Impact of blood-brain barrier permeabilization induced by ultrasound associated to microbubbles on the brain delivery and kinetics of cetuximab: An immunoPET study using 89Zr-cetuximab

Translating ultrasound-mediated drug delivery technologies for CNS applications

Ultrasound enhances drug delivery into the central nervous system (CNS) by opening barriers between the blood and CNS and by triggering release of drugs from carriers. A key challenge in translating setups from in vitro to in vivo settings is achieving equivalent acoustic energy delivery. Multiple devices have now been demonstrated to focus ultrasound to the brain, with concepts emerging to also target the spinal cord. Clinical trials to date have used ultrasound to facilitate the opening of the blood-brain barrier. While most have focused on feasibility and safety considerations, therapeutic benefits are beginning to emerge. To advance translation of these technologies for CNS applications, researchers should standardise exposure protocol and fine-tune ultrasound parameters. Computational modelling should be increasingly used as a core component to develop both in vitro and in vivo setups for delivering accurate and reproducible ultrasound to the CNS. This field holds promise for transformative advancements in the management and pharmacological treatment of complex and challenging CNS disorders.

Ultrasound-responsive microbubbles and nanodroplets: A pathway to targeted drug delivery

Ultrasound-responsive agents have shown great potential as targeted drug delivery agents, effectively augmenting cell permeability and facilitating drug absorption. This review focuses on two specific agents, microbubbles and nanodroplets, and provides a sequential overview of their drug delivery process. Particular emphasis is given to the mechanical response of the agents under ultrasound, and the subsequent physical and biological effects on the cells. Finally, the state-of-the-art in their pre-clinical and clinical implementation are discussed. Throughout the review, major challenges that need to be overcome in order to accelerate their clinical translation are highlighted.

Enhancing the safety of CAR-T cell therapy: Synthetic genetic switch for spatiotemporal control

Chimeric antigen receptor T (CAR-T) cell therapy is a promising and precise targeted therapy for cancer that has demonstrated notable potential in clinical applications. However, severe adverse effects limit the clinical application of this therapy and are mainly caused by uncontrollable activation of CAR-T cells, including excessive immune response activation due to unregulated CAR-T cell action time, as well as toxicity resulting from improper spatial localization. Therefore, to enhance controllability and safety, a control module for CAR-T cells is proposed. Synthetic biology based on genetic engineering techniques is being used to construct artificial cells or organisms for specific purposes. This approach has been explored in recent years as a means of achieving controllability in CAR-T cell therapy. In this review, we summarize the recent advances in synthetic biology methods used to address the major adverse effects of CAR-T cell therapy in both the temporal and spatial dimensions.

Theranostics in Neurooncology: Heading Toward New Horizons

Therapeutic approaches to brain tumors remain a challenge, with considerable limitations regarding delivery of drugs. There has been renewed and increasing interest in translating the popular theranostic approach well known from prostate and neuroendocrine cancer to neurooncology. Although far from perfect, some of these approaches show encouraging preliminary results, such as for meningioma and leptomeningeal spread of certain pediatric brain tumors. In brain metastases and gliomas, clinical results have failed to impress. Perspectives on these theranostic approaches regarding meningiomas, brain metastases, gliomas, and common pediatric brain tumors will be discussed. For each tumor entity, the general context, an overview of the literature, and future perspectives will be provided. Ongoing studies will be discussed in the supplemental materials. As most theranostic agents are unlikely to cross the blood-brain barrier, the delivery of these agents will be dependent on the successful development and clinical implementation of techniques enhancing permeability and retention. Moreover, the international community should strive toward sufficiently large and randomized studies to generate high-level evidence on theranostic approaches with radioligand therapies for central nervous system tumors.

Challenges of CRISPR/Cas-Based Cell Therapy for Type 1 Diabetes: How Not to Engineer a "Trojan Horse"

Type 1 diabetes mellitus (T1D) is an autoimmune disease caused by the destruction of insulin-producing β-cells in the pancreas by cytotoxic T-cells. To date, there are no drugs that can prevent the development of T1D. Insulin replacement therapy is the standard care for patients with T1D. This treatment is life-saving, but is expensive, can lead to acute and long-term complications, and results in reduced overall life expectancy. This has stimulated the research and development of alternative treatments for T1D. In this review, we consider potential therapies for T1D using cellular regenerative medicine approaches with a focus on CRISPR/Cas-engineered cellular products. However, CRISPR/Cas as a genome editing tool has several drawbacks that should be considered for safe and efficient cell engineering. In addition, cellular engineering approaches themselves pose a hidden threat. The purpose of this review is to critically discuss novel strategies for the treatment of T1D using genome editing technology. A well-designed approach to β-cell derivation using CRISPR/Cas-based genome editing technology will significantly reduce the risk of incorrectly engineered cell products that could behave as a "Trojan horse".

Improving the efficacy of anti-EGFR drugs in GBM: Where we are going?

