Vascular disrupting agents in clinical development

Metabolism is the tie: The Bertalanffy-type cancer growth model as common denominator of various modelling approaches

Cancer or tumour growth has been addressed from a variety of mathematical modelling perspectives in the past. Examples are single variable growth models, reaction diffusion models, compartment models, individual cell-based models, clonal competition models, to name only a few. In this paper, we show that the so called Bertalanffy-type growth model is a macroscopic model variant that can be conceived as an optimal condensed modelling approach that to a high degree preserves complexity with respect to the aforementioned more complex modelling variants. The derivation of the Bertalanffy-type model is crucially based on features of metabolism. Therefore, this model contains a shape parameter that can be interpreted as a resource utilisation efficiency. This shape parameter reflects features that are usually captured in much more complex models. To be specific, the shape parameter is related to morphological structures of tumours, which in turn depend on metabolic conditions. We, furthermore, show that a single variable variant of the Bertalanffy-type model can straightforwardly be extended to a multiclonal competition model. Since competition is crucially based on available shared or clone-specific resources, the metabolism-based approach is an obvious candidate to capture clonal competition. Depending on the specific context, metabolic reprogramming or other oncogene driven changes either lead to a suppression of cancer cells or to an improved competition resulting in outgrowth of tumours. The parametrisation of the Bertalanffy-type growth model allows to account for this observed variety of cancer characteristics. The shape parameter, conceived as a classifier for healthy and oncogenic phenotypes, supplies a link to survival and evolutionary stability concepts discussed in demographic studies, such as opportunistic versus equilibrium strategies.

ASA404, a vascular disrupting agent, as an experimental treatment approach for brain tumors

Malignant brain tumors, including gliomas, brain metastases and anaplastic meningiomas, are associated with poor prognosis, and represent an unmet medical need. ASA404 (DMXAA), a vascular disrupting agent, has demonstrated promising results in several preclinical tumor models and early phase clinical trials. However, two phase III trials in non-small cell lung cancer reported insufficient results. The aim of the present study was to determine the effects of ASA404 on brain tumors. The effects of ASA404 were evaluated in vitro and in vivo using subcutaneous, and orthotopical models for malignant glioma (U-87, LN-229, U-251, LN-308 and Tu-2449), brain metastasis (HT-29) and malignant meningioma (IOMM-Lee). The acute effects of ASA404 on tumor tissue were analyzed using conventional and immunohistochemical staining techniques [hematoxylin and eosin, MIB-1 antibody/proliferation maker protein Ki-67, cleaved caspase-8, stimulator of interferon genes (STING), ionized calcium-binding adapter molecule 1]. Furthermore, the sizes of subcutaneous tumors were measured and the symptom-free survival rates of animals with intracranial tumors receiving ASA404 treatment were analyzed. ASA404 demonstrated low toxicity in vitro, but exhibited strong effects on subcutaneous tumors 24 h following a single dose of ASA404 (25 mg/kg). ASA404 induced necrosis, hemorrhages and inhibited the proliferation, and growth of tumors in the subcutaneous glioma models. However, ASA404 failed to demonstrate comparable effects in any of the intracranial tumor models examined and did not result in a prolongation of survival. Expression of STING, the molecular target of ASA404, and infiltration of macrophages, the cells mediating ASA404 activity, did not differ between subcutaneous and intracranial tumors. In conclusion, ASA404 demonstrates clear efficacy in subcutaneous tumor models, but has no relevant activity in orthotopic brain tumor models. The expression of STING and infiltration with macrophages were not determined to be involved in the differential activity observed among tumor models. It is possible that the low penetration of ASA-404 into the brain prevents concentrations sufficient enough reaching the tumor in order to exhibit acute effects in vivo.

Localized microbubble cavitation-based antivascular therapy for improving HCC treatment response to radiotherapy

Hepatocellular carcinoma (HCC) is the third leading cause of cancer mortality worldwide and the fastest growing malignancy in the United States. With a 5-year survival rate below 12%, effective therapies for HCC are needed. Current treatments for HCC include microwave and radiofrequency ablation, high intensity focused ultrasound, liver transplant, surgical resection, and localized embolizations. However, each of these approaches has some limitation, making it imperative to develop improved methods for sensitizing tumors prior to therapy. We hypothesized that the use of ultrasound-triggered microbubble destruction (UTMD), which sensitizes tumors to radiotherapy by inducing vascular endothelial cell apoptosis, will selectively sensitize malignant tissue to radiotherapy and improve outcomes. To test this, 18 nude rats were inoculated in the right liver lobe with Hu7.5 HCC cells and after tumor formation, received 5 Gy radiotherapy, UTMD, or UTMD prior to radiotherapy. Compared to radiotherapy alone, there was a 170% reduction in tumor growth 7 days post treatment and a 3.2X improvement in median survival time when radiotherapy was combined with UTMD. These results indicate that UTMD is an effective adjunct when combined with radiotherapy to treat HCC.

