Current Opinion in Molecular Therapeutics最新文献

The catalytic role of ribozymes in RNA processing is well established. However, the proposal that ribozymes can be discovered by in vitro selection has resulted in the identification of a relatively small number of novel ribozyme catalysts. The limited repertoire of the native functional groups of RNA and its inherent instability have led to the hypothesis that ribozymes that contain non-natural functional groups (ie, modified nucleic acids) would provide greater catalytic activity toward non-RNA substrates. Moreover, because of their greater stability, reduced cost and ease of synthesis, native and modified deoxyribozymes have recently dominated the in vitro selection of enzymes that catalyze reactions involving non-RNA substrates. Deoxyribozymes bind easily to metal cofactors and provide a scaffold for templating chemical reactions, representing two significant advantages of deoxyribozymes compared with ribozymes for the catalytic transformation of non-RNA substrates. In addition, RNA processing illustrates the natural functions and limitations of ribozymes that have led to the shift in the emphasis of research from ribozymes to deoxyribozymes.

Chromatin remodeling guided by non-coding RNA (ncRNA) contributes mechanistically to the establishment of chromatin structure and to the maintenance of epigenetic memory. Various ncRNAs have been identified as regulators of chromatin structure and gene expression. The widespread occurrence of antisense transcription in eukaryotes emphasizes the prevalence of gene regulation by natural antisense transcripts. Recently, antisense ncRNAs have been implicated in the silencing of tumor suppressor genes through epigenetic remodeling events. Characterization of the antisense RNAs involved in the development or maintenance of oncogenic states may define ncRNAs as early biomarkers for the emergence of cancer, and could have a significant impact on the development of tools for disease diagnosis and treatment. In this review, current knowledge on the mechanisms of ncRNA-mediated transcriptional gene silencing in humans is discussed, and parallels between the establishment of a silent chromatin state mediated by siRNAs and long antisense ncRNAs are highlighted.

Sexually transmitted infections (STIs) are a major cause of morbidity and mortality worldwide. Although a vaccine is available for HPV, no effective vaccines exist for the HIV-1 and HSV-2 viral pathogens, and there are no cures for these infections. Furthermore, recent setbacks in clinical trials, such as the failure of the STEP trial to prevent HIV-1 infection, have emphasized the need to develop alternative approaches to interrupt the transmission of these pathogens. One alternative strategy is represented by the use of topically applied microbicides, and such agents are being developed against various viruses. RNAi-based microbicides have recently been demonstrated to prevent HSV-2 transmission, and may be useful for targeting multiple STIs. In this review, microbicides that are under development for the prevention of STIs are described, with a focus on topically applied microbicidal siRNAs.

During the past two decades, numerous recombinant antibody formats have been designed and produced by genetic engineering, extending and improving the activities of naturally occurring antibodies. However, while whole IgG molecules, antibody fragments and chemically modified derivatives thereof are being used clinically, alternative antibody formats still await regulatory approval. This review summarizes recent progress in the development of alternative antibody formats for therapeutic applications, with an emphasis on molecules that are in clinical testing.

A fundamental limitation in the treatment of brain tumors is that < 1% of most therapeutic agents administered systemically are able to cross the blood-brain barrier (BBB). The development of new strategies that circumvent the BBB should increase the likelihood of tumor response to selected therapeutic agents. Intranasal delivery (IND) is a practical, noninvasive method of bypassing the BBB to deliver therapeutic agents to the brain. This technique has demonstrated promising results in the treatment of neurological disorders. Telomerase is a reverse transcriptase that is expressed in the vast majority of malignant gliomas, although not in the healthy brain. Telomerase inhibition can therefore be used as a therapeutic strategy for selectively targeting malignant gliomas. The first successful IND of a telomerase inhibitor as a therapy for brain tumors was GRN-163, an oligonucleotide N3'-->5' thiophosphoramidate telomerase inhibitor, which was successfully administered into intracerebral tumors in rats with no apparent toxicity. GRN-163 exhibited favorable tumor uptake and inhibited tumor growth, leading to prolonged lifespan in treated animals. The IND of telomerase inhibitors represents a new therapeutic approach that appears to selectively kill tumor cells, without inducing toxic effects in the surrounding healthy brain tissue.

