Parallel discovery of selective and dual inhibitors of tryptophan dioxygenases IDO1 and TDO2 with a newly-modified enzymatic assay.

The expression of tryptophan catabolising enzyme indoleamine 2,3-dioxygenase 1 (IDO1) or tryptophan 2,3-dioxygenase 2 (TDO2) in cancers is associated with suppressed immunity and poor patient prognosis. Results from human clinical trials of IDO1 inhibitors have been disappointing. There is now a strong interest in the development of TDO2-selective or dual IDO1/TDO2 inhibitors that may surpass IDO1 inhibitors by providing broader efficacy and blocking constitutively-expressed hepatic TDO2. To expedite the discovery of novel TDO2-specific and dual inhibitors, an assay that enabled the efficient and accurate measurement of the inhibitory activity of compounds against both IDO1 and TDO2 enzymes, concurrently in the same experiment was established to screen 5,682 compounds that included the National Cancer Institute Diversity set 5, for inhibition of IDO1 and TDO2 activity. This screen identified 82 compounds that inhibited either IDO1, TDO2 or both enzymes > 50% at 20 µM. Thirty Pan Assay Interference compounds were removed from the list and the IC50 of the remaining 52 compounds against IDO1 and TDO2 was subsequently determined using the newly-developed concurrent assay. Ten compounds were confirmed as dual IDO1/TDO2 inhibitors having IC50 values under 50 µM against both enzymes and within 2-fold of each other. Six compounds with IC50 values between 1.39 and 8.41 µM were identified as potential TDO2-selective leads. The use of this concurrent protocol is anticipated to expedite the discovery of novel leads for dual and selective inhibitors against IDO1 and or TDO2 and speed the evaluation of novel analogues that will ensue.

Imprinted and ancient gene: a potential mediator of cancer cell survival during tryptophan deprivation.

BACKGROUND: Depletion of tryptophan and the accumulation of tryptophan metabolites mediated by the immunosuppressive enzyme indoleamine 2,3-dioxygenase 1 (IDO1), trigger immune cells to undergo apoptosis. However, cancer cells in the same microenvironment appear not to be affected. Mechanisms whereby cancer cells resist accelerated tryptophan degradation are not completely understood. We hypothesize that cancer cells co-opt IMPACT (the product of IMPrinted and AnCienT gene), to withstand periods of tryptophan deficiency. METHODS: A range of bioinformatic techniques including correlation and gene set variation analyses was applied to genomic datasets of cancer (The Cancer Genome Atlas) and normal (Genotype Tissue Expression Project) tissues to investigate IMPACT's role in cancer. Survival of IMPACT-overexpressing GL261 glioma cells and their wild type counterparts cultured in low tryptophan media was assessed using fluorescence microscopy and MTT bio-reduction assay. Expression of the Integrated Stress Response proteins was measured using Western blotting. RESULTS: We found IMPACT to be upregulated and frequently amplified in a broad range of clinical cancers relative to their non-malignant tissue counterparts. In a subset of clinical cancers, high IMPACT expression associated with decreased activity of pathways and genes involved in stress response and with increased activity of translational regulation such as the mTOR pathway. Experimental studies using the GL261 glioma line showed that cells engineered to overexpress IMPACT, gained a survival advantage over wild-type lines when cultured under limiting tryptophan concentrations. No significant difference in the expression of proteins in the Integrated Stress Response pathway was detected in tryptophan-deprived GL261 IMPACT-overexpressors compared to that in wild-type cells. IMPACT-overexpressing GL261 cells but not their wild-type counterparts, showed marked enlargement of their nuclei and cytoplasmic area when stressed by tryptophan deprivation. CONCLUSIONS: The bioinformatics data together with our laboratory studies, support the hypothesis that IMPACT mediates a protective mechanism allowing cancer cells to overcome microenvironmental stresses such as tryptophan deficiency.

Phagocytosis of Extracellular Vesicles Extruded From the Placenta by Ovarian Cancer Cells Inhibits Growth of the Cancer Cells.

