Ultrasonic gene and drug delivery to the cardiovascular system

Magnetic Nanodroplets for Enhanced Deep Penetration of Solid Tumors and Simultaneous Magnetothermal-Sensitized Immunotherapy against Tumor Proliferation and Metastasis

The central cells of solid tumors are more proliferative and metastatic than the marginal cells. Therefore, more intelligent strategies for targeting cells with deep spatial distributions in solid tumors remain to be explored. In this work, a biocompatible nanotheranostic agent with a lipid membrane-coated, Fe₃ O₄ and perfluoropentane (PFP)-loaded, cRGD peptide (specifically targeting the integrin αvβ3 receptor)-grafted, magnetic nanodroplets (MNDs) is developed. The MNDs exhibit excellent magnetothermal conversion and controllable magnetic hyperthermia (MHT) through alternating magnetic field regulation. Furthermore, MHT-mediated magnetic droplet vaporization (MDV) induces the expansion of the MNDs to transform them into ultrasonic microbubbles, increasing the permeability of tissue and the cell membrane via the ultrasound-targeted microbubble destruction (UTMD) technique and thereby promoting the deep penetration of MNDs in solid tumors. More importantly, MHT not only causes apoptotic damage by downregulating the expression of the HSP70, cyclin D1, and Bcl-2 proteins in tumor cells but also improves the response rate to T-cell-related immunotherapy by upregulating PD-L1 expression in tumor cells, thus inhibiting the growth of both primary and metastatic tumors. Overall, this work introduces a distinct application of nanoultrasonic biomedicine in cancer therapy and provides an attractive immunotherapy strategy for preventing the proliferation and metastasis of deeply distributed cells in solid tumors.

Comprehensive review on ultrasound-responsive theranostic nanomaterials: mechanisms, structures and medical applications

The field of theranostics has been rapidly growing in recent years and nanotechnology has played a major role in this growth. Nanomaterials can be constructed to respond to a variety of different stimuli which can be internal (enzyme activity, redox potential, pH changes, temperature changes) or external (light, heat, magnetic fields, ultrasound). Theranostic nanomaterials can respond by producing an imaging signal and/or a therapeutic effect, which frequently involves cell death. Since ultrasound (US) is already well established as a clinical imaging modality, it is attractive to combine it with rationally designed nanoparticles for theranostics. The mechanisms of US interactions include cavitation microbubbles (MBs), acoustic droplet vaporization, acoustic radiation force, localized thermal effects, reactive oxygen species generation, sonoluminescence, and sonoporation. These effects can result in the release of encapsulated drugs or genes at the site of interest as well as cell death and considerable image enhancement. The present review discusses US-responsive theranostic nanomaterials under the following categories: MBs, micelles, liposomes (conventional and echogenic), niosomes, nanoemulsions, polymeric nanoparticles, chitosan nanocapsules, dendrimers, hydrogels, nanogels, gold nanoparticles, titania nanostructures, carbon nanostructures, mesoporous silica nanoparticles, fuel-free nano/micromotors.

Ultrasound and Magnetic Responsive Drug Delivery Systems for Cardiovascular Application

With the increasing insight into molecular mechanisms of cardiovascular disease, a promising solution involves directly delivering genes, cells, and chemicals to the infarcted myocardium or impaired endothelium. However, the limited delivery efficiency after administration fails to reach the therapeutic dose and the adverse off-target effect even causes serious safety concerns. Controlled drug release via external stimuli seems to be a promising method to overcome the drawbacks of conventional drug delivery systems (DDSs). Microbubbles and magnetic nanoparticles responding to ultrasound and magnetic fields respectively have been developed as an important component of novel DDSs. In particular, several attempts have also been made for the design and fabrication of dual-responsive DDS. This review presents the recent advances in the ultrasound and magnetic fields responsive DDSs in cardiovascular application, followed by their current problems and future reformation.

Sonoporation Using Nanoparticle-Loaded Microbubbles Increases Cellular Uptake of Nanoparticles Compared to Co-Incubation of Nanoparticles and Microbubbles

Therapeutic agents can benefit from encapsulation in nanoparticles, due to improved pharmacokinetics and biodistribution, protection from degradation, increased cellular uptake and sustained release. Microbubbles in combination with ultrasound have been shown to improve the delivery of nanoparticles and drugs to tumors and across the blood-brain barrier. Here, we evaluate two different microbubbles for enhancing the delivery of polymeric nanoparticles to cells in vitro: a commercially available lipid microbubble (Sonazoid) and a microbubble with a shell composed of protein and nanoparticles. Various ultrasound parameters are applied and confocal microscopy is employed to image cellular uptake. Ultrasound enhanced cellular uptake depending on the pressure and duty cycle. The responsible mechanisms are probably sonoporation and sonoprinting, followed by uptake, and to a smaller degree enhanced endocytosis. The use of commercial Sonazoid microbubbles leads to significantly lower uptake than when using nanoparticle-loaded microbubbles, suggesting that proximity between cells, nanoparticles and microbubbles is important, and that mainly nanoparticles in the shell are taken up, rather than free nanoparticles in solution.

Microbubbles versus Extracellular Vesicles as Therapeutic Cargo for Targeting Drug Delivery

Extracellular vesicles (EVs) and microbubbles are nanoparticles in drug-delivery systems that are both considered important for clinical translation. Current research has found that both microbubbles and EVs have the potential to be utilized as drug-delivery agents for therapeutic targets in various diseases. In combination with EVs, microbubbles are capable of delivering chemotherapeutic drugs to tumor sites and neighboring sites of damaged tissues. However, there are no standards to evaluate or to compare the benefits of EVs (natural carrier) versus microbubbles (synthetic carrier) as drug carriers. Both drug carriers are being investigated for release patterns and for pharmacokinetics; however, few researchers have focused on their targeted delivery or efficacy. In this Perspective, we compare EVs and microbubbles for a better understanding of their utility in terms of delivering drugs to their site of action and future clinical translation.

