Composition and methods for imaging cells

1. A composition for imaging a cell having a first biomarker and a second biomarker that is different than the first biomarker, the composition comprising:

(a) a first imaging probe comprising: a first targeting moiety, an enzyme-activated contrast agent having an enzyme substrate, and a first linker region,

wherein the first linker region links the enzyme-activated contrast agent to the first targeting moiety,

wherein the enzyme-activated contrast agent is 1-(2-(β-Galactopyranosyloxy)propyl)-4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane) gadolinium(III) (EGadMe), and

wherein the first targeting moiety specifically complexes with the first biomarker; and

(b) a second imaging probe comprising: a second targeting moiety, an activator molecule comprising β-galactosidase or fragments thereof, and a second linker region,

wherein the second linker region links the activator molecule to the second targeting moiety,

wherein the β-galactosidase or fragments thereof of the activator molecule activates the enzyme-activated contrast agent by enzymatic cleavage of the enzyme substrate of the enzyme-activated contrast agent,

wherein the second targeting moiety is different than the first targeting moiety and specifically complexes with the second biomarker, and

wherein the composition produces a detectable signal when the first targeting moiety of the first imaging probe and the second targeting moiety of the second imaging probe complex with first and second biomarkers of the cell to bring the first imaging probe and the second imaging probe in proximity to each other so that the enzyme substrate of the enzyme-activated contrast agent of the first imaging probe is cleaved by the β-galactosidase or fragments thereof of the second imaging probe to produce the detectable signal; and

wherein the enzyme-activated contrast agent remains linked to the first targeting moiety via the first linker region after activation by the β-galactosidase or fragments thereof of the second imaging probe.

2. The composition of claim 1 , wherein at least one of the first and second biomarkers is extracellular.

3. The composition of claim 1 , wherein at least one of the first and second biomarkers is intracellular.

4. The composition of claim 1 , wherein at least one of the first and second biomarkers is selected from the group consisting of a cellular protease, a kinase, a protein, a cell surface receptor, fatty acid, and lipid.

5. The composition of claim 1 , wherein the first and second biomarkers are cancer cell surface receptors.

6. The composition of claim 1 , the first and second targeting moiety being selected from the group consisting of polypeptides, polynucleotides, lipids, small molecules, elemental compounds, antibodies, and antibody fragments.

7. The composition of claim 1 , wherein the linker region is a polymer.

8. The composition of claim 1 , wherein at least one of the first and second linker regions comprising at least one peptide linker.

9. The composition of claim 8 , the at least one peptide linker comprising a biotin-streptavidin-biotin linkage.

10. The composition of claim 1 , the activator molecule including first and second enzyme fragments, the first and second enzyme fragments forming an activator complex that interacts with the enzyme-activated contrast agent to produce the detectable signal.

11. The composition of claim 1 , wherein the enzyme-activated contrast agent comprises a self-immolative linker that connects a metal-ion chelator to the enzyme substrate, wherein the detectable signal is formed by enzymatic cleavage by the β-galactosidase or fragments thereof of the activator molecule of the second imaging probe.

12. A composition for imaging a cell having a first biomarker and a second biomarker that is different than the first biomarker, the composition comprising:

(a) a first imaging probe comprising: a first targeting moiety, an self-immolative enzyme-activated contrast agent having an enzyme substrate, and a first linker region,

wherein the first linker region links the self-immolative enzyme-activated contrast agent to the first targeting moiety,

wherein the self-immolative enzyme-activated contrast agent is 1-(2-(β-Galactopyranosyloxy)propyl)-4,7,10-tris(carboxymethyl)-1,4,7,10-tetraazacyclododecane) gadolinium(III) (EGadMe), and

wherein the first targeting moiety specifically complexing with the first biomarker; and

(b) a second imaging probe comprising: a second targeting moiety, an activator molecule comprising β-galactosidase or fragments thereof, and a second linker region,

wherein the second linker region links the activator molecule to the second targeting moiety,

wherein the β-galactosidase or fragments thereof of the activator molecule activates the self-immolative enzyme-activated contrast agent by enzymatic cleavage of the enzyme substrate of the self-immolative enzyme-activated contrast agent, and

wherein the second targeting moiety is different than the first targeting moiety and specifically complexes with the second biomarker;

wherein the composition produces a detectable signal when the first targeting moiety of the first imaging probe and the second targeting moiety of the second imaging probe complex with first and second biomarkers of the cell to bring the first imaging probe and the second imaging probe in proximity to each other so that the enzyme substrate of the self-immolative enzyme activated contrast agent of the first imaging probe is cleaved by the β-galactosidase or fragments thereof of the second imaging probe to produce the detectable signal,

wherein at least one of the first and second linker regions comprising a biotin-streptavidin-biotin linkage, and

wherein the self-immolative enzyme-activated contrast agent remains linked to the first targeting moiety via the first linker region after activation by the enzyme or fragments thereof of the second imaging probe.