Methods for preparing antibody-drug conjugates
This invention describes a method of conjugating a cell binding agent such as an antibody with an effector group (e.g., a cytotoxic agent) or a reporter group (e.g., a radionuclide), whereby the reporter or effector group is first reacted with a bifunctional linker and the mixture is then used without purification for the conjugation reaction with the cell binding agent. The method described in this invention is advantageous for preparation of stably-linked conjugates of cell binding agents, such as antibodies with effector or reporter groups. This conjugation method provides in high yields conjugates of high purity and homogeneity that are without inter-chain cross-linking and inactivated linker residues.
1. A process for preparing a purified conjugate in a solution, wherein the conjugate comprises an effector or a reporter molecule comprising a thiol group linked to an antibody that binds to CD33, the process comprising the steps of:
(a) contacting an effector or a reporter molecule comprising a thiol group with a bifunctional linker reagent represented by one of the following formulas
to covalently attach the linker to the thiol group of the effector or the reporter molecule and thereby prepare an unpurified first mixture comprising the effector or the reporter molecule having linkers bound thereto,
(b) conjugating an antibody to the effector or the reporter molecule having linkers bound thereto by reacting the unpurified first mixture with the antibody in a solution having a pH from about 6.5 to about 8.5 to prepare a second mixture, and
(c) subjecting the second mixture to tangential flow filtration, dialysis, gel filtration, adsorptive chromatography, selective precipitation or a combination thereof to thereby prepare the purified conjugate.
2. The process of claim 1 , wherein step (b) is carried out in a solution at a pH of about 8.1.
3. The process of claim 1 , wherein the second mixture in step (b) is substantially free of undesired cross-linked, hydrolyzed species formed due to intra-molecular or inter-molecular reactions.
4. The process of claim 1 , wherein the effector molecule is a cytotoxic agent.
5. The process of claim 4 , wherein the cytotoxic agent is an alkylating agent.
6. The process of claim 4 , wherein the cytotoxic agent is a maytansinoid.
7. The process of claim 1 , wherein the antibody is a monoclonal antibody.
8. The process of claim 1 , wherein the antibody is a human or a humanized monoclonal antibody.
9. The process of claim 1 , wherein the antibody is MY9.
10. The process of claim 8 , wherein the human or the humanized antibody is huMy9-6.
11. The process of claim 4 , wherein an excess of cytotoxic agent relative to the bifunctional linker reagent is used.
12. The process of claim 4 , wherein the process further comprises the step of quenching the excess cytotoxic agent in the unpurified first mixture with a quenching reagent between steps (a) and (b).
13. The process of claim 12 , wherein the quenching reagent is selected from the group consisting of 4-maleimidobutyric acid, 3-maleimidopropionic acid, N-ethylmaleimide, iodoacetamide, and iodoacetamidopropionic acid.
14. The process of claim 1 , wherein the bifunctional linker reagent is represented by the following formula:
15. The process of claim 1 , wherein tangential flow filtration is utilized in step (c).