Thrombin-responsive engineered nanoexcavator with full-thickness infiltration capability for pharmaceutical-free deep venous thrombosis theranostics

Although nanotechnology has shown great promise for treating multiple vascular diseases in recent years, simultaneous noninvasive detection and efficient dissolution of deep venous thrombosis (DVT) still remains challenging. In particular, long blockage areas and large thrombus thicknesses in DVT cause enormous difficulties for site-specific deep-seated thrombus theranostics. Therefore, based on the unique components of DVT, the novel concept of a thrombin-responsive full-thickness infiltration nonpharmaceutical nanoplatform for DVT theranostics is proposed here. The penetration depth is innovatively enhanced with efficient targeting and accumulation in the whole thrombi. Herein, we report a thrombin-responsive phase-transition liposome incorporating a liquid perfluoropentane (PFP) core and modified with two binding peptides, activatable cell-penetrating peptide (ACPP) and fibrin-binding ligand (FTP), which contribute to efficient liposome targeting and accumulation within the thrombi. This targeted nanoplatform is constructed to dig out the thrombus with the assistance of low-intensity focused ultrasound (LIFU), performing the destructive function of an excavator via an acoustic droplet vaporization effect (acting as a "nanoexcavator" system), which can activate and vaporize into microbubbles to enhance LIFU efficacy. The resulting microbubbles enable real-time monitoring of the therapeutic process with ultrasound imaging and high performance photoacoustic imaging after loading DIR. This non-invasive nonpharmaceutical thrombolytic strategy is an improvement over existing clinical methods without systemic side effects.

In situconversion of rose bengal microbubbles into nanoparticles for ultrasound imaging guided sonodynamic therapy with enhanced antitumor efficacy

Sonosensitizer microbubbles enhance drug accumulation and the antitumor efficacy of sonodynamic therapy by ultrasound mediated micro to nano conversion.

An activated-platelet-sensitive nanocarrier enables targeted delivery of tissue plasminogen activator for effective thrombolytic therapy

It remains a major challenge to develop a selective and effective fibrinolytic system for thrombolysis with minimal undesirable side effects. Herein, we report a multifunctional liposomal system (164.6 ± 5.3 nm in diameter) which can address this challenge through targeted delivery and controlled release of tissue plasminogen activator (tPA) at the thrombus site. The tPA-loaded liposomes were PEGylated to improve their stability, and surface coated with a conformationally-constrained, cyclic arginine-glycine-aspartic acid (cRGD) to enable highly selective binding to activated platelets. The in vitro drug release profiles at 37 °C showed that over 90% of tPA was released through liposomal membrane destabilization involving membrane fusion upon incubation with activated platelets within 1 h, whereas passive release of the encapsulated tPA in pH 7.4 PBS buffer was 10% after 6 h. The release of tPA could be readily manipulated by changing the concentration of activated platelets. The presence of activated platelets enabled the tPA-loaded, cRGD-coated, PEGylated liposomes to induce efficient fibrin clot lysis in a fibrin-agar plate model and the encapsulated tPA retained 97.4 ± 1.7% of fibrinolytic activity as compared with that of native tPA. Furthermore, almost complete blood clot lysis was achieved in 75 min, showing considerably higher and quicker thrombolytic activity compared to the tPA-loaded liposomes without cRGD labelling. These results suggest that the nano-sized, activated-platelet-sensitive, multifunctional liposomes could facilitate selective delivery and effective release of tPA at the site of thrombus, thus achieving efficient clot dissolution whilst minimising undesirable side effects.

Protein Kinase A as a Promising Target for Heart Failure Drug Development

Heart failure (HF) is a clinical syndrome characterized by impaired ability of the heart to fill or eject blood. HF is rather prevalent and it represents the foremost reason of hospitalization in the United States. The costs linked to HF overrun those of all other causes of disabilities, and death in the United States and all over the developed as well as the developing countries which amplify the supreme significance of its prevention. Protein kinase (PK) A plays multiple roles in heart functions including, contraction, metabolism, ion fluxes, and gene transcription. Altered PKA activity is likely to cause the progression to cardiomyopathy and HF. Thus, this review is intended to focus on the roles of PKA and PKA-mediated signal transduction in the healthy heart as well as during the development of HF. Furthermore, the impact of cardiac PKA inhibition/activation will be highlighted to identify PKA as a potential target for the HF drug development.

Gene delivery nanoparticles to modulate angiogenesis

Angiogenesis is naturally balanced by many pro- and anti-angiogenic factors while an imbalance of these factors leads to aberrant angiogenesis, which is closely associated with many diseases. Gene therapy has become a promising strategy for the treatment of such a disordered state through the introduction of exogenous nucleic acids that express or silence the target agents, thereby engineering neovascularization in both directions. Numerous non-viral gene delivery nanoparticles have been investigated towards this goal, but their clinical translation has been hampered by issues associated with safety, delivery efficiency, and therapeutic effect. This review summarizes key factors targeted for therapeutic angiogenesis and anti-angiogenesis gene therapy, non-viral nanoparticle-mediated approaches to gene delivery, and recent gene therapy applications in pre-clinical and clinical trials for ischemia, tissue regeneration, cancer, and wet age-related macular degeneration. Enhanced nanoparticle design strategies are also proposed to further improve the efficacy of gene delivery nanoparticles to modulate angiogenesis.

Pulsed-wave low-dose ultrasound hyperthermia selectively enhances nanodrug delivery and improves antitumor efficacy for brain metastasis of breast cancer

The clinical application of chemotherapeutics for brain tumors remains a challenge due to limitation of blood-brain barrier/blood-tumor barrier (BBB/BTB). In this study, we investigated the effects of low-dose focused ultrasound hyperthermia (UH) on the delivery and therapeutic efficacy of pegylated liposomal doxorubicin (PLD) for brain metastasis of breast cancer. Murine breast cancer cells (4T1-luc2) expressing firefly luciferase were implanted into mouse striatum as a brain tumor model. The mice were intravenously injected with PLD with/without transcranial pulsed-wave/continuous-wave UH (pUH/cUH) treatment on day-6 after tumor implantation. pUH (frequency: 500kHz, PRF: 1000Hz, duty cycle: 50%) was conducted under equal acoustic power (2.2-Watt) and sonication duration (10-min) as cUH. The amounts of doxorubicin accumulated in the normal brain and tumor tissues were measured with fluorometry. The tumor growth responses for the control, pUH, PLD, PLD+cUH, and PLD+pUH groups were evaluated with IVIS. The PLD distribution and cell apoptosis were assessed with immunofluorescence staining. The results showed that pUH significantly enhanced the PLD delivery into brain tumors and the tumor growth was further inhibited by PLD+pUH without damaging the sonicated normal brain tissues. This indicates that low-dose transcranial pUH is a promising method to selectively enhance nanodrug delivery and improve the brain tumor treatment.

