The superoxide anion (O2−) is a potentially harmful cellular by-product produced primarily by errors of oxidative phosphorylation in mitochondria (Cleveland and Liu, Nat. Med., 2000, 6, 1320–1321). Some of the targets for oxidation by superoxide in biological systems include the iron-sulfur dehydratases, aconitase and fumarases. Release of Fe(II) from these superoxide-inactivated enzymes results in Fenton-type production of hydroxyl radicals which are capable of attacking virtually any cellular target, most notably DNA (Fridovich, Annu. Rev. Biochem., 1995, 64, 97–112).
The enzymes known as the superoxide dismutases (SODs) provide defense against oxidative damage of biomolecules by catalyzing the dismutation of superoxide to hydrogen peroxide (H2O2) (Fridovich, Annu. Rev. Biochem., 1995, 64, 97–112). Two major classes of superoxide dismutases exist. One consists of a group of enzymes with active sites containing copper and zinc while the other class has either manganese or iron at the active site (Fridovich, Annu. Rev. Biochem., 1995, 64, 97–112).
The soluble superoxide dismutase 1 enzyme (also known as SOD1 and Cu/Zn superoxide dismutase) contains a zinc- and copper-type active site (Fridovich, Annu. Rev. Biochem., 1995, 64, 97–112). Lee et al. reported the molecular cloning and high-level expression of human cytoplasmic superoxide dismutase gene in E. coli in 1990 (Lee et al., Misaengmul Hakhoechi, 1990, 28, 91–97).
Mutations in the superoxide dismutase 1 gene are associated with a dominantly-inherited form of amyotrophic lateral sclerosis (ALS, also known as Lou Gehrig's disease) a disorder characterized by a selective degeneration of upper and lower motor neurons (Cleveland and Liu, Nat. Med., 2000, 6, 1320–1321). The deleterious effects of various mutations on superoxide dismutase 1 are most likely mediated through a gain of toxic function rather than a loss of superoxide dismutase 1 activity, as the complete absence of superoxide dismutase 1 in mice neither diminishes life nor provokes overt disease (Al-Chalabi and Leigh, Curr. Opin. Neurol., 2000, 13, 397–405; Alisky and Davidson, Hum. Gene Ther., 2000, 11, 2315–2329). According to Cleveland and Liu, there are two models for mutant superoxide dismutase 1 toxicity (Cleveland and Liu, Nat. Med., 2000, 6, 1320–1321). The “oxidative hypothesis” ascribes toxicity to binding of aberrant substrates such as peroxynitrite or hydrogen peroxide which gain access to the catalytic copper ion through mutation-dependent loosening of the native superoxide dismutase 1 protein conformation (Cleveland and Liu, Nat. Med., 2000, 6, 1320–1321). A second possible mechanism for mutant superoxide dismutase 1 toxicity involves the misfolding and aggregation of mutant superoxide dismutase 1 proteins (Cleveland and Liu, Nat. Med., 2000, 6, 1320–1321). The idea that aggregates contribute to ALS has received major support from the observation that murine models of superoxide dismutase 1 mutant-mediated disease feature prominent intracellular inclusions in motor neurons and, in some cases, in the astrocytes surrounding them as well (Bruijn et al., Science, 1998, 281, 1851–1854). Furthermore, Brujin et al. also demonstrate that neither elimination nor elevation of wild-type superoxide dismutase 1 was found to affect disease induced by mutant superoxide dismutase 1 in mice (Bruijn et al., Science, 1998, 281, 1851–1854).
The superoxide dismutase 1 gene is localized to chromosome 21q22.1 and has been found to be overexpressed in the brains of patients with Down syndrome, possibly as a reflection of the trisomic state of chromosome 21 (Gulesserian et al., J. Investig. Med., 2001, 49, 41–46).
