The use of nanoparticulate delivery systems in metronomic chemotherapy

Nanoparticle-mediated metronomic chemotherapy in cancer: A paradigm of precision and persistence

Current methods of cancer therapy have demonstrated enormous potential in tumor inhibition. However, a high dosage regimen of chemotherapy results in various complications which affect the normal body cells. Tumor cells also develop resistance against the prescribed drugs in the whole treatment regimen increasing the risk of cancer relapse. Metronomic chemotherapy is a modern treatment method that involves administering drugs at low doses continuously, allowing the drug sufficient time to take its effect. This method ensures that the toxicity of the drugs is to a minimum in comparison to conventional chemotherapy. Nanoparticles have shown efficacy in delivering drugs to the tumor cells in various cancer therapies. Combining nanoparticles with metronomic chemotherapy can yield better treatment results. This combination stimulates the immune system, improving cancer cells recognition by immune cells. Evidence from clinical and pre-clinical trials supports the use of metronomic delivery for drug-loaded nanoparticles. This review focuses on the functionalization of nanoparticles for improved drug delivery and inhibition of tumor growth. It emphasizes the mechanisms of metronomic chemotherapy and its conjunction with nanotechnology. Additionally, it explores tumor progression and the current methods of chemotherapy. The challenges associated with nano-based metronomic chemotherapy are outlined, paving the way for prospects in this dynamic field.

Recent advances in near-infrared-II hollow nanoplatforms for photothermal-based cancer treatment

Near-infrared-II (NIR-II, 1000–1700 nm) light-triggered photothermal therapy (PTT) has been regarded as a promising candidate for cancer treatment, but PTT alone often fails to achieve satisfactory curative outcomes. Hollow nanoplatforms prove to be attractive in the biomedical field owing to the merits including good biocompatibility, intrinsic physical-chemical nature and unique hollow structures, etc. On one hand, hollow nanoplatforms themselves can be NIR-II photothermal agents (PTAs), the cavities of which are able to carry diverse therapeutic units to realize multi-modal therapies. On the other hand, NIR-II PTAs are capable of decorating on the surface to combine with the functions of components encapsulated inside the hollow nanoplatforms for synergistic cancer treatment. Notably, PTAs generally can serve as good photoacoustic imaging (PAI) contrast agents (CAs), which means such kind of hollow nanoplatforms are also expected to be multifunctional all-in-one nanotheranostics. In this review, the recent advances of NIR-II hollow nanoplatforms for single-modal PTT, dual-modal PTT/photodynamic therapy (PDT), PTT/chemotherapy, PTT/catalytic therapy and PTT/gas therapy as well as multi-modal PTT/chemodynamic therapy (CDT)/chemotherapy, PTT/chemo/gene therapy and PTT/PDT/CDT/starvation therapy (ST)/immunotherapy are summarized for the first time. Before these, the typical synthetic strategies for hollow structures are presented, and lastly, potential challenges and perspectives related to these novel paradigms for future research and clinical translation are discussed.

Combination of metronomic administration and target delivery strategies to improve the anti-angiogenic and anti-tumor effects of triptolide

The metronomic administration of a low-dose cytotoxic agent with no prolonged drug-free breaks is an anti-angiogenic cancer treatment method. The use of nano-formulations in this manner enhances anti-tumor efficacy and reduces toxicity by inhibiting angiogenic activity, reduces adverse effects, and changes the biodistribution of TP in the body, steering TP away from potentially endangering healthy tissues. The present study uses liposomes and Asn-Gly-Arg (NGR) peptide conjugated aminopeptidase N(APN)-targeted liposomes for triptolide (TP), as a model for the investigation of targeted metronomic administration and subsequent effects on the toxicity profile and efficacy of the chemotherapeutic agent. Metronomic NGR-PEG-TP-LPs have been found to have enhanced anti-tumor activity, a phenomenon that is attributed to an increase in angiogenic inhibition properties. In vitro experiments demonstrate that the viability, migration, and tube formation of human umbilical vein endothelial cells (HUVECs) are obviously suppressed in comparison with that of other treatment groups. In vivo experiments also demonstrate that the anti-tumor efficacy of targeted metronomic administration is superior to that of liposome-administered treatments given at maximum tolerated dose (MTD) schemes, as is evidenced by markedly decreased tumor volume, vessel density, and the volume of circulating endothelial progenitor cells (CEPCs) in serum. Moreover, we observed that the metronomic administration of NGR-PEG-TP-LPs could elevate thrombospondin-1 (TSP-1) expression in tumors, a finding that is consistent with the promotion of TSP-1 secretion specifically from HUVECs. Additionally, metronomic NGR-PEG-TP-LPs have minimal drug-associated toxicity (weight loss, hepatotoxicity and nephrotoxicity in mice). Our research demonstrates the significance of targeted metronomic administration using liposomes for anti-angiogenic cancer therapy.

