Vascular disrupting agents in clinical development

Targeting the tumour vasculature: from vessel destruction to promotion

As angiogenesis was recognized as a core hallmark of cancer growth and survival, several strategies have been implemented to target the tumour vasculature. Yet to date, attempts have rarely been so diverse, ranging from vessel growth inhibition and destruction to vessel normalization, reprogramming and vessel growth promotion. Some of these strategies, combined with standard of care, have translated into improved cancer therapies, but their successes are constrained to certain cancer types. This Review provides an overview of these vascular targeting approaches and puts them into context based on our subsequent improved understanding of the tumour vasculature as an integral part of the tumour microenvironment with which it is functionally interlinked. This new knowledge has already led to dual targeting of the vascular and immune cell compartments and sets the scene for future investigations of possible alternative approaches that consider the vascular link with other tumour microenvironment components for improved cancer therapy.

Multi-parametric investigations on the effects of vascular disrupting agents based on a platform of chorioallantoic membrane of chick embryos

Background

Vascular disrupting agents (VDAs) are known to specifically target preexisting tumoural vasculature. However, systemic side effects as safety or toxicity issues have been reported from clinical trials, which call for further preclinical investigations. The purpose is to gain insights into their non-specific off-targeting effects on normal vasculature and provide clues for exploring underlying molecular mechanisms.

Methods

Based on a recently introduced platform consisting laser speckle contrast imaging (LSCI), chick embryo chorioallantoic membrane (CAM), and assisted deep learning techniques, for evaluation of vasoactive medicines, hemodynamics on embryonic day 12 under constant intravascular infusion of two VDAs were qualitatively observed and quantitatively measured in real time for 30 min. Blood perfusion, vessel diameter, vessel density, and vessel total length were further analyzed and compared between blank control and medicines dose groups by using multi-factor analysis of variance (ANOVA) analysis with factorial interactions. Conventional histopathology and fluorescent immunohistochemistry (FIHC) assays for endothelial cytoskeleton including ß-tubulin and F-actin were qualitatively demonstrated, quantitatively analyzed and further correlated with hemodynamic and vascular parameters.

Results

The normal vasculature was systemically negatively affected by VDAs with statistical significance (P<0.0001), as evidenced by four positively correlated parameters, which can explain the side-effects observed among clinical patients. Such effects appeared to be dose dependent (P<0.0001). FIHC assays qualitatively and quantitatively verified the results and exposed molecular mechanisms.

Conclusions

LSCI-CAM platform combining with deep learning technique proves useful in preclinical evaluations of vasoactive medications. Such new evidences provide new reference to clinical practice.

Molecular Dynamics and Machine Learning reveal distinguishing mechanisms of Competitive Ligands to perturb α,β-Tubulin

The mechanisms of action of ligands competing for the Colchicine Binding Site (CBS) of the α,β-Tubulin are non-standard compared to the commonly witnessed ligand-induced inhibition of proteins. This is because their potencies are not solely judged by the binding affinity itself, but also by their capacity to bias the conformational states of the dimer. Regarding the latter requirement, it is observed that ligands competing for the same pocket that binds colchicine exhibit divergence in potential clinical outcomes. Molecular dynamics-based ∼5.2 µs sampling of α,β-Tubulin complexed with four different ligands has revealed that each ligand has its customized way of influencing the complex. Primarily, it is the proportion of twisting and/or bending characteristic of modes of the intrinsic dynamics which is revealed to be 'fundamental' to tune this variation in the mechanism. The milder influence of 'bending' makes a ligand (TUB092), better classifiable under the group of vascular disrupting agents (VDAs), which are phenotypically effective on cytoskeletons; whereas a stronger impact of 'bending' makes the classical ligand Colchicine (COL) a better Anti-Mitotic agent (AMA). Two other ligands BAL27862 (2RR) and Nocodazole (NZO) fall in the intermediate zone as they fail to explicitly induce bending modes. Random Forest Classification method and K-means Clustering is applied to reveal the efficiency of Machine Learning methods in classifying the Tubulin conformations according to their ligand-specific perturbations and to highlight the significance of specific amino acid residues, mostly positioned in the α-β and β-β interfaces involved in the mechanism. These key residues responsible to yield discriminative actions of the ligands are likely to be highly useful in future endeavours to design more precise inhibitors.

The Development of HDAC and Tubulin Dual-Targeting Inhibitors for Cancer Therapy

Histone deacetylases (HDACs) are a class of enzymes that are responsible for the removal of acetyl groups from the ε-N-acetyl lysine of histones, allowing histones to wrap DNA more tightly. HDACs play an essential role in many biological processes, such as gene regulation, transcription, cell proliferation, angiogenesis, migration, differentiation and metastasis, which make it an excellent target for anticancer drug discovery. The search for histone deacetylase inhibitors (HDACis) has been intensified, with numerous HDACis being discovered, and five of them have reached the market. However, currently available HDAC always suffers from several shortcomings, such as limited efficacy, drug resistance, and toxicity. Accordingly, dual-targeting HDACis have attracted much attention from academia to industry, and great advances have been achieved in this area. In this review, we summarize the progress on inhibitors with the capacity to concurrently inhibit tubulin polymerization and HDAC activity and their application in cancer treatment.

Emerging nanotechnological approaches to regulating tumor vasculature for cancer therapy

Abnormal angiogenesis stands for one of the most striking manifestations of malignant tumor. The pathologically and structurally abnormal tumor vasculature facilitates a hostile tumor microenvironment, providing an ideal refuge exclusively for cancer cells. The emergence of vascular regulation drugs has introduced a distinctive class of therapeutics capable of influencing nutrition supply and drug delivery efficacy without the need to penetrate a series of physical barriers to reach tumor cells. Nanomedicines have been further developed for more precise regulation of tumor vasculature with the capacity of co-delivering multiple active pharmaceutical ingredients, which overall reduces the systemic toxicity and boosts the therapeutic efficacy of free drugs. Additionally, precise structure design enables the integration of specific functional motifs, such as surface-targeting ligands, droppable shells, degradable framework, or stimuli-responsive components into nanomedicines, which can improve tissue-specific accumulation, enhance tissue penetration, and realize the controlled and stimulus-triggered release of the loaded cargo. This review describes the morphological and functional characteristics of tumor blood vessels and summarizes the pivotal molecular targets commonly used in nanomedicine design, and then highlights the recent cutting-edge advancements utilizing nanotechnologies for precise regulation of tumor vasculature. Finally, the challenges and future directions of this field are discussed.

Antitumor effect of anti-vascular therapy with STING agonist depends on the tumor microenvironment context

Introduction

Targeting tumor vasculature is an efficient weapon to fight against cancer; however, activation of alternative pathways to rebuild the disrupted vasculature leads to rapid tumor regrowth. Immunotherapy that exploits host immune cells to elicit and sustain potent antitumor response has emerged as one of the most promising tools for cancer treatment, yet many treatments fail due to developed resistance mechanisms. Therefore, our aim was to examine whether combination of immunotherapy and anti-vascular treatment will succeed in poorly immunogenic, difficult-to-treat melanoma and triple-negative breast tumor models.

Methods

Our study was performed on B16-F10 melanoma and 4T1 breast tumor murine models. Mice were treated with the stimulator of interferon genes (STING) pathway agonist (cGAMP) and vascular disrupting agent combretastatin A4 phosphate (CA4P). Tumor growth was monitored. The tumor microenvironment (TME) was comprehensively investigated using multiplex immunofluorescence and flow cytometry. We also examined if such designed therapy sensitizes investigated tumor models to an immune checkpoint inhibitor (anti-PD-1).

