Amatoxin-conjugates with improved linkers

1. A conjugate comprising a target-binding moiety linked via a linker L to an amatoxin, wherein the linker L is connected to the amatoxin via

(i) the γ C-atom of amatoxin amino acid 1, particularly via an amide linkage;

(ii) an oxygen atom bound to the δ C-atom of amatoxin amino acid 3, particularly via an ester linkage, an ether linkage or a urethane linkage; or

(iii) the 6′ C-atom of amatoxin amino acid 4, particularly via an oxygen atom bound to the 6′ C-atom of amatoxin amino acid 4; in each case wherein the linker L is connected to the target-binding moiety via a urea moiety.

2. The conjugate of claim 1 , wherein the conjugate has a structure selected from one of the following structures:

(i) amatoxin-γC(O)—NH-L-NH—C(O)—NH-target-binding moiety;

(ii) amatoxin-δC-O—C(O)-L-NH—C(O)—NH-target-binding moiety;

(iii) amatoxin-δC-O-L-NH—C(O)—NH-target-binding moiety;

(iv) amatoxin-δC-O—C(O)—NH-L-NH—C(O)—NH-target-binding moiety; and

(v) amatoxin-6′C—O-L-NH—C(O)—NH-target-binding moiety.

3. The conjugate of claim 1 , wherein the target-binding moiety is connected to the linker L via an amino group present in the target-binding moiety, wherein said amino group forms part of said urea moiety.

4. The conjugate of claim 1 , wherein the amatoxin is selected from α-amanitin, β-amanitin, γ-amanitin, ε-amanitin, amanin, amaninamide, amanullin, or amanullinic acid, or from salts or analogues thereof.

5. The conjugate of claim 1 , wherein the linker L is an alkylene, heteroalkylene, alkenylene, heteroalkenylene, alkynylene, heteroalkynylene, cycloalkylene, heterocycloalkylene, arylene, heteroarylene, aralkylene, or a heteroaralkylene group, optionally substituted.

6. The conjugate of claim 1 , wherein the linker L comprises a moiety selected from one of the following moieties: a disulfide, an ether, an amine, an ester, a carboxamide, a urethane, and a urea moiety.

7. The conjugate of claim 1 , wherein the target-binding moiety specifically binds to an epitope that is present on a tumour cell, particularly wherein the target-binding moiety specifically binds to an epitope of epithelial cell adhesion molecule (EpCAM).

8. The conjugate of claim 1 , wherein the target-binding moiety is selected from the group consisting of:

(i) antibody or antigen-binding fragment thereof;

(ii) antibody-like protein; and

(iii) nucleic acid aptamer.

9. The conjugate of claim 8 , wherein the antibody or the antigen-binding fragment thereof is selected from a diabody, a tetrabody, a nanobody, a chimeric antibody, a deimmunized antibody, a humanized antibody or a human antibody.

10. The conjugate of claim 8 , wherein the antigen binding fragment is selected from the group consisting of Fab, F(ab′) 2 , Fd, Fv, single-chain Fv, and disulfide-linked Fvs (dsFv).

11. The conjugate of claim 1 for use as a medicament.

12. The conjugate of claim 1 for the treatment of cancer in a patient, wherein the cancer is selected from the group consisting of pancreatic cancer, cholangiocarcinoma, breast cancer, colorectal cancer, lung cancer, prostate cancer, ovarian cancer, stomach cancer, kidney cancer, malignant melanoma, leukemia, and malignant lymphoma.

13. Pharmaceutical composition comprising the conjugate according to claim 1 and further comprising one or more pharmaceutically acceptable diluents, carriers, excipients, fillers, binders, lubricants, glidants, disintegrants, adsorbents; and/or preservatives.

14. An amatoxin-conjugation molecule comprising a linker L connected to an amatoxin via

(i) the γ C-atom of amatoxin amino acid 1, particularly via an amide linkage;

(ii) an oxygen atom bound to the δ C-atom of amatoxin amino acid 3, particularly via an ester linkage, an ether linkage or a urethane linkage; or

(iii) the 6′ C-atom of amatoxin amino acid 4, particularly via an oxygen atom bound to the 6′ C-atom of amatoxin amino acid 4;

in each case wherein the linker L comprises a carbamic acid derivative —NH—C(O)—X, wherein X is a leaving group that can be replaced by a primary amine of a target-binding moiety.

15. The amatoxin-conjugation molecule claim 14 , wherein X is selected from: t butyloxy, -succinimidyloxy, -1-O-succinimidyloxy-3-sulfonate (-Sulfo-NHS), —O-(4-nitrophenyloxy), —O-(3-nitrophenyloxy), —O-(2,4-dinitrophenyloxy), —O-(2,4-dichloro-6-nitrophenyloxy), -pentafluorophenyloxy, -pentachlorophenyloxy, —O-(2,4,5-trichlorophenyloxy), —O-(3,4-dihydro-3-hydroxy-4-oxo-1,2,3-benzotriazine-3-yl), —O-(endo-1-hydroxy-5-norbornene-2,3-dicarboximide-1-yl), -1-phthalimidoyloxy, -1-benzotriazolyloxy, -1-(7-aza-benzotriazolyl)oxy, and —N-imidazolyl.

16. A method for synthesizing a conjugate of any one of claims 1 to 12 , comprising the step of reacting an amatoxin-conjugation molecule of claim 14 or 15 with a target-binding moiety comprising a primary amino group.