Up-regulating blood brain barrier permeability of nanoparticles via multivalent effect

Pantothenate-encapsulated liposomes combined with exercise for effective inhibition of CRM1-mediated PKM2 translocation in Alzheimer's therapy

Alzheimer's disease (AD) is a complex neurodegenerative condition characterized by metabolic imbalances and neuroinflammation, posing a formidable challenge in medicine due to the lack of effective treatments. Despite considerable research efforts, a cure for AD remains elusive, with current therapies primarily focused on symptom management rather than addressing the disease's underlying causes. This study initially discerned, through Mendelian randomization analysis that elevating pantothenate levels significantly contributes to the prophylaxis of Alzheimer's disease. We explore the therapeutic potential of pantothenate encapsulated in liposomes (Pan@TRF@Liposome NPs), targeting the modulation of CRM1-mediated PKM2 nuclear translocation, a critical mechanism in AD pathology. Additionally, we investigate the synergistic effects of exercise, proposing a combined approach to AD treatment. Exercise-induced metabolic alterations share significant similarities with those associated with dementia, suggesting a potential complementary effect. The Pan@TRF@Liposome NPs exhibit notable biocompatibility, showing no liver or kidney toxicity in vivo, while demonstrating stability and effectiveness in modulating CRM1-mediated PKM2 nuclear translocation, thereby reducing neuroinflammation and neuronal apoptosis. The combined treatment of exercise and Pan@TRF@Liposome NP administration in an AD animal model leads to improved neurofunctional outcomes and cognitive performance. These findings highlight the nanoparticles' role as effective modulators of CRM1-mediated PKM2 nuclear translocation, with significant implications for mitigating neuroinflammation and neuronal apoptosis. Together with exercise, this dual-modality approach could offer new avenues for enhancing cognitive performance and neurofunctional outcomes in AD, marking a promising step forward in developing treatment strategies for this challenging disorder.

Tumor Abnormality-Oriented Nanomedicine Design

Anticancer nanomedicines have been proven effective in mitigating the side effects of chemotherapeutic drugs. However, challenges remain in augmenting their therapeutic efficacy. Nanomedicines responsive to the pathological abnormalities in the tumor microenvironment (TME) are expected to overcome the biological limitations of conventional nanomedicines, enhance the therapeutic efficacies, and further reduce the side effects. This Review aims to quantitate the various pathological abnormalities in the TME, which may serve as unique endogenous stimuli for the design of stimuli-responsive nanomedicines, and to provide a broad and objective perspective on the current understanding of stimuli-responsive nanomedicines for cancer treatment. We dissect the typical transport process and barriers of cancer drug delivery, highlight the key design principles of stimuli-responsive nanomedicines designed to tackle the series of barriers in the typical drug delivery process, and discuss the "all-into-one" and "one-for-all" strategies for integrating the needed properties for nanomedicines. Ultimately, we provide insight into the challenges and future perspectives toward the clinical translation of stimuli-responsive nanomedicines.

Dual targeting micelles loaded with paclitaxel and lapatinib for combinational therapy of brain metastases from breast cancer

Due to the presence of the blood–brain barrier (BBB), the delivery of general drugs into the brain tissue remains to be a tricky problem. For patients with brain metastases from breast cancer, drug delivery systems must overcome this physical barrier. Targeted nano vehicles arise as a promising alternative to deliver drugs to brain tissues successively. Herein, a dual targeting micelle drug delivery system loaded with paclitaxel (PTX) and lapatinib (LPTN) was developed for combinational therapy of brain metastases. In our study, it was shown the micelles modified with Angiopep-2 had high loading efficiency of paclitaxel and lapatinib (Ang-MIC-PTX/LP). In addition, Ang-MIC-PTX/LP could transport across the in vitro BBB model and accumulate in breast cancer cells. After intravenous injection, Ang-MIC significantly accumulated in the brain metastasis. Ang-MIC-PTX/LP could also extend the life span of brain metastasis mouse models. Overall, this study provided a promising method for treatment of brain metastases from breast cancer.