Results

The use of STING agonist cGAMP as monotherapy was insufficient to effectively inhibit tumor growth due to low levels of STING protein in 4T1 tumors. However, when additionally combined with an anti-vascular agent, a significant therapeutic effect was obtained. In this model, the obtained effect was related to the TME polarization and the stimulation of the innate immune response, especially activation of NK cells. Combination therapy was unable to activate CD8+ T cells. Due to the lack of PD-1 upregulation, no improved therapeutic effect was observed when additionally combined with the anti-PD-1 inhibitor. In B16-F10 tumors, highly abundant in STING protein, cGAMP as monotherapy was sufficient to induce potent antitumor response. In this model, the therapeutic effect was due to the infiltration of the TME with activated NK cells. cGAMP also caused the infiltration of CD8+PD-1+ T cells into the TME; hence, additional benefits of using the PD-1 inhibitor were observed.

Conclusion

The study provides preclinical evidence for a great influence of the TME on the outcome of applied therapy, including immune cell contribution and ICI responsiveness. We pointed the need of careful TME screening prior to antitumor treatments to achieve satisfactory results.

Use of photoacoustic imaging for monitoring vascular disrupting cancer treatments

Vascular disrupting agents disrupt tumor vessels, blocking the nutritional and oxygen supply tumors need to thrive. This is achieved by damaging the endothelium lining of blood vessels, resulting in red blood cells (RBCs) entering the tumor parenchyma. RBCs present in the extracellular matrix are exposed to external stressors resulting in biochemical and physiological changes. The detection of these changes can be used to monitor the efficacy of cancer treatments. Spectroscopic photoacoustic (PA) imaging is an ideal candidate for probing RBCs due to their high optical absorption relative to surrounding tissue. The goal of this work is to use PA imaging to monitor the efficacy of the vascular disrupting agent 5,6-Dimethylxanthenone-4-acetic acid (DMXAA) through quantitative analysis. Then, 4T1 breast cancer cells were injected subcutaneously into the left hind leg of eight BALB/c mice. After 10 days, half of the mice were treated with 15 mg/kg of DMXAA and the other half were injected with saline. All mice were imaged using the VevoLAZR X PA system before treatment, 24 and 72 hours after treatment. The imaging was done at six wavelengths and linear spectral unmixing was applied to the PA images to quantify three forms of hemoglobin (oxy, deoxy and met-hemoglobin). After imaging, tumors were histologically processed and H&E and TUNEL staining were used to detect the tissue damage induced by the DMXAA treatment. The total hemoglobin concentration remained unchanged after treatment for the saline treated mice. For DMXAA treated mice, a 10% increase of deoxyhemoglobin concentration was detected 24 hours after treatment and a 22.6% decrease in total hemoglobin concentration was observed by 72 hours. A decrease in the PA spectral slope parameters was measured 24 hours after treatment. This suggests that DMXAA induces vascular damage, causing red blood cells to extravasate. Furthermore, H&E staining of the tumor showed areas of bleeding with erythrocyte deposition. These observations are further supported by the increase in TUNEL staining in DMXAA treated tumors, revealing increased cell death due to vascular disruption. This study demonstrates the capability of PA imaging to monitor tumor vessel disruption by the vascular disrupting agent DMXAA.

Design, synthesis, and antitumor evaluation of trimethoxyflavonoid with arylurea structure against hepatocellular carcinoma

Simultaneous targeting of tumor vasculature and inhibitors of tumor cell glycolysis may be a promising antitumor strategy. Here, we reported the total synthesis and biological evaluation of A-ring arylurea flavonoid derivatives with B-ring trimethoxy group, which exhibited potent antitumor activity against a variety of tumor cells in vitro. Most of the derivatives showed in vitro antitumor activity on HepG-2, HGC-27, MDA-MB-231, and A549 cells. Among them, compounds 8e, 8f, 8g, 8h, 8j, and 8l also exhibited significant anti-proliferation effects on liver tumor cell subtypes BEL-7402 and SMMC-7721. Compound 8l had the lowest IC₅₀ value (5.61 ± 0.39 μM) on HepG-2 cells, and showed the effects of inhibiting colony formation, arresting the cell cycle in G₀ /G₁ phase, and inducing apoptosis in a concentration-dependent manner. In addition, the toxicity of compound 8l on human normal cells LO2 and GES-1 was lower than that of sorafenib. The inhibitory effects of compound 8l on the expression of glycolytic rate-limiting enzymes HKII, PFK-1, PKM2 and vascular endothelial growth factor were further evaluated. Corresponding reduction in intracellular lactate was also detected after compound 8 treatment. Our results support an antitumor strategy targeting tumor vasculature and glycolysis to discover and develop a new generation of antitumor drugs.

CKD-516 potentiates the anti-cancer activity of docetaxel against epidermal growth factor receptor tyrosine kinase inhibitor-resistant lung cancer

Lung cancer is the leading cause of cancer death. Although docetaxel has been used as a second- or third-line treatment for non-small cell lung cancer (NSCLC), the objective response rate is less than 10%. Hence, there is a need to improve the clinical efficacy of docetaxel monotherapy; combination therapy should be considered. Here, we show that CKD-516, a vascular disruption agent, can be combined with docetaxel to treat epidermal growth factor receptor (EGFR)-tyrosine kinase inhibitor (TKI)-resistant NSCLC. CKD-516 was orally bioavailable; neither CKD-516 nor docetaxel affected the mean plasma concentration-time profile or pharmacokinetic parameters of the other drug. CKD-516 and docetaxel synergistically inhibited the growth of H1975 (with an L858R/T790M double mutation of EGFR) and A549 (with a KRAS mutation) lung cancer cell lines. In addition, docetaxel plus CKD-516 delayed tumor growth in-and extended the lifespan of-tumor-bearing mice. Thus, combination CKD-516 and docetaxel therapy could be used to treat EGFR-TKI-resistant NSCLC.

Demonstrating Tumor Vascular Disrupting Activity of the Small-Molecule Dihydronaphthalene Tubulin-Binding Agent OXi6196 as a Potential Therapeutic for Cancer Treatment

The vascular disrupting activity of a promising tubulin-binding agent (OXi6196) was demonstrated in mice in MDA-MB-231 human breast tumor xenografts growing orthotopically in mammary fat pad and syngeneic RENCA kidney tumors growing orthotopically in the kidney. To enhance water solubility, OXi6196, was derivatized as its corresponding phosphate prodrug salt OXi6197, facilitating effective delivery. OXi6197 is stable in water, but rapidly releases OXi6196 in the presence of alkaline phosphatase. At low nanomolar concentrations OXi6196 caused G2/M cell cycle arrest and apoptosis in MDA-MB-231 breast cancer cells and monolayers of rapidly growing HUVECs underwent concentration-dependent changes in their morphology. Loss of the microtubule structure and increased bundling of filamentous actin into stress fibers followed by cell collapse, rounding and blebbing was observed. OXi6196 (100 nM) disrupted capillary-like endothelial networks pre-established with HUVECs on Matrigel®. When prodrug OXi6197 was administered to mice bearing orthotopic MDA-MB-231-luc tumors, dynamic bioluminescence imaging (BLI) revealed dose-dependent vascular shutdown with >80% signal loss within 2 h at doses ≥30 mg/kg and >90% shutdown after 6 h for doses ≥35 mg/kg, which remained depressed by at least 70% after 24 h. Twice weekly treatment with prodrug OXi6197 (20 mg/kg) caused a significant tumor growth delay, but no overall survival benefit. Similar efficacy was observed for the first time in orthotopic RENCA-luc tumors, which showed massive hemorrhage and necrosis after 24 h. Twice weekly dosing with prodrug OXi6197 (35 mg/kg) caused tumor growth delay in most orthotopic RENCA tumors. Immunohistochemistry revealed extensive necrosis, though with surviving peripheral tissues. These results demonstrate effective vascular disruption at doses comparable to the most effective vascular-disrupting agents (VDAs) suggesting opportunities for further development.