The therapies targeting mutations of driver genes in cancer have advanced into clinical trials for a variety of tumors. In glioblastoma (GBM), epidermal growth factor receptor (EGFR) is the most commonly mutated oncogene, and targeting EGFR has been widely investigated as a promising direction. However, the results of EGFR pathway inhibitors have not been satisfactory. Limited blood-brain barrier (BBB) permeability, drug resistance, and pathway compensation mechanisms contribute to the failure of anti-EGFR therapies. This review summarizes recent research advances in EGFR-targeted therapy for GBM and provides insight into the reasons for the unsatisfactory results of EGFR-targeted therapy. By combining the results of preclinical studies with those of clinical trials, we discuss that improved drug penetration across the BBB, the use of multi-target combinations, and the development of peptidomimetic drugs under the premise of precision medicine may be promising strategies to overcome drug resistance in GBM.

Anticancer drug delivery by focused ultrasound-mediated blood-brain/tumor barrier disruption for glioma therapy: From benchside to bedside

The therapeutic management of gliomas remains particularly challenging. Brain tumors present multiple obstacles that make therapeutic innovation complex, mainly due to the presence of blood-tumor and blood-brain barriers (BTB and BBB, respectively) which prevent penetration of anticancer agents into the brain parenchyma. Focused ultrasound-mediated BBB disruption (FUS-BBBD) provides a physical method for non-invasive, local, and reversible BBB disruption. The safety of this technique has been demonstrated in small and large animal models. This approach promises to enhance drug delivery into the brain tumor and therefore to improve survival outcomes by repurposing existing drugs. Several clinical trials continue to be initiated in the last decade. In this review, we provide an overview of the rationale behind the use of FUS-BBBD in gliomas and summarize the preclinical studies investigating different approaches (free drugs, drug-loaded microbubbles and drug-loaded nanocarriers) in combination with this technology in in vivo glioma models. Furthermore, we discuss the current state of clinical trials and devices developed and review the challenges to overcome for clinical use of FUS-BBBD in glioma therapy.

Imaging the impact of blood-brain barrier disruption induced by focused ultrasound on P-glycoprotein function

The P-glycoprotein (P-gp/ABCB1) is a major efflux transporter which impedes the brain delivery of many drugs across the blood-brain barrier (BBB). Focused ultrasound with microbubbles (FUS) enables BBB disruption, which immediate and delayed impact on P-gp function remains unclear. Positron emission tomography (PET) imaging using the radiolabeled substrate [11C]metoclopramide provides a sensitive and translational method to study P-gp function at the living BBB. A FUS protocol was devised in rats to induce a substantial and targeted disruption of the BBB in the left hemisphere. BBB disruption was confirmed by the Evan's Blue extravasation test or the minimally-invasive contrast-enhanced MRI. The expression of P-gp was measured 24 h or 48 h after FUS using immunostaining and fluorescence microscopy. The brain kinetics of [11C]metoclopramide was studied by PET at baseline, and both immediately or 24 h after FUS, with or without half-maximum P-gp inhibition (tariquidar 1 mg/kg). In each condition (n = 4-5 rats per group), brain exposure of [11C]metoclopramide was estimated as the area-under-the-curve (AUC) in regions corresponding to the sonicated volume in the left hemisphere, and the contralateral volume. Kinetic modeling was performed to estimate the uptake clearance ratio (R1) of [11C]metoclopramide in the sonicated volume relative to the contralateral volume. In the absence of FUS, half-maximum P-gp inhibition increased brain exposure (+135.0 ± 12.9%, p < 0.05) but did not impact R1 (p > 0.05). Immediately after FUS, BBB integrity was selectively disrupted in the left hemisphere without any detectable impact on the brain kinetics of [11C]metoclopramide compared with the baseline group (p > 0.05) or the contralateral volume (p > 0.05). 24 h after FUS, BBB integrity was fully restored while P-gp expression was maximally down-regulated (-45.0 ± 4.5%, p < 0.001) in the sonicated volume. This neither impacted AUC nor R1 in the FUS + 24 h group (p > 0.05). Only when P-gp was inhibited with tariquidar were the brain exposure (+130 ± 70%) and R1(+29.1 ± 15.4%) significantly increased in the FUS + 24 h/tariquidar group, relative to the baseline group (p < 0.001). We conclude that the brain kinetics of [11C]metoclopramide specifically depends on P-gp function rather than BBB integrity. Delayed FUS-induced down-regulation of P-gp function can be detected. Our results suggest that almost complete down-regulation is required to substantially enhance the brain delivery of P-gp substrates.

ImmunoPET Directed to the Brain: A New Tool for Preclinical and Clinical Neuroscience

Immuno-positron emission tomography (immunoPET) is a non-invasive in vivo imaging method based on tracking and quantifying radiolabeled monoclonal antibodies (mAbs) and other related molecules, such as antibody fragments, nanobodies, or affibodies. However, the success of immunoPET in neuroimaging is limited because intact antibodies cannot penetrate the blood-brain barrier (BBB). In neuro-oncology, immunoPET has been successfully applied to brain tumors because of the compromised BBB. Different strategies, such as changes in antibody properties, use of physiological mechanisms in the BBB, or induced changes to BBB permeability, have been developed to deliver antibodies to the brain. These approaches have recently started to be applied in preclinical central nervous system PET studies. Therefore, immunoPET could be a new approach for developing more specific PET probes directed to different brain targets.