Angiopep-2-Modified Nanoparticles for Brain-Directed Delivery of Therapeutics: A Review

Nanotechnology has opened up a world of possibilities for the treatment of brain disorders. Nanosystems can be designed to encapsulate, carry, and deliver a variety of therapeutic agents, including drugs and nucleic acids. Nanoparticles may also be formulated to contain photosensitizers or, on their own, serve as photothermal conversion agents for phototherapy. Furthermore, nano-delivery agents can enhance the efficacy of contrast agents for improved brain imaging and diagnostics. However, effective nano-delivery to the brain is seriously hampered by the formidable blood-brain barrier (BBB). Advances in understanding natural transport routes across the BBB have led to receptor-mediated transcytosis being exploited as a possible means of nanoparticle uptake. In this regard, the oligopeptide Angiopep-2, which has high BBB transcytosis capacity, has been utilized as a targeting ligand. Various organic and inorganic nanostructures have been functionalized with Angiopep-2 to direct therapeutic and diagnostic agents to the brain. Not only have these shown great promise in the treatment and diagnosis of brain cancer but they have also been investigated for the treatment of brain injury, stroke, epilepsy, Parkinson's disease, and Alzheimer's disease. This review focuses on studies conducted from 2010 to 2021 with Angiopep-2-modified nanoparticles aimed at the treatment and diagnosis of brain disorders.

Imaging epileptic foci in mouse models via a low-density lipoprotein receptor-related protein-1 targeting strategy

Background

In the setting of drug-resistant epilepsy (DRE), the success of surgery depends on the ability to accurately locate the epileptic foci to be resected or disconnected. However, the epileptic foci in a considerable percentage of the DRE patients cannot be adequately localised. This warrants the need for a reliable imaging strategy to identify the “concealed” epileptic regions.

Methods

Brain specimens from DRE patients and kainate-induced epileptic mouse models were immuno-stained to evaluate the integrity of the blood-brain barrier (BBB). The expression of low-density lipoprotein receptor-related protein-1 (LRP1) in the epileptic region of DRE patients and kainate models was studied by immunofluorescence. A micellar-based LRP1-targeted paramagnetic probe (Gd³⁺-LP) was developed and its ability to define the epileptic foci was investigated by magnetic resonance imaging (MRI).

Findings

The integrity of the BBB in the epileptic region of DRE patients and kainate mouse models were demonstrated. LRP1 expression levels in the epileptic foci of DRE patients and kainate models were 1.70–2.38 and 2.32–3.97 folds higher than in the control brain tissues, respectively. In vivo MRI demonstrated that Gd³⁺-LP offered 1.68 times higher (P < 0.05) T1-weighted intensity enhancement in the ipsilateral hippocampus of chronic kainite models than the control probe without LRP1 specificity.

Interpretation

The expression of LRP1 is up-regulated in vascular endothelium, activated glia in both DRE patients and kainate models. LRP1-targeted imaging strategy may provide an alternative strategy to define the “concealed” epileptic foci by overcoming the intact BBB.

Funding

This work was supported by the National Natural Science Foundation, Shanghai Science and Technology Committee, Shanghai Municipal Science and Technology, Shanghai Municipal Health and Family Planning Commission and the National Postdoctoral Program for Innovative Talents.

Current Status and Challenges Associated with CNS-Targeted Gene Delivery across the BBB

The era of the aging society has arrived, and this is accompanied by an increase in the absolute numbers of patients with neurological disorders, such as Alzheimer’s disease (AD) and Parkinson’s disease (PD). Such neurological disorders are serious costly diseases that have a significant impact on society, both globally and socially. Gene therapy has great promise for the treatment of neurological disorders, but only a few gene therapy drugs are currently available. Delivery to the brain is the biggest hurdle in developing new drugs for the central nervous system (CNS) diseases and this is especially true in the case of gene delivery. Nanotechnologies such as viral and non-viral vectors allow efficient brain-targeted gene delivery systems to be created. The purpose of this review is to provide a comprehensive review of the current status of the development of successful drug delivery to the CNS for the treatment of CNS-related disorders especially by gene therapy. We mainly address three aspects of this situation: (1) blood-brain barrier (BBB) functions; (2) adeno-associated viral (AAV) vectors, currently the most advanced gene delivery vector; (3) non-viral brain targeting by non-invasive methods.

AKT activation by SC79 to transiently re-open pathological blood brain barrier for improved functionalized nanoparticles therapy of glioblastoma

Glioblastoma (GBM) is one of the malignant tumors with high mortality, and the presence of the blood brain barrier (BBB) severely limits the penetration and tissue accumulation of therapeutic agents in the lesion of GBM. Active targeting nanotechnologies can achieve efficient drug delivery in the brain, while still have a very low success rate. Here we revealed a previously unexplored phenomenon that chemotherapy with active targeting nanotechnologies causes pathological BBB functional recovery through VEGF-PI3K-AKT signaling pathway inhibition, accompanied with up-regulated expression of Claudin-5 and Occludin. Seriously, pathological BBB functional recovery induces a significant decrease of intracerebral active targeting nanotechnologies transport during GBM multiple administration, leading to chemotherapy failure in GBM therapeutics. To address this issue, we chose AKT agonist SC79 to transiently re-open functional recovering pathological BBB for continuously intracerebral delivery of brain targeted nanotherapeutics, finally producing an observable anti-GBM effect in vivo, which may offer new sight for other CNS disease treatment.

