Co-administration of combretastatin A4 nanoparticles and anti-PD-L1 for synergistic therapy of hepatocellular carcinoma

Background

According to data estimated by the WHO, primary liver cancer is currently the fourth most common malignant tumor and the second leading cause of death around the world. Hepatocellular carcinoma (HCC) is one of the most common primary liver malignancies, so effective therapy is highly desired for HCC.

Results

In this study, the use of poly(l-Aspartic acid)-poly(ethylene glycol)/combretastatin A4 (CA4-NPs) was aimed to significantly disrupt new blood vessels in tumor tissues for targeted hepatic tumor therapy. Here, PEG-b-PAsp-g-CA4 showed significantly prolonged retention in plasma and tumor tissue. Most importantly, CA4-NPs were mainly distributed at the tumor site because of the triple target effects—enhanced permeability and retention (EPR) effect, acid-sensitive (pH = 5.5) effect to the tumor microenvironment (TME), and good selectivity of CA4 for central tumor blood vessel. Considering that CA4-NPs might induce severe hypoxic conditions resulting in high expression of HIF-1α in tumor tissues, which could induce the overexpression of PD-L1, herein we also used a programmed death-ligand 1 antibody (aPD-L1) to prevent immunosuppression. This way of complementary combination is able to achieve an ideal treatment effect in tumor site where CA4-NPs and aPD-L1 could respond to the inner area and peripheral area, respectively. As a result, a significant decrease in tumor volume and weight was observed in the combination group of CA4-NPs plus aPD-L1 compared with CA4-NPs or aPD-L1 monotherapy in subcutaneous Hepa1-6 hepatic tumor models.

Conclusions

We presented a new idea that co-administration of CA4-NPs and aPD-L1 possessed notable anti-tumor efficacy for HCC treatment.

Graphic abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-021-00865-w.

Roadmap for metal nanoparticles in radiation therapy: current status, translational challenges, and future directions

This roadmap outlines the potential roles of metallic nanoparticles (MNPs) in the field of radiation therapy. MNPs made up of a wide range of materials (from Titanium, Z = 22, to Bismuth, Z = 83) and a similarly wide spectrum of potential clinical applications, including diagnostic, therapeutic (radiation dose enhancers, hyperthermia inducers, drug delivery vehicles, vaccine adjuvants, photosensitizers, enhancers of immunotherapy) and theranostic (combining both diagnostic and therapeutic), are being fabricated and evaluated. This roadmap covers contributions from experts in these topics summarizing their view of the current status and challenges, as well as expected advancements in technology to address these challenges.

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.

Co-administration of combretastatin A4 nanoparticles and sorafenib for systemic therapy of hepatocellular carcinoma

Effective systemic therapy is highly desired for the treatment of hepatocellular carcinoma (HCC). In this study, a combination of nanoparticles of poly(L-glutamic acid)-graft-methoxy poly(ethylene glycol)/combretastatin A4 sodium salt (CA4-NPs) plus sorafenib is developed for the cooperative systemic treatment of HCC. The CA4-NPs leads to the disruption of established tumor blood vessels and extensive tumor necrosis, however, inducing increased expression of VEGF-A and angiogenesis. Sorafenib reduces the VEGF-A induced angiogenesis and further inhibits tumor proliferation, cooperating with the CA4-NPs. A significant decrease in tumor volume and prolonged survival time are observed in the combination group of CA4-NPs plus sorafenib compared with CA4-NPs or sorafenib monotherapy in subcutaneous and orthotopic H22 hepatic tumor models. Seventy-one percent of the mice are alive without residual tumor at 96 days post tumor inoculation for the subcutaneous models treated with CA4-NPs 30 or 35 mg·kg^-1 plus sorafenib 30 mg·kg^-1. Our findings suggest that co-administration of sorafenib and CA4-NPs possesses significant antitumor efficacy for HCC treatment. STATEMENT OF SIGNIFICANCE: Effective systemic therapy is highly desired for the treatment of hepatocellular carcinoma (HCC). Herein, we demonstrate that a combination of nanoparticles of poly(L-glutamic acid)-graft-methoxy poly(ethylene glycol)/combretastatin A4 sodium salt (CA4-NPs) plus sorafenib is a promising synergistic approach for systemic treatment of HCC. The CA4-NPs leads to the disruption of established tumor blood vessels and extensive tumor necrosis, however, inducing increased expression of VEGF-A and angiogenesis. Sorafenib reduces the VEGF-A induced angiogenesis and further inhibits tumor proliferation, cooperating with the CA4-NPs.