OBJECTIVE: Ovarian cancer is a common gynecological cancer, and parity is negatively associated with the incidence of this disease. This negative association is hypothesized to be due in part to shifting the balance of estrogen and progesterone toward more progesterone and reduced ovulation during pregnancy. However, studies suggested that parity is also associated with estrogen-independent gynecological cancers suggesting balance of hormones may not be the only protective factor. Extracellular vesicles (EVs) play an important role in cell-to-cell communication in physiological and pathological conditions. During pregnancy, large amounts of EVs are extruded from the placenta, and they seem to be involved in the remarkable adaptation of a woman's body to normal pregnancy. We hypothesized that EVs extruded from the placenta play a role in this protective effect. METHODS: Placental EVs were collected from first-trimester placentae, and cancer cell EVs were isolated from ovarian cancer cells. The EVs were exposed to ovarian cancer cells for 48 hours. The proliferation of cancer cells and the cell cycle were measured. In addition, phagocytosis of deported placental EVs by cancer cells was also measured. RESULTS: The proliferation of cancer cells was significantly reduced by treatment with placental EVs (P = 0.001, analysis of variance), but not EVs from monocytes (P = 0.195), compared with untreated cancer cells. Furthermore, placental EVs also prevented the proliferation of cancer cells induced by cancer cell-derived EVs (P = 0.001). This inhibition of proliferation of ovarian cancer cells was partially due to phagocytosis of placental EVs by cancer cells. Phagocytosis of placental EVs delayed progression through the cell cycle. Calreticulin, a phagocytic "eat me" signal carried by placental EVs significantly inhibited ovarian cancer growth (P = 0.001). CONCLUSIONS: Our data demonstrated that EVs extruded from the placenta prevented ovarian cancer cell growth by a mechanism that involved delaying progression of the cell cycle after phagocytosis of the EVs.

Formation of fluorophores from the kynurenine pathway metabolite N-formylkynurenine and cyclic amines involves transamidation and carbon-carbon bond formation at the 2-position of the amine.

BACKGROUND: Tryptophan catabolism along the kynurenine pathway is associated with a number of pathologies including cataract formation and cancer. Whilst the chemical reactions of kynurenine are well studied, less is known about the reactivity of its precursor N-formylkynurenine (NFK). We previously reported the generation of a strong fluorophore in an aqueous reaction of NFK with piperidine, and herein we describe its structure and mechanism of formation. METHODS: Compounds were identified using NMR, mass and UV spectroscopic techniques. The products from the reaction of amines with amino acids were quantified using HPLC-MS. RESULTS: The novel fluorophore was identified as a tetrahydroquinolone adduct (PIP-THQ), where piperidine is N-formylated and attached at its 2-position to the quinolone. NFK is initially deaminated to generate an unsaturated enone, which forms an adduct with piperidine and is subsequently converted into the fluorophore. Testing of a variety of other secondary amines showed that only cyclic amines unsubstituted at both positions adjacent to nitrogen could form fluorophores efficiently. The amino acids tryptophan and kynurenine, which lack the formamide group do not form such fluorophores. CONCLUSIONS: NFK forms fluorophores in a not previously published reaction with cyclic amines. GENERAL SIGNIFICANCE: Our study is the first to provide evidence for concurrent transamidation and substitution at the 2-position of a cyclic amine occurring under moderately-heated aqueous conditions with no added catalysts. The high reactivity of NFK demonstrated here could result in formation of biologically relevant metabolites yet to be characterised.

The chemotherapeutic agent DMXAA potently and specifically activates the TBK1-IRF-3 signaling axis.

