Delivery of therapeutic RNA molecules to cancer cells by bacteria.

Delivery of RNA-based therapeutics, for example RNA interference (RNAi) effectors, to target cells is one of the major obstacles for the development of RNA-based therapies. Since it has been known for a long time that bacteria can mediate tumor shrinkage, it was obvious to use nonpathogenic bacteria to produce and deliver therapeutic RNA molecules into target cells to induce RNAi. During the last years, two bacteria-based concepts were developed for this strategy, transkingdom RNAi (tkRNAi) and bacteria-mediated RNAi (bmRNAi). The first concept, tkRNAi, delivers RNAi effectors into target cells by invasive bacteria, which themselves produce therapeutic shRNAs. The bmRNAi technology utilizes invasive bacteria conveying RNAi effector-encoding DNA constructs that will act as a matrix for transcription of these sequences in the target cell by the host cell's transcription machinery.

Bacterial vectors and delivery systems in cancer therapy.

Live bacterial vectors may be useful tools for the development of novel cancer therapies that can be added to the repertoire of existing drugs. Several bacterial strains effectively colonize solid tumors and act as antitumor therapeutics. The naturally occurring tumor-colonizing characteristics of bacterial species such as Salmonella sp, Clostridium sp and Escherichia coli can be further modified by genetic manipulations, making these bacterial systems excellent vehicles for the production and targeted delivery of therapeutic molecules into cancer cells. This feature review summarizes recent research on cancer therapy using genetically modified bacteria. Different approaches - bactofection, DNA vaccination, and bacterially mediated protein and RNAi delivery - in which modified bacteria are used as anticancer therapeutics, are discussed.

Engineered E. coli as vehicles for targeted therapeutics.

Improving the means of drug delivery has become an important field of pharmaceutical research. The development of safe and advanced vectors for gene therapy and other novel therapies will allow for targeted delivery of pharmaceutically active agents and carries promise to improve therapies both through increased efficiency (e.g. improved cellular uptake of the active drug) as well as lower toxicity (e.g. through targeted delivery only to the cells requiring treatment) for a large number of pharmaceutical agents. Here we are reviewing the nascent field using live bacteria as vectors for therapeutic and preventive agents in a wide range of areas, from vaccine purposes to gene therapy and delivery of therapeutic RNA interference. This review focuses particularly on the use of E. coli derived strains for therapeutic delivery.

Delivery of short hairpin RNAs by transkingdom RNA interference modulates the classical ABCB1-mediated multidrug-resistant phenotype of cancer cells.

Delivery of RNA interference (RNAi)-mediating agents to target cells is one of the major obstacles for the development of RNAi-based therapies. One strategy to overcome this barrier is transkingdom RNAi (tkRNAi). This technology uses non-pathogenic bacteria to produce and deliver therapeutic short hairpin RNA (shRNA) into target cells to induce RNAi. In this study, the tkRNAi approach was used for modulation of the "classical" ABCB1-mediated multidrug resistance (MDR) in human cancer cells. Subsequent to treatment with anti-ABCB1 shRNA expression vector bearing E. coli, MDR cancer cells (EPG85 257RDB) showed 45% less ABCB1 mRNA expression. ABCB1 protein expression levels were reduced to a point at which merely a weak band could be detected. Drug accumulation was enhanced 11-fold, to an extent that it reached 45% of the levels in non-resistant cells and resistance to daunorubicin was decreased by 40%. The data provide the proof-of-concept that tkRNAi is suitable for modulation of "classical" MDR in human cancer cells. Overall, the prototype tkRNAi system tested here did not yet attain the levels of gene silencing seen with conventional siRNAs nor virally delivered shRNAs; but the tkRNAi system for gene-silencing of ABCB1 is still being optimized, and may become a powerful tool for delivery of RNAi effectors for the reversal of cancer MDR in future.

Transkingdom RNA interference (tkRNAi): a novel method to induce therapeutic gene silencing.

RNA interference is a phenomenon in which specific, endogenous genes are silenced by mRNA degradation. This technology is highly regarded as a potential therapeutic due to its high efficacy and low toxicity. However, the difficulty of delivering RNAi to target cells has impeded the development of RNAi-based therapies. One method to overcome this barrier is the use of a nonpathogenic bacteria vector, Escherichia coli, to deliver RNAi to target cells with high efficacy. In transkingdom interference RNAi (tkRNAi) delivery, E. coli were engineered to transcribe short RNA (shRNA) from a plasmid (TRIP) containing the invasin gene Inv and the listeriolysin O gene Hly. tkRNAi is successful in eliciting efficient gene silencing in vitro and in vivo.

Targeting PKC: a novel role for beta-catenin in ER stress and apoptotic signaling.