Sequence-selective gene targeting constitutes an attractive drug-discovery approach for genetic therapy, with the aim of reducing or enhancing the activity of specific genes at the transcriptional level, or as part of a methodology for targeted gene repair. The pseudopeptide DNA mimic peptide nucleic acid (PNA) can recognize duplex DNA with high sequence specificity and affinity in triplex, duplex and double-duplex invasive modes or non-invasive triplex modes. Novel PNA modification has improved the affinity for DNA recognition via duplex invasion, double-duplex invasion and triplex recognition considerably. Such modifications have also resulted in new approaches to targeted gene repair and sequence-selective double-strand cleavage of genomic DNA.

To date, only five drugs have been approved for the treatment of Alzheimer's disease (AD); however, these agents impact the symptoms rather than the progression of the disease. It is well established that nerve growth factor (NGF) enhances the function and survival of basal forebrain cholinergic neurons that are vulnerable in AD. However, NGF does not cross the blood-brain barrier, and intraventricular NGF injections in animals and humans were associated with significant side effects. Adeno-associated virus (AAV)-based gene delivery is a novel technology being developed for administration of NGF to the brain to treat AD symptoms and progression. Indeed, the efficacy of ex vivo gene delivery was demonstrated in patients with AD who experienced improvements in cerebral metabolism and cognition compared with pre-operative function without adverse events. CERE-110 (AAV2-NGF), under development by Ceregene Inc, is an AAV serotype 2-based vector expressing human NGF delivered to the nucleus basalis of Meynert by stereotactic injection for the treatment of AD. Animal studies have established the preclinical efficacy of CERE-110, revealing an excellent safety profile. CERE-110 has passed phase I clinical testing and a multicenter phase II clinical trial has commenced. CERE-110 is a promising candidate for the treatment of AD.

Glembatumumab vedotin (CR-011-vc-MMAE) is a mAb-drug conjugate being developed by Celldex Therapeutics Inc for the treatment of glycoprotein non-metastatic melanoma protein B (GPNMB)-expressing cancers. Glembatumumab is a fully human mAb directed against an extracellular domain of GPNMB expressed in human breast cancers and melanomas. Glembatumumab is conjugated to the potent microtubule inhibitor monomethyl auristatin E using a cathepsin cleavable valine-citrulline (vc) dipeptide linker. Glembatumumab vedotin has demonstrated potent antitumor activity in preclinical studies, including in GPNMB-expressing cell lines. In human melanoma xenograft mice, intravenous glembatumumab vedotin was associated with complete tumor regression without significant toxicity. In two phase I/II clinical trials, intravenous glembatumumab vedotin demonstrated antitumor activity in patients with breast cancer or melanoma. Skin rash was the most common toxicity reported, which may have been caused by the expression of GPNMB in healthy skin. Glembatumumab vedotin had a relatively short t(1/2) , prompting the evaluation of more frequent dosing schedules. Prospective, randomized clinical trials will likely be required to determine the therapeutic potential of glembatumumab vedotin in the treatment of breast cancer and melanoma.

siRNAs are widely used for the control of gene expression in molecular biology and experimental pharmacology. siRNA molecules are the most efficient and specific inhibitors of gene expression to have been discovered, acting at nanomolar and subnanomolar concentrations. Challenges associated with nuclease stability, selecting effective sequences, reducing off-target effects and achieving efficient delivery to target cells and tissues have significantly limited the biomedical applications of siRNA. However, chemical modification is a powerful tool for improving the properties of siRNA. This review examines recent data regarding chemical modifications used to develop potent effectors of gene silencing. The correlation between thermal stability and potency, and between nuclease resistance and duration of the silencing effect, are discussed with relation to chemically modified siRNAs.

In development by MedImmune LLC, under license from Genaera Corp, MEDI-528 is an injectable, humanized mAb against IL-9 for the potential treatment of asthma. In asthma, airway inflammation is usually adequately minimized with standard-of-care treatments, such as inhaled corticosteroids and leukotriene modifiers, but it is sometimes less responsive to such therapies and other anti-inflammatory approaches are required. Several T-helper cell type 2-derived cytokines, such as IL-4, -5, -9 and -13, play a major role in the development of disease pathogenic features in asthma, including airway eosinophilia, increased IgE production, mucus hypersecretion and airway hyperreactivity. As an IL-9 antagonist, MEDI-528 appears to inhibit a range of asthma pathogenic features in antigen-exposed mice. To date, clinical data are modest, although insufficient to judge the efficacy of the drug in humans, and larger and longer-term clinical trials are required. MEDI-528, along with other anticytokine therapies targeting different ILs, remains under investigation in early-phase trials for asthma. Time will tell if this form of therapy can be used as an add-on to less efficacious anti-inflammatory therapy or can replace the existing anti-inflammatory therapies in the treatment of asthma.