Transformable nanoparticles triggered by cancer-associated fibroblasts for improving drug permeability and efficacy in desmoplastic tumors

Cancer-associated fibroblasts (CAFs) are important barriers for nanoparticles (NPs) to deeply penetrate into tumors and severely limit the antitumor efficacy of nanomedicines. Herein, we proposed a CAF-triggered transformable drug delivery system based on a cleavable peptide responsive to fibroblast activation protein-α (FAP-α) specifically overexpressed on the surface of CAFs. The NPs were composed of cationic poly(amidoamine) (PAMAM) dendrimers cross-linked by our designed peptide, a chemotherapeutical drug was incorporated onto PAMAM using disulfide bonds and finally, hyaluronic acid (HA) was conjugated to improve the tumor targetability as well as biocompatibility through electrostatic interactions. These NPs had an initial size of ∼200 nm and negative zeta potential favorable for stable blood circulation; however, after docking with CAFs, they dissociated into smaller NPs and exposed the relative positive surface charge to facilitate penetration and enter the tumor cells together with CAFs. An interesting finding was that this system intracellularly released different levels of drugs in these two kinds of cells, which was beneficial for the disruption of the stromal barrier and increasing the local drug accumulation. Our investigation confirmed that the constructed system could alleviate the biological barriers and hold promising therapeutic efficiency for desmoplastic solid tumors.

A multifunctional low-generation dendrimer-based nanoprobe for the targeted dual mode MR/CT imaging of orthotopic brain gliomas

An RGD peptide-targeted low-generation dendrimer nanoprobe can cross the blood-brain barrier for dual-modal MR/CT imaging of an orthotopic brain glioma.

Effect of flow on targeting and penetration of angiopep-decorated nanoparticles in a microfluidic model blood-brain barrier

The blood-brain barrier (BBB) limits transport of nanoparticles from the circulation to the brain parenchyma. Angiopep-2, a peptide which functions as a brain transport vector, can be coupled to nanoparticles in order to facilitate binding and internalization by brain endothelial cells (ECs), and subsequent BBB penetration. This multi-step process may be affected by blood flow over brain ECs, as flow influences endothelial cell phenotype as well as interactions of nanoparticles with ECs. In the present study a microfluidic BBB model was constructed to evaluate binding and internalization by brain ECs, as well as BBB penetration of Angiopep-2 coupled liposomes (Ang2-Liposomes) in static and flow conditions. Ang2 conjugation to liposomes markedly improved binding relative to unconjugated liposomes. Ang2-Liposomes bound and were internalized efficiently by brain endothelial cells after static incubation or with 1 dyne/cm² of fluid shear stress (FSS), while binding was reduced at a FSS of 6 dyne/cm². Penetration of the model microfluidic BBB by Ang2-Liposomes was higher at a FSS of 1 dyne/cm² and 6 dyne/cm² than with static incubation. Analysis of barrier function and control experiments for receptor-mediated penetration provided insight into the magnitude of transcellular versus paracellular transport at each tested FSS. Overall, the results demonstrate that flow impacted the binding and BBB penetration of Ang2-functionalized nanoparticles. This highlights the relevance of the local flow environment for in vitro modeling of the performance of nanoparticles functionalized with BBB penetrating ligands.

Peptide-Functionalized Nanoinhibitor Restrains Brain Tumor Growth by Abrogating Mesenchymal-Epithelial Transition Factor (MET) Signaling

