October 12, 2011

TRIGGERING ANTI-TUMOR KILLING WITH APTAMERS
John J. Rossi, PhD

T-cell mediated killing of tumor cells is a critical process in fighting cancer. However, even when T-cells are recruited to tumor cells, they often are not stimulated to kill the tumor. This is due to a requirement for co-stimulation in which the tumor cell itself must secrete a ligand that activates a specific receptor on T-cells. This in turn activates the T-cell killing function. Many tumors do not secrete such co-stimulatory ligands. thereby abrogating the T-cell mediated anti-tumor effects. A possible solution to this problem is to provide the co-stimulatory ligand to T-cells.

As discussed in an article within the November 2011 issue of Molecular Therapy, Eli Gilboa, PhD and colleagues have devised a clever and powerful solution to the co-stimulation challenge. In this study they used in vitro evolved RNA aptamers which bind specifically and with high affinity to cell surface receptors, thereby mimicking the function of the natural ligands. They specifically developed aptamers that bind the T-cell specific 4-1BB receptor, which must dimerize to function. To activate this receptor, they made a dimeric 4-1BB aptamer that triggers receptor dimerization. In order to enhance the specificity of the activated T-cell killing, a third aptamer was linked to the dimerized 4-1BB aptamers. They reasoned that linking the third aptamer would allow selective recognition of tumors bearing the cell surface receptor for the aptamer, which in combination with the T-cell activating aptamers should result in selective killing of tumor cells.

September 26, 2011

A TRACTABLE MODEL OF HUMAN CARDIAC DEVELOPMENT
Nicole M. Kane, PhD

Stem cell-derived cardiac cells hold great promise for the regeneration of damaged heart tissue after cardiovascular disease or injury; however, there are currently several issues that impede the immediate use of these cells in a therapeutic setting. One such issue is the heterogeneity of cell types formed during differentiation and the resulting poor generation efficiency of the desired cell type.

As outlined in the manuscript in the September 2011 issue of Molecular Therapy, Dr. James E. Dixon and colleagues have approached this problem by implementing a genetics-based screen to identify four key developmental factors (GATA4, TBX5, NKX2.5 and BAF60c) that can direct the differentiation of human embryonic stem (hES) cells toward cardiac cells. [more]

September 23, 2011

BULDGING AT THE SEEDS ABROGATES OFF-TARGETING OF siRNAs
John J. Rossi, PhD

Since the first descriptions of RNA interference in human cells a decade ago, the applications of small interfering RNAs (siRNAs) for studies of gene function as well as therapeutics have grown significantly. One of the major attractions of siRNAs is their sequence specificity as they guide base specific cleavage of target mRNAs. This notion was somewhat dispelled by microarray analyses of the transcriptome following siRNA applications which demonstrated that a single siRNA could affect the expression of dozens of non-targeted transcripts. It was quickly realized that this was due to the ability of siRNAs to mimic endogenous microRNAs, which bind to their targets with partial complementarity and only require what is called “seed sequence” base pairing between bases 2-7/8 of the guide strand with the target mRNA 3’UTR. [more]

July 12, 2011

SMART BOMBS FOR TARGETED DELIVERY OF THERAPEUTIC SMALL RNAs
John J. Rossi, PhD

RNA interference (RNAi) has been touted as a powerful new therapeutic approach for the treatment of a variety of diseases. The triggers for RNAi are short double stranded RNAs called small interfering RNAs (siRNAs). A major roadblock in the therapeutic application of siRNAs is their delivery to target cells and tissues. Targeted delivery of siRNAs is considered a safe pathway to avoid undesired inhibition of gene expression in non-diseased tissues.

The strategies for targeted delivery to date include complexing of siRNAs with antibodies, ligand containing nanoparticles, vitamins, cholesterol, peptides and receptor targeting aptamers. Each of these approaches has merit, but all are limited to some extent by trapping of the siRNAs in the endosome (a compartment within the cell), which prevents the therapeutic siRNAs from distributing throughout the cell.

The manuscript by Palanca-Wessels et al., in the July issue of Molecular Therapy, provides a novel solution to the problems of targeted siRNA delivery accompanied by endosomal escape. This group of researchers took advantage of a monoclonal antibody (a cell that triggers an immune response to cancer), that binds to CD22 which is a protein detected in 60 to 80 percent of B-cell malignancies. Common B-cell malignancies include many forms of cancer, such as lymphoma.[more]

July 7, 2011

MAGIC BULLET TARGETING SUBCELLULAR ORGANELLE: MITOCHONDRIA
Yuhua Wang, PhD and Leaf Huang, PhD

Mitochondria, known as “cellular power plants,” are the membrane-bound organelles in the mammalian cells that play an essential role in generating adenosine triphosphate (ATP), the main fuel source for the work of the cells. Apart from that, mitochondria are also responsible for the maintenance of oxidation-reduction homeostasis, intracellular calcium level and apoptosis-survival signal. Impairment of mitochondria has been demonstrated to cause neurodegenerative disease, cancer, diabetes, aging and other disorders. Although scientists have been dedicated to conducting research for in-depth understanding of mitochondria dysfunctions and development of therapy to effectively treat them, no specific therapeutic regimes have been conceived for any kind of mitochondrial diseases. This is primarily because therapeutic molecules can barely be delivered to the site of action by virtue of two barriers: cytoplasm membrane and mitochondria membranes. [More]

GENE THERAPY FOR PROSTATE CANCER - A NEW THERAPEUTIC HOPE?
Alan L. Parker, PhD

Prostate cancer remains a major killer in the westernised world. In the United States alone, around 230,000 men each year are diagnosed with the disease, accounting for over 30,000 deaths annually. Low risk (early stage) cancer can be managed with surgery and radiotherapy, resulting in good 10 year progression free survival rates. For more advanced cases, the prognosis is significantly poorer with a high chance of recurrence. In this scenario, the development of new generations of therapies including gene therapies could improve patient survival. [More]

June 7, 2011

CURING SICK STEM CELLS VIA GENE THERAPY
Stuart A. Nicklin, PhD

Repairing heart muscle following a heart attack by stimulating new blood vessels to grow and increase oxygen delivery is an important therapeutic approach in cardiovascular disease. This is being studied using gene and cell therapy approaches to stimulate blood vessel cells to divide. The potential for triggering stem cells (immature cells in the body which can develop into a number of different specific mature cell types in a process termed “differentiation”) to promote new blood vessel growth has been pursued actively in recent years. However, using immature stem cells is challenging as our understanding of how they develop into specific cell types is incomplete.

Another option is the use of “progenitor cells,” which are stem cell-like cells which can divide and generate new tissue, but which have already been “pushed” into becoming a specific cell type via a process termed “lineage commitment.” An “endothelial progenitor cell,” or “circulating angiogenic cell,” is a cell that circulates in the bloodstream to repair damaged blood vessels and potentially to help generate new vessels. These cells can be easily purified from the patient’s blood and cultured in the laboratory before being re-injected into the patient as a therapeutic approach.

Here, Dr. Michael Ward and colleagues have made an important finding regarding these cells. By isolating them from patients with cardiovascular disease and healthy subjects for comparison, they show that circulating angiogenic cells from patients are not fully functional, preventing them from forming new blood vessels. Since the cardiovascular disease patients are very sick, they also have unhealthy circulating angiogenic cells.

[More]