Studies of transgenic mice carrying a mutant human superoxide dismutase 1 gene have been used to evaluate potential therapies for ALS and one such study has indicated that creatine produced a dose-dependent improvement in motor performance and extended survival in mice containing the glycine 93 to alanine mutation (Klivenyi et al., Nat. Med., 1999, 5, 347–350). Although creatine is currently suggested as a dietary supplement for patients with ALS, the protective effect of creatine in humans has yet to be confirmed (Rowland, J. Neurol. Sci., 2000, 180, 2–6).
Additional transgenic mice studies have led to the finding that oxidative reactions triggered by superoxide dismutase 1 mutants result in inactivation of the glial glutamate transporter (Human GLUT1) which in turn, causes neuronal degeneration (Trotti et al., Nat. Neurosci., 1999, 2, 427–433).
Inhibition of superoxide dismutase 1 through copper chelation or zinc supplementation extends the life of mice that overexpress a mutant form superoxide dismutase by 1 to 2 months (Hottinger et al., Eur. J. Neurosci., 1997, 9, 1548–1551). As reviewed by Alisky and Davidson, a number of pharmacological agents have been used to inhibit the toxicity of superoxide dismutase 1 mutants in the transgenic mouse model for human ALS, including: vitamin E, riluzole, gabapentin, caspase inhibitors, nitric oxide synthase inhibitors, glutamate receptor inhibitors and glutathione (Alisky and Davidson, Hum. Gene Ther., 2000, 11, 2315–2329). In addition, investigational gene therapy for ALS has included overexpression of a number of genes which provide protection from superoxide dismutase 1 mutant toxicity (Alisky and Davidson, Hum. Gene Ther., 2000, 11, 2315–2329).
Two abnormal superoxide dismutase 1 mRNAs, exon 2-skipping and exon 2 and 3-skipping species, were identified from occipital brain tissue of ALS patients carrying no mutations in the superoxide dismutase 1 gene (Kawata et al., NeuroReport, 2000, 11, 2649–2653).
Disclosed and claimed in PCT publication WO 94/19493 are oligonucleotide sequences encoding SOD1 and generally claimed is the use of an antisense DNA homolog of a gene encoding SOD1 in either mutant and wild-type forms in the preparation of a medicament for treating a patient with a disease (Brown et al., 1994).
The expression of superoxide dismutase 1 in PC12 rat pheochromocytoma neuronal cells was inhibited by either of two 1-mer antisense oligonucleotides targeting rat superoxide dismutase 1 nucleotides 54–74 and 497–517, leading to cellular apoptosis. The progression of cellular death was reversed by treatment with antioxidants (Troy and Shelanski, Proc. Natl. Acad. Sci. U.S.A., 1994, 91, 6384–6387).
The method of delivery of the previously described oligonucleotides to the rat PC12 cells (Troy and Shelanski, Proc. Natl. Acad. Sci. U.S.A., 1994, 91, 6384–6387) was subsequently improved by linking the oligonucleotides to a vector peptide via a disulfide bond (Troy et al., J. Neurosci., 1996, 16, 253–261).
Induction of apoptosis was also seen in studies using a 30-mer phosphorothioate oligonucleotide targeting the start codon of superoxide dismutase 1 in rat spinal cord cultures in vitro (Rothstein et al., Proc. Natl. Acad. Sci. U.S.A., 1994, 91, 4155–4159).
Mutations of the superoxide dismutase 1 gene have been unambiguously implicated in ALS. However, investigational therapies involving inhibition of these mutants have yet to be tested as therapeutic protocols. Furthermore, evidence suggests that inhibition of the wild-type superoxide dismutase gene is not deleterious to organisms (Bruijn et al., Science, 1998, 281, 1851–1854). Consequently there remains a long felt need for agents capable of effectively and selectively inhibiting superoxide dismutase 1 function.
Antisense technology is emerging as an effective means for reducing the expression of specific gene products and may therefore prove to be uniquely useful in a number of therapeutic, diagnostic, and research applications for the modulation of superoxide dismutase 1 expression.
The present invention provides compositions and methods for modulating human superoxide dismutase 1 expression, including modulation of alternatively spliced forms of superoxide dismutase 1.