Po-n Chu

Magnetic resonance monitoring of focused ultrasound/magnetic nanoparticle targeting delivery of therapeutic agents to the brain

The superparamagnetic properties of magnetic nanoparticles (MNPs) allow them to be guided by an externally positioned magnet and also provide contrast for MRI. However, their therapeutic use in treating CNS pathologies in vivo is limited by insufficient local accumulation and retention resulting from their inability to traverse biological barriers. The combined use of focused ultrasound and magnetic targeting synergistically delivers therapeutic MNPs across the blood–brain barrier to enter the brain both passively and actively. Therapeutic MNPs were characterized and evaluated both in vitro and in vivo, and MRI was used to monitor and quantify their distribution in vivo. The technique could be used in normal brains or in those with tumors, and significantly increased the deposition of therapeutic MNPs in brains with intact or compromised blood–brain barriers. Synergistic targeting and image monitoring are powerful techniques for the delivery of macromolecular chemotherapeutic agents into the CNS under the guidance of MRI.

Blood-Brain Barrier Disruption with Focused Ultrasound Enhances Delivery of Chemotherapeutic Drugs for Glioblastoma Treatment

PURPOSE To demonstrate the feasibility of using focused ultrasound to enhance delivery of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) to glioblastomas in rats with induced tumors and determine if such an approach increases treatment efficacy. MATERIALS AND METHODS All animal experiments were approved by the animal committee and adhered to the experimental animal care guidelines. A 400-kHz focused ultrasound generator was used to transcranially disrupt the blood-brain barrier (BBB) in rat brains by delivering burst-tone ultrasound energy in the presence of microbubbles. The process was monitored in vivo by using magnetic resonance (MR) imaging. Cultured C6 glioma cells implanted in Sprague-Dawley rats were used as the tumor model. BCNU (13.5 mg/kg) was administered intravenously and its concentration in brains was quantified by using high-performance liquid chromatography. MR imaging was used to evaluate the effect of treatments longitudinally, including analysis of tumor progression and animal survival, and brain tissues were histologically examined. Methods including the two-tailed unpaired t test and the Mantel-Cox test were used for statistical analyses, with a significance level of .05. RESULTS Focused ultrasound significantly enhanced the penetration of BCNU through the BBB in normal (by 340%) and tumor-implanted (by 202%) brains without causing hemorrhaging. Treatment of tumor-implanted rats with focused ultrasound alone had no beneficial effect on tumor progression or on animal survival up to 60 days. Administration of BCNU only transiently controlled tumor progression; nevertheless, relative to untreated controls, animal survival was improved by treatment with BCNU alone (increase in median survival time [IST(median)], 15.7%, P = .023). Treatment with focused ultrasound before BCNU administration controlled tumor progression (day 31: 0.05 cm(3) + or - 0.1 [standard deviation] vs 0.28 cm(3) + or - 0.1) and improved animal survival relative to untreated controls (IST(median), 85.9%, P = .0015). CONCLUSION This study demonstrates a means of increasing localized chemotherapeutic drug delivery for brain tumor treatment and strongly supports the feasibility of this treatment in a clinical setting.

Smart Multifunctional Hollow Microspheres for the Quick Release of Drugs in Intracellular Lysosomal Compartments

Prepared to self-destruct: when poly(D, L-lactic-co-glycolic acid) (PLGA) hollow microspheres containing NaHCO(3) entered the endocytic organelles of a live cell, the NaHCO(3) in the aqueous core reacted with protons that infiltrated from the compartment to generate CO(2) gas. The evolution of CO(2) bubbles led to the formation of small holes in the PLGA shell and thus rapid release of the encapsulated drug doxorubicin.

Focused Ultrasound-Induced Blood–Brain Barrier Opening to Enhance Temozolomide Delivery for Glioblastoma Treatment: A Preclinical Study