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.

Cytosolic DNA Sensing in Organismal Tumor Control

Besides constituting a first layer of defense against microbial challenges, the detection of cytosolic DNA is fundamental for mammalian organisms to control malignant transformation and tumor progression. The accumulation of DNA in the cytoplasm can initiate the proliferative inactivation (via cellular senescence) or elimination (via regulated cell death) of neoplastic cell precursors. Moreover, cytosolic DNA sensing is intimately connected to the secretion of cytokines that support innate and adaptive antitumor immunity. Here, we discuss the molecular mechanisms whereby cytosolic DNA enables cell-intrinsic and -extrinsic oncosuppression, and their relevance for the development of novel therapeutic approaches that reinstate anticancer immunosurveillance.

B cell MHC class II signaling: A story of life and death

MHC class II regulates B cell activation, proliferation, and differentiation during cognate B cell-T cell interaction. This is, in part, due to the MHC class II signaling in B cells. Activation of MHC Class II in human B cells or "primed" murine B cells leads to tyrosine phosphorylation, calcium mobilization, AKT, ERK, JNK activation. In addition, crosslinking MHC class II with monoclonal Abs kill malignant human B cells. Several humanized anti-HLA-DR/MHC class II monoclonal Abs entered clinical trials for lymphoma/leukemia and MHC class II-expressing melanomas. Mechanistically, MHC class II is associated with a wealth of transmembrane proteins including the B cell-specific signaling proteins CD79a/b, CD19 and a group of four-transmembrane proteins including tetraspanins and the apoptotic protein MPYS/STING. Furthermore, MHC class II signals are compartmentalized in the tetraspanin-enriched microdomains. In this review, we discuss our current understanding of MHC class II signaling in B cells focusing on its physiological significance and the therapeutic potential.

Anti-angiogenic agents for the treatment of solid tumors: Potential pathways, therapy and current strategies - A review

Recent strategies for the treatment of cancer, other than just tumor cell killing have been under intensive development, such as anti-angiogenic therapeutic approach. Angiogenesis inhibition is an important strategy for the treatment of solid tumors, which basically depends on cutting off the blood supply to tumor micro-regions, resulting in pan-hypoxia and pan-necrosis within solid tumor tissues. The differential activation of angiogenesis between normal and tumor tissues makes this process an attractive strategic target for anti-tumor drug discovery. The principles of anti-angiogenic treatment for solid tumors were originally proposed in 1972, and ever since, it has become a putative target for therapies directed against solid tumors. In the early twenty first century, the FDA approved anti-angiogenic drugs, such as bevacizumab and sorafenib for the treatment of several solid tumors. Over the past two decades, researches have continued to improve the performance of anti-angiogenic drugs, describe their drug interaction potential, and uncover possible reasons for potential treatment resistance. Herein, we present an update to the pre-clinical and clinical situations of anti-angiogenic agents and discuss the most recent trends in this field.

Inhibiting Solid Tumor Growth In Vivo by Non-Tumor-Penetrating Nanomedicine

Nanomedicine (NM) cannot penetrate deeply into solid tumors, which is partly attributed to the heterogeneous microenvironment and high interstitial fluid pressure of solid tumors. To improve NM efficacy, there has been tremendous effort developing tumor-penetrating NMs by miniaturizing NM sizes or controlling NM surface properties. But progress along the direction of developing tumor penetrating nanoparticle has been slow and improvement of the overall antitumor efficacy has been limited. Herein, a novel strategy of inhibiting solid tumor with high efficiency by dual-functional, nontumor-penetrating NM is demonstrated. The intended NM contains 5,6-dimethylxanthenone-4-acetic acid (DMXAA), a vascular-disrupting agent, and doxorubicin (DOX), a cytotoxic drug. Upon arriving at the target tumor site, sustained release of DMXAA from NMs results in disruption of tumor vessel functions, greatly inhibiting the interior tumor cells by cutting off nutritional supply. Meanwhile, the released DOX kills the residual cells at the tumor exterior regions. The in vivo studies demonstrate that this dual-functional, nontumor penetrating NM exhibits superior anticancer activity, revealing an alternative strategy of effective tumor growth inhibition.

