Patent Application
20210355488
The present disclosure is generally related to molecules for inhibiting CRISPR enzymes.
The discovery of gene editing and programmable genomic control by clustered regularly interspaced short palindromic repeat (CRISPR) RNAs (crRNAs) and their CRISPR-associated (CAS) proteins holds tremendous promise for future therapeutics and curing genetic disease. The prototypical CRISPR-associated protein, Cas9 from S. pyogenes, naturally binds two RNAs, a CRISPR RNA (crRNA) guide and a trans-acting CRISPR RNA (tracrRNA), to assemble a CRISPR ribonucleoprotein (crRNP). Despite the potential, CRISPR enzymes suffer from several disadvantages in use, such as potential off-target effects that can be exacerbated when uncontrolled. The safety of CRISPR, such as unforeseen adverse events in patients, remains an important concern for practical drug development. To fully implement safe CRISPR-based therapeutics, it may be necessary to develop “kill switch” inhibitors that can halt activity of CRISPR. Several therapeutic drugs have required development of fail-safe antidotes to counter unexpected side effects and protect patients. For example, vitamin K and prothrombin complex concentrations are used as antidotes to reverse adverse reactions or overdoses of anticoagulants like warfarin.
Natural anti-CRISPR proteins have been found in bacteria and bacteriophage genomes that can shut down CRISPR systems by inhibiting DNA binding or blocking conformational state changes required for catalysis. Recent characterization of natural anti-CRISPR proteins, such as AcrIIA2/4, provides inspiration for design of biomolecules that may serve as drugs to mitigate potential problems with CRISPR-based therapies.
There is an urgent need to develop strategies and molecules that can inhibit CRISPR either for safety concerns or to optimize specificity of enzymes. Other than the recent (2017) findings of natural anti-CRISPR proteins, which have not been developed therapeutically, there are currently no technologies for effectively inhibiting CRISPR enzymes or CRISPR-based mechanisms with drug-like molecules. The nucleic acid-based inhibitors described here are substantially smaller than the known anti-CRISPR proteins and can be further engineered with additional chemical modifications, which allows for tuning drug-like properties and making them much better drug candidates than anti-CRISPR proteins. Several nucleic acid-based drugs are now FDA approved and nucleic acids are emerging as an exciting new class of drugs. Currently, therapeutic nucleic acid molecules can be used for target organs and tissues, like the liver, brain and central nervous system. Tissues amenable to delivery of these agents are expected to grow. In addition, the CRISPR inhibitors described here have useful applications in basic research and biotechnology.
In a general and overall sense, the invention provides a variety of inhibitor molecules having an ability to inhibit a CRISPR enzyme. In some embodiments, these inhibitor molecules comprise an artificial nucleic acid construct.
In some aspects, the inhibitor molecule may comprise an artificial nucleic acid construct having a first polynucleotide. This first polynucleotide may be selected from the group consisting of: a polynucleotide that interacts with a protospacer adjacent motif (PAM)-interaction (PI) domain of a CRISPR-associated (Cas) protein, a polynucleotide that interacts with a guide sequence of a crRNA or an equivalent position of a single-guide RNA, and a polynucleotide that interacts with a repeat region of a tracrRNA or an equivalent position of a single-guide RNA. In a particular embodiment, the first polynucleotide may be a polynucleotide that interacts with a PI domain of a Cas protein
In another aspect, the inhibitor molecule may comprise a first polynucleotide, a second polynucleotide and a linker. By way of example, the first polynucleotide may be a polynucleotide that interacts with a PI domain of a Cas protein. In some embodiments, the second polynucleotide may be selected from the group consisting of a polynucleotide that interacts with a guide sequence of a crRNA or an equivalent position of a single-guide RNA, and a polynucleotide that interacts with a repeat region of a tracrRNA or an equivalent position of a single-guide RNA. Preferably, the linker molecule may be operably connected to the first polynucleotide and operably connected to the second polynucleotide.
The following drawings form part of the present specification and are included to further demonstrate certain aspects of the present invention. The invention may be better understood by reference to one or more of these drawings in combination with the detailed description of specific embodiments presented herein. However, those of skill in the art will understand that the drawings, described below, are for illustrative purposes only. The drawings are not intended to limit the scope of the present teachings in any way.
The present disclosure provides CRISPR inhibitor molecules comprising an artificial nucleic acid construct. In some aspects, the artificial nucleic acid construct comprises a first polynucleotide selected from the group consisting of: a polynucleotide that interacts with a protospacer adjacent motif (PAM)-interaction (PI) domain of a CRISPR-associated (Cas) protein, a polynucleotide that interacts with a guide sequence of a crRNA or an equivalent position of a single-guide RNA, and a polynucleotide that interacts with a repeat region of a tracrRNA or an equivalent position of a single-guide RNA.
In some embodiments, the first polynucleotide may be a polynucleotide that interacts with a PI domain of a Cas protein.
In another embodiment, the first polynucleotide may be a polynucleotide that interacts with a guide sequence of a crRNA or an equivalent position of a single-guide RNA.
In yet another embodiment, the first polynucleotide may be a polynucleotide that interacts with a repeat region of a tracrRNA or an equivalent position of a single-guide RNA.
In another aspect, the CRISPR inhibitor molecule comprises a nucleic acid construct having a first polynucleotide selected from the group consisting of: a polynucleotide that interacts with a protospacer adjacent motif (PAM)-interaction (PI) domain of a CRISPR-associated (Cas) protein, a polynucleotide that interacts with a guide sequence of a crRNA or an equivalent position of a single-guide RNA, and a polynucleotide that interacts with a repeat region of a tracrRNA or an equivalent position of a single-guide RNA, a second polynucleotide and a linker molecule. In a particular embodiment, the first polynucleotide may be a polynucleotide that interacts with a PI domain of a Cas protein.