Refining the delivery and therapeutic efficacy of cetuximab using focused ultrasound in a mouse model of glioblastoma: An 89Zr-cetuximab immunoPET study

INTRODUCTION

Glioblastoma (GBM) is the most common and deadly form of primary brain tumor. Between 30 % and 60 % of GBM are characterized by overexpression of the Epidermal Growth Factor Receptor (EGFR). The anti-EGFR antibody Cetuximab (CTX) showed a favorable effect for EGFR⁺ colorectal cancer but failed to demonstrate efficacy for GBM. Insufficient CTX passage through the blood-brain barrier (BBB) and the blood-tumor barrier (BTB) is assumed to be the primary determinant of the limited efficacy of this immunotherapy.

OBJECTIVE

Using positron emission tomography (PET) imaging, we have previously demonstrated that focused ultrasound (FUS) combined with microbubbles (µB) allowed significant and persistent delivery of CTX across the BBB in healthy mice. In the current study, we investigated by PET imaging the combination impact of CTX and FUS on orthotopic GBM preclinical model.

METHODS

After radiolabeling CTX with the long half-life isotope ⁸⁹Zr, PET images have been acquired overtime in mice bearing U251 (EGFR⁺) with or without FUS treatment. Autoradiography combined with immunofluorescence staining was used to corroborate CTX delivery with EGFR expression. A survival study was conducted simultaneously to evaluate the therapeutic benefit of repeated CTX monotherapy associated or not with FUS.

RESULTS

Ex vivo analysis confirmed that FUS enhanced and homogenized the delivery of CTX into all the FUS exposure area, including the tumor and the contralateral hemisphere at the early-time-point. Interestingly, FUS did not improve the long-term accumulation and retention of CTX in the tumor compared with the control group (no FUS). No significant difference in the CTX treatment efficacy, determined by the survival between FUS and non-FUS groups, has been either observed. This result is consistent with the absence of change in the CTX distribution through the GBM tumor after FUS. The neuroinflammation induced by FUS is not significant enough to explain the failure of the CTX delivery improvement.

CONCLUSION

All together, these data suggest that the role of FUS combined with µB on the CTX distribution, even after multiple therapeutic sessions and glial cell activation is insufficient to improve survival of GBM mice compared with CTX treatment alone in this model.

CXCR4-targeted nitric oxide nanoparticles deliver PD-L1 siRNA for immunotherapy against glioblastoma

While immunotherapy has emerged as a promising strategy to treat glioblastoma multiforme (GBM), the limited availability of immunotherapeutic agents in tumors due to the presence of the blood-brain barrier (BBB) and immunosuppressive tumor microenvironment dampens efficacy. Nitric oxide (NO) plays a role in modulating both the BBB and tumor vessels and could thus be delivered to disrupt the BBB and improve the delivery of immunotherapeutics into GBM tumors. Herein, we report an immunotherapeutic approach that utilizes CXCR4-targeted lipid‑calcium-phosphate nanoparticles with NO donors (LCP-NO NPs). The delivery of NO resulted in enhanced BBB permeability and thus improved gene delivery across the BBB. CXCR4-targeted LCP-NO NPs delivered siRNA against the immune checkpoint ligand PD-L1 to GBM tumors, silenced PD-L1 expression, increased cytotoxic T cell infiltration and activation in GBM tumors, and suppressed GBM progression. Thus, the codelivery of NO and PD-L1 siRNA by these CXCR4-targeted NPs may serve as a potential immunotherapy for GBM.

Pharmacokinetics and pharmacodynamics of approved monoclonal antibody therapy for colorectal cancer

INTRODUCTION

The introduction of monoclonal antibodies to the chemotherapy backbone treatment has challenged the paradigm of metastatic colorectal cancer (mCRC) treatment. Their mechanism of action and pharmacokinetics are complex but important to understand in order to improve patient selection and treatment outcomes for mCRC population.

AREAS COVERED

This review examines the scientific data, pharmacodynamics, and pharmacokinetics of approved monoclonal antibodies used to treat mCRC patients, including agents targeting signaling via VEGFR (bevacizumab and ramucirumab), EGFR (cetuximab and panitumumab), HER2/3 target therapy, and immunotherapy agents such as pembrolizumab or nivolumab. Efficacy and mechanism of action of bispecific antibodies are also covered.

EXPERT OPINION

mCRC is a heterogeneous disease and the optimal selection and sequence of treatments is challenging. Monoclonal antibodies have complex pharmacokinetics and pharmacodynamics, with important interactions between them. The arrival of bioequivalent molecules to the market increases the need for the characterization of pharmacokinetics and pharmacodynamics of classic monoclonal antibodies to reach bioequivalent novel molecules.

