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Background: Magnetic resonance elastography (MRE) is an emerging imaging technique that affords non-invasive quantitative assessment and visualization of tissue mechanical properties in vivo. Methods: In this study, MRE was used to quantify (kPa) the absolute value of the complex shear modulus |G*|, elasticity Gd and viscosity Gl of SW620 human colorectal cancer xenografts before and 24 h after treatment with either 200 mg kg−1 of the vascular disrupting agent ZD6126 (N-acetylcolchinol-O-phosphate) or vehicle control, and the data were compared with changes in water diffusivity measured by diffusion-weighted magnetic resonance imaging. Results: A heterogeneous distribution of |G*|, Gd and Gl was observed pre-treatment with an intertumoral coefficient of variation of 13% for |G*|. There were no significant changes in the vehicle-treated cohort. In contrast, ZD6126 induced a significant decrease in the tumour-averaged |G*| (P

Vascular disrupting agents (VDAs) are an exciting new group of targeted therapies under active clinical research in many solid tumors, in particular, lung cancer. Small-molecule VDAs are the focus of current clinical research, and consist of the flavonoids and the tubulin-binding agents. Toxicities of single-agent VDAs are characterized by acute, transient, and generally noncumulative side effects including headaches, nausea and vomiting, tumor pain, hypertension, and tachycardia. Flavonoid agents can also cause infusion site pain, visual disturbances, electrocardiac abnormalities, and symptoms consistent with an acute release of serotonin. Tubulin-binding agents can result in cardiac ischemia, abdominal pain, neuromotor abnormalities and cerebellar ataxia, and acute hemodynamic changes. Clinical trials investigating VDAs in combination with traditional chemotherapy have also shown the potential for significant pharmacologic and adverse toxicity interactions. Further research will need to focus on pharmacokinetic and pharmacodynamic parameters to optimize dosing schedules, determine effective combinations with chemotherapy, and minimize toxicities associated with VDAs.

Background ZD6126 is a novel vascular-targeting agent that disrupts the endothelial tubulin cytoskeleton causing selective occlusion of tumor vasculature and extensive tumor necrosis. This Phase I clinical study was conducted to evaluate the dose and administration schedule of ZD6126. Methods Adult patients with solid tumors refractory to existing treatments received a 10-min, single-dose intravenous infusion of ZD6126 every 14 or 21 days. Subsequent dose escalation was performed, based on the incidence of adverse events (AEs) within the first cycle of drug administration. Blood samples were obtained for pharmacokinetic analysis, and the effects of ZD6126 on tumor vasculature were visualized using DCE-MRI technology. Results Forty-four patients received ZD6126 (5−112 mg/m2 in the 21-day schedule, n = 35; 40−80 mg/m2 in the 14-day schedule, n = 9). Common AEs were similar in both groups and included abdominal pain, nausea and vomiting, which appeared to be dose related. The incidence of abdominal pain at 112 mg/m2 in the 21-day study prevented further dose escalation. Pharmacokinetic studies confirmed that ZD6126 is rapidly hydrolyzed to ZD6126 phenol. There was no difference in the pharmacokinetics of ZD6126 phenol upon repeat administration or between the two dosing regimens. DCE-MRI evaluation has demonstrated the antivascular effects of ZD6126. Conclusions This study identified that ZD6126 administered every 2 or 3 weeks at 80 mg/m2 was well tolerated, with mild but manageable gastrointestinal AEs. In approximately 11% (5 out of 44) of patients, ZD6126 was associated with cardiac events categorized as dose limiting toxicities (one patient with asymptomatic decreased left ventricular ejection fraction (LVEF), two with increased troponin concentrations, one with myocardial ischemia, and one with ECG signs of myocardial ischemia).

Purpose To investigate the use of the transverse magnetic resonance imaging (MRI) relaxation rate R 2 ∗ (s -1 ) as a biomarker of tumor vascular response to monitor vascular disrupting agent (VDA) therapy. Methods and Materials Multigradient echo MRI was used to quantify R 2 ∗ in rat GH3 prolactinomas. R 2 ∗ is a sensitive index of deoxyhemoglobin in the blood and can therefore be used to give an index of tissue oxygenation. Tumor R 2 ∗ was measured before and up to 35 min after treatment, and 24 h after treatment with either 350 mg/kg 5,6-dimethylxanthenone-4-acetic acid (DMXAA) or 100 mg/kg combretastatin-A4-phosphate (CA4P). After acquisition of the MRI data, functional tumor blood vessels remaining after VDA treatment were quantified using fluorescence microscopy of the perfusion marker Hoechst 33342. Results DMXAA induced a transient, significant ( p 2 ∗ 7 min after treatment, whereas CA4P induced no significant changes in tumor R 2 ∗ over the first 35 min. Twenty-four hours after treatment, some DMXAA-treated tumors demonstrated a decrease in R 2 ∗ , but overall, reduction in R 2 ∗ was not significant for this cohort. Tumors treated with CA4P showed a significant ( p 2 ∗ 24 h after treatment. The degree of Hoechst 33342 uptake was associated with the degree of R 2 ∗ reduction at 24 h for both agents. Conclusions The reduction in tumor R 2 ∗ or deoxyhemoglobin levels 24 h after VDA treatment was a result of reduced blood volume caused by prolonged vascular collapse. Our results suggest that DMXAA was less effective than CA4P in this rat tumor model.

The effects of the anti-vascular agent ZD6126 were studied in volume matched subcutaneous DU-145 human prostate cancer xenografts in SCID mice using two different MRI techniques, diffusion and vascular imaging. Diffusion weighted MRI was performed before and at 24 h, 48 h and 72 h following a single dose of 200 mg/kg. Tumor vascular volume and permeability surface area product (PSP) were determined 24 h post antivascular therapy following an identical dose using dynamic contrast enhanced MRI of the macromolecular contrast agent albumin-gadolinium diethylenetriaminepentaacetate (albumin-GdDTPA). Consistent with the mechanism of action of ZD6126, significantly lower vascular volume was detected at 24 h whereas diffusion changes were evident at 48 h. Diffusion MRI findings correlated well with histological determination of the necrotic fraction in the tumors by 48 h. Both diffusion and vascular imaging are useful noninvasive techniques to detect response of tumors to antivascular therapy with ZD6126 in the DU-145 human prostate cancer xenograft model.

Vascular disrupting agents (VDAs) are a new class of potential anticancer drugs that selectively destroy tumor vasculature and shutdown blood supply to solid tumors, causing extensive tumor cell necrosis. VDAs target established tumor blood vessels, which are distinct from antiangiogenic agents that prevent the formation of new blood vessels. There are two types of VDAs, small molecules and ligand-directed agents. Most of the small molecule VDAs are tubulin inhibitors, including CA4P, ZD6126, AVE8062, OXi-4503, NPI-2358, MN-029 and EPC2407. The others are synthetic flavonoids including FAA and DMXAA that induce the production of local cytokines such as TNF-alpha. VDAs have shown good antitumor efficacy in animal models, especially in combination with established anticancer agents. Several VDAs, including CA4P and DMXAA, have demonstrated good safety profile as well as some promising efficacy in phase I clinical trials. Currently CA4P and DMXAA are in phase II clinical trials and AVE8062, OXi-4503, NPI-2358 and MN-029 are in phase I clinical trials. This review will focus on recent progress in the discovery and development of small molecule VDAs, including recently published patent applications and issued patents related with small molecule VDAs.

Current experimental and clinical knowledge supports the optimisation of endothelial cell targeting using a strategy combining anti-EGFR drugs with antivascular agents. The purpose of the present study was to examine the effects of the association of ZD6126, an antivascular microtubule-destabilising agent, with gefitinib and irradiation on the growth of six head and neck human cancer cell lines xenografted in nude mice and to study predictive and molecular factors responsible for antitumour effects. CAL33- and Hep-2-grafted cell lines were the most sensitive to ZD6126 treatment, with VEGF levels significantly higher (P=0.0336) in these tumour xenografts compared to Detroit 562- and CAL27-grafted cell lines with relatively low VEGF levels that were not sensitive to ZD6126. In contrast, neither IL8 levels nor EGFR expression was linked to the antitumour effects of ZD6126. ZD6126 in combination with gefitinib resulted in a synergistic cytotoxic interaction with greater antitumour effects than gefitinib alone. The synergistic interaction between ZD6126 and gefitinib was corroborated by a significant decrease in CD31 labelling. The present study may serve for future innovative clinical applications, as it suggests that VEGF tumour levels are possible predictors for ZD6126 antitumour efficacy. It also supports the notion of antitumour supra-additivity when combining gefitinib and ZD6126, and identifies neoangiogenesis as the main determinant of this synergistic combination.