Micro-HCCs in rats with liver cirrhosis: paradoxical targeting effects with vascular disrupting agent CA4P

We sought to investigate anticancer efficacy of a vascular disrupting agent (VDA) combretastatin A-4 phosphate (CA4P) in relation to tumor size among hepatocellular carcinomas (HCCs) in rats using magnetic resonance imaging (MRI) and postmortem techniques. Nineteen rats with 43 chemically-induced HCCs of 2.8–20.9 mm in size on liver cirrhosis received CA4P intravenously at 10 mg/kg. Tumor-diameter was measured by T2-weighted imaging (T2WI) to define microcancers (< 5 mm) versus larger HCCs. Vascular responses and tissue necrosis were detected by diffusion-weighted imaging (DWI), contrast-enhanced T1-weighted imaging (CE-T1WI) and dynamic contrast enhanced (DCE-) MRI, which were validated by microangiography and histopathology. MRI revealed nearly complete necrosis in 5 out of 7 micro-HCCs, but diverse therapeutic necrosis in larger HCCs with a positive correlation with tumor size. Necrosis in micro-HCCs was 36.9% more than that in larger HCCs. While increased diffusion coefficient (ADC_diff) suggested tumor necrosis, perfusion coefficient (ADC_perf) indicated sharply decreased blood perfusion in cirrhotic liver together with a reduction in micro-HCCs. DCE revealed lowered tumor blood flow from intravascular into extravascular extracellular space (EES). Microangiography and histopathology revealed hypo- and hypervascularity in 4 and 3 micro-HCCs, massive, partial and minor degrees of tumoral necrosis in 5, 1 and 1 micro-HCCs respectively, and patchy necrotic foci in cirrhotic liver. CD34-PAS staining implicated that poorly vascularized micro-HCCs growing on liver cirrhosis tended to respond better to CA4P treatment. In this study, more complete CA4P-response occurred unexpectedly in micro-HCCs in rats, along with CA4P-induced necrotic foci in cirrhotic liver. These may help to plan clinical applications of VDAs in patients with HCCs and liver cirrhosis.

A Novel Theranostic Strategy for MMP-14-Expressing Glioblastomas Impacts Survival

Glioblastoma (GBM) has a dismal prognosis. Evidence from preclinical tumor models and human trials indicates the role of GBM-initiating cells (GIC) in GBM drug resistance. Here, we propose a new treatment option with tumor enzyme-activatable, combined therapeutic and diagnostic (theranostic) nanoparticles, which caused specific toxicity against GBM tumor cells and GICs. The theranostic cross-linked iron oxide nanoparticles (CLIO) were conjugated to a highly potent vascular disrupting agent (ICT) and secured with a matrix-metalloproteinase (MMP-14) cleavable peptide. Treatment with CLIO-ICT disrupted tumor vasculature of MMP-14-expressing GBM, induced GIC apoptosis, and significantly impaired tumor growth. In addition, the iron core of CLIO-ICT enabled in vivo drug tracking with MR imaging. Treatment with CLIO-ICT plus temozolomide achieved tumor remission and significantly increased survival of human GBM-bearing mice by more than 2-fold compared with treatment with temozolomide alone. Thus, we present a novel therapeutic strategy with significant impact on survival and great potential for clinical translation. Mol Cancer Ther; 16(9); 1909-21. ©2017 AACR.

Water-Soluble Combretastatin A4 Phosphate Orally Delivered via Composite Nanoparticles With Improved Inhibition Effect Toward S180 Tumors

Combretastatin A4 phosphate (CA4P) is a novel vascular disrupting agent for cancer therapy. However, frequent dosing and negative patient compliance have been encountered over CA4P by injection administration due to its quite short-term action and acute side effects. Therefore, it is significant to develop an oral formulation of CA4P. We established a novel method to prepare CA4P-loaded nanoparticles (CA4P-NPs) for oral administration by combining methoxy poly(ethylene glycol)-b-polylactide (PELA) and poly(d,l-lactic-co-glycolic acid) (PLGA) polymers. Transport study in vitro was evaluated on Madin-Darby canine kidney cell models, and antitumor effect evaluation in vivo was performed on S180 subcutaneous xenotransplanted tumor models in mice. The highest entrapment efficiency of CA4P-NPs was achieved when the weight ratio of PELA to PLGA was optimized to 1:1. The apparent permeability coefficient of CA4P-NPs was found to be 2.08-fold higher than that of free CA4P in transport study. CA4P-NPs reached an absolute bioavailability of 77.6% with the tumor inhibition ratio of 41.2% that was significantly superior to free CA4P. These results suggest a promising application of this composite nanoparticle for the oral delivery of water-soluble drugs.