Vascular disrupting agents (VDAs) represent a novel approach to the treatment of cancer, resulting in the collapse of tumor vasculature and tumor death. 5,6-dimethylxanthenone-4-acetic acid (DMXAA) is a VDA currently in advanced phase II clinical trials, yet its precise mechanism of action is unknown despite extensive preclinical and clinical investigations. Our data demonstrate that DMXAA is a novel and specific activator of the TANK-binding kinase 1 (TBK1)-interferon (IFN) regulatory factor 3 (IRF-3) signaling pathway. DMXAA treatment of primary mouse macrophages resulted in robust IRF-3 activation and approximately 750-fold increase in IFN-beta mRNA, and in contrast to the potent Toll-like receptor 4 (TLR4) agonist lipopolysaccharide (LPS), signaling was independent of mitogen-activated protein kinase (MAPK) activation and elicited minimal nuclear factor kappaB-dependent gene expression. DMXAA-induced signaling was critically dependent on the IRF-3 kinase, TBK1, and IRF-3 but was myeloid differentiation factor 88-, Toll-interleukin 1 receptor domain-containing adaptor inducing IFN-beta-, IFN promoter-stimulator 1-, and inhibitor of kappaB kinase-independent, thus excluding all known TLRs and cytosolic helicase receptors. DMXAA pretreatment of mouse macrophages induced a state of tolerance to LPS and vice versa. In contrast to LPS stimulation, DMXAA-induced IRF-3 dimerization and IFN-beta expression were inhibited by salicylic acid. These findings detail a novel pathway for TBK1-mediated IRF-3 activation and provide new insights into the mechanism of this new class of chemotherapeutic drugs.

Discovery and characterisation of hydrazines as inhibitors of the immune suppressive enzyme, indoleamine 2,3-dioxygenase 1 (IDO1).

Screening of a fragment library identified 2-hydrazinobenzothiazole as a potent inhibitor of indoleamine 2,3-dioxygenase 1 (IDO1), an enzyme expressed by tumours that suppresses the immune system. Spectroscopic studies indicated that 2-hydrazinobenzothiazole interacted with the IDO1 haem and in silico docking predicted that the interaction was through hydrazine. Subsequent studies of hydrazine derivatives identified phenylhydrazine (IC50=0.25 ± 0.07 µM) to be 32-fold more potent than 2-hydrazinobenzothiazole (IC50=8.0 ± 2.3 µM) in inhibiting rhIDO1 and that it inhibited cellular IDO1 at concentrations that were noncytotoxic to cells. Here, phenylhydrazine is shown to inhibit IDO1 through binding to haem.

Formation of an N-formylkynurenine-derived fluorophore and its use for measuring indoleamine 2,3-dioxygenase 1 activity.

Indoleamine 2,3-dioxygenase 1 (IDO1) is a tryptophan-catabolizing enzyme whose expression by a broad range of clinical tumors is associated with immunosuppression and poor patient outcome. Here we describe a new fluorescence assay for measuring IDO1 activity suitable for high-throughput screening of compound libraries for novel IDO1 inhibitors. This assay is easy to perform, requiring the addition of only one reagent prior to readout. In place of measuring kynurenine, it uses the in situ formation of an N-formylkynurenine-derived fluorophore (NFKPIP) measured at an excitation wavelength of 400 nm and an emission wavelength of 500 nm. The fluorescence intensity of the NFKPIP formed is directly related to the amount of enzyme activity, and the signal is stable over 8 h. This assay has a lower limit of detection, equating to 153 nM N-formylkynurenine, which is over 30-fold lower than the limits of detection of existing assays for IDO1 activity. When we compared the performance of the new assay with that of the published colorimetric absorbance assay in screening the National Cancer Institute Diversity Set III of 1,597 compounds for IDO1 inhibitors, we obtained an identical list of the 25 most active compounds in the two assays. Although 93 compounds (aldehydes, ketones, and aromatic amines) in the library interfered with the absorbance readout, only 18 compounds (conjugated systems and fused cycles) interfered with the readout of the new fluorescence assay. IC(50) values determined using the new assay for three known IDO1 inhibitors-1,4-naphthoquinone, 4-amino-N-(3-chloro-4-fluorophenyl)-N'-hydroxy-1,2,5-oxadiazole-3-carboximidamide and 4-phenyl-1H-imidazole-were consistent with their literature values, further validating the new assay for measuring IDO1 activity.

A pilot in vivo study: potential ovarian cancer therapeutic by placental extracellular vesicles.

