Antivascular therapy of cancer: DMXAA

Treatment strategies and molecular mechanism of radiotherapy combined with immunotherapy in colorectal cancer

Radiotherapy (RT) remodels the tumor immune microenvironment (TIME) and modulates the immune response to indirectly destroy tumor cells, in addition to directly killing tumor cells. RT combined with immunotherapy may significantly enhance the efficacy of RT in colorectal cancer by modulating the microenvironment. However, the molecular mechanisms by which RT acts as an immunomodulator to modulate the immune microenvironment remain unclear. Further, the optimal modalities of RT combined with immunotherapy for the treatment of colorectal cancer, such as the time point of combining RT and immunization, the fractionation pattern and dosage of radiotherapy, and other methods to improve the efficacy, are also being explored parallelly. To address these aspects, in this review, we summarized the mechanisms by which RT modulates TIME and concluded the progress of RT combined with immunization in preclinical and clinical trials. Finally, we discussed heavy ion radiation therapy and the efficacy of prediction markers and other immune combination therapies. Overall, combining RT with immunotherapy to enhance antitumor effects will have a significant clinical implication and will help to facilitate individualized treatment modalities.

Integrated anti-vascular and immune-chemotherapy for colorectal carcinoma using a pH-responsive polymeric delivery system

Colorectal carcinoma (CRC) has become one of the most prevalent malignant tumors and exploring a potential therapeutic strategy with diminished drug-associated adverse effects to combat CRC is urgent. Herein, we designed a pH-responsive polymer to efficiently encapsulate a stimulator of interferon genes (STING) agonist (5,6- dimethylxanthenone-4-acetic acid, termed ASA404) and a common clinically used chemotherapeutic agent (1-hexylcarbamoyl-5-fluorouracil, termed HCFU). Investigations in vitro demonstrated that polymer encapsulation endowed the system with a pH-dependent disassembly behavior (pHt 6.37), which preferentially selected cancerous cells with a favorable dose reduction (dose reduction index (DRI) of HCFU was 4.09). Moreover, the growth of CRC in tumor-bearing mice was effectively suppressed, with tumor suppression rates up to 94.74%, and a combination index (CI) value of less than one (CI = 0.41 for CT26 cell lines), indicating a significant synergistic therapeutic effect. Histological analysis of the tumor micro-vessel density and enzyme-linked immunosorbent assay (ELISA) tests indicated that the system increased TNF-α and IFN-β levels in serum. Therefore, this research introduces a pH-responsive polymer-based theranostic platform with great potential for immune-chemotherapeutic and anti-vascular combination therapy of CRC.

Stimulating STING for cancer therapy: Taking the extracellular route

Ten years ago, the second messenger cGAMP was discovered as the activator of the anti-cancer STING pathway. The characterization of cGAMP's paracrine action and dominant extracellular hydrolase ENPP1 cemented cGAMP as an intercellular immunotransmitter that coordinates the innate and adaptive immune systems to fight cancer. In this Perspective, I look back at a decade of discovery of extracellular cGAMP biology and drug development aiming to supply or preserve extracellular cGAMP for cancer treatment. Reviewing our understanding of the cell type-specific regulatory mechanisms of STING agonists, including their transporters and degradation enzymes, I explain on a molecular and cellular level the successes and challenges of direct STING agonists for cancer therapy. Based on what we know now, I propose new ways to stimulate the STING pathway in a manner that is not only cancer specific, but also cell type specific to fully harness the anti-cancer effect of cGAMP while avoiding collateral damage.

cGAS-STING pathway mediates activation of dendritic cell sensing of immunogenic tumors

Type I interferons (IFN-I) play pivotal roles in tumor therapy for three decades, underscoring the critical importance of maintaining the integrity of the IFN-1 signaling pathway in radiotherapy, chemotherapy, targeted therapy, and immunotherapy. However, the specific mechanism by which IFN-I contributes to these therapies, particularly in terms of activating dendritic cells (DCs), remains unclear. Based on recent studies, aberrant DNA in the cytoplasm activates the cyclic GMP-AMP synthase (cGAS)- stimulator of interferon genes (STING) signaling pathway, which in turn produces IFN-I, which is essential for antiviral and anticancer immunity. Notably, STING can also enhance anticancer immunity by promoting autophagy, inflammation, and glycolysis in an IFN-I-independent manner. These research advancements contribute to our comprehension of the distinctions between IFN-I drugs and STING agonists in the context of oncology therapy and shed light on the challenges involved in developing STING agonist drugs. Thus, we aimed to summarize the novel mechanisms underlying cGAS-STING-IFN-I signal activation in DC-mediated antigen presentation and its role in the cancer immune cycle in this review.

Nanovaccines: An effective therapeutic approach for cancer therapy

Cancer vaccines hold considerable promise for the immunotherapy of solid tumors. Nanomedicine offers several strategies for enhancing vaccine effectiveness. In particular, molecular or (sub) cellular vaccines can be delivered to the target lymphoid tissues and cells by nanocarriers and nanoplatforms to increase the potency and durability of antitumor immunity and minimize negative side effects. Nanovaccines use nanoparticles (NPs) as carriers and/or adjuvants, offering the advantages of optimal nanoscale size, high stability, ample antigen loading, high immunogenicity, tunable antigen presentation, increased retention in lymph nodes, and immunity promotion. To induce antitumor immunity, cancer vaccines rely on tumor antigens, which are administered in the form of entire cells, peptides, nucleic acids, extracellular vesicles (EVs), or cell membrane-encapsulated NPs. Ideal cancer vaccines stimulate both humoral and cellular immunity while overcoming tumor-induced immune suppression. Herein, we review the key properties of nanovaccines for cancer immunotherapy and highlight the recent advances in their development based on the structure and composition of various (including synthetic and semi (biogenic) nanocarriers. Moreover, we discuss tumor cell-derived vaccines (including those based on whole-tumor-cell components, EVs, cell membrane-encapsulated NPs, and hybrid membrane-coated NPs), nanovaccine action mechanisms, and the challenges of immunocancer therapy and their translation to clinical applications.

