Thrombus imaging aptamers and methods of using same
Provided herein are imaging agents, antidotes to the imaging agents and methods of using the same to image a thrombus or blood clot or thrombin including sites of thrombin accumulation and to diagnose and treat thrombosis. The imaging agents include an aptamer capable of binding the thrombus or thrombin in particular linked to a reporter moiety. The imaging agents may be used to label the thrombus or sites of thrombin accumulation. Antidotes capable of binding to the aptamer in the imaging agent are also provided. The antidotes may further be linked to a quencher capable of quenching the reporter moiety.
1 . An imaging agent comprising (a) an aptamer linked to (b) a reporter moiety, wherein said aptamer is capable of binding thrombin with a Kd<500 nM, wherein the aptamer comprises a nucleotide sequence having at least 70% sequence identity to SEQ ID NO: 1 or comprises a nucleotide sequence including from 5′ to 3′ a first stem forming region comprising at least three nucleotides, a first loop region comprising the nucleotide sequence AACA, a second stem forming region comprising at least three nucleotides, a second loop region comprising the nucleotide sequence C U/A GXAG U/A A, a third stem forming region comprising at least three nucleotides capable of forming a stem with the second stem forming region, a third loop region comprising at least one nucleotide and up to 5 nucleotides, and a fourth stem forming region comprising at least three nucleotides capable of forming a stem with the first stem forming region, wherein A is adenine, C is cytosine, G is guanine, U is uracil and X is any base in the nucleotide sequences.
2 . The imaging agent of claim 1 , wherein said reporter moiety is selected from the group consisting of a fluorophore moiety, an optical moiety, a magnetic moiety, a radiolabel moiety, an X-ray moiety, an ultrasound imaging moiety, a photoacoustic imaging moiety, a nanoparticle-based moiety, and a combination of two or more of the recited moieties.
3 . The imaging agent of claim 2 , wherein said reporter moiety comprises a fluorophore moiety.
4 . The imaging agent of claim 1 , wherein said aptamer and said reporter moiety are linked by a covalent bond.
5 . The imaging agent of claim 4 , wherein said aptamer and said reporter moiety are linked at the 5′ or 3′ end of said aptamer.
6 . The imaging agent of claim 1 , wherein said aptamer and said reporter moiety are linked by a tag system.
7 . The imaging agent of claim 1 , wherein the aptamer and the reporter moiety are linked with a 5′-Thiol-modified C6 linker.
8 . The imaging agent of claim 7 , wherein the reporter moiety comprises a maleimide modified dye.
9 . The imaging agent of claim 8 , wherein the reporter moiety is Cy5.5.
10 . The imaging agent of claim 1 , wherein the aptamer and the reporter moiety are linked with a 5′-amine-modified C6 linker.
11 . The imaging agent of claim 10 , wherein the reporter moiety comprises a N-hydroxysuccinimide ester modified dye.
12 . The imaging agent of claim 11 , wherein the reporter moiety is Alexa Fluor 680.
13 . The imaging agent of claim 6 , wherein the tag system is selected from the group consisting of biotin/avidin, biotin/streptavidin, and biotin/deglycosylated avidin.
14 . A method for imaging a thrombus or site of thrombin accumulation comprising administering the imaging agent of claim 1 and generating an image of at least a portion of the thrombus using an imaging modality, wherein the imaging agent labels said thrombus or site of thrombin accumulation in the image by binding of the aptamer to the thrombus.
15 . The method of claim 14 , further comprising administering an antidote to reverse or block the labeling of the thrombus or thrombin by the imaging agent, the antidote comprising a nucleotide sequence having at least 70% sequence identity to a nucleotide sequence selected from the group consisting of SEQ ID NO: 2, SEQ ID NO: 3 and SEQ ID NO: 4 and is complementary to at least 10 nucleotides of the aptamer.
16 . A method for generating a subtraction image of a thrombus or thrombin accumulation in a subject comprising:
(a) administering the imaging agent of claim 1 wherein the aptamer binds to a thrombus or thrombin;
(b) generating a first image of a portion of the subject;
(c) administering an antidote that binds to the aptamer of the imaging agent in (a); wherein the antidote has at least 70% sequence identity to a nucleotide sequence selected from the group consisting of SEQ ID NO: 2, SEQ ID NO: 3 and SEQ ID NO: 4 and is complementary to at least 10 nucleotides of the aptamer;
(d) generating a second image of the portion of the subject; and
(e) subtracting the second image of (d) from the first image of (b) to generate said subtracted image.
17 . A method of diagnosing an arterial or venous thrombosis in a subject comprising:
(a) administering the imaging agent of claim 1 wherein the aptamer binds to a thrombus or thrombin;
(b) generating a first image of a portion of the subject;
(c) administering an antidote that binds to the aptamer of the imaging agent in (a); wherein the antidote has at least 70% sequence identity to a nucleotide sequence selected from the group consisting of SEQ ID NO: 2, SEQ ID NO: 3 and SEQ ID NO: 4 and is complementary to at least 10 nucleotides of the aptamer;
(d) generating a second image of the portion of the subject; and
(e) subtracting the second image of (d) from the first image of (b) and using the subtracted image to determine if a thrombus is present and diagnosing the arterial or venous thrombosis in the subject if the thrombus is present.