Tumor rim cells: From resistance to vascular targeting agents to complete tumor ablation

Current vascular targeting strategies pursue two main goals: anti-angiogenesis agents aim to halt sprouting and the formation of new blood vessels, while vascular disrupting agents along with coaguligands seek to compromise blood circulation in the vessels. The ultimate goal of such therapies is to deprive tumor cells out of oxygen and nutrients long enough to succumb cancer cells to death. Most of vascular targeting agents presented promising therapeutic potential, but the final goal which is cure is rarely achieved. Nevertheless, in both preclinical and clinical settings, tumors tend to grow back, featuring a highly invasive, metastatic, and extremely resistant form. This review highlights the critical significance of tumor rim cells as the main factor, determining therapy success with vascular targeting agents. We present an overview of different single and combination treatments with vascular targeting agents that enable efficient targeting of tumor rim cells and long-lasting tumor cure. Understanding the nature of tumor rim cells, how they establish, how they manage to survive of vascular targeting agents, and how they contribute in tumor refractoriness, may open new avenues to the development of beneficial strategies, capable to eliminate residual rim cells, and enable tumor ablation once and forever.

Concurrent anti-vascular therapy and chemotherapy in solid tumors using drug-loaded acoustic nanodroplet vaporization

Drug-loaded nanodroplets (NDs) can be converted into gas bubbles through ultrasound (US) stimulation, termed acoustic droplet vaporization (ADV), which provides a potential strategy to simultaneously induce vascular disruption and release drugs for combined physical anti-vascular therapy and chemotherapy. Doxorubicin-loaded NDs (DOX-NDs) with a mean size of 214nm containing 2.48mg DOX/mL were used in this study. High-speed images displayed bubble formation and cell debris, demonstrating the reduction in cell viability after ADV. Intravital imaging provided direct visualization of disrupted tumor vessels (vessel size <30μm), the extravasation distance was 12μm in the DOX-NDs group and increased over 100μm in the DOX-NDs+US group. Solid tumor perfusion on US imaging was significantly reduced to 23% after DOX-NDs vaporization, but gradually recovered to 41%, especially at the tumor periphery after 24h. Histological images of the DOX-NDs+US group revealed tissue necrosis, a large amount of drug extravasation, vascular disruption, and immune cell infiltration at the tumor center. Tumor sizes decreased 22%, 36%, and 68% for NDs+US, DOX-NDs, and DOX-NDs+US, respectively, to prolong the survival of tumor-bearing mice. Therefore, this study demonstrates that the combination of physical anti-vascular therapy and chemotherapy with DOX-NDs vaporization promotes uniform treatment to improve therapeutic efficacy.

STATEMENT OF SIGNIFICANCE

Tumor vasculature plays an important role for tumor cell proliferation by transporting oxygen and nutrients. Previous studies combined anti-vascular therapy and drug release to inhibit tumor growth by ultrasound-stimulated microbubble destruction or acoustic droplet vaporization. Although the efficacy of combined therapy has been demonstrated; the relative spatial distribution of vascular disruption, drug delivery, and accompanied immune responses within solid tumors was not discussed clearly. Herein, our study used drug-loaded nanodroplets to combined physical anti-vascular and chemical therapy. The in vitro cytotoxicity, intravital imaging, and histological assessment were used to evaluate the temporal and spatial cooperation between physical and chemical effect. These results revealed some evidences for complementary action to explain the high efficacy of tumor inhibition by combined therapy.

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.

Microtubule destabilising agents: far more than just antimitotic anticancer drugs

Vinca alkaloids have been approved as anticancer drugs for more than 50 years. They have been classified as cytotoxic chemotherapy drugs that act during cellular mitosis, enabling them to target fast growing cancer cells. With the evolution of cancer drug development there has been a shift towards new "targeted" therapies to avoid the side effects and general toxicities of "cytotoxic chemotherapies" such as the vinca alkaloids. Due to their original classification, many have overlooked the fact that vinca alkaloids, taxanes and related drugs do have a specific molecular target: tubulin. They continue to be some of the most effective anticancer drugs, perhaps because their actions upon the microtubule network extend far beyond the ability to halt cells in mitosis, and include the induction of apoptosis at all phases of the cell cycle. In this review, we highlight the numerous cellular consequences of disrupting microtubule dynamics, expanding the textbook knowledge of microtubule destabilising agents and providing novel opportunities for their use in cancer therapy.