The biological links between cancer and pregnancy are of interest due to parallel proliferative, immunosuppressive, and invasive mechanisms between tumour and placental cells. However, the proliferation and invasion of placental cells are strictly regulated. The understanding of this regulation is largely unknown. Placental extracellular vesicles (EVs) may play an important role in this regulation, as placental EVs are known to contribute to maternal adaptation, including adaptation of the vascular and immune systems. We have previously reported that placental EVs significantly inhibited ovarian cancer cell proliferation by delaying the progression of the cell cycle. We, therefore, performed this pilot in vivo study to investigate whether placental EVs can also inhibit ovarian tumour growth in a SKOV-3 human tumour xenograft model. A single intraperitoneal injection of placental EVs at 15 days post tumour implantation, significantly inhibited the growth of the tumours in our in vivo model. Signs of cellular necrosis were observed in the ovarian tumour tissues, but not in other organs collected from mice that had been treated with placental EVs. Expression of receptor-interacting kinase 1 (RIPK1) and mixed linkage kinase domain-like (MLKL), which are mediators of necroptosis were not observed in our xenografted tumours. However, extensive infiltration of CD169+ macrophages and NK cells in ovarian tumour tissues collected from placental micro-EVs treated mice were observed. We demonstrate here that inhibition of ovarian tumour growth in our xenograft model by placental EVs involves cellular necrosis and infiltration of CD169+ macrophages and NK cells into the tumour tissues.

Evaluation of Novel Inhibitors of Tryptophan Dioxygenases for Enzyme and Species Selectivity Using Engineered Tumour Cell Lines Expressing Either Murine or Human IDO1 or TDO2.

Indoleamine 2, 3-dioxygenase 1 (IDO1) is commonly expressed by cancers as a mechanism for evading the immune system. Preclinical and clinical studies have indicated the potential of combining IDO1 inhibitors with immune therapies for the treatment of cancer, strengthening an interest in the discovery of novel dioxygenase inhibitors for reversing tumour-mediated immune suppression. To facilitate the discovery, development and investigation of novel small molecule inhibitors of IDO1 and its hepatic isozyme tryptophan dioxygenase (TDO2), murine tumour cells were engineered to selectively express either murine or human IDO1 and TDO2 for use as tools to dissect both the species specificity and isoenzyme selectivity of newly discovered inhibitors. Lewis lung carcinoma (LLTC) lines were engineered to express either murine or human IDO1 for use to test species selectivity of the novel inhibitors; in addition, GL261 glioma lines were engineered to express either human IDO1 or human TDO2 and used to test the isoenzyme selectivity of individual inhibitors in cell-based assays. The 20 most potent inhibitors against recombinant human IDO1 enzyme, discovered from a commissioned screening of 40,000 compounds in the Australian WEHI compound library, returned comparable IC50 values against murine or human IDO1 in cell-based assays using the LLTC-mIDO1 and LLTC-hIDO1 line, respectively. To test the in vivo activity of the hits, transfected lines were inoculated into syngeneic C57Bl/6 mice. Individual LLTC-hIDO1 tumours showed variable expression of human IDO1 in contrast to GL261-hIDO1 tumours which were homogenous in their IDO1 expression and were subsequently used for in vivo studies. W-0019482, the most potent IDO1 inhibitor identified from cell-based assays, reduced plasma and intratumoural ratios of kynurenine to tryptophan (K:T) and delayed the growth of subcutaneous GL261-hIDO1 tumours in mice. Synthetic modification of W-0019482 generated analogues with dual IDO1/TDO2 inhibitory activity, as well as inhibitors that were selective for either TDO2 or IDO1. These results demonstrate the versatility of W-0019482 as a lead in generating all three subclasses of tryptophan dioxygenase inhibitors which can be applied for investigating the individual roles and interactions between IDO1 and TDO2 in driving cancer-mediated immune suppression.

Activation of the nucleotide oligomerization domain signaling pathway by the non-bacterially derived xanthone drug 5'6-dimethylxanthenone-4-acetic acid (Vadimezan).