STING activation counters glioblastoma by vascular alteration and immune surveillance

Glioblastoma (GBM) is an aggressive brain tumor with a median survival of 15 months and has limited treatment options. Immunotherapy with checkpoint inhibitors has shown minimal efficacy in combating GBM, and large clinical trials have failed. New immunotherapy approaches and a deeper understanding of immune surveillance of GBM are needed to advance treatment options for this devastating disease. In this study, we used two preclinical models of GBM: orthotopically delivering either GBM stem cells or employing CRISPR-mediated tumorigenesis by adeno-associated virus, to establish immunologically proficient and non-inflamed tumors, respectively. After tumor development, the innate immune system was activated through long-term STING activation by a pharmacological agonist, which reduced tumor progression and prolonged survival. Recruitment and activation of cytotoxic T-cells were detected in the tumors, and T-cell specificity towards the cancer cells was observed. Interestingly, prolonged STING activation altered the tumor vasculature, inducing hypoxia and activation of VEGFR, as measured by a kinome array and VEGF expression. Combination treatment with anti-PD1 did not provide a synergistic effect, indicating that STING activation alone is sufficient to activate immune surveillance and hinder tumor development through vascular disruption. These results guide future studies to refine innate immune activation as a treatment approach for GBM, in combination with anti-VEGF to impede tumor progression and induce an immunological response against the tumor.

cGAS-STING signaling in the tumor microenvironment

The cGAS-STING signaling is an important pathway involved in the regulation of tumor microenvironment, which affects many cellular functions including immune activation. Its role in combating tumor progression is widely recognized, especially with its function in inducing innate and adaptive immune responses, on which many immunotherapies have been developed. However, a growing number of findings also suggest a diversity of its roles in shaping tumor microenvironment, including functions that promote tumor progression. Here, we summarize the functions of the cGAS-STING signaling in tumor microenvironment to maintain tumor survival and proliferation through facilitating the forming of an immunosuppressive tumor microenvironment and discuss the current advances of STING-related immunotherapies.

Tumor Vascular Destruction and cGAS-STING Activation Induced by Single Drug-Loaded Nano-Micelles for Multiple Synergistic Therapies of Cancer

Cancer and its metastasis/recurrence still threaten human health, despite various advanced treatments being employed. It is of great significance to develop simple drug formulations to enhance the efficacy and synergistic integration of various monotherapies. Herein, DMXAA, a vasodestructive agent with cGAS-STING stimulation capacity, is integrated with polyethylene glycol grafted poly (lactic-co-glycolic) acid co-polymer (PLGA-PEG), obtaining PLGA-PEG/DMXAA (PPD) nanoparticles to induce the tumor-specific vascular destruction for multiple synergistic therapies of cancer. PPD could induce the formation of blood clots in the tumor after intravenous injection, which subsequently mediate photothermal therapy and further promote the release of oxygen for enhanced radiotherapy. Meanwhile, the enhanced vascular injury can induce perfect starvation therapy of tumor. More importantly, PPD-mediated therapies could trigger potent systemic anti-tumor immunity via inducing the immunogenic death of tumor cells and activating the cGAS-STING pathway. Together with anti-PD-L1, PPD-mediated therapies could not only remove the primary tumors, but also effectively eliminate the distant tumors, metastasis, and recurrence. Therefore, the modulation of tumor composition induced by a single drug-loaded nano-micelle could be utilized to enhance the therapeutic effect of multiple treatments for synergistic and systemic antitumor response, providing a practical strategy for cancer therapy.

Targeting the stimulator of interferon genes (STING) in breast cancer

Breast cancer has a high occurrence rate globally and its treatment has demonstrated clinical efficacy with the use of systemic chemotherapy and immune checkpoint blockade. Insufficient cytotoxic T lymphocyte infiltration and the accumulation of immunosuppressive cells within tumours are the primary factors responsible for the inadequate clinical effectiveness of breast cancer treatment. The stimulator of interferon genes (STING) represents a pivotal protein in the innate immune response. Upon activation, STING triggers the activation and enhancement of innate and adaptive immune functions, resulting in therapeutic benefits for malignant tumours. The STING signalling pathway in breast cancer is influenced by various factors such as deoxyribonucleic acid damage response, tumour immune microenvironment, and mitochondrial function. The use of STING agonists is gaining momentum in breast cancer research. This review provides a comprehensive overview of the cyclic guanosine monophosphate-adenosine monophosphate synthase-STING pathway, its agonists, and the latest findings related to their application in breast cancer.

Combination of STING and TLR 7/8 Agonists as Vaccine Adjuvants for Cancer Immunotherapy

Immunostimulatory adjuvants that potently activate antigen-presenting cells and (in turn) prime cytotoxic T cells are a key component of anticancer vaccines. In this study, we investigated a multi-adjuvant approach combining a TLR 7/8 agonist (522) and a STING agonist (DMXAA) to promote enhanced antigen cross-presentation, stimulate specific antitumor T-cell responses, and provide improved anticancer efficacy. In vitro experiments using bone marrow-derived dendritic cells (BMDCs) confirmed enhanced activation with the 522-DMXAA combination based on both co-stimulatory molecule expression and pro-inflammatory cytokine secretion. The immunization of mice with vaccines comprising both 522 and DMXAA resulted in greater antitumor efficacy in B16F10 melanoma and MB49 bladder tumor models relative to mono-agonist vaccines. Flow cytometry-based analysis of immune cells from immunized mice revealed the significant activation of antigen-presenting cells, increased numbers of activated and Ag-specific CD8+ T cells in the spleen and lymph nodes, modest NK cell activation, and an overall reduction in CD206⁺ macrophages. These results were supported by an increase in the levels of IFN-γ and a reduction in IL-10 levels in the sera. Taken together, these findings demonstrate the potential of the TLR7/8 and STING agonist combination as vaccine adjuvants to activate both innate and adaptive immune responses.

A self-activating nanoized vascular disrupting agent for selective anti-tumor therapy

Vascular disrupting agents (VDAs) have great potential in antitumor therapy, while the efficiency is limited by cardiovascular toxicity. In this study, a self-activating nanoized plinabulin (poly (_l-glutamic acid) grafted Azo-Plinabulin, AzoP-NP) was constructed. The AzoP-NPs can selectively be activated to an amino derivative of plinabulin (AmP) by intrinsic tumor hypoxia, disrupting tumor vessels and amplifying hypoxia, whilst be activated by self-amplified tumor hypoxia, then selectively inhibit tumor growth. In 4T1 tumor model, the AzoP-NPs had a selective biodistribution in tumor, as the free AmP in tumors at 24 h after AzoP-NPs treatment was 18.6 fold of that after AmP treatment and significantly higher than that in other tissues. Accordingly, AzoP-NPs resulted in no obvious acute cardiovascular toxicity (plasma von Willebrand factor in PBS, AzoP-NPs and AmP group: 143.1, 184.0 and 477.6 ng/mL) and a significantly stronger tumor inhibition than AmP. And the sustained release of drug in AzoP-NPs led to a higher maximum tolerated dose (MTD) (MTD of AzoP-NPs and AmP: > 80 vs 20 mg/kg). In addition, AzoP-NPs amplified tumor hypoxic, and synergized the anti-tumor effect of Tirapazamine (TPZ), a hypoxia-activated drug in clinical trials, with an inhibition rate of 97.7% and Q value of 1.89. Therefore, our findings provide new insights into next generation VDAs and their application in tumor therapy.

