Cathal J. Kearney

Ultrasound-triggered disruption and self-healing of reversibly cross-linked hydrogels for drug delivery and enhanced chemotherapy

Significance Drug-releasing polymers give clinicians the ability to deliver chemotherapy directly to tumors, sparing the rest of the body from toxic side effects. Most devices deliver a constant, unchangeable drug dose over time. However, we found that cancer cells are more sensitive to short-term, high-dose “bursts” of the chemotherapeutic mitoxantrone than to constant doses over longer periods, suggesting a benefit for implantable devices that allow external control over dose and timing. Biocompatible, injectable alginate hydrogels displayed the ability to self-heal damage induced by ultrasound pulses, enabling on-demand delivery of mitoxantrone, in vitro and in vivo, and mitoxantrone-loaded gels implanted near tumors were more effective at eliminating tumor growth when a daily pulse of ultrasound was applied. Biological systems are exquisitely sensitive to the location and timing of physiologic cues and drugs. This spatiotemporal sensitivity presents opportunities for developing new therapeutic approaches. Polymer-based delivery systems are used extensively for attaining localized, sustained release of bioactive molecules. However, these devices typically are designed to achieve a constant rate of release. We hypothesized that it would be possible to create digital drug release, which could be accelerated and then switched back off, on demand, by applying ultrasound to disrupt ionically cross-linked hydrogels. We demonstrated that ultrasound does not permanently damage these materials but enables nearly digital release of small molecules, proteins, and condensed oligonucleotides. Parallel in vitro studies demonstrated that the concept of applying temporally short, high-dose “bursts” of drug exposure could be applied to enhance the toxicity of mitoxantrone toward breast cancer cells. We thus used the hydrogel system in vivo to treat xenograft tumors with mitoxantrone, and found that daily ultrasound-stimulated drug release substantially reduced tumor growth compared with sustained drug release alone. This approach of digital drug release likely will be applicable to a broad variety of polymers and bioactive molecules, and is a potentially useful tool for studying how the timing of factor delivery controls cell fate in vivo.

Macroscale delivery systems for molecular and cellular payloads

Macroscale drug delivery (MDD) devices are engineered to exert spatiotemporal control over the presentation of a wide range of bioactive agents, including small molecules, proteins and cells. In contrast to systemically delivered drugs, MDD systems act as a depot of drug localized to the treatment site, which can increase drug effectiveness while reducing side effects and confer protection to labile drugs. In this Review, we highlight the key advantages of MDD systems, describe their mechanisms of spatiotemporal control and provide guidelines for the selection of carrier materials. We also discuss the combination of MDD technologies with classic medical devices to create multifunctional MDD devices that improve integration with host tissue, and the use of MDD technology in tissue-engineering strategies to direct cell behaviour. As our ever-expanding knowledge of human biology and disease provides new therapeutic targets that require precise control over their application, the importance of MDD devices in medicine is expected to increase.

Refilling drug delivery depots through the blood

Significance Drug delivery depots used in the clinic today are single use, with no ability to refill once exhausted of drug. Our system exploits nucleic acid complementarity to refill drug-delivering depots through the blood. The utility of this approach is demonstrated by its ability to inhibit tumor growth to a greater extent than strategies that rely on enhanced permeability and retention alone. We anticipate our approach will be directly applicable to therapies for many diseases, including cancer, wound healing, and inflammation, and for drug reloading of vascular grafts and stents. Local drug delivery depots have significant clinical utility, but there is currently no noninvasive technique to refill these systems once their payload is exhausted. Inspired by the ability of nanotherapeutics to target specific tissues, we hypothesized that blood-borne drug payloads could be modified to home to and refill hydrogel drug delivery systems. To address this possibility, hydrogels were modified with oligodeoxynucleotides (ODNs) that provide a target for drug payloads in the form of free alginate strands carrying complementary ODNs. Coupling ODNs to alginate strands led to specific binding to complementary-ODN–carrying alginate gels in vitro and to injected gels in vivo. When coupled to a drug payload, sequence-targeted refilling of a delivery depot consisting of intratumor hydrogels completely abrogated tumor growth. These results suggest a new paradigm for nanotherapeutic drug delivery, and this concept is expected to have applications in refilling drug depots in cancer therapy, wound healing, and drug-eluting vascular grafts and stents.

Substance P Promotes Wound Healing in Diabetes by Modulating Inflammation and Macrophage Phenotype

Diabetic foot ulceration is a major complication of diabetes. Substance P (SP) is involved in wound healing, but its effect in diabetic skin wounds is unclear. We examined the effect of exogenous SP delivery on diabetic mouse and rabbit wounds. We also studied the impact of deficiency in SP or its receptor, neurokinin-1 receptor, on wound healing in mouse models. SP treatment improved wound healing in mice and rabbits, whereas the absence of SP or its receptor impaired wound progression in mice. Moreover, SP bioavailability in diabetic skin was reduced as SP gene expression was decreased, whereas the gene expression and protein levels of the enzyme that degrades SP, neutral endopeptidase, were increased. Diabetes and SP deficiency were associated with absence of an acute inflammatory response important for wound healing progression and instead revealed a persistent inflammation throughout the healing process. SP treatment induced an acute inflammatory response, which enabled the progression to the proliferative phase and modulated macrophage activation toward the M2 phenotype that promotes wound healing. In conclusion, SP treatment reverses the chronic proinflammatory state in diabetic skin and promotes healing of diabetic wounds.