The effect of vascular disrupting agent ZD6126 with time on the sensitivity to the hypoxic cytotoxin tirapazamine (TPZ) and gamma-rays was examined in large and small solid tumors.Mice bearing SCC VII tumors 1 or 1.5 cm in diameter received 5-bromo-2'-deoxyuridine (BrdU) continuously to label all proliferating (P) cells, followed by injection with or without ZD6126. In the absence of ZD6126, or 1 or 24 h following ZD6126 injection, the response to TPZ or gamma-ray irradiation in quiescent (Q) cells was assessed in terms of induced micronucleus (MN) frequency using immunofluorescence staining for BrdU. The MN frequency in the total cell population was determined from the tumors not pretreated with BrdU. Another group of tumor-bearing mice received a series of test doses of gamma-rays while alive or after tumor clamping to obtain hypoxic fractions (HFs) in the tumors.One hour after ZD6126 injection, both small and large tumors showed lower and higher sensitivity, and 24 h after, higher and lower sensitivity, to gamma-rays and TPZ, respectively, than the tumors not treated with ZD6126. Further, they showed larger and smaller HFs 1 and 24 h after ZD6126 injection, respectively. Without ZD6126 and 1 h after injection, small tumors were more sensitive to gamma-rays and less sensitive to TPZ than large tumors, probably due to the smaller HFs than large tumors. In contrast, 24 h after the injection, these differences in sensitivity and the HF between small and large tumors were reversed. The changes in sensitivity and the size of the HF were more marked in the total cell population than in Q cells.Following ZD6126 treatment, in terms of tumor control, especially large tumors and total tumor cell population, administering TPZ 1 h later and gamma-ray irradiation 24 h later were effective. Intratumor physiologic factors such as the size of the HF, depending on the time after ZD6126 injection, have to be taken into account when combining another treatment with ZD6126.

The aim of this study was to use magnetic resonance (MR) techniques to non-invasively compare the effects of the three leading vascular disrupting agents, namely combretastatin A-4 disodium phosphate (CA4DP), 5,6-dimethylxanthenone-4acetic acid (DMXAA) and ZD6126. A C3H mouse mammary carcinoma grown in the right rear foot of female CDF1 mice was used and treatments performed when tumours had reached 200 mm 3 in volume. Drugs were prepared fresh before each experiment and intraperitoneally injected into restrained non-anaesthetised mice. Tumour response was evaluated using 31 P-MR spectroscopy and T1- and T2- weighted imaging with a 7-Tesla, horizontal bore magnet, before and up to 24 hours after treatment. All three drugs significantly decreased bioenergetic status and pH, and did so in a time and dose dependent fashion, but there were differences; the decrease by CA4DP occurred more rapidly than for DMXAA or ZD6126, while DMXAA had a narrow window of activity compared to CA4DP and ZD6126. Changes in T1 weighted images for all three agents suggested a dose dependent increase in tumour oedema within three hours after treatment, consistent with an increase in vessel permeability. Using T2 weighted images there was some evidence of haemaorrhagic necrosis by DMXAA, but such necrosis was limited following treatment with CA4DP or ZD6126.

ZD6126 is a vascular targeting agent, developed for the treatment of solid tumors. In vivo, ZD6126 is rapidly converted into the tubulin-binding agent N-acetylcolchinol. We have previously reported that in vitro N-acetylcolchinol disrupts microtubules and induces rapid changes in endothelial cell morphology, which in a tumor would lead to a rapid loss of tumor vessel integrity and subsequent extensive tumor necrosis. The aim of this study was to investigate the effect of cytotoxic antineoplastic drugs—cisplatin, doxorubicin, vincristine, paclitaxel, and docetaxel—on endothelial cell response to N-acetylcolchinol. We found that cisplatin and doxorubicin did not interfere with the ability of N-acetylcolchinol to cause morphologic changes in human umbilical vein endothelial cells, whereas vincristine showed additive effects. In contrast, the microtubule-stabilizing agents paclitaxel (1-10 μmol/L) and docetaxel (0.1-1 μmol/L) prevented the morphologic changes induced by N-acetylcolchinol in human umbilical vein endothelial cells. The effect was observed when cells were exposed to paclitaxel and N-acetylcolchinol together or when paclitaxel was given shortly before N-acetylcolchinol. Paclitaxel and N-acetylcolchinol interacted at the level of microtubule organization, as shown in immunofluorescence analysis of the cytoskeleton. The protective effect was reversible because 4 hours after paclitaxel wash out, cells recovered the sensitivity to N-acetylcolchinol. In vivo, pretreatment of mice with paclitaxel inhibited the vascular targeting activity of ZD6126 on newly formed vessels in the Matrigel plug assay and ZD6126-induced necrosis in tumors. These findings indicate that paclitaxel, depending on the timing and schedule of administration, can affect the vascular targeting activity of ZD6126, which may have an effect on the optimal scheduling of therapies based on the combined use of microtubule-stabilizing and microtubule-destabilizing agents.

The selective targeting of established tumor vasculature represents an attractive new anticancer drug strategy, distinct from inhibiting angiogenesis. This is based on the concept that, in contrast to targeting individual tumor cells, the killing of relatively few vascular endothelial cells could result in the death of a large area of tumor (from lack of oxygen and nutrients), drug delivery to vasculature is less challenging than to large solid tumors (which may harbor regions of hypoxia) and, moreover, cells that comprise vasculature (such as endothelial cells) are more genetically stable than tumor cells and hence less likely to acquire changes causing drug resistance. There is accumulating evidence that there are inherent differences in the vasculature of tumors, both morphologic and biochemical, in comparison to normal organs, thus providing a rational basis for this approach. Vascular disrupting agents (VDAs) are now being tested clinically; several are also in late preclinical development. A major class of small molecule VDA is those targeting tubulin, e.g., combretastatin A4 phosphate (CA4P), ZD6126 and AVE8062A. Another distinct non-tubulin based compound, the flavonoid 5,6-dimethyl xanthenone 4-acetic acid (DMXAA, AS1404) induces direct apoptosis of endothelial cells and secondary induction of various vasoactive agents (such as serotonin and tumor necrosis factor α). These agents have all completed Phase I clinical evaluation; dose-limiting toxicities are generally non-overlapping with conventional cytotoxics; there has been evidence of efficacy. A common theme, now being pursued clinically, is that VDAs are expected to show maximum therapeutic benefit when used, intermittently rather than chronically and in combination with either conventional cytotoxics (such as platins or taxanes) or radiotherapy. Thereby, complementary kill of the central compartment of tumors (by VDAs) and the proliferating, well oxygenated, periphery (by cytotoxics or radiotherapy) , is predicted. Non-invasive imaging techniques such as dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) have proven useful in the clinical monitoring of VDAs. A variety of additional small molecule anti-tubulin agents, N-cadherin inhibitors and antibody-based products (e.g., delivering effectors such as tissue factor to tumor blood vessels) are in earlier stages of development. The vascular targeting field is entering a particularly exciting phase; the next 1-2 years will be crucial in establishing clinical proof of principle for this approach.

Purpose The aim of this study was to evaluate the antitumor efficacy of the vascular targeting agent ZD6126 ( N -acetylcochinol- O -phosphate) in the rodent squamous cell carcinoma (SCC) VII carcinoma model, in combination with boron neutron capture therapy (BNCT). Methods and materials Sodium borocaptate- 10 B (BSH, 125 mg/kg, i.p.) or l - p -boronophenylalanine- 10 B (BPA, 250 mg/kg, i.p.) was injected into SCC VII tumor–bearing mice, and 15 min later, ZD6126 (100 mg/kg, i.p.) was administered. Then, the 10 B concentrations in tumors and normal tissues were measured by prompt γ-ray spectrometry. On the other hand, for the thermal neutron beam exposure experiment, SCC VII tumor–bearing mice were continuously given 5-bromo-2′-deoxyuridine (BrdU) to label all proliferating (P) cells in the tumors, followed by treatment with a 10 B-carrier and ZD6126 in the same manner as the above-mentioned 10 B pharmacokinetics analyses. To obtain almost similar intratumor 10 B concentrations during neutron exposure, thermal neutron beam irradiation was started from the time point of 30 min after injection of BSH only, 90 min after BSH injection for combination with ZD6126, 120 min after the injection of BPA only, and 180 min after BPA injection for combination with ZD6126. Right after irradiation, the tumors were excised, minced, and trypsinized. The tumor cell suspensions thus obtained were incubated with cytochalasin-B (a cytokinesis blocker), and the micronucleus (MN) frequency in cells without BrdU labeling (quiescent [Q] cells) was determined using immunofluorescence staining for BrdU. Meanwhile, the MN frequency in total (P + Q) tumor cells was determined from the tumors that were not pretreated with BrdU. The clonogenic cell survival assay was also performed in mice given no BrdU. Results Pharmacokinetics analyses showed that combination with ZD6126 greatly increased the 10 B concentrations in tumors after 60 min after BSH injection and after 120 min after BPA injection. The concentrations of 10 B from BSH in normal tissues were also raised by combination with ZD6126, although not so clearly as those in tumors. Combination with ZD6126 had almost no effect on the concentrations of 10 B from BPA in normal tissues. The clonogenic surviving fractions of total tumor cells and the MN frequencies of both total and Q tumor cells were reduced and increased by combination with ZD6126, respectively, whether BSH or BPA was employed. However, the degrees of these changes in the clonogenic surviving fractions and the MN frequencies were more obviously observed in tumors from BSH-injected mice than from BPA-injected mice, and in Q tumor cells than in total tumor cells regardless of the employed 10 B-carrier. Conclusions Combination with ZD6126 was regarded as more promising in BSH-BNCT than BPA-BNCT, and more effective for enhancing the sensitivity of the Q tumor cells than that of the total tumor cells. This resulted in the decrease in the extended difference in the sensitivity between the total and Q tumor cells caused by the use of 10 B-carrier for BNCT.