Angiogenesis inhibitors as therapeutic agents in cancer: Challenges and future directions

Angiogenesis has become an attractive target for cancer therapy since the US Food and Drug Administration (FDA) approved the first angiogenesis inhibitor (bevacizumab) for the treatment of metastatic colorectal cancer in 2004. In following years, a large number of angiogenesis inhibitors have been discovered and developed, ranging from monoclonal antibodies, endogenous peptides, to small organic molecules and microRNAs. Many of them are now entering the clinical trial, or achieving approval for clinical use. However, major limitations have been observed about angiogenesis inhibitors by continued clinical investigations, such as resistance, enhancing tumor hypoxia and reducing delivery of chemotherapeutic agents, which might be the main reason for poor improvement in overall survival after angiogenesis inhibitor administration in clinic. Therefore, optimal anti-angiogenic therapy strategies become critical. The present review summarizes recent researches in angiogenesis inhibitors, and proposes a perspective on future directions in this field.

Natural products against cancer angiogenesis

The process of angiogenesis is quite well-known nowadays. Some medicines and extracts affecting this process are already used routinely in supporting the conventional treatment of many diseases that are considered angiogenic such as cancer. However, we must be aware that the area of currently used drugs of this type is much narrower than the theoretical possibilities existing in therapeutic angiogenesis. Plant substances are a large and diverse group of compounds that are found naturally in fruits, vegetables, spices, and medicinal plants. They also have different anticancer properties. The aim of this literature review article is to present the current state of knowledge concerning the molecular targets of tumor angiogenesis and the active substances (polyphenols, alkaloids, phytohormones, carbohydrates, and terpenes) derived from natural sources, whose activity against cancer angiogenesis has been confirmed.

Hepatocellular Carcinoma: Intra-arterial Delivery of Doxorubicin-loaded Hollow Gold Nanospheres for Photothermal Ablation-Chemoembolization Therapy in Rats

Purpose To determine if combretastatin A-4 phosphate disodium (CA4P) can enhance the tumor uptake of doxorubicin (Dox)-loaded, polyethylene glycol (PEG)-coated hollow gold nanospheres (HAuNS) mixed with ethiodized oil for improved photothermal ablation (PTA)-chemoembolization therapy (CET) of hepatocellular carcinoma (HCC) in rats. Materials and Methods Animal experiments were approved by the institutional animal care and use committee and performed from February 2014 to April 2015. Male Sprague-Dawley rats (n = 45; age, 12 weeks) were inoculated with N1S1 HCC cells in the liver, and 8 days later, were randomly divided into two groups of 10 rats. Group 1 rats received intrahepatic arterial injection of PEG-HAuNS and ethiodized oil alone; group 2 received pretreatment with CA4P and injection of PEG-HAuNS and ethiodized oil 5 minutes later. The gold content of tumor and liver tissue at 1 hour or 24 hours after injection was quantified by using neutron activation analysis (n = 5 per time point). Five rats received pretreatment CA4P, PEG-copper 64-HAuNS, and ethiodized oil and underwent micro-positron emission tomography (PET)/computed tomography (CT). In a separate study, three groups of six rats with HCC were injected with saline solution (control group); CA4P, Dox-loaded PEG-coated HAuNS (Dox@PEG-HAuNS), and ethiodized oil (CET group); or CA4P, Dox@PEG-HAuNS, ethiodized oil, and near-infrared irradiation (PTA-CET group). Temperature was recorded during laser irradiation. Findings were verified at postmortem histopathologic and/or autoradiographic examination. Wilcoxon rank-sum test and Pearson correlation analyses were performed. Results PEG-HAuNS uptake in CA4P-pretreated HCC tumors was significantly higher than that in non-CA4P-pretreated tumors at both 1 hour (P < .03) and 24 hours (P < .01). Mean ± standard deviation of tumor-to-liver PEG-HAuNS uptake ratios at 1 hour and 24 hours, respectively, were 5.63 ± 3.09 and 1.68 ± 0.77 in the CA4P-treated group and 1.29 ± 2.40 and 0.14 ± 0.11 in the non-CA4P-treated group. Micro-PET/CT allowed clear delineation of tumors, enabling quantitative imaging analysis. Laser irradiation increased temperature to 60°C and 43°C in the tumor and adjacent liver, respectively. Mean HCC tumor volumes 10 days after therapy were 1.68 cm³ ± 1.01, 3.96 cm³ ± 1.75, and 6.13 cm³ ± 2.27 in the PTA-CET, CET, and control groups, respectively, with significant differences between the PTA-CET group and other groups (P < .05). Conclusion CA4P pretreatment caused a higher concentration of Dox@PEG-HAuNS to be trapped inside the tumor, thereby enhancing the efficacy of anti-HCC treatment with PTA-CET in rats. ^© RSNA, 2016 Online supplemental material is available for this article.

