Combining radiotherapy with AZD2171, a potent inhibitor of vascular endothelial growth factor signaling: pathophysiologic effects and therapeutic benefit

Natural Radiosensitizers in Radiotherapy: Cancer Treatment by Combining Ionizing Radiation with Resveratrol

Conventional cancer treatment is mainly based on the surgical removal of the tumor followed by radiotherapy and/or chemotherapy. When surgical removal is not possible, radiotherapy and, less often, chemotherapy is the only way to treat patients. However, despite significant progress in understanding the molecular mechanisms of carcinogenesis and developments in modern radiotherapy techniques, radiotherapy (alone or in combination) does not always guarantee treatment success. One of the main causes is the radioresistance of cancer cells. Increasing the radiosensitivity of cancer cells improves the processes leading to their elimination during radiotherapy and prolonging the survival of cancer patients. In order to enhance the effect of radiotherapy in the treatment of radioresistant neoplasms, radiosensitizers are used. In clinical practice, synthetic radiosensitizers are commonly applied, but scientists have recently focused on using natural products (phytocompounds) as adjuvants in radiotherapy. In this review article, we only discuss naturally occurring radiosensitizers currently in clinical trials (paclitaxel, curcumin, genistein, and papaverine) and those whose radiation sensitizing effects, such as resveratrol, have been repeatedly confirmed by many independent studies.

Atezolizumab-bevacizumab plus Y-90 TARE for the treatment of hepatocellular carcinoma: preclinical rationale and ongoing clinical trials

INTRODUCTION

The treatment algorithm of advanced hepatocellular carcinoma (HCC) has evolved since the introduction of immunotherapy. The IMbrave150 trial set atezolizumab-bevacizumab as a new standard-of-care first-line treatment for unresectable HCC patients. However, for patients with intermediate or advanced stage with portal vein thrombosis but without distant metastases, ⁹⁰Yttrium transarterial radioembolization (⁹⁰Y-TARE) is considered the treatment of choice.

AREAS COVERED

We discuss the main evidence regarding the use of ⁹⁰Y-TARE in HCC, the recent progress of immunotherapy in this tumor, and the preclinical rationale of combining VEGF blockade with the other two treatment strategies.

EXPERT OPINION

HCC has an extremely heterogeneous tumor immune microenvironment. This may explain the inconsistent outcomes obtained with immune-checkpoint inhibitors. The identification of patients who could benefit most from immunotherapy is crucial; however, reliable markers of response are lacking. Radiation therapy and VEGF inhibition have an established synergism with immunotherapy, mainly linked to enhanced antigen presentation and reduced immunosuppressive immune infiltrate. Combining an immune-checkpoint inhibitor with VEGF blockade and ⁹⁰Y-TARE might hence overcome primary resistances observed when each of these treatments is administerd alone.

Apatinib Combined With Radiotherapy Enhances Antitumor Effects in an In Vivo Nasopharyngeal Carcinoma Model

Vascular endothelial growth factor (VEGF) and its receptor (VEGFR) are highly expressed in nasopharyngeal carcinoma; therefore, blocking the binding of VEGF and VEGFR may be a potential way to treat nasopharyngeal carcinoma. Apatinib inhibits tumor angiogenesis. Previous studies have suggested that treatment with apatinib has an antitumor effect on nasopharyngeal carcinoma. This study will investigate the effect of apatinib combined with radiotherapy. In this study, nude mice injected with CNE-2 nasopharyngeal carcinoma cells were randomly divided into 6 groups. Therapeutic effects were assessed by evaluating tumor inhibition rate, phosphorylation of VEGFR-2, CD31, partial oxygen pressure, and tumor metabolism. We found that the tumor inhibition of mice in the treated groups was better compared to that of the control group. In mice treated with apatinib alone, angiogenesis was prevented, and the tumor tissue partial oxygen pressure was reduced, thereby achieving an antitumor effect. Moreover, the tumor inhibitory effect of combined treatment was stronger than treatment with either apatinib or radiotherapy alone. Compared with monotherapy treatment, combined treatment better resisted angiogenesis. Apatinib combined with radiotherapy to treat nasopharyngeal carcinoma has synergistic effects, which may be related to enhanced antiangiogenesis.

