Ras proteins are key elements in the regulation of cellular proliferation, differentiation and survival. Mutational activation of Ras or of components of its effector pathways are detected in one-third of human cancers and are essential for the genesis and maintenance of the tumoral phenotype. Research efforts have been dedicated to the development of therapeutic agents that inhibit aberrant Ras signals and, subsequently, tumor progression. However, many of these initiatives have proven less successful than expected. This review summarizes the current status of developments in Ras research, the challenges that have arisen during preclinical and clinical stages, and how novel approaches to targeting Ras pathways have introduced new strategies toward the development of antitumoral agents that are alternative or complementary to those currently in use. These new approaches would be aimed at disrupting key protein-protein interactions that are essential for the conveyance of Ras aberrant signals or would be directed against new proteins recently demonstrated to be critical participants in Ras-regulated pathways.
The gene therapy vector tgAAG76 (rAAV 2/2.hRPE65p.hRPE65) is in joint development by Targeted Genetics Corp, Moorfields Eye Hospital and the University of London. The vector is a recombinant adeno-associated virus vector that contains the human RPE65 gene under the control of the human RPE65 promoter region and the bovine growth hormone polyadenylation signal. The vector was designed for administration into the subretinal space of patients affected by a hereditary blinding disorder, Leber congenital amaurosis type 2, which is caused by mutations in the RPE65 gene. Interim results from an ongoing phase I/II clinical trial assessing tgAAG76 in three patients with Leber congenital amaurosis type 2 were considered to accomplish the primary outcome of the trial, which was the safety of the procedure, with no severe side effects observed to date. One of the three patients had a significant increase in sensitivity to light and the better capacity to ambulate an obstacle course under dim light conditions compared with baseline. Completion of the clinical trial was anticipated in the second half of 2010.
Gene therapy research has expanded from its original concept of replacing absent or defective DNA with functional DNA to include the manipulation (increase or decrease) of gene expression by the delivery of modified genes, siRNA or other genetic material via multiple vectors, including naked plasmid DNA, viruses and even cells. Specific tissues or cell types are targeted in order to decrease the risks of systemic or side effects. As with the development of any drug, there is an amount of empiricism in the choice of gene target, route of administration, dosing and, in particular, the scaling-up from preclinical models to clinical trials. High-throughput experimental and computational systems biology studies that account for the complexities of host-disease-therapy interactions hold significant promise in assisting in the development and optimization of gene therapies, including personalized therapies and the identification of biomarkers to evaluate the success of such strategies. This review describes some of the obstacles and successes in gene therapy, using the specific example of growth factor gene delivery to promote angiogenesis and blood vessel remodeling in ischemic diseases; anti-angiogenic gene therapy in cancer is also discussed. In addition, the opportunities for systems biology and in silico modeling to improve on current outcomes are highlighted.
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.
The growing prospect of avian influenza viruses achieving sustained interhuman transmission, combined with the recent emergence of a novel swine-origin A/H1N1 influenza strain, has brought the issue of influenza vaccine production capacity into sharp focus. It is becoming increasingly clear that traditional egg-based manufacturing processes may be insufficient to meet global vaccine demands in a pandemic situation that is caused by a highly pathogenic influenza virus. This review introduces the concepts of modern, cell culture-derived influenza vaccines and their manufacture, and explains the advantages of these vaccines in terms of both speed and efficiency of production as well as immunogenic efficacy. Vaccine production technologies using the mammalian cell lines Vero, MDCK and PER.C6, as well as the baculovirus/insect cell platform, are described in detail. Clinical data are provided from cell culture-derived vaccines that are at an advanced stage of development, and insights are provided into recent developments in the preclinical evaluation of more experimental technologies.
MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression by binding to complementary sequences in mRNAs encoding downstream target genes. A large variety of cellular processes, including differentiation, development, apoptosis and cell cycle progression, are dependent on miRNA-mediated suppression of gene expression for their regulation. As such, it is unsurprising that these small RNA molecules are associated with signaling networks that are often altered in various diseases, including cancer. This review focuses on the function of miRNAs in three of the most well-documented signaling pathways that are dysregulated in tumors: the NF kappa B and Ras prosurvival signaling cascades and the tumor suppressor p53 pathway. Recent findings that connect these pathways through various miRNA families are reviewed, and support for using miRNA therapy as a novel method to counteract these tumor-promoting signaling events are presented.
Whole-cell vaccination has demonstrated efficacy in small phase I and II clinical trials. However, in the past 3 years several high-profile phase III trials have failed to meet the predicted endpoints, including trials of the GVAX technologies (BioSante Pharmaceuticals Inc [formerly Cell Genesys Inc]) conducted by Cell Genesys. This review discusses the potential reasons for the failure of selected phase III trials and summarizes the current status of whole-cell vaccination, with specific reference to trials conducted in the past 2 years. Recently, new paradigms have emerged in the field of cancer vaccine research. In particular, the potential use of combination therapies that incorporate immune modulators and standard radio- and chemotherapy to synergize with whole-cell vaccines is discussed. In addition, key measures for improvements within the field that may be required for the generation of effective antitumor immunity are identified.