Ultrasound-mediated blood-brain barrier opening: An effective drug delivery system for theranostics of brain diseases

Blood-brain barrier (BBB) remains a significant obstacle to drug therapy for brain diseases. Focused ultrasound (FUS) combined with microbubbles (MBs) can locally and transiently open the BBB, providing a potential strategy for drug delivery across the BBB into the brain. Nowadays, taking advantage of this technology, many therapeutic agents, such as antibodies, growth factors, and nanomedicine formulations, are intensively investigated across the BBB into specific brain regions for the treatment of various brain diseases. Several preliminary clinical trials also have demonstrated its safety and good tolerance in patients. This review gives an overview of the basic mechanisms, ultrasound contrast agents, evaluation or monitoring methods, and medical applications of FUS-mediated BBB opening in glioblastoma, Alzheimer's disease, and Parkinson's disease.

Molecular Imaging of Ultrasound-Mediated Blood-Brain Barrier Disruption in a Mouse Orthotopic Glioblastoma Model

Glioblastoma (GBM) is an aggressive and malignant primary brain tumor. The blood-brain barrier (BBB) limits the therapeutic options available to tackle this incurable tumor. Transient disruption of the BBB by focused ultrasound (FUS) is a promising and safe approach to increase the brain and tumor concentration of drugs administered systemically. Non-invasive, sensitive, and reliable imaging approaches are required to better understand the impact of FUS on the BBB and brain microenvironment. In this study, nuclear imaging (SPECT/CT and PET/CT) was used to quantify neuroinflammation 48 h post-FUS and estimate the influence of FUS on BBB opening and tumor growth in vivo. BBB disruptions were performed on healthy and GBM-bearing mice (U-87 MG xenograft orthotopic model). The BBB recovery kinetics were followed and quantified by [99mTc]Tc-DTPA SPECT/CT imaging at 0.5 h, 3 h and 24 h post-FUS. The absence of neuroinflammation was confirmed by [18F]FDG PET/CT imaging 48 h post-FUS. The presence of the tumor and its growth were evaluated by [68Ga]Ga-RGD₂ PET/CT imaging and post-mortem histological analysis, showing that tumor growth was not influenced by FUS. In conclusion, molecular imaging can be used to evaluate the time frame for systemic treatment combined with transient BBB opening and to test its efficacy over time.

Impact of Radiolabeling Strategies on the Pharmacokinetics and Distribution of an Anti-PD-L1 PET Ligand

Molecular imaging with PET offers an alternative method to quantify programmed-death-ligand 1 (PD-L1) to accurately select patients for immunotherapies. More and more clinical and preclinical trials involve radiolabeling of antibody fragments for their desirably fast clearance and high tumor penetration. As the radiolabeling strategy can significantly impact pharmacokinetics and biodistribution, we explored in this work a site-specific radiofluorination strategy on an anti-PD-L1 fragment antigen-binding (Fab) and compared the pharmacokinetic and biodistribution properties with the same Fab labeled using stochastic radiolabeling chemistry. We applied an enzymatic bioconjugation mediated by a variant of the lipoic acid ligase (LplA) that promotes the formation of an amide bond between a short peptide cloned onto the C terminus of the Fab. A synthetic analogue of the enzyme natural substrate, lipoic acid, was radiolabeled with fluorine-18 for site-specific conjugation by LplA. We compared the biodistribution of the site-specifically labeled Fab with a stochastically labeled Fab on lysine side chains in tumor-bearing mice. The two methods of fluorination demonstrate a comparable whole-body biodistribution. The ⁸⁹Zr-labeled Fab had different biodistribution compared to either ¹⁸F-labeled Fab. We attribute the difference to [⁸⁹Zr] metabolism. Fab-LAP-[¹⁸F]FPyOctA therefore reflects better the true pharmacokinetic profile of the Fab.

Perfluorocarbon Nanodroplets as Potential Nanocarriers for Brain Delivery Assisted by Focused Ultrasound-Mediated Blood–Brain Barrier Disruption

The management of brain diseases remains a challenge, particularly because of the difficulty for drugs to cross the blood–brain barrier. Among strategies developed to improve drug delivery, nano-sized emulsions (i.e., nanoemulsions), employed as nanocarriers, have been described. Moreover, focused ultrasound-mediated blood–brain barrier disruption using microbubbles is an attractive method to overcome this barrier, showing promising results in clinical trials. Therefore, nanoemulsions combined with this technology represent a real opportunity to bypass the constraints imposed by the blood–brain barrier and improve the treatment of brain diseases. In this work, a stable freeze-dried emulsion of perfluorooctyl bromide nanodroplets stabilized with home-made fluorinated surfactants able to carry hydrophobic agents is developed. This formulation is biocompatible and droplets composing the emulsion are internalized in multiple cell lines. After intravenous administration in mice, droplets are eliminated from the bloodstream in 24 h (blood half-life (t_1/2) = 3.11 h) and no long-term toxicity is expected since they are completely excreted from mice’ bodies after 72 h. In addition, intracerebral accumulation of tagged droplets is safely and significantly increased after focused ultrasound-mediated blood–brain barrier disruption. Thus, the proposed nanoemulsion appears as a promising nanocarrier for a successful focused ultrasound-mediated brain delivery of hydrophobic agents.