Therapeutic application of anti-angiogenic nanomaterials in cancers

Angiogenesis, the formation of new blood vessels from pre-existing vasculature, plays a vital role in physiological and pathological processes (embryonic development, wound healing, tumor growth and metastasis). The overall balance of angiogenesis inside the human body is maintained by pro- and anti-angiogenic signals. The processes by which drugs inhibit angiogenesis as well as tumor growth are called the anti-angiogenesis technique, a most promising cancer treatment strategy. Over the last couple of decades, scientists have been developing angiogenesis inhibitors for the treatment of cancers. However, conventional anti-angiogenic therapy has several limitations including drug resistance that can create problems for a successful therapeutic strategy. Therefore, a new comprehensive treatment strategy using antiangiogenic agents for the treatment of cancer is urgently needed. Recently researchers have been developing and designing several nanoparticles that show anti-angiogenic properties. These nanomedicines could be useful as an alternative strategy for the treatment of various cancers using anti-angiogenic therapy. In this review article, we critically focus on the potential application of anti-angiogenic nanomaterial and nanoparticle based drug/siRNA/peptide delivery systems in cancer therapeutics. We also discuss the basic and clinical perspectives of anti-angiogenesis therapy, highlighting its importance in tumor angiogenesis, current status and future prospects and challenges.

Anti-vascular therapies in ovarian cancer: moving beyond anti-VEGF approaches

Resistance to chemotherapy is among the most important issues in the management of ovarian cancer. Unlike cancer cells, which are heterogeneous as a result of remarkable genetic instability, stromal cells are considered relatively homogeneous. Thus, targeting the tumor microenvironment is an attractive approach for cancer therapy. Arguably, anti-vascular endothelial growth factor (anti-VEGF) therapies hold great promise, but their efficacy has been modest, likely owing to redundant and complementary angiogenic pathways. Components of platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), epidermal growth factor (EGF), and other pathways may compensate for VEGF blockade and allow angiogenesis to occur despite anti-VEGF treatment. In addition, hypoxia induced by anti-angiogenesis therapy modifies signaling pathways in tumor and stromal cells, which induces resistance to therapy. Because of tumor cell heterogeneity and angiogenic pathway redundancy, combining cytotoxic and targeted therapies or combining therapies targeting different pathways can potentially overcome resistance. Although targeted therapy is showing promise, much more work is needed to maximize its impact, including the discovery of new targets and identification of individuals most likely to benefit from such therapies.

Re-engineering of PIP3-antagonist triazole PITENIN's chemical scaffold: development of novel antifungal leads

A novel 4-(1-phenyl-1-hydroxyethyl)-1-(o-hydroxyphenyl)-1H-1,2,3-triazole was designed by integrating the structural features of triazole PITENIN anticancer agents and the azole class of antifungal drugs.

Perfusion CT imaging of treatment response in oncology

Perfusion CT was first described in the 1970s but has become accepted as a clinical technique in recent years. In oncological practice Perfusion CT allows the downstream effects of therapies on the tumour vasculature to be monitored. From the dynamic changes in tumour and vascular enhancement following intravenous iodinated contrast agent administration, qualitative and quantitative parameters may be derived that reflect tumour perfusion, blood volume, and microcirculatory changes with treatment. This review outlines the mechanisms of action of available therapies and state-of-the-art imaging practice.

Nanoparticle Mediated Tumor Vascular Disruption: A Novel Strategy in Radiation Therapy

More than 50% of all cancer patients receive radiation therapy. The clinical delivery of curative radiation dose is strictly restricted by the proximal healthy tissues. We propose a dual-targeting strategy using vessel-targeted-radiosensitizing gold nanoparticles and conformal-image guided radiation therapy to specifically amplify damage in the tumor neoendothelium. The resulting tumor vascular disruption substantially improved the therapeutic outcome and subsidized the radiation/nanoparticle toxicity, extending its utility to intransigent or nonresectable tumors that barely respond to standard therapies.

Necrosis targeted combinational theragnostic approach using radioiodinated Sennidin A in rodent tumor models

Residual cancer cells and subsequent tumor relapse is an obstacle for curative cancer treatment. Tumor necrosis therapy (TNT) has recently been developed to cause residual tumor regression or destruction. Here, we exploited the avidity of the sennidin A (SA) tracer and radioiodinated SA (¹³¹I-SA) to necrotic tumors in order to further empower TNT. We showed high uptake and prolonged retention of SA in necrotic tumors and a quick clearance in other non-targeted tissues including the liver. On SPECT-CT images, tumor mass appeared persistently as a hotspot. Based on the prominent targetability of ¹³¹I-SA to the tumor necrosis, we designed a combinational theragnostic modality. The vascular disrupting agent (VDA) combretastatin A4 phosphate (CA4P) was used to cause massive tumor necrosis, which formed the target of ¹³¹I-SA that subsequently killed the residual tumor cells by cross-fire irradiation of beta particles. Consequently, ¹³¹I-SA combined with CA4P significantly inhibited tumor growth, extended tumor doubling time and prolonged mean animal survival. In conclusion, ¹³¹I-SA in combination with necrosis inducing drugs/therapies may generate synergetic tumoricidal effects on solid malignancies by means of primary debulking and secondary cleansing process.