The cytosolic nucleotide-binding oligomerization domain 1 (NOD1)/CARD4 and NOD2/CARD15 proteins are members of NOD-like receptors recognizing specific motifs within peptidoglycans of both Gram-negative and Gram-positive bacteria. NOD1 and NOD2 signal via the downstream adaptor serine/threonine kinase RIP2/CARDIAK/RICK to initiate NF-kappaB activation and the release of inflammatory cytokines/chemokines. In this report, we show that 5,6-dimethylxanthenone-4-acetic acid (DMXAA), a cell-permeable, small molecule that has anti-tumor activity, can also activate NOD1 and NOD2. This was demonstrated: 1) by using human embryonic kidney epithelial (HEK) 293 cells transfected with a NF-kappaB reporter plasmid in combination with NOD1 or NOD2 expression plasmids; 2) by inhibiting DMXAA-induced chemokine (CXCL10) mRNA and protein production in the AB12 mesothelioma cell line using a pharmacological inhibitor of RICK kinase, SB20358; and 3) by using small interfering RNA to knock down NOD2 and lentiviral short hairpin RNA to knock down RICK. These findings expand the potential ligands for the NOD-like receptors, suggesting that other xanthone compounds may act similarly and could be developed as anti-tumor agents. This information also expands our knowledge on the mechanisms of action of the anti-tumor agent DMXAA (currently in clinical trials) and may be important for its biological activity.

The role of autocrine TGFbeta1 in endothelial cell activation induced by phagocytosis of necrotic trophoblasts: a possible role in the pathogenesis of pre-eclampsia.

Pre-eclampsia is a disorder of pregnancy characterized by hypertension and endothelial cell dysfunction. The causes of pre-eclampsia are unclear but it is proposed that a factor released from the placenta triggers the maternal symptoms. One possible triggering factor is dead trophoblasts that are shed from the placenta, then deported to become trapped in the maternal pulmonary capillaries. It is hypothesized that trophoblasts die by apoptosis in normal pregnancy, but by necrosis in pre-eclampsia. Deported trophoblasts may be phagocytosed by the pulmonary endothelial cells and we have previously shown that phagocytosis of necrotic trophoblasts leads to the activation of endothelial cells, accompanied by the release of interleukin-6 from these cells. However, the mechanistic pathway linking phagocytosis of necrotic trophoblasts and endothelial cell activation is unknown. Here we show that, after phagocytosis of necrotic, but not apoptotic, trophoblasts, endothelial cells secrete TGFbeta1. Using recombinant endoglin to inhibit the function of TGFbeta1 we have shown that the TGFbeta1 does not directly activate endothelial cells but rather it induces endothelial IL-6 secretion. The IL-6 then induces endothelial cell activation. Inhibiting either TGFbeta1 or IL-6 prevented endothelial cell activation in response to phagocytosing necrotic trophoblasts, but inhibiting IL-6 did not prevent secretion of TGFbeta1, confirming the order of signalling. IL-6 also reduced endothelial cell-surface endoglin but increased the amount of soluble endoglin released from placental explants. These interactions between the IL-6 and TGFbeta1 pathways in both the endothelium and placenta may help to regulate the maternal response to deported trophoblasts in pregnancy.

Non-Invasive Biomarkers for Early Detection of Breast Cancer.

Breast cancer is the most common cancer in women worldwide. Accurate early diagnosis of breast cancer is critical in the management of the disease. Although mammogram screening has been widely used for breast cancer screening, high false-positive and false-negative rates and radiation from mammography have always been a concern. Over the last 20 years, the emergence of "omics" strategies has resulted in significant advances in the search for non-invasive biomarkers for breast cancer diagnosis at an early stage. Circulating carcinoma antigens, circulating tumor cells, circulating cell-free tumor nucleic acids (DNA or RNA), circulating microRNAs, and circulating extracellular vesicles in the peripheral blood, nipple aspirate fluid, sweat, urine, and tears, as well as volatile organic compounds in the breath, have emerged as potential non-invasive diagnostic biomarkers to supplement current clinical approaches to earlier detection of breast cancer. In this review, we summarize the current progress of research in these areas.

