Compositions and methods for specifically targeting tumors

Details Compositions and methods for specifically targeting tumors Compositions and methods for specifically targeting tumors

1996-08-30

2002-08-06

Eyler, Yvonne (Department: 1646)

Drug, bio-affecting and body treating compositions

Immunoglobulin, antiserum, antibody, or antibody fragment,...

Monoclonal antibody or fragment thereof

C424S085200, C435S007230, C530S350000, C514S002600

Reexamination Certificate

active

06428788

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to methods of specifically delivering an effector molecule to a tumor cell. In particular this invention relates to chimeric molecules that specifically bind to IL-13 receptors which, when combined with IL-4 receptor blockers, specifically deliver compounds or having a particular activity to tumors overexpressing IL-13 receptors.
BACKGROUND OF THE INVENTION
In a chimeric molecule, two or more molecules that exist separately in their native state are joined together to form a single entity (molecule) having the desired functionality of all of its constituent molecules. Frequently, one of the constituent molecules of a chimeric molecule is a “targeting molecule”. The targeting molecule is a molecule such as a ligand or an antibody that specifically binds to its corresponding target, for example a receptor on a cell surface. Thus, for example, where the targeting molecule is an antibody, the chimeric molecule will specifically bind (target) cells and tissues bearing the epitope to which the antibody is directed.
Another constituent of the chimeric molecule may be an “effector molecule”. The effector molecule refers to a molecule that is to be specifically transported to the target to which the chimeric molecule is specifically directed. The effector molecule typically has a characteristic activity that is desired to be delivered to the target cell. Effector molecules include cytotoxins, labels, radionuclides, other ligands, antibodies, drugs, prodrugs, liposomes, and the like.
In particular, where the effector component is a cytotoxin, the chimeric molecule may act as a potent cell-killing agent specifically targeting the cytotoxin to cells bearing a particular target molecule. For example, chimeric fusion proteins which include interleukin 4 (IL-4) or transforming growth factor (TGF&agr;) fused to Pseudomonas exotoxin (PE) or interleukin 2 (IL-2) fused to Diphtheria toxin (DT) have been shown to specifically target and kill cancer cells (Pastan et al.,
Ann. Rev. Biochem.,
61: 331-354 (1992)).
Generally, it is desirable to increase specificity and affinity and decrease cross-reactivity of chimeric cytotoxins with targets to be spared in order to increase their efficacy. To the extent a chimeric molecule preferentially selects and binds to its target (e.g. a tumor cell) and not to a non-target (e.g. a healthy cell), side effects of the chimeric molecule will be minimized. Unfortunately, many targets to which chimeric cytotoxins have been directed (e.g. the IL-2 receptor), while showing elevated expression on tumor cells, are also expressed to some extent, and often at significant levels, on healthy cells. Thus, chimeric cytotoxins directed to these targets frequently show adverse side-effects as they bind non-target (e.g., healthy) cells that also express the targeted receptor.
SUMMARY OF THE INVENTION
The present invention provides methods and compositions for specifically delivering an effector molecule to a tumor cell. In particular, the present invention provides methods and compositions for specifically targeting target tumor cells while offering reduced targeting of healthy cells than previously known methods and compositions.
The improved specific targeting of this invention is premised, in part, on two discoveries: The first discovery was that tumor cells, especially carcinomas such as renal cell carcinoma, Kaposi's sarcoma, and brain tumors such as gliomas and medulloblastomas overexpress IL-13 receptors at extremely high levels. The second discovery was that despite the fact that the IL-4 and IL-13 appear to share a common receptor on healthy cells, the receptors are “decoupled” in cancerous cells so that blocking of the IL-4 receptor confers protection of healthy cells without inhibiting the activity of IL-13 receptor directed molecules on cancerous cells. This permits IL-13 receptor-directed chimeric molecules (e.g., IL-13R-cytotoxins) to be administered at higher dosages with fewer adverse side-effects (e.g., IL-13R-cytotoxins administered with an IL-4R blocker will have a higher LD