Advances in targeted and immunobased therapies for colorectal cancer in the genomic era

Targeted therapies require information on specific defective signaling pathways or mutations. Advances in genomic technologies and cell biology have led to identification of new therapeutic targets associated with signal-transduction pathways. Survival times of patients with colorectal cancer (CRC) can be extended with combinations of conventional cytotoxic agents and targeted therapies. Targeting EGFR- and VEGFR-signaling systems has been the major focus for treatment of metastatic CRC. However, there are still limitations in their clinical application, and new and better drug combinations are needed. This review provides information on EGFR and VEGF inhibitors, new therapeutic agents in the pipeline targeting EGFR and VEGFR pathways, and those targeting other signal-transduction pathways, such as MET, IGF1R, MEK, PI3K, Wnt, Notch, Hedgehog, and death-receptor signaling pathways for treatment of metastatic CRC. Additionally, multitargeted approaches in combination therapies targeting negative-feedback loops, compensatory networks, and cross talk between pathways are highlighted. Then, immunobased strategies to enhance antitumor immunity using specific monoclonal antibodies, such as the immune-checkpoint inhibitors anti-CTLA4 and anti-PD1, as well as the challenges that need to be overcome for increased efficacy of targeted therapies, including drug resistance, predictive markers of response, tumor subtypes, and cancer stem cells, are covered. The review concludes with a brief insight into the applications of next-generation sequencing, expression profiling for tumor subtyping, and the exciting progress made in in silico predictive analysis in the development of a prescription strategy for cancer therapy.

Phenotype-based Discovery of 2-[(E)-2-(Quinolin-2-yl)vinyl]phenol as a Novel Regulator of Ocular Angiogenesis

Retinal angiogenesis is tightly regulated to meet oxygenation and nutritional requirements. In diseases such as proliferative diabetic retinopathy and neovascular age-related macular degeneration, uncontrolled angiogenesis can lead to blindness. Our goal is to better understand the molecular processes controlling retinal angiogenesis and discover novel drugs that inhibit retinal neovascularization. Phenotype-based chemical screens were performed using the ChemBridge Diverset(TM)library and inhibition of hyaloid vessel angiogenesis in Tg(fli1:EGFP) zebrafish. 2-[(E)-2-(Quinolin-2-yl)vinyl]phenol, (quininib) robustly inhibits developmental angiogenesis at 4-10 μmin zebrafish and significantly inhibits angiogenic tubule formation in HMEC-1 cells, angiogenic sprouting in aortic ring explants, and retinal revascularization in oxygen-induced retinopathy mice. Quininib is well tolerated in zebrafish, human cell lines, and murine eyes. Profiling screens of 153 angiogenic and inflammatory targets revealed that quininib does not directly target VEGF receptors but antagonizes cysteinyl leukotriene receptors 1 and 2 (CysLT1-2) at micromolar IC50values. In summary, quininib is a novel anti-angiogenic small-molecule CysLT receptor antagonist. Quininib inhibits angiogenesis in a range of cell and tissue systems, revealing novel physiological roles for CysLT signaling. Quininib has potential as a novel therapeutic agent to treat ocular neovascular pathologies and may complement current anti-VEGF biological agents.