Malignant gliomas are the most common primary brain tumors and are associated with aggressive growth, high morbidity, and mortality. Aberrant mesenchymal-epithelial transition factor (MET) activation occurs in approximately 30% of glioma patients and correlates with poor prognosis, elevated invasion, and increased drug resistance. Therefore, MET has emerged as an attractive target for glioma therapy. In this study, we developed a novel nanoinhibitor by conjugating MET-targeting cMBP peptides on the G4 dendrimer. Compared to the binding affinity of the free peptide ( K_D = 3.96 × 10^-7 M), the binding affinity of the nanoinhibitor to MET increased 3 orders of magnitude to 1.32 × 10^-10 M. This nanoinhibitor efficiently reduced the proliferation and invasion of human glioblastoma U87MG cells in vitro by blocking MET signaling with remarkably attenuated levels of phosphorylated MET ( pMET) and its downstream signaling proteins, such as pAKT and pERK1/2. Although no obvious therapeutic effect was observed after treatment with free cBMP peptide, in vivo T2-weighted magnetic resonance imaging (MRI) showed a significant delay in tumor growth after intravenous injection of the nanoinhibitor. The medium survival in mouse models was extended by 59%, which is similar to the effects of PF-04217903, a small molecule MET inhibitor currently in clinical trials. Immunoblotting studies of tumor homogenate verified that the nanoinhibitor restrained glioma growth by blocking MET downstream signaling. pMET and its downstream proteins pAKT and pERK1/2, which are involved in the survival and invasion of cancer cells, decreased in the nanoinhibitor-treated group by 44.2%, 62.2%, and 32.3%, respectively, compared with those in the control group. In summary, we developed a peptide-functionalized MET nanoinhibitor that showed extremely high binding affinity to MET and effectively inhibited glioma growth by blocking MET downstream signaling. To the best of our knowledge, this is the first report of therapeutic inhibition of glioma growth by blocking MET signaling with a novel nanoinhibitor. Compared to antibodies and chemical inhibitors in clinical trials, the nanoinhibitor blocks MET signaling and provides a new approach for the treatment of glioma with the advantages of high efficiency, affordability, and, most importantly, potentially reduced drug resistance.

Blood-brain barrier shuttle peptides: an emerging paradigm for brain delivery

Brain delivery is one of the major challenges in drug development because of the high number of patients suffering from neural diseases and the low efficiency of the treatments available. Although the blood-brain barrier (BBB) prevents most drugs from reaching their targets, molecular vectors - known as BBB shuttles - offer great promise to safely overcome this formidable obstacle. In recent years, peptide shuttles have received growing attention because of their lower cost, reduced immunogenicity, and higher chemical versatility than traditional Trojan horse antibodies and other proteins.

Modular peptide-functionalized gold nanorods for effective glioblastoma multicellular tumor spheroid targeting

Peptide functionalized gold nanorods for photothermally induced glioblastoma tumor shrinkage.

A novel strategy to achieve effective drug delivery: exploit cells as carrier combined with nanoparticles

Cell-mediated drug delivery systems employ specific cells as drug vehicles to deliver drugs to targeted sites. Therapeutics or imaging agents are loaded into these cells and then released in diseased sites. These specific cells mainly include red blood cells, leukocytes, stem cells and so on. The cell acts as a Trojan horse to transfer the drug from circulating blood to the diseased tissue. In such a system, these cells keep their original properties, which allow them to mimic the migration behavior of specific cells to carry drug to the targeted site after in vivo administration. This strategy elegantly combines the advantages of both carriers, i.e. the adjustability of nanoparticles (NPs) and the natural functions of active cells, which therefore provides a new perspective to challenge current obstacles in drug delivery. This review will describe a fundamental understanding of these cell-based drug delivery systems, and discuss the great potential of combinational application of cell carrier and NPs.

Current and evolving approaches for improving the oral permeability of BCS Class III or analogous molecules

The Biopharmaceutics Classification System (BCS) classifies pharmaceutical compounds based on their aqueous solubility and intestinal permeability. The BCS Class III compounds are hydrophilic molecules (high aqueous solubility) with low permeability across the biological membranes. While these compounds are pharmacologically effective, poor absorption due to low permeability becomes the rate-limiting step in achieving adequate bioavailability. Several approaches have been explored and utilized for improving the permeability profiles of these compounds. The approaches include traditional methods such as prodrugs, permeation enhancers, ion-pairing, etc., as well as relatively modern approaches such as nanoencapsulation and nanosizing. The most recent approaches include a combination/hybridization of one or more traditional approaches to improve drug permeability. While some of these approaches have been extremely successful, i.e. drug products utilizing the approach have progressed through the USFDA approval for marketing; others require further investigation to be applicable. This article discusses the commonly studied approaches for improving the permeability of BCS Class III compounds.