Dynamic contrast-enhanced magnetic resonance imaging of the liver: Applications in treatment of hepatic malignancies with vascular targeting agents

Dynamic contrast-enhanced magnetic resonance (DCE-MR) imaging of the liver as a trendy technique can be applied in various kinds of liver diseases to evaluate perfusion and vascular characteristics of liver tissue and tumor. It has been proved that DCE-MR imaging plays an important role in the treatment of liver malignancies with vascular targeting agents. This review aims to give an overview of DCE-MR imaging of the liver in terms of semi-quantitative analysis methods, common quantitative analysis models and contrast agents and discuss its application value in the treatment of liver malignancies with vascular targeting agents.

Eribulin mesylate reduces tumor microenvironment abnormality by vascular remodeling in preclinical human breast cancer models

Eribulin mesylate is a synthetic macrocyclic ketone analog of the marine sponge natural product halichondrin B and an inhibitor of microtubule dynamics. Some tubulin-binding drugs are known to have antivascular (antiangiogenesis or vascular-disrupting) activities that can target abnormal tumor vessels. Using dynamic contrast-enhanced MRI analyses, here we show that eribulin induces remodeling of tumor vasculature through a novel antivascular activity in MX-1 and MDA-MB-231 human breast cancer xenograft models. Vascular remodeling associated with improved perfusion was shown by Hoechst 33342 staining and by increased microvessel density together with decreased mean vascular areas and fewer branched vessels in tumor tissues, as determined by immunohistochemical staining for endothelial marker CD31. Quantitative RT-PCR analysis of normal host cells in the stroma of xenograft tumors showed that eribulin altered the expression of mouse (host) genes in angiogenesis signaling pathways controlling endothelial cell–pericyte interactions, and in the epithelial–mesenchymal transition pathway in the context of the tumor microenvironment. Eribulin also decreased hypoxia-associated protein expression of mouse (host) vascular endothelial growth factor by ELISA and human CA9 by immunohistochemical analysis. Prior treatment with eribulin enhanced the anti-tumor activity of capecitabine in the MDA-MB-231 xenograft model. These findings suggest that eribulin-induced remodeling of abnormal tumor vasculature leads to a more functional microenvironment that may reduce the aggressiveness of tumors due to elimination of inner tumor hypoxia. Because abnormal tumor microenvironments enhance both drug resistance and metastasis, the apparent ability of eribulin to reverse these aggressive characteristics may contribute to its clinical benefits.

Development of novel tumor-targeted theranostic nanoparticles activated by membrane-type matrix metalloproteinases for combined cancer magnetic resonance imaging and therapy

A major drawback with current cancer therapy is the prevalence of unrequired dose-limiting toxicity to non-cancerous tissues and organs, which is further compounded by a limited ability to rapidly and easily monitor drug delivery, pharmacodynamics and therapeutic response. In this report, the design and characterization of novel multifunctional "theranostic" nanoparticles (TNPs) is described for enzyme-specific drug activation at tumor sites and simultaneous in vivo magnetic resonance imaging (MRI) of drug delivery. TNPs are synthesized by conjugation of FDA-approved iron oxide nanoparticles ferumoxytol to an MMP-activatable peptide conjugate of azademethylcolchicine (ICT), creating CLIO-ICTs (TNPs). Significant cell death is observed in TNP-treated MMP-14 positive MMTV-PyMT breast cancer cells in vitro, but not MMP-14 negative fibroblasts or cells treated with ferumoxytol alone. Intravenous administration of TNPs to MMTV-PyMT tumor-bearing mice and subsequent MRI demonstrates significant tumor selective accumulation of the TNP, an observation confirmed by histopathology. Treatment with CLIO-ICTs induces a significant antitumor effect and tumor necrosis, a response not observed with ferumoxytol. Furthermore, no toxicity or cell death is observed in normal tissues following treatment with CLIO-ICTs, ICT, or ferumoxytol. These findings demonstrate proof of concept for a new nanotemplate that integrates tumor specificity, drug delivery and in vivo imaging into a single TNP entity through attachment of enzyme-activated prodrugs onto magnetic nanoparticles. This novel approach holds the potential to significantly improve targeted cancer therapies, and ultimately enable personalized therapy regimens.

Perfusion CT imaging of colorectal cancer

Imaging plays an important role in the assessment of colorectal cancer, including diagnosis, staging, selection of treatment, assessment of treatment response, surveillance and investigation of suspected disease relapse. Anatomical imaging remains the mainstay for size measurement and structural evaluation; however, functional imaging techniques may provide additional insights into the tumour microenvironment. With dynamic contrast-enhanced CT techniques, iodinated contrast agent kinetics may inform on regional tumour perfusion, shunting and microvascular function and provide a surrogate measure of tumour hypoxia and angiogenesis. In colorectal cancer, this may be relevant for clinical practice in terms of tumour phenotyping, prognostication, selection of individualized treatment and therapy response assessment.

