HIV-based vectors and angiogenesis following rabbit hindlimb ischemia1

Current Advances in RNA Therapeutics for Human Diseases

Following the discovery of nucleic acids by Friedrich Miescher in 1868, DNA and RNA were recognized as the genetic code containing the necessary information for proper cell functioning. In the years following these discoveries, vast knowledge of the seemingly endless roles of RNA have become better understood. Additionally, many new types of RNAs were discovered that seemed to have no coding properties (non-coding RNAs), such as microRNAs (miRNAs). The discovery of these new RNAs created a new avenue for treating various human diseases. However, RNA is relatively unstable and is degraded fairly rapidly once administered; this has led to the development of novel delivery mechanisms, such as nanoparticles to increase stability as well as to prevent off-target effects of these molecules. Current advances in RNA-based therapies have substantial promise in treating and preventing many human diseases and disorders through fixing the pathology instead of merely treating the symptomology similarly to traditional therapeutics. Although many RNA therapeutics have made it to clinical trials, only a few have been FDA approved thus far. Additionally, the results of clinical trials for RNA therapeutics have been ambivalent to date, with some studies demonstrating potent efficacy, whereas others have limited effectiveness and/or toxicity. Momentum is building in the clinic for RNA therapeutics; future clinical care of human diseases will likely comprise promising RNA therapeutics. This review focuses on the current advances of RNA therapeutics and addresses current challenges with their development.

Endometrial VEGF induces placental sFLT1 and leads to pregnancy complications

There is strong evidence that overproduction of soluble fms-like tyrosine kinase-1 (sFLT1) in the placenta is a major cause of vascular dysfunction in preeclampsia through sFLT1-dependent antagonism of VEGF. However, the cause of placental sFLT1 upregulation is not known. Here we demonstrated that in women with preeclampsia, sFLT1 is upregulated in placental trophoblasts, while VEGF is upregulated in adjacent maternal decidual cells. In response to VEGF, expression of sFlt1 mRNA, but not full-length Flt1 mRNA, increased in cultured murine trophoblast stem cells. We developed a method for transgene expression specifically in mouse endometrium and found that endometrial-specific VEGF overexpression induced placental sFLT1 production and elevated sFLT1 levels in maternal serum. This led to pregnancy losses, placental vascular defects, and preeclampsia-like symptoms, including hypertension, proteinuria, and glomerular endotheliosis in the mother. Knockdown of placental sFlt1 with a trophoblast-specific transgene caused placental vascular changes that were consistent with excess VEGF activity. Moreover, sFlt1 knockdown in VEGF-overexpressing animals enhanced symptoms produced by VEGF overexpression alone. These findings indicate that sFLT1 plays an essential role in maintaining vascular integrity in the placenta by sequestering excess maternal VEGF and suggest that a local increase in VEGF can trigger placental overexpression of sFLT1, potentially contributing to the development of preeclampsia and other pregnancy complications.

Angiopoietin-2 expression is correlated with angiogenesis and overall survival in oral squamous cell carcinoma

This study sought to determine the expression of angiopoietin-2 (Ang-2) and vascular endothelial cell growth factor (VEGF) in oral squamous cell carcinoma (OSCC) and assess their correlations with tumor progression, angiogenesis, vessel maturation, and clinical survival. Tumor tissue from 102 OSCC patients, adjacent noncancerous oral tissue from 79 OSCC patients, and normal oral mucosa from 35 control patients were examined for Ang-2 and VEGF expression using conventional immunohistochemistry. Microvessel density (MVD) and vessel maturation index (VMI) were assessed by double-label immunohistochemistry staining using anti-CD34 and anti-alpha-smooth muscle actin, respectively. Although the proportion of OSCC samples positive for Ang-2 or VEGF expression was significantly higher than that observed in the adjacent noncancerous tissue and normal oral mucosa (P < 0.001), neither Ang-2 nor VEGF expression was associated with the clinicopathological parameters analyzed in OSCC patients. However, MVD and VMI were significantly associated with the expression of Ang-2 (P = 0.001 and P = 0.014, respectively); VEGF expression was associated MVD (P = 0.004). The MVD of OSCC tissues expressing both Ang-2 and VEGF was significantly higher than observed in the double-negative samples (P < 0.05). Multivariate regression and Kaplan-Meier analyses revealed that Ang-2 was negatively associated with the overall survival of OSCC patients. Expression of Ang-2 was associated with angiogenesis and vessel maturation in OSCC. Further studies will evaluate the prognostic value of determining Ang-2 expression in OSCC.

Mechanistic, technical, and clinical perspectives in therapeutic stimulation of coronary collateral development by angiogenic growth factors

Stimulation of collateral vessel development in the heart by angiogenic growth factor therapy has been tested in animals and humans for almost two decades. Discordance between the outcome of preclinical studies and clinical trials pointed to the difficulties of translation from animal models to patients. Lessons learned in this process identified specific mechanistic, technical, and clinical hurdles, which need to be overcome. This review summarizes current understanding of the mechanisms leading to the establishment of a functional coronary collateral network and the biological processes growth factor therapies should stimulate even under conditions of impaired natural adaptive vascular response. Vector delivery methods are recommended to maximize angiogenic gene therapy efficiency and reduce side effects. Optimization of clinical trial design should include the choice of clinical end points which provide mechanistic proof-of-concept and also reflect clinical benefits (e.g., surrogates to assess increased collateral flow reserve, such as myocardial perfusion imaging). Guidelines are proposed to select patients who may respond to the therapy with high(er) probability. Both short and longer term strategies are outlined which may help to make therapeutic angiogenesis (TA) work in the future.