A non-viral suicide gene delivery system traversing the blood brain barrier for non-invasive glioma targeting treatment

Herpes simplex virus type I thymidine kinase gene (HSV-TK) in viral vector is a promising strategy against glioblastoma multiforme (GBM). However, the biosafety risk restricts its application in clinic. In this work, poly (l-lysine)-grafted polyethylenimine (PEI-PLL), which combines the high transfection efficiency of polyethylenimine and the good biodegradability of poly (l-lysine), was adopted as the non-viral vector backbone. Angiopep-2, a blood brain barrier (BBB) crossing and glioma targeting bifunctional peptide was conjugated on PEI-PLL via polyethyleneglycol (PEG) and designated as PPA. The optimal transfection ratio of PPA/DNA complexes nanoparticles (PPA NPs) was firstly characterized. Next, the glioma targeting of the PPA NPs was confirmed through cellular uptake and transfection analysis. The in vivo imaging studies demonstrated that the PPA NPs could not only penetrate BBB but also accumulate in striatum and cortex via systemic administration. Moreover, the PPA/HSV-TK NPs showed remarkably anti-glioma effect and survival benefit in an invasive orthotopic human GBM mouse model through inhibiting proliferation and inducing apoptosis (p<0.05 vs control). This study firstly illustrated that the cationic polymer PPA could be exploited as an efficient gene vector to cross the BBB, and innovatively provided a potential non-viral nanomedicine for noninvasive suicide gene therapy in the glioma treatment.

Progress and perspectives on targeting nanoparticles for brain drug delivery

Due to the ability of the blood-brain barrier (BBB) to prevent the entry of drugs into the brain, it is a challenge to treat central nervous system disorders pharmacologically. The development of nanotechnology provides potential to overcome this problem. In this review, the barriers to brain-targeted drug delivery are reviewed, including the BBB, blood-brain tumor barrier (BBTB), and nose-to-brain barrier. Delivery strategies are focused on overcoming the BBB, directly targeting diseased cells in the brain, and dual-targeted delivery. The major concerns and perspectives on constructing brain-targeted delivery systems are discussed.

Multivalent Conjugates of Sonic Hedgehog Accelerate Diabetic Wound Healing

Despite their preclinical promise, few recombinant growth factors have been fully developed into effective therapies, in part, due to the short interval of therapeutic activity after administration. To address this problem, we developed nanoscale polymer conjugates for multivalent presentation of therapeutic proteins that enhance the activation of targeted cellular responses. As an example of this technology, we conjugated multiple Sonic hedgehog (Shh) proteins onto individual hyaluronic acid biopolymers to generate multivalent protein clusters at defined ratios (i.e., valencies) that yield enhanced Shh pathway activation at equivalent concentrations relative to unconjugated Shh. In this study, we investigated whether these multivalent conjugates (mvShh) could be used to improve the therapeutic function of Shh. We found that a single treatment with mvShh significantly accelerated the closure of full-thickness wounds in diabetic (db/db) mice compared to either an equivalent dose of unconjugated Shh or the vehicle control. Furthermore, we identified specific indicators of wound healing in fibroblasts and endothelial cells (i.e., transcriptional activation and cell migration) that were activated by mvShh in vitro and at concentrations approximately an order of magnitude lower than the unconjugated Shh. Taken together, our findings suggest that mvShh conjugates exhibit greater potency to activate the Shh pathway, and this multivalency advantage improves its therapeutic effect to accelerate wound closure in a diabetic animal model. Our strategy of multivalent protein presentation using nanoscale polymer conjugates has the potential to make a significant impact on the development of protein-based therapies by improving their in vivo performance.

Nanoparticles for brain-specific drug and genetic material delivery, imaging and diagnosis

The poor access of therapeutic drugs and genetic material into the central nervous system due to the presence of the blood-brain barrier often limits the development of effective noninvasive treatments and diagnoses of neurological disorders. Moreover, the delivery of genetic material into neuronal cells remains a challenge because of the intrinsic difficulty in transfecting this cell type. Nanotechnology has arisen as a promising tool to provide solutions for this problem. This review will cover the different approaches that have been developed to deliver drugs and genetic material efficiently to the central nervous system as well as the main nanomaterials used to image the central nervous system and diagnose its disorders.