The polynucleotide component of the polynucleotide constructs described herein that interacts with a protospacer adjacent motif (PAM), may further be described as an anti-PAM oligonucleotide. The anti-PAM oligonucleotide may comprise a stem-loop (hairpin) polynucleotide construct. The loops, by way of example, may comprise DNA, RNA, ANA, FANA, 2′5′-linked RNA, or any combination thereof. FANA and ANA refer to 2′-deoxy-2′-fluoroarabinonucleic acid and arabinonucleic acid, respectively. The stem in the polynucleotide hairpin may comprise DNA or DNA analogs such as FANA, ANA, or any combination of these.
The second polynucleotide may be selected from the group consisting of a polynucleotide that interacts with a guide sequence of a crRNA or an equivalent position of a single-guide RNA, and a polynucleotide that interacts with a repeat region of a tracrRNA or an equivalent position of a single-guide RNA. Preferably, the linker molecule may be operably connected to the first polynucleotide and operably connected to the second polynucleotide. In some embodiments, the first polynucleotide may be a polynucleotide that interacts with a PI domain of a Cas protein.
The CRISPR inhibitor molecule may comprise an artificial nucleic acid construct comprising a first polynucleotide, a second polynucleotide and a linker molecule, where the second polynucleotide may be a polynucleotide that interacts with a guide sequence of a crRNA or an equivalent position of a single-guide RNA. In some embodiments, the linker molecule may be operably connected to the first polynucleotide and operably connected to the second polynucleotide. In those embodiments of the nucleic acid construct that are absent a linker, the first polynucleotide and the second polynucleotide may be directly fused to one another.
In some embodiments, the first polynucleotide may be a polynucleotide that interacts with a PI domain of a Cas protein, and the CRISPR inhibitor molecule may further comprise a second polynucleotide and a linker molecule. The second polynucleotide may be a polynucleotide that interacts with a repeat region of a tracrRNA or an equivalent position of a single-guide RNA. Preferably, the linker molecule may be operably connected to the first polynucleotide and operably connected to the second polynucleotide.
In some embodiments, the first polynucleotide that interacts with the PI domain of the Cas protein may comprise: 2′-deoxyribonucleotides only, at least one 2′-deoxyribonucleic analogs, a mixture of 2′-deoxyribonucleotide and 2′-deoxynucleotide analogs, or 2′-deoxyribonucleotide analogs only such as FANA, ANA, alpha-L locked nucleic acid (alpha-L-LNA), phosphorothioate deoxyribonucleic acid (PS-DNA), and combinations of these. Alternatively, the first polynucleotide that interacts with the PI domain of the Cas protein may comprise a sequence of SEQ ID NO: 1 or a sequence at least 95% identical thereto or a functional fragment thereof, or a sequence of SEQ ID NO: 2 or a sequence at least 95% identical thereto or a functional fragment thereof.
In some embodiments, the first polynucleotide that interacts with the PI domain of the Cas protein may comprise one or more of the following: 2′-deoxyribonucleotide, a 2′-deoxyribonucleotide analog, a ribonucleotide, a ribonucleotide analog, or any combination thereof.
In some embodiments, the second polynucleotide that interacts with the guide sequence of the crRNA or the equivalent position of the single-guide RNA may comprise: ribonucleotides only, at least one ribonucleotide analog, a mixture of ribonucleotides and ribonucleotide analogs, or ribonucleotide analogs only such as 2′-FNA, LNA, 2′-OMe RNA, and combinations of these. Alternatively, the second polynucleotide that interacts with the guide sequence of the crRNA or the equivalent position of the single-guide RNA may comprise a sequence of SEQ ID NO: 3 or a sequence at least 95% identical thereto or a functional fragment thereof.
In some embodiments, the second polynucleotide that interacts with the guide sequence of the crRNA or the equivalent position of the single-guide RNA may comprise one or more of the following: a 2′-deoxyribonucleotide, a 2′-deoxyribonucleotide analog, a ribonucleotide, a ribonucleotide analog, or any combination thereof.
In further embodiments, the second polynucleotide that interacts with the repeat region of the tracrRNA or the equivalent position of the single-guide RNA may comprise: ribonucleotides only, at least one ribonucleotide analog, a mixture of ribonucleotides and ribonucleotide analogs, or ribonucleotide analogs only. Alternatively, the second polynucleotide that interacts with the repeat region of the tracrRNA or the equivalent position of the single-guide RNA may comprise a sequence of: SEQ ID NO: 4 or a sequence at least 95% identical thereto or a functional fragment thereof, SEQ ID NO: 5 or a sequence at least 95% identical thereto or a functional fragment thereof, SEQ ID NO: 6 or a sequence at least 95% identical thereto or a functional fragment thereof, or SEQ ID NO: 7 or a sequence at least 95% identical thereto or a functional fragment thereof.
In further embodiments, the second polynucleotide that interacts with the repeat region of the tracrRNA or the equivalent position of the single-guide RNA may comprise one or more of the following: a 2′-deoxyribonucleotide, a 2′-deoxyribonucleotide analog, a ribonucleotide, a ribonucleotide analog, or any combination thereof.