50
). In addition, reduction and elimination of any binding between an IL-13R directed chimera and IL-4 receptors will leave greater concentrations of the chimera free in the circulation to bind to IL-13 receptors. These features (among others) coupled with the extremely high level of IL-13 receptor expression on target tumor cells permits the specific delivery of relatively high concentrations of IL-13R-directed chimerics to their IL-13R-bearing target cells.
Thus, in one embodiment, this invention provides a method of specifically delivering an effector molecule to a tumor cell bearing an IL-13 receptor (preferably an IL-13 receptor that is not shared with IL-4). The method involves the steps of: providing a chimeric molecule comprising an effector molecule attached to a targeting molecule that specifically binds to an IL-13 receptor; and contacting the tumor cell with the chimeric molecule in the presence of a blocker of an interleukin-4 receptor (IL-4R). The blocker is preferably present in a concentration sufficient to block binding of the targeting molecule to the IL-4 receptor. The chimeric molecule thus specifically binds to the tumor cell. In a preferred embodiment, particularly where the blocker is a molecule that also occurs endogenously (e.g., IL-4) the blocker is present in a concentration greater than that found in the environment in which the tumor cells and/or healthy (non-tumerous) cells normally occur. Preferred blockers include, but are not limited to an interleukin-4, an interleukin-4 antagonist, and an interleukin-4 receptor binding antibody (anti-IL-4R Ab). Interleukin-4 antogonists are selected whose antagonistic activity is mediated by binding to the IL-4 receptor not to IL-4 itself thus, they act as IL-4 competitors or competitive antagonists. Particularly preferred blockers specifically bind to the 140 kDa subunit of the IL-4 receptor. Preferred blockers include interleukin antagonists such as an interleukin-4 having a mutation in &agr;-Helix D with more preferred blockers including [Y124D]hIL4 and [R121D, Y124D]hIL4.
In preferred chimeric molecules, the targeting molecule is either a ligand, such as IL-13 or an anti-IL-13 receptor antibody. The targeting molecule may be chemically conjugated to the effector molecule, or where both targeting and effector molecules are polypeptides, the targeting molecule may be joined to the effector molecule through one or more peptide bonds thereby forming a fusion protein. Suitable effector molecules include a cytotoxin, a label, a radionuclide, a drug, a prodrug, a liposome, a ligand, and an antibody. In a particularly preferred embodiment, the effector is a cytotoxin, (e.g., Pseudomonas exotoxin, Diphtheria toxin, ricin, abrin, or a cytotoxic prodrug) with Pseudomonas exotoxin or Diptheria toxin (especially truncated forms in which the native binding domain is eliminated) being more preferred and Pseudomonas exotoxin (e.g., PE38QQR, PE4E, etc.) being most preferred. Where the Pseudomonas exotoxin is fused to an IL-13 targeting molecule, preferred fusion proteins include, but are not limited to IL-13-PE38QQR, IL-13-PE4E, cpIL-13-PE38QQR, and cpIL-13-PE4E.
As indicated above, the chimeric molecule is preferably contacted with the tumor cell in the presence of an IL-4 receptor (IL-4R) blocker. Preferred IL-13R-directed chimera/blocker combinations include, but are not limited to IL-13-PE38QQR or IL-13-PE4E and [Y124D]hIL4 or [R121D, Y124D]hIL4.
Preferred targets for the methods of this invention include cells, tissues, or organs that express, more preferably overexpress IL-13 receptors. Particularly preferred targets are tumor cells that overexpress IL-13 receptors. Such tumor cells include, but are not limited to renal cell carcinoma cells, brain tumor cells (e.g., glioma cells, medulloblastoma cells, etc.), and Kaposi's sarcoma cells.
In another embodiment, this invention provides a method of impairing growth of tumor cells beari

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