Enhancement of the action of the antivascular drug 5,6-dimethylxanthenone-4-acetic acid (DMXAA; ASA404) by non-steroidal anti-inflammatory drugs.

AIM: 5,6-Dimethylxanthenone-4-acetic acid (DMXAA) (ASA404), a low molecular weight antivascular drug currently in clinical trial, acts both directly on the tumour vascular endothelium and indirectly through the induction of inflammatory cytokines and other vasoactive molecules from macrophages and other host cells. We wished to determine whether co-administration of non-steroidal anti-inflammatory drugs (NSAIDs) could modulate the antivascular effects of DMXAA in mice. METHODS: The effects of diclofenac, salicylate, ibuprofen, celecoxib and rofecoxib on the antitumour response to DMXAA were compared using growth delay assays of Colon 38 adenocarcinomas in C57Bl mice. Concentrations of DMXAA in mice were measured by high performance liquid chromatography. RESULTS: Administration of DMXAA alone (25 mg/kg i.p.) or of NSAIDs alone induced small tumour growth delays from 2 to 7 days. Co-administration of each of the NSAIDs augmented DMXAA effects with tumour growth delays from 4.5 to >20 days. The possibility of a pharmacokinetic interaction was investigated using diclofenac and it was found that diclofenac did not affect DMXAA pharmacokinetics. CONCLUSIONS: NSAIDs increase the antitumour activity of DMXAA in a murine tumour model. The effects are consistent with hypothesis that NSAIDs antagonises some of the protective effects of prostaglandins released in response to vascular injury. Co-administration of NSAIDs with DMXAA might be considered as a possible strategy for use in combination cancer therapy.

The vascular disrupting agent, DMXAA, directly activates dendritic cells through a MyD88-independent mechanism and generates antitumor cytotoxic T lymphocytes.

5,6-Di-methylxanthenone-4-acetic acid (DMXAA) is a small molecule in the flavanoid class that has antitumor activity. Although classified as a "vascular disrupting agent," we have recently conducted studies showing that DMXAA has remarkable efficacy in a range of tumors, working primarily as an immune modulator that activates tumor-associated macrophages and induces a subsequent CD8(+) T-cell-mediated response. To more completely analyze the effect of DMXAA on CD8(+) T-cell generation, we treated mice bearing tumors derived from EG7 thymoma cells that express the well-characterized chicken ovalbumin neotumor antigen. Treatment with DMXAA led to cytokine release, tumor cell necrosis, and ultimately reduction in tumor size that was lymphocyte dependent. Within 24 h of administration, we observed dendritic cell activation in tumor-draining lymph nodes (TDLN). This was followed by a rapid and marked increase in the number of tetramer-specific CD8(+) T cells in the spleens of treated animals. In contrast, the vascular disrupting agent combretastatin A4-phosphate, which caused a similar amount of immediate tumor necrosis, did not activate dendritic cells, nor induce an effective antitumor response. Using in vitro systems, we made the observation that DMXAA has the ability to directly activate mouse dendritic cells, as measured by increased expression of costimulatory molecules and proinflammatory cytokine release via a pathway that does not require the Toll-like receptor adaptor molecule MyD88. DMXAA thus has the ability to activate tumor-specific CD8(+) T cells through multiple pathways that include induction of tumor cell death, release of stimulatory cytokines, and direct activation of dendritic cells.

IFN-beta-dependent inhibition of tumor growth by the vascular disrupting agent 5,6-dimethylxanthenone-4-acetic acid (DMXAA).

By attacking established tumor vasculature, vascular disrupting agents (VDAs) represent an alternative approach to the treatment of cancer. One such VDA, 5,6-dimethylxanthenone-4-acetic acid (DMXAA), is scheduled for phase III trials for prostate and lung cancer in combination with conventional chemotherapies. In this work, we identify interferon-beta (IFN-beta) as a central mediator in the host's response to DMXAA. In mice bearing Lewis lung adenocarcinomas, a single intraperitoneal dose of DMXAA was shown to effect a highly significant reduction in tumor growth rate in wild-type mice that was not seen in IFN-beta-null mice. Moreover, intratumoral cytokine expression was shown to be dependent on host-derived IFN-beta, as DMXAA-treated IFN-beta-null mice demonstrated a lack of induction of not only IFN-beta but also the antiangiogenic cytokine, IP-10, in excised tumor tissue. These results support the conclusion that DMXAA derives its potent anticancer properties in part through elicitation of IFN-beta expression by host-derived elements.