Enhancing Doxorubicin Delivery in Solid Tumor by Superhydrophobic Amorphous Calcium Carbonate-Doxorubicin Silica Nanoparticles with Focused Ultrasound

The current approach of delivering chemotherapy via pH-sensitive amorphous calcium carbonate-doxorubicin silica nanoparticles (ADS NPs) faces the challenge of insufficient drug dose due to drug instability within the bloodstream and poor tumor penetration. To overcome these long-standing obstacles, we proposed a superhydrophobic coating on the surface of the ADS NPs that could be easily modified via fluorination (ADSF NPs). The surface of fluorinated ADS NPs was further modified with a phospholipid layer to reduce aggregation and improve biocompatibility (ADSFL NPs). The contact angle and mean size of ADSFL NPs were 30.2 ± 4.4° and 353.1 ± 54.2 nm, respectively. The superhydrophobic layer generated interfacial nanobubbles on the outer shell of the NPs that reduced water-induced leakage of doxorubicin (DOX) sevenfold compared with the uncoated group and induced a cavitation effect upon ultrasound (US) sonication. Moreover, release of DOX from the ADSFL NPs could be triggered by US, and this release was further improved 1.6-fold in acidic aqueous conditions, indicating that the ADSFL NPs retained pH responsiveness. Enhanced sonography contrast and histological examination demonstrated that US could trigger cavitation activities from ADSFL NPs in vivo to induce vessel disruption and enhance the fluorescence intensity of DOX within the tumor region threefold under US imaging guidance compared with the ADSFL NPs-only group.

Discovery of a Novel Vascular Disrupting Agent Inhibiting Tubulin Polymerization and HDACs with Potent Antitumor Effects

Most vascular disrupting agents (VDAs) fail to prevent the regrowth of blood vessels at the edge of tumors, causing tumor rebound and relapse. Herein, a series of novel multifunctional vascular disrupting agents (VDAs) capable of inhibiting microtubule polymerization and histone deacetylases (HDACs) were designed and synthesized using the tubulin polymerization inhibitor TH-0 as the lead compound. Among them, compound TH-6 exhibited the most potent antiproliferative activity (IC₅₀ = 18-30 nM) against a panel of cancer cell lines. As expected, TH-6 inhibited tubulin assembly and increased the acetylation level of HDAC substrate proteins in HepG2 cells. Further in vivo antitumor assay displayed that TH-6 effectively inhibited tumor growth with no apparent toxicity. More importantly, TH-6 disrupted both the internal and peripheral tumor vasculatures, which contributed to the persistent tumor inhibitory effects after drug withdrawal. Altogether, TH-6 deserves to be further investigated for the new approach to clinical cancer therapy.

3D-Cultured Vascular-Like Networks Enable Validation of Vascular Disruption Properties of Drugs In Vitro

Vascular-disrupting agents are an interesting class of anticancer compounds because of their combined mode of action in preventing new blood vessel formation and disruption of already existing vasculature in the immediate microenvironment of solid tumors. The validation of vascular disruption properties of these drugs in vitro is rarely addressed due to the lack of proper in vitro angiogenesis models comprising mature and long-lived vascular-like networks. We herein report an indirect coculture model of human umbilical vein endothelial cells (HUVECs) and human dermal fibroblasts (HDFs) to form three-dimensional profuse vascular-like networks. HUVECs embedded and sandwiched in the collagen scaffold were cocultured with HDFs located outside the scaffold. The indirect coculture approach with the vascular endothelial growth factor (VEGF) producing HDFs triggered the formation of progressively maturing lumenized vascular-like networks of endothelial cells within less than 7 days, which have proven to be viably maintained in culture beyond day 21. Molecular weight-dependent Texas red-dextran permeability studies indicated high vascular barrier function of the generated networks. Their longevity allowed us to study the dose-dependent response upon treatment with the three known antiangiogenic and/or vascular disrupting agents brivanib, combretastatin A4 phosphate (CA4P), and 6´-sialylgalactose (SG) via semi-quantitative brightfield and qualitative confocal laser scanning microscopic (CLSM) image analysis. Compared to the reported data on in vivo efficacy of these drugs in terms of antiangiogenic and vascular disrupting effects, we observed similar trends with our 3D model, which are not reflected in conventional in vitro angiogenesis assays. High-vascular disruption under continuous treatment of the matured vascular-like network was observed at concentrations ≥3.5 ng·ml⁻¹ for CA4P and ≥300 nM for brivanib. In contrast, SG failed to induce any significant vascular disruption in vitro. This advanced model of a 3D vascular-like network allows for testing single and combinational antiangiogenic and vascular disrupting effects with optimized dosing and may thus bridge the gap between the in vitro and in vivo experiments in validating hits from high-throughput screening. Moreover, the physiological 3D environment mimicking in vitro assay is not only highly relevant to in vivo studies linked to cancer but also to the field of tissue regeneration.

Destruction of tumor vasculature by vascular disrupting agents in overcoming the limitation of EPR effect

Nanomedicine greatly improves the efficiency in the delivery of antitumor drugs into the tumor, but insufficient tumoral penetration impairs the therapeutic efficacy of most nanomedicines. Vascular disrupting agent (VDA) nanomedicines are distributed around the tumor vessels due to the low tissue penetration in solid tumors, and the released drugs can selectively destroy immature tumor vessels and block the supply of oxygen and nutrients, leading to the internal necrosis of the tumors. VDAs can also improve the vascular permeability of the tumor, further increasing the extravasation of VDA nanomedicines in the tumor site, markedly reducing the dependence of nanomedicines on the enhanced permeability and retention effect (EPR effect). This review highlights the progress of VDA nanomedicines in recent years and their application in cancer therapy. First, the mechanisms of different VDAs are introduced. Subsequently, different strategies of delivering VDAs are described. Finally, multiple combination strategies with VDA nanomedicines in cancer therapy are described in detail.

Self-Assembled Amphiphilic Fluorinated Random Copolymers for the Encapsulation and Release of the Hydrophobic Combretastatin A-4 Drug

Water-soluble amphiphilic random copolymers composed of tri(ethylene glycol) methacrylate (TEGMA) or poly(ethylene glycol) methyl ether methacrylate (PEGMA) and perfluorohexylethyl acrylate (FA) were synthesized by ARGET-ATRP, and their self-assembling and thermoresponsive behavior in water was studied by dynamic light scattering (DLS) and UV-vis spectroscopy. The copolymer ability to self-fold in single-chain nano-sized structures (unimer micelles) in aqueous solutions was exploited to encapsulate Combretastatin A-4 (CA-4), which is a very hydrophobic anticancer drug. The cloud point temperature (Tcp) was found to linearly decrease with increasing drug concentration in the drug/copolymer system. Moreover, while CA-4 was preferentially incorporated into the unimer micelles of TEGMA-ran-FA, the drug was found to induce multi-chain, submicro-sized aggregation of PEGMA-ran-FA. Anyway, the encapsulation efficiency was very high (≥81%) for both copolymers. The drug release was evaluated in PBS aqueous solutions both below and above Tcp for TEGMA-ran-FA copolymer and below Tcp, but at two different drug loadings, for PEGMA-ran-FA copolymer. In any case, the release kinetics presented similar profiles, characterized by linear trends up to ≈10-13 h and ≈7 h for TEGMA-ran-FA and PEGMA-ran-FA, respectively. Then, the release rate decreased, reaching a plateau. The release from TEGMA-ran-FA was moderately faster above Tcp than below Tcp, suggesting that copolymer thermoresponsiveness increased the release rate, which occurred anyway by diffusion below Tcp. Cytotoxicity tests were carried out on copolymer solutions in a wide concentration range (5-60 mg/mL) at 37 °C by using Balb/3T3 clone A31 cells. Interestingly, it was found that the concentration-dependent micro-sized aggregation of the amphiphilic random copolymers above Tcp caused a sort of "cellular asphyxiation" with a loss of cell viability clearly visible for TEGMA-ran-FA solutions (Tcp below 37 °C) with higher copolymer concentrations. On the other hand, cells in contact with the analogous PEGMA-ran-FA (Tcp above 37 °C) presented a very good viability (≥75%) with respect to the control at any given concentration.