Novel phase I trial design to evaluate the addition of cediranib or selumetinib to preoperative chemoradiotherapy for locally advanced rectal cancer: the DREAMtherapy trial

BACKGROUND

The DREAMtherapy (Dual REctal Angiogenesis MEK inhibition radiotherapy) trial is a novel intertwined design whereby two tyrosine kinase inhibitors (cediranib and selumetinib) were independently evaluated with rectal chemoradiotherapy (CRT) in an efficient manner to limit the extended follow-up period often required for radiotherapy studies.

PATIENTS AND METHODS

Cediranib or selumetinib was commenced 10 days before and then continued with RT (45 Gy/25#/5 wks) and capecitabine (825 mg/m2 twice a day (BID)). When three patients in the cediranib 15-mg once daily (OD) cohort were in the surveillance period, recruitment to the selumetinib cohort commenced. This alternating schedule was followed throughout. Three cediranib (15, 20 and 30 mg OD) and two selumetinib cohorts (50 and 75 mg BID) were planned. Circulating and imaging biomarkers of inflammation/angiogenesis were evaluated.

RESULTS

In case of cediranib, dose-limiting diarrhoea, fatigue and skin reactions were seen in the 30-mg OD cohort, and therefore, 20 mg OD was defined as the maximum tolerated dose. Forty-one percent patients achieved a clinical or pathological complete response (7/17), and 53% (9/17) had an excellent clinical or pathological response (ECPR). Significantly lower level of pre-treatment plasma tumour necrosis factor alpha (TNFα) was found in patients who had an ECPR. In case of selumetinib, the 50-mg BID cohort was poorly tolerated (fatigue and diarrhoea); a reduced dose cohort of 75-mg OD was opened which was also poorly tolerated, and further recruitment was abandoned. Of the 12 patients treated, two attained an ECPR (17%).

CONCLUSIONS

This novel intertwined trial design is an effective way to independently investigate multiple agents with radiotherapy. The combination of cediranib with CRT was well tolerated with encouraging efficacy. TNFα emerged as a potential predictive biomarker of response and warrants further evaluation.

Oxygen-enhanced MRI Is Feasible, Repeatable, and Detects Radiotherapy-induced Change in Hypoxia in Xenograft Models and in Patients with Non-small Cell Lung Cancer

PURPOSE

Hypoxia is associated with poor prognosis and is predictive of poor response to cancer treatments, including radiotherapy. Developing noninvasive biomarkers that both detect hypoxia prior to treatment and track change in tumor hypoxia following treatment is required urgently.

EXPERIMENTAL DESIGN

We evaluated the ability of oxygen-enhanced MRI (OE-MRI) to map and quantify therapy-induced changes in tumor hypoxia by measuring oxygen-refractory signals in perfused tissue (perfused Oxy-R). Clinical first-in-human study in patients with non-small cell lung cancer (NSCLC) was performed alongside preclinical experiments in two xenograft tumors (Calu6 NSCLC model and U87 glioma model).

RESULTS

MRI perfused Oxy-R tumor fraction measurement of hypoxia was validated with ex vivo tissue pathology in both xenograft models. Calu6 and U87 experiments showed that MRI perfused Oxy-R tumor volume was reduced relative to control following single fraction 10-Gy radiation and fractionated chemoradiotherapy (P < 0.001) due to both improved perfusion and reduced oxygen consumption rate. Next, evaluation of 23 patients with NSCLC showed that OE-MRI was clinically feasible and that tumor perfused Oxy-R volume is repeatable [interclass correlation coefficient: 0.961 (95% CI, 0.858-0.990); coefficient of variation: 25.880%]. Group-wise perfused Oxy-R volume was reduced at 14 days following start of radiotherapy (P = 0.015). OE-MRI detected between-subject variation in hypoxia modification in both xenograft and patient tumors.

CONCLUSIONS

These findings support applying OE-MRI biomarkers to monitor hypoxia modification, to stratify patients in clinical trials of hypoxia-modifying therapies, to identify patients with hypoxic tumors that may fail treatment with immunotherapy, and to guide adaptive radiotherapy by mapping regional hypoxia.