In another embodiment, the linker molecule may comprise polyethylene glycol. Alternatively, the linker molecule may comprise poly-deoxythymidylic acid (poly-dT), or any other single stranded oligonucleotide with spacer functionality. The linker molecule may generally comprise a polynucleic acid of any chemistry. The linker may also generally comprise a single nucleic acid of any chemistry.
In another embodiment, the CRISPR inhibitor molecule comprises a nucleic acid construct having a first polynucleotide and a second polynucleotide. The first polynucleotide may be operably connected to the second polynucleotide. In some embodiments, the first polynucleotide and the second polynucleotide may be directly fused to one another.
In yet another embodiment, the Cas protein may comprise Cas9, Cas12a (Cpf1), or dead Cas9 (dCas9). Alternatively, the Cas protein may be any other suitable CAS protein from a CRISPR system. The CRISPR system may be natural or synthetic. In some embodiments, the Cas protein is Cas9. While one source of Cas9 protein is from Streptococcus pyogenes, other sources of Cas protein known to those of skill in the art may also be used. Other sources of Cas protein include, but are not limited to, Staphylococcus aureus, Campylobacter jejuni, Neisseria meningitides, Francisilla Novicida, Streptococcus thermophiles, Geobacillus stearothermophilus, and numerous other bacterial species.
2′-deoxyribinucleotides of the present invention are generally understood to refer to 2′-deoxyribonucleic acid molecules that do not contain any chemical modifications.
2′-deoxyribonucleotide analogs of the present invention include any suitable chemically modified nucleotide that maintains the properties of a 2′-deoxyrobonucleotide, or mimics a 2′-deoxyribonucleotide in certain properties, including base pairing and Cas9 interaction. A number of 2′-deoxyribonucleotide analogs are well-known to a person of skill in the art and can be used in certain embodiments of the present invention. Examples include, but are not limited to, arabinonucleic acid (ANA), 2′-fluoro-arabinonucleic acid (FANA), alpha-L locked nucleic acid (alpha-L-LNA), phosphorothioate deoxyribonucleic acid (PS-DNA), acyclic or unlocked nucleic acid (UNA), or any combination thereof.
Ribonucleotides of the present invention are generally understood to refer to ribonucleic acid molecules that do not contain any chemical modifications.
Ribonucleotide analogs of the present invention include any suitable chemically modified nucleotide that maintains the properties of a ribonucleotide, or mimics a ribonucleotide with respect to certain properties, including base pairing or Cas9 interaction. A number of ribonucleotide analogs are well-known to a person of skill in the art and can be used in certain embodiments of the present invention. Examples include, but are not limited to, 2′-fluorinated ribonucleic acid (2′-FRNA), 2′,5′-linked ribonucleic acid (2′,5′-RNA), 2′-O-methyl ribonucleic acid (2′-OMe-RNA), 2′-methoxyethyl ribonucleic acid (2′-MOE-RNA), 2′-fluorinated-4′-O-methyl ribonucleic acid (2′F,4′OMe-RNA), 2′,4′-di-O-methyl ribonucleic acid (2′,4′-diOMe-RNA), 2′,4′ di-fluorinated ribonucleic acid (2′,4′-di-RNA), locked nucleic acid (LNA), and bicyclic or bridged nucleic acid (BNA), or any combination thereof.
While most of the polynucleotides disclosed herein have conventional phosphodiester internucleotide linkages and are suitable for use in the disclosed embodiments, other internucleotide linkages are well-known to the skilled artisan and can be used in additional embodiments of the present disclosure. Thus the present disclosure also provides polynucleotides that have one or more internucleotide linkages that are not a phosphodiester internucleotide linkage. In some embodiments, the polynucleotides comprises at least one internucleotide linkage selected from the group consisting of phosphodiester, phosphorothioate, phosphotriester, phosphorodithioate, boranophosphate, Rp- and/or Sp-phosphorothioate, 3′ thioformacetal, methylene, amide, methylphosphonate, phosphoramidate, amide and any combination thereof.
Expression vectors including the artificial nucleic acid constructs of the present disclosure are also provided. These expression vectors may comprise a plasmid or virus. The nucleic acid constructs of the present disclosure may contain a promoter operably linked to a transcribable nucleic acid molecule operably linked to a 3′ transcription termination nucleic acid molecule. In addition, the artificial nucleic acid constructs may further include, but are not limited to, additional regulatory nucleic acid molecules from, e.g., the 3′-untranslated region (3′ UTR). The nucleic acid constructs can also include a 5′ untranslated region (5′ UTR) of an mRNA nucleic acid molecule. This 5′ UTR will serve, by way of example, a role in translation initiation and provide a genetic component as part of an expression vector. These additional upstream and downstream regulatory nucleic acid molecules and sequences may be derived from a source that is native or heterologous with respect to the other elements present in the artificial nucleic acid constructs described herein.
The following definitions and methods are provided to better define the present invention and to guide those of ordinary skill in the art in the practice of the present invention. Unless otherwise noted, terms are to be understood according to conventional usage by those of ordinary skill in the relevant art. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of skill in the art to which the disclosure pertains. Although any methods and materials similar to or equivalent to those described herein can be used in the practice or testing of the present technology, the preferred methods and materials are described herein.
Reference to an element by the indefinite article “a” or “an” does not exclude the possibility that more than one element is present, unless the context clearly requires that there be one and only one element. The indefinite article “a” or “an” thus usually means “at least one.”
