Design of multi-modal antenna arrays for microwave hyperthermia and 1H/1⁹F MRI monitoring of drug release

This simulation-based study presented a novel hybrid RF antenna array designed for neck cancer treatment within a 7T MRI system. The proposed design aimed to provide microwave hyperthermia to release 19F-labeled anticancer drugs from thermosensitive liposomes, facilitating drug concentration monitoring through 19F imaging and enabling 1H anatomical imaging and MR thermometry for temperature control. The design featured a bidirectional microstrip for generating the magnetic |B1|-fields required for 1H and 19F MR imaging, along with a patch antenna for localized RF heating. The bidirectional microstrip was operated at 300 MHz and 280 MHz through the placement of excitation ports at the ends of the antenna and an asymmetric structure along the antenna. Additionally, a patch antenna was positioned at the center. Based on this setup, an array of six antennas was designed. Simulation results using a tissue-mimicking simulation model confirmed the intensity and uniformity of |B1|-fields for both 19F and 1H nuclei, demonstrating the suitability of the design for clinical imaging. RF heating from the patch antennas was effectively localized at the center of the cancer model. In simulations with a human model, average |B1|-fields were 0.21 μT for 19F and 0.12 μT for 1H, with normalized-absolute-average-deviation values of 81.75% and 87.74%, respectively. Hyperthermia treatment was applied at 120 W for 600 s, achieving an average temperature of 40.22°C in the cancer model with a perfusion rate of 1 ml/min/kg. This study demonstrated the potential of a hybrid antenna array for integrating 1H MR, 19F drug monitoring, and hyperthermia.

MR-labelled liposomes and focused ultrasound for spatiotemporally controlled drug release in triple negative breast cancers in mice

Rationale: Image-guided, triggerable, drug delivery systems allow for precisely placed and highly localised anti-cancer treatment. They contain labels for spatial mapping and tissue uptake tracking, providing key location and timing information for the application of an external stimulus to trigger drug release. High Intensity Focused Ultrasound (HIFU or FUS) is a non-invasive approach for treating small tissue volumes and is particularly effective at inducing drug release from thermosensitive nanocarriers. Here, we present a novel MR-imageable thermosensitive liposome (iTSL) for drug delivery to triple-negative breast cancers (TNBC). Methods: A macrocyclic gadolinium-based Magnetic Resonance Imaging (MRI) contrast agent was covalently linked to a lipid. This was incorporated at 30 mol% into the lipid bilayer of a thermosensitive liposome that was also encapsulating doxorubicin. The resulting iTSL-DOX formulation was assessed for physical and chemical properties, storage stability, leakage of gadolinium or doxorubicin, and thermal- or FUS-induced drug release. Its effect on MRI relaxation time was tested in phantoms. Mice with tumours were used for studies to assess both tumour distribution and contrast enhancement over time. A lipid-conjugated near-infrared fluorescence (NIRF) probe was also included in the liposome to facilitate the real time monitoring of iTSL distribution and drug release in tumours by NIRF bioimaging. TNBC (MDA-MB-231) tumour-bearing mice were then used to demonstrate the efficacy at retarding tumour growth and increasing survival. Results: iTSL-DOX provided rapid FUS-induced drug release that was dependent on the acoustic power applied. It was otherwise found to be stable, with minimum leakage of drug and gadolinium into buffers or under challenging conditions. In contrast to the usually suggested longer FUS treatment we identified that brief (~3 min) FUS significantly enhanced iTSL-DOX uptake to a targeted tumour and triggered near-total release of encapsulated doxorubicin, causing significant growth inhibition in the TNBC mouse model. A distinct reduction in the tumours' average T1 relaxation times was attributed to the iTSL accumulation. Conclusions: We demonstrate that tracking iTSL in tumours using MRI assists the application of FUS for precise drug release and therapy.

Minireview: Biophysical Mechanisms of Cell Membrane Sonopermeabilization. Knowns and Unknowns

Microbubble-assisted ultrasound has emerged as a promising method for the delivery of low-molecular-weight chemotherapeutic molecules, nucleic acids, therapeutic peptides, and antibodies in vitro and in vivo. Its clinical applications are under investigation for local delivery drug in oncology and neurology. However, the biophysical mechanisms supporting the acoustically mediated membrane permeabilization are not fully established. This review describes the present state of the investigations concerning the acoustically mediated stimuli (i.e., mechanical, chemical, and thermal stimuli) as well as the molecular and cellular actors (i.e., membrane pores and endocytosis) involved in the reversible membrane permeabilization process. The different hypotheses, which were proposed to give a biophysical description of the membrane permeabilization, are critically discussed.

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.

Sonochemotherapy: from bench to bedside

The combination of microbubbles and ultrasound has emerged as a promising method for local drug delivery. Microbubbles can be locally activated by a targeted ultrasound beam, which can result in several bio-effects. For drug delivery, microbubble-assisted ultrasound is used to increase vascular- and plasma membrane permeability for facilitating drug extravasation and the cellular uptake of drugs in the treated region, respectively. In the case of drug-loaded microbubbles, these two mechanisms can be combined with local release of the drug following destruction of the microbubble. The use of microbubble-assisted ultrasound to deliver chemotherapeutic agents is also referred to as sonochemotherapy. In this review, the basic principles of sonochemotherapy are discussed, including aspects such as the type of (drug-loaded) microbubbles used, the routes of administration used in vivo, ultrasound devices and parameters, treatment schedules and safety issues. Finally, the clinical translation of sonochemotherapy is discussed, including the first clinical study using sonochemotherapy.