Consequences of increased vascular permeability induced by treatment of mice with 5,6-dimethylxanthenone-4-acetic acid (DMXAA) and thalidomide.

PURPOSE: 5,6-Dimethylxanthenone-4-acetic acid (DMXAA) (AS1404), a small-molecule vascular disrupting agent currently in clinical trial, increases vascular permeability and decreases blood flow in both murine and human tumours. DMXAA induces tumour necrosis factor (TNF) in mice and the effects on vascular permeability are hypothesised to result from both direct (DMXAA) and indirect (TNF) effects. Skin temperature decreases in mice treated with high doses of DMXAA, raising the question of whether host toxicity is mediated by the induction of increased vascular permeability in normal tissue. Thalidomide is an anti-inflammatory agent that potentiates the anti-tumour activity of DMXAA but decreases induction of TNF in plasma. We wished to determine how it potentiated the effects of DMXAA. METHODS: Vascular permeability was measured in Colon 38 tumour and liver tissue by uptake of Evans Blue dye. Blood haematocrit and body temperature were also measured. RESULTS: Tumour vascular permeability was increased following administration of DMXAA (25 mg/kg i.p.), minimally affected following thalidomide (100 mg/kg i.p.) but strongly increased following co-administration of both drugs. In contrast, dye uptake into liver tissue was decreased following administration of DMXAA, thalidomide or both drugs. Administration of DMXAA at a potentially toxic dose (35 mg/kg i.p. or 50 mg/kg orally) was found to decrease body temperature and to increase the blood haematocrit, while administration of thalidomide alone (100 mg/kg i.p.) had no effect. Co-administration of thalidomide potentiated the effects of DMXAA on both body temperature and haematocrit but surprisingly did not increase toxicity. CONCLUSIONS: The results are consistent with the hypothesis that the host toxicity of high-dose DMXAA is mediated by effects on host vasculature. Co-administration of thalidomide increases the effective dose of DMXAA by reducing clearance but also, by inhibiting production of circulating TNF, reduces the host toxicity of DMXAA.

Synthesis and biological activity of azido analogues of 5,6-dimethylxanthenone-4-acetic acid for use in photoaffinity labeling.

5,6-Dimethylxanthenone-4-acetic acid (1) is scheduled for phase III clinical trials as a vascular disrupting agent. However, its biochemical receptor(s) have yet to be identified. In this report, the synthesis of azido analogues of 1 that could be used for photoaffinity labeling of proteins as an approach toward identifying its molecular targets is described. While 5-azidoxanthenone-4-acetic acid (2) and 5-azido-6-methylxantheone-4-acetic acid (3) were found to have biological activities similar to that of 1, 6-azido-5-methylxanthenone-4-acetic acid (4) was unstable and could not be evaluated. Both azido compounds 2 and 3 activated NF-kappaB, induced the production of tumor necrosis factor in cultured mouse splenocytes, and induced hemorrhagic necrosis of colon 38 tumors in mice. Photoreaction of lysates from spleen cells with tritiated 2 resulted in two radiolabeled protein bands at 50 and 14 kDa that could be competitively inhibited with cold 1 and cold 2. The azido compounds 2 and 3 exhibit all the requirements for use in photoaffinity labeling of potential receptor(s) for 1.

Antitumour action of 5,6-dimethylxanthenone-4-acetic acid in rats bearing chemically induced primary mammary tumours.