Anticancer properties of arylchromenes and arylchromans: an overview

Cancers are a set of pathologies originated by cells that have the ability to divide and multiply uncontrollably, associated with the capacity to invade and colonize adjacent tissues. Chemotherapy is one of the main approaches of treatment for cancer patients. Despite of the numerous antineoplastic drugs available, cancer cannot be cured; particularly at the late stages deprived of any side effect. Arylchromenes and arylchromans are a group of small molecules, of natural or synthetic origin, of great interest as prototypes for the drug development, especially against cancer. In this chapter, we will present the antineoplastic activity studies of the most promising examples of these arylchromenes and arylchroman derivatives.

A H2O2-responsive theranostic platform for chemiluminescence detection and synergistic therapy of tumor

Chemiluminescence substances that respond to hydrogen peroxide (H2O2) in the tumor microenvironment have the potential to achieve accurate tumor imaging. Here, Pluronic F-127 (PF127) and polymers containing oxalate ester (POE)...

TEM1-targeting PEGylated PLGA shikonin nanoformulation for immunomodulation and eradication of ovarian cancer

Introduction: Tumor endothelial marker 1 (TEM1) is expressed by tumor vascular endothelial cells in various cancers. Methods: Here, we developed poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) PEGylated with polyethylene glycol (PEG) and functionalized with anti-TEM1 antibody fragment (78Fc) and loaded them with necroptosis-inducing agent shikonin (SHK) (78Fc-PLGA-SHK NPs). Results: The nanoformulation showed a smooth spherical shape (~120 nm; the ζ potential of -30 mV) with high drug entrapment and bioconjugation efficiencies (~92% and ~90%, respectively) and a sustained-release profile in serum. Having significant toxicity in vitro (e.g., MS1 and TC1 cells), the nanoformulation dramatically increased the cytotoxicity in the TC1 murine lung carcinoma subcutaneous and intravenous/metastatic models as aggressive tumor models. The injection of the 78Fc-PLGA-SHK NPs to the MS1-xenograft mice resulted in significantly higher accumulation and effects in the TEM1-positive tumor targets, while they were excreted via urine track without retaining in the liver/spleen. In the TC1 subcutaneous model, C57/BL6 mice treated with the 78Fc-PLGA-SHK NPs revealed a significant therapeutic effect. The mice, which were tumor-free after receiving the nanoformulation, were re-challenged with the TC1 cells to investigate the immune response. These animals became tumor-free a week after the injection of TC1 cells. Conclusion: Based on these findings, we propose the 78Fc-PLGA-SHK NPs as a highly effective immunostimulating nanomedicine against the TEM1-expressing cells for targeted therapy of solid tumors including ovarian cancer.

Pegylated liposomal encapsulation improves the antitumor efficacy of combretastatin A4 in murine 4T1 triple-negative breast cancer model

Combretastatin A4 (CA4), a vascular disrupting agent has been recently proposed as an anticancer agent. However, its low water solubility and low bioavailability limited its clinical efficacy. Overcomingthis issue requires developing new delivery strategies to enhance its anticancer effects. Here, we prepared various PEGylated liposomal formulations containing CA4 composed of different molar ratios of HSPC/DSPE-mPEG₂₀₀₀/Cholesterol/CA4 (F1: 80:5:10:5; F2: 75:5:15:5; F3: 70:5:20:5; F4: 60:5:30:5 and F5: 50:5:40:5) by the thin-film hydration method plus sonication and extrusion. All formulations had a particle diameter of 100-150 nm, a monomodal distribution with low polydispersity index and a negative zeta potential. Among the formulations only F1, F2, and F3 showed a high CA4 encapsulation efficiency; so their anticancer effects on triple-negative breast cancer (TNBC) were investigated in vitro and in vivo. The release study showed that F3 liposomes had significantly lower CA4 release compared to the F1 and F2 liposomes in different pH of 5.5, 6.5, and 7.4. We found that, CA4-loaded liposomes effectively inhibited both proliferation and migration of 4T1 and MDA-MB-231 TNBC cell lines by inducing cell cycle arrest at the G2/M phase and decreasing MMP-2 and MMP-9 expression and activity. In vivo studies revealed that F3 liposomes were highly accumulated at the tumor site and more effectively delayed tumor growth andprolonged the overall survival than other groups in 4T1 breast tumor-bearing mice. Taken together, encapsulation of CA4 in PEGylated F3 liposomes enhances its anti-tumor activity and may be serve as a promising approach for TNBC treatment and merits further investigation.

Microtubule Targeting Agents in Disease: Classic Drugs, Novel Roles

Microtubule-targeting agents (MTAs) represent one of the most successful first-line therapies prescribed for cancer treatment. They interfere with microtubule (MT) dynamics by either stabilizing or destabilizing MTs, and in culture, they are believed to kill cells via apoptosis after eliciting mitotic arrest, among other mechanisms. This classical view of MTA therapies persisted for many years. However, the limited success of drugs specifically targeting mitotic proteins, and the slow growing rate of most human tumors forces a reevaluation of the mechanism of action of MTAs. Studies from the last decade suggest that the killing efficiency of MTAs arises from a combination of interphase and mitotic effects. Moreover, MTs have also been implicated in other therapeutically relevant activities, such as decreasing angiogenesis, blocking cell migration, reducing metastasis, and activating innate immunity to promote proinflammatory responses. Two key problems associated with MTA therapy are acquired drug resistance and systemic toxicity. Accordingly, novel and effective MTAs are being designed with an eye toward reducing toxicity without compromising efficacy or promoting resistance. Here, we will review the mechanism of action of MTAs, the signaling pathways they affect, their impact on cancer and other illnesses, and the promising new therapeutic applications of these classic drugs.

Clinical Application of Tumor Vascular Disrupting Therapy: A Systematic Review and Meta-Analysis

Purpose

The occurrence, progression, invasion and metastasis of tumors depend on a tumor vascular network. Vascular disrupting agents (VDAs) are a new class of drugs targeting the tumor vasculature, by blocking the existing tumor blood vessels. However, there is no clear consensus on the clinical efficacy of tumor vascular disrupting therapy. In this study, we performed the first systematic review and meta-analysis of published clinical trials focused on tumor vascular disrupting therapies.

Materials and Methods

We searched PubMed, EMBASE, and the Cochrane Library to identify clinical trials that used VDAs to treat tumors. After literature screening and data extraction, according to inclusion and exclusion labels, meta-analysis was performed using RevMan5.3 software.