Purpose: ZD6126 is a novel vascular targeting agent currently undergoing clinical evaluation. It acts by destabilizing the microtubulin of fragile and proliferating neoendothelial cells in tumors. The drug leads to blood vessel congestion, the selective destruction of the vasculature, and extensive necrosis in experimental tumors. The aim of the study reported here was to assess the ability of dynamic contrast enhanced magnetic resonance imaging (MRI) to measure the antivascular effects of ZD6126 in tumors. Experimental Design: The work was carried out in mice bearing C38 colon adenocarcinoma and in patients with advanced cancers. MRI was performed before and 6 h (human tumors) or 24 h (C38 tumors) after i.v. drug administration. Contrast agent (gadolinium diethylenetriaminepentaacetate) enhancement was characterized by the initial area under the gadolinium diethylenetriaminepentaacetate uptake versus time curve (IAUC). IAUC reflects blood flow, vascular permeability, and the fraction of interstitial space. Results: The median IAUC was reduced in all C38 tumors after ZD6126 administration [by 6–48% at 50 mg/kg (n = 3)], 58–91% at 100 mg/kg (n = 4), and 11–93% at 200 mg/kg (n = 6). In contrast, the administration of vehicle only led to no consistent change in median IAUC (n = 4). The ZD6126-induced changes in median IAUC appeared to be dose dependent (P = 0.045). No ZD6126-induced changes were apparent in murine muscle. Similar effects were seen in preliminary data from human tumors (11 tumors studied, 9 patients). At doses of 80 mg/m2 and higher, the median IAUC post-ZD6126 treatment was reduced in all of the tumors studied (8 tumors, 6 patients) to 36–72% from the baseline value. There was a significant trend of increasing reductions with increasing exposure (P < 0.01). No drug-induced changes in human muscle or spleen IAUC were apparent. The reproducibility of the median IAUC parameter was investigated in patients. In 19 human tumors (measured in 19 patients) inter- and intratumor coefficients of variation were 64 and 18%. Conclusions: The contrast enhanced-MRI measured median IAUC is a useful end point for quantifying ZD6126 antivascular effects in human tumors.

The purpose of this study was to examine the effects of ZD6126, a novel vascular-targeting agent, on tumour growth and angiogenesis in an orthotopic model of gastric cancer. TMK-1 human gastric adenocarcinoma cells were injected into the gastric wall of nude mice. After the tumours were established (day 14), therapy was initiated. Mice (n=11-12/group) received (a). vehicle, (b). ZD6126 at 100 mg x kg day(-1) i.p. one time per week or (c) ZD6126 at 100 mg x kg day(-1) i.p. five times per week. Tumour mass, volume and the presence or absence of peritoneal carcinomatosis were determined at sacrifice on day 38. Tumours from each group were stained for markers of blood vessels, proliferation and apoptosis. To further define the time frame of the vascular-targeting effects of chronic therapy with ZD6126, TMK-1 cells were again injected into the gastric wall of mice in a second experiment. On day 14, a single i.p. injection of ZD6126 100 mg x kg(-1) mouse(-1) or vehicle was delivered. Groups of three mice each were killed and the tumours harvested at days 1, 3 and 5 post-ZD6126 injection. Tumours were processed and stained for endothelial and tumour cell apoptosis and proliferation. No overt toxicity was observed with ZD6126 therapy. ZD6126 led to a marked inhibition of tumour growth (82% decrease vs control (P0.001)). ZD6126 also led to a significant decrease in the incidence of peritoneal carcinomatosis (10 out of 12 controls, vs one out of 12 ZD6126) (P0.01). Histological analysis of tumours revealed large regions of central necrosis in the treated group, as well as a dramatic increase in tumour cell apoptosis (7.4-fold increase (P0.001)), consistent with the vascular-targeting activity of ZD6126. Mice treated with ZD6126 demonstrated a 59% decrease in PCNA-positive cells (P0.02), indicating reduced tumour cell proliferation. In addition, tumours treated with ZD6126 exhibited a 40% decrease in microvessel density (P0.05). Results from mice treated with a single injection of ZD6126 demonstrated the acute effects this agent has on the tumour vasculature. The ratio of endothelial cell apoptosis to endothelial cell proliferation was increased within 24 h of a single injection. In conclusion, ZD6126 significantly inhibited tumour growth and metastasis in an orthotopic model of human gastric adenocarcinoma, without detectable problematic adverse effects. These data suggest that ZD6126 may be worthy of investigation in the treatment of primary gastric adenocarcinoma.

Purpose: Combretastatin A4 (CA4) phosphate (CA4P) inhibits microtubule polymerization and is toxic to proliferating endothelial cells in vitro. It causes reversible vascular shutdown in established tumors in vivo, consistent with an antivascular mechanism of action. The present study investigated escalating doses of CA4P administered intravenously to patients with advanced cancer. Patients and Methods: Patients with solid malignancies and good performance status received CA4P as a 10-minute infusion daily for 5 days repeated every 3 weeks. Pharmacokinetic sampling was performed during cycle 1. Patients receiving ≥ 52 mg/m2/d had serial dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) studies to measure changes in tumor perfusion with CA4P treatment. Results: Thirty-seven patients received 133 treatment cycles. CA4P dose levels ranged from 6 mg/m2 to 75 mg/m2 daily. Severe pain at sites of known tumor was dose limiting at 75 mg/m2. Dose-limiting cardiopulmonary toxicity (syncope and dyspnea or hypoxia) was noted as well in two patients treated at 75 mg/m2. Other toxicities included hypotension, ataxia, dyspnea, nausea or vomiting, headache, and transient sensory neuropathy. Plasma CA4P and CA4 area under the concentration-time curve and maximal concentration values increased linearly with dose. Tumor perfusion, as measured by the first-order rate constant of gadolinium plasma to tissue transfer during DCE-MRI studies, was found to decrease in eight of 10 patients. Relationships were also demonstrated between perfusion changes and pharmacokinetic indices. A partial response was observed in a patient with metastatic soft tissue sarcoma, and 14 patients exhibited disease stability for a minimum of two cycles. Conclusion: Doses of CA4P on a daily times five schedule of 52 to 65 mg/m2 were reasonably well-tolerated. The 52 mg/m2 dose is recommended for further study based on cumulative phase I experience with CA4P. Antitumor efficacy was observed, and the use of DCE-MRI provided a valuable noninvasive measure of the vascular effects of CA4P treatment.

Advances in the understanding of tumour biology have led to the discovery of new targets that control specific mechanisms essential for tumour spread, growth and survival. In order to fully explore the anticancer potential of these novel approaches, AstraZeneca is developing a broad pipeline of agents targeting a variety of key processes in tumour progression and metastasis. These include two novel antiangiogenic agents, ZD6474 and AZD2171, which are both orally available inhibitors of vascular endothelial growth factor receptor-tyrosine kinase, AZD2171 being a highly potent inhibitor; ZD6474 also has activity against epidermal growth factor receptor tyrosine kinase. Once-daily administration of these agents has been shown to result in effective inhibition of tumour growth in a broad spectrum of human xenograft models. In contrast to this approach, which prevents new vessel formation, the vascular-targeting agent ZD6126 disrupts the microtubular network responsible for maintaining the shape of immature endothelial cells, thereby selectively destroying the existing tumour vasculature and leading to extensive central necrosis. Other agents with a variety of novel antitumour strategies are also in development. These include AZD0530, an orally available Src kinase inhibitor, and AZD3409, an oral prenyl transferase inhibitor, both of which have potential for broad antitumour activity. In addition, an oral, selective, cyclin-dependent kinase inhibitor (AZD5438).

Purpose: Combretastatin A4 phosphate (CA4P) is a novel vascular targeting agent. Dynamic contrast enhanced magnetic resonance imaging (DCE-MRI) studies were performed to examine changes in parameters related to blood flow and vascular permeability in tumor and normal tissue after CA4P treatment. Materials and Methods: Changes in kinetic DCE-MRI parameters (transfer constant [Ktrans] and area under contrast medium-time curve [AUC]) over 24 hours after treatment with CA4P were measured in 18 patients in a phase I trial and compared with those obtained in the rat P22 carcinosarcoma model, using the same imaging technique. Rats were treated with 30 mg/kg of CA4P; patients received escalating doses from 5 to 114 mg/m2. Results: A similar pattern and time course of change in tumor and normal tissue parameters was seen in rats and humans. Rat tumor Ktrans was reduced by 64% 6 hours after treatment with CA4P (30 mg/kg). No significant reductions in kidney or muscle parameters were seen. Significant reductions were seen in tumor Ktrans in six of 16 patients treated at ≥ 52 mg/m2, with a significant group mean reduction of 37% and 29% at 4 and 24 hours, respectively, after treatment. The mean reduction in tumor initial area under the gadolinium–diethylenetriamine pentaacetic acid concentration-time curve (AUC) was 33% and 18%, respectively, at these times. No reduction was seen in muscle Ktrans or in kidney AUC in group analysis of the clinical data. Conclusion: CA4P acutely reduces Ktrans in human as well as rat tumors at well-tolerated doses, with no significant changes in kidney or muscle, providing proof of principle that this drug has tumor antivascular activity in rats and humans.

