Enhanced Radiosensitization for Cancer Treatment with Gold Nanoparticles through Sonoporation.

We demonstrate the megavoltage (MV) radiosensitization of a human liver cancer line by combining gold-nanoparticle-encapsulated microbubbles (AuMBs) with ultrasound. Microbubbles-mediated sonoporation was administered for 5 min, at 2 h prior to applying radiotherapy. The intracellular concentration of gold nanoparticles (AuNPs) increased with the inertial cavitation of AuMBs in a dose-dependent manner. A higher inertial cavitation dose was also associated with more DNA damage, higher levels of apoptosis markers, and inferior cell surviving fractions after MV X-ray irradiation. The dose-modifying ratio in a clonogenic assay was 1.56 ± 0.45 for a 10% surviving fraction. In a xenograft mouse model, combining vascular endothelial growth factor receptor 2 (VEGFR2)-targeted AuMBs with sonoporation significantly delayed tumor regrowth. A strategy involving the spatially and temporally controlled release of AuNPs followed by clinically utilized MV irradiation shows promising results that make it worthy of further translational investigations.

In vivo photoacoustic molecular imaging with simultaneous multiple selective targeting using antibody-conjugated gold nanorods.

The use of gold nanorods for photoacoustic molecular imaging with simultaneous multiple targeting is reported. Multiple targeting is done by utilizing the tunable optical absorption property of gold nanorods. This technique allows multiple molecular signatures to be obtained by simply switching laser wavelength. HER2 and EGFR were chosen as the primary target molecules for examining two cancer cells, OECM1 and Cal27. Both in vitro and in vivo mouse model imaging experiments were performed, with contrast enhancement of up to 10 dB and 3.5 dB, respectively. The potential in improving cancer diagnosis is demonstrated.

Photoacoustic imaging of multiple targets using gold nanorods.

Photoacoustic (PA) imaging has been used mainly for anatomical and functional imaging. Although functionalized nanoparticles also have been developed for PA molecular imaging, only single targeting has been demonstrated. In this study, PA imaging of multiple targets using gold nanorods is demonstrated experimentally using HER2 and CXCR4 as target molecules. The two corresponding monoclonal antibodies were conjugated to two types of gold nanorod with different aspect ratios. Gold nanorods with mean aspect ratios of 5.9 and 3.7 exhibited peak optical absorptions at 1000 and 785 nm, respectively. Appropriate selection of laser irradiation wavelength enhances PA signals by 7-12 dB and allows signals from gold nanorods corresponding to specific bindings to be distinguished. This approach potentially allows the expression levels of different oncogenes of cancer cells to be revealed simultaneously.

Nanodroplet-Vaporization-Assisted Sonoporation for Highly Effective Delivery of Photothermal Treatment.

Sonoporation refers to the use of ultrasound and acoustic cavitation to temporarily enhance the permeability of cellular membranes so as to enhance the delivery efficiency of therapeutic agents into cells. Microbubble-based ultrasound contrast agents are often used to facilitate these cavitation effects. This study used nanodroplets to significantly enhance the effectiveness of sonoporation relative to using conventional microbubbles. Significant enhancements were demonstrated both in vitro and in vivo by using gold nanorods encapsulated in nanodroplets for implementing plasmonic photothermal therapy. Combined excitation by ultrasound and laser radiation is used to trigger the gold nanodroplets to induce a liquid-to-gas phase change, which induces cavitation effects that are three-to-fivefold stronger than when using conventional microbubbles. Enhanced cavitation also leads to significant enhancement of the sonoporation effects. Our in vivo results show that nanodroplet-vaporization-assisted sonoporation can increase the treatment temperature by more than 10 °C above that achieved by microbubble-based sonoporation.

Infrared-active quadruple contrast FePt nanoparticles for multiple scale molecular imaging.

A single nanomaterial with multiple imaging contrasts and functions is highly desired for multiscale theragnosis. Herein, we demonstrate single 1-1.9 µm infrared-active FePt alloy nanoparticles (FePt NPs) offering unprecedented four-contrast-in-one molecular imaging - computed tomography (CT), magnetic resonance imaging (MRI), photoacoustic (PA) imaging, and high-order multiphoton luminescence (HOMPL) microscopy. The PA response of FePt NPs outperforms that of infrared-active gold nanorods by 3- to 5.6-fold under identical excitation fluence and particle concentrations. HOMPL (680 nm) of an isolated FePt NP renders spatial full-width-at-half-maximum values of 432 nm and 300 nm beyond the optical diffraction limit for 1230-nm and 920-nm excitation, respectively. The in vivo targeting function was successfully visualized using HOMPL, PA imaging, CT, and MRI, thereby validating FePt as a single nanomaterial system covering up to four types (Optical/PA/CT/MRI) of molecular imaging contrast, ranging from the microscopic level to whole-body scale investigation.