The purpose of this study is to assess the preclinical therapeutic efficacy of magnetic resonance imaging (MRI)-monitored focused ultrasound (FUS)-induced blood-brain barrier (BBB) disruption to enhance Temozolomide (TMZ) delivery for improving Glioblastoma Multiforme (GBM) treatment. MRI-monitored FUS with microbubbles was used to transcranially disrupt the BBB in brains of Fisher rats implanted with 9L glioma cells. FUS-BBB opening was spectrophotometrically determined by leakage of dyes into the brain, and TMZ was quantitated in cerebrospinal fluid (CSF) and plasma by LC-MS\MS. The effects of treatment on tumor progression (by MRI), animal survival and brain tissue histology were investigated. Results demonstrated that FUS-BBB opening increased the local accumulation of dyes in brain parenchyma by 3.8-/2.1-fold in normal/tumor tissues. Compared to TMZ alone, combined FUS treatment increased the TMZ CSF/plasma ratio from 22.7% to 38.6%, reduced the 7-day tumor progression ratio from 24.03 to 5.06, and extended the median survival from 20 to 23 days. In conclusion, this study provided preclinical evidence that FUS BBB-opening increased the local concentration of TMZ to improve the control of tumor progression and animal survival, suggesting its clinical potential for improving current brain tumor treatment.

Novel magnetic/ultrasound focusing system enhances nanoparticle drug delivery for glioma treatment

Malignant glioma is a common and severe primary brain tumor with a high recurrence rate and an extremely high mortality rate within 2 years of diagnosis, even when surgical, radiological, and chemotherapeutic interventions are applied. Intravenously administered drugs have limited use because of their adverse systemic effects and poor blood-brain barrier penetration. Here, we combine 2 methods to increase drug delivery to brain tumors. Focused ultrasound transiently permeabilizes the blood-brain barrier, increasing passive diffusion. Subsequent application of an external magnetic field then actively enhances localization of a chemotherapeutic agent immobilized on a novel magnetic nanoparticle. Combining these techniques significantly improved the delivery of 1,3-bis(2-chloroethyl)-1-nitrosourea to rodent gliomas. Furthermore, the physicochemical properties of the nanoparticles allowed their delivery to be monitored by magnetic resonance imaging (MRI). The resulting suppression of tumor progression without damaging the normal regions of the brain was verified by MRI and histological examination. This noninvasive, reversible technique promises to provide a more effective and tolerable means of tumor treatment, with lower therapeutic doses and concurrent clinical monitoring.

Magnetic resonance imaging enhanced by superparamagnetic iron oxide particles: Usefulness for distinguishing between focused ultrasound-induced blood–brain barrier disruption and brain hemorrhage

To investigate the usefulness of a fully flow‐compensated heavy T2*‐weighted imaging enhanced by superparamagnetic iron oxide (SPIO) particles for distinguishing between focused ultrasound‐induced disruption of blood–brain barrier (BBB) and brain hemorrhage.

Cooperative dual-activity targeted nanomedicine for specific and effective prostate cancer therapy.

A key issue in cancer therapy is how to enhance the tumor-targeting efficacy of chemotherapeutic agents. In this study, we developed a cooperative dual-targeted delivery platform for paclitaxel (PTX) that has potential application as a powerful prostate cancer treatment. The nanomedicine was prepared by first conjugating PTX to nontoxic high-magnetization nanocarriers which can be actively guided and targeted by an external magnet. Next, the surface was functionalized with carboxylated o-(2-aminoethyl)polyethyleneglycol (NH(2)-EPEG-COOH) to enable uptake by the reticuloendothelial system. Antiprostate-specific membrane antigen antibodies (APSMAs) were then conjugated onto the carrier to recognize the extracellular domain of the prostate-cancer specific membrane antigen (PSMA), thus binding to cancer cells as a secondary active targeting mechanism. We found a significant enhancement of PTX concentration at the tumor site by nearly 20-fold. In addition, the drug half-life was prolonged more than 4.1-fold (from 24 to 99 h) at 37 °C. Low-dose (4.5 mg/kg) injection of the dual-targeted therapeutic nanomedicine in the presence of magnetic targeting significantly prolonged the median survival of nude mice from 35 to 58 days compared to mice that received a high dose (6 mg/kg) of free PTX. This report demonstrates the potential utility of targeted nanomedicine in the clinical treatment of cancer.

