Nanoparticles Hitchhike on Monocytes for Glioblastoma Treatment after Low-Dose Radiotherapy

Enzyme-responsive liposomes for controlled drug release

Compared to other nanovectors, liposomes exhibit unique advantages, such as good biosafety and high drug-loading capacity. However, slow drug release from conventional liposomes makes most payloads unavailable, restricting the therapeutic efficacy. Therefore, in the last ∼20 years, enzyme-responsive liposomes have been extensively investigated, which liberate drugs under the stimulation of enzymes overexpressed at disease sites. In this review, we elaborate on the research progress on enzyme-responsive liposomes. The involved enzymes mainly include phospholipases, particularly phospholipase A2, matrix metalloproteinases, cathepsins, and esterases. These enzymes can cleave ester bonds or specific peptide sequences incorporated in the liposomes for controlled drug release by disrupting the primary structure of liposomes, detaching protective polyethylene glycol shells, or activating liposome-associated prodrugs. Despite decades of efforts, there are still a lack marketed products of enzyme-responsive liposomes. Therefore, more efforts should be made to improve the safety and effectiveness of enzyme-responsive liposomes and address the issues associated with production scale-up.

Cell-mediated nanoparticle delivery systems: towards precision nanomedicine

Cell-mediated nanoparticle delivery systems (CMNDDs) utilize cells as carriers to deliver the drug-loaded nanoparticles. Unlike the traditional nanoparticle drug delivery approaches, CMNDDs take the advantages of cell characteristics, such as the homing capabilities of stem cells, inflammatory chemotaxis of neutrophils, prolonged blood circulation of red blood cells, and internalization of macrophages. Subsequently, CMNDDs can easily prolong the blood circulation, cross biological barriers, such as the blood-brain barrier and the bone marrow-blood barrier, and rapidly arrive at the diseased areas. Such advantageous properties make CMNDDs promising delivery candidates for precision targeting. In this review, we summarize the recent advances in CMNDDs fabrication and biomedical applications. Specifically, ligand-receptor interactions, non-covalent interactions, covalent interactions, and internalization are commonly applied in constructing CMNDDs in vitro. By hitchhiking cells, such as macrophages, red blood cells, monocytes, neutrophils, and platelets, nanoparticles can be internalized or attached to cells to construct CMNDDs in vivo. Then we highlight the recent application of CMNDDs in treating different diseases, such as cancer, central nervous system disorders, lung diseases, and cardiovascular diseases, with a brief discussion about challenges and future perspectives in the end.

The application strategy of liposomes in organ targeting therapy

Liposomes-microscopic phospholipid bubbles with bilayered membrane structure-have been a focal point in drug delivery research for the past 30 years. Current liposomes possess a blend of biocompatibility, drug loading efficiency, prolonged circulation and targeted delivery. Tailored liposomes, varying in size, charge, lipid composition, and ratio, have been developed to address diseases in specific organs, thereby enhancing drug circulation, accumulation at lesion sites, intracellular delivery, and treatment efficacy for various organ-specific diseases. For further successful development of this field, this review summarized liposomal strategies for targeting different organs in series of major human diseases, including widely studied cardiovascular diseases, liver and spleen immune diseases, chronic or acute kidney injury, neurodegenerative diseases, and organ-specific tumors. It highlights recent advances of liposome-mediated therapeutic agent delivery for disease intervention and organ rehabilitation, offering practical guidelines for designing organ-targeted liposomes. This article is categorized under: Therapeutic Approaches and Drug Discovery > Emerging Technologies Biology-Inspired Nanomaterials > Lipid-Based Structures.

Cathepsin B-Responsive Programmed Brain Targeted Delivery System for Chemo-Immunotherapy Combination Therapy of Glioblastoma

Tumor-associated macrophages (TAMs) are closely related to the progression of glioblastoma multiform (GBM) and its development of therapeutic resistance to conventional chemotherapy. TAM-targeted therapy combined with conventional chemotherapy has emerged as a promising strategy to combat GBM. However, the presence of the blood-brain barrier (BBB) severely limits the therapeutic efficacy. Meanwhile, the lack of ability to distinguish different targeted cells also poses a challenge for precise therapy. Herein, we propose a cathepsin B (CTSB)-responsive programmed brain-targeted delivery system (D&R-HM-MCA) for simultaneous TAM-targeted and GBM-targeted delivery. D&R-HM-MCA could cross the BBB via low density lipoprotein receptor-associated protein 1 (LRP1)-mediated transcytosis. Upon reaching the GBM site, the outer angiopep-2 modification could be detached from D&R-HM-MCA via cleavage of the CTSB-responsive peptide, which could circumvent abluminal LRP1-mediated efflux. The exposed p-aminophenyl-α-d-mannopyranoside (MAN) modification could further recognize glucose transporter-1 (GLUT1) on GBM and macrophage mannose receptor (MMR) on TAMs. D&R-HM-MCA could achieve chemotherapeutic killing of GBM and simultaneously induce TAM polarization from anti-inflammatory M2 phenotype to pro-inflammatory M1 phenotype, thus resensitizing the chemotherapeutic response and improving anti-GBM immune response. This CTSB-responsive brain-targeted delivery system not only can improve brain delivery efficiency, but also can enable the combination of chemo-immunotherapy against GBM. The effectiveness of this strategy may provide thinking for designing more functional brain-targeted delivery systems and more effective therapeutic regimens.