ImmunoPET: Antibody-Based PET Imaging in Solid Tumors

Immuno-positron emission tomography (immunoPET) is a molecular imaging modality combining the high sensitivity of PET with the specific targeting ability of monoclonal antibodies. Various radioimmunotracers have been successfully developed to target a broad spectrum of molecules expressed by malignant cells or tumor microenvironments. Only a few are translated into clinical studies and barely into clinical practices. Some drawbacks include slow radioimmunotracer kinetics, high physiologic uptake in lymphoid organs, and heterogeneous activity in tumoral lesions. Measures are taken to overcome the disadvantages, and new tracers are being developed. In this review, we aim to mention the fundamental components of immunoPET imaging, explore the groundbreaking success achieved using this new technique, and review different radioimmunotracers employed in various solid tumors to elaborate on this relatively new imaging modality.

Application and Design of Switches Used in CAR

Among the many oncology therapies, few have generated as much excitement as CAR-T. The success of CAR therapy would not have been possible without the many discoveries that preceded it, most notably, the Nobel Prize-winning breakthroughs in cellular immunity. However, despite the fact that CAR-T already offers not only hope for development, but measurable results in the treatment of hematological malignancies, CAR-T still cannot be safely applied to solid tumors. The reason for this is, among other things, the lack of tumor-specific antigens which, in therapy, threatens to cause a lethal attack of lymphocytes on healthy cells. In the case of hematological malignancies, dangerous complications such as cytokine release syndrome may occur. Scientists have responded to these clinical challenges with molecular switches. They make it possible to remotely control CAR lymphocytes after they have already been administered to the patient. Moreover, they offer many additional capabilities. For example, they can be used to switch CAR antigenic specificity, create logic gates, or produce local activation under heat or light. They can also be coupled with costimulatory domains, used for the regulation of interleukin secretion, or to prevent CAR exhaustion. More complex modifications will probably require a combination of reprogramming (iPSc) technology with genome editing (CRISPR) and allogenic (off the shelf) CAR-T production.

Low-Intensity Focused Ultrasound Technique in Glioblastoma Multiforme Treatment

Glioblastoma is one of the central nervous system most aggressive and lethal cancers with poor overall survival rate. Systemic treatment of glioblastoma remains the most challenging aspect due to the low permeability of the blood-brain barrier (BBB) and blood-tumor barrier (BTB), limiting therapeutics extravasation mainly in the core tumor as well as in its surrounding invading areas. It is now possible to overcome these barriers by using low-intensity focused ultrasound (LIFU) together with intravenously administered oscillating microbubbles (MBs). LIFU is a non-invasive technique using converging ultrasound waves which can alter the permeability of BBB/BTB to drug delivery in a specific brain/tumor region. This emerging technique has proven to be both safe and repeatable without causing injury to the brain parenchyma including neurons and other structures. Furthermore, LIFU is also approved by the FDA to treat essential tremors and Parkinson's disease. It is currently under clinical trial in patients suffering from glioblastoma as a drug delivery strategy and liquid biopsy for glioblastoma biomarkers. The use of LIFU+MBs is a step-up in the world of drug delivery, where onco-therapeutics of different molecular sizes and weights can be delivered directly into the brain/tumor parenchyma. Initially, several potent drugs targeting glioblastoma were limited to cross the BBB/BTB; however, using LIFU+MBs, diverse therapeutics showed significantly higher uptake, improved tumor control, and overall survival among different species. Here, we highlight the therapeutic approach of LIFU+MBs mediated drug-delivery in the treatment of glioblastoma.

Drug delivery across the blood-brain barrier for the treatment of pediatric brain tumors - An update

Even though the last decade has seen a surge in the identification of molecular targets and targeted therapies in pediatric brain tumors, the blood brain barrier (BBB) remains a significant challenge in systemic drug delivery. This continues to undermine therapeutic efficacy. Recent efforts have identified several strategies that can facilitate enhanced drug delivery into pediatric brain tumors. These include invasive methods such as intra-arterial, intrathecal, and convection enhanced delivery and non-invasive technologies that allow for transient access across the BBB, including focused ultrasound and nanotechnology. This review discusses current strategies that are being used to enhance delivery of different therapies across the BBB to the tumor site - a major unmet need in pediatric neuro-oncology.