Targeting protein kinase C (PKC) isoforms by the small molecule inhibitor enzastaurin has shown promising preclinical activity in a wide range of tumor cells. We further delineated its mechanism of action in multiple myeloma (MM) cells and found a novel role of beta-catenin in regulating growth and survival of tumor cells. Specifically, inhibition of PKC leads to rapid accumulation of beta-catenin by preventing the phosphorylation required for its proteasomal degradation. Microarray analysis and small-interfering RNA (siRNA)-mediated gene silencing in MM cells revealed that accumulated beta-catenin activates early endoplasmic reticulum stress signaling via eIF2alpha, C/EBP-homologous protein (CHOP), and p21, leading to immediate growth inhibition. Furthermore, accumulated beta-catenin contributes to enzastaurin-induced cell death. Sequential knockdown of beta-catenin, c-Jun, and p73, as well as overexpression of beta-catenin or p73 confirmed that accumulated beta-catenin triggers c-Jun-dependent induction of p73, thereby conferring MM cell apoptosis. Our data reveal a novel role of beta-catenin in endoplasmic reticulum (ER) stress-mediated growth inhibition and a new proapoptotic mechanism triggered by beta-catenin on inhibition of PKC isoforms. Moreover, we identify p73 as a potential novel therapeutic target in MM. Based on these and previous data, enzastaurin is currently under clinical investigation in a variety of hematologic malignancies, including MM.

RNAi therapeutics: an update on delivery.

RNA interference (RNAi) has rapidly advanced from a laboratory observation into a major area of research within biology and medicine. RNAi is triggered by short interfering RNAs (siRNAs) of between 19 and 21 nucleotides in length, which induces the targeted cleavage of mRNA with sequences of homology to the siRNA. Because of its high degree of specificity and efficacy, the potential for RNAi-based therapeutics was recognized at an early stage. However, development of RNAi-based agents has been hindered because siRNAs are unstable in serum and delivery across the cell membrane is highly inefficient. Numerous methods have been developed to facilitate delivery of RNAi in animals and patients, each with their own set of advantages and disadvantages. This review discusses publications between 2005 to 2007 in the area of RNAi delivery, with a particular focus on in vivo application and clinical trials.

High-intensity focused ultrasound for the targeted destruction of uterine tissues: experiences from a pilot study using a mobile HIFU unit.

BACKGROUND: High intensity focused ultrasound (HIFU) is a novel method which offers the non-invasive ablation of tissues without harming overlying organs or skin. It has been introduced successfully in urology for the ablation of prostatic hyperplasia and seems to be promising in the treatment of uterine fibroids. In this study we aimed to examine the feasibility and possible side effects of HIFU treatment of uterine tissues using an experimental mobile HIFU unit with ultrasound guidance. METHODS: For these experiments, a 1.07 MHz ultrasound source was used which allows treatment depths between 0 and 10 cm. In 12 patients scheduled to have abdominal hysterectomy, 5-60 impulses of HIFU were applied through the intact skin upon uterine tissues directly prior to the surgical procedure. Tissue intensities lay between 3,200 and 6,300 W/cm(2) and a fixed pulse length of 4 s was used. RESULTS: No side effects were encountered other than one first-degree skin burn and the treatment was well tolerated. Histology showed clearly demarcated coagulative necrosis in the targeted tissues. Treatment was concluded in less than 45 min for each patient. CONCLUSION: Focused ultrasound is an effective method to selectively destroy tissue within the uterus and the transabdominal access route is very feasible. This study shows that a mobile ultrasound source can be used safely and effectively to destroy uterine tissues, such as fibroids, without major side effects.

Cequent Pharmaceuticals, Inc.: the biological pitcher for RNAi therapeutics.

Cequent Pharmaceuticals, Inc. is a recently established biopharmaceutical company that aims to develop clinically compatible therapies based on RNAi, a potent gene-silencing mechanism discovered in 1998. The company's proprietary technology, transkingdom RNAi (tkRNAi), uses nonpathogenic bacteria to produce and deliver shRNA into target cells to induce RNAi. Our initial focus is on the development of a tkRNAi-based therapy for familial adenatomous polyposis, an inherited form of colon cancer. Cequent's first tkRNAi-based drug for familial adenatomous polyposis, CEQ501, is currently in advanced preclinical testing. As part of its ongoing activities, Cequent plans to develop additional tkRNAi-based products for indications within and outside the GI tract. Our overall goal is to establish tkRNAi as a platform for developing a wide range of RNAi-based therapies.

Delivery of RNA interference.

Over the last few years, RNA Interference (RNAi), a naturally occurring mechanism of gene regulation conserved in plant and mammalian cells, has opened numerous novel opportunities for basic research across the field of biology. While RNAi has helped accelerate discovery and understanding of gene functions, it also has great potential as a therapeutic and potentially prophylactic modality. Challenging diseases failing conventional therapeutics could become treatable by specific silencing of key pathogenic genes. More specifically, therapeutic targets previously deemed "undruggable" by small molecules, are now coming within reach of RNAi based therapy. For RNAi to be effective and elicit gene silencing response, the double-stranded RNA molecules must be delivered to the target cell. Unfortunately, delivery of these RNA duplexes has been challenging, halting rapid development of RNAi-based therapies. In this review we present current advancements in the field of siRNA delivery methods, including the pros and cons of each method.