Targeting the vasculature of tumours: combining VEGF pathway inhibitors with radiotherapy

The development of blood vessels by the process of angiogenesis underpins the growth and metastasis of many tumour types. Various angiogenesis inhibitors targeted against vascular endothelial growth factor A (VEGF-A) and its receptors have entered the clinic more than a decade ago. However, despite substantial clinical improvements, their overall efficacy proved to be significantly lower than many of the pre-clinical studies had predicted. Antiangiogenic agents have been combined with chemotherapy, radiotherapy and more recently immunotherapy in many pre-clinical and clinical studies in an effort to improve their efficacy. To date, only their use alongside chemotherapy is approved as part of standard treatment protocols. Most pre-clinical studies have reported improved tumour control from the addition of antiangiogenic therapies to radiotherapy and progress has been made in unravelling the complex mechanisms through which VEGF inhibition potentiates radiotherapy responses. However, the efficacy of this combination is variable, and many questions still remain as to how best to administer the two modalities to achieve optimal response and minimal toxicity. One important limiting factor is that, unlike some other targeted therapies, antiangiogenic agents are not administered to selected patient populations, since biomarkers for identifying responders have not yet been established. Here, we outline VEGF biology and review current approaches that aim to identify biomarkers for stratifying patients for treatment with angiogenesis inhibitors. We also discuss current progress in elucidating mechanisms of interaction between radiotherapy and VEGF inhibitors. Ongoing clinical trials will determine whether these combinations will ultimately improve treatment outcomes for cancer patients.

Targeting Enox1 in tumor stroma increases the efficacy of fractionated radiotherapy

The goal of this investigation was to clarify the question of whether targeting Enox1 in tumor stroma would synergistically enhance the survival of tumor-bearing mice treated with fractionated radiotherapy. Enox1, a NADH oxidase, is expressed in tumor vasculature and stroma. However, it is not expressed in many tumor types, including HT-29 colorectal carcinoma cells. Pharmacological inhibition of Enox1 in endothelial cells inhibited repair of DNA double strand breaks, as measured by γH2AX and 53BP1 foci formation, as well as neutral comet assays. For 4 consecutive days athymic mice bearing HT-29 hindlimb xenografts were injected with a small molecule inhibitor of Enox1 or solvent control. Tumors were then administered 2 Gy of x-rays. On day 5 tumors were administered a single ‘top-up’ fraction of 30 Gy, the purpose of which was to amplify intrinsic differences in the radiation fractionation regimen produced by Enox1 targeting. Pharmacological targeting of Enox1 resulted in 80% of the tumor-bearing mice surviving at 90 days compared to only 40% of tumor-bearing mice treated with solvent control. The increase in survival was not a consequence of reoxygenation, as measured by pimonidazole immunostaining. These results are interpreted to indicate that targeting of Enox1 in tumor stroma significantly enhances the effectiveness of 2 Gy fractionated radiotherapy and identifies Enox1 as a potential therapeutic target.

Akt inhibition improves long-term tumour control following radiotherapy by altering the microenvironment

Radiotherapy is an important anti-cancer treatment, but tumour recurrence remains a significant clinical problem. In an effort to improve outcomes further, targeted anti-cancer drugs are being tested in combination with radiotherapy. Here, we have studied the effects of Akt inhibition with AZD5363. AZD5363 administered as an adjuvant after radiotherapy to FaDu and PE/CA PJ34 tumours leads to long-term tumour control, which appears to be secondary to effects on the irradiated tumour microenvironment. AZD5363 reduces the downstream effectors VEGF and HIF-1α, but has no effect on tumour vascularity or oxygenation, or on tumour control, when administered prior to radiotherapy. In contrast, AZD5363 given after radiotherapy is associated with marked reductions in tumour vascular density, a decrease in the influx of CD11b+ myeloid cells and a failure of tumour regrowth. In addition, AZD5363 is shown to inhibit the proportion of proliferating tumour vascular endothelial cells in vivo, which may contribute to improved tumour control with adjuvant treatment. These new insights provide promise to improve outcomes with the addition of AZD5363 as an adjuvant therapy following radiotherapy.