Ultrasound and nanomaterial: an efficient pair to fight cancer

Ultrasounds are often used in cancer treatment protocols, e.g. to collect tumor tissues in the right location using ultrasound-guided biopsy, to image the region of the tumor using more affordable and easier to use apparatus than MRI and CT, or to ablate tumor tissues using HIFU. The efficacy of these methods can be further improved by combining them with various nano-systems, thus enabling: (i) a better resolution of ultrasound imaging, allowing for example the visualization of angiogenic blood vessels, (ii) the specific tumor targeting of anti-tumor chemotherapeutic drugs or gases attached to or encapsulated in nano-systems and released in a controlled manner in the tumor under ultrasound application, (iii) tumor treatment at tumor site using more moderate heating temperatures than with HIFU. Furthermore, some nano-systems display adjustable sizes, i.e. nanobubbles can grow into micro-bubbles. Such dual size is advantageous since it enables gathering within the same unit the targeting properties of nano bubbles via EPR effect and the enhanced ultrasound contrasting properties of micro bubbles. Interestingly, the way in which nano-systems act against a tumor could in principle also be adjusted by accurately selecting the nano-system among a large choice and by tuning the values of the ultrasound parameters, which can lead, due to their mechanical nature, to specific effects such as cavitation that are usually not observed with purely electromagnetic waves and can potentially help destroying the tumor. This review highlights the clinical potential of these combined treatments that can improve the benefit/risk ratio of current cancer treatments.

Diagnosis of Glioblastoma by Immuno-Positron Emission Tomography

Simple Summary

Neuroimaging has transformed the way brain tumors are diagnosed and treated. Although different non-invasive modalities provide very helpful information, in some situations, they present a limited value. By merging the specificity of antibodies with the resolution, sensitivity, and quantitative capabilities of positron emission tomography (PET), “Immuno-PET” allows us to conduct the non-invasive diagnosis and monitoring of patients over time using antibody-based probes as an in vivo, integrated, quantifiable, 3D, full-body “immunohistochemistry”, like a “virtual biopsy”. This review provides and focuses on immuno-PET applications and future perspectives of this promising imaging approach for glioblastoma.

Abstract

Neuroimaging has transformed neuro-oncology and the way that glioblastoma is diagnosed and treated. Magnetic Resonance Imaging (MRI) is the most widely used non-invasive technique in the primary diagnosis of glioblastoma. Although MRI provides very powerful anatomical information, it has proven to be of limited value for diagnosing glioblastomas in some situations. The final diagnosis requires a brain biopsy that may not depict the high intratumoral heterogeneity present in this tumor type. The revolution in “cancer-omics” is transforming the molecular classification of gliomas. However, many of the clinically relevant alterations revealed by these studies have not yet been integrated into the clinical management of patients, in part due to the lack of non-invasive biomarker-based imaging tools. An innovative option for biomarker identification in vivo is termed “immunotargeted imaging”. By merging the high target specificity of antibodies with the high spatial resolution, sensitivity, and quantitative capabilities of positron emission tomography (PET), “Immuno-PET” allows us to conduct the non-invasive diagnosis and monitoring of patients over time using antibody-based probes as an in vivo, integrated, quantifiable, 3D, full-body “immunohistochemistry” in patients. This review provides the state of the art of immuno-PET applications and future perspectives on this imaging approach for glioblastoma.

Radioimmunotherapy Combined With Low-Intensity Ultrasound and Microbubbles: A Potential Novel Strategy for Treatment of Solid Tumors

The prognosis of advanced malignant tumors is very poor, and effective treatment is limited. Radioimmunotherapy (RIT) is a novel treatment method. However, its anti-tumor effect is relatively low in solid tumors, which is mainly due to the blood-tumor barrier preventing RIT from penetrating the tumor, resulting in an insufficient dose. Low-intensity ultrasound with microbubbles (USMB) has proven capable of opening the blood-tumor barrier. The combination of the two technologies may overcome the poor anti-tumor effect of RIT and promote the clinical application of RIT in solid tumors. In this article, we reviewed the current research status of RIT in the treatment of solid tumors and the opportunities and challenges of USMB combined with RIT.

[18F]2-Fluoro-2-deoxy-sorbitol PET Imaging for Quantitative Monitoring of Enhanced Blood-Brain Barrier Permeability Induced by Focused Ultrasound

Focused ultrasound in combination with microbubbles (FUS) provides an effective means to locally enhance the delivery of therapeutics to the brain. Translational and quantitative imaging techniques are needed to noninvasively monitor and optimize the impact of FUS on blood-brain barrier (BBB) permeability in vivo. Positron-emission tomography (PET) imaging using [¹⁸F]2-fluoro-2-deoxy-sorbitol ([¹⁸F]FDS) was evaluated as a small-molecule (paracellular) marker of blood-brain barrier (BBB) integrity. [¹⁸F]FDS was straightforwardly produced from chemical reduction of commercial [¹⁸F]2-deoxy-2-fluoro-D-glucose. [¹⁸F]FDS and the invasive BBB integrity marker Evan’s blue (EB) were i.v. injected in mice after an optimized FUS protocol designed to generate controlled hemispheric BBB disruption. Quantitative determination of the impact of FUS on the BBB permeability was determined using kinetic modeling. A 2.2 ± 0.5-fold higher PET signal (n = 5; p < 0.01) was obtained in the sonicated hemisphere and colocalized with EB staining observed post mortem. FUS significantly increased the blood-to-brain distribution of [¹⁸F]FDS by 2.4 ± 0.8-fold (V_T; p < 0.01). Low variability (=10.1%) of V_T values in the sonicated hemisphere suggests reproducibility of the estimation of BBB permeability and FUS method. [¹⁸F]FDS PET provides a readily available, sensitive and reproducible marker of BBB permeability to noninvasively monitor the extent of BBB disruption induced by FUS in vivo.

