Dual conjugation process for preparing antibody-drug conjugates

1. An antibody-drug conjugate comprising an antibody and therapeutic moieties conjugated to cysteine residues in the antibody via a cleavable or non-cleavable linker, wherein said therapeutic moieties are conjugated to one or more engineered cysteines and to one or more reduced interchain cysteines of the antibody, wherein said antibody has an engineered cysteine at heavy chain position 41, or light chain position 40 or 41 according to the Kabat numbering system, or a combination thereof, wherein said antibody-drug conjugate has an average DAR of from 2.0 to 6.0; and wherein said antibody-drug conjugate was made by a process that comprises:

(a) selectively reducing the cysteine-engineered antibody with a compound according to formula (I), (II), (III), (IV), (V), (VI) or (VII)

or a salt thereof;

(b) further reducing the selectively reduced antibody of step (a) with an interchain disulfide bond reducing agent to form one or more reduced interchain cysteines; and

(c) conjugating the therapeutic moieties via cleavable or non-cleavable linkers to the one or more engineered cysteines and to at least one reduced interchain cysteine of the further reduced antibody of step (b) to form said antibody-drug conjugate.

2. An antibody-drug conjugate comprising an antibody and therapeutic moieties conjugated to cysteine residues in said antibody via a cleavable or non-cleavable linker, wherein the antibody comprises one engineered cysteine at heavy chain position 41, light chain position 40 or 41 according to the Kabat numbering system;

wherein therapeutic moieties are conjugated via the cleavable or non-cleavable linker to the engineered cysteine as well as to one or more reduced interchain cysteines of the antibody; and

wherein the antibody-drug conjugate has an average DAR of 2.0 to about 3.

3. The antibody-drug conjugate according to claim 2 , having an average DAR of 2.2 to about 3.

4. A pharmaceutical composition comprising an antibody-drug conjugate according to claim 2 and one or more pharmaceutically acceptable excipients.

5. The antibody-drug conjugate according to claim 2 , wherein the antibody is a monospecific or bispecific antibody or antibody fragment comprising at least one heavy chain and light chain variable region binding to a target selected from the group consisting of annexin A1, B7H4, CA6, CA9, CA15-3, CA19-9, CA27-29, CA125, CA242, CCR2, CCR5, CD2, CD19, CD20, CD22, CD30, CD33, CD37, CD38, CD40, CD44, CD47, CD56, CD70, CD74, CD79, CD115, CD123, CD138, CD203c, CD303, CD333, CEA, CEACAM, CLCA-1, CLL-1, c-MET, Cripto, DLL3, EGFL, EGFR, EPCAM, Eph, endothelin B receptor (ETBR), FAP, FcRL5 (CD307), FGFR, FOLR1, GCC, GPNMB, HER2, HMW-MAA, integrin α, IGF1R, TM4SF1, Lewis A like carbohydrate, Lewis X, Lewis Y, LIV1, mesothelin, MUC1, MUC16, NaPi2b, Nectin-4, PD-1, PD-L1, PSMA, PTK7, SLC44A4, STEAP-1, 5T4 antigen, TF (tissue factor), TF-Ag, Tag72, TNFR, TROP2, VEGFR and VLA.

6. The antibody-drug conjugate according to claim 5 , wherein said antibody binds to a target selected from PSMA or 5T4 antigen.

7. The antibody-drug conjugate according to claim 2 , wherein said engineered cysteine is at heavy chain position 41.

8. The antibody-drug conjugate according to claim 7 , wherein said therapeutic moiety is selected from the group consisting of a duocarmycin, a CBI dimer, a calicheamicin, a PBD, a PBD dimer, a maytansinoid, a tubulysin, a camptothecin, an amanitin, and an auristatin derivative.

9. The antibody-drug conjugate according to claim 8 , wherein said therapeutic moiety is a duocarmycin.

10. The antibody-drug conjugate according to claim 8 , wherein said linker and therapeutic moiety is vc-seco-DUBA.

11. The antibody-drug conjugate according to claim 10 , wherein said average DAR is 2.2 to 2.6.

12. The antibody-drug conjugate according to claim 11 , wherein said antibody binds to a target selected from PSMA or 5T4 antigen.

13. The antibody-drug conjugate according to claim 9 , wherein the interchain disulfide bond reducing agent is present in an amount of from 0.25 to 2 molar equivalents per molar equivalent of antibody.

14. The antibody-drug conjugate according to claim 13 , wherein said disulfide bond reducing agent is tris(3-sulfophenyl)phosphine, tris(2-carboxyethyl)phosphine or dithiothreitol.

15. The antibody-drug conjugate according to claim 14 , wherein said antibody has only one engineered cysteine.

16. The antibody-drug conjugate according to claim 15 , wherein said average DAR is 2.0 to about 3.

17. The antibody-drug conjugate according to claim 16 , wherein said engineered cysteine is at heavy chain position 41.

18. The antibody-drug conjugate according to claim 9 , wherein the engineered cysteine antibody is reacted with a compound according to formula (I), (II) or (III), or a salt thereof.