A Tumor Vascular-Targeted Interlocking Trimodal Nanosystem That Induces and Exploits Hypoxia

Vascular-targeted photodynamic therapy (VTP) is a recently approved strategy for treating solid tumors. However, the exacerbated hypoxic stress makes tumor eradication challenging with such a single modality approach. Here, a new graphene oxide (GO)-based nanosystem for rationally designed, interlocking trimodal cancer therapy that enables VTP using photosensitizer verteporfin (VP) (1) with codelivery of banoxantrone dihydrochloride (AQ4N) (2), a hypoxia-activated prodrug (HAP), and HIF-1α siRNA (siHIF-1α) (3) is reported. The VTP-induced aggravated hypoxia is highly favorable for AQ4N activation into AQ4 (a topoisomerase II inhibitor) for chemotherapy. However, the hypoxia-induced HIF-1α acts as a "hidden brake," through downregulating CYP450 (the dominant HAP-activating reductases), to substantially hinder AQ4N activation. siHIF-1α is rationally adopted to suppress the HIF-1α expression upon hypoxia and further enhance AQ4N activation. This trimodal nanosystem significantly delays the growth of PC-3 tumors in vivo compared to the control nanoparticles carrying VP, AQ4N, or siHIF-1α alone or their pairwise combinations. This multimodal nanoparticle design presents, the first example exploiting VTP to actively induce hypoxia for enhanced HAP activation. It is also revealed that HAP activation is still insufficient under hypoxia due to the hidden downregulation of the HAP-activating reductases (CYP450), and this can be well overcome by GO nanoparticle-mediated siHIF-1α intervention.

Metronomic chemotherapy and nanocarrier platforms

The therapeutic concept of administering chemotherapeutic agents continuously at lower doses, relative to the maximum tolerated dose (MTD) without drug-free breaks over extended periods -known as "metronomic chemotherapy"- is a promising approach for anti-angiogenic cancer therapy. In comparison with MTD chemotherapy regimens, metronomic chemotherapy has demonstrated reduced toxicity. However, as a monotherapy, metronomic chemotherapy has failed to provide convincing results in clinical trials. Therapeutic approaches including combining the anti-angiogenic "metronomic" therapy with conventional radio-/chemo-therapy and/or targeted delivery of chemotherapeutic agents to tumor tissues via their encapsulation with nanocarrier-based platforms have proven to potentiate the overall therapeutic outcomes. In this review, therefore, we focused on the mutual contribution made by nanoscale drug delivery platforms to the therapeutic efficacy of metronomic-based chemotherapy. In addition, the influence that the dosing schedule has on the overall therapeutic efficacy of metronomic chemotherapy is discussed.

Endocytic Pathways Used by Andes Virus to Enter Primary Human Lung Endothelial Cells

Andes virus (ANDV) is the major cause of hantavirus pulmonary syndrome (HPS) in South America. Despite a high fatality rate (up to 40%), no vaccines or antiviral therapies are approved to treat ANDV infection. To understand the role of endocytic pathways in ANDV infection, we used 3 complementary approaches to identify cellular factors required for ANDV entry into human lung microvascular endothelial cells. We screened an siRNA library targeting 140 genes involved in membrane trafficking, and identified 55 genes required for ANDV infection. These genes control the major endocytic pathways, endosomal transport, cell signaling, and cytoskeleton rearrangement. We then used infectious ANDV and retroviral pseudovirions to further characterize the possible involvement of 9 of these genes in the early steps of ANDV entry. In addition, we used markers of cellular endocytosis along with chemical inhibitors of known endocytic pathways to show that ANDV uses multiple routes of entry to infect target cells. These entry mechanisms are mainly clathrin-, dynamin-, and cholesterol-dependent, but can also occur via a clathrin-independent manner.

Tumor priming using metronomic chemotherapy with neovasculature-targeted, nanoparticulate paclitaxel

Normalization of the tumor microenvironment is a promising approach to render conventional chemotherapy more effective. Although passively targeted drug nanocarriers have been investigated to this end, actively targeted tumor priming remains to be explored. In this work, we demonstrate an effective tumor priming strategy using metronomic application of nanoparticles actively targeted to tumor neovasculature. F56 peptide-conjugated paclitaxel-loaded nanoparticles (F56-PTX-NP) were formulated from PEGylated polylactide using an oil in water emulsion approach. Metronomic F56-PTX-NP specifically targeted tumor vascular endothelial cells (ECs), pruned vessels with strong antiangiogenic activity and induced thrombospondin-1 (TSP-1) secretion from ECs. The treatment induced tumor vasculature normalization as evidenced by significantly increased coverage of basement membrane and pericytes. The tumor microenvironment was altered with enhanced pO2, lower interstitial fluid pressure, and enhanced vascular perfusion and doxorubicin delivery. A "normalization window" of at least 9 days was induced, which was longer than other approaches using antiangiogenic agents. Together, these results show that metronomic, actively-targeted nanomedicine can induce tumor vascular normalization and modulate the tumor microenvironment, opening a window of opportunity for effective combination chemotherapies.