Enhancing anti-tumour innate immunity by targeting the DNA damage response and pattern recognition receptors in combination with radiotherapy

Radiotherapy is one of the most effective and frequently used treatments for a wide range of cancers. In addition to its direct anti-cancer cytotoxic effects, ionising radiation can augment the anti-tumour immune response by triggering pro-inflammatory signals, DNA damage-induced immunogenic cell death and innate immune activation. Anti-tumour innate immunity can result from recruitment and stimulation of dendritic cells (DCs) which leads to tumour-specific adaptive T-cell priming and immunostimulatory cell infiltration. Conversely, radiotherapy can also induce immunosuppressive and anti-inflammatory mediators that can confer radioresistance. Targeting the DNA damage response (DDR) concomitantly with radiotherapy is an attractive strategy for overcoming radioresistance, both by enhancing the radiosensitivity of tumour relative to normal tissues, and tipping the scales in favour of an immunostimulatory tumour microenvironment. This two-pronged approach exploits genomic instability to circumvent immune evasion, targeting both hallmarks of cancer. In this review, we describe targetable DDR proteins (PARP (poly[ADP-ribose] polymerase); ATM/ATR (ataxia-telangiectasia mutated and Rad3-related), DNA-PKcs (DNA-dependent protein kinase, catalytic subunit) and Wee1 (Wee1-like protein kinase) and their potential intersections with druggable immunomodulatory signalling pathways, including nucleic acid-sensing mechanisms (Toll-like receptors (TLR); cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) and retinoic acid-inducible gene-I (RIG-I)-like receptors), and how these might be exploited to enhance radiation therapy. We summarise current preclinical advances, recent and ongoing clinical trials and the challenges of therapeutic combinations with existing treatments such as immune checkpoint inhibitors.

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.

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)...

Smart Nanogatekeepers for Tumor Theranostics

Nanoparticulate drug delivery systems (nano-DDSs) are required to reliably arrive and persistently reside at the tumor site with minimal off-target side effects for clinical theranostics. However, due to the complicated environment and high interstitial pressure in tumor tissue, they can return to the bloodstream and cause secondary side effects in normal organs. Recently, a number of nanogatekeepers have been engineered via structure-transformable/stable strategies to overcome this undesirable dilemma. The emerging structure-transformable nanogatekeepers for tumor imaging and therapy are first overviewed here, particularly for nanogatekeepers undergoing structural transformation in tumor microenvironments, cell membranes, and organelles. Thereafter, intelligent structure-stable nanogatekeepers through reversible activation and artificial individualization receptors are overviewed. Finally, the ongoing challenges and prospects of nanogatekeepers for clinical translation are briefly discussed.

Flavonoid-Inspired Vascular Disrupting Agents: Exploring Flavone-8-Acetic Acid and Derivatives in the New Century

Naturally occurring flavonoids are found as secondary metabolites in a wide number of plants exploited for both medicine and food and have long been known to be endowed with multiple biological activities, making them useful tools for the treatment of different pathologies. Due to the versatility of the scaffolds and the vast possibilities of appropriate decoration, they have also been regarded as fruitful sources of lead compounds and excellent chemical platforms for the development of bioactive synthetic compounds. Flavone-8-acetic acid (FAA) and 5,6-dimethylxanthone acetic acid (DMXAA) emerged for their antitumour potential due to the induction of cytokines and consequent rapid haemorrhagic necrosis of murine tumour vasculature, and different series of derivatives have been designed thereafter. Although the promising DMXAA failed in phase III clinical trials because of strict species-specificity, a boost in research came from the recent identification of the stimulator of interferon genes (STING), responsible for supporting tumoural innate immune responses, as a possible biological target. Consequently, in the last decade a renewal of interest for these flavonoid-based structures was noticed, and novel derivatives have been synthesised and evaluated for a deeper understanding of the molecular features needed for affecting human cells. Undoubtedly, these natural-derived molecules deserve further investigation and still appear attractive in an anticancer perspective.

STING Agonists as Cancer Therapeutics

The interrogation of intrinsic and adaptive resistance to cancer immunotherapy has identified lack of antigen presentation and type I interferon signaling as biomarkers of non-T-cell-inflamed tumors and clinical progression. A myriad of pre-clinical studies have implicated the cGAS/stimulator of interferon genes (STING) pathway, a cytosolic DNA-sensing pathway that drives activation of type I interferons and other inflammatory cytokines, in the host immune response against tumors. The STING pathway is also increasingly understood to have other anti-tumor functions such as modulation of the vasculature and augmentation of adaptive immunity via the support of tertiary lymphoid structure development. Many natural and synthetic STING agonists have entered clinical development with the first generation of intra-tumor delivered cyclic dinucleotides demonstrating safety but only modest systemic activity. The development of more potent and selective STING agonists as well as novel delivery systems that would allow for sustained inflammation in the tumor microenvironment could potentially augment response rates to current immunotherapy approaches and overcome acquired resistance. In this review, we will focus on the latest developments in STING-targeted therapies and provide an update on the clinical development and application of STING agonists administered alone, or in combination with immune checkpoint blockade or other approaches.

STINGing the Tumor Microenvironment to Promote Therapeutic Tertiary Lymphoid Structure Development

Tertiary lymphoid structures (TLS), also known as ectopic lymphoid structures (ELS) or tertiary lymphoid organs (TLO), represent a unique subset of lymphoid tissues noted for their architectural similarity to lymph nodes, but which conditionally form in peripheral tissues in a milieu of sustained inflammation. TLS serve as regional sites for induction and expansion of the host B and T cell repertoires via an operational paradigm involving mature dendritic cells (DC) and specialized endothelial cells (i.e. high endothelial venules; HEV) in a process directed by TLS-associated cytokines and chemokines. Recent clinical correlations have been reported for the presence of TLS within tumor biopsies with overall patient survival and responsiveness to interventional immunotherapy. Hence, therapeutic strategies to conditionally reinforce TLS formation within the tumor microenvironment (TME) via the targeting of DC, vascular endothelial cells (VEC) and local cytokine/chemokine profiles are actively being developed and tested in translational tumor models and early phase clinical trials. In this regard, a subset of agents that promote tumor vascular normalization (VN) have been observed to coordinately support the development of a pro-inflammatory TME, maturation of DC and VEC, local production of TLS-inducing cytokines and chemokines, and therapeutic TLS formation. This mini-review will focus on STING agonists, which were originally developed as anti-angiogenic agents, but which have recently been shown to be effective in promoting VN and TLS formation within the therapeutic TME. Future application of these drugs in combination immunotherapy approaches for greater therapeutic efficacy is further discussed.

