Complete inhibition of ABCB1 and ABCG2 at the blood-brain barrier by co-infusion of erlotinib and tariquidar to improve brain delivery of the model ABCB1/ABCG2 substrate [11C]erlotinib

Long acting tariquidar loaded stearic acid-modified hydroxyapatite enhances brain penetration and antitumor effect of temozolomide

Temozolomide (TMZ) is the first line chemotherapy for glioblastoma (GBM) treatment, but the P-glycoprotein (P-gp) expressed in blood-brain barrier (BBB) will pump out TMZ from the brain leading to decreased TMZ concentration. Tariquidar (TQD), a selective and potent P-gp inhibitor, may be suitable for combination therapy to increase concentration of TMZ in brain. Hydroxyapatite (HAP) is a biodegradable material with sustained release characteristics, and stearic acid surface-modified HAP (SA-HAP) can increase hydrophobicity to facilitate TQD loading. TQD-loaded stearic acid surface-modified HAP (SA-HAP-TQD) was prepared with optimal size and high TQD loading efficiency, and in vitro release and cellular uptake of SA-HAP-TQD showed that SA-HAP-TQD were taken up into lysosome and continuously released TQD from macrophages. In vivo studies have found that over 70 % of SA-HAP was degraded and 80 % of TQD was released from SA-HAP-TQD 28 days after administration. SA-HAP-TQD could increase brain penetration of TMZ, but it would not enhance adverse effects of TMZ in healthy mice. SA-HAP-TQD and TMZ combination had longer median survival than TMZ single therapy in GL261 orthotopic model. These results suggest that SA-HAP-TQD has sustained release characteristics and are potential for improving antitumor effect with TMZ treatment.

Brain PET imaging using 11C-flumazenil and 11C-buprenorphine does not support the hypothesis of a mutual interaction between buprenorphine and benzodiazepines at the neuroreceptor level

Among opioids, buprenorphine presents a favorable safety profile with a limited risk of respiratory depression. However, fatalities have been reported when buprenorphine is combined to a benzodiazepine. Potentiation of buprenorphine interaction with opioid receptors (ORs) with benzodiazepines, and/or vice versa, is hypothesized to explain this drug-drug interaction (DDI). The mutual DDI between buprenorphine and benzodiazepines was investigated at the neuroreceptor level in nonhuman primates (n = 4 individuals) using brain PET imaging and kinetic modelling. The binding potential (BPND) of benzodiazepine receptor (BzR) was assessed using 11C-flumazenil PET imaging before and after administration of buprenorphine (0.2 mg, i.v.). Moreover, the brain kinetics and receptor binding of buprenorphine were investigated in the same individuals using 11C-buprenorphine PET imaging before and after administration of diazepam (10 mg, i.v.). Outcome parameters were compared using a two-way ANOVA. Buprenorphine did not impact the plasma nor brain kinetics of 11C-flumazenil. 11C-flumazenil BPND was unchanged following buprenorphine exposure, in any brain region (p > 0.05). Similarly, diazepam did not impact the plasma or brain kinetics of 11C-buprenorphine. 11C-buprenorphine volume of distribution (VT) was unchanged following diazepam exposure, in any brain region (p > 0.05). To conclude, our PET imaging findings do not support a neuropharmacokinetic or neuroreceptor-related mechanism of the buprenorphine/benzodiazepine interaction.

Characterization of prevalent tyrosine kinase inhibitors and their challenges in glioblastoma treatment

Glioblastoma multiforme (GBM) is a highly aggressive malignant primary tumor in the central nervous system. Despite extensive efforts in radiotherapy, chemotherapy, and neurosurgery, there remains an inadequate level of improvement in treatment outcomes. The development of large-scale genomic and proteomic analysis suggests that GBMs are characterized by transcriptional heterogeneity, which is responsible for therapy resistance. Hence, knowledge about the genetic and epigenetic heterogeneity of GBM is crucial for developing effective treatments for this aggressive form of brain cancer. Tyrosine kinases (TKs) can act as signal transducers, regulate important cellular processes like differentiation, proliferation, apoptosis and metabolism. Therefore, TK inhibitors (TKIs) have been developed to specifically target these kinases. TKIs are categorized into allosteric and non-allosteric inhibitors. Irreversible inhibitors form covalent bonds, which can lead to longer-lasting effects. However, this can also increase the risk of off-target effects and toxicity. The development of TKIs as therapeutics through computer-aided drug design (CADD) and bioinformatic techniques enhance the potential to improve patients' survival rates. Therefore, the continued exploration of TKIs as drug targets is expected to lead to even more effective and specific therapeutics in the future.

