Ribozymes in treatment of inherited retinal disease

Reduction in severity of a herpes simplex virus type 1 murine infection by treatment with a ribozyme targeting the UL20 gene RNA

Hammerhead ribozymes were designed to target mRNA of several essential herpes simplex virus type 1 (HSV-1) genes. A ribozyme specific for the late gene U(L)20 was packaged in an adenovirus vector (Ad-U(L)20 Rz) and evaluated for its capacity to inhibit the viral replication of several HSV-1 strains, including that of the wild-type HSV-1 (17syn+ and KOS) and several acycloguanosine-resistant strains (PAAr5, tkLTRZ1, and ACGr4) in tissue culture. The Ad-U(L)20 Rz was also tested for its ability to block an HSV-1 infection, using the mouse footpad model. Mouse footpads were treated with either the Ad-U(L)20 Rz or an adenoviral vector expressing green fluorescent protein (Ad-GFP) and then infected immediately thereafter with 10(4) PFU of HSV-1 strain 17syn+. Ad-U(L)20 ribozyme treatment consistently led to a 90% rate of protection for mice from lethal HSV-1 infection, while the survival rate in the control groups was less than 45%. Consistent with this protective effect, treatment with the Ad-U(L)20 Rz reduced the viral DNA load in the feet, the dorsal root ganglia, and the spinal cord relative to that of the Ad-GFP-treated animals. This study suggests that ribozymes targeting essential genes of the late kinetic class may represent a new therapeutic strategy for inhibiting HSV infection.

Potential clinical application of antioncogene ribozymes for human lung cancer

Non-small-cell lung cancer frequently contains oncogenetic defects (mutations in ras, retinoblastoma, and p53 genes) that contribute to disease pathophysiology. Recent studies and clinical trials have focused on gene therapy approaches that either replace the function of defective tumor-suppressor genes such as p53 or inactivate mutant oncogenes such as ras. Ribozymes are RNA molecules with highly specific intrinsic enzymatic activity against target RNA sequences, which can discriminate mutant sequences that differ by a single base from their wild-type counterparts. Following binding to the RNA substrate by base-pair complementation, the ribozyme cleaves the target RNA irreversibly, then releases itself for new rounds of subsequent cleavage, resulting in significantly improved target:effector stoichiometry as compared with antisense oligonucleotides of the same specificity. Transcript-specific ribozymes have been used extensively for experimental oncogene inactivation. Ribozymes are effective for targeting mutant ras, p53, or the multidrug-resistant gene product for lung cancer cells in vitro. However, their in vivo effect is not well defined against this malignancy. We recently characterized the antitumor properties of an anti-K-ras ribozyme specific for the K-ras codon 12 mutation (GGT-->GTT). When delivered as a transgene by an adenoviral vector (ADV), the K-ras ribozyme (KRbz) suppressed growth of lung tumor xenografts expressing the relevant mutation, whereas the corresponding antisense sequence lacking catalytic activity did not. Multiple intratumoral (3-5) injections of KRbz-ADV were effective in producing complete tumor regressions of preexisting tumor xenografts. Clinical trials are under consideration to examine the applicability of this anti-K-ras ribozyme for treatment of non-small-cell lung cancers expressing the relevant mutation.

Development of hammerhead ribozymes to modulate endogenous gene expression for functional studies

Hammerhead ribozymes are catalytic RNAs that are being used to inhibit endogenous gene expression to study key components of basic biochemical pathways such as angiogenesis. In addition, these ribozymes have the potential to be used as components of gene therapy protocols for the treatment of disease states. We detail here a set of protocols for the design and testing of hammerhead ribozymes that will efficiently inhibit gene expression both in cell culture and in vivo.

Ribozyme uses in retinal gene therapy

In this chapter we discuss the design, delivery and preclinical testing of mutation-specific ribozymes for the treatment of dominantly inherited retinal disease. We focus particular attention on the initial screening of ribozymes in vitro, because the activity of RNA enzymes in cell-free systems can be used to predict their suitability for animal experiments. Current techniques for delivering genes of interest to cells of the retina using viral vectors are then briefly surveyed emphasizing vector properties that best match to the needs of a ribozyme-based therapy. Using these considerations, analysis of ribozyme gene therapy for an autosomal dominant RP-like disease in a rodent model is outlined emphasizing the desirability of combining biochemical, morphological and electrophysiological measures of therapy. Finally, we describe alternative, perhaps more general, ribozyme approaches that have yet to be tested in the context of retinal disease.