Combination of cell delivery and thermoinducible transcription for in vivo spatiotemporal control of gene expression: a feasibility study

Spatiotemporally-controlled transgene expression in hydroxyapatite-fibrin composite scaffolds using high intensity focused ultrasound

Conventional tissue engineering approaches rely on scaffold-based delivery of exogenous proteins, genes, and/or cells to stimulate regeneration via growth factor signaling. However, scaffold-based approaches do not allow active control of dose, timing, or spatial localization of a delivered growth factor once the scaffold is implanted, yet these are all crucial parameters in promoting tissue regeneration. To address this limitation, we developed a stable cell line containing a heat-activated and rapamycin-dependent gene expression system. In this study, we investigate how high intensity focused ultrasound (HIFU) can spatiotemporally control firefly luciferase (fLuc) transgene activity both in vitro and in vivo by the tightly controlled generation of hyperthermia. Cells were incorporated into composite scaffolds containing fibrin and hydroxyapatite particles, which yielded significant increases in acoustic attenuation and heating in response to HIFU compared to fibrin alone. Using 2.5 MHz HIFU, transgene activation was observed at acoustic intensities of 201 W/cm2 and higher. Transgene activation was spatially patterned in the scaffolds by rastering HIFU at speeds up to 0.15 mm/s. In an in vivo study, a 67-fold increase in fLuc activity was observed in scaffolds exposed to HIFU and rapamycin versus rapamycin only at 2 days post implantation. Repeated activation of transgene expression was also demonstrated 8 days after implantation. No differences in in vivo scaffold degradation or compaction were observed between +HIFU and -HIFU groups. These results highlight the potential utility of using this heat-activated and rapamycin-dependent gene expression system in combination with HIFU for the controlled stimulation of tissue regeneration.

Imaging of conditional gene silencing in vivo using a bioluminescence-based method with thermo-inducible microRNAs

RNA interference (RNAi)-based gene therapy has great potential in cancer and infectious disease treatment to correct abnormal up-regulation of gene expression. We show a new original method uses synthetic microRNAs combined with a thermo-inducible promoter to reduce specific gene expression. The targeted gene is the luciferase firefly reporter gene overexpressed in a subcutaneous tumor which allows the RNAi monitoring by bioluminescence imaging (BLI). The inducible inhibition was first demonstrated in vitro using genetically modified cells lines and then in vivo using the corresponding xenograft model in mice. Achieving spatio-temporal control, we demonstrate the feasibility to induce, in vivo, a specific gene inhibition on demand. Future applications of this RNAi-based gene therapy, which can be restricted to pathological tissue, would offer wide-ranging potential for disease treatment.

Non-viral Gene Delivery

Although viral vectors comprise the majority of gene delivery vectors, their various safety, production, and other practical concerns have left a research gap to be addressed. The non-viral vector space encompasses a growing variety of physical and chemical methods capable of gene delivery into the nuclei of target cells. Major physical methods described in this chapter are microinjection, electroporation, and ballistic injection, magnetofection, sonoporation, optical transfection, and localized hyperthermia. Major chemical methods described in this chapter are lipofection, polyfection, gold complexation, and carbon-based methods. Combination approaches to improve transfection efficiency or reduce immunological response have shown great promise in expanding the scope of non-viral gene delivery.

In Vivo Imaging of Local Gene Expression Induced by Magnetic Hyperthermia

The present work aims to demonstrate that colloidal dispersions of magnetic iron oxide nanoparticles stabilized with dextran macromolecules placed in an alternating magnetic field can not only produce heat, but also that these particles could be used in vivo for local and noninvasive deposition of a thermal dose sufficient to trigger thermo-induced gene expression. Iron oxide nanoparticles were first characterized in vitro on a bio-inspired setup, and then they were assayed in vivo using a transgenic mouse strain expressing the luciferase reporter gene under transcriptional control of a thermosensitive promoter. Iron oxide nanoparticles dispersions were applied topically on the mouse skin or injected subcutaneously with Matrigel™ to generate so-called pseudotumors. Temperature was monitored continuously with a feedback loop to control the power of the magnetic field generator and to avoid overheating. Thermo-induced luciferase expression was followed by bioluminescence imaging 6 h after heating. We showed that dextran-coated magnetic iron oxide nanoparticle dispersions were able to induce in vivo mild hyperthermia compatible with thermo-induced gene expression in surrounding tissues and without impairing cell viability. These data open new therapeutic perspectives for using mild magnetic hyperthermia as noninvasive modulation of tumor microenvironment by local thermo-induced gene expression or drug release.

