Tumor-Derived Extracellular Vesicles Breach the Intact Blood-Brain Barrier via Transcytosis

The restrictive nature of the blood-brain barrier (BBB) creates a major challenge for brain drug delivery with current nanomedicines lacking the ability to cross the BBB. Extracellular vesicles (EVs) have been shown to contribute to the progression of a variety of brain diseases including metastatic brain cancer and have been suggested as promising therapeutics and drug delivery vehicles. However, the ability of native tumor-derived EVs to breach the BBB and the mechanism(s) involved in this process remain unknown. Here, we demonstrate that tumor-derived EVs can breach the intact BBB in vivo, and by using state-of-the-art in vitro and in vivo models of the BBB, we have identified transcytosis as the mechanism underlying this process. Moreover, high spatiotemporal resolution microscopy demonstrated that the endothelial recycling endocytic pathway is involved in this transcellular transport. We further identify and characterize the mechanism by which tumor-derived EVs circumvent the low physiologic rate of transcytosis in the BBB by decreasing the brain endothelial expression of rab7 and increasing the efficiency of their transport. These findings identify previously unknown mechanisms by which tumor-derived EVs breach an intact BBB during the course of brain metastasis and can be leveraged to guide and inform the development of drug delivery approaches to deliver therapeutic cargoes across the BBB for treatment of a variety of brain diseases including, but not limited to, brain malignancies.

Dual and multi-targeted nanoparticles for site-specific brain drug delivery

In recent years, nanomedicines have emerged as a promising method for central nervous system drug delivery, enabling the drugs to overcome the blood-brain barrier and accumulate preferentially in the brain. Despite the current success of brain-targeted nanomedicines, limitations still exist in terms of the targeting specificity. Based on the molecular mechanism, the exact cell populations and subcellular organelles where the injury occurs and the drugs take effect have been increasingly accepted as a more specific target for the next generation of nanomedicines. Dual and multi-targeted nanoparticles integrate different targeting functionalities and have provided a paradigm for precisely delivering the drug to the pathological site inside the brain. The targeting process often involves the sequential or synchronized navigation of the targeting moieties, which allows highly controlled drug delivery compared to conventional targeting strategies. Herein, we focus on the up-to-date design of pathological site-specific nanoparticles for brain drug delivery, highlighting the dual and multi-targeting strategies that were employed and their impact on improving targeting specificity and therapeutic effects. Furthermore, the background discussion of the basic properties of a brain-targeted nanoparticle and the common lesion features classified by neurological pathology are systematically summarized.

Manipulation of Mitophagy by "All-in-One" nanosensitizer augments sonodynamic glioma therapy

Limited penetration of chemotherapeutic drugs through the blood brain barrier (BBB), and the increased chemo-resistance of glioma cells due to macroautophagy/autophagy, result in high tumor recurrence and extremely limited survival of glioma patients. Ultrasound-targeted microbubble destruction (UTMD) is a technique of transient and reversible BBB disruption, which greatly facilitates intracerebral drug delivery. In addition, sonodynamic therapy (SDT) based on ultrasound stimulation and a sonosensitizer, can be a safe and noninvasive strategy for treating glioma. We innovatively designed a smart "all-in-one" nanosensitizer platform by incorporating the sonoactive chlorin e6 (Ce6) and an autophagy inhibitor-hydroxychloroquine (HCQ) into angiopep-2 peptide-modified liposomes (designated as ACHL), which integrates multiple diagnostic and therapeutic functions. ACHL selectively accumulated in the brain tumors during the optimal time-window of transient UTMD-mediated BBB opening. The nanosensitizer then responded to a second ultrasonic stimulation, and simultaneously unloaded HCQ and generated ROS in the glioma cells. The sonotherapy triggered apoptosis as well as MAPK/p38-PINK1-PRKN-dependent mitophagy, in which the antioxidant relieved the sonotoxicity and MAPK/p38 activation, while the inhibition of MAPK/p38 attenuated the progression toward mitophagy by compromising redistribution of PRKN. Moreover, HCQ blocking autophagosome degradation, augmented intracellular ROS production and resulted in an oxidative-damage regenerative loop. ACHL-SDT treatment using this construct significantly inhibited the xenograft-tumor growth and prolonged the survival time of tumor-bearing mice, exhibiting an improved therapeutic efficiency. All together, we demonstrated a precision sonotherapy with simultaneous apoptosis induction and mitophagy inhibition, which served as an intelligently strategic sense of working alongside, providing new insights into the theranostics of brain tumors.