Dissimilar Effect of P-Glycoprotein and Breast Cancer Resistance Protein Inhibition on the Distribution of Erlotinib to the Retina and Brain in Humans and Mice

P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are two ATP-binding cassette efflux transporters that are coexpressed at the human blood-brain barrier (BBB) and blood-retina barrier (BRB). While pharmacological inhibition of P-gp and/or BCRP results in increased brain distribution of dual P-gp/BCRP substrate drugs, such as the tyrosine kinase inhibitor erlotinib, the effect of P-gp and/or BCRP inhibition on the retinal distribution of such drugs has hardly been investigated. In this study, we used positron emission tomography (PET) imaging to assess the effect of transporter inhibition on the distribution of [11C]erlotinib to the human retina and brain. Twenty two healthy volunteers underwent two PET scans after intravenous (i.v.) injection of a microdose (<5 μg) of [11C]erlotinib, a baseline scan, and a second scan either with concurrent i.v. infusion of tariquidar to inhibit P-gp (n = 5) or after oral intake of single ascending doses of erlotinib (300 mg, 650 mg, or 1000 mg, n = 17) to saturate erlotinib transport. In addition, transport of [3H]erlotinib to the retina and brain was assessed in mice by in situ carotid perfusion under various drug transporter inhibition settings. In comparison to the baseline PET scan, coadministration of tariquidar or erlotinib led to a significant decrease of [11C]erlotinib total volume of distribution (VT) in the human retina by -25 ± 8% (p ≤ 0.05) and -41 ± 16% (p ≤ 0.001), respectively. In contrast, erlotinib intake led to a significant increase in [11C]erlotinib VT in the human brain (+20 ± 16%, p ≤ 0.001), while administration of tariquidar did not result in any significant changes. In situ carotid perfusion experiments showed that both P-gp and BCRP significantly limit the distribution of erlotinib to the mouse retina and brain but revealed a similar discordant effect at the mouse BRB and BBB following co-perfusion with tariquidar and erlotinib as in humans. Co-perfusion with prototypical inhibitors of solute carrier transporters did not reveal a significant contribution of organic cation transporters (e.g., OCTs and OCTNs) and organic anion-transporting polypeptides (e.g., OATP2B1) to the retinal and cerebral distribution of erlotinib. In conclusion, we observed a dissimilar effect after P-gp and/or BCRP inhibition on the retinal and cerebral distribution of [11C]erlotinib. The exact mechanism for this discrepancy remains unclear but may be related to the function of an unidentified erlotinib uptake carrier sensitive to tariquidar inhibition at the BRB. Our study highlights the great potential of PET to study drug distribution to the human retina and to assess the functional impact of membrane transporters on ocular drug distribution.

Advances in the structure, mechanism and targeting of chemoresistance-linked ABC transporters

Cancer cells frequently display intrinsic or acquired resistance to chemically diverse anticancer drugs, limiting therapeutic success. Among the main mechanisms of this multidrug resistance is the overexpression of ATP-binding cassette (ABC) transporters that mediate drug efflux, and, specifically, ABCB1, ABCG2 and ABCC1 are known to cause cancer chemoresistance. High-resolution structures, biophysical and in silico studies have led to tremendous progress in understanding the mechanism of drug transport by these ABC transporters, and several promising therapies, including irradiation-based immune and thermal therapies, and nanomedicine have been used to overcome ABC transporter-mediated cancer chemoresistance. In this Review, we highlight the progress achieved in the past 5 years on the three transporters, ABCB1, ABCG2 and ABCC1, that are known to be of clinical importance. We address the molecular basis of their broad substrate specificity gleaned from structural information and discuss novel approaches to block the function of ABC transporters. Furthermore, genetic modification of ABC transporters by CRISPR-Cas9 and approaches to re-engineer amino acid sequences to change the direction of transport from efflux to import are briefly discussed. We suggest that current information regarding the structure, mechanism and regulation of ABC transporters should be used in clinical trials to improve the efficiency of chemotherapeutics for patients with cancer.