IF7-Conjugated Nanoparticles Target Annexin 1 of Tumor Vasculature against P-gp Mediated Multidrug Resistance

Multidrug resistance is the main cause of clinical chemotherapeutic failure. Antiangiogenic cancer therapy with nanomedicine that allows the targeted delivery of antiangiogenic agents to tumor endothelial cells may contribute to innovative strategies for treating multidrug-resistant cancers. In this study, we developed a new nanodrug delivery system (nano-DDS), with improved antiangiogenic efficacy against multidrug resistant human breast cancer MCF-7/ADR cells. Here, the IF7 ligand was a peptide designed to bind the annexin 1 (Anxa 1), a highly specific marker of the tumor vasculature surface, with high affinity and specificity. IF7-conjugated Anxa 1-targeting nanoparticles containing paclitaxel (IF7-PTX-NP) allowed controlled drug release and displayed favorable prolonged circulation in vivo. IF7-PTX-NP was significantly internalized by human umbilical vein endothelial cells (HUVEC) through the IF7-Anxa 1 interaction, and this facilitated uptake enhanced the expected antiangiogenic activity of inhibiting HUVEC proliferation, migration, and tube formation in a Matrigel plug relative to those of Taxol and PTX-NP. As IF7-PTX-NP targeted the tumor vessels, more nanoparticles accumulated in MCF-7/ADR tumors, and more importantly, induced significant apoptosis of the tumor vascular endothelial cells and necrosis of the tumor tissues. Low dose paclitaxel (1 mg/kg) formulated in IF7-PTX-NP showed significant anticancer efficacy, delaying the growth of MCF-7/ADR tumors. The same efficacy was only obtained with an 8-fold dose of paclitaxel (8 mg/kg) as Taxol plus XR9576, a potent P-gp inhibitor. The anticancer efficacy of IF7-PTX-NP was strongly associated with the improved antiangiogenic effect, evident as a dramatic reduction in the tumor microvessel density and pronounced increase in apoptotic tumor cells, with no obvious toxicity to the mice. This nano-DDS, which targets the tumor neovasculature, offers a promising strategy for the treatment of multidrug-resistant cancer.

Delta-like ligand 4-targeted nanomedicine for antiangiogenic cancer therapy

Tumor angiogenesis is a multistep process involved with multiple molecular events in cancer microenvironment. Several molecular-targeted agents aiming to suppress tumor angiogenesis have been successfully translated into cancer clinic. However, new strategies are still urgently desired to be excavated to overcome the poor response and resistance in some antiangiogenic therapies. Recently, Delta-like ligand 4 (Dll4) is identified to be specifically over-expressed on tumor vascular endothelial cells (EC), and the Dll4-Notch pathway serves as a critical regulator in the development and maintenance of tumor angiogenesis. The intensively up-regulated phenotype of Dll4 on the membrane of tumor vascular EC implies that Dll4 may act as a targetable address for drug delivery system (DDS) to achieve targeted antiangiogenic cancer therapy. Here, a nano-DDS, GD16 peptide (H2N-GRCTNFHNFIYICFPD-CONH2, containing a disulfide bond between Cys3 and Cys13) conjugated nanoparticles loading paclitaxel (GD16-PTX-NP), which can specifically target the angiogenic marker Dll4, was fabricated for the investigation of antiangiogenic therapeutic efficacy in human head and neck cancer FaDu (Dll4-negative) xenograft in nude mice. The results demonstrate that GD16-PTX-NP achieved controlled drug release and exhibited favorable in vivo long-circulating feature. GD16-PTX-NP exerted enhanced antiangiogenic activity in the inhibition of human umbilical vein endothelial cell (HUVEC) viability, motility, migration, and tube formation, and in the Matrigel plug model as well, which can be definitely ascribed to the active internalization mediated by the interaction of GD16 and the over-expressed Dll4 on EC. GD16-PTX-NP showed accurate in vivo tumor neovasculature targeting property in FaDu tumor, where the paclitaxel was specifically delivered into the tumor vascular EC, leading to significant apoptosis of tumor vascular EC and necrosis of tumor tissues. The antiangiogenic activity of GD16-PTX-NP significantly contributed to its in vivo anticancer efficacy in Fadu tumor; moreover, no overt toxicity to the mice was observed. Our research firstly presents the potency and significance of a Dll4-targeted nanomedicine in antiangiogenic cancer therapy.