ABBREVIATIONS

ACHL: Angiopep-2-modified liposomes loaded with Ce6 and hydroxychloroquine; ACL: Angiopep-2-modified liposomes loaded with Ce6; BBB: blood brain barrier; Ce6: chlorin e6; CHL: liposomes loaded with Ce6 and hydroxychloroquine; CL: liposomes loaded with Ce6; CNS: central nervous system; DDS: drug delivery system; EB: Evans blue; FUS: focused ultrasound; HCQ: hydroxychloroquine; LRP1: low density lipoprotein receptor-related protein 1; MAP1LC3/LC3: microtubule-associated protein 1 light chain 3; MAPK: mitogen-activated protein kinase; MBs: microbubbles; MTG: MitoTracker Green; MTR: MitoTracker Red; MTT: 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide; PBS: phosphate-buffered saline; PDI: polydispersity index; PINK1: PTEN induced kinase 1; PRKN/parkin: parkin RBR E3 ubiquitin protein ligase; ROS: reactive oxygen species; SDT: sonodynamic therapy; SQSTM1: sequestome 1; TA: terephthalic acid; TEM: transmission electron microscopy; TUNEL: terminal deoxynucleotidyl transferase mediated dUTP nick-end labeling; US: ultrasound; UTMD: ultrasound-targeted microbubble destruction.

Transcytosis - An effective targeting strategy that is complementary to "EPR effect" for pancreatic cancer nano drug delivery

Numerous nano drug delivery systems have been developed for preclinical cancer research in the past 15 years with the hope for a fundamental change in oncology. The robust nanotherapeutic research has yielded early-stage clinical products as exemplified by the FDA-approved nano formulations (Abraxane® for paclitaxel and Onyvide® for irinotecan) for the treatment of solid tumors, including pancreatic ductal adenocarcinoma (PDAC). It is generally believed that enhanced permeability and retention (EPR) plays a key role in nanocarriers' accumulation in preclinical tumor models and is a clinically relevant phenomenon in certain cancer types. However, use of EPR effect as an across-the-board explanation for nanoparticle tumor access is likely over-simplified, particularly in the stroma rich solid tumors such as PDAC. Recently, ample evidences including our own data showed that it is possible to use transcytosis as a major mechanism for PDAC drug delivery. In this mini-review, we summarize the key studies that discuss how transcytosis can be employed to enhance EPR effect in PDAC, and potentially, other cancer malignancies. We also mentioned other vasculature engineering approaches that work beyond the classic EPR effect.

Hyaluronic Acid-Conjugated with Hyperbranched Chlorin e6 Using Disulfide Linkage and Its Nanophotosensitizer for Enhanced Photodynamic Therapy of Cancer Cells

The main purpose of this study is to synthesize novel types of nanophotosensitizers that are based on hyperbranched chlorin e6 (Ce6) via disulfide linkages. Moreover, hyperbranched Ce6 was conjugated with hyaluronic acid (HA) for CD44-receptor mediated delivery and redox-sensitive photodynamic therapy (PDT) against cancer cells. Hyperbranched Ce6 was considered to make novel types of macromolecular photosensitizer since most of the previous studies regarding nanophotosensizers are concerned with simple conjugation between monomeric units of photosensitizer and polymer materials. Hyperbranched Ce6 was synthesized by conjugation of Ce6 each other while using disulfide linkage. To synthesize Ce6 tetramer, carboxyl groups of Ce6 were conjugated with cystamine and three equivalents of Ce6 were then conjugated again with the end of amine groups of Ce6-cystamine. To synthesize Ce6 decamer as a hyperbranched Ce6, six equivalents of Ce6 was conjugated with the end of Ce6 tetramer via cystamine linkage. Furthermore, HA-cystamine was attached with Ce6 tetramer or Ce6 decamer to synthesize HA-Ce6 tetramer (Ce6tetraHA) or HA-Ce6 decamer (Ce6decaHA) conjugates. Ce6tetraHA and Ce6decaHA nanophotosensitizers showed small diameters of less than 200 nm. The addition of dithiothreitol (DTT) and hyaluronidase (HAse) induced a faster Ce6 release rate in vitro drug release study, which indicated that Ce6tetraHA nanophotosensitizers possess redox-sensitive and HAse-sensitive release properties. Ce6tetraHA nanophotosensitizers showed higher intracellular Ce6 accumulation, higher ROS generation, and higher PDT efficacy than that of Ce6 alone. Ce6tetraHA nanophotosensitizers responded to the CD44 receptor of cancer cell surface, i.e., the pre-treatment of HA blocked CD44 receptor of U87MG or HCT116 cells and then inhibited delivery of nanophotosensitizers in vitro cell culture study. Furthermore, in vivo tumorxenograft study showed that fluorescence intensity in the tumor tissues was stronger than those of other organs, while CD44 receptor blocking by HA pretreatment induced a decrease of fluorescence intensity in tumor tissues when compared to liver. These results indicated that Ce6tetraHA nanophotosensitizers delivered to tumors by redox-sensitive and CD44-sensitive manner.

