bound to a moiety.

8. The DNA origami device of claim 7, wherein the moiety comprises a linker oligonucleotide having a sequence complementary to the sequence of the handle domain, and wherein the moiety is bound to the handle domain through the hybridization of the linker oligonucleotide to the handle domain.

9. The DNA origami device of claim 7, wherein the moiety comprises at least one of: an antibody, an antibody fragment, a cell surface receptor ligand, a biologically active fragment of a cell surface receptor ligand, a small molecule, a nucleic acid, a DNAzyme, an aptamer, a lipid, a glycan, a glycoprotein, a glycolipid, a proteoglycan, a nanoparticle, a quantum dot, a fluorophore, and a nanocrystal.

10. The DNA origami device of claim 6, wherein one of the staple strands comprises a second handle domain capable of binding to a second moiety, wherein staple strands are selected such that:
a moiety bound by the second handle domain is positioned on an inner surface of the DNA origami device when the device is in the closed configuration; and
the transition to the open configuration causes a moiety bound by the second handle domain to be positioned on an outer surface of the DNA origami device.

11. The DNA origami device of claim 6, wherein at least one antigen is a cancer cell-specific antigen.

12. The DNA origami device of claim 1, wherein staple strands are selected such that the DNA origami device comprises a first domain and a second domain, wherein a first end of the first domain is attached to a first end of the second domain by at least one single-stranded DNA hinge and the second end of the first domain is attached to the second end of the second domain by the hybridization of the aptamer domain to the latch domain.

13. The DNA origami device of claim 12, wherein staple strands are selected such that the second end of the first domain becomes unattached to the second end of the second domain if the aptamer domain is contacted by a respective antigen.

14. The DNA origami device of claim 2, wherein the first antigen and the second antigen are different from one another.

15. A DNA origami device comprising a scaffold strand and a plurality of staple strands, wherein:
one of the staple strands comprises a handle domain bound to a moiety; and
staple strands are selected such that:
the DNA origami device has a shape that (a) allows a particle smaller than the inner cross-section of the DNA origami device to access an inner surface of the DNA origami device, and (b) sterically precludes a particle larger than the inner cross-section of the DNA origami device from accessing the inner surface; and
the moiety bound by the handle domain is positioned on the inner surface.

16. A method of delivering a moiety to a cell expressing an antigen, comprising contacting the cell with the DNA origami device of claim 1 carrying the moiety, thereby allowing the antigen to displace the latch domain from the aptamer domain, causing the device to transition to the open configuration, and allowing the moiety to contact the cell.

17. A method of sequestering a particle smaller than the inner cross-section of the DNA origami device in size, comprising contacting the particle with a DNA origami device of claim 1 carrying a moiety, wherein the moiety is capable of specifically binding to the particle.

18. The method of claim 17, further comprising delivering the sequestered particle to a cell expressing an antigen, comprising contacting the cell with the DNA origami device in which the particle has been sequestered, thereby allowing the antigen to displace the latch domain from the aptamer domain, causing the device to transition to the open configuration and allowing the particle to contact the cell.

19. A DNA origami device comprising a scaffold strand and a plurality of staple strands,
one of the staple strands comprises an aptamer domain capable of binding to an antigen;
another of the staple strands comprises a latch domain hybridized to the aptamer domain, the latch domain sequence selected such that the aptamer domain is capable of binding to the antigen such that the antigen displaces the latch domain;
the aptamer domain and the latch domain, when hybridized to one another, hold the device in a closed configuration; and
the device transitions to an open configuration when the aptamer domain and the latch domain are not hybridized to one another,
wherein the plurality of staple strands are selected such that: one of the staple strands comprises a handle domain, wherein
a moiety bound by the handle domain is positioned on an inner surface of the DNA origami device when the device is in the closed configuration; and
the transition to the open configuration causes a moiety bound by the handle domain to be positioned on an outer surface of the DNA origami device.

20. The DNA origami device of claim 19, wherein the moiety comprises a linker oligonucleotide having a sequence complementary to the sequence of the handle domain, and wherein the moiety is bound to the handle domain through the hybridization of the linker oligonucleotide to the handle domain.

21. The DNA origami device of claim 19, wherein the moiety comprises at least one of: an antibody, an antibody fragment, a cell surface receptor ligand, a biologically active fragment of a cell surface receptor ligand, a small molecule, a nucleic acid, a DNAzyme, an aptamer, a lipid, a glycan, a glycoprotein, a glycolipid, a proteoglycan, a nanoparticle, a quantum dot, a fluorophore, and a nanocrystal.

22. The DNA origami device of claim 19, wherein one of the staple strands comprises a second handle domain capable of binding to a second moiety, wherein staple strands are selected such that:
a moiety bound by the second handle domain is positioned on an inner surface of the DNA origami device when the device is in the closed configuration; and
the transition to the open configuration causes a moiety bound by the second handle domain to be positioned on an outer surface of the DNA origami device.

23. The DNA origami device of claim 19, wherein the antigen is a cancer cell-specific antigen.

24. A DNA origami device comprising a scaffold strand and a plurality of staple strands, one of the staple strands comprises an aptamer domain capable of binding to an antigen;
another of the staple strands comprises a latch domain hybridized to the aptamer domain, the latch domain sequence selected such that the aptamer domain is capable of binding to the antigen such that the antigen displaces the latch domain;
the aptamer domain and the latch domain, when hybridized to one another, hold the device in a closed configuration; and
the device transitions to an open configuration when the aptamer domain and the latch domain are not hybridized to one another, and wherein the DNA origami device further includes a locking staple having a single-stranded toehold domain, wherein the locking staple is selected such that the presence of the locking staple on the DNA origami device prevents transition to the open configuration; and contacting the locking staple with an oligonucleotide having a complementary sequence displaces the locking staple from the DNA origami device.