The VEGFR Inhibitor Cediranib Improves the Efficacy of Fractionated Radiotherapy in a Colorectal Cancer Xenograft Model

BACKGROUND/PURPOSE

Radiotherapy (RT) increases local tumor control in locally advanced rectal cancer, but complete histological response is seen in only a minority of cases. Antiangiogenic therapy has been proposed to improve RT efficacy by "normalizing" the tumor microvasculature. Here, we examined whether cediranib, a pan-vascular endothelial growth factor (VEGF) receptor tyrosine kinase inhibitor, improves microvascular function and tumor control in combination with RT in a mouse colorectal cancer (CRC) model.

METHODS

CRC xenografts (HT29) were grown subcutaneously in mice. Animals were treated for 5 consecutive days with vehicle, RT (1.8 Gy daily), cediranib (6 mg/kg po), or combined therapy (cediranib 2 h prior to radiation). Tumor volume was measured with calipers. Vascular changes were analyzed by dynamic contrast-enhanced MRI, oxygenation and interstitial fluid pressure probes and histology. To investigate vascular changes more in detail, a second set of mice were fitted with titanium dorsal skinfold window chambers, wherein a HT29 tumor cell suspension was injected. In vivo fluorescence microscopy was performed before and after treatment (same treatment protocol).

RESULTS

In vivo microscopy analyses showed that VEGFR inhibition with cediranib led to a "normalization" of the vessel wall, with decreased microvessel permeability (p < 0.0001) and tortuosity (p < 0.01), and a trend to decreased vessel diameters. This seemed to lead to lower tumor hypoxia rates in the cediranib and combination groups compared to the control and RT groups. This led to an increased tumor control in the combination group compared to controls or monotherapy (p < 0.0001).

CONCLUSIONS

The combination of RT with cediranib enhances tumor control in a CRC xenograft mouse model. Microvascular analyses suggest that cediranib leads to vascular normalization and improved oxygenation.

Histone deacetylase enzyme silencing using shRNAs enhances radiosensitivity of SW579 thyroid cancer cells

The aim of the present study was to screen the enzymes that are associated with the radiosensitivity of SW579 thyroid cancer cells, and investigate whether radiation, combined with specific RNA interference on the screened enzymes, enhances radiosensitivity of SW579 thyroid cancer cells. Quantitative polymerase chain reaction (qPCR) was used to analyze epigenetic enzyme expression changes before and after radiotherapy, and four enzymes, histone deacetylase 1 (HDAC1), HDAC2, HDAC4 and HDAC6 were screened. Western blot analysis was performed to analyze the change in HDAC1, HDAC2, HDAC4 and HDAC6 protein expression following radiotherapy. Short hairpin RNA (ShRNA)‑HDAC1, shRNA‑HDAC2, shRNA‑HDAC4 and shRNA‑HDAC6 plasmids were constructed and SW579 cells were transfected with corresponding shRNA‑HDACs. Reverse transcription‑qPCR was used to detect whether downregulation of HDAC mRNAs had been effective. In addition, shRNA and shRNA negative control (NC) pools were established and transfected into the SW579 cells. The samples were divided into four groups; control, trichostatin A, shRNA pool and shRNA NC pool, to analyze the effective enhancement of specific shRNA on radiosensitivity in thyroid cancer cells. The morphological changes were observed in the SW579 cells, and the number of tumor cells decreased markedly in the shRNA pool group compared with that of the other three groups. Therefore, it was concluded that HDACs present a potential target for increasing the sensitivity of thyroid cancer cells to radiotherapy, and shRNA‑HDAC interference combined with radiotherapy promotes the radiosensitivity of tumors.