Characterization of a setup to test the impact of high-amplitude pressure waves on living cells

The impact of pressure waves on cells may provide several possible applications in biology and medicine including the direct killing of tumors, drug delivery or gene transfection. In this study we characterize the physical properties of mechanical pressure waves generated by a nanosecond laser pulse in a setup with well-defined cell culture conditions. To systematically characterize the system on the relevant length and time scales (micrometers and nanoseconds) we use photon Doppler velocimetry (PDV) and obtain velocity profiles of the cell culture vessel at the passage of the pressure wave. These profiles serve as input for numerical pressure wave simulations that help to further quantify the pressure conditions on the cellular length scale. On the biological level we demonstrate killing of glioblastoma cells and quantify experimentally the pressure threshold for cell destruction.

Gold nanorod-mediated hyperthermia enhances the efficacy of HPMA copolymer-90Y conjugates in treatment of prostate tumors

INTRODUCTION

The treatment of prostate cancer using a radiotherapeutic (90)Y labeled N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer can be enhanced with localized tumor hyperthermia. An (111)In labeled HPMA copolymer system for single photon emission computerized tomography (SPECT) was developed to observe the biodistribution changes associated with hyperthermia. Efficacy studies were conducted in prostate tumor bearing mice using the (90)Y HPMA copolymer with hyperthermia.

METHODS

HPMA copolymers containing 1, 4, 7, 10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) were synthesized by reversible addition-fragmentation transfer (RAFT) copolymerization and subsequently labeled with either (111)In for imaging or (90)Y for efficacy studies. Radiolabel stability was characterized in vitro with mouse serum. Imaging and efficacy studies were conducted in DU145 prostate tumor bearing mice. Imaging was performed using single photon emission computerized tomography (SPECT). Localized mild tumor hyperthermia was achieved by plasmonic photothermal therapy using gold nanorods.

RESULTS

HPMA copolymer-DOTA conjugates demonstrated efficient labeling and stability for both radionuclides. Imaging analysis showed a marked increase of radiolabeled copolymer within the hyperthermia treated prostate tumors, with no significant accumulation in non-targeted tissues. The greatest reduction in tumor growth was observed in the hyperthermia treated tumors with (90)Y HPMA copolymer conjugates. Histological analysis confirmed treatment efficacy and safety.

CONCLUSION

HPMA copolymer-DOTA conjugates radiolabeled with both the imaging and treatment radioisotopes, when combined with hyperthermia can serve as an image guided approach for efficacious treatment of prostate tumors.

In vitro localized release of thermosensitive liposomes with ultrasound-induced hyperthermia

Localized drug delivery with ultrasound-induced hyperthermia can enhance the therapeutic index of chemotherapeutic drugs by improving efficacy and reducing systemic toxicity. A novel in vitro method for the activation of drug-loaded thermosensitive liposomes is described. In particular, a dual-compartment, acoustically transparent container is used in which thermosensitive liposomes suspended in cell culture medium are immersed in a thermally absorptive medium, glycerol. Hyperthermia is induced with ultrasound in the glycerol, which in turn heats the culture medium by thermal conduction. The method approximately mimics the in vivo scenario of thermosensitive liposomes collected in the interstitial spaces of tumors, where ultrasound induces hyperthermia in the tumor tissue, which in turn heats the thermosensitive liposomes by conduction and induces release of the encapsulated drug. The acoustic conditions for the desired hyperthermia are derived theoretically and validated experimentally. Eighty percent release of doxorubicin from thermosensitive liposomes is achieved.

Reversal of multidrug resistance by stimuli-responsive drug delivery systems for therapy of tumor

Multidrug resistance (MDR) is a major obstacle to successful cancer therapy, especially for chemotherapy. The new drug delivery system (DDS) provides promising approaches to reverse MDR, for which the poor cellular uptake and insufficient intracellular drug release remain rate-limiting steps for reaching the drug concentration level within the therapeutic window. Stimulus-coupled drug delivery can control the drug-releasing pattern temporally and spatially, and improve the accumulation of chemotherapeutic agents at targeting sites. In this review, the applications of DDS which is responsive to different types of stimuli in MDR cancer therapy is introduced, and the design, construction, stimuli-sensitivity and the effect to reverse MDR of the stimuli-responsive DDS are discussed.

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.

Hyperthermia-triggered drug delivery from temperature-sensitive liposomes using MRI-guided high intensity focused ultrasound

In the continuous search for cancer therapies with a higher therapeutic window, localized temperature-induced drug delivery may offer a minimal invasive treatment option. Here, a chemotherapeutic drug is encapsulated into a temperature-sensitive liposome (TSL) that is released at elevated temperatures, for example, when passing through a locally heated tumor. Consequently, high drug levels in the tumor tissue can be achieved, while reducing drug exposure to healthy tissue. Although the concept of temperature-triggered drug delivery was suggested more than thirty years ago, several chemical and technological challenges had to be addressed to advance this approach towards clinical translation. In particular, non-invasive focal heating of tissue in a controlled fashion remained a challenge. For the latter, high intensity focused ultrasound (HIFU) allows non-invasive heating to establish hyperthermia (40-45 °C) of tumor tissue over time. Magnetic resonance imaging (MRI) plays a pivotal role in this procedure thanks to its superb spatial resolution for soft tissue as well as the possibility to acquire 3D temperature information. Consequently, MRI systems emerged with an HIFU ultrasound transducer embedded in the patient bed (MR-HIFU), where the MRI is utilized for treatment planning, and to provide spatial and temperature feedback to the HIFU. For tumor treatment, the lesion is heated to 42 °C using HIFU. At this temperature, the drug-loaded TSLs release their payload in a quantitative fashion. The concept of temperature-triggered drug delivery has been extended to MR image-guided drug delivery by the co-encapsulation of a paramagnetic MRI contrast agent in the lumen of TSLs. This review will give an overview of recent developments in temperature-induced drug delivery using HIFU under MRI guidance.