Results

In this meta-analysis, we included 2659 patients from eight randomized controlled trials involving non-small-cell lung cancer, prostate, epithelial ovarian, fallopian tube, and primary peritoneal carcinoma. Compared with the control arm, the experimental arm exhibited an effective improvement of 0.5-year and 1-year survival, as well as the 6-month progression-free survival rate. There was no significant difference between patients in the experimental compared to the control arm with respect to objective response and disease control rates, and 12-month progression-free survival.

Conclusion

Vascular disrupting therapy can effectively prolong the survival of cancer patients. However, for indicators of short-term efficacy, such as objective response rate and disease control rate, there is still a lack of high-quality, large-scale clinical trial data to confirm the effectiveness of VDAs.

Tumor vasculature-targeting nanomedicines

Uncontrolled tumor growth and subsequent distant metastasis are highly dependent on an adequate nutrient supply from tumor blood vessels, which have relatively different pathophysiological characteristics from those of normal vasculature. Obviously, strategies targeting tumor vasculature, such as anti-angiogenic drugs and vascular disrupting agents, are attractive methods for cancer therapy. However, the off-target effects and high dose administration of these drug regimens critically restrict their clinical applications. In recent years, nanomedicines focused on tumor vasculature have been shown to be superior to traditional therapeutic methods and do not induce side effects. This review will first highlight the recent development of tumor vasculature-targeting nanomedicines from the following four aspects: 1) angiogenesis-inhibiting nanomedicines (AINs); 2) vasculature-disrupting nanomedicines (VDNs); 3) vasculature infarction nanomedicines (VINs); and 4) vasculature-regulating nanomedicines (VRNs). Furthermore, the design principles, limitations, and future directions are also discussed. STATEMENT OF SIGNIFICANCE: Based on the essential roles of tumor blood vessels, the therapeutic strategies targeting tumor vasculature have exhibited good clinical therapeutic outcomes. However, poor patient adherence to free drug administration limits their clinical usage. Nanomedicines have great potential to overcome the abovementioned obstacle. This review summarizes the tumor-vasculature targeting nanomedicines from four aspects: 1) angiogenesis-inhibiting nanomedicines (AINs); 2) vasculature-disrupting nanomedicines (VDNs); 3) vasculature infarction nanomedicines (VINs); and 4) vasculature regulating nanomedicines (VRNs). In addition, this review provides perspectives on this research field.

3-D Super-Resolution Ultrasound Imaging for Monitoring Early Changes in Breast Cancer after Treatment with a Vascular-Disrupting Agent

The purpose of this research project was to evaluate the use of 3-dimensional (3-D) super-resolution ultrasound (SR-US) imaging to assess any early changes in breast cancer after treatment with a vascular-disrupting agent (VDA). A Vevo 3100 ultrasound system (FUJIFILM VisualSonics Inc) equipped with an MX 201 transducer was used for image acquisition. A total of 2.5 × 107 microbubbles (MBs) were injected into the tail vein of anesthetized breast cancer-bearing mice using repeat bolus injections every 5 min. A total of 10 stacks of ultrasound images were collected as the transducer was mechanically moved across the tumor at 0.6 mm intervals yielding a 6-mm thick volume. At each tumor location, a stack contained 1 × 104 frames of ultrasound data that were acquired at 463 frames/sec and stored as in-phase/quadrature (IQ) format. After motion correction, each temporal stack of ultrasound images was processed separately for clutter signal removal, which was followed by MB localization and enumeration before generation of the final SR-US image. After reconstruction of the 3-D SR-US volume dataset, the tumor microvasculature was enhanced using a multiscale vessel enhancement filter. Vessels from the resultant microvascular network were then segmented using an adaptive thresholding method. Finally, mean microvascular density (MVD) measurements from each tumor volume were computed as a summarizing statistic. While no differences were found between baseline SR-US image-derived measures of MVD (p = 0.76), these same measurements were significantly lower at 24 h after VDA treatment (p < 0.001). Overall, 3-D SR-US imaging detected early tumor changes following treatment with a vascular-targeted drug.

Discovery of new vascular disrupting agents based on evolutionarily conserved drug action, pesticide resistance mutations, and humanized yeast

Thiabendazole (TBZ) is an FDA-approved benzimidazole widely used for its antifungal and antihelminthic properties. We showed previously that TBZ is also a potent vascular disrupting agent and inhibits angiogenesis at the tissue level by dissociating vascular endothelial cells in newly formed blood vessels. Here, we uncover TBZ's molecular target and mechanism of action. Using human cell culture, molecular modeling, and humanized yeast, we find that TBZ selectively targets only 1 of 9 human β-tubulin isotypes (TUBB8) to specifically disrupt endothelial cell microtubules. By leveraging epidemiological pesticide resistance data and mining chemical features of commercially used benzimidazoles, we discover that a broader class of benzimidazole compounds, in extensive use for 50 years, also potently disrupt immature blood vessels and inhibit angiogenesis. Thus, besides identifying the molecular mechanism of benzimidazole-mediated vascular disruption, this study presents evidence relevant to the widespread use of these compounds while offering potential new clinical applications.

The Proper Administration Sequence of Radiotherapy and Anti-Vascular Agent-DMXAA Is Essential to Inhibit the Growth of Melanoma Tumors

Vascular disrupting agents (VDAs), such as DMXAA, effectively destroy tumor blood vessels and cause the formation of large areas of necrosis in the central parts of the tumors. However, the use of VDAs is associated with hypoxia activation and residues of rim cells on the edge of the tumor that are responsible for tumor regrowth. The aim of the study was to combine DMXAA with radiotherapy (brachytherapy) and find the appropriate administration sequence to obtain the maximum synergistic therapeutic effect. We show that the combination in which tumors were irradiated prior to VDAs administration is more effective in murine melanoma growth inhibition than in either of the agents individually or in reverse combination. For the first time, the significance of immune cells' activation in such a combination is demonstrated. The inhibition of tumor growth is linked to the reduction of tumor blood vessels, the increased infiltration of CD8⁺ cytotoxic T lymphocytes and NK cells and the polarization of macrophages to the cytotoxic M1 phenotype. The reverse combination of therapeutic agents showed no therapeutic effect and even abolished the effect of DMXAA. The combination of brachytherapy and vascular disrupting agent effectively inhibits the growth of melanoma tumors but requires careful planning of the sequence of administration of the agents.

Light-assisted gadofullerene nanoparticles disrupt tumor vasculatures for potent melanoma treatment

The traditional photodynamic therapy (PDT) using a photosensitizer and oxygen under light generates reactive oxygen species (ROS) to kill tumor cells. However, its treatment efficiency is limited by insufficient oxygen in tumor cells. Herein, β-alanine modified gadofullerene nanoparticles (GFNPs) were explored to disrupt tumor vasculatures assisted by light for potent melanoma treatment. As tumor vasculatures are oxygen-rich, the yields of photo-induced singlet oxygen (1O2) by GFNPs are not subjected to the hypoxemia of tumor tissues. Different from the small molecule photosensitizer Chlorin e6 (Ce6), GFNPs realize high-efficiency tumor vascular disruption under light observed by using the mice tumor vascular dorsal skin fold chamber (DSFC) model. The tumor vascular disruption efficiency of GFNPs is size-dependent, and the smallest one (hydration diameter of ca. 126 nm) is more efficient. Mechanistically, the high yields of photo-induced 1O2 by GFNPs can lead to the destruction of the tumor vascular endothelial adherent junction protein-VE cadherin and the decrease of tumor vascular endothelial cells-CD31 proteins, inducing rapid tumor necrosis. In conclusion, our work provides an insight into the design of well-sized nanoparticles to powerfully treat melanoma assisted by light, as well as greatly extending the applications of PDT for robust tumor therapy.