Expression of VEGFR and PDGFR-α/-β in 187 canine nasal carcinomas

Radiotherapy represents the standard of care for intranasal carcinomas. Responses to tyrosine kinase inhibitors (TKIs) have been reported but data on expression of target receptor tyrosine kinases (rTKs) is limited. This study characterizes the expression of vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR)-α and PDGFR-β in canine intranasal carcinomas. Histological samples from 187 dogs were retrieved. Immunohistochemistry was performed using commercially available antibodies. Expression of rTKs was classified into weak, moderate or intense and additionally recorded as cytoplasmic, membranous, cytoplasmic-membranous, nuclear or stromal. VEGFR was expressed in 158 dogs with predominantly moderate expression (36.9%) and a cytoplasmic-membranous expression pattern (70.9%). PDGFR-α was detected in 133 with predominantly weak expression (57.9%) and cytoplasmic pattern (87.9%). PDGFR-β was identified in 74 patients with a predominantly moderate expression (17.6%) and cytoplasmic expression pattern (63.5%). Co-expression of rTKs was common. These results confirm expression of VEGFR, PDGFR-α and PDGFR-β in canine intranasal carcinomas and support the utility of TKIs.

Dual Action Enhancement of Gold Nanoparticle Radiosensitization by Pentamidine in Triple Negative Breast Cancer

Triple negative breast cancer (TNBC) is an aggressive disease with a high risk of recurrence and death. Here, we present a novel strategy to enhance the radiotherapy of TNBC by combining gold nanoparticles (AuNPs) with pentamidine, a clinically approved anti-parasitic agent with anti-cancer properties. The radiosensitization effects of PEG-stabilized AuNPs (PEG-AuNPs) in combination with pentamidine were evaluated in two human TNBC cell lines (MDA-MB-231 and MDA-MB-436). Our results showed that PEG-AuNPs alone sensitized both cell lines to radiation, achieving dose enhancement factors of 1.26 and 1.15 in MDA-MB-231 and MDA-MB-436, respectively. In combination with pentamidine, the greatest dose enhancement was achieved in MDA-MB-231 after 24 h of treatment with 500 μM PEG-AuNPs and 20 μM pentamidine (dose enhancement factor of 1.55). Based on the in vitro data, it is projected that this combination would result in a 10 log increase in cell kill compared to radiation alone in a clinical setting, where 50 Gy is administered to breast cancer patients in 25 fractions over 5 weeks. Studies to elucidate the underlying mechanism of radiosensitization revealed that the adsorption of pentamidine onto the PEG-AuNP surface increased the cellular uptake of gold compared to PEG-AuNPs alone. In addition, the combination resulted in a significantly greater number of residual DNA double-strand breaks compared to that of either agent alone after a 2 Gy dose. Taken together, the dual action of pentamidine on the physical and biological pathways of radiosensitization by PEG-AuNPs results in superior radiotherapeutic effects of the combined treatment group in MDA-MB-231.

Oxygen-Enhanced MRI Accurately Identifies, Quantifies, and Maps Tumor Hypoxia in Preclinical Cancer Models

There is a clinical need for noninvasive biomarkers of tumor hypoxia for prognostic and predictive studies, radiotherapy planning, and therapy monitoring. Oxygen-enhanced MRI (OE-MRI) is an emerging imaging technique for quantifying the spatial distribution and extent of tumor oxygen delivery in vivo. In OE-MRI, the longitudinal relaxation rate of protons (ΔR1) changes in proportion to the concentration of molecular oxygen dissolved in plasma or interstitial tissue fluid. Therefore, well-oxygenated tissues show positive ΔR1. We hypothesized that the fraction of tumor tissue refractory to oxygen challenge (lack of positive ΔR1, termed "Oxy-R fraction") would be a robust biomarker of hypoxia in models with varying vascular and hypoxic features. Here, we demonstrate that OE-MRI signals are accurate, precise, and sensitive to changes in tumor pO2 in highly vascular 786-0 renal cancer xenografts. Furthermore, we show that Oxy-R fraction can quantify the hypoxic fraction in multiple models with differing hypoxic and vascular phenotypes, when used in combination with measurements of tumor perfusion. Finally, Oxy-R fraction can detect dynamic changes in hypoxia induced by the vasomodulator agent hydralazine. In contrast, more conventional biomarkers of hypoxia (derived from blood oxygenation-level dependent MRI and dynamic contrast-enhanced MRI) did not relate to tumor hypoxia consistently. Our results show that the Oxy-R fraction accurately quantifies tumor hypoxia noninvasively and is immediately translatable to the clinic.