Inflammation-Driven Nanohitchhiker Enhances Postoperative Immunotherapy by Alleviating Prostaglandin E2-Mediated Immunosuppression

Inflammation contributes to the immunosuppressive microenvironment and leads to the recurrence of surgically resected tumors. The COX-2/PGE2 axis is considered a key player in shaping the immunosuppression microenvironment. However, targeted modulation of the postoperative tumor microenvironment is challenging. To specifically curb the inflammation and alleviate immunosuppression, here, we developed a PGE2 inhibitor celecoxib (CXB)-loaded bionic nanoparticle (CP@CM) coated with activated murine vascular endothelial cell (C166 cells) membrane to target postoperative melanoma and inhibit its recurrence. CP@CM adhered to inflammatory white blood cells (WBCs) through the adhesion molecules, including ICAM-1, VCAM-1, E-selectin, and P-selection, expressed on the surface of C166 cells. Leveraging the natural tropism of the WBC to the inflammatory postoperative tumor site, CP@CM efficiently targeted postoperative tumors. In melanoma postoperative recurrence models, CXB significantly reduced PGE2 secretion and the recruitment of immunosuppressive cells such as myeloid-derived suppressor cells (MDSCs) and regulatory T cells (Treg) by inhibiting the activity of COX-2. This was followed by an increase in the infiltration of CD8+ T cells and CD4+ T cells in tumor tissues. Additionally, the immune responses were further enhanced by combining a PD-L1 monoclonal antibody. Ultimately, this immunotherapeutic strategy reversed the tumor immunosuppressive microenvironment and inhibited tumor recurrence, demonstrating a promising potential for postoperative immunotherapy for melanoma.

Bioinspired Lipoproteins of Furoxans-Gemcitabine Preferentially Targets Glioblastoma and Overcomes Radiotherapy Resistance

Radiotherapy (RT) resistance is an enormous challenge in glioblastoma multiforme (GBM) treatment, which is largely associated with DNA repair, poor distribution of reactive radicals in tumors, and limited delivery of radiosensitizers to the tumor sites. Inspired by the aberrant upregulation of RAD51 (a critical protein of DNA repair), scavenger receptor B type 1 (SR-B1), and C-C motif chemokine ligand 5 (CCL5) in GBM patients, a reduction-sensitive nitric oxide (NO) donor conjugate of gemcitabine (RAD51 inhibitor) (NG) is synthesized as radio-sensitizer and a CCL5 peptide-modified bioinspired lipoprotein system of NG (C-LNG) is rationally designed, aiming to preferentially target the tumor sites and overcome the RT resistance. C-LNG can preferentially accumulate at the orthotopic GBM tumor sites with considerable intratumor permeation, responsively release the gemcitabine and NO, and then generate abundant peroxynitrite (ONOO- ) upon X-ray radiation, thereby producing a 99.64% inhibition of tumor growth and a 71.44% survival rate at 120 days in GL261-induced orthotopic GBM tumor model. Therefore, the rationally designed bioinspired lipoprotein of NG provides an essential strategy to target GBM and overcome RT resistance.

MRI Detection of Lymph Node Metastasis through Molecular Targeting of C-C Chemokine Receptor Type 2 and Monocyte Hitchhiking

Biopsy is the clinical standard for diagnosing lymph node (LN) metastasis, but it is invasive and poses significant risk to patient health. Magnetic resonance imaging (MRI) has been utilized as a noninvasive alternative but is limited by low sensitivity, with only ∼35% of LN metastases detected, as clinical contrast agents cannot discriminate between healthy and metastatic LNs due to nonspecific accumulation. Nanoparticles targeted to the C-C chemokine receptor 2 (CCR2), a biomarker highly expressed in metastatic LNs, have the potential to guide the delivery of contrast agents, improving the sensitivity of MRI. Additionally, cancer cells in metastatic LNs produce monocyte chemotactic protein 1 (MCP1), which binds to CCR2+ inflammatory monocytes and stimulates their migration. Thus, the molecular targeting of CCR2 may enable nanoparticle hitchhiking onto monocytes, providing an additional mechanism for metastatic LN targeting and early detection. Hence, we developed micelles incorporating gadolinium (Gd) and peptides derived from the CCR2-binding motif of MCP1 (MCP1-Gd) and evaluated the potential of MCP1-Gd to detect LN metastasis. When incubated with migrating monocytes in vitro, MCP1-Gd transport across lymphatic endothelium increased 2-fold relative to nontargeting controls. After administration into mouse models with initial LN metastasis and recurrent LN metastasis, MCP1-Gd detected metastatic LNs by increasing MRI signal by 30-50% relative to healthy LNs. Furthermore, LN targeting was dependent on monocyte hitchhiking, as monocyte depletion decreased accumulation by >70%. Herein, we present a nanoparticle contrast agent for MRI detection of LN metastasis mediated by CCR2-targeting and demonstrate the potential of monocyte hitchhiking for enhanced nanoparticle delivery.