Spatiotemporal control of gene expression in bone-marrow derived cells of the tumor microenvironment induced by MRI guided focused ultrasound

The tumor microenvironment is an interesting target for anticancer therapies but modifying this compartment is challenging. Here, we demonstrate the feasibility of a gene therapy strategy that combined targeting to bone marrow-derived tumor microenvironment using genetically modified bone-marrow derived cells and control of transgene expression by local hyperthermia through a thermo-inducible promoter. Chimera were obtained by engraftment of bone marrow from transgenic mice expressing reporter genes under transcriptional control of heat shock promoter and inoculated sub-cutaneously with tumors cells. Heat shocks were applied at the tumor site using a water bath or magnetic resonance guided high intensity focused ultrasound device. Reporter gene expression was followed by bioluminescence and fluorescence imaging and immunohistochemistry. Bone marrow-derived cells expressing reporter genes were identified to be mainly tumor-associated macrophages. We thus provide the proof of concept for a gene therapy strategy that allows for spatiotemporal control of transgenes expression by macrophages targeted to the tumor microenvironment.

Use of Hydroxyapatite Doping to Enhance Responsiveness of Heat-Inducible Gene Switches to Focused Ultrasound

Recently, we demonstrated that ultrasound-based hyperthermia can activate cells containing a heat-activated and ligand-inducible gene switch in a spatio-temporally controlled manner. These engineered cells can be incorporated into hydrogel scaffolds (e.g., fibrin) for in vivo implantation, where ultrasound can be used to non-invasively pattern transgene expression. Due to their high water content, the acoustic attenuation of fibrin scaffolds is low. Thus, long ultrasound exposures and high acoustic intensities are needed to generate sufficient hyperthermia for gene activation. Here, we demonstrate that the attenuation of fibrin scaffolds and the resulting hyperthermia achievable with ultrasound can be increased significantly by doping the fibrin with hydroxyapatite (HA) nanopowder. The attenuation of a 1% (w/v) fibrin scaffold with 5% (w/v) HA was similar to soft tissue. Transgene activation of cells harboring the gene switch occurred at lower acoustic intensities and shorter exposures when the cells were encapsulated in HA-doped fibrin scaffolds versus undoped scaffolds. Inclusion of HA in the fibrin scaffold did not affect the viability of the encapsulated cells.

Remote spatiotemporally controlled and biologically selective permeabilization of blood-brain barrier

The blood-brain barrier (BBB), comprised of brain endothelial cells with tight junctions (TJ) between them, regulates the extravasation of molecules and cells into and out of the central nervous system (CNS). Overcoming the difficulty of delivering therapeutic agents to specific regions of the brain presents a major challenge to treatment of a broad range of brain disorders. Current strategies for BBB opening are invasive, not specific, and lack precise control over the site and timing of BBB opening, which may limit their clinical translation. In the present report, we describe a novel approach based on a combination of stem cell delivery, heat-inducible gene expression and mild heating with high-intensity focused ultrasound (HIFU) under MRI guidance to remotely permeabilize BBB. The permeabilization of the BBB will be controlled with, and limited to where selected pro-inflammatory factors will be secreted secondary to HIFU activation, which is in the vicinity of the engineered stem cells and consequently both the primary and secondary disease foci. This therapeutic platform thus represents a non-invasive way for BBB opening with unprecedented spatiotemporal precision, and if properly and specifically modified, can be clinically translated to facilitate delivery of different diagnostic and therapeutic agents which can have great impact in treatment of various disease processes in the central nervous system.