Monotherapy and Combination Therapy Using Anti-Angiogenic Nanoagents to Fight Cancer

Anti-angiogenic therapy, targeting vascular endothelial cells (ECs) to prevent tumor growth, has been attracting increasing attention in recent years, beginning with bevacizumab (Avastin) through its Phase II/III clinical trials on solid tumors. However, these trials showed only modest clinical efficiency; moreover, anti-angiogenic therapy may induce acquired resistance to the drugs employed. Combining advanced drug delivery techniques (e.g., nanotechnology) or other therapeutic strategies (e.g., chemotherapy, radiotherapy, phototherapy, and immunotherapy) with anti-angiogenic therapy results in significantly synergistic effects and has opened a new horizon in fighting cancer. Herein, clinical difficulties in using traditional anti-angiogenic therapy are discussed. Then, several promising applications of anti-angiogenic nanoagents in monotherapies and combination therapies are highlighted. Finally, the challenges and perspectives of anti-angiogenic cancer therapy are summarized. A useful introduction to anti-angiogenic strategies, which may significantly improve therapeutic outcomes, is thus provided.

Critical role of miR-26a-5p/Wnt5a signaling in gambogic acid-induced inhibition of gastric cancer

Gastric cancer (GC) represents the fifth most human malignant disease and the third-most common cause of cancer-related death. Gambogic acid (GA) is a natural compound with a polyprenylated xanthone structure and possesses remarkable antitumor activity in a variety of cancer cells. However, the mechanism underlying the inhibitory effect of GA in GC is far from being completely understood. The goal of the present study is to investigate whether potential microRNAs are involved in antitumor effect of GA toward GC and to elucidate the possible mechanisms. We identified that miR-26a-5p was significantly increased by GA in GC cell lines and xenograft tumor. Downregulation of miR-26a-5p not only prevented GA-induced inhibition on GC cell growth, but also suppressed GA-induced apoptosis of GC cells. Informatics assay predicted that Wnt5a was regulated by miR-26a-5p and GA-induced downregulation of Wnt5a was prevented by anti-miR-26a-5p. Reporter gene assay showed that miR-26a-5p could negatively regulate Wnt5a through direct binding with 3'-UTR messenger RNA of Wnt5a. Thus, upregulation of Wnt5a exhibited the same action tendency for GA-induced GC cell growth and apoptosis as observed by downregulation of miR-26a-5p. In conclusion, these results indicated that the inhibitory effect of GA on GC was mediated by the upregulation of miR-26a-5p and downregulation of Wnt5a. Our study provided new clues for the potential therapeutic effect of GA against GC and highlighted the importance of miR-26a-5p/Wnt5a pathway in the regulation of GC development.

Challenges and Opportunities in the Clinical Development of STING Agonists for Cancer Immunotherapy

Immune checkpoint inhibitors (ICI) have revolutionised cancer therapy. However, they have been effective in only a small subset of patients and a principal mechanism underlying immune-refractoriness is a 'cold' tumour microenvironment, that is, lack of a T-cell-rich, spontaneously inflamed phenotype. As such, there is a demand to develop strategies to transform the tumour milieu of non-responsive patients to one supporting T-cell-based inflammation. The cyclic guanosine monophosphate-adenosine monophosphate synthase-stimulator of interferon genes (cGAS-STING) pathway is a fundamental regulator of innate immune sensing of cancer, with potential to enhance tumour rejection through the induction of a pro-inflammatory response dominated by Type I interferons. Recognition of these positive immune-modulatory properties has rapidly elevated the STING pathway as a putative target for immunotherapy, leading to a myriad of preclinical and clinical studies assessing natural and synthetic cyclic dinucleotides and non-nucleotidyl STING agonists. Despite pre-clinical evidence of efficacy, clinical translation has resulted into disappointingly modest efficacy. Poor pharmacokinetic and physiochemical properties of cyclic dinucleotides are key barriers to the development of STING agonists, most of which require intra-tumoral dosing. Development of systemically administered non-nucleotidyl STING agonists, or conjugation with liposomes, polymers and hydrogels may overcome pharmacokinetic limitations and improve drug delivery. In this review, we summarise the body of evidence supporting a synergistic role of STING agonists with currently approved ICI therapies and discuss whether, despite the numerous obstacles encountered to date, the clinical development of STING agonist as novel anti-cancer therapeutics may still hold the promise of broadening the reach of cancer immunotherapy.

Bacteria-triggered tumor-specific thrombosis to enable potent photothermal immunotherapy of cancer

We discovered that attenuated Salmonella after intravenous injection would proliferate within various types of solid tumors but show rapid clearance in normal organs, without rendering notable toxicity. Bacteria-induced inflammation would trigger thrombosis in the infected tumors by destroying tumor blood vessels. Six types of tested tumors would all turn into darkened color with strong near-infrared absorbance, as observed by photoacoustic imaging. Under laser irradiation, those bacterial-infected tumors would be effectively ablated. Because of the immune-stimulation function, such bacteria-based photothermal therapy (PTT) would subsequently trigger antitumor immune responses, which could be further enhanced by immune checkpoint blockade to effectively suppress the growth of abscopal tumors. A robust immune memory effect to reject rechallenged tumors is also observed after bacteria-based PTT. Our work demonstrates that bacteria by themselves could act as a tumor-specific PTT agent to enable photoimmunotherapy cancer therapy to inhibit tumor metastasis and recurrence.

Trial watch: STING agonists in cancer therapy

Stimulator of interferon response cGAMP interactor 1 (STING1, best known as STING) is an endoplasmic reticulum-sessile protein that serves as a signaling hub, receiving input from several pattern recognition receptors, most of which sense ectopic DNA species in the cytosol. In particular, STING ensures the production of type I interferon (IFN) in response to invading DNA viruses, bacterial pathogens, as well as DNA leaking from mitochondria or the nucleus (e.g., in cells exposed to chemotherapy or radiotherapy). As a type I IFN is critical for the initiation of anticancer immune responses, the pharmaceutical industry has generated molecules that directly activate STING for use in oncological indications. Such STING agonists are being tested in clinical trials with the rationale of activating STING in tumor cells or tumor-infiltrating immune cells (including dendritic cells) to elicit immunostimulatory effects, alone or in combination with a range of established chemotherapeutic and immunotherapeutic regimens. In this Trial Watch, we discuss preclinical evidence and accumulating clinical experience shaping the design of Phase I and Phase II trials that evaluate the safety and preliminary efficacy of STING agonists in cancer patients.

