Evgenios Neofytou

Drug Release from Electric- Field-Responsive Nanoparticles

We describe a new temperature and electric field dual-stimulus responsive nanoparticle system for programmed drug delivery. Nanoparticles of a conducting polymer (polypyrrole) are loaded with therapeutic pharmaceuticals and are subcutaneously localized in vivo with the assistance of a temperature-sensitive hydrogel (PLGA-PEG-PLGA). We have shown that drug release from the conductive nanoparticles is controlled by the application of a weak, external DC electric field. This approach represents a novel interactive drug delivery system that can show an externally tailored release profile with an excellent spatial, temporal, and dosage control.

Wireless power transfer to deep-tissue microimplants

Significance Advances in miniaturization paved the way for tiny medical devices that circumvent conventional surgical implantation, but no suitable method for powering them deep in the body has been demonstrated. Existing methods for energy storage, harvesting, or transfer require large components that do not scale to millimeter dimensions. We report a wireless powering method that overcomes this challenge by inducing spatially focused and adaptive electromagnetic energy transport via propagating modes in tissue. We use the method to realize a tiny electrostimulator that is orders of magnitude smaller than conventional pacemakers. The demonstrated performance characteristics far exceed requirements for advanced electronic function and should enable new generations of miniaturized electronic implants. The ability to implant electronic systems in the human body has led to many medical advances. Progress in semiconductor technology paved the way for devices at the scale of a millimeter or less (“microimplants”), but the miniaturization of the power source remains challenging. Although wireless powering has been demonstrated, energy transfer beyond superficial depths in tissue has so far been limited by large coils (at least a centimeter in diameter) unsuitable for a microimplant. Here, we show that this limitation can be overcome by a method, termed midfield powering, to create a high-energy density region deep in tissue inside of which the power-harvesting structure can be made extremely small. Unlike conventional near-field (inductively coupled) coils, for which coupling is limited by exponential field decay, a patterned metal plate is used to induce spatially confined and adaptive energy transport through propagating modes in tissue. We use this method to power a microimplant (2 mm, 70 mg) capable of closed-chest wireless control of the heart that is orders of magnitude smaller than conventional pacemakers. With exposure levels below human safety thresholds, milliwatt levels of power can be transferred to a deep-tissue (>5 cm) microimplant for both complex electronic function and physiological stimulation. The approach developed here should enable new generations of implantable systems that can be integrated into the body at minimal cost and risk.

IFATS Collection: Adipose Stromal Cells Adopt a Proangiogenic Phenotype Under the Influence of Hypoxia

Evolving evidence suggests a possible role for adipose stromal cells (ASCs) in adult neovascularization, although the specific cues that stimulate their angiogenic behavior are poorly understood. We evaluated the effect of hypoxia, a central mediator of new blood vessel development within ischemic tissue, on proneovascular ASC functions. Murine ASCs were exposed to normoxia (21% oxygen) or hypoxia (5%, 1% oxygen) for varying lengths of time. Vascular endothelial growth factor (VEGF) secretion by ASCs increased as an inverse function of oxygen tension, with progressively higher VEGF expression at 21%, 5%, and 1% oxygen, respectively. Greater VEGF levels were also associated with longer periods in culture. ASCs were able to migrate towards stromal cell‐derived factor (SDF)‐1, a chemokine expressed by ischemic tissue, with hypoxia augmenting ASC expression of the SDF‐1 receptor (CXCR4) and potentiating ASC migration. In vivo, ASCs demonstrated the capacity to proliferate in response to a hypoxic insult remote from their resident niche, and this was supported by in vitro studies showing increasing ASC proliferation with greater degrees of hypoxia. Hypoxia did not significantly alter the expression of endothelial surface markers by ASCs. However, these cells did assume an endothelial phenotype as evidenced by their ability to tubularize when seeded with differentiated endothelial cells on Matrigel. Taken together, these data suggest that ASCs upregulate their proneovascular activity in response to hypoxia, and may harbor the capacity to home to ischemic tissue and function cooperatively with existing vasculature to promote angiogenesis. STEM CELLS 2009;27:266–274