Corticorelin is a synthetic analog of the naturally occurring human peptide corticotropin-releasing factor (CRF). Several studies have indicated the ability of CRF to reduce the brain edema caused by brain tumors. Peritumoral brain edema (PBE), caused by an intracerebral tumor, manifests several features of vasogenic edema, which is a type of edema characterized by disruption of the blood-brain barrier. Traditionally, PBE has been treated using corticosteroids, primarily dexamethasone. Introduced more than four decades ago, dexamethasone revolutionized the treatment of PBE, but the side effects and withdrawal symptoms associated with corticosteroids propelled the investigation of other drugs. Clinical trials with the synthetic human CRF (hCRF) corticorelin (Xerecept, NEU-3002; Celtic Pharmaceutical Holdings) have indicated that this drug has a distinct advantage over classical corticosteroids in the treatment of PBE. Fewer and/or milder side effects have been reported for corticorelin compared with dexamethasone, although at higher doses of corticorelin several side effects, including hypotension and transient flushing, have been reported. Nevertheless, corticorelin was reasonably well tolerated in patients and healthy volunteers, and may be a good candidate for reducing PBE and associated neural damage, as well as improving neurological symptoms.
More than 60 million individuals have been infected with HIV and approximately half of these individuals have died since the epidemic started. The quest for an effective vaccine to prevent HIV transmission, which is likely to be the most effective approach to halt the epidemic, has been and continues to be an insurmountable challenge. Traditional vaccine strategies that have been effective for other vaccines have proven unsuccessful or impractical for HIV because of safety concerns. Nonetheless, substantial efforts have been directed at the development and clinical testing of HIV vaccines during the past two decades. Four major HIV vaccine efficacy trials conducted by VaxGen Inc (AIDSVAX 003 and AIDSVAX 004) and the NIH-supported HIV Vaccine Trials Network (HVTN 502 and HVTN 503) failed to demonstrate efficacy; however, a recent trial conducted in Thailand (RV144 trial) demonstrated a low level of efficacy, resulting in some renewed optimism. Dissecting the causes for vaccine failure and, more importantly, for the partial level of efficacy observed in the RV144 trial should provide important guidance to the field. This review discusses the ongoing HIV vaccine trials and also highlights recent scientific advances that have provided the field with new leads to invigorate the search for effective vaccines.
Cancer stem cells (CSCs) form a highly tumorigenic core in most human tumors. Although there is no consensus regarding CSC phenotype from different tumor types, CSCs from different cancers share a primitive undifferentiated nature, including a capacity to expand and differentiate, albeit aberrantly, into the major cell types observed in the corresponding tumor. This review focuses on the development of therapeutics targeting CSCs, for which new assays that replace those reporting the inhibition of cell division and rapid tumor shrinkage will be required to account for the quiescent nature and properties of CSCs. The inhibition of signaling pathways related to the stem cell nature of the CSCs may appear an attractive target for novel therapeutics, but these targets could result in significant unwanted off-target effects against essential healthy tissue stem cells. Instead, the ideal therapies targeting CSCs will be directed against functions that contribute to the oncogenic nature of CSCs relative to healthy stem cells, an altogether more challenging task.
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.
Convection-enhanced delivery (CED) has been introduced to overcome the inability of many pharmacological agents to cross the blood-brain barrier, making these agents potentially effective in situ and suitable for the treatment of brain disorders. To achieve CED, drugs are pumped continuously through stereotactically placed catheters directly into the brain, or into or within the vicinity of a tumor mass. This medical technology has been applied to the local delivery of small-molecule drugs, including standard chemotherapeutics, and novel experimental targeted drugs, including targeted cytotoxins. When administered by an experienced clinician, the CED of a molecularly targeted cytotoxin has resulted in a significantly better outcome in patients with recurrent glioblastoma multiforme (GBM). More recent gene therapy clinical trials have also demonstrated that such treatments impact on the course of the disease when administered using CED. The use of CED to administer gene therapy for brain neoplasms may improve the efficacy of this treatment. However, CED is under development, and issues such as the type of catheters to use and their placement, as well as the pharmacological formulation and stability of drugs or vectors, are being studied to achieve efficacious delivery into the desired regions of the diseased brain. This review discusses the use of CED to deliver gene therapy for brain tumors, particularly gliomas, such as GBM.