Purpose: A phase I trial was performed with combretastatin A4 phosphate (CA4P), a novel tubulin-binding agent that has been shown to rapidly reduce blood flow in animal tumors. Patients and Methods: The drug was delivered by a 10-minute weekly infusion for 3 weeks followed by a week gap, with intrapatient dose escalation. Dose escalation was accomplished by doubling until grade 2 toxicity was seen. The starting dose was 5 mg/m2. Results: Thirty-four patients received 167 infusions. CA4P was rapidly converted to the active combretastatin A4 (CA4), which was further metabolized to the glucuronide. CA4 area under the curve (AUC) increased from 0.169 at 5 mg/m2 to 3.29 μmol • h/L at 114 mg/m2. The mean CA4 AUC in eight patients at 68 mg/m2 was 2.33 μmol • h/L compared with 5.8 μmol • h/L at 25 mg/kg (the lowest effective dose) in the mouse. The only toxicity that possibly was related to the drug dose up to 40 mg/m2 was tumor pain. Dose-limiting toxicity was reversible ataxia at 114 mg/m2, vasovagal syncope and motor neuropathy at 88 mg/m2, and fatal ischemia in previously irradiated bowel at 52 mg/m2. Other drug-related grade 2 or higher toxicities seen in more than one patient were pain, lymphopenia, fatigue, anemia, diarrhea, hypertension, hypotension, vomiting, visual disturbance, and dyspnea. One patient at 68 mg/m2 had improvement in liver metastases of adrenocortical carcinoma. Conclusion: CA4P was well tolerated in 14 of 16 patients at 52 or 68 mg/m2; these are doses at which tumor blood flow reduction has been recorded.

The aim of these studies was to evaluate factors that contribute to the selectivity of the novel vascular targeting agent ZD6126.Human umbilical vein endothelial cells (HUVECs) were treated with ZD6126 phenol, and effects on morphology, detachment, and cytotoxicity (sulforhodamine-B dye incorporation) were determined. Hras5-transformed mouse 3T3 fibroblasts were implanted s.c. in athymic nude rats, and effects on the tumor were assessed after either i.v. bolus or 24-h minipump infusion of ZD6126.In vitro, ZD6126 phenol ( approximately 0.1 microm) rapidly (40 min) destabilized the tubulin cytoskeleton of proliferating endothelial cells, resulting in cell shape change ("rounding up") and cell detachment at noncytotoxic drug concentrations. In vivo, in rats, an i.v. bolus dose of ZD6126 (20 mg/kg) was rapidly broken down to ZD6126 phenol, which has a short plasma elimination half-life ( approximately 1 h). Peak plasma levels of ZD6126 phenol were well above the level required to induce HUVEC morphology changes in vitro, but cytotoxic concentrations were not maintained. A single i.v. bolus dose (50 and 20 mg/kg) of ZD6126 was well tolerated and resulted in extensive central tumor necrosis in the Hras5 model. Administration of ZD6126 using a 24-h s.c. minipump resulted in decreased ( approximately 30-fold) peak plasma levels, but maintained cytotoxic drug levels over 24 h. Infusion of 50 mg/kg ZD6126 over 24 h was not tolerated. Infusion of 20 mg/kg ZD6126 resulted in increased toxicity compared with the i.v. bolus doses of ZD6126 and did not result in any increased tumor necrosis after 24 h.ZD6126 phenol induces rapid morphologic changes in HUVECs at noncytotoxic drug levels. These rapid morphologic effects combined with the rapid elimination of ZD6126 phenol contribute to the selective effects of ZD6126 on tumor vasculature at well-tolerated doses.

PURPOSE: 5,6-Dimethylxanthenone-4-acetic acid (DMXAA) causes vascular shutdown in preclinical models. Dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) studies were performed in the phase I trials to examine changes related to blood flow and permeability in tumor and muscle. PATIENTS AND METHODS: Sixteen patients treated with DMXAA from 500 to 4,900 mg/m2 had DCE-MRI examinations before and after treatment. The maximum gradient, the maximum enhancement, and the area under the signal-intensity–time curve (AUC) over the first 90 seconds were calculated for each pixel in regions of interest (ROIs) in muscle and tumor, and the median value for each ROI was obtained. Changes after treatment were compared with 95% limits of agreement for an individual and for groups using data from our reproducibility study. RESULTS: Nine of 16 patients had significant reductions in AUC 24 hours after the first dose of DMXAA, and eight of 11 patients had reductions of up to 66% in AUC 24 hours after the last dose. Mean reductions in gradient, enhancement, and AUC were 25%, 18%, and 31%, respectively, 24 hours after the last dose, significantly greater than the 95% limits of change for a group of 11 patients. Enhancement and AUC in muscle 24 hours after the first dose were significantly reduced, but no significant changes were seen 24 hours after the last dose. CONCLUSION: DMXAA significantly reduces DCE-MRI parameters related to tumor blood flow, over a wide dose range, consistent with the reported tumor vascular targeting activity. Further clinical evaluation of DMXAA is warranted.

Purpose: 5,6-dimethylxanthenone-4-acetic acid (DMXAA) selectively damages tumor vasculature and is currently in clinical trial as an antitumor agent. Its ability to induce synthesis of tumor necrosis factor (TNF), and its apparent selectivity for poorly-perfused regions in tumors, suggests it possible use in combination with radiotherapy. This investigation examines activity of DMXAA as a radiation modifier using two murine tumors. Methods and Materials: Tumor growth delay was evaluated using i.m. RIF-1 and MDAH-MCa-4 tumors irradiated in unanaesthetised, restrained mice (cobalt-60) using single dose or multiple fractions (8 x 2.5 Gy over 4 days) with DMXAA administered i.p. at various times in relation to irradiation. Results: Administration of DMXAA (80 μmol/kg, i.p. ) immediately after radiation resulted in a large increase in tumor growth delay, giving a radiation dose modifying factor of 2.3 for RIF-1 and 3.9 for MDAH-MCa-4. The combination was less active when radiation was given 1–4 h after DMXAA, but was highly active 12–48 h after DMXAA. At the latter times, clamping the tumor blood supply caused a large increase in radioresistance. These studies suggest that cells surviving DMXAA are hypoxic for only a short period. DMXAA increased overall growth delay when administered daily during fractionated irradiation, giving an approximately additive response. Conclusions: The marked synergy between DMXAA and single dose ionising radiation may reflect the complementarity of these agents at the microregional level, with DMXAA preferentially killing hypoxic cells in poorly perfused regions. Despite additional hypoxia shortly after DMXAA treatment, surviving cells appear to reoxygenate quickly which makes it feasible to use DMXAA before and during fractionated radiotherapy. The combination of fractionated radiation and DMXAA appears to be less effective than for single dose radiation (possibly because of the smaller contribution of hypoxia under these conditions), but may be therapeutically useful.

The tumour blood flow inhibitor 5,6-dimethylxanthenone-4-acetic acid (DMXAA) causes dramatic haemorrhagic necrosis in murine tumours, but activity is seen only at doses close to the toxic limit. This study investigates two approaches for increasing the therapeutic ratio of DMXAA. The first approach combines DMXAA with a second tumour blood flow inhibitor, 5-hydroxytryptamine (5-HT). Co-administration of 5-HT (700 micromol kg(-1)) to C3H mice caused marked enhancement of DMXAA effects against MDAH-MCa-4 tumours, with dose-modifying factors (DMFs) of >3 for blood flow inhibition (at 4 h), 2.3 for necrosis (at 12 h) and 2.0 for growth delay, without compromising the maximum tolerated dose of DMXAA (90 micromol kg(-1)). The data are consistent with ischaemic injury to the tumour being the major mechanism of anti-tumour activity. The second approach combines DMXAA (+/- 5-HT) with hypoxia-selective bioreductive drugs. Anti-tumour activity of all three bioreductive drugs tested (tirapazamine, CI-1010, SN 23816) was strongly potentiated by DMXAA, suggesting that there is a population of reversibly hypoxic tumour cells after DMXAA treatment. Co-administration of 5-HT further potentiated anti-tumour activity, but also increased host toxicity of tirapazamine and CI-1010 so that little therapeutic benefit was achieved. In contrast, the host toxicity of the dinitrobenzamide mustard SN 23816 was only slightly increased by DMXAA/5-HT, whereas the tumour growth delay at the maximum tolerated dose of SN 23816 was increased from 3.5 to 26.5 days. This study demonstrates that 5-HT and/or bioreductive drugs can improve the therapeutic activity of DMXAA in mice, and that with SN 23816 both approaches can be used together to provide considerably enhanced anti-tumour activity.

Several studies show that the antitumour activity of melphalan (MEL) and other alkylating agents can be enhanced by the selective inhibition of tumour blood flow, although the mechanism(s) underlying these interactions are unclear. 5,6-Dimethylxanthenone-4-acetic acid (DMXAA), a new anticancer agent currently in phase I clinical trial, inhibits blood flow in murine tumours. DMXAA increased the activity of MEL against the MDAH-MCa-4 mouse mammary tumour maximally when MEL was given about 2 h after DMXAA, without compromising the maximal dose of the alkylating agent that could be given. The plasma pharmacokinetics of MEL were unchanged by DMXAA pretreatment, but the area under the concentration-time curve (AUC) for the tumour increased by 33% as a result of decreasing clearance (consistent with falling tumour blood flow). However, inhibition of tumour blood flow also leads to microenvironmental changes (e.g. acidosis and hypoxia) that might influence sensitivity to MEL. The sensitivity of KHT cells (freshly isolated from tumours) to MEL in vitro was increased by lowering of either pH or oxygen concentration (pO2), with an overall dose-modifying factor of 15 being recorded for aerobic cells at pH 7.4 versus hypoxic cells at pH 6.5. The cellular uptake of MEL by KHT cells was increased by 74% under hypoxia. Thus, This study was supported by the National Cancer Institute, USA (contract NO1-CM-47019), and the Health Research Council of New Zealand DMXAA appears to augment the antitumour activity of MEL through two different mechanisms, increased exposure (via decreased tumour clearance of MEL) and increased sensitivity resulting from changes to the tumour microenvironment, both of which result from inhibition of tumour blood flow.