Combretastatin A-4 inspired novel 2-aryl-3-arylamino-imidazo-pyridines/pyrazines as tubulin polymerization inhibitors, antimitotic and anticancer agents

Novel 2-aryl-3-arylamino-imidazo-pyridines/pyrazines that exhibit potent tubulin polymerization inhibition, anticancer activity, anti-migration of cancer cells, chromosomal damage, and apoptosis have been developed.

Synthesis and biological evaluation of Combretastatin A-4 derivatives containing a 3'-O-substituted carbonic ether moiety as potential antitumor agents

Background

Combretastatin A-4 (CA-4), which is an excellent antineoplastic agent, was isolated from Combretum caffrum. To date, structural modification studies of CA-4 have focused predominantly on the construction of new therapeutic agents for drug discovery. As a part of our ongoing work towards the modification of natural products, we have focused on the 3’-O-substituent groups in the B-ring of CA-4 under the hypothesis that these novel derivatives will possess good bioactivities and behave as effective antiproliferative pro-drugs.

Results

A series of novel CA-4 derivatives, which contained a 3’-O-substituted carbonic ether moiety, were synthesized and evaluated for their antitumor activities against four tumor cell lines, including MDA-MB-231, MCF-7, K562 and A549 cells. These derivatives exhibited clear antitumor activities, and CA-4E, in particular, showed the highest bioactivity of all of the derivatives tested against all four tumor cell lines, with IC₅₀ values in the range of 1 to 180 nM. Based on its high bioactivity, CA-4E was subsequently selected to investigate the antitumor mechanism of these synthetic compounds. The cell cycle results demonstrated that CA-4E induced time- and dose-dependent G2/M arrest in a similar manner to CA-4, although its effect was more powerful than that of CA-4, and the apoptosis data showed that CA-4E induced cellular apoptosis in a dose-dependent manner.

Conclusions

The newly synthesized CA-4 derivatives exhibited good antitumor activities in vitro, with CA-4E, in particular, showing the highest bioactivity of all of the compounds tested. Furthermore, CA-4E induced time- and dose-dependent G2/M arrest and cellular apoptosis in a dose-dependent manner. Taken together, these results suggest that CA-4E should be subjected to further investigation as a potential anticancer drug candidate.

Synthesis and in vitro cytotoxic activity of novel chalcone-like agents

OBJECTIVE(S)

Chalcones and their rigid analogues represent an important class of small molecules having anticancer activities. Therefore, in this study the synthesis and cytotoxic activity of new 3-benzylidenchroman-4-ones were described as rigid chalcone analogues.

MATERIALS AND METHODS

The reaction of resorcinol with 3-chloropropionic acid in the presence of CF3SO3H was afforded corresponding propiophenone. It was cyclized using 2M NaOH to give 7-hydroxy-4-chromanone. O-Alkylation of 7-hydroxy-4-chromanone with alkyl iodide in the presence of K2CO3 gave 7-alkoxychroman-4-one. Finally, condensation of chroman-4-one derivatives with different aldehydes afforded target compounds in good yields. The newly synthesized compounds were tested in vitro against different human cancer cell lines including K562 (human erythroleukemia), MDA-MB-231 (human breast cancer), and SK-N-MC (human neuroblastoma) cells. The cell viability was evaluated using MTT colorimetric assay.

RESULTS

Most of the compounds showed good inhibitory activity against cancer cells. Among them, compound 4a containing 7-hydroxy group on chromanone ring and 3-bromo-4-hydroxy-5-methoxy substitution pattern on benzylidene moiety was the most potent compound with IC50 values ≤ 3.86 µg/ml. It was 6-17 times more potent than etoposide against tested cell lines.

CONCLUSION

We described synthesis and cytotoxic activity of poly-functionalized 3-benzylidenechroman-4-ones as new chalcone-like agents. These compounds can be considered as conformationally constrained congeners of chalcones to tolerate the poly-functionalization on the core structures for further optimization.

Beyond bevacizumab: investigating new angiogenesis inhibitors in ovarian cancer

INTRODUCTION

Ovarian cancer is the most lethal gynecological cancer, mainly because of the advanced stage of the disease at diagnosis, with recent research investigating novel targets and agents into the clinical practice, with the aim to improve prognosis and quality of life. Angiogenesis is a significant target for ovarian cancer therapy.

AREAS COVERED

Areas covered in this review include the most common molecular pathways of angiogenesis, which have provided novel targets for tailored therapy in ovarian cancer patients. These therapeutic strategies comprise monoclonal antibodies and tyrosine kinase inhibitors. These drugs have as molecular targets such as vascular endothelial growth factor (VEGF), VEGF receptor, platelet-derived growth factor, fibroblast growth factor, angiopoietin and Ephrin type-A receptor 2.

EXPERT OPINION

The expansion in understanding the molecular biology that characterizes cancer cells has led to the rapid development of new agents to target important pathways, but the heterogeneity of ovarian cancer biology indicates that there is no predominant defect. This review attempts to discuss progress till date in tackling a more general target applicable to ovarian cancer angiogenesis.