Localized Delivery of shRNA against PHD2 Protects the Heart from Acute Myocardial Infarction through Ultrasound-Targeted Cationic Microbubble Destruction

Hypoxia-inducible factor 1α (HIF-1α) plays a critical protective role in ischemic heart disease. Under normoxic conditions, HIF-1α was degraded by oxygen-dependent prolyl hydroxylase-2 (PHD2). Gene therapy has become a promising strategy to inhibit the degradation of HIF-1α and to improve cardiac function after ischemic injury. However, conventional gene delivery systems are difficult to achieve a targeted and localized gene delivery into the ischemic myocardia. Here, we report the localized myocardial delivery of shRNA against PHD2 through ultrasound-targeted microbubble destruction (UTMD) for protection the heart from acute myocardial infarction. In this study, a novel cationic microbubble was fabricated by using of the thin-film hydration and sonication method. The resulting microbubbles had a 28.2 ± 2.21 mV surface zeta potential and could greatly improve DNA binding performance, achieving 17.81 ± 1.46 μg of DNA loading capacity per 5 × 10⁸ microbubbles. Combined with these cationic microbubbles, UTMD-mediated gene delivery was evaluated and the gene transfection efficiency was optimized in the H9C2 cardiac cells. Knockdown of PHD2 gene was successfully realized by UTMD-mediated shPHD2 transfection, resulting in HIF-1α-dependent protective effects on H9C2 cells through increasing the expression of HIF-1α, VEGF and bFGF. We further employed UTMD-mediated shPHD2 transfection into the localized ischemic myocardia in a rat ischemia model, demonstrating significantly reduced infarct size and greatly improved the heart function. The silencing of PHD2 and the up-regulation of its downstream genes in the treated myocardia were confirmed. Histological analysis further revealed numbers of HIF-1α- and VEGF-, and CD31-positive cells/mm² in the shPHD2-treated group were significantly greater than those in the sham or control vector groups (P < 0.05). In conclusion, our study provides a promising strategy to realize ultrasound-mediated localized myocardial shRNA delivery to protect the heart from acute myocardial infarction via cationic microbubbles.

Inhibition of prostate cancer growth using doxorubicin assisted by ultrasound-targeted nanobubble destruction

Ultrasound (US)-targeted microbubble destruction has been widely used as an effective drug-delivery system. However, nanobubbles (NBs) have better stability and stronger penetration than microbubbles, and drug delivery assisted by US-targeted NB destruction (UTND) still needs to be investigated. Our aim was to investigate the effect of doxorubicin (DOX) on the inhibition of prostate cancer growth under UTND. Contrast-enhanced US imaging of transplanted PC3 prostate cancer in mice showed that under a combination of 1 W/cm² US power and a 100 Hz intermittent pulse with a “5 seconds on, 5 seconds off” mode, NBs with an average size of (485.7±33) nm were effectively destroyed within 15 minutes in the tumor location. PC3 cells and 20 tumor-bearing mice were divided into four groups: a DOX group, a DOX + NB group, a DOX + US group, and a DOX + NB + US group. The cell growth-inhibition rate and DOX concentration of xenografts in the DOX + NB + US group were highest. Based on another control group and these four groups, another 25 tumor-bearing mice were used to observe the treatment effect of nine DOX injections under UTND. The xenografts in the DOX + NB + US group decreased more obviously and had more cellular apoptosis than other groups. Finally, electron microscopy was used to estimate the cavitation effect of NBs under US irradiation in the control group, NB group, US group, and NB + US group. The results of scanning electron microscopy showed that PC3 cells in the DOX + NB + US group had more holes and significantly increased cell-surface folds. Meanwhile, transmission electric microscopy confirmed that more lanthanum nitrate particles entered the parenchymal cells in xenografts in the NB + US group compared with the other groups. This study suggested that UTND technology could be an effective method to promote drugs to function in US-irradiated sites, and the underlying mechanism may be associated with a cavitation effect.

Optical Verification of Microbubble Response to Acoustic Radiation Force in Large Vessels With In Vivo Results

OBJECTIVE

The objective of this study was to optically verify the dynamic behaviors of adherent microbubbles in large blood vessel environments in response to a new ultrasound technique using modulated acoustic radiation force.

MATERIALS AND METHODS

Polydimethylsiloxane (PDMS) flow channels coated with streptavidin were used in targeted groups to mimic large blood vessels. The custom-modulated acoustic radiation force beam sequence was programmed on a Verasonics research scanner. In vitro experiments were performed by injecting a biotinylated lipid-perfluorobutane microbubble dispersion through flow channels. The dynamic response of adherent microbubbles was detected acoustically and simultaneously visualized using a video camera connected to a microscope. In vivo verification was performed in a large abdominal blood vessel of a murine model for inflammation with injection of biotinylated microbubbles conjugated with P-selectin antibody.

RESULTS

Aggregates of adherent microbubbles were observed optically under the influence of acoustic radiation force. Large microbubble aggregates were observed solely in control groups without targeted adhesion. Additionally, the dispersion of microbubble aggregates were demonstrated to lead to a transient acoustic signal enhancement in control groups (a new phenomenon we refer to as "control peak"). In agreement with in vitro results, the control peak phenomenon was observed in vivo in a murine model.

CONCLUSIONS

This study provides the first optical observation of microbubble-binding dynamics in large blood vessel environments with application of a modulated acoustic radiation force beam sequence. With targeted adhesion, secondary radiation forces were unable to produce large aggregates of adherent microbubbles. Additionally, the new phenomenon called control peak was observed both in vitro and in vivo in a murine model for the first time. The findings in this study provide us with a better understanding of microbubble behaviors in large blood vessel environments with application of acoustic radiation force and could potentially guide future beam sequence designs or signal processing routines for enhanced ultrasound molecular imaging.