Pharmacodynamic Analysis of Magnetic Resonance Imaging-Monitored Focused Ultrasound-Induced Blood-Brain Barrier Opening for Drug Delivery to Brain Tumors

Microbubble-enhanced focused ultrasound (FUS) can enhance the delivery of therapeutic agents into the brain for brain tumor treatment. The purpose of this study was to investigate the influence of brain tumor conditions on the distribution and dynamics of small molecule leakage into targeted regions of the brain after FUS-BBB opening. A total of 34 animals were used, and the process was monitored by 7T-MRI. Evans blue (EB) dye as well as Gd-DTPA served as small molecule substitutes for evaluation of drug behavior. EB was quantified spectrophotometrically. Spin-spin (R1) relaxometry and area under curve (AUC) were measured by MRI to quantify Gd-DTPA. We found that FUS-BBB opening provided a more significant increase in permeability with small tumors. In contrast, accumulation was much higher in large tumors, independent of FUS. The AUC values of Gd-DTPA were well correlated with EB delivery, suggesting that Gd-DTPA was a good indicator of total small-molecule accumulation in the target region. The peripheral regions of large tumors exhibited similar dynamics of small-molecule leakage after FUS-BBB opening as small tumors, suggesting that FUS-BBB opening may have the most significant permeability-enhancing effect on tumor peripheral. This study provides useful information toward designing an optimized FUS-BBB opening strategy to deliver small-molecule therapeutic agents into brain tumors.

Magnetic-resonance imaging for kinetic analysis of permeability changes during focused ultrasound-induced blood-brain barrier opening and brain drug delivery.

Focused ultrasound (FUS) with the presence of microbubbles has been shown to induce transient and local opening of the blood-brain barrier (BBB) for the delivery of therapeutic molecules which normally cannot penetrate into the brain. The success of FUS brain-drug delivery relies on its integration with in-vivo imaging to monitor kinetic change of therapeutic molecules into the brain. In this study, we developed a dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) technique for kinetic analysis of delivered molecules during FUS-BBB opening. Three kinetic parameters (Ktrans, Ve, Kep) were characterized dynamically to describe BBB-permeability at two FUS exposure conditions (0.4 or 0.8MPa) over 24h. Ktrans, defined as the influx volume transfer constant from plasma to EES, and Ve, the EES volume fraction, were both found to be pressure-dependent. Ktrans and Ve showed a peak increase of 0.0086-0.0131min(-1) (for 0.4-0.8MPa pressure), and 0.0431-0.0692, respectively, immediately after FUS exposure. Both parameters subsequently decreased exponentially as a function of time, with estimated half-lives of decay of 2.89-5.3 and 2.2-4.93h, respectively. The kinetics of Kep, defined as the efflux rate constant from the extracellular extravascular space (EES) to the plasma, were complementary to Ktrans, with an initial decrease from 0.2010 to 0.1901min(-1) followed by a significantly longer recovery time (half-life of 17.39-99.92h). Our observations strongly supported the existence of imbalanced and mismatched kinetics of influx (Ktrans) and efflux (Kep) between the plasma and EES, indicating the existence of directional permeability during FUS-BBB opening. We further showed that kinetic change determined by DCE-MRI correlated well with the concentration of Evans Blue (EB)-albumin (coefficient of 0.74-0.89). These findings suggest that MRI kinetic monitoring may serve as an alternative method for in-vivo monitoring of pharmacokinetics and pharmacodynamics (PK/PD) change of therapeutic agents during drug delivery to the brain, and provide useful information for future optimization of FUS-BBB opening.

Neuromodulation accompanying focused ultrasound-induced blood-brain barrier opening

Burst-mode focused ultrasound (FUS) induces microbubble cavitation in the vasculature and temporarily disrupts the blood-brain barrier (BBB) to enable therapeutic agent delivery. However, it remains unclear whether FUS-induced BBB opening is accompanied by neuromodulation. Here we characterized the functional effects of FUS-induced BBB opening by measuring changes in somatosensory evoked potentials (SSEPs) and blood-oxygen-level dependent (BOLD) responses. Rats underwent burst-mode FUS (mechanical index (MI) of 0.3, 0.55 or 0.8) to the forelimb region in the left primary somatosensory cortex to induce BBB opening. Longitudinal measurements were followed for up to 1 week to characterize the temporal dynamics of neuromodulation. We observed that 0.8-MI FUS profoundly suppressed SSEP amplitude and prolonged latency, and this effect lasted 7 days. 0.55-MI FUS resulted in minimal and short-term suppression of SSEP for less than 60 minutes and didn’t affect latency. BOLD responses were also suppressed in an MI-dependent manner, mirroring the effect on SSEPs. Furthermore, repetitive delivery of 0.55-MI FUS every 3 days elicited no accumulative effects on SSEPs or tissue integrity. This is the first evidence that FUS-induced BBB opening is accompanied by reversible changes in neuron responses, and may provide valuable insight toward the development of FUS-induced BBB opening for clinical applications.