Current state of therapeutic focused ultrasound applications in neuro-oncology

INTRODUCTION

Despite manifold advances in oncology, cancers of the central nervous system remain among the most lethal. Unique features of the brain, including distinct cellular composition, immunological privilege, and physical barriers to therapeutic delivery, likely contribute to the poor prognosis of patients with neuro-oncological disease. Focused ultrasound is an emerging technology that allows transcranial delivery of ultrasound energy to focal brain targets with great precision.

METHODS

A review of the clinical and preclinical focused ultrasound literature was performed to obtain data regarding the current state of the focused ultrasound in context of neuro-oncology. A narrative review was then constructed to provide an overview of current and future applications of this technology.

RESULTS

Focused ultrasound can facilitate direct control of tumors by thermal or mechanical ablation, as well as enhance delivery of diverse therapeutics by disruption of the blood-brain barrier without local tissue damage. Indeed, ultrasound-sensitive drug formulations or sonosensitizers may be combined with ultrasound blood-brain barrier disruption to achieve high local drug concentration while limiting systemic exposure to therapeutics. Furthermore, focused ultrasound can induce radiosensitization, immunomodulation, and neuromodulation. Here we review applications of focused ultrasound with a focus on approaches currently under clinical investigation for the treatment of neuro-oncological disease, such as blood-brain barrier disruption for drug delivery and thermal ablation. We also discuss design of clinical trials, selection of patient cohorts, and emerging approaches to improve the efficacy of transcranial ultrasound, such as histotripsy, as well as combinatorial strategies to exploit synergistic biological effects of existing cancer therapies and ultrasound.

CONCLUSIONS

Focused ultrasound is a promising and actively expanding therapeutic modality for diverse neuro-oncological diseases.

Modelling Lipid-Coated Microbubbles in Focused Ultrasound Applications at Subresonance Frequencies

We present a computational study of the behaviour of a lipid-coated SonoVue microbubble with initial radius 1 µm ≤ R₀ ≤ 2 µm, excited at frequencies (200-1500 kHz) significantly below the linear resonance frequency and pressure amplitudes of up to 1500 kPa-an excitation regime used in many applications of focused ultrasound. The bubble dynamics are simulated using the Rayleigh-Plesset equation and the Gilmore equation, in conjunction with the Marmottant model for the lipid monolayer coating. Also, a new continuously differentiable variant of the Marmottant model is introduced. Below the onset of inertial cavitation, a linear regime is identified in which the maximum pressure at the bubble wall is linearly proportional to the excitation pressure amplitude and the mechanical index. This linear regime is bounded by the Blake pressure, and, in line with recent in vitro experiments, the onset of inertial cavitation is found to occur at an excitation pressure amplitude of approximately 130-190 kPa, depending on the initial bubble size. In the nonlinear regime the maximum pressure at the bubble wall is found to be readily predicted by the maximum bubble radius, and both the Rayleigh-Plesset and Gilmore equations are shown to predict the onset of sub- and ultraharmonic frequencies of the acoustic emissions compared with in vitro experiments. Neither the surface dilational viscosity of the lipid monolayer nor the compressibility of the liquid has a discernible influence on the quantities studied, but accounting for the lipid coating is critical for accurate prediction of the bubble behaviour. The Gilmore equation is shown to be valid for the bubbles and excitation regime considered, and the Rayleigh-Plesset equation also provides accurate qualitative predictions, even though it is outside its range of validity for many of the cases considered.

Converging technologies: targeting the hallmarks of cancer using ultrasound and microbubbles

Various complex biological effects occur when ultrasonic compression waves travel through biological material. The myriad of biological outcomes instigated by ultrasound are evident when viewed through the lens of the hallmarks of cancer. Herein, we summarise the therapeutic potential of ultrasound, enhanced by microbubbles, for the treatment of cancer.

Ultrasound-Mediated Blood-Brain Barrier Opening Improves Whole Brain Gene Delivery in Mice

Gene therapy represents a powerful therapeutic tool to treat diseased tissues and provide a durable and effective correction. The central nervous system (CNS) is the target of many gene therapy protocols, but its high complexity makes it one of the most difficult organs to reach, in part due to the blood-brain barrier that protects it from external threats. Focused ultrasound (FUS) coupled with microbubbles appears as a technological breakthrough to deliver therapeutic agents into the CNS. While most studies focus on a specific targeted area of the brain, the present work proposes to permeabilize the entire brain for gene therapy in several pathologies. Our results show that, after i.v. administration and FUS sonication in a raster scan manner, a self-complementary AAV9-CMV-GFP vector strongly and safely infected the whole brain of mice. An increase in vector DNA (19.8 times), GFP mRNA (16.4 times), and GFP protein levels (17.4 times) was measured in whole brain extracts of FUS-treated GFP injected mice compared to non-FUS GFP injected mice. In addition to this increase in GFP levels, on average, a 7.3-fold increase of infected cells in the cortex, hippocampus, and striatum was observed. No side effects were detected in the brain of treated mice. The combining of FUS and AAV-based gene delivery represents a significant improvement in the treatment of neurological genetic diseases.

