FAP-activated therapeutic agents, and uses related thereto

A prodrug represented by Formula I:

• or a pharmaceutically acceptable salt thereof, wherein:
• R1 represents (C1-C10)alkyl, (C1-C10)alkoxy, (C1-C10)alkyl-C(O)—(C1-C10)alkyl, (C3-C8)cycloalkyl, (C3-C8)cycloalkyl(C1-C10)alkyl, aryl, aryl(C1-C10)alkyl, heteroaryl, or heteroaryl(C1-C10)alkyl, wherein any R1 is optionally substituted with one or more substituents independently selected from the group consisting of halo, hydroxy, carboxylate, cyano, amino, nitro, and thio (—SH);
• or
• represents an N-terminally blocked alpha amino acid residue, wherein X is O;
• R2 represents H or a (C1-C6)alkyl;
• R3 represents a (C1-C6)alkyl;
• R4 is absent or represents a (C1-C6)alkyl, —OH, —NH2, or halogen;
• X represents O or S;
• L represents a bond, or
• represents a self-immolative linker;
• and
• Cyt′ represents a radical of an anthracycline or derivative thereof.