As used herein, “patient” or “subject” means an individual having symptoms of, or at risk for, cancer, disease or other malignancy. A patient may be human or non-human and may include, for example, an animal such as a horse, dog, cow, pig or other animal. Likewise, a patient or subject may include a human patient including adults or juveniles (e.g., children). Moreover, a patient or subject may mean any living organism, preferably a mammal (e.g., human or non-human) from whom a blood volume is desired to be determined and/or monitored from the administration of compositions contemplated herein.
As used herein, “about” means within a statistically meaningful range of a value or values such as a stated concentration, length, molecular weight, pH, sequence identity, timeframe, temperature or volume. Such a value or range can be within an order of magnitude, typically within 20%, more typically within 10%, and even more typically within 5% of a given value or range. The allowable variation encompassed by “about” will depend upon the particular system under study, and can be readily appreciated by one of skill in the art. As used herein, the terms “subject” and “patient” are used interchangeably irrespective of whether the subject has or is currently undergoing any form of treatment.
As used herein, the terms “subject” and “subjects” refer to any vertebrate, including, but not limited to, a mammal (e.g., cow, pig, camel, llama, horse, goat, rabbit, sheep, hamsters, guinea pig, cat, dog, rat, and mouse, a non-human primate (for example, a monkey, such as a cynomolgus monkey, chimpanzee, etc.) and a human). Preferably, the subject is a human.
The term “construct” is understood to refer to any recombinant or synthetic polynucleotide molecule such as a plasmid, cosmid, virus, autonomously replicating polynucleotide molecule, phage, or linear or circular single-stranded or double-stranded DNA or RNA polynucleotide molecule, derived from any source, biological or chemical, capable of genomic integration or autonomous replication, comprising a polynucleotide molecule where one or more polynucleotide molecule has been linked in a functionally operative manner, i.e. operably linked.
An “expression vector”, “vector”, “vector construct”, “expression construct”, “plasmid”, or “recombinant DNA construct” is generally understood to refer to a nucleic acid that has been generated via human intervention, including by recombinant means or direct chemical synthesis, with a series of specified nucleic acid elements that permit transcription or translation of a particular nucleic acid in, for example, a host cell. The expression vector can be part of a plasmid, virus, or nucleic acid fragment. Typically, the expression vector can include a nucleic acid to be transcribed operably linked to a promoter.
The terms “heterologous DNA sequence”, “exogenous DNA segment” or “heterologous nucleic acid,” as used herein, each refer to a sequence that originates from a source foreign to the particular host cell or, if from the same source, is modified from its original form. Thus, a heterologous gene in a host cell includes a gene that is endogenous to the particular host cell but has been modified through, for example, the use of DNA shuffling. The terms also include non-naturally occurring multiple copies of a naturally occurring DNA sequence. Thus, the terms refer to a DNA segment that is foreign or heterologous to the cell, or homologous to the cell but in a position within the host cell nucleic acid in which the element is not ordinarily found. Exogenous DNA segments are expressed to yield exogenous polypeptides. Conversely, a homologous DNA sequence is a DNA sequence that is naturally associated with a host cell into which it is introduced.
“Operably linked” or “functionally linked” refers preferably to the association of nucleic acid sequences on a single nucleic acid fragment so that the function of one is affected by the other. For example, a regulatory DNA sequence is said to be “operably linked to” or “associated with” a DNA sequence that codes for an RNA or a polypeptide if the two sequences are situated such that the regulatory DNA sequence affects expression of the coding DNA sequence (i.e., that the coding sequence or functional RNA is under the transcriptional control of the promoter). Coding sequences can be operably-linked to regulatory sequences in sense or antisense orientation. The two nucleic acid molecules may be part of a single contiguous nucleic acid molecule and may be adjacent. For example, a promoter is operably linked to a gene of interest if the promoter regulates or mediates transcription of the gene of interest in a cell. Operably linked or functionally linked may also refer to the physical connection or nucleic acid sequences.
A “promoter” is generally understood as a nucleic acid control sequence that directs transcription of a nucleic acid. An inducible promoter is generally understood as a promoter that mediates transcription of an operably linked gene in response to a particular stimulus. A promoter can include necessary nucleic acid sequences near the start site of transcription, such as, in the Case of a polymerase II type promoter, a TATA element. A promoter can optionally include distal enhancer or repressor elements, which can be located as much as several thousand base pairs from the start site of transcription.
A “transcribable nucleic acid molecule” as used herein refers to any nucleic acid molecule capable of being transcribed into a RNA molecule. Methods are known for introducing constructs into a cell in such a manner that the transcribable nucleic acid molecule is transcribed into a functional mRNA molecule that is translated and therefore expressed as a protein product. Constructs may also be constructed to be capable of expressing antisense RNA molecules, in order to inhibit translation of a specific RNA molecule of interest. For the practice of the present disclosure, conventional compositions and methods for preparing and using constructs and host cells are well known to one skilled in the art (see e.g.: Ausubel et al.; Elhai and Wolk; Sambrook and Russel, 2001; and Sambrook and Russel, 2006).
Nucleotide and/or amino acid sequence identity percent (%) is understood as the percentage of nucleotide or amino acid residues that are identical with nucleotide or amino acid residues in a candidate sequence in comparison to a reference sequence when the two sequences are aligned. To determine percent identity, sequences are aligned and if necessary, gaps are introduced to achieve the maximum percent sequence identity. Sequence alignment procedures to determine percent identity are well known to those of skill in the art. Often publicly available computer software such as BLAST, BLAST2, ALIGN2 or Megalign (DNASTAR) software is used to align sequences. Those skilled in the art can determine appropriate parameters for measuring alignment, including any algorithms needed to achieve maximal alignment over the full-length of the sequences being compared. When sequences are aligned, the percent sequence identity of a given sequence A to, with, or against a given sequence B (which can alternatively be phrased as a given sequence A that has or comprises a certain percent sequence identity to, with, or against a given sequence B) can be calculated as: percent sequence identity=X/Y100, where X is the number of residues scored as identical matches by the sequence alignment program's or algorithm's alignment of A and B and Y is the total number of residues in B. If the length of sequence A is not equal to the length of sequence B, the percent sequence identity of A to B will not equal the percent sequence identity of B to A.