Human Engineered Heart Muscles Engraft and Survive Long Term in a Rodent Myocardial Infarction Model

RATIONALE Tissue engineering approaches may improve survival and functional benefits from human embryonic stem cell-derived cardiomyocyte transplantation, thereby potentially preventing dilative remodeling and progression to heart failure. OBJECTIVE Assessment of transport stability, long-term survival, structural organization, functional benefits, and teratoma risk of engineered heart muscle (EHM) in a chronic myocardial infarction model. METHODS AND RESULTS We constructed EHMs from human embryonic stem cell-derived cardiomyocytes and released them for transatlantic shipping following predefined quality control criteria. Two days of shipment did not lead to adverse effects on cell viability or contractile performance of EHMs (n=3, P=0.83, P=0.87). One month after ischemia/reperfusion injury, EHMs were implanted onto immunocompromised rat hearts to simulate chronic ischemia. Bioluminescence imaging showed stable engraftment with no significant cell loss between week 2 and 12 (n=6, P=0.67), preserving ≤25% of the transplanted cells. Despite high engraftment rates and attenuated disease progression (change in ejection fraction for EHMs, -6.7±1.4% versus control, -10.9±1.5%; n>12; P=0.05), we observed no difference between EHMs containing viable and nonviable human cardiomyocytes in this chronic xenotransplantation model (n>12; P=0.41). Grafted cardiomyocytes showed enhanced sarcomere alignment and increased connexin 43 expression at 220 days after transplantation. No teratomas or tumors were found in any of the animals (n=14) used for long-term monitoring. CONCLUSIONS EHM transplantation led to high engraftment rates, long-term survival, and progressive maturation of human cardiomyocytes. However, cell engraftment was not correlated with functional improvements in this chronic myocardial infarction model. Most importantly, the safety of this approach was demonstrated by the lack of tumor or teratoma formation.

Protein–Polymer Hybrid Nanoparticles for Drug Delivery

Amphiphilic bovine serum albumin-poly(methyl methacrylate) conjugate forms nanoparticles with the uniform size of ~100 nm by self-assembling. Loaded with the hydrophobic anti-tumor drug camptothecin, the nanoparticle efficiently delivers drugs into cancer cells, and thus inhibits ~79% of tumor growth in animals compared with free drug.

Hurdles to clinical translation of human induced pluripotent stem cells.

Human pluripotent stem cells are known to have the capacity to renew indefinitely, being intrinsically able to differentiate into many different cell types. These characteristics have generated tremendous enthusiasm about the potential applications of these cells in regenerative medicine. However, major challenges remain with the development and testing of novel experimental stem cell therapeutics in the field. In this Review, we focus on the nature of the preclinical challenges and discuss potential solutions that could help overcome them. Furthermore, we discuss the use of allogeneic versus autologous stem cell products, including a review of their respective advantages and disadvantages, major clinical requirements, quality standards, time lines, and costs of clinical grade development.

Transdermal deferoxamine prevents pressure-induced diabetic ulcers

Significance Diabetes is the leading cause of nontraumatic amputations. There are no effective therapies to prevent diabetic ulcer formation and only modestly effective technologies to help with their healing. To enhance diabetic wound healing we designed a transdermal delivery system containing the FDA-approved small molecule deferoxamine, an iron chelator that increases defective hypoxia inducible factor-1 alpha transactivation in diabetes by preventing iron-catalyzed reactive oxygen stress. This system overcomes the challenge of delivering hydrophilic molecules through the normally impermeable stratum corneum and both prevents diabetic ulcer formation and improves the healing of existing diabetic wounds. This represents a prophylactic pharmacological agent to prevent ulcer formation that is rapidly translatable into the clinic and has the potential to ultimately transform the care and prevention of diabetic complications. There is a high mortality in patients with diabetes and severe pressure ulcers. For example, chronic pressure sores of the heels often lead to limb loss in diabetic patients. A major factor underlying this is reduced neovascularization caused by impaired activity of the transcription factor hypoxia inducible factor-1 alpha (HIF-1α). In diabetes, HIF-1α function is compromised by a high glucose-induced and reactive oxygen species-mediated modification of its coactivator p300, leading to impaired HIF-1α transactivation. We examined whether local enhancement of HIF-1α activity would improve diabetic wound healing and minimize the severity of diabetic ulcers. To improve HIF-1α activity we designed a transdermal drug delivery system (TDDS) containing the FDA-approved small molecule deferoxamine (DFO), an iron chelator that increases HIF-1α transactivation in diabetes by preventing iron-catalyzed reactive oxygen stress. Applying this TDDS to a pressure-induced ulcer model in diabetic mice, we found that transdermal delivery of DFO significantly improved wound healing. Unexpectedly, prophylactic application of this transdermal delivery system also prevented diabetic ulcer formation. DFO-treated wounds demonstrated increased collagen density, improved neovascularization, and reduction of free radical formation, leading to decreased cell death. These findings suggest that transdermal delivery of DFO provides a targeted means to both prevent ulcer formation and accelerate diabetic wound healing with the potential for rapid clinical translation.