PEG-PLA nanoparticles modified with APTEDB peptide for enhanced anti-angiogenic and anti-glioma therapy

Tumor neovasculature and tumor cells dual-targeting chemotherapy can not only destroy the tumor neovasculature, cut off the supply of nutrition and starve the tumor cells, but also directly kill tumor cells, holding great potential in overcoming the drawbacks of anti-angiogenic therapy only and improving the anti-glioma efficacy. In the present study, by taking advantage of the specific expression of fibronectin extra domain B (EDB) on both glioma neovasculature endothelial cells and glioma cells, we constructed EDB-targeted peptide APTEDB-modified PEG-PLA nanoparticles (APT-NP) for paclitaxel (PTX) loading to enable tumor neovasculature and tumor cells dual-targeting chemotherapy. PTX-loaded APT-NP showed satisfactory encapsulated efficiency, loading capacity and size distribution. In human umbilical vein endothelial cells, APT-NP exhibited significantly elevated cellular accumulation via energy-dependent, caveolae and lipid raft-involved endocytosis, and improved PTX-induced apoptosis therein. Both in vitro tube formation assay and in vivo matrigel angiogenesis analysis confirmed that APT-NP significantly improved the antiangiogenic ability of PTX. In U87MG cells, APT-NP showed elevated cellular internalization and also enhanced the cytotoxicity of the loaded PTX. Following intravenous administration, as shown by both in vivo live animal imaging and tissue distribution analysis, APT-NP achieved a much higher and specific accumulation within the glioma. As a result, APT-NP-PTX exhibited improved anti-glioma efficacy over unmodified nanoparticles and Taxol(®) in both subcutaneous and intracranial U87MG xenograft models. These findings collectively indicated that APTEDB-modified nanoparticles might serve as a promising nanocarrier for tumor cells and neovasculature dual-targeting chemotherapy and hold great potential in improving the efficacy anti-glioma therapy.

Selective eradication of tumor vascular pericytes by peptide-conjugated nanoparticles for antiangiogenic therapy of melanoma lung metastasis

Antiangiogenic cancer therapy based on nanoparticulate drug delivery systems (nano-DDS) is emerging as a promising new approach besides the proved molecular-targeted antiangiogenic agents. The current nano-DDS are restricted to the targeting to tumor vascular endothelial cells, but seldom efforts have been made to target the tumor vascular pericytes which are also actively involved in tumor angiogenesis. In this study, we developed a new nano-DDS, TH10 peptide (TAASGVRSMH) conjugated nanoparticles loading docetaxel (TH10-DTX-NP) that can target the NG2 proteoglycan highly expressed in tumor vascular pericytes, for the investigation of therapeutic efficacy in the mice bearing B16F10-luc-G5 melanoma experimental lung metastasis. The results demonstrated that TH10-DTX-NP achieved controlled drug release in PBS and the mixture of rat plasma and PBS (1:1, v/v), and exhibited favorable in vivo long-circulating feature. TH10 peptide conjugation facilitated the nanoparticle internalization in pericytes via the interaction between TH10 and NG2 receptor, leading to more inhibition of pericyte viability and migration. TH10-conjugated nanoparticles could accurately target the vascular pericytes of B16F10-luc-G5 lung metastasis, where DTX-induced pronounceable pericyte apoptosis. TH10-DTX-NP significantly prolonged the mice survival with no obvious toxicity, and this enhanced antitumor effect was closely related with the decreased pericyte density and microvessel density in the lung metastases. The present research reveals the potency and significance of targeting tumor vascular pericytes using nano-DDS in antiangiogenic cancer therapy.

How nanotechnology can enhance docetaxel therapy

Docetaxel has been recognized as one of the most efficient anticancer drugs over the past decade; however, its poor water solubility and systemic toxicity have greatly limited its clinical application. In recent decades, the emergence of nanotechnology has provided new drug delivery systems for docetaxel, which can improve its water solubility, minimize the side effects and increase the tumor-targeting distribution by passive or active targeting. This review focuses on the research progress in nanoformulations related to docetaxel delivery – such as polymer-based, lipid-based, and lipid-polymer hybrid nanocarriers, as well as inorganic nanoparticles – addressing their structures, characteristics, preparation, physicochemical properties, methods by which drugs are loaded into them, and their in vitro and in vivo efficacies. Further, the targeted ligands used in the docetaxel nanoformulations, such as monoclonal antibodies, peptides, folic acid, transferrin, aptamers and hyaluronic acid, are described. The issues to overcome before docetaxel nanoformulations can be used in clinical and commercial applications are also discussed.