Microenvironment-Mediated Modeling of Tumor Response to Vascular-Targeting Drugs

The tumor-associated microvasculature is one of the key elements of the microenvironment that helps shape, and is shaped by, tumor progression. Given the important role of the vasculature in tumor progression, and the fact that tumor and normal vasculature are physiologically and molecularly distinct, much effort has gone into the development of vascular-targeting drugs that in theory should target tumors without significant risk to normal tissue. In this chapter, a multiscale hybrid mathematical model of tumor-vascular interactions is presented to provide a theoretical basis for assessing tumor response to vascular-targeting drugs. Model performance is calibrated to quantitative clinical data on tumor response to angiogenesis inhibitors (AIs), preclinical data on response to a cytotoxic chemotherapy, and qualitative preclinical data on response to vascular disrupting agents (VDAs). The calibrated model is then used to explore two questions of clinical interest. First, the hypothesis that AIs and VDAs are complementary treatments, rather than redundant, is explored. The model predicts a minimal increase in antitumor activity as a result of adding a VDA to an AI treatment regimen, and in fact at times the combination can exert less antitumor activity than stand-alone AI treatment. Second, the question of identifying an optimal dosing strategy for treating with an AI and a cytotoxic agent is addressed. Using a stochastic optimization scheme, an intermittent schedule for both chemotherapy and AI administration is identified that can eradicate the simulated tumors. We propose that this schedule may have increased clinical antitumor activity compared to currently used treatment protocols.

Pharmacokinetic strategies to improve drug penetration and entrapment within solid tumors

Despite the discovery of a large number of anticancer agents, cancer still remains among the leading causes of death since the middle of the twentieth century. Solid tumors possess a high degree of genetic instability and emergence of treatment resistance. Tumor resistance has emerged for almost all approved anticancer drugs and will most probably emerge for newly discovered anticancer agents as well. The use of pharmacokinetic approaches to increase anticancer drug concentrations within the solid tumor compartment and prolong its entrapment might diminish the possibility of resistance emergence at the molecular pharmacodynamic level and might even reverse tumor resistance. Several novel treatment modalities such as metronomic therapy, angiogenesis inhibitors, vascular disrupting agents and tumor priming have been introduced to improve solid tumor treatment outcomes. In the current review we will discuss the pharmacokinetic aspect of these treatment modalities in addition to other older treatment modalities, such as extracellular matrix dissolving agents, extracellular matrix synthesis inhibitors, chemoembolization and cellular efflux pump inhibition. Many of these strategies showed variable degrees of success/failure; however, reallocating these modalities based on their influence on the intratumoral pharmacokinetics might improve their understanding and treatment outcomes.

Recent advances in vascular disrupting agents in cancer therapy

Vascular disrupting agents (VDAs) are an important class of compounds that exhibit selective activity against pre-existing tumor vasculature, causing rapid shutdown of the tumor blood flow and consequent necrosis of the tumor mass. The VDAs can be divided into flavonoid compounds, which are related to flavone acetic acid, and tubulin-binding agents. Tubulin-binding agents represent the largest group of VDAs and are characterized by different chemical structures, although most of them are derivatives of the lead compound combretastatin (CA-4). They demonstrated clinical activity, although recent findings have established that they have insufficient activity as single agents. Several resistance mechanisms occur, such as the resistance of the tumor rim cells, while promising results have been described in combination with other chemotherapeutics.

Bavituximab plus paclitaxel and carboplatin for the treatment of advanced non-small-cell lung cancer

OBJECTIVE

Bavituximab is a phosphatidylserine (PS)-targeting monoclonal antibody with immune-modulating and tumor-specific vascular targeting properties. Preclinical studies have shown activity against numerous solid tumors and at least an additive effect in combination with chemotherapy. This study evaluated bavituximab in combination with paclitaxel and carboplatin in patients with previously untreated, locally advanced or metastatic non-small-cell lung cancer (NSCLC).

PATIENTS AND METHODS

This phase II, open-label study (NCT00687817) was conducted in 49 patients with stage IIIB/IV NSCLC utilizing a Simon two-stage design. Patients were treated with up to six cycles of carboplatin area under the concentration-time curve (AUC) 5 plus paclitaxel 175 mg/m2 every 21 days with weekly bavituximab 3 mg/kg followed by bavituximab monotherapy until progression or unacceptable toxicity.

RESULTS

The primary efficacy endpoint of overall response rate (ORR) was 40.8% (complete response [CR] 2.0%, partial response [PR] was 38.8%). Median progression-free survival (PFS) and overall survival (OS) were 6.0 and 12.4 months, respectively. Treatment-related adverse events (AEs) occurred in 40.8% of patients. The most common treatment-related AEs were anemia (10.2%), asthenia, vomiting, paresthesia, anorexia, and fatigue (6.1% each). One patient with a central, cavitating squamous tumor developed fatal hemoptysis and aspiration.

CONCLUSION

Bavituximab in combination with paclitaxel-carboplatin as first-line therapy demonstrated a tolerable safety profile and potential efficacy in this single-arm phase II trial in patients with advanced local or metastatic NSCLC. Randomized trials with this regimen are in progress.