In Vitro and In Vivo Evaluation of ABCG2 (BCRP) Inhibitors Derived from Ko143

Breast cancer resistance protein (BCRP, ABCG2) is an efflux transporter that plays a crucial role in multidrug resistance to antineoplastic drugs. Ko143, an analogue of the natural product fumitremorgin C, is a potent inhibitor of ABCG2 but is rapidly hydrolyzed to an inactive metabolite in vivo. To identify ABCG2 inhibitors with improved metabolic stability, we have assessed a series of Ko143 analogues for their ability to inhibit ABCG2-mediated transport in ABCG2-transduced MDCK II cells and determined the stability of the most potent compounds in liver microsomes. The most promising analogues were evaluated in vivo by positron emission tomography. In vitro, three of the tested analogues were potent ABCG2 inhibitors and stable in microsomes. In vivo, they increased the distribution of the ABCG2/ABCB1 substrate [¹¹C]tariquidar to the brain both in wild-type (with Abcb1a/b transport blocked by tariquidar) and Abcb1a/b(-/-) mice. One analogue was more potent than Ko143 in both animal models.

Influence of germline variations in drug transporters ABCB1 and ABCG2 on intracerebral osimertinib efficacy in patients with non-small cell lung cancer

Background

Central nervous system (CNS) metastases are present in approximately 40% of patients with metastatic epidermal growth factor receptor-mutated (EGFRm+) non-small cell lung cancer (NSCLC). The EGFR-tyrosine kinase inhibitor osimertinib is a substrate of transporters ABCB1 and ABCG2 and metabolized by CYP3A4. We investigated relationships between single nucleotide polymorphisms (SNPs) ABCB1 3435C>T, ABCG2 421C>A and 34G>A, and CYP3A4∗22 and CNS treatment efficacy of osimertinib in EGFRm+ NSCLC patients.

Methods

Patients who started treatment with osimertinib for EGFRm+ NSCLC between November 2014 and June 2021 were included in this retrospective observational multicentre cohort study. For patients with baseline CNS metastases, the primary endpoint was CNS progression-free survival (CNS-PFS; time from osimertinib start until CNS disease progression or death). For patients with no or unknown baseline CNS metastases, the primary endpoint was CNS disease-free survival (CNS-DFS; time from osimertinib start until occurrence of new CNS metastases). Relationships between SNPs and baseline characteristics with CNS-PFS and CNS-DFS were studied with competing-risks survival analysis. Secondary endpoints were relationships between SNPs and PFS, overall survival, severe toxicity, and osimertinib pharmacokinetics.

Findings

From 572 included patients, 201 had baseline CNS metastases. No SNP was associated with CNS-PFS. Genotype ABCG2 34GA/AA and/or ABCB1 3435CC --present in 35% of patients-- was significantly associated with decreased CNS-DFS (hazard ratio 0.28; 95% CI 0.11-0.73; p = 0.009) in the multivariate analysis. This remained significant after applying a Bonferroni correction and internal validation through bootstrapping. ABCG2 421CA/AA was related to more severe toxicity (27.0% versus 16.5%; p = 0.010).

Interpretation

ABCG2 34G>A and ABCB1 3435C>T are predictors for developing new CNS metastases during osimertinib treatment, probably because of diminished drug levels in the CNS. ABCG2 421C>A was significantly related with the incidence of severe toxicity. Pre-emptive genotyping for these SNPs could individualize osimertinib therapy. Addition of ABCG2 inhibitors for patients without ABCG2 34G>A should be studied further, to prevent new CNS metastases during osimertinib treatment.