Several agents have now been identified which exert their anti-tumour effects in large part via the tumour vasculature; these include TNF alpha and flavone acetic acid (FAA). More recently, Vincristine and Vinblastine have also been shown to cause a prolonged and selective decrease in tumour perfusion. Vinblastine, unlike, FAA, causes no increase in plasma TNF alpha levels in mice bearing the CaNT tumour, suggesting 2 distinct mechanisms of anti-vascular activity for these structurally diverse agents. Since FAA and Vinblastine also show quite different normal tissue toxicities, which are separately dose-limiting, we have examined the strategy of combining these 2 agents. When Vinblastine preceded FAA by 24 hr or less, tumour growth delay was significantly enhanced without a concomitant increase in toxicity. The level of enhancement was not significantly reduced by a 5-fold decrease in Vinblastine dose, though any reduction in the dose of FAA caused a rapid reduction in treatment effectiveness. Investigation of the functional vasculature of treated tumours suggested that increased anti-vascular effects may contribute to the enhanced growth inhibition of the combined treatment. Our results demonstrate the potential benefit of combining 2 different classes of anti-vascular agent, using Vinblastine and FAA (or 5,6-MeXAA) as prototype drugs.

Background Head and neck squamous cell carcinoma (HNSCC) is the 5th most common cancer worldwide. Locally advanced HNSCC are treated with either radiation or chemo-radiotherapy, but still associated with high mortality rate, underscoring the need to develop novel therapies. Oncolytic viruses have been garnering increasing interest as anti-cancer agents due to their preferential killing of transformed cells. In this study, we evaluated the therapeutic potential of mutant vesicular stomatitis virus (VSVΔ51) against the human hypopharyngeal FaDu tumour model in vitro and in vivo. Results Our data demonstrated high toxicity of the virus against FaDu cells in vitro, which was associated with induction of apoptosis. In vivo, systemic injection of 1 × 109 pfu had minimal effect on tumour growth; however, when combined with two doses of ionizing radiation (IR; 5 Gy each) or a single injection of the vascular disrupting agent (ZD6126), the virus exhibited profound suppression of tumour growth, which translated to a prolonged survival in the treated mice. Concordantly, VSVΔ51 combined with ZD6126 led to a significant increase in viral replication in these tumours. Conclusions Our data suggest that the combinations of VSVΔ51 with either IR or ZD6126 are potentially novel therapeutic opportunities for HNSCC.

A key problem in solid tumor therapy is tumor regrowth from a residual viable rim after treatment with a vascular disrupting agent (VDA). As a potential solution, we studied a combined treatment of a VDA and antiangiogenic. This study was approved by the institutional ethical committee for the use and care of laboratory animals. Rats with implanted liver tumors were randomized into four treatment groups: 1) Zd6126 (Zd); 2) Thalidomide (Tha); 3) Zd in combination with Tha (ZdTha); and 4) controls. Multiparametric MRIs were performed and quantified before and after treatment. Circulating endothelial progenitor cells (EPCs) and plasma stromal cell-derived factor-1α (SDF-1α) were monitored. Tumor apoptosis, necrosis, and microvessels were verified by histopathology. A single use of Zd or Tha did not significantly delay tumor growth. The combined ZdTha showed enhanced antitumor efficacy due to synergistic effects; it induced a cumulative tumor apoptosis or necrosis, which resulted in significant delay in tumor growth and reduction in the viable tumor rim; it also reduced tumor vessel permeability; and it improved tumor hemodynamic indexes, most likely via a transient normalization of tumor vasculature induced by Tha. A stepwise linear regression analysis showed that the apparent diffusion coefficient was an independent predictor of tumor growth. We found no significant increases in Zd-induced circulating EPCs or plasma SDF-1α. ZdTha showed improved therapeutic efficacy in solid tumors compared to either agent alone. The therapeutic effects were successfully tracked in vivo with multiparametric MRI.

Background. Vascular-disrupting agents (VDAs) represent a new class of chemotherapeutic agent that targets the existing vasculature in solid tumors. Preclinical and early-phase trials have demonstrated the promising therapeutic benefits of VDAs but have also uncovered a distinctive toxicity profile highlighted by cardiovascular events. Methods. We reviewed all preclinical and prospective phase I–III clinical trials published up to August 2010 in MEDLINE and the American Association of Cancer Research and American Society of Clinical Oncology meeting abstracts of small-molecule VDAs, including combretastatin A4 phosphate (CA4P), combretastatin A1 phosphate (CA1P), MPC-6827, ZD6126, AVE8062, and ASA404. Results. Phase I and II studies of CA1P, ASA404, MPC-6827, and CA4P all reported cardiovascular toxicities, with the most common cardiac events being National Cancer Institute Common Toxicity Criteria (version 3) grade 1–3 hypertension, tachyarrhythmias and bradyarrhythmias, atrial fibrillation, and myocardial infarction. Cardiac events were dose-limiting toxicities in phase I trials with VDA monotherapy and combination therapy. Conclusions. Early-phase trials of VDAs have revealed a cardiovascular toxicity profile similar to that of their vascular-targeting counterparts, the angiogenesis inhibitors. As these agents are added to the mainstream chemotherapeutic arsenal, careful identification of baseline cardiovascular risk factors would seem to be a prudent strategy. Close collaboration with cardiology colleagues for early indicators of serious cardiac adverse events will likely minimize toxicity while optimizing the therapeutic potential of VDAs and ultimately enhancing patient outcomes.

We investigated the influence of two types of vascular damaging agents (VDAs) (DMXAA vs. ZD6126) and sequence of administration (VDA 24 h before HYP vs. HYP 1 h before VDA) to evaluate the effect on hypericin (HYP) accumulation and distribution in necrotic tumors. Frozen sections of dorsally inoculated RIF-1 tumors were analyzed by fluorescence microscopy and H&E stained for histological evaluation. The localization of HYP was assessed both qualitatively and semi-quantitatively in necrotic tumor, viable tumor, or nontarget host tissue. Whereas the type of VDA did not influence HYP accumulation and distribution, a clear advantage could be seen when administering VDA 24 h before HYP compared to HYP 1 h before VDA, pointing toward the absence of a “trapping” mechanism. In DMXAA-treated and not in ZD6126-treated tumors, spotty fluorescence was observed which is likely to be a consequence of neutrophil phagocytosis. Dexamethasone treatment neither did influence this phenomenon nor did change HYP uptake in necrotic tumor. We conclude that HYP accumulation is optimal when it is administered after VDA injection. We also found that HYP accumulation in necrosis is not changed when using VDAs with different working mechanisms. This insight provides a rationale for tumor necrosis therapy (TNT) using iodine-131-labeled hypericin ([131I]-HYP) in combination with VDAs.

Susceptibility contrast magnetic resonance imaging (MRI), utilising ultrasmall superparamagnetic iron oxide (USPIO) particles, was evaluated for the quantitation of vessel size index (Rv, mu m), a weighted average measure of tumour blood vessel calibre, and fractional tumour blood volume (fBV, %), in orthotopically propagated murine PC3 prostate tumour xenografts. Tumour vascular architecture was assessed in vivo by MRI prior to and 24 hr after treatment with 200 mg/kg of the vascular disrupting agent ZD6126. A Bayesian hierarchical model (BHM) was used to reduce the uncertainty associated with quantitation of Rv and fBV. Quantitative histological analyses of the uptake of Hoechst 33342 for perfused vasculature, and haematoxylin and eosin staining for necrosis, were also performed to qualify the MRI data. A relatively large median Rv of 40.3 38.mu m (90% confidence interval (CI90) = 37.4, 44.0 mu m) and a high fBV of 5.4% (CI90 = 5.3, 5.5%) were determined in control tumours, which agreed with histologically determined vessel size index. Treatment with ZD6126 significantly (p < 0.01) reduced tumour Rv (34.2 mu m, CI90 = 31.2, 38.0 mu m) and fBV (3.9%, CI90 = 3.8, 4.1%), which were validated against histologically determined significant reductions in perfusion and vessel size, and increased necrosis. Together these data (i) highlight the use of a BHM to optimise the inferential power available from susceptibility contrast MRI data, (ii) provide strong evaluation and qualification of Rv and fBV as non-invasive imaging biomarkers of tumour vascular morphology, (iii) reveal the presence of a different vascular phenotype and (iv) demonstrate that ZD6126 exhibits good anti-vascular activity against orthotopic prostate tumours.

ZD6126 is a vascular-disrupting agent that affects the endothelial tubulin cytoskeleton causing selective occlusion of tumor vasculature and extensive tumor cell necrosis. The present study evaluated the antitumor and antivascular activities of ZD6126 in the clinically relevant murine renal cell carcinoma (RENCA) model and also evaluated biological response to therapy using color Doppler imaging as biomarker. Mice were implanted with RENCA tumor cells (day 0) and established tumors were treated with ZD6126 (100 mg/kg i.p.) or vehicle with repeated intermittent doses on day 10, 14 and 18. ZD6126 treatment led to a significant reduction in tumor size and was associated with extensive tumor necrosis and a reduction in tumor blood flow versus controls. MVD increased with intermittent treatment (day 10, 14 and 18). In an additional study, animals were treated at day 19 and quantitative three-dimensional microvascular corrosion casting was performed to enable detailed assessment of the tumor vascular architecture. Corrosion casting showed that tumor vessel architecture is affected by treatment, whereas pre-existing vessels in control tissues are practically not affected. Inter-vessel and inter-branch distances as well as vessel diameters are influenced by treatment. In conclusion, ZD6126 showed potent antitumor efficacy in the RENCA model and our data suggest that decrease in tumor blood flow may be a useful surrogate marker of treatment effect.