CLINICALTRIALSGOV IDENTIFIER

NCT00687817.

DMXAA causes tumor site-specific vascular disruption in murine non-small cell lung cancer, and like the endogenous non-canonical cyclic dinucleotide STING agonist, 2'3'-cGAMP, induces M2 macrophage repolarization

The vascular disrupting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA), a murine agonist of the stimulator of interferon genes (STING), appears to target the tumor vasculature primarily as a result of stimulating pro-inflammatory cytokine production from tumor-associated macrophages (TAMs). Since there were relatively few reports of DMXAA effects in genetically-engineered mutant mice (GEMM), and models of non-small cell lung cancer (NSCLC) in particular, we examined both the effectiveness and macrophage dependence of DMXAA in various NSCLC models. The DMXAA responses of primary adenocarcinomas in K-rasLA1/+ transgenic mice, as well as syngeneic subcutaneous and metastatic tumors, generated by a p53R172HΔg/+; K-rasLA1/+ NSCLC line (344SQ-ELuc), were assessed both by in vivo bioluminescence imaging as well as by histopathology. Macrophage-dependence of DMXAA effects was explored by clodronate liposome-mediated TAM depletion. Furthermore, a comparison of the vascular structure between subcutaneous tumors and metastases was carried out using micro-computed tomography (micro-CT). Interestingly, in contrast to the characteristic hemorrhagic necrosis produced by DMXAA in 344SQ-ELuc subcutaneous tumors, this agent failed to cause hemorrhagic necrosis of either 344SQ-ELuc-derived metastases or autochthonous K-rasLA1/+ NSCLCs. In addition, we found that clodronate liposome-mediated depletion of TAMs in 344SQ-ELuc subcutaneous tumors led to non-hemorrhagic necrosis due to tumor feeding-vessel occlusion. Since NSCLC were comprised exclusively of TAMs with anti-inflammatory M2-like phenotype, the ability of DMXAA to re-educate M2-polarized macrophages was examined. Using various macrophage phenotypic markers, we found that the STING agonists, DMXAA and the non-canonical endogenous cyclic dinucleotide, 2'3'-cGAMP, were both capable of re-educating M2 cells towards an M1 phenotype. Our findings demonstrate that the choice of preclinical model and the anatomical site of a tumor can determine the vascular disrupting effectiveness of DMXAA, and they also support the idea of STING agonists having therapeutic utility as TAM repolarizing agents.

DISRUPT: a randomised phase 2 trial of ombrabulin (AVE8062) plus a taxane-platinum regimen as first-line therapy for metastatic non-small cell lung cancer

BACKGROUND

DISRUPT evaluated whether adding the vascular-disrupting agent ombrabulin to a taxane-platinum doublet in the first-line setting improved progression-free survival (PFS) in patients with metastatic non-small cell lung cancer (NSCLC).

METHODS

Patients were randomised to ombrabulin 35 mg/m(2) or placebo followed by a taxane-platinum regimen every 3 weeks.

RESULTS

Overall, 176 patients were randomised. After 124 events, median PFS was not significantly improved with ombrabulin vs placebo (5.65 vs 5.45 months; HR 0.948; 60% CI 0.813-1.106; one-sided P=0.39). The two groups showed similar overall survival (median 11.0 months in both groups), objective response rate (32% ombrabulin; 31% placebo) and safety profiles.

CONCLUSION

This study did not meet its primary endpoint of improving PFS by adding ombrabulin to a taxane-platinum regimen for first-line treatment of metastatic NSCLC.

A phase 2 trial of verubulin for recurrent glioblastoma: a prospective study by the Brain Tumor Investigational Consortium (BTIC)