The partitioning of nanoparticles to endothelium or interstitium during ultrasound-microbubble-targeted delivery depends on peak-negative pressure

Patients diagnosed with advanced peripheral arterial disease often face poor prognoses and have limited treatment options. For some patient populations, the therapeutic growth of collateral arteries (i.e. arteriogenesis) that bypass regions affected by vascular disease may become a viable treatment option. Our group and others are developing therapeutic approaches centered on the ability of ultrasound-activated microbubbles to permeabilize skeletal muscle capillaries and facilitate the targeted delivery of pro-arteriogenic growth factor-bearing nanoparticles. The development of such approaches would benefit significantly from a better understanding of how nanoparticle diameter and ultrasound peak-negative pressure affect both total nanoparticle delivery and the partitioning of nanoparticles to endothelial or interstitial compartments. Toward this goal, using Balb/C mice that had undergone unilateral femoral artery ligation, we intra-arterially co-injected nanoparticles (50 and 100 nm) with microbubbles, applied 1 MHz ultrasound to the gracilis adductor muscle at peak-negative pressures of 0.7, 0.55, 0.4, and 0.2 MPa, and analyzed nanoparticle delivery and distribution. As expected, total nanoparticle (50 and 100 nm) delivery increased with increasing peak-negative pressure, with 50 nm nanoparticles exhibiting greater tissue coverage than 100 nm nanoparticles. Of particular interest, increasing peak-negative pressure resulted in increased delivery to the interstitium for both nanoparticle sizes, but had little influence on nanoparticle delivery to the endothelium. Thus, we conclude that alterations to peak-negative pressure may be used to adjust the fraction of nanoparticles delivered to the interstitial compartment. This information will be useful when designing ultrasound protocols for delivering pro-arteriogenic nanoparticles to skeletal muscle.

Targeted microbubbles: a novel application for the treatment of kidney stones

Kidney stone disease is endemic. Extracorporeal shockwave lithotripsy was the first major technological breakthrough where focused shockwaves were used to fragment stones in the kidney or ureter. The shockwaves induced the formation of cavitation bubbles, whose collapse released energy at the stone, and the energy fragmented the kidney stones into pieces small enough to be passed spontaneously. Can the concept of microbubbles be used without the bulky machine? The logical progression was to manufacture these powerful microbubbles ex vivo and inject these bubbles directly into the collecting system. An external source can be used to induce cavitation once the microbubbles are at their target; the key is targeting these microbubbles to specifically bind to kidney stones. Two important observations have been established: (i) bisphosphonates attach to hydroxyapatite crystals with high affinity; and (ii) there is substantial hydroxyapatite in most kidney stones. The microbubbles can be equipped with bisphosphonate tags to specifically target kidney stones. These bubbles will preferentially bind to the stone and not surrounding tissue, reducing collateral damage. Ultrasound or another suitable form of energy is then applied causing the microbubbles to induce cavitation and fragment the stones. This can be used as an adjunct to ureteroscopy or percutaneous lithotripsy to aid in fragmentation. Randall's plaques, which also contain hydroxyapatite crystals, can also be targeted to pre-emptively destroy these stone precursors. Additionally, targeted microbubbles can aid in kidney stone diagnostics by virtue of being used as an adjunct to traditional imaging methods, especially useful in high-risk patient populations. This novel application of targeted microbubble technology not only represents the next frontier in minimally invasive stone surgery, but a platform technology for other areas of medicine.

A setup for the assessment of the effect of tubular confinement on the acoustic response of microbubbles

Ultrasound contrast agents are gas filled microbubbles which produced enhanced echoes in ultrasound imaging thus allowing the acquisition of detailed information on the path of blood. It is theoretically known that the size of a vessel affects the behavior of a microbubble, which could potentially be used to discriminate different sized vessels. This information would be useful in the monitoring of neovascularization in tumor growth or treatment. However, currently it is not possible to identify the vessel diameter by any means of signal processing of microbubble echoes. In order to assess microbubble behavior when confined in tubes we compared the acoustic backscatter from biSphere™ microbubbles both free in water and flowing in 200 μm diameter tubes that are similar in size to arterioles. Experimental systems that allow the interrogation of individual microbubbles were designed and modified to allow investigation of both free microbubbles and those in tubes. Unprocessed single microbubble RF data were collected, allowing the calculation of both the fundamental and second harmonic components of the backscattered signal. Microbubbles confined in tubes had lower amplitude response compared to unconfined microbubbles. On consecutive insonations of the same microbubble, free microbubbles produced echoes above noise more often than confined microbubbles. This setup may be used to investigate microbubble behavior in a range of smaller tubes with diameters similar to capillaries thus enabling signal processing design for vessel differentiation.

Ultrasound-based measurement of molecular marker concentration in large blood vessels: a feasibility study

Ultrasound molecular imaging has demonstrated efficacy in pre-clinical studies for cancer and cardiovascular inflammation. However, these techniques often require lengthy protocols because of waiting periods or additional control microbubble injections. Moreover, they are not capable of quantifying molecular marker concentration in human tissue environments that exhibit variable attenuation and propagation path lengths. Our group recently investigated a modulated acoustic radiation force-based imaging sequence, which was found to detect targeted adhesion independent of control measurements. In the present study, this sequence was tested against various experimental parameters to determine its feasibility for quantitative measurements of molecular marker concentration. Results indicated that measurements obtained from the sequence (residual-to-saturation ratio, Rresid) were independent of acoustic pressure and attenuation (p > 0.13, n = 10) when acoustic pressures were sufficiently low. The Rresid parameter exhibited a linear relationship with measured molecular marker concentration (R(2) > 0.94). Consequently, feasibility was illustrated in vitro, for quantification of molecular marker concentration in large vessels using a modulated acoustic radiation force-based sequence. Moreover, these measurements were independent of absolute acoustic reflection amplitude and used short imaging protocols (3 min) without control measurements.

EGFP gene transfection into the synovial joint tissues of rats with rheumatoid arthritis by ultrasound-mediated microbubble destruction

The aim of the present study was to explore the feasibility of enhancing green fluorescent protein (EGFP) gene transfection into the synovial joint tissues of rats with rheumatoid arthritis (RA) by ultrasound-mediated microbubble destruction. An optimal SonoVue dose was determined using 40 normal rats categorized into five groups according to the various doses of microbubbles used. At 1 week after ultrasound irradiation, the rats were sacrificed. Damage to the joint synovial tissues was observed with hematoxylin and eosin histopathological staining under a microscope. A further 44 normal rats were used to establish a rat model of RA, and were then categorized into four groups: EGFP, ultrasound + EGFP, microbubbles + EGFP and ultrasound + microbubbles + EGFP. The last group was irradiated with ultrasound for 10 min following the injection of 300 μl SonoVue and 10 μg EGFP into the joint cavity. Rats were sacrificed after 3 days and synovial tissue was collected from the knee joints for observation of EGFP with fluorescence microscopy and analysis by quantitative polymerase chain reaction. EGFP expression was observed in the synovial tissues of all groups. However, high EGFP expression levels were observed in the ultrasound + microbubbles + EGFP group. No statistically significant differences (P>0.05) were observed in the EGFP expression levels between the EGFP, ultrasound + EGFP and microbubbles + EGFP groups. However, EGFP expression levels in the EGFP, ultrasound + EGFP and microbubbles + EGFP groups significantly differed (P<0.05) from that in the ultrasound + microbubbles + EGFP group. Therefore, ultrasound-mediated microbubble destruction improved EGFP transfection efficiency into the joint synovial tissues of rats with RA.