Sustained Delivery of VEGF Maintains Innervation and Promotes Reperfusion in Ischemic Skeletal Muscles Via NGF/GDNF Signaling

Tissue reinnervation following trauma, disease, or transplantation often presents a significant challenge. Here, we show that the delivery of vascular endothelial growth factor (VEGF) from alginate hydrogels ameliorates loss of skeletal muscle innervation after ischemic injury by promoting both maintenance and regrowth of damaged axons in mice. Nerve growth factor (NGF) and glial-derived neurotrophic factor (GDNF) mediated VEGF-induced axonal regeneration, and the expression of both is induced by VEGF presentation. Using both in vitro and in vivo modeling approaches, we demonstrate that the activity of NGF and GDNF regulates VEGF-driven angiogenesis, controlling endothelial cell sprouting and blood vessel maturation. Altogether, these studies produce evidence of new mechanisms of VEGF action, further broaden the understanding of the roles of NGF and GDNF in angiogenesis and axonal regeneration, and suggest approaches to improve axonal and ischemic tissue repair therapies.

CLINICAL APPLICATION OF EXTRACORPOREAL SHOCK WAVE THERAPY IN ORTHOPEDICS: FOCUSED VERSUS UNFOCUSED SHOCK WAVES

For the past decade extracorporeal shock wave therapy has been applied to a wide range of musculoskeletal disorders. The many promising results and the introduction of shock wave generators that are less expensive and easier to handle has added to the growing interest. Based on their nature of propagation, shock waves can be divided into two types: focused and unfocused. Although several physical differences between these different types of shock waves have been described, very little is known about the clinical outcome using these different modalities. The aim of the present review is to investigate differences in outcome in select orthopaedic applications using focused and unfocused shock waves.

Sequential Release of Nanoparticle Payloads from Ultrasonically Burstable Capsules

In many biomedical contexts ranging from chemotherapy to tissue engineering, it is beneficial to sequentially present bioactive payloads. Explicit control over the timing and dose of these presentations is highly desirable. Here, we present a capsule-based delivery system capable of rapidly releasing multiple payloads in response to ultrasonic signals. In vitro, these alginate capsules exhibited excellent payload retention for up to 1 week when unstimulated and delivered their entire payloads when ultrasonically stimulated for 10-100 s. Shorter exposures (10 s) were required to trigger delivery from capsules embedded in hydrogels placed in a tissue model and did not result in tissue heating or death of encapsulated cells. Different types of capsules were tuned to rupture in response to different ultrasonic stimuli, thus permitting the sequential, on-demand delivery of nanoparticle payloads. As a proof of concept, gold nanoparticles were decorated with bone morphogenetic protein-2 to demonstrate the potential bioactivity of nanoparticle payloads. These nanoparticles were not cytotoxic and induced an osteogenic response in mouse mesenchymal stem cells. This system may enable researchers and physicians to remotely regulate the timing, dose, and sequence of drug delivery on-demand, with a wide range of clinical applications ranging from tissue engineering to cancer treatment.

DNA Origami: Folded DNA‐Nanodevices That Can Direct and Interpret Cell Behavior

DNA origami is a DNA-based nanotechnology that utilizes programmed combinations of short complementary oligonucleotides to fold a large single strand of DNA into precise 2D and 3D shapes. The exquisite nanoscale shape control of this inherently biocompatible material is combined with the potential to spatially address the origami structures with diverse cargoes including drugs, antibodies, nucleic acid sequences, small molecules, and inorganic particles. This programmable flexibility enables the fabrication of precise nanoscale devices that have already shown great potential for biomedical applications such as: drug delivery, biosensing, and synthetic nanopore formation. Here, the advances in the DNA-origami field since its inception several years ago are reviewed with a focus on how these DNA-nanodevices can be designed to interact with cells to direct or probe their behavior.

Switchable Release of Entrapped Nanoparticles from Alginate Hydrogels

Natural biological processes are intricately controlled by the timing and spatial distribution of various cues. To mimic this precise level of control, the physical sizes of gold nanoparticles are utilized to sterically entrap them in hydrogel materials, where they are subsequently released only in response to ultrasound. These nanoparticles can transport bioactive factors to cells and direct cell behavior on-demand.

Extracorporeal shock wave-induced proliferation of periosteal cells

The cambium cells of the periosteum are an important cell source for select tissue engineering/regenerative medicine applications due to their osteogenic and chondrogenic potential. However, the cambium layer is only 2–5 cells thick, which complicates its harvest, and the low cell number limits its suitability for certain applications. Extracorporeal shock waves (ESWs) have been reported to cause periosteal osteogenesis following cambium layer thickening. This study quantified the proliferation of cambium cells in the femur and tibia of adult rats following ESW treatment at two different energy flux densities. Four days after application of ESWs, there was a significant (3‐ to 6‐fold) increase in cambium layer thickness and cell number. Proliferation was seen with an energy flux density as low as 0.15 mJ/mm2. The tibial cambium cells were more proliferative than those of the femur, with the cells closest to the ESW source proliferating the most. Within the thickened periosteum, α‐smooth muscle actin and von Willebrand Factor expression were upregulated, suggesting a vascular role in ESW osteogenesis. Bone formation was seen within the stimulated periosteum at day 4. We propose that non‐invasive ESWs can be used to rapidly stimulate cambium cell proliferation, providing a larger cell population for use as a progenitor cell source for tissue engineering applications, than can normally be provided by periosteum.