In some embodiments, numbers expressing quantities of ingredients, properties such as molecular weight, reaction conditions, and so forth, used to describe and claim certain embodiments of the present disclosure are to be understood as being modified in some instances by the term “about.” In some embodiments, the term “about” is used to indicate that a value includes the standard deviation of the mean for the device or method being employed to determine the value. In some embodiments, the numerical parameters set forth in the written description and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by a particular embodiment. In some embodiments, the numerical parameters should be construed in light of the number of reported significant digits and by applying ordinary rounding techniques. Notwithstanding that the numerical ranges and parameters setting forth the broad scope of some embodiments of the present disclosure are approximations, the numerical values set forth in the specific examples are reported as precisely as practicable. The numerical values presented in some embodiments of the present disclosure may contain certain errors necessarily resulting from the standard deviation found in their respective testing measurements. The recitation of ranges of values herein is merely intended to serve as a shorthand method of referring individually to each separate value falling within the range. Unless otherwise indicated herein, each individual value is incorporated into the specification as if it were individually recited herein.
The ten is “comprise,” “have” and “include” are open-ended linking verbs. Any forms or tenses of one or more of these verbs, such as “comprises,” “comprising,” “has,” “having,” “includes” and “including,” are also open-ended. For example, any method that “comprises,” “has” or “includes” one or more steps is not limited to possessing only those one or more steps and can also cover other unlisted steps. Similarly, any composition or device that “comprises,” “has” or “includes” one or more features is not limited to possessing only those one or more features and can cover other unlisted features.
All methods described herein can be performed in any suitable order unless otherwise indicated herein or otherwise clearly contradicted by context. The use of any and all examples, or exemplary language (e.g. “such as”) provided with respect to certain embodiments herein is intended merely to better illuminate the present disclosure and does not pose a limitation on the scope of the present disclosure otherwise claimed. No language in the specification should be construed as indicating any non-claimed element essential to the practice of the present disclosure.
Groupings of alternative elements or embodiments of the present disclosure disclosed herein are not to be construed as limitations. Each group member can be referred to and claimed individually or in any combination with other members of the group or other elements found herein. One or more members of a group can be included in, or deleted from, a group for reasons of convenience or patentability. When any such inclusion or deletion occurs, the specification is herein deemed to contain the group as modified thus fulfilling the written description of all Markush groups used in the appended claims.
All publications, patents, patent applications, and other references cited in this application are incorporated herein by reference in their entirety for all purposes to the same extent as if each individual publication, patent, patent application or other reference was specifically and individually indicated to be incorporated by reference in its entirety for all purposes. Citation of a reference herein shall not be construed as an admission that such is prior art to the present disclosure.
Having described the present disclosure in detail, it will be apparent that all of the compositions and methods disclosed and claimed herein can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this disclosure have been described in tennis of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and methods and in the steps or in the sequence of steps of the methods described herein without departing from the concept, spirit and scope of the invention. More specifically, it will be apparent that certain agents which are both chemically and physiologically related may be substituted for the agents described herein while the same or similar results would be achieved. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims. Furthermore, it should be appreciated that all examples in the present disclosure are provided as non-limiting examples.
The following Table 1 provides a series of nucleic acid constructs.
CGG
S
U
S
GAACAGCUCCUCGC
UUA UUU UAA CUU GCU AU
-(Hexa PEG)-AUU UUA ACU
UGC UAU
-(Hexa PEG)-GUU UUA GAG
CUAUGC UGU
-(Hexa PEG)-GUU UUA GAG
CUAUGC UGU
-(Hexa PEG)-A*U*U* U*U*A*
A*C*U* U*G*C* U*A*U*
-(Hexa PEG)-A*U*U*
U*A*
C*U* G*C* U*A*U*
-(Linker)-AUU UUA ACU
UGC UAU
-(Linker)-GUU UUA GAG
CUAUGC UGU
-(Linker)-GUU UUA GAG
CUAUGC UGU
-(Linker)-A*U*U *U*U*A*
A*C*U* U*G*C* U*A*U*
-(Linker)-A*U*U*
U*A*
C*U* G*C* U*A*U*
,
)
S = PS linker
The following non-limiting examples are provided to further illustrate the present disclosure. It should be appreciated by those of skill in the art that the techniques disclosed in the examples that follow represent approaches the inventors have found function well in the practice of the present disclosure, and this can be considered to constitute examples of modes for its practice. However, those of skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments that are disclosed and still obtain a like or similar result without departing from the spirit and scope of the present disclosure.