Funding

No funding was received for this trial.

A beginner's guide on the use of brain organoids for neuroscientists: a systematic review

BACKGROUND

The first human brain organoid protocol was presented in the beginning of the previous decade, and since then, the field witnessed the development of many new brain region-specific models, and subsequent protocol adaptations and modifications. The vast amount of data available on brain organoid technology may be overwhelming for scientists new to the field and consequently decrease its accessibility. Here, we aimed at providing a practical guide for new researchers in the field by systematically reviewing human brain organoid publications.

METHODS

Articles published between 2010 and 2020 were selected and categorised for brain organoid applications. Those describing neurodevelopmental studies or protocols for novel organoid models were further analysed for culture duration of the brain organoids, protocol comparisons of key aspects of organoid generation, and performed functional characterisation assays. We then summarised the approaches taken for different models and analysed the application of small molecules and growth factors used to achieve organoid regionalisation. Finally, we analysed articles for organoid cell type compositions, the reported time points per cell type, and for immunofluorescence markers used to characterise different cell types.

RESULTS

Calcium imaging and patch clamp analysis were the most frequently used neuronal activity assays in brain organoids. Neural activity was shown in all analysed models, yet network activity was age, model, and assay dependent. Induction of dorsal forebrain organoids was primarily achieved through combined (dual) SMAD and Wnt signalling inhibition. Ventral forebrain organoid induction was performed with dual SMAD and Wnt signalling inhibition, together with additional activation of the Shh pathway. Cerebral organoids and dorsal forebrain model presented the most cell types between days 35 and 60. At 84 days, dorsal forebrain organoids contain astrocytes and potentially oligodendrocytes. Immunofluorescence analysis showed cell type-specific application of non-exclusive markers for multiple cell types.

CONCLUSIONS

We provide an easily accessible overview of human brain organoid cultures, which may help those working with brain organoids to define their choice of model, culture time, functional assay, differentiation, and characterisation strategies.

Marsdenia tenacissima extract prevents the malignant progression of glioma through upregulating lncRNA MEG3 and SFRP1-dependent inhibition of Wnt/β-catenin pathway

BACKGROUND/AIM

Recent studies have highlighted the tumor-suppressive effect of Marsdenia tenacissima extract (MTE) on human cancers. This research unveils the potential impact of MTE on glioma and ascertains the relevant molecular mechanisms.

METHODS

Glioma cells were treated with MTE, with normal human astrocytes (NHAs) as controls. A battery of function experiments, including the CCK-8 viability test, colony formation assay, scratch migration assay, and Transwell invasion assay, was executed to address the responses of glioma cells to MTE treatment and gain or loss of function of lncMEG3, miR-542-3p, and SFRP1. FISH, RIP, and dual-luciferase reporter assays were adopted for assessing gene interactions. U251-GFP-Luc cells were delivered into nude mice through intracranial injection to develop an orthotopic glioma model for in vivo validation.

RESULTS

200 mg/mL MTE could suppress the proliferating, migrating, and invading properties of glioma cells but not affect those of NHAs. MTE treatment enhanced the expression of lncMEG3, which competes with SFRP1 for binding miR-542-3p. SFRP1 could inactivate the Wnt/β-catenin pathway. Animal experimentation substantiated the antitumor activity and mechanism of MTE in nude mice.

CONCLUSIONS

MTE suppresses glioma via the lncMEG3/miR-542-3p/SFRP1/Wnt/β-catenin axis. These findings contribute to a theoretical basis for the use of MTE for glioma patients.

