Chemical compounds

Details Chemical compounds Chemical compounds

1997-06-23

1999-11-16

Huff, Sheela

Drug, bio-affecting and body treating compositions

Conjugate or complex of monoclonal or polyclonal antibody,...

4241821, 424 117, 424 11, 514 12, 5303911, 5303917, 536 231, 536 234, 562 11, 4353201, A61K 39395

Patent

active

059852810

DESCRIPTION:

BRIEF SUMMARY
CROSS-REFERENCES TO RELATED APPLICATIONS



BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to antibody directed enzyme prodrug therapy (ADEPT) using a non-naturally occuring mutant form of a host enzyme, especially a mutant form of ribonuclease.
2. Description of the Related Art
Targeting of drugs selectively to kill cancer cells in a patient has long been a problem for medical research. ADEPT is one approach to overcome the problem. ADEPT uses a tumour selective antibody conjugated to an enzyme. The conjugate is administered to the patient (usually intravenously), allowed to localise at the tumour site(s) and clear from the general circulation. Subsequently a prodrug is administered to the patient which is converted by the enzyme (localised at the tumour sites) into a cytotoxic drug which kills tumour cells. Since one molecule of enzyme can catalyse generation of many cytotoxic drug molecules an amplification effect is produced. Furthermore tumour cells not displaying the antigen recognised by the antibody (tumours usually display microheterogeneity) are also killed by enzymically amplified generation of the cytotoxic drug. A known system uses the procaryotic enzyme carboxypeptidase G2 (CPG2) as the enzyme component (see WO 88/07378). A drawback of systems using procaryotic enzymes is that the normal gut flora may contain procaryotic organisms capable of triggering non-selective cytotoxic drug generation.
A further problem with known systems is that repeated administration of the conjugate results in a host immune response rendering the therapy less effective. The antibody component is generally a mouse monoclonal which can be humanised using known techniques to reduce immunogenicity. However reduction of the immunogenicity of the enzyme component has proved more problematic. This is because the enzyme component must not be present naturally in the human host circulation otherwise premature conversion of prodrug to cytotoxic drug will occur and no selective toxicity to tumours will be observed. Akzo in WO90/02939 have proposed use of human enzymes for ADEPT with selectivity being maintained by choice of a human enzyme not normally present in the circulation such as lysozyme. Akzo have chosen human lysozyme as their enzyme and because of the nature of the substrate requirements [being an endoglycosidase it requires .beta..sub.1-4 linked polymers of N-acetylglucosamine (NAG-chitin) for cleavage] they are forced into producing prodrugs containing such functionalities. To prevent cell entry they further elaborate the oligomer with taurine residues--relying on the sulphonic acids to prevent cell entry and hence cytotoxicity--20 fold less--FIG. 13 in WO90/02939.
Use of a mammalian enzyme such as alkaline phosphatase (Senter et al: U.S. Pat. No. 4,975,278) or a human enzyme such as beta-glucuronidase (Behringwerke DE 42336237) or lysozyme (Akzo; WO 90/07929) for ADEPT has the advantage that such enzymes should have reduced, or lack, immunogenicity compared with non-mammalian enzymes. A disadvantage of using a mammalian or human enzyme is that it is present endogenously in patients and there will thus be the potential for turnover for prodrug to drug which is not due to the administered antibody-enzyme conjugate. This is likely to lead to enhanced toxicity with this type of ADEPT approach. Prodrugs for alkaline phosphatase are rapidly converted to drugs both in mice (Doyle, T. W. and Vyas, D. M., Cancer Treatment Reviews 17, 127-131, 1990) and in man (Hande et al. Clinical Pharmacology and Therapeutics 53, 233, 1993) in the absence of any administered conjugate due to the widespread distribution of endogenous alkaline phosphatase, thus confirming this is a critical problem for this enzyme. Human data on prodrugs for beta-glucuronidase or lysozyme are not available. Glucuronidase and lysozyme are present in the plasma and in other tissue sites. Akzo report lysozyme is present in milk, tears, saliva, spleen, leukocytes and monocytes. Behringwerke in DE423637 report activated marcophag

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