Treatment options are limited for recurrent glioblastoma (GBM). Verubulin is a microtubule destabilizer and vascular disrupting agent that achieve high brain concentration relative to plasma in animals. Adults with recurrent GBM who failed prior standard therapy were eligible. The primary endpoint was 1-month progression-free survival (PFS-1) for bevacizumab refractory (Group 2) and 6-month progression-free survival (PFS-6) for bevacizumab naïve patients (Group 1). Verubulin was administered at 3.3 mg/m(2) as a 2-h intravenous infusion once weekly for 3 consecutive weeks in a 4-week cycle. The planned sample size was 34 subjects per cohort. 56 patients (37 men, 19 women) were enrolled, 31 in Group 1 and 25 in Group 2. The PFS-6 for Group 1 was 14% and the PFS-1 for Group 2 was 20%. Median survival from onset of treatment was 9.5 months in Group 1 and 3.4 months in Group 2. Best overall response was partial response (n = 3; 10% in Group 1; n = 1; 4.2% in Group 2) and stable disease (n = 7; 23% in Group 1; n = 5; 21% in Group 2). In Group 1, 38.7% of patients experienced a serious adverse event; however only 3.2% were potentially attributable to study drug. In Group 2, 44% of patients experienced a serious adverse event although none were attributable to study drug. Accrual was terminated early for futility. Single agent verubulin, in this dose and schedule, is well tolerated, associated with moderate but tolerable toxicity but has limited activity in either bevacizumab naïve or refractory recurrent GBM.

Population and target considerations for triple-negative breast cancer clinical trials

Triple-negative breast cancer (TNBC) is an aggressive disease subtype that has a poor prognosis. Extensive epidemiological evidence demonstrates clear socioeconomic and demographic associations with increased likelihood of TNBC in both poorer and minority populations. Thus, biological aggressiveness with few known therapeutic directions generates disparities in breast cancer outcomes for vulnerable populations. Emerging molecular evidence of potential targets in triple-negative subpopulations offers great potential for future clinical trial directions. However, trials must appropriately consider populations at risk for aggressive subtypes of disease in order to address this disparity most completely. New US FDA draft guidance documents provide both flexible outcomes for accelerated approvals as well as flexibility in design with adaptive trials. Careful planning with design, potential patient population and choices of molecular targets informed by biomarkers will be critical to address TNBC clinical care.

Vascular-disrupting agents in oncology

INTRODUCTION

Vascular-disrupting agents (VDAs) are a new class of oncology drugs, which specifically target established tumor neovasculature and have a relatively low toxicity profile. VDAs generally have non-overlapping side effects when concomitantly used with conventional cytotoxics. Several members of the VDA class have recently progressed through mid-to-late stages of clinical trials.

AREAS COVERED

We examined recent publications on preclinical findings and Phase I/II/III clinical trial data on mechanisms of actions, toxicities, and optimal use of VDA class drugs. It is becoming apparent that VDAs should be used in combination with other classes of cytotoxic agents for the optimization of their effect in treating various cancers. In this article we describe doses, timing of delivery, and sequence of combined therapy. We also address the combined mechanisms of actions of VDAs and conventional cytotoxic medications.

EXPERT OPINION

Vascular-disrupting agents represent a new class of promising anticancer agents, which exhibit synergistic and/or additive effects in combination with many conventional cytotoxics. Pharmacological evaluation of the optimal combinations of VDAs with agents of other classes and drug interactions need to be continued. Further clinical and preclinical studies are required for distinguishing cancer patients' subpopulations that would most benefit from VDAs, identifying tumor biomarkers predictive of response as well as reliable and reproducible imaging and/or biological assays indicative of pharmacodynamic effects, and establishing clinical algorithms for treatment.

Mechanisms of tumor resistance to small-molecule vascular disrupting agents: treatment and rationale of combination therapy

Small-molecule vascular disrupting agents (VDAs) target the established tumor blood vessels, resulting in rapidly and selectively widespread ischemia and necrosis of central tumor; meanwhile, blood flow in normal tissues is relatively unaffected. Although VDAs therapy is considered an important option for treatment, its use is still limited. The tumor cells at the periphery are less sensitive to vascular shutdown than those at the center, and subsequently avoid a nutrient-deprived environment. This phenomenon is referred to as tumor resistance to VDAs treatment. The viable periphery rim of tumor cells contributes to tumor regeneration, metastasis, and ongoing progression. However, there is no systematic review of the plausible mechanisms of repopulation of the viable tumor cells following VDAs therapy. The purpose of this review is to provide insights into mechanisms of tumor surviving small-molecule VDAs therapy, and the synergetic treatment to the remaining viable tumor cells at the periphery.