Utilisation of Chick Embryo Chorioallantoic Membrane as a Model Platform for Imaging-Navigated Biomedical Research

The fertilised chick egg and particularly its chorioallantoic membrane (CAM) have drawn continuing interest in biomedicine and bioengineering fields, especially for research on vascular study, cancer, drug screening and development, cell factors, stem cells, etc. This literature review systemically introduces the CAM's structural evolution, functions, vascular features and the circulation system, and cell regulatory factors. It also presents the major and updated applications of the CAM in assays for pharmacokinetics and biodistribution, drug efficacy and toxicology testing/screening in preclinical pharmacological research. The time course of CAM applications for different assays and their advantages and limitations are summarised. Among these applications, two aspects are emphasised: (1) potential utility of the CAM for preclinical studies on vascular-disrupting agents (VDAs), promising for anti-cancer vascular-targeted therapy, and (2) modern imaging technologies, including modalities and their applications for real-time visualisation, monitoring and evaluation of the changes in CAM vasculature as well as the interactions occurring after introducing the tested medical, pharmaceutical and biological agents into the system. The aim of this article is to help those working in the biomedical field to familiarise themselves with the chick embryo CAM as an alternative platform and to utilise it to design and optimise experimental settings for their specific research topics.

MnO2 Nanoflowers Induce Immunogenic Cell Death under Nutrient Deprivation: Enabling an Orchestrated Cancer Starvation-Immunotherapy

MnO2 nanoparticles have been widely employed in cancer immunotherapy, playing a subsidiary role in assisting immunostimulatory drugs by improving their pharmacokinetics and/or creating a favorable microenvironment. Here, the stereotype of the subsidiary role of MnO2 nanoparticles in cancer immunotherapy is challenged. This study unravels an intrinsic immunomodulatory property of MnO2 nanoparticles as a unique nutrient-responsive immunogenic cell death (ICD) inducer, capable of directly modulating immunosurveillance toward tumor cells. MnO2 nanoflowers (MNFs) constructed via a one pot self-assembly approach selectively induce ICD to nutrient-deprived but not nutrient-replete cancer cells, which is confirmed by the upregulated damage associated molecular patterns in vitro and a prophylactic vaccination in vivo. The underlying mechanism of the MNFs-mediated selective ICD induction is likely associated with the concurrently upregulated oxidative stress and autophagy. Built on their unique immunomodulatory properties, an innovative nanomaterials orchestrated cancer starvation-immunotherapy is successfully developed, which is realized by the in situ vaccination with MNFs and vascular disrupting agents that cut off intratumoral nutrient supply, eliciting potent efficacy for suppressing local and distant tumors. These findings open up a new avenue toward biomedical applications of MnO2 materials, enabling an innovative therapeutics paradigm with great clinical significance.

Engineered nanomedicines for tumor vasculature blockade therapy

Tumor vasculature blockade therapy (TVBT), including angiogenesis inhibition, vascular disruption, and vascular infarction, provides a promising treatment modality for solid tumors. However, low selectivity, drug resistance, and possible severe side effects have limited the clinical transformation of TVBT. Engineered nanoparticles offer potential solutions, including prolonged circulation time, targeted transportation, and controlled release of TVBT agents. Moreover, engineered nanomedicines provide a promising combination platform of TVBT with chemotherapy, radiotherapy, photodynamic therapy, photothermal therapy, ultrasound therapy, and gene therapy. In this article, we offer a comprehensive summary of the current progress of engineered nanomedicines for TVBT and also discuss current deficiencies and future directions for TVBT development. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Role of Regular Physical Exercise in Tumor Vasculature: Favorable Modulator of Tumor Milieu

The tumor vessel network has been investigated as a precursor of an inhospitable tumor microenvironment, including its repercussions in tumor perfusion, oxygenation, interstitial fluid pressure, pH, and immune response. Dysfunctional tumor vasculature leads to the extravasation of blood to the interstitial space, hindering proper perfusion and causing interstitial hypertension. Consequently, the inadequate delivery of oxygen and clearance of by-products of metabolism promote the development of intratumoral hypoxia and acidification, hampering the action of immune cells and resulting in more aggressive tumors. Thus, pharmacological strategies targeting tumor vasculature were developed, but the overall outcome was not satisfactory due to its transient nature and the higher risk of hypoxia and metastasis. Therefore, physical exercise emerged as a potential favorable modulator of tumor vasculature, improving intratumoral vascularization and perfusion. Indeed, it seems that regular exercise practice is associated with lasting tumor vascular maturity, reduced vascular resistance, and increased vascular conductance. Higher vascular conductance reduces intratumoral hypoxia and increases the accessibility of circulating immune cells to the tumor milieu, inhibiting tumor development and improving cancer treatment. The present paper describes the implications of abnormal vasculature on the tumor microenvironment and the underlying mechanisms promoted by regular physical exercise for the re-establishment of more physiological tumor vasculature.

Noninvasive imaging of tumor hypoxia after nanoparticle-mediated tumor vascular disruption

We have previously demonstrated that endothelial targeting of gold nanoparticles followed by external beam irradiation can cause specific tumor vascular disruption in mouse models of cancer. The induced vascular damage may lead to changes in tumor physiology, including tumor hypoxia, thereby compromising future therapeutic interventions. In this study, we investigate the dynamic changes in tumor hypoxia mediated by targeted gold nanoparticles and clinical radiation therapy (RT). By using noninvasive whole-body fluorescence imaging, tumor hypoxia was measured at baseline, on day 2 and day 13, post-tumor vascular disruption. A 2.5-fold increase (P<0.05) in tumor hypoxia was measured two days after combined therapy, resolving by day 13. In addition, the combination of vascular-targeted gold nanoparticles and radiation therapy resulted in a significant (P<0.05) suppression of tumor growth. This is the first study to demonstrate the tumor hypoxic physiological response and recovery after delivery of vascular-targeted gold nanoparticles followed by clinical radiation therapy in a human non-small cell lung cancer athymic Foxn1^nu mouse model.

Vascular disrupting agent induced aggregation of gold nanoparticles for photothermally enhanced tumor vascular disruption

Although vascular disrupting agents (VDAs) have been extensively implemented in current clinical tumor therapy, the notable adverse events caused by long-term dosing severely limit the therapeutic efficacy. To improve this therapy, we report a strategy for VDA-induced aggregation of gold nanoparticles to further destroy tumor vascular by photothermal effect. This strategy could effectively disrupt tumor vascular and cut off the nutrition supply after just one treatment. In the murine tumor model, this strategy results in notable tumor growth inhibition and gives rise to a 92.7% suppression of tumor growth. Besides, enhanced vascular damage could also prevent cancer cells from distant metastasis. Moreover, compared with clinical therapies, this strategy still exhibits preferable tumor suppression and metastasis inhibition ability. These results indicate that this strategy has great potential in tumor treatment and could effectively enhance tumor vascular damage and avoid the side effects caused by frequent administration.

Glioblastoma: Targeting Angiogenesis and Tyrosine Kinase Pathways

Angiogenesis is a hallmark of glioblastoma (GBM) and remains an important therapeutic target in its treatment, especially for recurrent GBM. GBMs are characterized by the release of vascular endothelial growth factor (VEGF), an important regulator and promoter of angiogenesis. Therefore, antiangiogenic therapies (AATs) targeting VEGF or VEGF receptors (VEGFRs) were designed and thought to be an effective tool for controlling the growth of GBM. However, recent results of different clinical trials using humanized monoclonal antibodies against VEGF (bevacizumab), as well as tyrosine kinase inhibitors (TKIs) that target different VEGFRs alone or in combination with other therapeutic agents demonstrated mixed results, with the majority of reports indicating that GBM developed resistance against antiangiogenic treatments.