In recent years, oncolytic viruses have been genetically engineered to target cancer cells selectively. Adenovirus is one such oncolytic virus that is being tested in clinical trials for the treatment of cancer. The observation that cells infected with replication-competent adenoviruses undergo autophagy has provided new options for investigating the mechanism of adenovirus-induced cell death. It has been suggested that the use of autophagy inducers, such as rapamycin, can enhance the oncolytic potency of recombinant adenoviruses. Additionally, several research groups have established that inserting microRNA (miRNA)-targeted sequences into the adenoviral genome can modulate adenoviral protein expression to confer tissue and tumor selectivity. Furthermore, the capability of adenoviruses to inhibit the expression of the DNA repair enzyme MGMT and to chemosensitize glioma cells to temozolomide has been demonstrated. This review discusses three aspects of the use of oncolytic adenoviruses to treat cancer: (i) the induction of autophagy and autophagic cell death during adenoviral replication; (ii) the opportunities and strategies involved in the exploitation of miRNA specificity to generate tissue- and tumor-selective oncolytic viruses; and (iii) the rationale for combining oncolytic adenoviruses with chemotherapeutic agents.
MVA-85A, in development by Oxford-Emergent Tuberculosis Consortium Ltd and the EU-funded research program TB-VAC, is a live attenuated viral vaccine expressing the immunodominant tuberculosis ( TB) antigen 85A, and is intended for use in a heterologous prime-boost strategy to prevent TB. MVA-85A is highly immunogenic in both animals and humans, eliciting strong polyfunctional CD4+ T-cell responses when administered as a boost following BCG vaccination or when administered to individuals previously exposed to TB. Animal studies have demonstrated trends toward reduced pathology and bacillary burden for animals vaccinated with BCG prime followed by MVA-85A boost compared with BCG alone; however, these positive effects appear to be modest, and interpretation is limited by the small number of animals tested. The vaccine has an excellent safety profile in BCG-naive, previously BCG-vaccinated and TB-exposed adults, as well as in BCG-vaccinated adolescents and children. At the time of publication, MVA-85A was in a more advanced stage of clinical development than other novel TB vaccine candidates, with a large-scale, proof-of-concept phase IIb clinical trial underway for the determination of safety, immunogenicity and prevention of TB in infants.
The use of viruses as therapeutic agents against cancer is an old concept that has had a significant revival in the past two decades, in parallel with advances in methods to modify viral genomes genetically. From the initial stage of proof of concept, the field of virotherapy quickly progressed to the clinical setting, where serious limitations, yet promising opportunities, were identified. After demonstrating good safety profiles in humans, the objective in virotherapy has become to improve the efficacy of oncolytic viruses. Virotherapy approaches include incorporating therapeutic genes, evaluating alternative viruses with stronger oncolytic potential, employing new methods to improve biodistribution, and establishing greater insight into the influence of the immune system on both the success and failure of therapies. This review summarizes the most significant advances in recent years in the design of virotherapy for effective tumor treatment.
Pharmacogenetics, genomics and epigenetics have attracted the interest of both pharmaceutical research groups and the medical community. The promise of these rapidly developing research fields and the expected consequences for medicine and for the pharmaceutical industry are timely topics of interest in molecular therapeutics. Of particular interest is their role in supporting the ability to customize medical care to individual patients.
Commercially available prophylactic HPV vaccines for cervical cancer prevention have limited use in women with previous viral exposure. Therefore, a therapeutic HPV vaccine would benefit patients with HPV-associated genital diseases. Being developed by Cancer Research Technology Ltd, under license from Xenova Group plc, TA-CIN (Tissue Antigen - Cervical Intraepithelial Neoplasia) is a fusion protein vaccine comprising the HPV16 viral proteins L2, E6 and E7 for the treatment of HPV16-associated genital diseases. In mouse models, TA-CIN induced dose-dependent HPV16-specific CD4 and CD8 T-cell responses, which were enhanced when boosted with the vaccinia-based vector vaccine TA-HPV (Therapeutic Antigen - HPV). A phase I clinical trial of TA-CIN in healthy volunteers reported no serious adverse events and HPV16-specific cellular immune responses. Phase II trials in patients with anogenital and vulval intraepithelial neoplasia investigated heterologous prime/boost strategies with TA-CIN/TA-HPV and TA-HPV/TA-CIN, but neither of the regimens offered advantages over single-agent TA-HPV. A recent phase II trial investigating imiquimod/TA-CIN in patients with vulval intraepithelial neoplasia demonstrated significant infiltration of CD4 and CD8 T-cells in lesion responders and complete lesion regression in 63% of patients. More comprehensive case-controlled trials are needed to define responders to immunotherapy with TA-CIN and verify its prophylactic and therapeutic properties.
Results from recent clinical trials of the therapeutic vaccines sipuleucel-T (Dendreon Corp), PROSTVAC-VF-TRICOM (National Cancer Institute/BN ImmunoTherapeutics Inc) and BiovaxID (Biovest International Inc) are highlighted. These data support the further development of such vaccines, and provide guidance for the development of improved agents and protocols for the use of therapeutic vaccination to treat cancer.