The vascular disrupting agent STA-9584 exhibits potent antitumor activity by selectively targeting microvasculature at both the center and periphery of tumors

Vascular disrupting agents (VDAs) are an emerging class of therapeutics targeting the existing vascular network of solid tumors. However, their clinical progression has been hampered because of limited single-agent efficacy, primarily caused by the persistence of surviving cells at the well perfused "viable rim" of tumors, which allows rapid tumor regrowth to occur. In addition, off-target adverse events, including cardiovascular toxicities, underscore a need for compounds with improved safety profiles. Here, we characterize the mechanism of action, antitumor efficacy, and cardiovascular safety profile of (S)-2-amino-N-(2-methoxy-5-(5-(3,4,5-trimethoxyphenyl)isoxazol-4-yl)phenyl)-3-phenylpropanamide hydrochloride (STA-9584), a novel tubulin-binding VDA. In vitro, 2-methoxy-5-(5-(3,4,5-trimethoxyphenyl)isoxazol-4-yl)aniline (STA-9122) (active metabolite of STA-9584) displayed increased potency relative to other tubulin-binding agents and was highly cytotoxic to tumor cells. STA-9584 induced significant tumor regressions in prostate and breast xenograft models in vivo and, in an aggressive syngeneic model, demonstrated superior tumor growth inhibition and a positive therapeutic index relative to combretastatin A-4 phosphate (CA4P). It is noteworthy that histological analysis revealed that STA-9584 disrupted microvasculature at both the center and periphery of tumors. Compared with CA4P, STA-9584 induced a 73% increase in central necrotic area, 77% decrease in microvasculature, and 7-fold increase in tumor cell apoptosis in the remaining viable rim 24 h post-treatment. Ultrasound imaging confirmed that STA-9584 rapidly and efficiently blocked blood flow in highly perfused tumor regions. Moreover, cardiovascular effects were evaluated in the Langendorff assay and telemetered dogs, and cardiovascular toxicity was not predicted to be dose-limiting. This bioactivity profile distinguishes STA-9584 from the combretastatin class and identifies the compound as a promising new therapeutic VDA candidate.

Proapoptotic activation of death receptor 5 on tumor endothelial cells disrupts the vasculature and reduces tumor growth

The proapoptotic death receptor DR5 has been studied extensively in cancer cells, but its action in the tumor microenvironment is not well defined. Here, we uncover a role for DR5 signaling in tumor endothelial cells (ECs). We detected DR5 expression in ECs within tumors but not normal tissues. Treatment of tumor-bearing mice with an oligomeric form of the DR5 ligand Apo2L/TRAIL induced apoptosis in tumor ECs, collapsing blood vessels and reducing tumor growth: Vascular disruption and antitumor activity required DR5 expression on tumor ECs but not malignant cells. These results establish a therapeutic paradigm for proapoptotic receptor agonists as selective tumor vascular disruption agents, providing an alternative, perhaps complementary, strategy to their use as activators of apoptosis in malignant cells.

DMXAA (Vadimezan, ASA404) is a multi-kinase inhibitor targeting VEGFR2 in particular

The flavone acetic acid derivative DMXAA [5,6-dimethylXAA (xanthenone-4-acetic acid), Vadimezan, ASA404] is a drug that displayed vascular-disrupting activity and induced haemorrhagic necrosis and tumour regression in pre-clinical animal models. Both immune-mediated and non-immune-mediated effects contributed to the tumour regression. The vascular disruption was less in human tumours, with immune-mediated effects being less prominent, but nonetheless DMXAA showed promising effects in Phase II clinical trials in non-small-cell lung cancer. However, these effects were not replicated in Phase III clinical trials. It has been difficult to understand the differences between the pre-clinical findings and the later clinical trials as the molecular targets for the agent have never been clearly established. To investigate the mechanism of action, we sought to determine whether DMXAA might target protein kinases. We found that, at concentrations achieved in blood during clinical trials, DMXAA has inhibitory effects against several kinases, with most potent effects being on members of the VEGFR (vascular endothelial growth factor receptor) tyrosine kinase family. Some analogues of DMXAA were even more effective inhibitors of these kinases, in particular 2-MeXAA (2-methylXAA) and 6-MeXAA (6-methylXAA). The inhibitory effects were greatest against VEGFR2 and, consistent with this, we found that DMXAA, 2-MeXAA and 6-MeXAA were able to block angiogenesis in zebrafish embryos and also inhibit VEGFR2 signalling in HUVECs (human umbilical vein endothelial cells). Taken together, these results indicate that at least part of the effects of DMXAA are due to it acting as a multi-kinase inhibitor and that the anti-VEGFR activity in particular may contribute to the non-immune-mediated effects of DMXAA on the vasculature.