Ultrasound-mediated microbubble destruction increases renal interstitial capillary permeability in early diabetic nephropathy rats

Diabetic nephropathy (DN) is defined as persistent proteinuria corresponding to a urinary albumin excretion rate >300 μg/mg in the absence of other non-diabetic renal diseases. The aim of this study was to determine if ultrasound (US)-mediated microbubble (MB) destruction could increase renal interstitial capillary permeability in early DN rats. Diabetes was induced with streptozotocin. DN rats presented with mild micro-albuminuria 30 d after onset of diabetes. DN rats (N = 120) were divided into four groups that received Evans blue (EB) followed by: (i) no treatment (control group); (ii) continuous ultrasonic irradiation for 5 min (frequency = 7.00 MHz, mechanical index = 0.9, peak rarefactional pressure = 2.38 MPa: US group); (iii) microbubble injection (0.05 mL/kg: MB group); and (iv) both ultrasound and microbubble injection (US + MB group). Another 8 DN rats were subjected to ultrasound and microbubbles and then injected with EB after 24 h (recovery group). EB content, EB extravasation and E-selectin mRNA and protein expression significantly increased, and interstitial capillary walls became discontinuous in the US + MB group. Neither hemorrhage nor necrosis was observed on renal histology. Urine samples were collected 24 h post-treatment. There was no hematuria, and the urinary albumin excretion rate did not increase after ultrasound-microbubble interaction detected by urinalysis. EB content returned to the control group level after 24 h, as assessed for the recovery group. In conclusion, ultrasound-mediated microbubble destruction locally increased renal interstitial capillary permeability in DN rats, and should be considered a therapy for enhancing drug and gene delivery to the kidney in the future.

Understanding ultrasound induced sonoporation: definitions and underlying mechanisms

In the past two decades, research has underlined the potential of ultrasound and microbubbles to enhance drug delivery. However, there is less consensus on the biophysical and biological mechanisms leading to this enhanced delivery. Sonoporation, i.e. the formation of temporary pores in the cell membrane, as well as enhanced endocytosis is reported. Because of the variety of ultrasound settings used and corresponding microbubble behavior, a clear overview is missing. Therefore, in this review, the mechanisms contributing to sonoporation are categorized according to three ultrasound settings: i) low intensity ultrasound leading to stable cavitation of microbubbles, ii) high intensity ultrasound leading to inertial cavitation with microbubble collapse, and iii) ultrasound application in the absence of microbubbles. Using low intensity ultrasound, the endocytotic uptake of several drugs could be stimulated, while short but intense ultrasound pulses can be applied to induce pore formation and the direct cytoplasmic uptake of drugs. Ultrasound intensities may be adapted to create pore sizes correlating with drug size. Small molecules are able to diffuse passively through small pores created by low intensity ultrasound treatment. However, delivery of larger drugs such as nanoparticles and gene complexes, will require higher ultrasound intensities in order to allow direct cytoplasmic entry.

Phase transitions of perfluorocarbon nanoemulsion induced with ultrasound: a mathematical model

While ultrasound has been used in many medical and industrial applications, only recently has research been done on phase transformations induced by ultrasound. This paper presents a numerical model and the predicted results of the phase transformation of a spherical nanosized droplet of perfluorocarbon in water. Such a model has applications in acoustic droplet vaporization, the generation of gas bubbles for medical imaging, therapeutic delivery and other biomedical applications. The formation of a gas phase and the subsequent bubble dynamics were studied as a function of acoustic parameters, such as frequency and amplitude, and of the physical aspects of the perfluorocarbon nanodroplets, such as chemical species, temperature, droplet size and interfacial energy. The model involves simultaneous applications of mass, energy and momentum balances to describe bubble formation and collapse, and was developed and solved numerically. It was found that, all other parameters being constant, the maximum bubble size and collapse velocity increases with increasing ultrasound amplitude, droplet size, vapor pressure and temperature. The bubble size and collapse velocity decreased with increasing surface tension and frequency. These results correlate with experimental observations of acoustic droplet vaporization.

Binding dynamics of targeted microbubbles in response to modulated acoustic radiation force

Detection of molecular targeted microbubbles plays a foundational role in ultrasound-based molecular imaging and targeted gene or drug delivery. In this paper, an empirical model describing the binding dynamics of targeted microbubbles in response to modulated acoustic radiation forces in large vessels is presented and experimentally verified using tissue-mimicking flow phantoms. Higher flow velocity and microbubble concentration led to faster detaching rates for specifically bound microbubbles (p < 0.001). Higher time-averaged acoustic radiation force intensity led to faster attaching rates and a higher saturation level of specifically bound microbubbles (p < 0.05). The level of residual microbubble signal in targeted experiments after cessation of radiation forces was the only response parameter that was reliably different between targeted and control experiments (p < 0.05). A related parameter, the ratio of residual-to-saturated microbubble signal (Rresid), is proposed as a measurement that is independent of absolute acoustic signal magnitude and therefore able to reliably detect targeted adhesion independently of control measurements (p < 0.01). These findings suggest the possibility of enhanced detection of specifically bound microbubbles in real-time, using relatively short imaging protocols (approximately 3 min), without waiting for free microbubble clearance.

Ultrasound-targeted microbubble destruction-mediated gene delivery into canine livers

Ultrasound (US) was applied to a targeted canine liver lobe simultaneously with injection of plasmid DNA (pDNA)/microbubble (MB) complexes into a portal vein (PV) segmental branch and occlusion of the inferior vena cava (IVC) to facilitate DNA uptake. By using a 1.1 MHz, 13 mm diameter transducer, a fivefold increase in luciferase activity was obtained at 3.3 MPa peak negative pressure (PNP) in the treated lobe. For more effective treatment of large tissue volumes in canines, a planar unfocused transducer with a large effective beam diameter (52 mm) was specifically constructed. Its apodized dual element configuration greatly reduced the near-field transaxial pressure variations, resulting in a remarkably uniform field of US exposure for the treated tissues. Together with a 15 kW capacity US amplifier, a 692-fold increase of gene expression was achieved at 2.7 MPa. Transaminase and histology analysis indicated minimal tissue damage. These experiments represent an important developmental step toward US-mediated gene delivery in large animals and clinics.