Synthesis of combretastatin A4 analogues on steroidal framework and their anti-breast cancer activity

Combretastatin A4 analogues were synthesized on steroidal framework from gallic acid with a possibility of anti-breast cancer agents. Twenty two analogues were synthesized and evaluated for cytotoxicity against human breast cancer cell lines (MCF-7 & MDA-MB 231). The best analogue 22 showed potent antitubulin effect. Docking experiments also supported strong binding affinity of 22 to microtubule polymerase. In cell cycle analysis, 22 induced apoptosis in MCF-7 cells significantly. It was found to be non-toxic up to 300 mg/kg dose in Swiss albino mice in acute oral toxicity. This article is part of a Special Issue entitled "Synthesis and biological testing of steroid derivatives as inhibitors".

Radioiodinated hypericin: its biodistribution, necrosis avidity and therapeutic efficacy are influenced by formulation

PURPOSE

To study whether formulation influences biodistribution, necrosis avidity and tumoricidal effects of the radioiodinated hypericin, a necrosis avid agent for a dual-targeting anticancer radiotherapy.

METHODS

Iodine-123- and 131-labeled hypericin ((123)I-Hyp and (131)I-Hyp) were prepared with Iodogen as oxidant, and formulated in dimethyl sulfoxide (DMSO)/PEG400 (polyethylene glycol 400)/water (25/60/15, v/v/v) or DMSO/saline (20:80, v/v). The formulations with excessive Hyp were optically characterized. Biodistribution, necrosis avidity and tumoricidal effects were studied in rats (n = 42) without and with reperfused liver infarction and implanted rhabdomyosarcomas (R1). To induce tumor necrosis, R1-rats were pre-treated with a vascular disrupting agent. Magnetic resonance imaging, tissue-gamma counting, autoradiography and histology were used.

RESULTS

The two formulations differed significantly in fluorescence and precipitation. (123)I-Hyp/Hyp in DMSO/PEG400/water exhibited high uptake in necrosis but lower concentration in the lung, spleen and liver (p < 0.01). Tumor volumes of 0.9 ± 0.3 cm(3) with high radioactivity (3.1 ± 0.3% ID/g) were detected 6 days post-treatment. By contrast, (131)I-Hyp/Hypin DMSO/saline showed low uptake in necrosis but high retention in the spleen and liver (p < 0.01). Tumor volumes reached 2.6 ± 0.7 cm(3) with low tracer accumulation (0.1 ± 0.04%ID/g).

CONCLUSIONS

The formulation of radioiodinated hypericin/hypericin appears crucial for its physical property, biodistribution, necrosis avidity and tumoricidal effects.

Current status of bevacizumab in advanced ovarian cancer

Ovarian cancer is the most lethal gynecological cancer, mainly because of the delay in diagnosis. Recently, much effort has been put into investigating and introducing novel targeted agents into clinical practice, with the aim of improving prognosis and quality of life. Angiogenesis is a possible target. The aim of this review is to investigate the most common molecular pathways of angiogenesis, which have provided novel targets for tailored therapy in patients with ovarian cancer. These therapeutic strategies include monoclonal antibodies and tyrosine-kinase inhibitors. These drugs have as molecular targets vascular endothelial growth factor, vascular endothelial growth factor receptors, platelet-derived growth factor, fibroblast growth factor, and angiopoietin. Bevacizumab was investigated in several Phase III studies, with interesting results. Today, there is strong evidence for introducing bevacizumab in the treatment of patients with advanced and recurrent ovarian cancer. Nevertheless, further investigations and large clinical trials are needed to understand the safety and effectiveness of bevacizumab, the optimal duration and timing of treatment, and activity in association with other chemotherapeutic and targeted agents. It also is necessary to identify biologic factors predictive of efficacy to choose the most appropriate antiangiogenic agent in the integrated treatment of epithelial ovarian cancer.

Endothelial cell heterogeneity

The endothelial lining of blood vessels shows remarkable heterogeneity in structure and function, in time and space, and in health and disease. An understanding of the molecular basis for phenotypic heterogeneity may provide important insights into vascular bed-specific therapies. First, we review the scope of endothelial heterogeneity and discuss its proximate and evolutionary mechanisms. Second, we apply these principles, together with their therapeutic implications, to a representative vascular bed in disease, namely, tumor endothelium.

A review of vascular disrupting agents as a concomitant anti-tumour modality with radiation

Background

Tumour vasculature plays an important role in the development, maintenance and sustainability of a tumour. Endothelial cells which are recruited into the tumour stroma facilitate the formation of essential blood vessels that deliver nutrients and oxygen to tumour cells. A growing body of research is showing that there are synergistic anti-tumour effects when anti-vascular agents are combined with radiation. More recent reports have described favourable radiation response as a function of vascular targeting and blood vessel breakdown, primarily through interactions of radiation with vascular endothelial cells. Vascular disrupting agents are being utilised in several forms that include molecular targeting, biophysical assault and biological interference.