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.

Discovery of triazoloquinoxaline as novel STING agonists via structure-based virtual screening

Stimulator of interferon genes (STING) is an endoplasmic reticulum adaptor facilitating innate immune signaling. Activation of STING leads to expression of interferons (IFNs) and pro-inflammatory cytokines which is associated with antiviral and antitumor responses. It is imperative to discovery potent compounds that precisely modulate STING. Herein, we describe the discovery of triazoloquinoxaline 1a as a novel STING agonist via Structure-based Virtual Screening. Specifically, biochemical and cell-based assays suggested that 1a stimulated concentration-dependently mRNA expression of IFNβ, CXCL-10 and IL-6. Furthermore, 1a significantly induced phosphorylation of STING, TANK-binding kinases1 (TBK1) and interferon regulatory factor 3 (IRF3), suggesting the activation of STING and its downstream TBK1-IRF3 signaling axis. In addition, 1a activated secretion of secreted alkaline phosphatase (SEAP) in dose-dependent manner and EC₅₀ was 16.77 ± 3.814 μM, which is comparable with EC₅₀ of 2'3'-cGAMP (9.212 ± 2.229 μM). These studies revealed that 1a is a promising STING agonist possessing the potential to be further developed for antiviral and antitumor treatment.

Co-Administration of Vadimezan and Recombinant Coagulase-NGR Inhibits Growth of Melanoma Tumor in Mice

Purpose: Tumor vascular targeting appeared as an appealing approach to fight cancer, though, the results from the clinical trials and drugs in the market were proved otherwise. The promise of anti-angiogenic therapy as the leading tumor vascular targeting strategy was negatively affected with the discovery that tumor vascularization can occur non-angiogenic mechanisms such as co-option. An additional strategy is induction of tumor vascular infarction and ischemia. Methods: Such that we used truncated coagulase (tCoa) coupled to tumor endothelial targeting moieties to produce tCoa-NGR fusion proteins. We showed that tCoa-NGR can bypass coagulation cascade to induce selective vascular thrombosis and infarction of mild and highly proliferative solid tumors in mice. Moreover, combination therapy can be used to improve the potential of cancer vascular targeting modalities. Herein, we report combination of tCoa-NGR with vascular disrupting agent (VDA), vadimezan. Results: Our results show that synergistic work of these two agents can significantly suppress growth of B16-F10 melanoma tumors in C57/BL6 mice. Conclusion: For the first time, we used the simultaneous benefits of two strategies for inducing thrombosis and destruction of tumor vasculature as spatial co-operation. The tCoa-NGR induce thrombosis which reduces blood flow in the peripheral tumor region. And combined with the action of DMXAA, which target inner tumor mass, growth and proliferation of melanoma tumors can be significantly suppressed.

Anti-vascular nano agents: a promising approach for cancer treatment

Anti-vascular agents (AVAs) are a class of promising therapeutic agents with tumor vasculature targeting properties, which can be divided into two types: anti-angiogenic agents (AAAs, inhibit angiogenesis factors) and vascular disrupting agents (VDAs, disrupt established tumor vasculature). AVAs exhibit an enhanced anti-cancer effect by cutting off the oxygen and nutrition supplement channels of tumors. However, the intrinsic drawbacks, such as poor hydrophilicity, undesirable membrane permeability and inferior tumor targeting ability, discount their anti-vascular efficacy. Fortunately, the development of nanotechnology has brought an opportunity for efficient delivery of AVAs to tumour sites with great therapeutic efficacy. The works summarized in this review will provide an understanding of recent advances of anti-vascular nano agents (AVNAs) with a goal to define the mechanism of anti-vascular-based cancer therapy and discuss the challenges and opportunities of AVNAs for clinical translation.

Mitochondrial Integrity Regulated by Lipid Metabolism Is a Cell-Intrinsic Checkpoint for Treg Suppressive Function

Regulatory T cells (Tregs) subdue immune responses. Central to Treg activation are changes in lipid metabolism that support their survival and function. Fatty acid binding proteins (FABPs) are a family of lipid chaperones required to facilitate uptake and intracellular lipid trafficking. One family member, FABP5, is expressed in T cells, but its function remains unclear. We show that in Tregs, genetic or pharmacologic inhibition of FABP5 function causes mitochondrial changes underscored by decreased OXPHOS, impaired lipid metabolism, and loss of cristae structure. FABP5 inhibition in Tregs triggers mtDNA release and consequent cGAS-STING-dependent type I IFN signaling, which induces heightened production of the regulatory cytokine IL-10 and promotes Treg suppressive activity. We find evidence of this pathway, along with correlative mitochondrial changes in tumor infiltrating Tregs, which may underlie enhanced immunosuppression in the tumor microenvironment. Together, our data reveal that FABP5 is a gatekeeper of mitochondrial integrity that modulates Treg function.

STING pathway agonism as a cancer therapeutic

The fact that a subset of human cancers showed evidence for a spontaneous adaptive immune response as reflected by the T cell-inflamed tumor microenvironment phenotype led to the search for candidate innate immune pathways that might be driving such endogenous responses. Preclinical studies indicated a major role for the host STING pathway, a cytosolic DNA sensing pathway, as a proximal event required for optimal type I interferon production, dendritic cell activation, and priming of CD8⁺ T cells against tumor-associated antigens. STING agonists are therefore being developed as a novel cancer therapeutic, and a greater understanding of STING pathway regulation is leading to a broadened list of candidate immune regulatory targets. Early phase clinical trials of intratumoral STING agonists are already showing promise, alone and in combination with checkpoint blockade. Further advancement will derive from a deeper understanding of STING pathway biology as well as mechanisms of response vs resistance in individual cancer patients.