Potential Strategies to Address the Major Clinical Barriers Facing Stem Cell Regenerative Therapy for Cardiovascular Disease: A Review

Importance Although progress continues to be made in the field of stem cell regenerative medicine for the treatment of cardiovascular disease, significant barriers to clinical implementation still exist. Objectives To summarize the current barriers to the clinical implementation of stem cell therapy in patients with cardiovascular disease and to discuss potential strategies to overcome them. Evidence Review Information for this review was obtained through a search of PubMed and the Cochrane database for English-language studies published between January 1, 2000, and July 25, 2016. Ten randomized clinical trials and 8 systematic reviews were included. Findings One of the major clinical barriers facing the routine implementation of stem cell therapy in patients with cardiovascular disease is the limited and inconsistent benefit observed thus far. Reasons for this finding are unclear but may be owing to poor cell retention and survival, as suggested by numerous preclinical studies and a small number of human studies incorporating imaging to determine cell fate. Additional studies in humans using imaging to determine cell fate are needed to understand how these factors contribute to the limited efficacy of stem cell therapy. Treatment strategies to address poor cell retention and survival are under investigation and include the following: coadministration of immunosuppressive and prosurvival agents, delivery of cardioprotective factors packaged in exosomes rather than the cells themselves, and use of tissue-engineering strategies to provide structural support for cells. If larger grafts are achieved using these strategies, it will be imperative to carefully monitor for the potential risks of tumorigenicity, immunogenicity, and arrhythmogenicity. Conclusions and Relevance Despite important achievements to date, stem cell therapy is not yet ready for routine clinical implementation. Significant research is still needed to address the clinical barriers outlined herein before the next wave of large clinical trials is under way.

Wirelessly powering miniature implants for optogenetic stimulation

Conventional methods for in vivo optogenetic stimulation require optical fibers or mounted prosthesis. We present an approach for wirelessly powering implantable stimulators using electromagnetic midfield. By exploiting the properties of the midfield, we demonstrate the ability to generate high intensity light pulses in a freely moving animal.

Comparison of Magnetic Resonance Imaging and Serum Biomarkers for Detection of Human Pluripotent Stem Cell-Derived Teratomas.

Summary The use of cells derived from pluripotent stem cells (PSCs) for regenerative therapies confers a considerable risk for neoplastic growth and teratoma formation. Preclinical and clinical assessment of such therapies will require suitable monitoring strategies to understand and mitigate these risks. Here we generated human-induced pluripotent stem cells (iPSCs), selected clones that continued to express reprogramming factors after differentiation into cardiomyocytes, and transplanted these cardiomyocytes into immunocompromised rat hearts post-myocardial infarction. We compared magnetic resonance imaging (MRI), cardiac ultrasound, and serum biomarkers for their ability to delineate teratoma formation and growth. MRI enabled the detection of teratomas with a volume >8 mm3. A combination of three plasma biomarkers (CEA, AFP, and HCG) was able to detect teratomas with a volume >17 mm3 and with a sensitivity of more than 87%. Based on our findings, a combination of serum biomarkers with MRI screening may offer the highest sensitivity for teratoma detection and tracking.