Renal Clearable Nanodots-Engineered Erythrocytes with Enhanced Circulation and Tumor Accumulation for Photothermal Therapy of Hepatocellular Carcinoma

Living cell-mediated nanodelivery system is considered a promising candidate for targeted antitumor therapy; however, their use is restricted by the adverse interactions between carrier cells and nanocargos. Herein, a novel erythrocyte-based nanodelivery system is developed by assembling renal-clearable copper sulfide (CuS) nanodots on the outer membranes of erythrocytes via a lipid fusion approach, and demonstrate that it is an efficient photothermal platform against hepatocellular carcinoma. After intravenous injection of the nanodelivery system, CuS nanodots assembled on erythrocytes can be released from the system, accumulate in tumors in response to the high shear stress of bloodstream, and show excellent photothermal antitumor effect under the near infrared laser irradiation. Therefore, the erythrocyte-mediated nanodelivery system holds many advantages including prolonged blood circulation duration and enhanced tumor accumulation. Significantly, the elimination half-life of the nanodelivery system is 74.75 ± 8.77 h, which is much longer than that of nanodots (33.56 ± 2.36 h). Moreover, the other two kinds of nanodots can be well assembled onto erythrocytes to produce other erythrocyte-based hitchhiking platforms. Together, the findings promote not only the development of novel erythrocyte-based nanodelivery systems as potential platforms for tumor treatment but also their further clinical translation toward personalized healthcare.

Repurposing of pexidartinib for microglia depletion and renewal

Pexidartinib (PLX3397) is a small molecule receptor tyrosine kinase inhibitor of colony stimulating factor 1 receptor (CSF1R) with moderate selectivity over other members of the platelet derived growth factor receptor family. It is approved for treatment of tenosynovial giant cell tumors (TGCT). CSF1R is highly expressed by microglia, which are macrophages of the central nervous system (CNS) that defend the CNS against injury and pathogens and contribute to synapse development and plasticity. Challenged by pathogens, apoptotic cells, debris, or inflammatory molecules they adopt a responsive state to propagate the inflammation and eventually return to a homeostatic state. The phenotypic switch may fail, and disease-associated microglia contribute to the pathophysiology in neurodegenerative or neuropsychiatric diseases or long-lasting detrimental brain inflammation after brain, spinal cord or nerve injury or ischemia/hemorrhage. Microglia also contribute to the growth permissive tumor microenvironment of glioblastoma (GBM). In rodents, continuous treatment for 1-2 weeks via pexidartinib food pellets leads to a depletion of microglia and subsequent repopulation from the remaining fraction, which is aided by peripheral monocytes that search empty niches for engraftment. The putative therapeutic benefit of such microglia depletion or forced renewal has been assessed in almost any rodent model of CNS disease or injury or GBM with heterogeneous outcomes, but a tendency of partial beneficial effects. So far, microglia monitoring e.g. via positron emission imaging is not standard of care for patients receiving Pexidartinib (e.g. for TGCT), so that the depletion and repopulation efficiency in humans is still largely unknown. Considering the virtuous functions of microglia, continuous depletion is likely no therapeutic option but short-lasting transient partial depletion to stimulate microglia renewal or replace microglia in genetic disease in combination with e.g. stem cell transplantation or as part of a multimodal concept in treatment of glioblastoma appears feasible. The present review provides an overview of the preclinical evidence pro and contra microglia depletion as a therapeutic approach.

In situ cellular hitchhiking of nanoparticles for drug delivery

Since the inception of the concept of "magic bullet", nanoparticles have evolved to be one of the most effective carriers in drug delivery. Nanoparticles improve the therapeutic efficacy of drugs offering benefits to treating various diseases. Unlike free drugs which freely diffuse and distribute through the body, nanoparticles protect the body from the drug by reducing non-specific interactions while also improving the drug's pharmacokinetics. Despite acquiring some FDA approvals, further clinical application of nanoparticles is majorly hindered by its limited ability to overcome biological barriers resulting in uncontrolled biodistribution and high clearance. The use of cell-inspired systems has emerged as a promising approach to overcome this challenge as cells are biocompatible and have improved access to tissues and organs. One of such is the hitchhiking of nanoparticles to circulating cells such that they are recognized as 'self' components evading clearance and resulting in site-specific drug delivery. In this review, we discuss the concept of nanoparticle cellular hitchhiking, highlighting its advantages, the principles governing the process and the challenges currently limiting its clinical translation. We also discuss in situ hitchhiking as a tool for overcoming these challenges and the considerations to be taken to guide research efforts in advancing this promising technology.