Contrast imaging and gene delivery through the combined use of novel cationic liposomal microbubbles and ultrasound in rat carotid arteries

INTRODUCTION

Lipid-coated cationic microbubbles represent a new class of agents with both diagnostic and therapeutic applications. The main goal of this study was to evaluate the efficiency of gene transfer through the combined use of microbubbles and ultrasound in rat carotid arteries. Furthermore, we assessed whether the cationic liposomal microbubbles could allow long-term enhanced imaging, comparing with SonoVue(®).

MATERIAL AND METHODS

Normal rat carotid arteries were imaged after intravenous bolus injections of 0.5 ml/kg of two contrast agents (SonoVue(®) and the cationic liposomal microbubbles). Forty Sprague-Dawley rats were divided into 5 groups according to ultrasound parameters and were treated with or without microbubbles. All rats were sacrificed after being transfected for 2 days. The level of protein expression was determined by western blot analysis.

RESULTS

The enhancing time of self-made microbubbles was much longer than that of SonoVue(®) in rat carotid arteries (p < 0.05). The results of the western blot analysis revealed that the expression of SR-BI DNA in the carotid artery was highest in the SR-BI + US/CLM group (p < 0.05).

CONCLUSIONS

These results suggest that the novel cationic liposomal microbubbles enhance image quality over a longer period than does SonoVue(®). Additionally, the combination of ultrasound and this new type of microbubble can act synergistically to increase SR-BI DNA transfection.

Real-time imaging and kinetics measurements of focused ultrasound-induced extravasation in skeletal muscle using SPECT/CT

Drugs need to overcome several biological barriers such as the endothelium and cellular membranes in order to reach their target. Promising new therapeutics, many of which are charged and macromolecular, are not able to passively extravasate, let alone cross cell membranes, and stay mainly in the blood pool upon intravenous injection until clearance. Using focused ultrasound (fUS) in combination with circulating microbubbles (MBs) leads to temporary localized tissue permeabilization allowing extravasation of (macro) molecules from the vascular system. Thus, fUS is a promising approach for localized drug delivery. However, little is known about the permeabilization kinetics in skeletal muscle. In this study, we used single photon emission computed tomography (SPECT) to characterize the kinetics of extravasation of ¹¹¹In-labeled bovine serum albumin (BSA), a model macromolecular drug, in muscle treated with fUS and MBs. The same fUS protocol was applied to 6 groups of mice with different times, ∆t, between fUS application and BSA injection (∆t=-10, 2.5, 10, 30, 60, 90 min) followed by SPECT imaging. For ∆t ≤30min we observed an exponential accumulation of activity in an area of the treated muscle which extended to a volume larger than the fUS pattern with highest accumulation for short waiting times ∆t. The extent of extravasation decreased exponentially with increasing ∆t, with a calculated half-life of ca. 21 min, defining the time window of extravasation. The same treatment without MBs did not induce extravasation of BSA thus supporting MBs and drug co-injection strategies. These results provide essential information for the development of fUS based strategies for localized drug delivery.

Breakup of finite thickness viscous shell microbubbles by ultrasound: a simplified zero-thickness shell model

A simplified three-dimensional (3-D) zero-thickness shell model was developed to recover the non-spherical response of thick-shelled encapsulated microbubbles subjected to ultrasound excitation. The model was validated by comparison with previously developed models and was then used to study the mechanism of bubble break-up during non-spherical deformations resulting from the presence of a nearby rigid boundary. The effects of the shell thickness and the bubble standoff distance from the solid wall on the bubble break-up were studied parametrically for a fixed insonification frequency and amplitude. A diagram of bubble shapes versus the normalized shell thickness and wall standoff was derived, and the potential bubble shapes at break-up from reentrant jets were categorized resulting in four distinct zones.

Enhanced gene expression of systemically administered plasmid DNA in the liver with therapeutic ultrasound and microbubbles

Ultrasound-mediated delivery (USMD) of novel therapeutic agents in the presence of microbubbles is a potentially safe and effective method for gene therapy offering many desired characteristics, such as low toxicity, potential for repeated treatment, and organ specificity. In this study, we tested the capability of USMD to improve gene expression in mice livers using glycogen storage disease Type Ia as a model disease under systemic administration of naked plasmid DNA. Image-guided therapeutic ultrasound was used in two studies to provide therapeutic ultrasound to mice livers. In the first study, involving wild-type mice, control animals received naked plasmid DNA (pG6Pase 150 μg) via the tail vein, followed by an infusion of microbubbles; the treated animals additionally received therapeutic ultrasound (1 MHz). Following the procedure, the animals were left to recover and were subsequently euthanized after 2 d and liver samples were extracted. Reverse transcription polymerase chain reaction (RT-PCR) assays were performed on the samples to quantify mRNA expression. In addition, Western blot assays of FLAG-tagged glucose-6-phosphatase (G6Pase) were performed to evaluate protein expression. Ultrasound-exposed animals showed a 4-fold increase in G6Pase RNA in the liver, in comparison with control animals. Furthermore, results from Western blot analysis demonstrated a 2-fold increased protein expression in ultrasound-exposed animals after two days ( p < 0.05). A second pilot study was performed with G6Pase knockout mice, and the animals were monitored for correction of hypoglycemia over a period of 3 weeks before tissue analysis. The RT-PCR assays of samples from these animals demonstrated increased G6Pase RNA in the liver following ultrasound treatment. These results demonstrate that USMD can increase gene expression of systemically injected naked pDNA in the liver and also provide insight into the development of realistic approaches that can be translated into clinical practice.