Nanomaterial-based blood-brain-barrier (BBB) crossing strategies

Increasing attention has been paid to the diseases of central nervous system (CNS). The penetration efficiency of most CNS drugs into the brain parenchyma is rather limited due to the existence of blood-brain barrier (BBB). Thus, BBB crossing for drug delivery to CNS remains a significant challenge in the development of neurological therapeutics. Because of the advantageous properties (e.g., relatively high drug loading content, controllable drug release, excellent passive and active targeting, good stability, biodegradability, biocompatibility, and low toxicity), nanomaterials with BBB-crossability have been widely developed for the treatment of CNS diseases. This review summarizes the current understanding of the physiological structure of BBB, and provides various nanomaterial-based BBB-crossing strategies for brain delivery of theranostic agents, including intranasal delivery, temporary disruption of BBB, local delivery, cell penetrating peptide (CPP) mediated BBB-crossing, receptor mediated BBB-crossing, shuttle peptide mediated BBB-crossing, and cells mediated BBB-crossing. Clinicians, biologists, material scientists and chemists are expected to be interested in this review.

Boosting often overlooked long wavelength emissions of rare-earth nanoparticles for NIR-II fluorescence imaging of orthotopic glioblastoma

Rare-earth nanoparticles (RE NPs) with narrow long wavelength emissions have been recently investigated for their potential application for fluorescence imaging in the second near-infrared window (NIR-II). Previously these RE NPs have a very limited application in the diagnosis and treatment of deep-seated tumors such as brain tumors, due to their weak fluorescence in the range of 1300-1700 nm. Herein, we report a significant enhancement of more than 10 times regular emission of NaNdF₄ nanoparticles at 1340 nm wavelength by coating them with an inert layer of NaLuF₄, followed by sensitizing with a near-infrared dye (IR-808). We deliver these highly bright nanoparticles into the brain by using focused ultrasound to temporarily open the blood-brain barrier (BBB), and then detect the orthotopic glioblastoma by fluorescence imaging at 1340 nm. The images obtained from long wavelength fluorescence (i.e. 1340 nm) exhibited better resolution and contrast compared to the short wavelength fluorescence (i.e. 1060 nm). Our study not only provides insights for enhancing often overlooked emissions of rare-earth nanoparticles for NIR-II fluorescence imaging of deep-seated tumors, but also demonstrates great potential of focused ultrasound based technology in delivering nanotheranostic agents.

A Novel Drug Design Strategy: An Inspiration from Encaging Tumor by Metallofullerenol Gd@C82(OH)22

Cancer remains a major threat to human health worldwide. Cytotoxicity has imposed restrictions on the conventional cytotoxic drug-based chemotherapy. The rapidly-developing nanomedicine has shown great promise in revolutionizing chemotherapy with improved efficiency and reduced toxicity. Gd@C₈₂(OH)₂₂, a novel endohedral metallofullerenol, was first reported by our research group to suppress tumor growth and metastasis efficiently without obvious toxicity. Gd@C₈₂(OH)₂₂ imprisons tumors by facilitating the formation of surrounding fibrous layers which is different from chemotherapeutics that poison tumor cells. In this review, the authors first reported the antineoplastic activity of metallofullerenol Gd@C₈₂(OH)₂₂ followed by further discussions on its new anti-cancer molecular mechanism—tumor encaging. On this basis, the unparalleled advantages of nanomedicine in the future drug design are discussed. The unique interaction modes of Gd@C₈₂(OH)₂₂ with specific targeted biomolecules may shed light on a new avenue for drug design. Depending on the surface characteristics of target biomolecules, nanomedicine, just like a transformable and dynamic key, can self-assemble into suitable shapes to match several locks for the thermodynamic stability, suggesting the target-tailoring ability of nanomedicine.