Platelet-Mimicking Biotaxis Targeting Vasculature-Disrupted Tumors for Cascade Amplification of Hypoxia-Sensitive Therapy

Tumorous vasculature plays key roles in sustaining tumor growth. Vascular disruption is accompanied by internal coagulation along with platelet recruitment and the resulting suppression of oxygen supply. We intend to artificially create this physiological process to establish the mutual feedback between vascular disruption and platelet-mimicking biotaxis for the cascade amplification of hypoxia-dependent therapy. To prove this concept, mesoporous silica nanoparticles are co-loaded with a hypoxia-activated prodrug (HAP) and a vessel-disruptive agent and then coated with platelet membranes. Upon entering into tumors, our nanotherapeutic can disrupt local vasculature for tumor inhibition. This platelet membrane-coated nanoplatform shares the hemorrhage-tropic function with parental platelets and can be persistently recruited by the vasculature-disrupted tumors. In this way, the intratumoral vascular disruption and tumor targeting are biologically interdependent and mutually reinforced. Relying on this mutual feedback, tumorous hypoxia was largely promoted by more than 20-fold, accounting for the effective recovery of the HAP's cytotoxicity. Consequently, our bioinspired nanodesign has demonstrated highly specific and effective antitumor potency via the biologically driven cooperation among intratumoral vascular disruption, platelet-mimicking biotaxis, cascade hypoxia amplification, and hypoxia-sensitive chemotherapy. This study offers a paradigm of correlating the therapeutic design with the physiologically occurring events to achieve better therapy performance.

Synthetic Chiral Derivatives of Xanthones: Biological Activities and Enantioselectivity Studies

Many naturally occurring xanthones are chiral and present a wide range of biological and pharmacological activities. Some of them have been exhaustively studied and subsequently, obtained by synthesis. In order to obtain libraries of compounds for structure activity relationship (SAR) studies as well as to improve the biological activity, new bioactive analogues and derivatives inspired in natural prototypes were synthetized. Bioactive natural xanthones compromise a large structural multiplicity of compounds, including a diversity of chiral derivatives. Thus, recently an exponential interest in synthetic chiral derivatives of xanthones (CDXs) has been witnessed. The synthetic methodologies can afford structures that otherwise could not be reached within the natural products for biological activity and SAR studies. Another reason that justifies this trend is that both enantiomers can be obtained by using appropriate synthetic pathways, allowing the possibility to perform enantioselectivity studies. In this work, a literature review of synthetic CDXs is presented. The structures, the approaches used for their synthesis and the biological activities are described, emphasizing the enantioselectivity studies.

Carboxyxanthones: Bioactive Agents and Molecular Scaffold for Synthesis of Analogues and Derivatives

Xanthones represent a structurally diverse group of compounds with a broad range of biological and pharmacological activities, depending on the nature and position of various substituents in the dibenzo-γ-pyrone scaffold. Among the large number of natural and synthetic xanthone derivatives, carboxyxanthones are very interesting bioactive compounds as well as important chemical substrates for molecular modifications to obtain new derivatives. A remarkable example is 5,6-dimethylxanthone-4-acetic acid (DMXAA), a simple carboxyxanthone derivative, originally developed as an anti-tumor agent and the first of its class to enter phase III clinical trials. From DMXAA new bioactive analogues and derivatives were also described. In this review, a literature survey covering the report on carboxyxanthone derivatives is presented, emphasizing their biological activities as well as their application as suitable building blocks to obtain new bioactive derivatives. The data assembled in this review intends to highlight the therapeutic potential of carboxyxanthone derivatives and guide the design for new bioactive xanthone derivatives.

Synthesis of xanthone derivatives and anti-hepatocellular carcinoma potency evaluation: induced apoptosis

Twenty-one xanthone derivatives (XDs) were synthesized by a microwave-assisted technique. Their in vitro inhibition potency against the growth of four cancer cell lines was evaluated. XD-1 ∼ [6,9,10-trihydroxy-3,3-dimethyl-5-(2-methylbut-3-en-2-yl)-3H,7H-pyrano[2,3-c]xanthen-7-one] was confirmed as the most active agent against HepG2 cell line growth with IC₅₀ of 18.6 ± 2.31 μM. Apoptosis analysis indicated different contributions of early/late apoptosis and necrosis to cell death for XD-1. XD-1 arrested HepG2 cells on the G0/G1 phase, as indicated by the decreased expressions of cyclin D and CDK2 and the increased expressions of p21. Western blot implied that XD-1 regulated p53/MDM2 to a better healthier state. Moreover, XD-1-induced cell apoptosis was mitochondrion-mediated, as evidenced by caspase activation and involved the PI3K/AKT/mTOR signaling pathway. All the evidence supports that XD-1 is a significant anti-cancer agent for HCC.

Twenty-one xanthone derivatives (XDs) were synthesized by a microwave-assisted technique.

Incorporation of nitric oxide donor into 1,3-dioxyxanthones leads to synergistic anticancer activity

Fifty 1,3-dioxyxanthone nitrates (4a ∼ i-n, n = 1-6) were designed and synthesized based on molecular similarity strategy. Incorporation of nitrate into 1,3-dioxyxanthones with electron-donating groups at 6-8 position brought about synergistic anticancer effect. Among them, compound 4g-4 was confirmed the most active agent against HepG-2 cells growth with an IC₅₀ of 0.33 ± 0.06 μM. It dose-dependently increased intramolecular NO levels. This activity was attenuated by either NO scavenger PTIO or mitochondrial aldehyde dehydrogenase (mtADH) inhibitor PCDA. Apoptosis analysis indicated different contributions of early/late apoptosis and necrosis to cell death for different dose of 4g-4. 4g-4 arrested more cells on S phase. Results from Western Blot implied that 4g-4 regulated p53/MDM2 to promote cancer cell apoptosis. All the evidences support that 4g-4 is a promising anti-cancer agent.

A tissue factor-cascade-targeted strategy to tumor vasculature: a combination of EGFP-EGF1 conjugation nanoparticles with photodynamic therapy

Tumor requires tumor vasculature to supply oxygen and nutrients so as to support its continued growth, as well as provide a main route for metastatic spread. In this study, a TF-cascade-targeted strategy aiming to disrupt tumor blood vessels was developed by combination of TF-targeted HMME-loaded drug delivery system and PDT. PDT is a promising new modality in the treatment of cancers, which employs the interaction between a tumor-localizing photosensitizer and light of an appropriate wavelength to bring about ROS-induced cell death. In vitro results showed that protein EGFP-EGF1modification could significantly contribute to the uptake of nanoparticles by TF over-expressed BCECs. In vivo multispectral fluorescent imaging, the EGFP-EGF1 conjugated nanoparticles showed significantly higher accumulation in tumor tissues than non-conjugated ones. Tumor tissue slides further presented that EGFP-EGF1 conjugated nanoparticles showed significantly higher accumulation in tumor vasculature than non-conjugated ones. In vitro study demonstrated that PDT increased TF expression of BCECs. In vivo imaging, ex vivo imaging and tumor tissue slides showed that PDT further contribute EGFP-EGF1-NP accumulation in tumor. These promising results indicated that PDT enhanced EGFP-EGF1modified PEG-PLGA nanoparticle accumulation in tumor vaculature. Considering that EGFP-EGF1 conjugation enhanced nanoparticles uptake by TF over-expressed endothelium and PDT increased endothelium TF expression. We conclude that PDT triggered a TF cascade targeted effect. A combination of both EGFP-EGF1 modification and PDT provided a positive feed-back target effect to tumor vessels and might have a great potential for tumor therapy.

