Drug – bio-affecting and body treating compositions – Designated organic active ingredient containing – Carbohydrate doai
Reexamination Certificate
1999-11-09
2002-01-15
Nguyen, Dave T. (Department: 1633)
Drug, bio-affecting and body treating compositions
Designated organic active ingredient containing
Carbohydrate doai
C424S093200, C435S320100, C435S325000, C435S455000, C435S458000
Reexamination Certificate
active
06339070
ABSTRACT:
This application is a national stage application filed under 35 U.S.C. 371 of International Patent Appln. No. PCT/GB98/01294, filed May 5, 1998.
This invention relates particularly to gene directed enzyme prodrug therapy (GDEPT) using in situ antibody generation to provide enhanced selectivity, particularly for use in cancer therapy.
Known gene therapy based prodrug therapeutic approaches include virus-directed enzyme prodrug therapy (VDEPT) and gene-directed enzyme prodrug therapy (GDEPT), the latter term encompassing both VDEPT and non-viral delivery systems. VDEPT involves targeting tumour cells with a viral vector carrying a gene which codes for an enzyme capable of activating a prodrug. The viral vector enters the tumour cell and enzyme is expressed from the enzyme gene inside the cell. In GDEPT, alternative approaches such as microinjection, liposomal delivery and receptor mediated DNA uptake as well as viruses may be used to deliver the gene encoding the enzyme.
In both VDEPT and GDEPT the enzyme gene can be transcriptionally regulated by DNA sequences capable of being selectively activated in mammalian cells e.g. tumour cells (EP 415 731 (Wellcome); Huber et al, Proc. Natl. Acad. Sci. USA. 88, 8039-8043, 1991). While giving some degree of selectivity, gene expression may also occur in non-target cells and this is clearly undesirable when the approach is being used to activate prodrugs into potent cytotoxic agents. In addition these regulatory sequences will generally lead to reduced expression of the enzyme compared with using viral promoters and this will lead to a reduced ability to convert prodrug in the target tissue.
Expression and localisation of the prodrug activating enzyme inside the cell has disadvantages. Prodrug design is severely limited by the fact that the prodrug has to be able to cross the cell membrane and enter the cell but not be toxic until it is converted to the drug inside the cell by the activating enzyme. Most prodrugs utilise hydrophilic groups to prevent cell entry and thus reduce cytotoxicity. Prodrug turnover by activating enzyme produces a less hydrophilic drug which can enter cells to produce anti-cancer effects. This approach can not be used when the activating enzyme is expressed inside the cell. Another disadvantage is that target cells which lack intracellular activating enzyme will be difficult to attack because they are unable to generate active drug. To achieve this desirable “bystander activity” (or “neighbouring cell kill”), the active drug will have to be capable of diffusion out of the cell containing activating enzyme to reach target cells which lack enzyme expression. Many active drugs when produced inside a cell will be unable to escape from the cell to achieve this bystander effect.
Modifications of GDEPT have been put forward to overcome some of the problems described above. Firstly vectors have been described which are said to express the activating enzyme on the surface of the target cell (WO 96/03515) by attaching a signal peptide and transmembrane domain to the activating enzyme. The approach, if viable, would overcome the problems of having the activating enzyme located inside the cell but would still have to rely on transcriptionally regulated sequences capable of being selectively expressed in target cells to restrict cell expression. As described above there are disadvantages of using such sequences. Secondly vectors have been described which result in secretion of the enzyme from the target cell (WO 96/16179). In this approach the enzyme would be able to diffuse away from its site of generation since it is extracellular and not attached to the cell surface. Enzyme which has diffused away from the target site would be capable of activating prodrug at non-target sites leading to unwanted toxicity. To achieve some selectivity it is suggested that enzyme precursors could be used which are cleaved by pathology associated proteases to form active enzyme. Some selectivity is likely to be achieved by this approach but its unlikely that activation will only occur at target sites. In addition, once activated, the enzyme will still be free to diffuse away from the target site and thus suffer from the same drawback described above.
For GDEPT approaches, three levels of selectivity can be observed. Firstly, there is selectivity at the cell infection stage such that only specific cell types are targeted. For example cell selectivity can be provided by the gene delivery system per se. An example of this type of selectivity is set out in International Patent Application WO 95/26412 (UAB Research Foundation) which describes the use of modified adenovirus fiber proteins incorporating cell specific ligands. Other examples of cell specific targeting include ex vivo gene transfer to specific cell populations such as lymphocytes and direct injection of DNA into muscle tissue.
The second level of selectivity is control of gene expression after cell infection such as for example by the use of cell or tissue specific promoters. If the gene has been delivered to a cell type in a selective manner then it is important that a promoter is chosen that is compatible with activity in the cell type.
The third level of selectivity can be considered as the selectivity of the expressed gene construct. Selectivity at this level has received scant attention to date. In International patent application WO 96/16179 (Wellcome Foundation) it is suggested that enzyme precursors could be used which are cleaved by pathology associated proteases to form active enzyme. Some selectivity is likely to be achieved by this approach but it is unlikely that activation will only occur at target sites. In addition, once activated, the enzyme will still be free to diffuse away from the target site and thus suffer from the same drawback of activating prodrug at non-target sites leading to unwanted toxicity.
There exists a need for more selective GDEPT systems to reduce undesirable effects in normal tissues arising from erroneous prodrug activation.
The present invention is based on the discovery that antibody-heterologous enzyme gene constructs can be expressed intracellularly and used in GDEPT systems (or other systems such as AMIRACS—see below) for cell targeting arising from antibody specificity to deliver cell surface available enzyme in a selective manner. This approach may be used optionally in combination with any other suitable specificity enhancing technique(s) such as targeted cell infection and/or tissue specific expression.
According to one aspect of the present invention there is provided a gene construct encoding a cell targeting antibody and a heterologous enzyme for use as a medicament in a mammalian host wherein the gene construct is capable of expressing the antibody and enzyme as a conjugate within a target cell in the mammalian host and wherein the conjugate can leave the cell thereafter for selective localisation at a cell surface antigen recognised by the antibody.
According to another aspect of the present invention there is provided a gene construct encoding a cell targeting moiety and a heterologous prodrug activating enzyme for use as a medicament in a mammalian host wherein the gene construct is capable of expressing the cell targeting moiety and heterologous prodrug activating enzyme as a conjugate within a cell in the mammalian host and wherein the conjugate is directed to leave the cell thereafter for selective localisation at a cell surface antigen recognised by the cell targeting moiety.
The “cell targeting moiety” is defined as any polypeptide or fragment thereof which selectively binds to a particular cell type in a host through recognition of a cell surface antigen. Preferably the cell targeting moiety is an antibody. Cell targeting moieties other than antibodies include ligands as described for use in Ligand Directed Enzyme Prodrug Therapy as described in International patent application WO 97/26918, Cancer Research Campaign Technology Limited, such as for example epidermal growth factor, heregulin, c-erbB2 and vascular endothelial gro
Blakey David Charles
Emery Stephen Charles
Nguyen Dave T.
Zeneca Limited
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