PURPOSE: To evaluate the antitumour activity of 5,6-dimethylxanthenone-4-acetic acid (DMXAA), a vascular disrupting agent currently under phase II clinical trials in combination with cancer chemotherapy, in rats bearing chemically induced primary mammary tumours. METHODS: Tumours were induced in female Wistar rats by injection of N-nitroso-N-methylurea at 100 mg/kg subcutaneously. A clinically relevant single dose of DMXAA (1,800 mg/m(2)) was given to animals when tumours were measurable. Tumour volume, extent of necrosis and cytokine profiles were measured. RESULTS: Compared with the control group, DMXAA treatment significantly delayed tumour doubling time and extended the time from treatment to euthanasia. Four of five DMXAA-treated animals showed necrosis involving 3.7-41.2% of the area of the tumour section at 24 h compared with none of four control animals (P < 0.028, Chi-square test). Intratumoural levels of TNFalpha, IL-6, VEGF and IL-1alpha were increased 4 h after DMXAA treatment. CONCLUSIONS: This study shows for the first time that DMXAA has significant in vivo antitumour activity against non-transplanted autochthonous tumours and in a host species other than the mouse.

NF-kappaB-independent induction of endothelial cell apoptosis by the vascular disrupting agent DMXAA.

BACKGROUND: DMXAA (5,6-dimethylxanthenone-4-acetic acid; AS1404), a vascular disrupting agent currently in clinical trials, induces tumour endothelial cell apoptosis in vivo in mice and in cancer patients. DMXAA activates NF-kappaB in many different cell types. In this study, whether DMXAA-induced endothelial cell apoptosis was NF-kappaB dependent was determined. MATERIALS AND METHODS: HUVEC endothelial and T24 endothelial-like cells were treated with DMXAA and apoptosis was measured by terminal deoxynucleotidyl transferase biotin-dUTP nick end labelling (TUNEL). NF-kappaB activation was measured by electrophoretic mobility shift assays (EMSA). T24 cells were transfected with IkappaBalphaM, a mutant form of the IkappaBalpha gene which cannot be phosphorylated and degraded, hence preventing NF-kappaB expression. RESULTS: No NF-kappaB up-regulation was detected in apoptotic HUVEC treated with DMXAA. The IkappaBalphaM-transfected T24 cells showed similar apoptotic responses to those of parental cells. CONCLUSION: The DMXAA-induced apoptosis is neither mediated by, nor inhibited by, the expression of the NF-kappaB pathway.

Activation of tumor-associated macrophages by the vascular disrupting agent 5,6-dimethylxanthenone-4-acetic acid induces an effective CD8+ T-cell-mediated antitumor immune response in murine models of lung cancer and mesothelioma.

5,6-Dimethylxanthenone-4-acetic acid (DMXAA) is a small molecule in the flavanoid class that has antitumor activity thought to be due to ability to induce high local levels of tumor necrosis factor (TNF)-alpha that disrupt established blood vessels within tumors. The drug has completed phase 1 testing in humans and is currently in phase 2 trials in combination with chemotherapy. Although characterized as a "vascular disrupting agent," there are some studies suggesting that DMXAA also has effects on the immune system that are important for its efficacy. The goal of this study was to carefully define the immune effects of DMXAA in a series of murine lung cancer and mesothelioma cell lines with varying immunologic characteristics. We show that DMXAA efficiently activated tumor-associated macrophages to release a variety of immunostimulatory cytokines and chemokines, including TNF-alpha; IFN-inducible protein-10; interleukin-6; macrophage inflammatory protein-2; monocyte chemotactic protein-1; and regulated on activation, normal T-cell expressed, and secreted. DMXAA treatment was highly effective in both small and large flank tumors. Animals cured of tumors by DMXAA generated a systemic memory response and were resistant to tumor cell rechallenge. DMXAA treatment led to initial tumor infiltration with macrophages that was followed by an influx of CD8(+) T cells. These CD8(+) T cells were required for antitumor efficacy because tumor inhibitory activity was lost in nude mice, mice depleted of CD8(+) T cells, and perforin knockout mice, but not in CD4(+) T-cell-depleted mice. These data show that activation of tumor-associated macrophages by DMXAA is an efficient way to generate a CD8(+) T-cell-dependent antitumor immune response even in animals with relatively nonimmunogenic tumors. Given these properties, DMXAA might also be useful in boosting other forms of immunotherapy.