The ability of solid tumours to promote a pathological neovasculature is essential to their survival, growth and metastasis. Therefore, agents that damage or inhibit the formation of tumour blood vessels have the potential for significant anti-cancer activity (Folkman, 2002). It is critical that these interventions selectively target tumour blood vessels so that vascular toxicity to normal tissues is limited. Encouragingly, there are major biological differences between the immature disorganised microvasculature of malignant tumours and normal microvessel networks, and these differences provide the basis for therapeutic selectivity (Hinnen and Eskens, 2007). One class of vascular-targeting anti-cancer agents is the vascular-disrupting agents (VDAs). These drugs selectively disrupt endothelial cells within the tumour microvasculature, resulting in rapid shutdown of tumour blood flow (Hinnen and Eskens, 2007; Tozer et al, 2008). In animal models, this typically results in necrosis of the central region of the tumour, with a thin peripheral rim of surviving tumour cells that are presumably supplied by vessels in the adjacent normal tissue. Agents in this class include combretastatin A4 phosphate, 5,6-dimethylxanthenone-4-acetic acid, ZD6126 and others (Rustin et al, 2003; Stevenson et al, 2003; Beerepoot et al, 2006; McKeage et al, 2006). Although different mechanisms of action are operative, some VDA are tubulin-interactive small molecules that selectively inhibit microtubule polymerisation in endothelial cells (Tozer et al, 2008; Schwartz, 2009). Tumour endothelium is dependent on its microtubule cytoskeleton for structural and functional integrity, and disruption of microtubules can trigger a series of changes that shutdown blood flow in the tumour microvasculature (Hinnen and Eskens, 2007). Several VDA are currently in clinical development and some have shown clinical anti-cancer efficacy (Dowlati et al, 2002; McKeage et al, 2008). CYT997 is a synthetic small molecule that inhibits tubulin polymerisation, disrupts cellular microtubules and demonstrates potent cytotoxic activity against tumour cell lines in vitro (Burns et al, 2009b). It also showed significant vascular-disrupting activity in preclinical tumour models (Burns et al, 2009a). CYT997 is orally bioavailable and repeat-dose animal toxicology studies have evaluated both intravenous (i.v.) and oral schedules. Common toxicities included hypocellularity of spleen, thymus and bone marrow, leucopenia and mucosal hemorrhage and ulceration in the gastrointestinal tract. Mild bradycardia was observed at higher doses, but there were no other cardiovascular or neurological toxicities (Cytopia Research Pty Ltd, 2009). We now report the results of a phase I dose-finding study of CYT997 administered by continuous 24-h i.v. infusion in patients with refractory advanced cancer. Pharmacodynamic (PD) evaluations of vascular-disrupting activity were performed, including measurement of plasma von Willebrand factor (vWF) and circulating endothelial cells (CECs), and assessment of the tumour microvasculature with dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). We also evaluated plasma levels of caspase-cleaved cytokeratin-18 (CK-18) as a surrogate marker of tumour apoptosis.

Vascular disrupting agents (VDAs) are able to affect selectively tumour endothelial cell morphology resulting in vessel occlusion and widespread tumour cell necrosis. However, single-agent antitumour activity of VDAs is typically limited, as tumour regrowth occurs rapidly following drug treatment. To improve the therapeutic effectiveness of VDAs, we investigated liposomal targeting using ZD6126 as a model VDA. ZD6126 is a phosphate-prodrug of the tubulin-binding vascular disrupting agent ZD6126 phenol. ZD6126 was encapsulated into long circulating PEG-liposomes for passive targeting and PEG-liposomes conjugated with peptide ligands containing the RGD-motif for active targeting to alpha(v)-integrins on tumour endothelial cells. ZD6126 could be stably encapsulated, and liposomes displayed minimal leakage in vitro (

The blood supply to all solid tumours consists of parasitized normal vessels and new vessels which have been induced to grow by the presence of the tumour. These vessels are inadequate in many respects, being tortuous, thin-walled, chaotically arranged, lacking innervation and with no predetermined direction of flow. The walls consist of a basement membrane lined with rapidly proliferating immature endothelial cells, and are more permeable than normal vessels. The spacing of the vessels and their average diameters are not optimal for nutrient provision. This paper focuses on the evidence that many existing therapies may already have, as part of their action, a vascular mediated process of killing tumour cells. This may result from local changes within individual vessels or from systemic alterations in blood pressure, viscosity, coagulability etc. The hallmarks of vascular injury are identified and the dangers of discarding useful anticancer agent by failing to understand their mechanism of action are highlighted.

Purpose: The tumor microenvironment is complex and heterogeneous, populated by tortuous irregular vasculature, hypoxic cells, and necrotic regions. These factors can all contribute to the biodistribution difficulties encountered by most cancer therapeutic agents. Antisense oligodeoxynucleotides (ASO) are a class of therapeutics where limited information is available about their distribution within a solid tumor environment. Experimental Design: To assess ASO distribution, a fluorescein-labeled phosphorothionated ASO based on the G3139 mismatch control was injected systemically (i.v.) into tumor-bearing severe combined immunodeficient mice. Hoechst 33342 was injected i.v. to visualize active vasculature. Unstained sections were imaged through tiled fluorescence stereomicroscopy and then quantitated using novel algorithms. Tumor sections from four human tumor models were examined (CaSki, DU-145, C666-1, and C15) for hypoxia, apoptosis/necrosis, and morphology. Results: For all four tumors, ASO accumulated within regions of hypoxia, necrosis, and apoptosis. Scatter plots of ASO versus active vasculature generated for each individual tumor revealed a consistent pattern of distribution of the ASO within each model. In C666-1 xenografts, the slopes of these scatter plots were significantly reduced from 0.41 to 0.16 when pretreated with the antivascular agent ZD6126 48 h before ASO injection. This was accompanied by the formation of large disseminated necrotic regions in the tumor, along with a 13.1 mmHg reduction in interstitial fluid pressure. Conclusions: These data suggest the possibility that these algorithms might offer a generalizable and objective methodology to describe the distribution of molecular therapeutic agents within a tumor microenvironment and to quantitatively assess distribution changes in response to combination therapies.

Targeting of the tumor stroma, including the tumor vasculature, represents a new frontier in the treatment of malignancy. Preclinical studies and clinical experiences have established that stroma-directed novel agents must be combined with conventional therapies in order to achieve relevant therapeutic efficacy. Here we review our preclinical experience on combinations of paclitaxel with a tyrosine kinase receptor inhibitor of angiogenesis (SU6668) and a vascular disrupting agent (VDA, ZD6126), and discuss the critical factors that determine the outcome of these treatments. We also analyze the relevance of the intrinsic sensitivity of the tumor to the drugs, as well as the possibility that the two combined agents synergistically affect the vasculature or independently target the host and the tumor compartments. Finally, we discuss the need to carefully optimize scheduling and sequencing, through the use of reliable end points, in order to avoid negative pharmacological interactions and to improve the antineoplastic efficacy of paclitaxel-based combination treatments.

The clinical success of small-molecule vascular disrupting agents (VDAs) depends on their combination with conventional therapies. Scheduling and sequencing remain key issues in the design of VDA-chemotherapy combination treatments. This study examined the antitumour activity of ZD6126, a microtubule destabilising VDA, in combination with paclitaxel (PTX), a microtubule-stabilising cytotoxic drug, and the influence of schedule and sequence on the efficacy of the combination. Nude mice bearing MDA-MB-435 xenografts received weekly cycles of ZD6126 (200 mg kg(-1) i.p.) administered at different times before or after PTX (10, 20, and 40 mg kg(-1) i.v.). ZD6126 given 2 or 24 h after PTX showed no significant benefit, a result that was attributed to a protective effect of PTX against ZD6126-induced vascular damage and tumour necrosis, a hallmark of VDA activity. Paclitaxel counteracting activity was reduced by distancing drug administrations, and ZD6126 given 72 h after PTX potentiated the VDA's antitumour activity. Schedules with ZD6126 given before PTX improved therapeutic activity, which was paralleled by a VDA-induced increase in cell proliferation in the viable tumour tissue. Paclitaxel given 72 h after ZD6126 yielded the best response (50% tumours regressing). A single treatment with ZD6126 followed by weekly administration of PTX was sufficient to achieve a similar response (57% remissions). These findings show that schedule, sequence and timing are crucial in determining the antitumour efficacy of PTX in combination with ZD6126. Induction of tumour necrosis and increased proliferation in the remaining viable tumour tissue could be exploited as readouts to optimise schedules and maximise therapeutic efficacy.