Isotopic Radiolabeling of Crizotinib with Fluorine-18 for In Vivo Pet Imaging

Crizotinib is a tyrosine kinase inhibitor approved for the treatment of non-small-cell lung cancer, but it is inefficient on brain metastases. Crizotinib is a substrate of the P-glycoprotein, and non-invasive nuclear imaging can be used to assess the brain penetration of crizotinib. Positron emission tomography (PET) imaging using fluorine-18-labeled crizotinib would be a powerful tool for investigating new strategies to enhance the brain distribution of crizotinib. We have synthesized a spirocyclic hypervalent iodine precursor for the isotopic labeling of crizotinib in a 2.4% yield. Because crizotinib is an enantiomerically pure drug, a chiral separation was performed to afford the (R)-precursor. A two-step radiolabeling process was optimized and automated using the racemic precursor to afford [18F](R,S)-crizotinib in 15 ± 2 radiochemical yield and 103 ± 18 GBq/µmol molar activity. The same radiolabeling process was applied to the (R)-precursor to afford [18F](R)-crizotinib with comparable results. As a proof-of-concept, PET was realized in a single non-human primate to demonstrate the feasibility of [18F](R)-crizotinib in in vivo imaging. Whole-body PET highlighted the elimination routes of crizotinib with negligible penetration in the brain (SUVmean = 0.1). This proof-of-concept paves the way for further studies using [18F](R)-crizotinib to enhance its brain penetration depending on the P-glycoprotein function.

Organoids and microphysiological systems: Promising models for accelerating AAV gene therapy studies

The FDA has predicted that at least 10-20 gene therapy products will be approved by 2025. The surge in the development of such therapies can be attributed to the advent of safe and effective gene delivery vectors such as adeno-associated virus (AAV). The enormous potential of AAV has been demonstrated by its use in over 100 clinical trials and the FDA’s approval of two AAV-based gene therapy products. Despite its demonstrated success in some clinical settings, AAV-based gene therapy is still plagued by issues related to host immunity, and recent studies have suggested that AAV vectors may actually integrate into the host cell genome, raising concerns over the potential for genotoxicity. To better understand these issues and develop means to overcome them, preclinical model systems that accurately recapitulate human physiology are needed. The objective of this review is to provide a brief overview of AAV gene therapy and its current hurdles, to discuss how 3D organoids, microphysiological systems, and body-on-a-chip platforms could serve as powerful models that could be adopted in the preclinical stage, and to provide some examples of the successful application of these models to answer critical questions regarding AAV biology and toxicity that could not have been answered using current animal models. Finally, technical considerations while adopting these models to study AAV gene therapy are also discussed.

Current Strategies to Enhance Delivery of Drugs across the Blood–Brain Barrier

The blood–brain barrier (BBB) has shown to be a significant obstacle to brain medication delivery. The BBB in a healthy brain is a diffusion barrier that prevents most substances from passing from the blood to the brain; only tiny molecules can pass across the BBB. The BBB is disturbed in specific pathological illnesses such as stroke, diabetes, seizures, multiple sclerosis, Parkinson’s disease, and Alzheimer’s disease. The goal of this study is to offer a general overview of current brain medication delivery techniques and associated topics from the last five years. It is anticipated that this review will stimulate readers to look into new ways to deliver medications to the brain. Following an introduction of the construction and function of the BBB in both healthy and pathological conditions, this review revisits certain contested questions, such as whether nanoparticles may cross the BBB on their own and if medications are selectively delivered to the brain by deliberately targeted nanoparticles. Current non-nanoparticle options are also discussed, including drug delivery via the permeable BBB under pathological circumstances and the use of non-invasive approaches to improve brain medication absorption.

The Development of Positron Emission Tomography Tracers for In Vivo Targeting the Kinase Domain of the Epidermal Growth Factor Receptor

Multiple small molecule PET tracers have been developed for the imaging of the epidermal growth factor receptor (EGFR). These tracers target the tyrosine kinase (TK) domain of the receptor and have been used for both quantifying EGFR expression and to differentiate between EGFR mutational statuses. However, the approaches for in vivo evaluation of these tracers are diverse and have resulted in data that are hard to compare. In this review, we analyze the historical development of the in vivo evaluation approaches, starting from the first EGFR TK PET tracer [11C]PD153035 to tracers developed based on TK inhibitors used for the clinical treatment of mutated EGFR expressing non-small cell lung cancer like [11C]erlotinib and [18F]afatinib. The evaluation of each tracer has been compiled to allow for a comparison between studies and ultimately between tracers. The main challenges for each group of tracers are thereafter discussed. Finally, this review addresses the challenges that need to be overcome to be able to efficiently drive EGFR PET imaging forward.

