Peptide vectors

A compound according to formula (I):

• X—B1—B2—B3—B4-Z (I)
• wherein:
• X is a cytotoxic or cytostatic agent;
• each of B1, B2, B3, and B4 is, independently for each occurrence, (Doc)m, (Aepa)n, —(C(O)-A1-A2-A3-A4-A5-C(O))s— or (amino acid)p, provided that at least one of B1, B2, B3, and B4 is —(C(O)-A1-A2-A3-A4-A5-C(O))s—, and that at least one of B1, B2, B3, and B4 is (Doc)m or (Aepa)n wherein at least one of m and n is not 0;
• each of A1 and A5 is, independently for each occurrence, CR1R2;
• each of R1 and R2 is, independently for each occurrence, H, F, Br, Cl, I, C(1-30)alkyl, C(2-30)alkenyl, substituted C(1-30)alkyl, substituted C(2-30)alkenyl, SR3, S(O)R4, or S(O)2R5, or R1 and R2 together can form a C(3-30)cycloalkyl, C(3-30)heterocycle, or C(5-30)aryl ring;
• each of R3, R4, and R5 is, independently for each occurrence, C(1-30)alkyl, C(2-30)alkenyl, substituted C(1-30)alkyl, or substituted C(2-30)alkenyl;
• each of A2, A3 and A4 is, independently for each occurrence, CR6R7, O, S, (CH2)t or absent;
• each of R6 and R7 is, independently for each occurrence, H, F, Br, Cl, I, C(1-30)alkyl, C(2-30)alkenyl, substituted C(1-30)alkyl, substituted C(2-30)alkenyl, SR3, S(O)R4, or S(O)2R5;
• or R6 and R7 together may form a ring system;
• m is, independently for each occurrence, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10;
• n is, independently for each occurrence, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10;
• p is, independently for each occurrence, 0, 1, or 2;
• s is, independently for each occurrence, 1, 2, 3, 4, or 5;
• t is, independently for each occurrence, 0, 1, 2, or 3;
• and
• Z is selected from the group consisting of somatostatin, a somatostatin analog, luteinizing hormone-releasing hormone (LHRH), an LHRH analog, bombesin, and a bombesin analog;
• provided that:
• when X is doxorubicin or a doxorubicin derivative, at least one of m and n is not 0;
• and
• when X is paclitaxel or a paclitaxel derivative, then B1 is (amino acid)p and
• p is 1 or 2;
• or a pharmaceutically acceptable salt thereof.