Intravascular ultrasound detection and delivery of molecularly targeted microbubbles for gene delivery

We are investigating the combination of microbubble-based targeted drug delivery and intravascular ultrasound (IVUS) imaging as a potential therapy to reduce incidence of restenosis following stent placement in atherosclerotic coronary arteries. The goal of these studies was to determine whether IVUS could be used to detect targeted microbubbles and enhance drug/gene delivery through targeting. Quiescent vascular smooth muscle cells (SMCs) were stimulated with cytokine IL-1β to induce the inflammatory cell surface marker vascular cell adhesion molecule 1 (VCAM-1). Molecular-targeted (VCAM-1 Ab or IgG control Ab), fluorescent-labeled microbubbles were conjugated with plasmid DNA expressing green fluorescent protein (GFP, pMax-GFP) and exposed to the inflamed SMCs under flow to measure adhesion compared with control microbubbles. Gene delivery was performed using a modified IVUS catheter to generate 1.5-MHz ultrasound at 200 kPa. Detection of adherent microbubbles to inflamed SMCs in culture and flow chambers was measured using an IVUS catheter and scanner. VCAM-1-targeted microbubbles enhanced adhesion to inflamed SMCs 100-fold over nontargeted microbubbles. Compared with noninflamed SMCs, VCAM-1-targeted microbubbles exhibited a 7.9-fold increase in adhesion to IL-1β-treated cells. Targeted microbubbles resulted in a 5.5-fold increase in plasmid DNA transfection over nontargeted microbubbles in conjunction with a focused 2.54-cm (1-in) diameter 1-MHz transducer and also enhanced transfection by the modified IVUS transducer at 1.5 MHz. Targeted microbubbles (at a density of 3 × 10⁴ microbubbles/mm²) increased IVUS image intensity 13.2 dB over non-microbubble-coated surfaces. Rupture of microbubbles from the modified IVUS transducer resulted in a 53% reduction in image intensity. Taken together, these results indicate that IVUS may be used to detect targeted microbubbles to inflamed vasculature and subsequently deliver a gene/drug locally.

Enhancing effect of ultrasound-mediated microbubble destruction on gene delivery into rat kidney via different administration routes

OBJECTIVE

To investigate the efficiency of β-galactosidase gene transfer into rat kidney with ultrasound-mediated microbubble destruction via different injection routes.

METHODS

A total of 25 Wistar rats were randomly divided into 5 groups. Four groups received a mixture of optison microbubbles (0.2 mL) and lacz plasmids (25 μg) injection via renal artery, tail vein, anterior tibial muscle and renal parenchyma, respectively. The control group received a mixture of PBS (xx mL) and lacz plasmids (25 μg) via renal artery. Three days after the gene transfer, ultrasound with fixed frequency and power (1 MHz, xxW) was delivered to the kidneys for 3 min. The efficiency of the gene transfer and expression was evaluated on the basis of β-galactosidase expression. The side effects of this method were evaluated by immunohistological method.

RESULTS

β-galactosidase expression could be observed only in tubules but not in glomeruli and interstitial area. The efficiency of renal artery group was higher than that of tail vein, anterior tibial muscle and renal parenchyma group (P<0.05). Immunohistochemical analysis revealed co-expression of β-galactosidase with a roximal tubule marker, megalin, which suggested that ultrasound enhanced gene transfer into the proximal tubular epithelial cells. No β-galactosidase expression was observed in the extrarenal organs. There were no evident pathological and biochemical changes after gene transfer.

CONCLUSIONS

Ultrasound-mediated microbubble destruction can transfer gene into kidney via renal artery, tail vein, anterior tibial muscle and renal parenchyma. Compared with renal artery, administrating microbubbles via tail vein and anterior tibial muscle are more convenient and less vulnerarious.

PEGylation for drug delivery to ischemic myocardium: pharmacokinetics and cardiac distribution of poly(ethylene glycol)s in mice with normal and ischemic myocardium

PEGylation now plays an important role in drug delivery and is considered as the method of choice for improving the pharmacokinetics and stability of parenteral agents. However, its application in treating cardiac diseases is still limited. To guide the design of PEGylation for drug delivery to ischemic myocardium, the effects of the molecular weight of PEG and the myocardial ischemic conditions on PEG levels in plasma and myocardium were studied in this work following intravenous administration of fluorescein isothiocyanate-labeled 20- and 40-kDa mPEGs to mice with normal and ischemic myocardium. The results show that myocardial ischemia caused some consistent changes in pharmacokinetic parameters of mPEGs. Due to the enhanced permeability and retention (EPR) effect caused by ischemia, the distribution of 20- and 40-kDa mPEGs in ischemic hearts was approximately 1.47- and 1.92-fold higher than that in normal hearts, respectively. Under the same heart condition (either normal or ischemic), the cardiac AUC(0.5-24h)s of the two mPEGs were comparable, although their plasma AUCs differed by nearly 4-fold; however, a smoother cardiac level-time profile was achieved by 40-kDa mPEG. This study addressed the relative importance of the EPR effect of ischemic zones and the molecular size of PEG in cardiac drug delivery, which is believed to be helpful for macromolecular drug design.

Adjuvant early and late cardioprotective therapy: access to the heart

Coronary heart disease is still the leading cause of death in industrialized nations, occurring either as acute coronary occlusion and myocardial infarction or as chronic ischaemic cardiomyopathy caused by continuous obstruction of one or more coronary arteries. Even after successful reperfusion, an additional loss of otherwise vital cardiomyocytes may occur in the primary ischaemic area, called lethal reperfusion injury. In experimental settings, delivery of therapeutic agents targeting the reperfusion injury reduces the infarct size by 30%. In addition to the choice of therapeutic agent and time point, the mode of application may be crucial for the therapeutic success. Therefore, this review focuses on the current and future administration techniques for early and late post-myocardial infarction therapies.

Production of uniformly sized serum albumin and dextrose microbubbles

Uniformly-sized preparations with average microbubble (MB) diameters from 1 to 7 μm were produced reliably by sonicating decafluorobutane-saturated solutions of serum albumin and dextrose. Detailed protocols for producing and size-separating the MBs are presented, along with the effects that changing each production parameter (serum albumin concentration, sonication power, sonication time, etc.) had on MB size distribution and acoustic stability. These protocols can be used to produce MBs for experimental applications or serve as templates for developing new protocols that yield MBs with physical and acoustic properties better suited to specific applications. Size stability and ultrasonic performance quality control tests were developed to assure that successive MB preparations perform identically and to distinguish the physical and acoustic properties of identically sized MBs produced with different serum albumin-dextrose formulations and sonication parameters. MBs can be stored at 5 °C for protracted periods (2 weeks to one year depending on formulation).