Predicting Clinical Efficacy of Vascular Disrupting Agents in Rodent Models of Primary and Secondary Liver Cancers: An Overview with Imaging-Histopathology Correlation

Vascular disrupting agents (VDAs) have entered clinical trials for over 15 years. As the leading VDA, combretastatin A4 phosphate (CA4P) has been evaluated in combination with chemotherapy and molecular targeting agents among patients with ovarian cancer, lung cancer and thyroid cancer, but still remains rarely explored in human liver cancers. To overcome tumor residues and regrowth after CA4P monotherapy, a novel dual targeting pan-anticancer theragnostic strategy, i.e., OncoCiDia, has been developed and shown promise previously in secondary liver tumor models. Animal model of primary liver cancer is time consuming to induce, but of value for more closely mimicking human liver cancers in terms of tumor angiogenesis, histopathological heterogeneity, cellular differentiation, tumor components, cancer progression and therapeutic response. Being increasingly adopted in VDA researches, multiparametric magnetic resonance imaging (MRI) provides imaging biomarkers to reflect in vivo tumor responses to drugs. In this article as a chapter of a doctoral thesis, we overview the construction and clinical relevance of primary and secondary liver cancer models in rodents. Target selection for CA4P therapy assisted by enhanced MRI using hepatobiliary contrast agents (CAs), and therapeutic efficacy evaluated by using MRI with a non-specific contrast agent, dynamic contrast enhanced (DCE) imaging, diffusion weighted imaging (DWI) are also described. We then summarize diverse responses among primary hepatocellular carcinomas (HCCs), secondary liver and pancreatic tumors to CA4P, which appeared to be related to tumor size, vascularity, and cellular differentiation. In general, imaging-histopathology correlation studies allow to conclude that CA4P tends to be more effective in secondary liver tumors and in more differentiated HCCs, but less effective in less differentiated HCCs and implanted pancreatic tumor. Notably, cirrhotic liver may be responsive to CA4P as well. All these could be instructive for future clinical trials of VDAs.

CaCO3 nanoparticles pH-sensitively induce blood coagulation as a potential strategy for starving tumor therapy

Based on the concept of starving tumor therapy, in this study we put forward a new idea that the pH-sensitive Ca²⁺ delivery of calcium carbonate nanoparticles (CaCO₃ NPs) induced blood coagulation of tumor vessels, and first explored the effect of CaCO₃ NPs on the in vitro and in vivo blood coagulation by acid stimulus. CaCO₃ NPs with a size of about 100 nm and a porous structure of several nanometers were synthesized in an emulsion system, which showed a high loading capacity (49%) of doxorubicin hydrochloride (DOX) with an encapsulation efficiency of 98% and a pH-sensitive drug delivery. The hemolysis test showed that CaCO₃ NPs were blood compatible. The in vitro Ca²⁺ delivery and blood clotting tests indicated that CaCO₃ NPs pH-sensitively released Ca²⁺, and caused rapid blood coagulation at pH 5.0 but no thrombus at pH 7.4. Confocal laser scanning microscopy showed that after uptake by MCF-7 or MDA-MB-231 breast cancer cells, CaCO₃ NPs mainly distributed in endosomes/lysosomes within the initial 2 h and then decomposed by acid stimulus, leading to the intracellular delivery of Ca²⁺ that subsequently migrated outside the cells. CaCO₃ NPs were nontoxic to NIH3T3 mouse fibroblasts, but highly toxic to both MCF-7 and MDA-MB-231 cells after loading DOX. After topical administration into the breast tumors of mice, CaCO₃ NPs evoked significant thrombosis and hemorrhage of tumor vasculature by hematoxylin-eosin and Masson's trichrome staining. These results indicated that CaCO₃ NPs could induce blood coagulation via acid stimulus, showing potential applications in blocking tumor vessels for starving tumor therapy.

Breast Cancer Brain Metastasis Response to Radiation After Microbubble Oxygen Delivery in a Murine Model

OBJECTIVES

Hypoxic cancer cells have been shown to be more resistant to radiation therapy than normoxic cells. Hence, this study investigated whether ultrasound (US)-induced rupture of oxygen-carrying microbubbles (MBs) would enhance the response of breast cancer metastases to radiation.

METHODS

Nude mice (n = 15) received stereotactic injections of brain-seeking MDA-MB-231 breast cancer cells into the right hemisphere. Animals were randomly assigned into 1 of 5 treatment groups: no intervention, 10 Gy radiation using a small-animal radiation research platform, nitrogen-carrying MBs combined with US-mediated MB rupture immediately before 10 Gy radiation, oxygen-carrying MBs immediately before 10 Gy radiation, and oxygen-carrying MBs with US-mediated MB rupture immediately before 10 Gy radiation. Tumor progression was monitored with 3-dimensional US, and overall survival was noted.

RESULTS

All groups except those treated with oxygen-carrying MB rupture and radiation had continued rapid tumor growth after treatment. Tumors treated with radiation alone showed a mean increase in volume ± SD of 337% ± 214% during the week after treatment. Tumors treated with oxygen-carrying MBs and radiation without MB rupture showed an increase in volume of 383% ± 226%. Tumors treated with radiation immediately after rupture of oxygen-carrying MBs showed an increase in volume of only 41% ± 1% (P = 0.045), and this group also showed a 1 week increase in survival time.

CONCLUSIONS

Adding US-ruptured oxygen-carrying MBs to radiation therapy appears to delay tumor progression and improve survival in a murine model of metastatic breast cancer.

Mechanisms of resistance to anti-angiogenic treatments

Hailed as the cancer treatment to end all the resistance to treatment, anti-angiogenic therapy turned out to be not quite what was promised. The hope that this therapeutic approach would not have suffered by the phenomenon of resistance was based on the fact that was targeting normal vessels rather than tumour cells prone to mutation and subject to drug induced selection. However, reality turned out to be more complex and since 1997, several mechanisms of resistance have been described to the point that the study of resistance to these drugs is now a very large field. Far from being exhaustive, this paper presents the main mechanisms discovered trough some examples.

Targeted-nanoliposomal combretastatin A4 (CA-4) as an efficient antivascular candidate in the metastatic cancer treatment

A number of antiangiogenic drugs have been approved by the Food and Drug Administration which are used in cancer therapy, and variety of other agents in several stages of clinical development or in preclinical assessment. Among these, combretastatin A4 (CA-4) is an under-researched inhibitor of angiogenesis that shows potential activity in the treatment of advanced tumors with migration capacity. However, its clinical application has been limited due to poor water solubility, low bioavailability, rapid metabolism, and systemic elimination. During the last decade, numerous investigations have been done to overcome these problems by using different CA-4 delivery systems or developing produgs of CA-4 or its structural analogs. Nevertheless, these strategies could not be efficient out of the undesired side effects on normal tissues. Nanoliposomal CA-4 not only benefits from the advantage of using liposomal drugs as opposed to free drugs but also can accumulate in the tumor site via specific targeting ligands, which leads to efficient targeting and enhancement of bioavailability. To the best of our knowledge, we consider an important attempt to understand different factors that might influence the CA-4 loading and release pattern of liposomes and the consequent results in tumor therapy. In this review, we shed light on various studied liposomal CA-4 formulations showing application thereof in cancer treatment.