Release and pharmacokinetics of near-infrared labeled albumin from monodisperse poly(d,l-lactic-co-hydroxymethyl glycolic acid) microspheres after subcapsular renal injection

Subcapsular renal injection is a novel administration method for local delivery of therapeutics for the treatment of kidney related diseases. The aim of this study was to investigate the feasibility of polymeric microspheres for sustained release of protein therapeutics in the kidney and study the subsequent redistribution of the released protein. For this purpose, monodisperse poly(d,l-lactic-co-hydroxymethyl glycolic acid) (PLHMGA) microspheres (40 μm in diameter) loaded with near-infrared dye-labeled bovine serum albumin (NIR-BSA) were prepared by a membrane emulsification method. Rats were injected with either free NIR-BSA or with NIR-BSA loaded microspheres (NIR-BSA-ms) and the pharmacokinetics of the released NIR-BSA was studied for 3 weeks by ex vivo imaging of organs and blood. Quantitative release data were obtained from kidney homogenates and possible metabolism of the protein was investigated by SDS-PAGE analysis of the samples. The ex vivo images showed a rapid decrease of the NIR signal within 24h in kidneys injected with free NIR-BSA, while, importantly, the signal of the labeled protein was still visible at day 21 in kidneys injected with NIR-BSA-ms. SDS-PAGE analysis of the kidney homogenates showed that intact NIR-BSA was released from the microspheres. The locally released NIR-BSA drained to the systemic circulation and subsequently accumulated in the liver, where it was degraded and excreted renally. The in vivo release of NIR-BSA was calculated after extracting the protein from the remaining microspheres in kidney homogenates. The in vivo release rate was faster (89 ± 4% of the loading in 2 weeks) compared to the in vitro release of NIR-BSA (38 ± 1% in 2 weeks). In conclusion, PLHMGA microspheres injected under the kidney capsule provide a local depot from which a formulated protein is released over a prolonged time-period.

Effect of ultrasound on the permeability of vascular wall to nano-emulsion droplets

The effect of ultrasound on the permeability of blood vessels to nano-emulsion droplets was investigated using excised mouse carotid arteries as model blood vessels. Perfluorocarbon nano-droplets were formed by perfluoro-15-crown-5-ether and stabilized by poly(ethylene oxide)-co-poly(DL-lactide) block co-polymer shells. Nano-droplet fluorescence was imparted by interaction with fluorescein isothiocyanate-dextran (molecular weight = 70,000 Da). The permeability of carotid arteries to nano-droplets was studied in the presence and absence of continuous wave or pulsed therapeutic 1-MHz ultrasound. The data indicated that the application of ultrasound resulted in permeabilization of the vascular wall to nano-droplets. The effect of continuous wave ultrasound was substantially stronger than that of pulsed ultrasound of the same total energy. No effect of blood vessel pre-treatment with ultrasound was observed.

Regulation of gene expression in human prostate cancer cells with artificially constructed promoters that are activated in response to ultrasound stimulation

We chose promoters responsive to sonication in LNCap cells, a prostate cancer cell line, out of a library composed of DNA fragments constructed by linking the TATA box sequence to randomly combined cis-acting elements of transcription factors activated in response to radiation in prostate cancer cells. When a plasmid containing the luciferase gene under control of a promoter was transfected into LNCap cells and sonicated with 1 MHz ultrasound at 0.5 W/cm(2), 10% DF for 60s, 13 promoters showed more than 10-fold enhancement compared with their counterparts without sonication 12h after sonication. As to their responsiveness to sonication, the best two promoters were then compared to clone 880-8, a derivative from clone 880 that was created by random introduction of point mutations and was shown to have an improved response to X-ray irradiation. We then took clone 880-8 for further analyses since it showed the highest enhancement to sonication, though not statistically significant from the others. Next, we employed a retrovirus vector and stably introduced the luciferase gene under control of clone 880-8 into LNCap cells to establish a cell line. When the cell line was sonicated with 1 MHz ultrasound at 0.5 W/cm(2), 10% DF for 60s, luciferase expression was enhanced up to 14.8-fold 12h after sonication. We then established another cell line by replacing the luciferase gene with the fcy::fur gene, a suicide gene, and when the cell line was sonicated with 1 MHz ultrasound at 0.5 W/cm(2), 10% DF for 60s, expression of the gene was enhanced, showing the maximum expression 12-24h after sonication. When the cells were incubated in medium containing 5-fluorocytosine, cell survival ratio decreased dose dependently with 5-fluorocytosine only after sonication treatment, suggesting this promoter could be utilized for gene expression control with ultrasound.

Ultrasound stimulation induces microRNA expression changes that could be involved in sonication-induced apoptosis

PURPOSE

The purpose of this study is to investigate the involvement of microRNAs (miRNAs) in sonication-induced apoptosis.