Some of the inhibitor molecules and crRNAs were commercially synthesized by Integrated DNA Technologies (IDT), while others were custom synthesized as shown in
TracrRNA and sgRNA was prepared by T7 in vitro transcription with DNA templates synthesized by IDT. Single-stranded DNA templates were annealed to T7 promoter oligo to generate double-stranded promoter regions, which support in vitro transcription by T7 RNA polymerase. Transcription reactions were performed by standard protocols for 2 hours. Briefly, reactions contained purified T7 RNA polymerase, 30 mM Tris (at pH 7.9), 12.5 mM NaCl, 40 mM MgCl2, 2% PEG8000, 0.05% Triton X-100, 2 mM spermidine, and 2.5 μM T7-DNA template. Afterward, the DNA template was degraded by the addition of 1 unit of DNase I for every 20 μL of reaction and incubated at 37° C. for 15 min. Reactions were phenol-chloroform extracted and gel-purified from denaturing polyacrylamide gels. Purified RNA was quantified by measuring absorbance at 260 nm and calculated extinction coefficients using nearest neighbor approximations and Beer's Law.
Plasmid encoding a Spy Cas9 with a C-terminal fusion of a nuclear localization signal (NLS) and a 6×-Histidine tag (pET-Cas9-NLS-6×His) was obtained from Addgene (62933). A dead Cas9 (dCas9) version was prepared by performing site-directed mutagenesis on this plasmid to generate H840A and D10A mutations (pET-dCas9-NLS-6×His).
Protein expression was induced in Rosetta (DE3) cells with 0.4 mM IPTG at 18° C. for 16 h. Cell pellets were resuspended in 6 mL of chilled binding buffer (20 mM Tris-HCl, pH 8.0, 250 mM NaCl, 1 mM PMSF, 5 mM imidazole) per 0.5 L of culture. Resuspended cells were sonicated and clarified by centrifugation. His-Pur Cobalt-CMA resin (Thermo Scientific) was equilibrated with binding buffer and the supernatant added to the equilibrated resin and incubated at 4° C. for 1 h. The supernatant was washed sequentially with increasing concentrations of NaCl in 50 mL volumes of wash buffer (Tris-HCl, pH 8, 0.25/0.5/0.75/1.0 M NaCl, 10 mM imidazole). Protein was eluted with 15 mL elution buffer (Tris-HCl, pH 8, 250 mM NaCl, 130 mM imidazole). Purified Cas9 was concentrated with Vivaspin 15 centrifugal concentrators (Sartorius, 30K MWCO). Concentration was approximated by UV absorbance at 280 nm using a calculated extinction coefficient (120,450 M-1 cm-1) and Beer's law. One volume of glycerol was added to a final of 50% and purified Cas9 stored as aliquots at −80° C.
The 5′ phosphate on T7-transcribed tracrRNA was removed using alkaline phosphatase following the manufacturer's recommended protocol. Synthetic duplex target DNA and crRNA lacks a 5′ phosphate and was directly labeled. 100 pmols of tracrRNA, crRNA, or antisense DNA target strand was radiolabeled with [γ-32P]-ATP using T4 polynucleotide kinase following the manufacturers recommended enzyme protocol. Reactions were phenol-chloroform extracted and radiolabeled RNA or DNA was gel-purified on 15% denaturing polyacrylamide gels (1×TBE, 7 M urea) by the crush-and-soak method. Gel-purified radiolabeled RNA and DNA was quantified by scintillation counting.
The active concentration of Cas9 and dCas9 proteins were determined by titration of increasing amounts of Cas9 or dCas9 with 0.5 μM crRNA:tracrRNA complex, where 500 cpms of radiolabeled crRNA was spiked into the reaction. Cas9 or dCas9 binding to crRNA:tracrRNA complex was determined by dot-blot filter binding assays (see below). At concentrations above the Kd value, binding is proportional to the amount of protein added and results in a straight line when plotting radioactivity versus protein. Once the Cas9 or dCas9 binding has saturated the crRNA:tracrRNA ligand, binding plateaus and is also a straight line. The value of x where the two lines intersect is equivalent to 0.5 μM of Cas9 or dCas9. To find this value, set the two linear equations equal to one another and algebraically solve for x.
For inhibitor binding by Cas9 RNP complexes, radiolabeled inhibitor (500 cpms/reaction) was combined with increasing concentrations of a pre-assembled dCas9-tracrRNA complex, with or without crRNA bound, in a final reaction of 40 μL 1× cleavage buffer (20 mM Tris-HCl, pH 7.5, 100 mM KCl, 5% glycerol, 1 mM DTT, 0.5 mM EDTA, 2 mM MgCl2) and 0.1 mg/mL of purified yeast tRNA. After incubation at 37° C. for 15 min, reactions were vacuum filtered over nitrocellulose membrane (Protran Premium NC, Amersham) using a 96-well dot blot apparatus. Wells were washed twice with 200 μL of 1× cleavage buffer. Membrane was then removed and washed with 1× PBS solution and air dried at RT. Binding of radioactive crRNA was then visualized by phosphorimager. Spots were quantified with ImageQuant software, plotted in Prism (GraphPad) and fit to a one-site binding hyperbola equation. Error bars for all quantified data represent experimental replicates, not technical replicates. Sample size was selected based on the expectation that 3 or more replicates will be representative of typical in vitro assay conditions.
PCR-amplified DNA (1 kb fragment) containing the EGFP target gene was purified by phenol-chloroform extraction and ethanol precipitation. The Cas9 pre-RNP complex was assembled (typical final concentrations: 0.5 μM Cas9, 0.25 μM tracrRNA) in a 1× cleavage buffer supplemented with 0.1 mg/mL of purified yeast tRNA. The concentration of tracrRNA was purposely set as the limiting component of the RNP complex and used to predict final RNP concentration. The crRNA (0.3 μM final), any inhibitors, and target DNA (100 ng) were spotted into tubes. The Cas9 pre-RNP was then added to these tubes to begin the reaction. A small molar excess of Cas9 and crRNA ensures complete assembly of tracrRNA into RNP complexes. Inhibitor molecules were added at the final concentrations indicated in each experiment.