Purpose

In the present review, we examine current advances in anti-vascular agents to enhance tumour response when combined with radiation therapy.

Methods

A comprehensive literature search was conducted on the US National Library of Medicine, National Institutes of Health (PubMed) using the following search keywords: vascular disrupting agents, radiation sensitisation, anti-angiogenic therapy, anti-vascular therapy, radiation therapy.

Conclusion

Current research suggests the applicability of vascular disrupting agents as an effective radiation sensitisation agent. Pre-clinical and clinical trials have been well developed to form the theoretical framework to apply this powerful modality to the treatment of cancer.

Combretazet-3 a novel synthetic cis-stable combretastatin A-4-azetidinone hybrid with enhanced stability and therapeutic efficacy in colon cancer

In recent years an extensive series of synthetic combretastatin A-4 (CA-4)-azetidinone (β-lactam) hybrids were designed and synthesised with a view to improve the stability, therapeutic efficacy and aqueous solubility of CA-4. Lead compounds containing a 3,4,5-trimethoxy aromatic ring at position 1 and a variety of substitution patterns at positions 3 and 4 of the β-lactam ring were screened in three adenocarcinoma-derived colon cancer cell lines (CT-26, Caco-2 and the CA-4 resistant cell line, HT-29). In both CT-26 and Caco-2 cells all β-lactam analogues analysed displayed potent therapeutic efficacy within the nanomolar range. Substitution of the ethylene bridge of CA-4 with the β-lactam ring together with the aforementioned aryl substitutions improved the therapeutic efficacy of CA-4 up to 300‑fold in the combretastatin refractory HT-29 cells. The lead compound combretazet-3 (CAZ-3); chemical name [4-(3-hydroxy-4-methoxyphenyl)-3-(4-hydroxyphenyl)-1-(3,4,5-trimethoxyphenyl)azetidin-2-one] demonstrated improved chemical stability together with enhanced therapeutic efficacy as compared with CA-4 whilst maintaining the natural biological properties of CA-4. Furthermore, CAZ-3 demonstrated significant tumour inhibition in a murine model of colon cancer. Our results suggest that combretastatin-azetidinone hybrids represent an effective novel therapy for the treatment of combretastatin resistant carcinomas.

KML001 displays vascular disrupting properties and irinotecan combined antitumor activities in a murine tumor model

KML001 is sodium metaarsenite, and has shown cytotoxic activity in human tumor cell lines. The anti-cancer mechanism of KML001 involves cancer cell destruction due to DNA damage at the telomeres of cancer cell chromosomes. In this study, we assessed the vascular disrupting properties of KML001 and investigated whether KML001 as VDA is able to increase anti-tumor activity in irinotecan combined treatment. We used a murine model of the CT26 colon carcinoma cell line. CT26 isograft mice treated intraperitoneally with 10 mg/kg KML001 displayed extensive central necrosis of tumor by 24 h. The vascular disrupting effects of KML001 were assessed by dynamic contrast enhanced magnetic resonance imaging. Gadopentetic acid-diethylene triaminepentaacetic acid contrast enhancement was markedly decreased in KML001-treated mice one day after treatment, whereas persistently high signal enhancement was observed in mice injected with saline. Rate constant K(ep) value representing capillary permeability was significantly decreased (p<0.05) in mice treated with KML001. Cytoskeletal changes of human umbilical vein endothelial cells (HUVECs) treated with 10 uM KML001 were assessed by immune blotting and confocal imaging. KML001 degraded tubulin protein in HUVECs, which may be related to vascular disrupting properties of KML001. Finally, in the mouse CT26 isograft model, KML001 combined with irinotecan significantly delayed tumor growth as compared to control and irinotecan alone. These results suggest that KML001 is a novel vascular disrupting agent, which exhibits significant vascular shut-down activity and enhances anti-tumor activity in combination with chemotherapy. These data further suggest an avenue for effective combination therapy in treating solid tumors.

Combination of vascular disrupting agents and ionizing radiation

Vascular disrupting agents (VDAs) are a relatively new class of drugs that target tumor vasculature and induce tumor blood flow shutdown and subsequent necrosis in the tumor core. The first generation of these agents is actively evaluated in clinical trials, whereas new molecules are developed in order to enhance efficacy and to overcome resistance mechanisms. VDA used as a single agent only cause a moderate tumor growth delay. So, strategy aiming at combining VDA to conventional cancer treatments is undergoing extensive investigations. A special emphasis has been put on combination with chemotherapeutic agents. Besides, numerous preclinical studies have also clearly established that the association of VDA to radiotherapy can improve antitumor treatment and may lead to a therapeutic gain. However, up to date, there is a lack of clinical trials evaluating such combinations, whereas it would be of great interest since radiotherapy is widely used as anticancer 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.