Development of viral vectors for use in cardiovascular gene therapy

Cardiovascular disease represents the most common cause of mortality in the developed world but, despite two decades of promising pre-clinical research and numerous clinical trials, cardiovascular gene transfer has so far failed to demonstrate convincing benefits in the clinical setting. In this review we discuss the various targets which may be suitable for cardiovascular gene therapy and the viral vectors which have to date shown the most potential for clinical use. We conclude with a summary of the current state of clinical cardiovascular gene therapy and the key trials which are ongoing.

Angiopoietin: a TIE(d) balance in tumor angiogenesis

Angiopoietins (ANG-1 and ANG-2) and their TIE-2 receptor tyrosine kinase have wide-ranging effects on tumor malignancy that includes angiogenesis, inflammation, and vascular extravasation. These multifaceted pathways present a valuable opportunity in developing novel inhibition strategies for cancer treatment. However, the regulatory role of ANG-1 and ANG-2 in tumor angiogenesis remains controversial. There is a complex interplay between complementary yet conflicting roles of both the ANGs in shaping the outcome of angiogenesis. Embryonic vascular development suggests that ANG-1 is crucial in engaging interaction between endothelial and perivascular cells. However, recruitment of perivascular cells by ANG-1 has recently been implicated in its antiangiogenic effect on tumor growth. It is becoming clear that TIE-2 signaling may function in a paracrine and autocrine manner directly on tumor cells because the receptor has been increasingly found in tumor cells. In addition, alpha(5)beta(1) and alpha(v)beta(5) integrins were recently recognized as functional receptors for ANG-1 and ANG-2. Therefore, both the ligands may have wide-ranging functions in cellular activities that affect overall tumor development. Collectively, these TIE-2-dependent and TIE-2-independent activities may account for the conflicting findings of ANG-1 and ANG-2 in tumor angiogenesis. These uncertainties have impeded development of a clear strategy to target this important angiogenic pathway. A better understanding of the molecular basis of ANG-1 and ANG-2 activity in the pathophysiologic regulation of angiogenesis may set the stage for novel therapy targeting this pathway.

Cardiovascular gene therapy: current status and therapeutic potential

Gene therapy is emerging as a potential treatment option in patients suffering from a wide spectrum of cardiovascular diseases including coronary artery disease, peripheral vascular disease, vein graft failure and in-stent restenosis. Thus far preclinical studies have shown promise for a wide variety of genes, in particular the delivery of genes encoding growth factors such as vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) to treat ischaemic vascular disease both peripherally and in coronary artery disease. VEGF as well as other genes such as TIMPs have been used to target the development of neointimal hyperplasia to successfully prevent vein graft failure and in-stent restenosis in animal models. Subsequent phase I trials to examine safety of these therapies have been successful with low levels of serious adverse effects, and albeit in the absence of a placebo group some suggestion of efficacy. Phase 2 studies, which have incorporated a placebo group, have not confirmed this early promise of efficacy. In the next generation of clinical gene therapy trials for cardiovascular disease, many parameters will need to be adjusted in the search for an effective therapy, including the identification of a suitable vector, appropriate gene or genes and an effective vector delivery system for a specific disease target. Here we review the current status of cardiovascular gene therapy and the potential for this approach to become a viable treatment option.

Multiple Reduced-intensity Conditioning Regimens Facilitate Correction of Fabry Mice After Transplantation of Transduced Cells

Hematopoietic cell transplantation can impact lysosomal storage disorders (LSDs) and will be enhanced by gene therapy. Transduced cells in LSDs often secrete the therapeutic hydrolase, which can be used by bystander cells. However, toxicity associated with myeloablative transplant preparative regimens limits many applications of this approach in gene therapy. We hypothesized that reduced-intensity (RI) conditioning regimens would allow stable engraftment of therapeutically transduced cells and allow correction of Fabry disease. We transplanted transduced cells into Fabry mice receiving eight different clinically relevant chemotherapy- and/or radiotherapy-based RI conditioning regimens generating modest and transient lymphoid/myeloid cell depletion. Two comprehensive transplantation Protocols were performed. Firstly, transplantation of 0.38 x 10(6) gene-modified stem/progenitor cells was nominally effective; none of the RI regimens led to stable alpha-galactosidase A (alpha-gal A) correction. Secondly, transduced cells were preselected for functional transgene expression and transplanted at a higher dose (0.72 x 10(6) cells). Each RI regimen yielded engraftment of functional transgene-positive cells through 180 days along with increased plasma alpha-gal A activity. Importantly, the RI regimens mediated broad organ enzyme correction and were not associated with immune responses against alpha-gal A. RI conditioning thus has an important role in gene therapy for LSDs; a variety of regimens can be effective in this context.

Gene therapy of the ischemic lower limb--Therapeutic angiogenesis

The limitations of surgical revascularisation and pharmacological treatment in peripheral arterial occlusive disease (PAOD) are well recognized. Therapeutic options for critical leg ischemia are consequently limited to percutaneous transluminal angioplasty (PTA) or surgical revascularisation. Unfortunately, many patients with critical leg ischemia are poor candidates for either procedure. Therapeutic angiogenesis is a novel promising tool to treat these patients. Experimental and clinical and trials of gene transfer for therapeutic angiogenesis have already shown some clinical efficacy. This review is focused on gene transfer techniques in preclinical and clinical therapeutic angiogenesis, angiogenic growth factors, vectors, delivery methods and routes. The results of clinical and experimental studies, safety and side effects of gene therapy, and the perspectives of future research are also discussed.