Purpose To assess tumor fractional blood volume (ξ), determined in vivo by susceptibility contrast magnetic resonance imaging (MRI) as a noninvasive imaging biomarker of tumor response to the vascular disrupting agent ZD6126. Methods and Materials The transverse MRI relaxation rate R2∗ of rat GH3 prolactinomas was quantified prior to and following injection of 2.5 mgFe/kg feruglose, an ultrasmall superparamagnetic iron oxide intravascular contrast agent, and ξ (%) was determined from the change in R2∗. The rats were then treated with either saline or 50 mg/kg ZD6126, and ξ measured again 24 hours later. Following posttreatment MRI, Hoechst 33342 (15 mg/kg) was administered to the rats and histological correlates from composite images of tumor perfusion and necrosis sought. Results Irrespective of treatment, tumor volume significantly increased over 24 hours. Saline-treated tumors showed no statistically significant change in ξ, whereas a significant (p = 0.002) 70% reduction in ξ of the ZD6126-treated cohort was determined. Hoechst 33342 uptake was associated with viable tumor tissue and was significantly (p = 0.004) reduced and restricted to the rim of the ZD6126-treated tumors. A significant positive correlation between posttreatment ξ and Hoechst 33342 uptake was obtained (r = 0.83, p = 0.002), providing validation of the MRI-derived measurements of fractional tumor blood volume. Conclusions These data clearly highlight the potential of susceptibility contrast MRI with ultrasmall superparamagnetic iron oxide contrast agents to provide quantitative imaging biomarkers of fractional tumor blood volume at high spatial resolution to assess tumor vascular status and response to vascular disrupting agents.

Vascular-disrupting agents (VDA) kill tumor cells by selectively disrupting blood circulation in tumors. In vivo analysis of this intensely studied class of anticancer agents is invaluable for preclinical assessment of pharmacodynamic end points and effective therapeutic windows. In this review, we consider the role of intravital video microscopy in measuring tumor vascular response to VDAs, the potential of which lies in the opportunity to quantitate specific variables and to obtain real-time information on how VDAs affect tumor microcirculation. (Cancer Res 2006; 66(24): 11517-9)

Purpose ZD6126 is a novel vascular-targeting agent that induces selective effects on the morphology of endothelial cells by disrupting the tubulin cytoskeleton. This leads to cell detachment and tumor vessel congestion, resulting in extensive central necrosis in a range of tumor xenograft models. Results from a phase I dose-escalation study of ZD6126 are reported. Patients and Methods Thirty-two patients with advanced cancer received weekly ZD6126 infusion (5 to 28 mg/m2). Assessments for safety and pharmacokinetics were performed. Circulating endothelial cells (CECs) were quantified as a pharmacodynamic marker of vascular damage. Results Maximum concentrations of the active species were observed 5 to 25 minutes from the start of infusion, and decayed in a biexponential manner with a half-life of 1 to 3 hours. Maximum serum concentration and area under the time-concentration curve increased with dose in a linear fashion across the dose range of 5 to 28 mg/m2. One patient treated at 10 mg/m2 with a history of ischemic heart disease experienced acute myocardial infarction 2 weeks after drug discontinuation. Four others had asymptomatic creatine phosphokinase–muscle-brain elevation. Maximum-tolerated dose (MTD) was reached at 20 mg/m2/wk. Dose-limiting toxicities at 28 mg/m2 were hypoxia caused by pulmonary embolism and an asymptomatic decrease in left ventricular ejection fraction. No objective antitumor responses were observed. CEC levels increased in the hours after infusion, indicating potential effect of the compound on the vasculature. Conclusion ZD6126 administered as a weekly infusion was clinically well tolerated. The MTD was reached at 20 mg/m2.

Interstitial fluid pressure (IFP) is elevated in tumors due to abnormal vasculature, lack of lymphatic drainage, and alterations in the tumor interstitium. ZD6126 is a tubulin-binding agent that selectively disrupts tumor vasculature resulting in tumor necrosis. This study examined the effect of ZD6126 on tumor IFP and the response of tumors with different IFP levels to ZD6126. Pretreatment IFP was measured using the wick-in-needle method in tumors (murine KHT-C and human CaSki) growing i.m. in the hind legs of mice. Mice were treated i.p. with a single dose of ZD6126 (100 or 200 mg/kg) and posttreatment IFP measurements were made. Blood flow imaging was conducted using Doppler optical coherence tomography, whereas oxygen partial pressure was measured using a fiber optic probe. Clonogenic assays were done to determine tumor cell survival. In KHT-C tumors, IFP dropped significantly at 1 hour posttreatment, returned to pretreatment values at 3 hours, and then declined to ∼25% of the pretreatment values by 72 hours. In CaSki tumors, the IFP decreased progressively, beginning at 1 hour, to ∼30% of pretreatment values by 72 hours. Clonogenic cell survival data indicated that ZD6126 was less effective in tumors with high IFP values (>25 mm Hg). Vascular disrupting agents, such as ZD6126, can affect IFP levels and initial IFP levels may predict tumor response to these agents. The higher cell survival in high IFP tumors may reflect greater microregional blood flow limitations in these tumors and reduced access of the drug to the target endothelial cells. (Cancer Res 2006; 66(4): 2074-80)

Human head and neck squamous cell carcinoma cells transfected with mutant TP53 (SAS/mp53) or with neo vector as a control (SAS/neo) were inoculated subcutaneously into both the hind legs of Balb/cA nude mice. Mice bearing the tumors received 5-bromo-2'-deoxyuridine (BrdU) continuously to label all proliferating (P) cells in the tumors. The mice then received a hypoxic cytotoxin, tirapazamine (TPZ) or TX-402, with or without a vascular targeting agent (VTA), ZD6126. Another group of mice given ZD6126 received a series of test doses of gamma-rays while alive or after tumor clamping to obtain hypoxic fractions (HFs) in the tumors. After each treatment, the tumor cells were isolated and incubated with a cytokinesis blocker (cytochalasin-B), and the micronucleus (MN) frequency in cells without BrdU labeling [quiescent (Q) cells] was determined using immunofluorescence staining for BrdU. The MN frequency in total (P+Q) tumor cells was determined from the tumors that were not pretreated with BrdU. Both hypoxic cytotoxins showed significantly greater toxicity toward SAS/mp53 and Q than SAS/neo and total tumor cells, respectively. The sensitivity to TX-402 was significantly higher than that to TPZ in both total and Q tumor cells of both tumors. The significant enhancive effect by ZD6126 combined with each hypoxic cytotoxin was similar irrespective of p53 status, and slightly greater for total than Q cells probably because of a more marked increase in the size of the HFs in total than Q cells on the use of ZD6126 in both tumors, resulting in a reduction of the difference in the sensitivity to the hypoxic cytotoxin between total and Q cells. In the treatment of conventional cancer therapy-resistant Q tumor cells or p53-mutated tumor cells, the use of hypoxic cytotoxin was very promising either alone or when VTA was co-administered. TX-402 might be more promising than TPZ, although further study of the toxicity to normal tissue is needed.

Aims To provide a comprehensive overview of the current state of development of a novel class of anti-cancer drugs, the vascular disrupting agents (VDAs), previously known as vascular targeting agents (VTAs). Materials and methods A comprehensive review, analysis and commentary of the published medical literature on VDAs was performed. Results Tumour vascular targeting therapy exploits known differences between normal and tumour blood vessels. VDAs target the pre-existing vessels of tumours (cf anti-angiogenics), and cause vascular shutdown leading to tumour cell death and rapid haemorrhagic necrosis within hours. It is becoming clear that VDAs have overlapping activity with anti-angiogenic drugs, which prevent the formation of new blood vessels. There are two types of VDA. First, biological or ligand-directed VDAs use antibodies, peptides or growth factors to target toxins or pro-coagulants to the tumour endothelium. In contrast, small molecule VDAs work either as tubulin-binding agents or through induction of local cytokine production. VDAs can kill tumour cells resistant to conventional chemotherapy and radiotherapy, and work best on cells in the poorly perfused hypoxic core of tumours, leaving a viable rim of well-perfused tumour tissue at the periphery, which rapidly regrows. Consequently, responses of tumours to VDAs given as single agents have been poor; however, combination therapy with cytotoxic chemotherapy, external-beam radiotherapy, and radioimmunotherapy, which target the peripheral tumour cells, has produced some excellent responses in animal tumours. VDAs are generally well tolerated with different side-effect profiles to current oncological therapies. Dynamic magnetic resonance imaging is most frequently used to obtain a pharmacodynamic end point to determine whether the VDA is acting on its intended target. Conclusions VDAs are a promising new class of drug, which offer the attractive possibility of inducing responses in all tumour types with combination therapy.

Purpose: To examine the antivascular and antitumor activity of the vascular targeting agent ZD6126 in combination with radiation in lung and head-and-neck (H&N) cancer models. The overall hypothesis was that simultaneous targeting of tumor cells (radiation) and tumor vasculature (ZD6126) might enhance tumor cell killing. Methods and Materials: A series of in vitro studies using human umbilical vein endothelial cells (HUVEC) and in vivo studies in athymic mice bearing human lung (H226) and H&N (squamous cell carcinoma [SCC]1, SCC6) tumor xenografts treated with ZD6126 and/or radiation were performed. Results: ZD6126 inhibited the capillary-like network formation in HUVEC. Treatment of HUVEC with ZD6126 resulted in cell cycle arrest in G2/M, with decrease of cells in S phase and proliferation inhibition in a dose-dependent manner. ZD6126 augmented the cell-killing effect of radiation and radiation-induced apoptosis in HUVEC. The combination of ZD6126 and radiation further decreased tumor vascularization in an in vivo Matrigel angiogenesis assay. In tumor xenografts, ZD6126 enhanced the antitumor activity of radiation, resulting in tumor growth delay. Conclusions: These preclinical studies suggest that ZD6126 can augment the radiation response of proliferating endothelial H&N and lung cancer cells. These results complement recent reports suggesting the potential value of combining radiation with vascular targeting/antiangiogenic agents.