Synergistic delivery of gold nanorods using multifunctional microbubbles for enhanced plasmonic photothermal therapy.

Plasmonic photothermal therapy (PPTT) using plasmonic nanoparticles as efficient photoabsorbing agents has been proposed previously. One critical step in PPTT is to effectively deliver gold nanoparticles into the cells. This study demonstrates that the delivery of gold nanorods (AuNRs) can be greatly enhanced by combining the following three mechanisms: AuNRs encapsulated in protein-shell microbubbles (AuMBs), molecular targeting, and sonoporation employing acoustic cavitation of microbubbles (MBs). Both in vitro and in vivo tests were performed. For molecular targeting, the AuMBs were modified with anti-VEGFR2. Once bound to the angiogenesis markers, the MBs were destroyed by ultrasound to release the AuNRs and the release was confirmed by photoacoustic measurements. Additionally, acoustic cavitation was induced during MB destruction for sonoporation (i.e., increase in transient cellular permeability). The measured inertial cavitation dose was positively correlated with the temperature increase at the tumor site. The quantity of AuNRs delivered into the cells was also determined by measuring the mass spectrometry and observed using third-harmonic-generation microscopy and two-photon fluorescence microscopy. A temperature increase of 20 °C was achieved in vitro. The PPTT results in vivo also demonstrated that the temperature increase (>45 °C) provided a sufficiently high degree of hyperthermia. Therefore, synergistic delivery of AuNRs was demonstrated.

Photoacoustic/ultrasound dual-modality contrast agent and its application to thermotherapy.

This study investigates a photoacoustic/ultrasound dual-modality contrast agent, including extending its applications from image-contrast enhancement to combined diagnosis and therapy with site-specific targeting. The contrast agent comprises albumin-shelled microbubbles with encapsulated gold nanorods (AuMBs). The gas-filled microbubbles, whose diameters range from submicrometer to several micrometers, are not only echogenic but also can serve as drug-delivery vehicles. The gold nanorods are used to enhance the generation of both photoacoustic and photothermal signals. The optical absorption peak of the gold nanorods is tuned to 760 nm and is invariant after microbubble encapsulation. Dual-modality contrast enhancement is first described here, and the applications to cellular targeting and laser-induced thermotherapy in a phantom are demonstrated. Photoacoustic imaging can be used to monitor temperature increases during the treatment. The targeting capability of AuMBs was verified, and the temperature increased by 26°C for a laser power of 980 mW, demonstrating the potential of combined diagnosis and therapy with the dual-modality agent. Targeted photo- or acoustic-mediated delivery is also possible.

Gold-nanorod contrast-enhanced photoacoustic micro-imaging of focused-ultrasound induced blood-brain-barrier opening in a rat model.

In this study, we develop a novel photoacoustic imaging technique based on gold nanorods (AuNRs) for quantitatively monitoring focused-ultrasound (FUS) induced blood-brain barrier (BBB) opening in a rat model in vivo. This study takes advantage of the strong near-infrared absorption (peak at ≈ 800 nm) of AuNRs and the extravasation tendency from BBB opening foci due to their nano-scale size to passively label the BBB disruption area. Experimental results show that AuNR contrast-enhanced photoacoustic microscopy (PAM) successfully reveals the spatial distribution and temporal response of BBB disruption area in the rat brains. The quantitative measurement of contrast enhancement has potential to estimate the local concentration of AuNRs and even the dosage of therapeutic molecules when AuNRs are further used as nano-carrier for drug delivery or photothermal therapy. The photoacoustic results also provide complementary information to MRI, being helpful to discover more details about FUS induced BBB opening in small animal models.

Photoacoustic flow measurements by use of laser-induced shape transitions of gold nanorods.

A quantitative technique for flow measurements based on a wash-in analysis is proposed. The technique makes use of the shape dependence of the optical absorption of gold nanorods and the transitions in their shape induced by pulsed laser irradiation. The photon-induced shape transition of gold nanorods involves mainly a rod-to-sphere conversion and a shift in the peak optical absorption wavelength. The application of a series of laser pulses will induce shape changes in gold nanorods as they flow through a region of interest, with quantitative flow information being derived from the photoacoustic signals from the irradiated gold nanorods measured as a function of time. To demonstrate the feasibility of the technique, a Nd:YAG laser operating at 1064 nm was used for irradiation and a 1 MHz ultrasonic transducer was used for acoustic detection. The flow velocity ranged from 0.35 to 2.83 mm/s. Excellent agreement between the measured velocities and the actual velocities was demonstrated, with a linear regression correlation coefficient of 0.93. This study is a pioneer work on wash-in flow estimation in photoacoustic imaging.