Contrast agent-free sonoporation: The use of an ultrasonic standing wave microfluidic system for the delivery of pharmaceutical agents

Sonoporation is a useful biophysical mechanism for facilitating the transmembrane delivery of therapeutic agents from the extracellular to the intracellular milieu. Conventionally, sonoporation is carried out in the presence of ultrasound contrast agents, which are known to greatly enhance transient poration of biological cell membranes. However, in vivo contrast agents have been observed to induce capillary rupture and haemorrhage due to endothelial cell damage and to greatly increase the potential for cell lysis in vitro. Here, we demonstrate sonoporation of cardiac myoblasts in the absence of contrast agent (CA-free sonoporation) using a low-cost ultrasound-microfluidic device. Within this device an ultrasonic standing wave was generated, allowing control over the position of the cells and the strength of the acoustic radiation forces. Real-time single-cell analysis and retrospective post-sonication analysis of insonated cardiac myoblasts showed that CA-free sonoporation induced transmembrane transfer of fluorescent probes (CMFDA and FITC-dextran) and that different mechanisms potentially contribute to membrane poration in the presence of an ultrasonic wave. Additionally, to the best of our knowledge, we have shown for the first time that sonoporation induces increased cell cytotoxicity as a consequence of CA-free ultrasound-facilitated uptake of pharmaceutical agents (doxorubicin, luteolin, and apigenin). The US-microfluidic device designed here provides an in vitro alternative to expensive and controversial in vivo models used for early stage drug discovery, and drug delivery programs and toxicity measurements.

βIIPKC and εPKC isozymes as potential pharmacological targets in cardiac hypertrophy and heart failure

Cardiac hypertrophy is a complex adaptive response to mechanical and neurohumoral stimuli and under continual stressor, it contributes to maladaptive responses, heart failure and death. Protein kinase C (PKC) and several other kinases play a role in the maladaptative cardiac responses, including cardiomyocyte hypertrophy, myocardial fibrosis and inflammation. Identifying specific therapies that regulate these kinases is a major focus of current research. PKC, a family of serine/threonine kinases, has emerged as potential mediators of hypertrophic stimuli associated with neurohumoral hyperactivity in heart failure. In this review, we describe the role of PKC isozymes that is involved in cardiac hypertrophy and heart failure. This article is part of a special issue entitled "Key Signaling Molecules in Hypertrophy and Heart Failure".

Noninvasive and localized neuronal delivery using short ultrasonic pulses and microbubbles

Focused ultrasound activation of systemically administered microbubbles is a noninvasive and localized drug delivery method that can increase vascular permeability to large molecular agents. Yet the range of acoustic parameters responsible for drug delivery remains unknown, and, thus, enhancing the delivery characteristics without compromising safety has proven to be difficult. We propose a new basis for ultrasonic pulse design in drug delivery through the blood-brain barrier (BBB) that uses principles of probability of occurrence and spatial distribution of cavitation in contrast to the conventionally applied magnitude of cavitation. The efficacy of using extremely short (2.3 μs) pulses was evaluated in 27 distinct acoustic parameter sets at low peak-rarefactional pressures (0.51 MPa or lower). The left hippocampus and lateral thalamus were noninvasively sonicated after administration of Definity microbubbles. Disruption of the BBB was confirmed by delivery of fluorescently tagged 3-, 10-, or 70-kDa dextrans. Under some conditions, dextrans were distributed homogeneously throughout the targeted region and accumulated at specific hippocampal landmarks and neuronal cells and axons. No histological damage was observed at the most effective parameter set. Our results have broadened the design space of parameters toward a wider safety window that may also increase vascular permeability. The study also uncovered a set of parameters that enhances the dose and distribution of molecular delivery, overcoming standard trade-offs in avoiding associated damage. Given the short pulses used similar to diagnostic ultrasound, new critical parameters were also elucidated to clearly separate therapeutic ultrasound from disruption-free diagnostic ultrasound.

See, reach, treat: ultrasound-triggered image-guided drug delivery

The integration of therapeutic interventions with diagnostic imaging has been recognized as one of the next technological developments that will have a major impact on medical treatments. Therapeutic applications using ultrasound, for example thermal ablation, hyperthermia or ultrasound-induced drug delivery, are examples for image-guided interventions that are currently being investigated. While thermal ablation using magnetic resonance-guided high-intensity focused ultrasound is entering the clinic, ultrasound-mediated drug delivery is still in a research phase, but holds promise to enable new applications in localized treatments. The use of ultrasound for the delivery of drugs has been demonstrated, particularly in the field of cardiology and oncology for a variety of therapeutics ranging from small-molecule drugs to biologics and nucleic acids exploiting temperature- or pressure-mediated delivery schemes.

Protein expression of mesenchymal stem cells after transfection of pcDNA3.1⁻-hVEGF₁₆₅ by ultrasound-targeted microbubble destruction

Ultrasound-targeted microbubble destruction (UTMD) has been proposed as a new technique for organ-specific gene transfer and drug delivery. This study was performed to investigate the effect of UTMD on marrow mesenchymal stem cells (MSCs) transfected with pcDNA3.1⁻-hVEGF₁₆₅.pcDNA3.1⁻-hVEGF₁₆₅ were transfected into the third passage of MSCs, with or without UTMD under different ultrasound conditions. Protein expression was quantified by hVEGF₁₆₅-ELISA kit after transfection for 24, 48, and 72 hours. UTMD-mediated transfection of MSCs yielded a significant protein expression. UTMD of mechanic index (MI) 0.6 for 90 seconds led to the highest level of protein expression.

Development of polymeric microbubbles targeted to prostate-specific membrane antigen as prototype of novel ultrasound contrast agents

Ultrasound-targeted microbubbles (MBs) offer new opportunities to enhance the capabilities of diagnostic ultrasound (US) imaging to specific pathological tissue. Herein, we report on the design and development of a novel prototype of US contrast agent based on polymeric MBs targeted to prostate-specific membrane antigen (PSMA) for use in the diagnosis of prostate cancer (PCa). First, a set of air-filled MBs by a variety of biocompatible polymers were prepared and characterized in terms of morphology and echogenic properties after exposure to US. MBs derived from poly(D,L-lactic-co-glycolic acid) (PLGA)-poly(ethylene glycol) (PEG) copolymer resulted as the most effective in terms of reflectivity. Such polymer was therefore preconjugated with a urea-based PSMA inhibitor molecular probe (DCL), and the obtained MBs were investigated in vitro for their targeting efficacy toward PSMA positive PCa (LNCaP) cells. Fluorescence microscopy proved a specific and efficient adhesion of targeted MBs to LNCaP cells. To our knowledge, this work reports the first model of polymeric MBs appropriately engineered to target PSMA, which might be further optimized and used for PCa diagnosis and potential carriers for selective drug delivery.