Improved Evaluation of Antivascular Cancer Therapy Using Constrained Tracer-Kinetic Modeling for Multiagent Dynamic Contrast-Enhanced MRI

Dynamic contrast-enhanced MRI (DCE-MRI) is a promising technique for assessing the response of tumor vasculature to antivascular therapies. Multiagent DCE-MRI employs a combination of low and high molecular weight contrast agents, which potentially improves the accuracy of estimation of tumor hemodynamic and vascular permeability parameters. In this study, we used multiagent DCE-MRI to assess changes in tumor hemodynamics and vascular permeability after vascular-disrupting therapy. Multiagent DCE-MRI (sequential injection of G5 dendrimer, G2 dendrimer, and Gd-DOTA) was performed in tumor-bearing mice before, 2 and 24 hours after treatment with vascular disrupting agent DMXAA or placebo. Constrained DCE-MRI gamma capillary transit time modeling was used to estimate flow F, blood volume fraction v_b, mean capillary transit time t_c, bolus arrival time t_d, extracellular extravascular fraction v_e, vascular heterogeneity index α^-1 (all identical between agents) and extraction fraction E (reflective of permeability), and transfer constant K^trans (both agent-specific) in perfused pixels. F, v_b, and α^-1 decreased at both time points after DMXAA, whereas t_c increased. E (G2 and G5) showed an initial increase, after which, both parameters restored. K^trans (G2 and Gd-DOTA) decreased at both time points after treatment. In the control, placebo-treated animals, only F, t_c, and K^trans Gd-DOTA showed significant changes. Histologic perfused tumor fraction was significantly lower in DMXAA-treated versus control animals. Our results show how multiagent tracer-kinetic modeling can accurately determine the effects of vascular-disrupting therapy by separating simultaneous changes in tumor hemodynamics and vascular permeability.Significance: These findings describe a new approach to measure separately the effects of antivascular therapy on tumor hemodynamics and vascular permeability, which could help more rapidly and accurately assess the efficacy of experimental therapy of this class. Cancer Res; 78(6); 1561-70. ©2018 AACR.

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.

TNF alpha signaling is associated with therapeutic responsiveness to vascular disrupting agents in endocrine tumors

ASA404 (Vadimezan) belongs to a class of agents with disrupting properties against tumor vasculature, which is partly mediated by TNFα-signaling. Preclinical and early clinical studies have indicated promising results for ASA404, while extended clinical trials performed poorly. Our aim was to investigate the potential therapeutic applicability of ASA404 against endocrine tumors. Moreover, as the reason for the unpredictable clinical anti-tumor activity of ASA 404 remained uncertain in previous studies, we compared two tumor models of endocrine origin with different responses to ASA404 treatment. Specifically, we determined anti-tumoral effects in preclinical models of neuroendocrine tumors of the gastroenteropancreatic system (BON) and adrenocortical cancer (NCI-H295R) in vitro and in xenograft models in vivo. Upon treatment of tumor bearing mice significant anti-tumoral effects, an increase in TNFα as well as activation of TNFα-specific downstream signaling were evident in the BON tumor model while no comparable effects were detectable for NCI-H295R. We identified TNFAIP3/A20, a key molecule of an inhibitory feedback-loop downstream of TNF-receptor 1, CD40, Toll-like receptors, NOD-like receptors and the interleukin-1 receptor signaling cascades, as overexpressed in the adrenocortical carcinoma tumor model. Subsequent analyses of clinical patient samples confirmed a correlation between tumor TNFAIP3 expression levels and overall survival in patients with ACC. Taken together our findings provide evidence that modulation of TNFα-signaling could be of relevance both for the clinical course of ACC patients and as a marker of treatment response.

Xanthones of Lichen Source: A 2016 Update

An update of xanthones encountered in lichens is proposed as more than 20 new xanthones have been described since the publication of the compendium of lichen metabolites by Huneck and Yoshimura in 1996. The last decades witnessed major advances regarding the elucidation of biosynthetic schemes leading to these fascinating compounds, accounting for the unique substitution patterns of a very vast majority of lichen xanthones. Besides a comprehensive analysis of the structures of xanthones described in lichens, their bioactivities and the emerging analytical strategies used to pinpoint them within lichens are presented here together with physico-chemical properties (including NMR data) as reported since 1996.

A cooperative polymeric platform for tumor-targeted drug delivery

A tumor-targeted drug delivery system with small-molecule vascular disrupting agents inducing coagulation environment inside tumor and coagulation-targeted nanoparticles accumulating there.

In the pursuit of effective treatments for cancer, an emerging strategy is “active targeting”, where nanoparticles are decorated with targeting ligands able to recognize and bind specific receptors overexpressed by tumor cells or tumor vasculature so that a greater fraction of the administered drugs are selectively trafficked to tumor sites. However, the implementation of this strategy has faced a major obstacle. The interpatient, inter- and intra-tumoral heterogeneity in receptor expression can pose challenges for the design of clinical trials and result in the paucity of targetable receptors within a tumor, which limits the effectiveness of “active targeting” strategy in cancer treatment. Here we report a cooperative drug delivery platform that overcomes the heterogeneity barrier unique to solid tumors. The cooperative platform comprises a coagulation-inducing agent and coagulation-targeted polymeric nanoparticles. As a typical small-molecule vascular disrupting agent (VDA), DMXAA can create a unique artificial coagulation environment with additional binding sites in a solid tumor by locally activating a coagulation cascade. Coagulation-targeted cisplatin-loaded nanoparticles, which are surface-decorated with a substrate of activated blood coagulation factor XIII, can selectively accumulate in the solid tumor by homing to the VDA-induced artificial coagulation environment through transglutamination. In vivo studies show that the cooperative tumor-selective platform recruits up to 7.5-fold increases in therapeutic cargos to the tumors and decreases tumor burden with low systemic toxicity as compared with non-cooperative controls. These indicate that the use of coagulation-targeted nanoparticles, in conjunction with free small-molecule VDAs, may be a valuable strategy for improving standard chemotherapy.