Standard reaction conditions were 37° C. for 10 min or 1 h in a final reaction volume of 40 μL. The reaction was stopped by the addition of 10 vol of 2% LiClO4 in acetone and precipitated for >1 h at −20° C. Precipitated reactions were centrifuged and washed with acetone, air dried, and re-suspended in 1× loading dye (10% glycerol, 1× TBE, orange G dye) containing 10 μg of Proteinase K. For time-course experiments, reactions were stopped at specified time points by the addition of 2% LiClO4 in acetone and placed on ice, then worked-up the same as other samples. After dissolving the pellet, the reactions were incubated at RT for 20 mM, then resolved on TBE-buffered 1% agarose gels. Gels were stained with ethidium bromide and visualized by UV imager.
The fraction of target cleaved was quantified using ImageJ software. The band intensity for the cleavage product band was divided by the combined intensity of cleavage product and uncut substrate bands and reported as fraction cleaved (i.e. “cut”/“cut+uncut”). Time course cleavage assay results were plotted using Prism (Graphpad) software and fit to a one-site binding hyperbola by non-linear regression. Error bars for all quantified data represent experimental replicates, not technical replicates. Samples size was selected based on the expectation that 3 or more replicates will be representative of typical in vitro assay conditions.
HEK cells expressing EGFP and Spy Cas9 were transfected with 20 pmols of sgRNA or crRNA:tracrRNA complex using RNAiMAX following the manufacturer's recommended protocol. Inhibitors were included at the same molar concentration as guide RNAs (20 pmols) and co-transfected. After 12 h, Opti-MEM was replaced with full media plus 1× Penicillin-Streptomycin solution and cells were grown for a total of 48 h post-transfection. Genomic DNA (gDNA) was harvested by washing the cells and dissolving them in a Tris-buffered (20 mM, pH 7.4) sarkosyl (0.1%) solution at 60° C. in the presence of Proteinase K (40 μg/mL). After 2.5 h, cell lysate was collected and precipitated with 200 mM NaCl and 75% ethanol. Genomic DNA is washed with 70% ethanol, dried, and quantified by qPCR using GAPDH genomic DNA primers. Based on a previously determined standard curve, approximately 100 ng of gDNA is amplified for 30 cycles using Phusion polymerase and primers that lie 200 bases upstream and 500 bases downstream of the expected cut site. PCR reactions are purified by mini-column purification and sent for Sanger sequencing using the forward Phusion primer. The Sanger sequencing results are then analyzed by TIDE analysis to predict the % editing efficiency.
The methods used were those as described in Examples 1-7, unless indicated otherwise.
The studies described above have resulted in a strategy and in the production of prototype molecules that provide for inhibition of CRISPR effector enzymes. The molecules were prepared using synthetic and chemically-modified oligonucleotides. A key feature of the molecules presented herein is high specificity and affinity for the CRISPR enzyme. This is achieved through designing the molecules to include oligonucleotide sequences that bind CRISPR enzymes at multiple points of contact. These oligonucleotides and their modifications are compiled in
While some inhibitors may function with only a single point of contact, the most effective inhibitors employ modules that engage two or more points of contact to an individual molecule. Additional modules may be added to further improve other pharmacologic properties of the inhibitors, including tissue delivery or cellular localization. Modules may also include nucleic acids that have been in vitro evolved and selected, such as aptamers, to specifically interact with points of contact on Cas proteins.
Several different prototype molecules were tested as proof-of-principle based on the general design strategy described above. Inhibitor candidates targeting each point of contact were initially designed and tested against Streptococcus pyogenes (Spy) Cas9 with or without its tracrRNA or crRNA guides (
These MCP nucleic acid inhibitors can further be optimized by systematically modifying each module. For example, altering the anti-tracr module's chemical nature (other RNA analogs besides 2′-O-methyl-RNA, such as 2′F-RNA. 2′-methoxyethyl (MOE) RNA, locked nucleic acid (LNA), and other bicyclo or bridged nucleic acids (BNAs)), altering the anti-PAM module sequence, size and chemical nature (DNA analogs, such as arabinonucleic acid (ANA), 2′F-ANA, alpha-L-LNA, and phosphorothioate (PS) DNA), adding modifications to improve nuclease resistance or cellular uptake (such as PS linkages or conjugates like cholesterol and small molecules) and adjusting the length and chemical nature of the linker(s) connecting binding modules.
