A compound of the formula: (i) formula: or a salt or solvate or stereoisomer thereof; wherein: D is a drug moiety; T is a targeting moiety; R 1 is hydrogen, unsubstituted or substituted C 1-3 alkyl, or unsubstituted or substituted heterocyclyl; L 1 is a bond, a second self-immolative linker, or a cyclization self-elimination linker; L 2 is a bond or a second self-immolative linker; wherein if L 1 is a second self-immolative linker or a cyclization self-elimination linker, then L 2 is a bond; wherein if L 2 is a second self-immolative linker, then L 1 is a bond; L 3 is a peptide linker; L 4 is a bond or a spacer; and A is an acyl unit; or (ii) formula (IIa): or a salt or solvate or stereoisomer thereof; wherein: p is 1 to 20; D is a drug moiety; T is a targeting moiety; R 1 is hydrogen, unsubstituted or substituted C 1-3 alkyl, or unsubstituted or substituted heterocyclyl; L 1 is a bond, a second self-immolative linker, or a cyclization self-elimination linker; L 2 is a bond or a second self-immolative linker; wherein if L 1 is a second self-immolative linker or a cyclization self-elimination linker, then L 2 is a bond; wherein if L 2 is a second self-immolative linker, then L 1 is a bond; L 3 is a peptide linker; L 4 is a bond or a spacer; and A is an acyl unit. (i) formula: or a salt or solvate or stereoisomer thereof; wherein: D is a drug moiety; T is a targeting moiety; R 1 is hydrogen, unsubstituted or substituted C 1-3 alkyl, or unsubstituted or substituted heterocyclyl; L 1 is a bond, a second self-immolative linker, or a cyclization self-elimination linker; L 2 is a bond or a second self-immolative linker; wherein if L 1 is a second self-immolative linker or a cyclization self-elimination linker, then L 2 is a bond; wherein if L 2 is a second self-immolative linker, then L 1 is a bond; L 3 is a peptide linker; L 4 is a bond or a spacer; and A is an acyl unit; or D is a drug moiety; T is a targeting moiety; R 1 is hydrogen, unsubstituted or substituted C 1-3 alkyl, or unsubstituted or substituted heterocyclyl; L 1 is a bond, a second self-immolative linker, or a cyclization self-elimination linker; L 2 is a bond or a second self-immolative linker; wherein if L 1 is a second self-immolative linker or a cyclization self-elimination linker, then L 2 is a bond; wherein if L 2 is a second self-immolative linker, then L 1 is a bond; L 3 is a peptide linker; L 4 is a bond or a spacer; and A is an acyl unit; or (ii) formula (IIa): or a salt or solvate or stereoisomer thereof; wherein: p is 1 to 20; D is a drug moiety; T is a targeting moiety; R 1 is hydrogen, unsubstituted or substituted C 1-3 alkyl, or unsubstituted or substituted heterocyclyl; L 1 is a bond, a second self-immolative linker, or a cyclization self-elimination linker; L 2 is a bond or a second self-immolative linker; wherein if L 1 is a second self-immolative linker or a cyclization self-elimination linker, then L 2 is a bond; wherein if L 2 is a second self-immolative linker, then L 1 is a bond; L 3 is a peptide linker; L 4 is a bond or a spacer; and A is an acyl unit. p is 1 to 20; D is a drug moiety; T is a targeting moiety; R 1 is hydrogen, unsubstituted or substituted C 1-3 alkyl, or unsubstituted or substituted heterocyclyl; L 1 is a bond, a second self-immolative linker, or a cyclization self-elimination linker; L 2 is a bond or a second self-immolative linker; wherein if L 1 is a second self-immolative linker or a cyclization self-elimination linker, then L 2 is a bond; wherein if L 2 is a second self-immolative linker, then L 1 is a bond; L 3 is a peptide linker; L 4 is a bond or a spacer; and A is an acyl unit.