Peptide-based multimeric targeted contrast agents

1. A contrast agent, or a pharmaceutically acceptable salt thereof, comprising a peptide, said peptide modified at its N- and its C-termini, independently, with a moiety comprising one or more metal chelate complexes, wherein said contrast agent has the formula:

wherein:

Chelate represents a metal chelate complex;

Linker represents a linker moiety;

Linker-subunit represents a linker-subunit moiety;

m is independently an integer from 1 to 10;

p is independently an integer from 0 to 5;

s is independently 0 or 1;

n is an integer from 3 to 50, inclusive;

R 1 is an amino acid side chain or a non-natural amino acid side chain; and

R 2 is independently a hydrogen or an aliphatic group.

2. The contrast agent of claim 1 , the contrast agent having a structure selected from the group consisting of:

wherein Gd is a paramagnetic metal ion Gd(III), and wherein the Gd(III) is coordinated to the DTPA moiety; and wherein the DTPA moiety is covalently linked to a moiety comprising a C(═O) group at an ethylene or acetate carbon on the DTPA moiety.

3. The contrast agent of claim 1 , the contrast agent having a structure selected from the group consisting of:

4. The contrast agent of claim 1 , the contrast agent having a structure selected from the group consisting of:

5. A pharmaceutically acceptable salt of a contrast agent of claims 1 - 4 , wherein said salt is a counter ion of organic or inorganic acids or bases, or mixtures thereof.

6. A pharmaceutically acceptable salt of a contrast agent of claims 1 - 4 , wherein said salt is a sodium salt.

7. A pharmaceutically acceptable salt of a contrast agent, said contrast agent having the structure:

8. The pharmaceutically acceptable salt of claim 7 , wherein said salt is a sodium salt.

9. A pharmaceutically acceptable salt of a contrast agent, said contrast agent having the structure:

10. The pharmaceutically acceptable salt of claim 9 , wherein said salt is a sodium salt.