One molecule with moderate/high binding activity was selected, Anti1_PAM-tracr (SEQ ID NO: 11), and its ability to block assembly and cleavage activity of dual RNA-guided (crRNA+tracrRNA) Spy Cas9 was tested. Activity was significantly reduced at early time points and never reached completion after 1 h of incubation when the inhibitor was at a 3-fold molar excess (
Based on these results, inhibitors with modules that simultaneously engage the protein and RNA guide component of CRISPR effector enzymes and RNP complexes will be highly effective. They take advantage of multiple, distinct modes of interaction, such as nucleic acid-protein binding and nucleic acid hybridization. Chemical modification with the correct chemistries in anti-tracr or anti-CRISPR modules also significantly improves the performance of inhibitors. Making base-pairing essentially irreversible under physiological conditions with strong Tm-stabilizing modifications, like bridged or bicyclo nucleic acids (BNAs such as LNA), could generate potent inhibitors. To test this idea, Anti_PAM-tracr inhibitor molecules were created where the anti-tracr module was chemically modified to 2′-F-RNA (Anti1_cr1, SEQ ID NO: 12) or 2′-F-RNA containing evenly spaced LNA nucleotides (Anti1_cr2, SEQ ID NO: 13). These inhibitor molecules both performed better than the control Anti1_PAM-tracr inhibitor when blocking enzyme activity in vitro (
The activity of a model inhibitor, Anti1_PAM-tracr, was also tested inside of cells. The crRNA and tracrRNA guides, or a sgRNA, targeting EGFP were co-transfected into HEK cells with equal molar amounts of Anti1_PAM-tracr. The HEK cells stably express EGFP and Spy Cas9. After 48 h of incubation to allow editing, a decrease in EGFP editing efficiency, determined by TIDE analysis, was observed for both dual RNA-guided and single RNA-guided Cas9 (
In summary, these studies demonstrate the design of a new strategy to inhibit CRISPR effector enzymes. This strategy is based on specifically designed nucleic acid constructs that possess the ability to make multiple points of contact with the CRISPR enzyme, and the resulting mimicry of natural guide RNA or target DNA binding to the effector enzyme. This strategy may extend to novel nucleic acids that are designed or in vitro evolved and selected (i.e. aptamers) to interact with CRISPR proteins at new points of contact in addition to those demonstrated here. This strategy should conceivably extend to all nucleic acid-guided CRISPR effector enzymes, including Cas12a (Cpf1), multi-component CRISPR enzymes (for example the Cascade complex) and enzymes from other CRISPR classes and enzyme types. Certain designs may also prove effective in inhibiting the DNA binding activity, and therefore function, of catalytically inactive CRISPR effectors, such as ‘dead’ Cas9.
The present example presents studies that include calculation of a binding affinity for one of the higher performing anti-CRISPR nucleic acids, Anti1_PAM-tracr_FL (
Linkers of many lengths and composition are demonstrated here to be tolerated, and shorter linkers also appeared to be more effective. Linker lengths from 27 atom polyethylene glycol (PEG) linkers down to 3 atom PEG linkers were examined and measured binding affinity (
The linker composed of just a T nucleotide seemed to perform the best in cell-based genome editing assays (
HEK 293T cells expressing both EGFP and SpCas9 were grown in Dulbecco's modified Eagle's medium with 1% non-essential amino acids, 5% Cosmic calf serum, 5% fetal bovine serum (FBS), and without antibiotics. Cells were reverse transfected (40,000 cells/well in a 96-well dish) with 5 pmols sgRNA in a final volume of 200 μL following the manufacturer's recommended protocol. Inhibitors were co-transfected with a sgRNA targeting EGFP at a 1:1 molar ratio. After 8 hours the media was replaced with full media, and the cells allowed to grow for 5 days with a fresh media change every 2 days. After 5 days, the cells were harvested and analyzed by flow cytometry.
Before flow cytometry, cells were harvested by trypsinization, washed with 1× PBS, and resuspended in 200 μL 1×PBS. Cells were counted on an Attune NXT flow cytometer (Thermo Fischer Scientific). 20,000 events were counted and analyzed using Attune® NxT Software. The cells were first gated based on forward and side scattering (FSC-A/SSC-A) to remove cell debris, and then gated to select single cells (FSC-H/FSC-A). Finally, cells were gated to select EGFP positive cells. The quadrant gate was based on the signal from non-EGFP expressing control cells. Untreated HEK293T cells expressing both SpCas9 and EGFP contained about 5% nonfluorescent cells. The average from six untreated replicates was used for background.
The examples set forth above are provided to give those of ordinary skill in the art a complete disclosure and description of how to make and use the embodiments of the methods for prediction of the selected modifications that may be made to a biomolecule of interest, and are not intended to limit the scope of what the inventors regard as the scope of the disclosure. Modifications of the above-described modes for carrying out the disclosure can be used by persons of skill in the art, and are intended to be within the scope of the following claims.
It is to be understood that the disclosure is not limited to particular methods or systems, which can, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting.
Research Tools:
The present invention also provides for the use of the various methods, constructs, and nucleic acid modification techniques described herein as a research tool for use in vitro or in cellulo (cell culture). For example, the nucleic acid constructs and fragments thereof, as well as the platform strategies described herein for CRISPR and other targeted strategies, may be used in devising methods and tolls useful for analyzing nucleic acid structure, either indirectly (e.g. by chemical probing, using electrophoresis, etc.) or directly (e.g. using fluorescence, NMR, or crystallography). Specific methods to prepare nucleic acid samples for structural analyses, as well as use of the herein described constructs and techniques for high through put screening of potential candidate molecules, is also provided.
In addition, the constructs and strategies provided herein may be employed as part of a method for further characterizing enzymes involved in nucleic acid biochemistry. By way of example, such processes may focus on CRISPR enzymes or other enzymes that act directly on DNA or RNA, or on proteins that interact with such species. Nucleic acids with inherent enzymatic activity are of particular interest, as are their involvement in multi-protein complexes.
In yet other applications, the nucleic acid constructs, methods and strategies disclosed herein may be employed in methods for the analysis of protein-nucleic acid interactions including ChIP, footprinting, interference, cross-linking, fluorescence techniques, one- and tri-hybrid strategies, in vivo methods, and analyses of mutants.
A number of embodiments of the disclosure have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, other embodiments are within the scope of the following claims.
The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting the invention described herein. Scope of the invention is thus indicated by the appended claims rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are intended to be embraced therein.
The following references are specifically incorporated herein in their entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2019/053891 | 9/30/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62738472 | Sep 2018 | US |
