Contrast agents for detection of enzyme activities based on melanin synthesis

A method, comprising:

• administering, to a patient suffering from a tumor, a composition comprising a compound comprising a melanin precursor that spontaneously synthesizes a melanin when in free form in vivo, and a peptide directly covalently bonded to or indirectly linked to the melanin precursor, wherein the direct covalent bond or the indirect link of the peptide to the melanin precursor blocks spontaneous synthesis of the melanin in vivo in the absence of protease activity;
• and
• surgically resecting the tumor, wherein the surgical resection is guided at least in part by contrast imparted by the melanin, wherein the melanin is spontaneously synthesized in the tumor after administering the composition.

A method, comprising:

• administering, to a patient suffering from a tumor, a composition comprising a compound comprising a melanin precursor that spontaneously synthesizes a melanin when in free form in vivo, and a peptide directly covalently bonded to or indirectly linked to the melanin precursor, wherein the direct covalent bond or the indirect link of the peptide to the melanin precursor blocks spontaneous synthesis of the melanin in vivo in the absence of protease activity;
• and
• thermally ablating the tumor, wherein the thermal ablating targets cells containing the melanin, wherein the melanin is spontaneously synthesized in the tumor after administering the composition.