Crossing the barrier: treatment of brain tumors using nanochain particles

Despite advancements in surgery and radiotherapy, the aggressive forms of brain tumors, such as gliomas, are still uniformly lethal with current therapies offering only palliation complicated by significant toxicities. Gliomas are characteristically diffuse with infiltrating edges, resistant to drugs and nearly inaccessible to systemic therapies due to the brain-tumor barrier. Currently, aggressive efforts are underway to further understand brain-tumor's microenvironment and identify brain tumor cell-specific regulators amenable to pharmacologic interventions. While new potent agents are continuously becoming available, efficient drug delivery to brain tumors remains a limiting factor. To tackle the drug delivery issues, a multicomponent chain-like nanoparticle has been developed. These nanochains are comprised of iron oxide nanospheres and a drug-loaded liposome chemically linked into a 100-nm linear, chain-like assembly with high precision. The nanochain possesses a unique ability to scavenge the tumor endothelium. By utilizing effective vascular targeting, the nanochains achieve rapid deposition on the vascular bed of glioma sites establishing well-distributed drug reservoirs on the endothelium of brain tumors. After reaching the target sites, an on-command, external low-power radiofrequency field can remotely trigger rapid drug release, due to mechanical disruption of the liposome, facilitating widespread and effective drug delivery into regions harboring brain tumor cells. Integration of the nanochain delivery system with the appropriate combination of complementary drugs has the potential to unfold the field and allow significant expansion of therapies for the disease where success is currently very limited. WIREs Nanomed Nanobiotechnol 2016, 8:678-695. doi: 10.1002/wnan.1387 For further resources related to this article, please visit the WIREs website.

Promising approaches to circumvent the blood-brain barrier: progress, pitfalls and clinical prospects in brain cancer

Brain drug delivery is a major challenge for therapy of central nervous system (CNS) diseases. Biochemical modifications of drugs or drug nanocarriers, methods of local delivery, and blood-brain barrier (BBB) disruption with focused ultrasound and microbubbles are promising approaches which enhance transport or bypass the BBB. These approaches are discussed in the context of brain cancer as an example in CNS drug development. Targeting to receptors enabling transport across the BBB offers noninvasive delivery of small molecule and biological cancer therapeutics. Local delivery methods enable high dose delivery while avoiding systemic exposure. BBB disruption with focused ultrasound and microbubbles offers local and noninvasive treatment. Clinical trials show the prospects of these technologies and point to challenges for the future.

Barriers to drug delivery in solid tumors

Over the last decade, significant progress has been made in the field of drug delivery. The advent of engineered nanoparticles has allowed us to circumvent the initial limitations to drug delivery such as pharmacokinetics and solubility. However, in spite of significant advances to tumor targeting, an effective treatment strategy for malignant tumors still remains elusive. Tumors possess distinct physiological features which allow them to resist traditional treatment approaches. This combined with the complexity of the biological system presents significant hurdles to the site-specific delivery of therapeutic drugs. One of the key features of engineered nanoparticles is that these can be tailored to execute specific functions. With this review, we hope to provide the reader with a clear understanding and knowledge of biological barriers and the methods to exploit these characteristics to design multifunctional nanocarriers, effect useful dosing regimens and subsequently improve therapeutic outcomes in the clinic.

Retro-inverso isomer of Angiopep-2: a stable d-peptide ligand inspires brain-targeted drug delivery

The blood-brain barrier (BBB) prevents most drugs from reaching the site of central nervous system (CNS) diseases, intensively confining the therapeutic efficiency. Angiopep-2 (here termed (L)Angiopep), which is a 19-mer peptide derived from human Kunitz domain, can trigger transcytosis and traverse the BBB by recognizing low density lipoprotein-related protein 1 (LRP-1) expressed on the brain capillary endothelial cells. Various enzymes in the blood and the BBB, however, present multiple metabolic barriers to peptide-inspired brain-targeted drug delivery. Here we designed a retro-inverso isomer of (L)Angiopep, termed (D)Angiopep, to inspire brain-targeted drug delivery. Both (D)Angiopep and (L)Angiopep displayed high uptake capacity in LRP-1 overexpressed cells, including bEnd.3 and U87 cells. (D)Angiopep demonstrated lower uptake efficiency in both cell lines than did (L)Angiopep, suggestive of lower binding affinity to LRP-1 of the d-peptide. (D)Angiopep was resistant to proteolysis in fresh rat blood serum, while more than 85% of (L)Angiopep disappeared within 2 h. Endocytosed (D)Angiopep and (L)Angiopep were found to be colocalized with lysosomal compartments of bEnd.3 cells, indicating that susceptibility to proteolysis of (L)Angiopep in the BBB may further attenuate its transcytosis efficiency. In vivo, (D)Angiopep modified PEG-DSPE micelles displayed high distribution in normal brain and intracranial glioblastoma. Due to the expression of LRP-1 on the BBB and glioblastoma cells, proteolytically stable (D)Angiopep holds much potential for designing two-order brain tumor targeted delivery systems.