Pyrrolobenzodiazepines and targeted conjugates

1. A conjugate of formula I:

L-(LU-D) p ,  (I)

or a pharmaceutically acceptable salt thereof, wherein

L is a Ligand Unit selected from the group consisting of an antibody, an antigen-binding fragment of an antibody and an Fc fusion protein;

LU is a Linker Unit of formula 1a:

-A 1 -L 1 -  (1a)

wherein:

L 1 is an amino acid sequence comprising a dipeptide of formula —NH—X 1 —X 2 —CO—, wherein —NH— is the amino group of X 1 , and CO is the carbonyl group of X 2 , and wherein the peptide is cleavable by the action of an enzyme to release D as a free drug, wherein the enzyme is a cathepsin;

A 1 is a Stretcher Unit, wherein A 1 comprises the functionality —CO— connected directly to the amino group of X 1 , thereby forming an amide link with —X 1 —, and wherein A 1 is further comprised of the structure of:

wherein

S is a sulfur atom derived from the Ligand Unit;

the wavy line indicates the point of attachment to the Ligand Unit; and the asterisk indicates the point of attachment to the remaining portion of A 1 ;

subscript p is from 1 to 20; and

D is a Drug Unit, wherein the Drug Unit is a PBD dimer having the structure selected from the group consisting of D1-D6:

wherein the asterisk indicates the point of attachment to LU; and

either:

(a) R 10 is H, and R 11 is OH or OR A , wherein R A is C 1-4 alkyl, or

(b) R 10 and R 11 form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound, or

(c) R 10 is H and R 11 is SO z M, wherein subscript z is 2 or 3 and M is a pharmaceutically acceptable cation;

and

R 10′ and R 11′ are the same as R 10 and R 11 , wherein if R 11 and R 11′ are each SO z M, then each M is an independently selected pharmaceutically acceptable monovalent cation or both M together is a pharmaceutically acceptable divalent cation.

2. The conjugate of claim 1 , wherein R 10 and R 11 form a nitrogen-carbon double bond.

3. The conjugate of claim 2 , wherein R 10′ and R 11′ form a nitrogen-carbon double bond.

4. The conjugate of claim 1 , wherein the dipeptide of formula —NH—X 1 —X 2 —CO— is selected from the group consisting of -Phe-Lys-, -Val-Ala-, -Val-Lys-, -Ala-Lys-, -Val-Cit-, -Phe-Cit-, -Leu-Cit-, -Ile-Cit-, -Phe-Arg-, and -Trp-Cit-, wherein Cit is citrulline.

5. The conjugate of claim 1 , wherein the Ligand Unit is an antibody or antigen binding fragment thereof and wherein the sulfur atom bonding the antibody Ligand Unit to A 1 of LU is from a reactive thiol group of a cysteine residue of the antibody or antigen binding fragment thereof.

6. The conjugate of claim 5 , wherein the cysteine residue is an introduced cysteine residue in the heavy chain or light chain of the antibody or antigen binding fragment thereof.

7. The conjugate of claim 6 , wherein the introduced cysteine is at amino acid heavy chain position 239 of the antibody, according to the EU numbering system.

8. The conjugate of claim 5 , wherein the antibody is a humanized 1F6 antibody.

9. The conjugate of claim 7 , wherein the antibody is a humanized 1F6 antibody.

10. A drug linker compound of formula V:

LU-D  (V)

or a salt thereof, wherein

LU is a Linker Unit having the formula of G 1 -L 1 , wherein

L 1 is an amino acid sequence comprising a dipeptide of formula —NH—X 1 —X 2 —CO—, wherein —NH— is the amino group of X 1 , and CO is the carbonyl group of X 2 , and wherein the peptide is cleavable by the action of an enzyme to release D as a fee drug, wherein the enzyme is a cathepsin;

G 1 is a Stretcher Unit for connection to a Ligand Unit, wherein G 1 is comprised of a maleimide group for reaction with a reactive thiol functional group provided by the Ligand Unit for said connection, and wherein G 1 further comprises the functionality —CO— connected directly to the amino group of X 1 , thereby forming an amide link with —X 1 —;

D is a Drug Unit, wherein the Drug Unit is a PBD dimer having the structure selected from the group consisting of D1-D6:

and salts thereof, wherein

the asterisk indicates the point of attachment to LU; and either:

(a) R 10 is H, and R 11 is OH or OR A , wherein R A is C 1-4 alkyl, or

(b) R 10 and R 11 form a nitrogen-carbon double bond between the nitrogen and carbon atoms to which they are bound, or

(c) R 10 is H and R 11 is SO z M, wherein subscript z is 2 or 3 and M is a cation; and

R 10′ and R 11′ are the same as R 10 and R 11 , wherein if R 11 and R 11′ are each SO z M, then each M is an independently selected monovalent cation or both M together is a divalent cation.

11. The drug linker compound of claim 10 , wherein the dipeptide of formula —NH—X 1 —X 2 —CO— is selected from the group consisting of -Phe-Lys-, -Val-Ala-, -Val-Lys-, -Ala-Lys-, -Val-Cit-, -Phe-Cit-, -Leu-Cit-, -Ile-Cit-, -Phe-Arg-, and -Trp-Cit-, wherein Cit is citrulline.

12. The drug linker compound of claim 10 , wherein R 10 and R 11 form a nitrogen-carbon double bond.

13. The drug linker compound of claim 12 , wherein R 10′ and R 11′ form a nitrogen-carbon double bond.

14. The drug linker compound of claim 13 , wherein L 1 is a dipeptide selected from the group consisting of valine-alanine, valine-citrulline and phenylalanine-lysine.

15. A method of preparing an antibody drug conjugate of claim 1 in which L is an antibody Ligand Unit,

the method comprising the step of contacting an antibody having a reactive cysteine thiol functional group with a Drug Linker compound of claim 10 so that the sulfur atom of the reactive thiol functional group reacts with the maleimide group of G 1 of the Drug Linker compound to form the Stretcher Unit (A 1 ) of the antibody drug conjugate,

wherein the reactive thiol functional group is obtained by disulfide reduction of the antibody or by introduction of a cysteine residue in the heavy chain of the antibody.