Toll-like receptor-targeted particles: A paradigm to manipulate the tumor microenvironment for cancer immunotherapy

The expression of Toll-like receptors (TLRs) on antigen presenting cells, especially dendritic cells, offers several sensitive mediators to trigger an adaptive immune response, which potentially can be exploited to detect and eliminate pathogenic objects. Consequently, numerous agonists that target TLRs are being used clinically either alone or in combination with other therapies to strengthen the immune system in the battle against cancer. This review summarizes the roles of TLRs in tumor biology, and focuses on relevant TLR-dependent antitumor pathways and the conjugation of TLR agonists as adjuvants to nano- and micro-particles for boosting responses leading to cancer suppression and eradication. STATEMENT OF SIGNIFICANCE: Toll-like receptors (TLRs), which express on antigen presenting cells, such as dendritic cells and macrophages, play an important role in sensing pathogenic agents and inducing adaptive immunity. As a result, several TLR agonists have been investigating as therapeutic agents individually or in combination with other treatment modalities for cancer treatment through boosting the immune system. This review aims to focus on the roles of TLRs in cancer and TLR-dependent antitumor pathways as well as the use of different nano- or micro-particles bearing TLR agonists for tumor inhibition and elimination.

Vascular Disrupting Agents in cancer treatment: Cardiovascular toxicity and implications for co-administration with other cancer chemotherapeutics

Destruction of the established tumour vasculature by a class of compound termed Vascular Disrupting Agents (VDAs) is showing considerable promise as a viable approach for the management of solid tumours. VDAs induce a rapid shutdown and collapse of tumour blood vessels, leading to ischaemia and consequent necrosis of the tumour mass. Their efficacy is hindered by the persistence of a viable rim of tumour cells, supported by the peripheral normal vasculature, necessitating their co-administration with additional chemotherapeutics for maximal therapeutic benefit. However, a major limitation for the use of many cancer therapeutics is the development of life-threatening cardiovascular toxicities, with significant consequences for treatment response and the patient's quality of life. The aim of this review is to outline VDAs as a cancer therapeutic approach and define the mechanistic basis of cardiovascular toxicities of current chemotherapeutics, with the overall objective of discussing whether VDA combinations with specific chemotherapeutic classes would be good or bad in terms of cardiovascular toxicity.

MRI Monitoring of Cerebral Blood Flow after the Delivery of Nanocombretastatin across the Blood Brain Tumor Barrier

Introduction of polymeric nanoparticles in cancer therapeutics is widely investigated since nanomedicine often enables the intratumoral delivery of drugs with increased efficacy with minimal side effects. In this study MRI monitoring was employed to study the therapeutic effect of nanocombretastatin (G3-CA4) in an orthotopic glioma model. Water insoluble combretastatin (CA4) was conjugated to a small-sized water soluble G3-succinamic acid PAMAM dendrimer. Nanoconstruct sizes were determined by TEM to be 3 to 5 nm. Intravenous (i.v.) delivery of G3-CA4 in an orthotopic glioma model produced a long-lived ischemia accompanied by necrosis at the core of the tumor but leaving a rim of viable tissue. In contrast, delivery of CA4 alone has no therapeutic effect in an experimental rat model of glioma.

Combretastatin A4-camptothecin micelles as combination therapy for effective anticancer activity

Cancer is a major worldwide health problem, for which chemotherapy is a common treatment option. However drug toxicity and the development of resistance to chemotherapy are two main challenges associated with the traditional anticancer drugs. Combined pharmacological therapy based on different mechanisms might be an effective strategy in cancer treatment, and could exhibit a synergistic therapeutic efficacy. Herein, we aim to combine combretastatin A4 (CA4) and camptothecin (Cpt) chemically into a codrug through two hydrophilic linkers utilizing click chemistry to improve their water solubility and anticancer activity. The synthesized amphiphilic structure could self-assemble into a micelle structure as confirmed by atomic force microscopy (AFM) and dynamic light scattering (DLS), which showed a high stability and improved water solubility at pH 7.4, with a low critical micelle concentration (CMC) value of 0.9 mM. Moreover, in vitro hydrolysis was observed upon incubation of the hybrid compound with an esterase enzyme, which suggested a complete disassembly into the starting active drugs. Finally, cytotoxicity studies on HeLa cancer cells showed that the codrug demonstrated an enhanced (five fold) cytotoxicity as compared with the free drugs. In addition the combination index (CI) was <1, which suggests a synergistic activity for the codrug. Moreover, the tested concentrations of the codrug were not significantly cytotoxic to a noncancerous fibroblast cell line. The imaging of HeLa cells treated with FITC-loaded micelles showed a rapid internalization. In conclusion, the codrug of CA4 and Cpt might be a potential novel anticancer drug as it demonstrated a synergistic cytotoxic activity that might spare noncancerous cells.

New naphthopyran analogues of LY290181 as potential tumor vascular-disrupting agents

A series of 19 analogues of the antiproliferative naphthopyran LY290181 were prepared for structure-activity relationship studies. We found the best activities for test compounds bearing small substituents at the meta position of the phenyl ring. The mode of action of LY290181 and eight new analogues was studied in detail. The compounds were highly anti-proliferative with IC₅₀ values in the sub-nanomolar to triple-digit nanomolar range. The new analogues led to G2/M arrest due to interruption of the microtubule dynamics. In 518A2 melanoma cells they caused a mitotic catastrophe which eventually led to apoptosis. The naphthopyrans also induced a disruption of the vasculature in the chorioallantoic membrane (CAM) of fertilized chicken eggs as well as in xenograft tumors in mice. In a preliminary therapy trial, the difluoro derivative 2b retarded the growth of resistant xenograft tumors in mice.

A single dose of intravenous combretastatin A4-phosphate is reasonably well tolerated and significantly reduces tumour vascularization in canine spontaneous cancers

Combretastatin A4-phosphate (CA4P) is an anti-tumour vascular targeting agent which selectively blocks tumour blood flow. Research on CA4P in rodent tumour models is extensive; however, knowledge of its effect on spontaneous cancer is scarce. This study was conducted in canine patients with spontaneous solid tumours. The goal was to assess the toxicity and efficacy of CA4P in various spontaneous tumour types. Eight dogs with spontaneous tumours were enrolled and treated with a single dose of 75 mg m^-2 intravenous CA4P. The dogs were screened and monitored before and after injection. Pre- and post-treatment tumour blood flow was analysed in vivo by power Doppler ultrasound (PDUS) and contrast-enhanced ultrasound (CEUS). Vessel destruction and tumour necrosis were evaluated by histopathology. Clinically relevant toxicity was limited to one case of temporary tetraparesis; other adverse events were mild. Significant cardiovascular changes were mostly confined to changes in heart rate and cTnI levels. Macroscopic tumour size reduction was evident in 2 dogs. Based on PDUS and CEUS, CA4P induced a significant decrease in vascular index and tumour blood flow. Post-treatment, histopathology revealed a significant increase of necrotic tumoural tissue and a significant reduction in microvessel density in tumoural tissue. Anti-vascular and necrotizing effects of CA4P were documented in a variety of canine spontaneous cancers with only minimal side effects. This is the first study reporting the administration of CA4P to canine cancer patients with in vivo and ex vivo assessment, and a first step toward implementing CA4P in combination therapies in veterinary oncology patients. The use of CA4P in canine patients was approved and registered by the Belgian Federal Agency for Medicines and Health Products (FAMHP) (approval number 0002588, registration number 6518 ID 2F12).