Enzymatic nucleic acid treatment of diseases of conditions...

Details Enzymatic nucleic acid treatment of diseases of conditions... Enzymatic nucleic acid treatment of diseases of conditions...

1999-09-22

2003-09-23

Lacourciere, Karen (Department: 1635)

Chemistry: molecular biology and microbiology

Animal cell, per se ; composition thereof; process of...

Method of regulating cell metabolism or physiology

C435S006120, C435S091100, C435S091300, C536S023100, C536S023200, C536S024300, C536S024310, C536S024330, C536S024500

Reexamination Certificate

active

06623962

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention concerns therapeutic compositions and methods for the treatment of cancer.
The present invention relates to therapeutic compositions and methods for the treatment or diagnosis of diseases or conditions related to EGFR expression levels, such as cancer. The following summary is not meant to be complete and is provided only for understanding of the invention that follows. This summary is not an admission that any of the work described below is prior art to the claimed invention.
The epidermal growth factor receptor (EGFR) is a 170 kDa transmembrane glycoprotein consisting of an extracellular ‘ligand’ binding domain, a transmembrane region and an intracellular domain with tyrosine kinase activity (Kung et al., 1994). The binding of growth factors to the EGFR results in down regulation of the ligand-receptor complex, autophosphorylation of the receptor and other protein substrates, leading ultimately to DNA synthesis and cell division. The external ligand binding domain is stimulated by EGF and also by TGF&agr;, amphiregulin and some viral growth factors (Modjtahedi & Dean, 1994).
The EGFR gene (c-erbB1), is located on chromosome 7, and is homologous to the avian erythroblastosis virus oncogene (v-erbB), which induces malignancies in chickens. The v-erbB gene codes for a truncated product that lacks the extracellular ligand binding domain. The tyrosine kinase domain of the EGFR has been found to have 97% homology to the v-erbB transforming protein (Downward et al., 1984).
EGFR is overexpressed in a number of malignant human tissues when compared to their normal tissue counterparts (for review see Khazaie et al., 1993). The gene for the receptor is both amplified and overexpressed in a number of cancer cells. Overexpression of the EGFR is often accompanied by the co-expression of the growth factors EGF and TGF&agr;, suggesting that an autocrine pathway for control of growth may play a major part in the progression of tumors (Spom & Roberts, 1985).
Growth factors and their receptors may play a role in the development of human brain tumors. A high incidence of overexpression, amplification, deletion and structural rearrangement of the gene coding for the EGFR has been found in biopsies of brain tumors (Ostrowski et al., 1994). In fact the amplification of the EGFR gene in glioblastoma multiforme tumors is one of the most consistent genetic alterations known, with the EGFR being overexpressed in approximately 40% of malignant gliomas (Black, 1991). It has also been demonstrated that in 50% of glioblastomas, amplification of the EGFR gene is accompanied by the co-expression of mRNA for at least one or both of the growth factors EGF and TNF&agr; (Ekstrand et al., 1991).
The amplified genes are frequently rearranged and associated with polymorphism leading to abnormal protein products (Wong et al., 1994). The rearrangements that have been characterized usually show deletions of part of the extracellular domain, resulting in the production of an EGFR protein that is smaller in size. Three classes of deletion mutant EGF receptor genes have been identified in glioblastoma tumors. Type I mutants lack the majority of the external domain, including the ligand binding site, type II mutants have a deletion in the domain adjacent to the membrane but can still bind ligands and type III, which is the most common and found in 17% of glioblastomas, have a deletion of 267 amino acids spanning domains I and II of the EGFR.
In addition to glioblastomas, abnormal EGFR expression has also been reported in a number of squamous epidermoid cancers and breast cancers (reviewed in Kung et al, 1994; Modjtahedi & Dean, 1994). Many patients with tumors that overexpress the EGFR have a poorer prognosis than those who do not (Khazaie et al., 1993). Consequently, therapeutic strategies which can potentially inhibit or reduce the aberrant expression of the EGFR receptor are of great interest as potential anti-cancer agents.
SUMMARY OF THE INVENTION
This invention relates to ribozymes, or enzymatic nucleic acid molecules, directed to cleave RNA species that are required for cellular growth responses. In particular, applicant describes the selection and function of ribozymes capable of cleaving RNA encoded by the receptor of epidernmal growth factor (EGFR). Such ribozymes may be used to inhibit the hyper-proliferation of tumor cells in one or more cancers.
In the present invention, ribozymes that cleave EGFR RNA are described. Those of ordinary skill in the art will understand that from the examples described that other ribozymes that cleave target RNAs required for cell proliferation may be readily designed and are within the invention. Such RNAs may have at least 90% homology to EGFR in humans with a normal EGFR gene.
By “inhibit” is meant that the activity of EGFR or level of RNAs encoded by EGFR is reduced below that observed in the absence of the nucleic acid, particularly, inhibition with ribozymes preferably is below that level observed in the presence of an inactive RNA molecule able to bind to the same site on the mRNA, but unable to cleave that RNA.
By “enzymatic nucleic acid molecule” it is meant a nucleic acid molecule which has complementarity in a substrate binding region to a specified gene target, and also has an enzymatic activity which is active to specifically cleave RNA in that target. That is, the enzymatic nucleic acid molecule is able to intermolecularly cleave RNA and thereby inactivate a target RNA molecule. This complementarity functions to allow sufficient, hybridization of the enzymatic nucleic acid molecule to the target RNA to allow the cleavage to occur. One hundred percent complementarity is preferred, but complementarity as low as 50-75% may also be useful in this invention.
The term enzymatic nucleic acid is used interchangeably with phrases such as ribozymes, catalytic RNA, enzymatic RNA, catalytic DNA, nucleozyme, DNAzyme, RNA enzyme, endoribonuclease, minizyme, leadzyme, oligozyme or DNA enzyme, as used in the art. All of these terminologies describe nucleic acid molecules with enzymatic activity.
By “equivalent” RNA to EGFR is meant to include those naturally occurring RNA molecules associated with cancer in various animals, including human.
By “complementarity” is meant a nucleic acid that can form hydrogen bond(s) with another RNA sequence by either traditional Watson-Crick or other non-traditional types (for example, Hoogsteen type) of base-paired interactions.
Seven basic varieties of naturally-occurring enzymatic RNAs are known presently. Each can catalyze the hydrolysis of RNA phosphodiester bonds in trans (and thus can cleave other RNA molecules) under physiological conditions. Table I summarizes some of the characteristics of these ribozymes. In general, enzymatic nucleic acids act by first binding to a target RNA. Such binding occurs through the target binding portion of an enzymatic nucleic acid which is held in close proximity to an enzymatic portion of the molecule that acts to cleave the target RNA. Thus, the enzymatic nucleic acid first recognizes and then binds a target RNA through complementary base-pairing, and once bound to the correct site, acts enzymatically to cut the target RNA. Strategic cleavage of such a target RNA will destroy its ability to direct synthesis of an encoded protein. After an enzymatic nucleic acid has bound and cleaved its RNA target, it is released from that RNA to search for another target and can repeatedly bind and cleave new targets.
The enzymatic nature of a ribozyme is advantageous over other technologies, since the concentration of ribozyme necessary to affect a therapeutic treatment is lower. This advantage reflects the ability of the ribozyme to act enzymatically. Thus, a single ribozyme molecule is able to cleave many molecules of target RNA. In addition, the ribozyme is a highly specific inhibitor, with the specificity of inhibition depending not only on the base-pairing mechanism of binding to the target RNA, but also on the mechanism of target RNA cleavage. Single mismatches, o

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