Monitoring Vascular Disrupting Therapy in a Rabbit Liver Tumor Model: Relationship between Tumor Perfusion Parameters at IVIM Diffusion-weighted MR Imaging and Those at Dynamic Contrast-enhanced MR Imaging

PURPOSE

To investigate whether perfusion-related intravoxel incoherent motion (IVIM) diffusion-weighted (DW) magnetic resonance (MR) imaging parameters correlate with dynamic contrast material-enhanced MR imaging parameters in between-subject and/or within-subject longitudinal settings for monitoring the therapeutic effects of a vascular disrupting agent (VDA) (CKD-516) in rabbit VX2 liver tumors.

MATERIALS AND METHODS

With institutional Animal Care and Use Committee approval, 21 VX2 liver tumor-bearing rabbits (treated, n = 15; control, n = 6) underwent IVIM DW imaging with 12 b values (0-800 sec/mm(2)) and dynamic contrast-enhanced MR imaging performed before (baseline) CKD-516 administration and 4 hours, 24 hours, and 7 days after administration. Perfusion-related IVIM DW imaging parameters of the tumors, including the pseudodiffusion coefficient (D*) and perfusion fraction (f), as well as dynamic contrast-enhanced MR imaging parameters, including the volume transfer coefficient (K(trans)) and initial area under the gadolinium concentration-time curve until 60 seconds (iAUC), were measured. IVIM DW imaging parameters were correlated with dynamic contrast-enhanced MR imaging parameters by using Pearson correlation analysis between subjects at each given time and by using a linear mixed model for within-subject longitudinal data.

RESULTS

In the treated group, D*, f, K(trans), and iAUC significantly decreased (-40.7% to -26.3%) at 4-hour follow-up compared with these values in the control group (-6.9% to +5.9%) (P < .05). For longitudinal monitoring of CKD-516 treatment, D* and f showed significant positive correlations with K(trans) and iAUC (P = .004 and P = .02; P < .001 and P = .006, respectively), while no significant correlations were observed between IVIM DW imaging and dynamic contrast-enhanced MR imaging parameters between subjects at any given time (P > .05).

CONCLUSION

In a rabbit tumor model, perfusion parameters serially quantified with IVIM DW imaging can be used as alternatives to dynamic contrast-enhanced MR imaging parameters in reflecting the dynamic changes in tumor perfusion during the within-subject longitudinal monitoring of VDA treatment.

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.

Treatment with a vascular disrupting agent does not increase recruitment of indium labelled human endothelial outgrowth cells in an experimental tumour model

Background

The effect of vascular disrupting agents in tumour therapy depends on both the immediate vascular shutdown, and on the following re-vascularization of the tumour. The aim of this study was to use a tumour model to investigate whether endothelial outgrowth cells (EOCs) influenced the short term treatment efficiency of combretastatin A-4 disodium phosphate (CA4P) and 5,6-dimethylxanthenone-4-acetic acid (DMXAA) by increasing EOC tumour recruitment.

Methods

In order to visualize the recruitment of EOCs to the tumours, umbilical cord blood derived human EOCs were labelled with ¹¹¹Indium-tropolone in a dose of 0.37 MBq pr 3×10⁶ cells and were injected intravenously into mice carrying a C3H mammary carcinoma on their right rear foot. DMXAA and CA4P in different concentrations and at different exposure times were used to create a hypoxic environment in the C3H mammary carcinoma in the mice. Three different mice strains with various degrees of functional immune system were used to study the homing capability of EOCs.

Results

Our data showed that approximately 4% of the total injected radioactive dose per gram of tissue was found in the tumour after treatment with CA4P and DMXAA. Regardless of the concentration and the treatment duration, CA4P did not increase EOC recruitment to the tumour in comparison to EOC recruitment in control tumours in any of the 3 mice strains studied.

Conclusion

Our data showed that regardless of the grade of the immune system, ranging from a fully working to a fully compromised immune system, treatment with CA4P did not increase recruitment of xenotransplanted EOCs to tumour tissue.

Synthesis and anticancer activities of 3-arylflavone-8-acetic acid derivatives

This paper describes the synthesis and the antiproliferative activities of compounds 9a-r, 3-aryl analogs of flavone-8-acetic acid that bear diverse substituents on the benzene rings at the 2- and 3-positions of the flavone nucleus. Their direct and indirect cytotoxicities were evaluated against HT-29 human colon adenocarcinoma cell lines, A549 lung adenocarcinoma cell lines and Human Peripheral Blood Mononuclear Cells (HPBMCs). The results indicate that most of the compounds bearing electron-withdrawing substituents (9b-m) exhibited moderate direct cytotoxicities. And compounds 9e and 9i showed comparable indirect cytotoxicities with 5, 6-dimethylxanthenone-4-acetic acid (DMXAA), and low direct cytotoxicities toward HPBMCs. Interestingly, the compounds 9n-r bearing methoxy groups at the 2- or 3-position of the flavone nucleus exhibited higher indirect cytotoxicities against A549 cell lines than DMXAA, and lower cytotoxicities against HPBMCs. In addition, compounds 9p-r were found to be able to induce tumor necrosis factor α (TNF-α) production in HPBMCs.

Preliminary Evidence That High-Dose Vitamin C has a Vascular Disrupting Action in Mice

High intravenous doses of vitamin C (ascorbic acid) have been reported to benefit cancer patients, but the data are controversial and there is incomplete knowledge of what physiological mechanisms might be involved in any response. Vitamin C is taken up efficiently by cells expressing SVCT2 transporters and since vascular endothelial cells express SVCT2, we explored the hypothesis that administration of high-dose vitamin C (up to 5 g/kg) to mice might affect vascular endothelial function. A single administration of vitamin C to mice induced time- and dose-dependent increases in plasma concentrations of the serotonin metabolite 5-hydroxyindole acetic acid (5-HIAA), a marker for vascular disrupting effects. Responses were comparable to those for the tumor vascular disrupting agents, vadimezan and fosbretabulin. High-dose vitamin C administration decreased tumor serotonin concentrations, consistent with the release of serotonin from platelets and its metabolism to 5-HIAA. High-dose vitamin C also significantly increased the degree of hemorrhagic necrosis in tumors removed after 24 h, and significantly decreased tumor volume after 2 days. However, the effect on tumor growth was temporary. The results support the concept that vitamin C at high dose increases endothelial permeability, allowing platelets to escape and release serotonin. Plasma 5-HIAA concentrations could provide a pharmacodynamic biomarker for vitamin C effects in clinical studies.