The promising shadow of microbubble over medical sciences: from fighting wide scope of prevalence disease to cancer eradication

Microbubbles are typically 0.5-10 μm in size. Their size tends to make it easier for medication delivery mechanisms to navigate the body by allowing them to be swallowed more easily. The gas included in the microbubble is surrounded by a membrane that may consist of biocompatible biopolymers, polymers, surfactants, proteins, lipids, or a combination thereof. One of the most effective implementation techniques for tiny bubbles is to apply them as a drug carrier that has the potential to activate ultrasound (US); this allows the drug to be released by US. Microbubbles are often designed to preserve and secure medicines or substances before they have reached a certain area of concern and, finally, US is used to disintegrate microbubbles, triggering site-specific leakage/release of biologically active drugs. They have excellent therapeutic potential in a wide range of common diseases. In this article, we discussed microbubbles and their advantageous medicinal uses in the treatment of certain prevalent disorders, including Parkinson's disease, Alzheimer's disease, cardiovascular disease, diabetic condition, renal defects, and finally, their use in the treatment of various forms of cancer as well as their incorporation with nanoparticles. Using microbubble technology as a novel carrier, the ability to prevent and eradicate prevalent diseases has strengthened the promise of effective care to improve patient well-being and life expectancy.

Nose-to-brain co-delivery of drugs for glioblastoma treatment using nanostructured system

Mutations on the epidermal growth factor receptor (EGFR), induction of angiogenesis, and reprogramming cellular energetics are all biological features acquired by tumor cells during tumor development, and also known as the hallmarks of cancer. Targeted therapies that combine drugs that are capable of acting against such concepts are of great interest, since they can potentially improve the therapeutic efficacy of treatments of complex pathologies, such as glioblastoma (GBM). However, the anatomical location and biological behavior of this neoplasm imposes great challenges for targeted therapies. A novel strategy that combines alpha-cyano-4-hydroxycinnamic acid (CHC) with the monoclonal antibody cetuximab (CTX), both carried onto a nanotechnology-based delivery system, is herein proposed for GBM treatment via nose-to-brain delivery. The biological performance of Poly (D,L-lactic-co-glycolic acid)/chitosan nanoparticles (NP), loaded with CHC, and conjugated with CTX by covalent bonds (conjugated NP) were extensively investigated. The NP platforms were able to control CHC release, indicating that drug release was driven by the Weibull model. An ex vivo study with nasal porcine mucosa demonstrated the capability of these systems to promote CHC and CTX permeation. Blot analysis confirmed that CTX, covalently associated to NP, impairs EGRF activation. The chicken chorioallantoic membrane assay demonstrated a trend of tumor reduction when conjugated NP were employed. Finally, images acquired by fluorescence tomography evidenced that the developed nanoplatform was effective in enabling nose-to-brain transport upon nasal administration. In conclusion, the developed delivery system exhibited suitability as an effective novel co-delivery approaches for GBM treatment upon intranasal administration.

Development of a multi-functional preclinical device for the treatment of glioblastoma

Glioblastoma multiforme (GBM) is one of the most common and aggressive malignant primary brain tumors in adults. The treatment of GBM is limited by the blood-brain barrier (BBB), which limits the diffusion of appropriate concentrations of therapeutic agents at the tumor site. Among experimental therapies, photo-thermal therapy (PTT) mediated by nanoparticles is a promising strategy. To propose a preclinical versatile research instrument for the development of new PTT for GBM, a multipurpose integrated preclinical device was developed. The setup is able to perform: i) BBB permeabilization by focused ultrasound sonication (FUS); ii) PTT with continuous wave laser; iii) in situ temperature monitoring with photo-acoustic (PA) measurements. In vivo preliminary subcutaneous and transcranial experiments were conducted on healthy or tumor-bearing mice. Transcranial FUS-induced BBB permeabilization was validated using single photon emission computed tomography (SPECT) imaging. PTT capacities were monitored by PA thermometry, and are illustrated through subcutaneous and transcranial in vivo experiments. The results show the therapeutic possibilities and ergonomy of such integrated device as a tool for the validation of future treatments.

Recent Advances on Ultrasound Contrast Agents for Blood-Brain Barrier Opening with Focused Ultrasound

The blood-brain barrier is the primary obstacle to efficient intracerebral drug delivery. Focused ultrasound, in conjunction with microbubbles, is a targeted and non-invasive way to disrupt the blood-brain barrier. Many commercially available ultrasound contrast agents and agents specifically designed for therapeutic purposes have been investigated in ultrasound-mediated blood-brain barrier opening studies. The new generation of sono-sensitive agents, such as liquid-core droplets, can also potentially disrupt the blood-brain barrier after their ultrasound-induced vaporization. In this review, we describe the different compositions of agents used for ultrasound-mediated blood-brain barrier opening in recent studies, and we discuss the challenges of the past five years related to the optimal formulation of agents.