METHODS

U937 cells derived from human leukemia were sonicated with 1-MHz ultrasound at 0.4 W/cm(2) and 10 % duty factor for 60 s, a condition inducing apoptosis. The total RNA was extracted from cells at various timings after sonication and subjected to microarray and real-time PCR for miRNA expression analyses.

RESULTS

Expression of several miRNAs was significantly affected by sonication. For miR-424* and miR-720, whose expressions were eminently decreased by sonication, cell lines overexpressing these miRNAs were established. Conversely, for miR-663B and miR-663, whose expressions were eminently increased by sonication, cell lines inhibiting these miRNA functions were established. When these cell lines were sonicated, a cell line inhibiting miR-663B function significantly increased sonication-induced apoptosis, suggesting this may be involved in cellular responses to sonication. Two genes that could induce apoptosis, KSR2 and CREBZF, were identified as potential target genes of miR-663B since potential target sequences on their 3' UTR mediated to decrease expression of a reporter gene.

CONCLUSION

These results suggest that miRNAs may be involved in cellular responses to ultrasound through their expression changes caused by sonication.

Control of the temperature rise in magnetic hyperthermia with use of an external static magnetic field

Our purpose in this study was to investigate the usefulness of a method for controlling the temperature rise in magnetic hyperthermia (MH) using an external static magnetic field (SMF), and to derive an empirical equation for describing the energy dissipation of magnetic nanoparticles (MNPs) in the presence of both the alternating magnetic field (AMF) and SMF through phantom experiments. We made a device that allows for MH in the presence of an SMF with a field-free point (FFP) using a Maxwell coil pair. We measured the temperature rise of MNPs under various conditions of AMF and SMF and various distances from the FFP (d), and calculated the specific absorption rate (SAR) from the initial slope of the temperature curve. The SAR values decreased with increasing strength of SMF (Hs) and d. The extent of their decrease with d increased with an increase of the gradient of SMF (Gs). The relationships between SAR and Hs and between SAR and d could be well approximated by Rosensweig's equation in which the amplitude of AMF (Hac) is replaced by √[Hac(2)]/√[Hac(2)+Hs(2)], except for the case when Gs was small. In conclusion, the use of an external SMF with an FFP will be effective for controlling the temperature rise in MH in order to reduce the risk of heating surrounding healthy tissues, and our empirical equation will be useful for estimating SAR in the presence of both the AMF and SMF and for designing an effective local heating system for MH.

Phase-shift, stimuli-responsive drug carriers for targeted delivery

The intersection of particles and directed energy is a rich source of novel and useful technology that is only recently being realized for medicine. One of the most promising applications is directed drug delivery. This review focuses on phase-shift nanoparticles (that is, particles of submicron size) as well as micron-scale particles whose action depends on an external-energy triggered, first-order phase shift from a liquid to gas state of either the particle itself or of the surrounding medium. These particles have tremendous potential for actively disrupting their environment for altering transport properties and unloading drugs. This review covers in detail ultrasound and laser-activated phase-shift nano- and micro-particles and their use in drug delivery. Phase-shift based drug-delivery mechanisms and competing technologies are discussed.

Phase-shift, stimuli-responsive perfluorocarbon nanodroplets for drug delivery to cancer

This review focuses on phase-shift perfluorocarbon nanoemulsions whose action depends on an ultrasound-triggered phase shift from a liquid to gas state. For drug-loaded perfluorocarbon nanoemulsions, microbubbles are formed under the action of tumor-directed ultrasound and drug is released locally into tumor volume in this process. This review covers in detail mechanisms involved in the droplet-to-bubble transition as well as mechanisms of ultrasound-mediated drug delivery.

Principles and basic concepts of molecular imaging

Advanced knowledge in molecular biology and new technological developments in imaging modalities and contrast agents calls for molecular imaging (MI) to play a major role in the near future in many human diseases (Weissleder and Mahmood Radiology 219:316-333, 2001). Imaging systems are providing higher signal-to-noise ratio and higher spatial and/or temporal resolution. New specific contrast agents offer the opportunity to drive new challenges for obtaining functional and biological information on tissue characteristics and tissue processes. All this information could be relevant for diagnosis, prognosis and treatment follow-up and to drive local therapies, enhancing local drug/gene delivery. The recent explosion of all these developments is a radical change of perspective in our imaging community because they could have a tremendous impact on our clinical practice and on teaching programs and they call for a more prominent multidisciplinary approach in this field of research.