Assessing the Functional Redundancy between P-gp and BCRP in Controlling the Brain Distribution and Biliary Excretion of Dual Substrates with PET Imaging in Mice

P-glycoprotein (P-gp) and breast cancer resistance protein (BCRP) are co-localized at the blood–brain barrier, where they display functional redundancy to restrict the brain distribution of dual P-gp/BCRP substrate drugs. We used positron emission tomography (PET) with the metabolically stable P-gp/BCRP substrates [¹¹C]tariquidar, [¹¹C]erlotinib, and [¹¹C]elacridar to assess whether a similar functional redundancy as at the BBB exists in the liver, where both transporters mediate the biliary excretion of drugs. Wild-type, Abcb1a/b^(−/−), Abcg2^(−/−), and Abcb1a/b^(−/−)Abcg2^(−/−) mice underwent dynamic whole-body PET scans after i.v. injection of either [¹¹C]tariquidar, [¹¹C]erlotinib, or [¹¹C]elacridar. Brain uptake of all three radiotracers was markedly higher in Abcb1a/b^(−/−)Abcg2^(−/−) mice than in wild-type mice, while only moderately changed in Abcb1a/b^(−/−) and Abcg2^(−/−) mice. The transfer of radioactivity from liver to excreted bile was significantly lower in Abcb1a/b^(−/−)Abcg2^(−/−) mice and almost unchanged in Abcb1a/b^(−/−) and Abcg2^(−/−) mice (with the exception of [¹¹C]erlotinib, for which biliary excretion was also significantly reduced in Abcg2^(−/−) mice). Our data provide evidence for redundancy between P-gp and BCRP in controlling both the brain distribution and biliary excretion of dual P-gp/BCRP substrates and highlight the utility of PET as an upcoming tool to assess the effect of transporters on drug disposition at a whole-body level.

Understanding the brain uptake and permeability of small molecules through the BBB: A technical overview

The brain is the most important organ in our body requiring its unique microenvironment. By the virtue of its function, the blood-brain barrier poses a significant hurdle in drug delivery for the treatment of neurological diseases. There are also different theories regarding how molecules are typically effluxed from the brain. In this review, we comprehensively discuss how the different pharmacokinetic techniques used for measuring brain uptake/permeability of small molecules have evolved with time. We also discuss the advantages and disadvantages associated with these different techniques as well as the importance to utilize the right method to properly assess CNS exposure to drug molecules. Even though very strong advances have been made we still have a long way to go to ensure a reduction in failures in central nervous system drug development programs.

Novel Receptor Tyrosine Kinase Pathway Inhibitors for Targeted Radionuclide Therapy of Glioblastoma

Glioblastoma (GB) remains the most fatal brain tumor characterized by a high infiltration rate and treatment resistance. Overexpression and/or mutation of receptor tyrosine kinases is common in GB, which subsequently leads to the activation of many downstream pathways that have a critical impact on tumor progression and therapy resistance. Therefore, receptor tyrosine kinase inhibitors (RTKIs) have been investigated to improve the dismal prognosis of GB in an effort to evolve into a personalized targeted therapy strategy with a better treatment outcome. Numerous RTKIs have been approved in the clinic and several radiopharmaceuticals are part of (pre)clinical trials as a non-invasive method to identify patients who could benefit from RTKI. The latter opens up the scope for theranostic applications. In this review, the present status of RTKIs for the treatment, nuclear imaging and targeted radionuclide therapy of GB is presented. The focus will be on seven tyrosine kinase receptors, based on their central role in GB: EGFR, VEGFR, MET, PDGFR, FGFR, Eph receptor and IGF1R. Finally, by way of analyzing structural and physiological characteristics of the TKIs with promising clinical trial results, four small molecule RTKIs were selected based on their potential to become new therapeutic GB radiopharmaceuticals.