Purpose: ZD6126 is a novel vascular-targeting agent that selectively disrupts the tubulin cytoskeleton of endothelial cells. In the immature vessels characteristic of tumor vasculature, this leads to endothelial cell contraction, blood vessel congestion, and, consequently, tumor cell death. ZD6126 has been shown to delay tumor growth in a range of xenograft models. The antitumor effect of ZD6126 can be increased in combination with cisplatin or radiation therapy, although the precise mechanism of this enhancement has not been demonstrated. ZD6126 treatment has also been shown to inhibit lung metastasis, and the present study has explored the potential to increase the antimetastatic effect of ZD6126 by combining with cisplatin, and the underlining mechanism has been investigated. Experimental Design: Human lung adenocarcinoma PC14PE6 cells were injected into the tail vein of nude mice. Five weeks after injection animals were treated with ZD6126 (200 mg/kg i.p.), cisplatin (6 mg/kg i.v.), or a combination of the two agents. The animals were sacrificed 24 hours later, and the extent of lung metastases and the presence of apoptotic cells were assessed. Results: Histologic analysis revealed that the ZD6126/cisplatin combination resulted in a 2 to 4-fold increase in the total number of tumor-associated apoptotic cells compared with either treatment alone. ZD6126 alone induced apoptosis of tumor-associated endothelial cells in tumors, and the extent of apoptosis was increased 2-fold in combination with cisplatin. The lung weight was significantly reduced, and the number of metastatic nodules significantly was lower in the combined treatment group than in the control group. Conclusions: These data suggest that the antimetastatic effect of the vascular-targeting agent ZD6126 can be increased by use in combination with cisplatin, which increases the incidence of endothelial cell apoptosis.

BACKGROUND Tumor endothelium represents a valuable target for cancer therapy. The vasculature plays a critical role in the survival and continued growth of solid tumor masses; in addition, the inherent differences between tumor blood vessels and blood vessels associated with normal tissue make the tumor vasculature a unique target on which to base the design of novel therapeutics, which may allow highly selective treatment of malignant disease. Therapeutic strategies that target and disrupt the already formed vessel networks of growing tumors are actively being pursued. The goal of these approaches is to induce a rapid and catastrophic shutdown of the vascular function of the tumor so that blood flow is arrested and tumor cell death due to the resulting oxygen and nutrient deprivation and buildup of waste products occurs. METHODS Biologic approaches and small-molecule drugs that can be used to damage tumor vasculature have been identified. Physiologic, histologic/morphologic, and immunohistochemical assessments have demonstrated that profound disruption of the tumor vessel network can be observed minutes to hours after treatment. The small-molecule agents that have made the greatest advances in the clinical setting (5,6-dimethylxanthenone-4-acetic acid [DMXAA], combretastatin A4 disodium phosphate [CA4DP], and ZD6126) are the focus of the current review. RESULTS Loss of patent blood vessels, decreased tumor blood flow, extensive necrosis, and secondary ischemia-induced tumor cell death have been well documented in a variety of preclinical tumor models treated with agents such as DMXAA, CA4DP, and ZD6126. The use of such agents in conjunction with irradiation and other chemotherapeutic agents has led to improved treatment outcomes. CONCLUSIONS The targeting of tumors' supportive blood vessel networks could lead to improvements in cancer cure rates. It is likely that this approach will prove to be most efficacious when used in concert with conventional treatment strategies. Cancer 2004. © 2004 American Cancer Society.

Purpose To evaluate the antitumor efficacy of a vascular targeting strategy that combines an agent that disrupts established tumor blood vessels (ZD6126) with one that interferes with new vessel formation (ZD6474) in models of human renal cell carcinoma (Caki-1) and Kaposi's sarcoma (KSY-1). Methods and materials Caki-1 and KSY-1 xenograft-bearing nude mice were treated with ZD6126 and ZD6474 either as single agents or in combination when the tumors reached a size of ∼200 mm 3 . ZD6126 therapy consisted of three doses of 100 mg/kg administered 1, 3, and 5 days after the tumor reached the starting size. ZD6474 was administered daily (25 mg/kg) on Days 1–5. In the combination studies, ZD6474 treatment began immediately after the first dose of ZD6126. The tumor response to treatment was evaluated using a regrowth delay endpoint. Results Significant tumor growth delays were observed in both tumor models with either agent with the treatment regimen used. In the Caki-1 and KSY-1 models, respectively, ZD6126 treatment resulted in a tumor growth delay of 23 and 26 days and ZD6474 produced a tumor growth delay of 24.5 and 14.5 days. When ZD6126 and ZD6474 were combined, the tumor growth delays increased to 55 (Caki-1) and 86 (KSY-1) days. In the KSY-1 model, the combination therapy also resulted in 3 of 8 long-term tumor-free survivors. Conclusion These results indicate that statistically significant antitumor efficacy can be achieved using a treatment strategy that combines a therapy that targets the established tumor blood vessels with one that interferes with the process of angiogenesis.

Purpose The aim of this study was to investigate the pathophysiologic effects induced by the novel vascular targeting agent ZD6126 in a C3H mouse mammary carcinoma and to evaluate the agent's ability to inhibit tumor growth either when given alone or in combination with radiation. Methods and materials A C3H mammary carcinoma grown in the right rear foot of female CDF1 mice was treated when at 200 mm 3 in size. ZD6126 was dissolved in saline and injected intraperitoneally. Blood perfusion was measured using the RbCl extraction procedure, tumor oxygen (pO 2 ) status was assessed with the Eppendorf electrode, and tumor necrosis was estimated from histologic sections. Radiation (240-kV X-rays) was locally administered to tumors of restrained nonanesthetized mice, and response was assessed using a tumor growth assay. Results ZD6126 induced a significant dose- and time-dependent decrease in tumor perfusion, reaching a maximal 70% reduction around 3 h after injecting 150–300 mg/kg. However, full recovery was seen within 6 h. A 200 mg/kg dose significantly decreased tumor oxygenation status at 3 h (median pO 2 decreased from 7 to 3 mm Hg; % pO 2 values ≤2.5 mm Hg increased from 30% to 55%) and by 24 h had significantly increased necrotic fraction from 14.5% to 25.2%. This ZD6126 dose resulted in a small, yet significant, 1.4 days inhibition of tumor growth when given alone. It also enhanced the tumor response to radiation, giving rise to a significant 1.3-fold increase in the slope of the radiation dose–response curve. Of the normal tissues, only muscle (at 3 h) and spleen (at 6 h) showed any significant reduction in perfusion after injecting 200 mg/kg, but these transient decreases were only 32% and 49%, respectively. Conclusions Our preclinical studies clearly demonstrate a tumor-specific reduction in blood perfusion by ZD6126. Although these changes were transient, they were sufficient to increase tumor necrosis, inhibit tumor growth, and enhance radiation response.

The antitumour action of 5,6-dimethylxanthenone-4-acetic acid (DMXAA) is mediated through tumour-selective antivascular effects and cytokine induction. This clinical phase I trial was conducted to examine its toxicity, maximum tolerated dose, pharmacokinetics (PK) and pharmacodynamics (PD). A secondary objective was to assess its antitumour efficacy. DMXAA was administered every 3 weeks as a 20-min i.v. infusion. Dose escalation initially followed a modified Fibonacci schema but was also guided by PK and toxicity. A total of 63 patients received 161 courses of DMXAA over 19 dose levels ranging from 6 to 4900 mg m(-2). DMXAA was well tolerated at lower doses and no drug-related myelosuppression was seen. Rapidly reversible dose-limiting toxicities were observed at 4900 mg m(-2), including confusion, tremor, slurred speech, visual disturbance, anxiety, urinary incontinence and possible left ventricular failure. Transient prolongation of the corrected cardiac QT interval was seen in 13 patients evaluated at doses of 2000 mg m(-2) and above. A patient with metastatic cervical carcinoma achieved an unconfirmed partial response at 1100 mg m(-2), progressing after eight courses. The results of PK and PD studies are reported separately. DMXAA has antitumour activity at well-tolerated doses.

ZD6126 is a vascular targeting agent that disrupts the tubulin cytoskeleton of proliferating neo-endothelial cells. This leads to the selective destruction and congestion of tumour blood vessels in experimental tumours, resulting in extensive haemorrhagic necrosis. In this study, the dose-dependent activity of ZD6126 in rat GH3 prolactinomas and murine RIF-1 fibrosarcomas was assessed using two magnetic resonance imaging (MRI) methods. Dynamic contrast-enhanced (DCE) MRI, quantified by an initial area under the time-concentration product curve (IAUC) method, gives values related to tumour perfusion and vascular permeability. Multigradient recalled echo MRI measures the transverse relaxation rate T(2)*, which is sensitive to tissue (deoxyhaemoglobin). Tumour IAUC and R(2)* (=1/T(2)*) decreased post-treatment with ZD6126 in a dose-dependent manner. In the rat model, lower doses of ZD6126 reduced the IAUC close to zero within restricted areas of the tumour, typically in the centre, while the highest dose reduced the IAUC to zero over the majority of the tumour. A decrease in both MRI end points was associated with the induction of massive central tumour necrosis measured histologically, which increased in a dose-dependent manner. Magnetic resonance imaging may be of value in evaluation of the acute clinical effects of ZD6126 in solid tumours. In particular, measurement of IAUC by DCE MRI should provide an unambiguous measure of biological activity of antivascular therapies for clinical trial.