Vasoactivity of rucaparib, a PARP-1 inhibitor, is a complex process that involves myosin light chain kinase, P2 receptors, and PARP itself

Therapeutic inhibition of poly(ADP-ribose) polymerase (PARP), as monotherapy or to supplement the potencies of other agents, is a promising strategy in cancer treatment. We previously reported that the first PARP inhibitor to enter clinical trial, rucaparib (AG014699), induced vasodilation in vivo in xenografts, potentiating response to temozolomide. We now report that rucaparib inhibits the activity of the muscle contraction mediator myosin light chain kinase (MLCK) 10-fold more potently than its commercially available inhibitor ML-9. Moreover, rucaparib produces additive relaxation above the maximal degree achievable with ML-9, suggesting that MLCK inhibition is not solely responsible for dilation. Inhibition of nitric oxide synthesis using L-NMMA also failed to impact rucaparib’s activity. Rucaparib contains the nicotinamide pharmacophore, suggesting it may inhibit other NAD+-dependent processes. NAD⁺ exerts P2 purinergic receptor-dependent inhibition of smooth muscle contraction. Indiscriminate blockade of the P2 purinergic receptors with suramin abrogated rucaparib-induced vasodilation in rat arterial tissue without affecting ML-9-evoked dilation, although the specific receptor subtypes responsible have not been unequivocally identified. Furthermore, dorsal window chamber and real time tumor vessel perfusion analyses in PARP-1^-/- mice indicate a potential role for PARP in dilation of tumor-recruited vessels. Finally, rucaparib provoked relaxation in 70% of patient-derived tumor-associated vessels. These data provide tantalising evidence of the complexity of the mechanism underlying rucaparib-mediated vasodilation.

Phase 1 trial of bevacizumab with concurrent chemoradiation therapy for squamous cell carcinoma of the head and neck with exploratory functional imaging of tumor hypoxia, proliferation, and perfusion

PURPOSE

A phase 1 trial was completed to examine the safety and feasibility of combining bevacizumab with radiation and cisplatin in patients with locoregionally advanced squamous cell carcinoma of the head and neck (HNSCC) treated with curative intent. Additionally, we assessed the capacity of bevacizumab to induce an early tumor response as measured by a series of biological imaging studies.

METHODS AND MATERIALS

All patients received a single induction dose of bevacizumab (15 mg/kg) delivered 3 weeks (±3 days) before the initiation of chemoradiation therapy. After the initial dose of bevacizumab, comprehensive head and neck chemoradiation therapy was delivered with curative intent to 70 Gy in 33 fractions with concurrent weekly cisplatin at 30 mg/m(2) and bevacizumab every 3 weeks (weeks 1, 4, 7) with dose escalation from 5 to 10 to 15 mg/kg. All patients underwent experimental imaging with [(18)F]fluorothymidine positron emission tomography (FLT-PET) (proliferation), [(61)Cu]Cu-diacetyl-bis(N4-methylthiosemicarbazone) PET (Cu-ATSM-PET) (hypoxia), and dynamic contrast-enhanced computed tomography (DCE-CT) (perfusion) at 3 time points: before bevacizumab monotherapy, after bevacizumab monotherapy, and during the combined therapy course.

RESULTS

Ten patients were enrolled. All had stage IV HNSCC, all achieved a complete response to treatment, and 9 of 10 remain alive, with a mean survival time of 61.3 months. All patients experienced grade 3 toxicity, but no dose-limiting toxicities or significant bleeding episodes were observed. Significant reductions were noted in tumor proliferation (FLT-PET), tumor hypoxia (Cu-ATSM-PET), and DCE-CT contrast enhancement after bevacizumab monotherapy, with further decreases in FLT-PET and Cu-ATSM-PET during the combined therapy course.

CONCLUSIONS

The incorporation of bevacizumab into comprehensive chemoradiation therapy regimens for patients with HNSCC appears safe and feasible. Experimental imaging demonstrates measureable changes in tumor proliferation, hypoxia, and perfusion after bevacizumab monotherapy and during chemoradiation therapy. These findings suggest opportunities to preview the clinical outcomes for individual patients and thereby design personalized therapy approaches in future trials.

Inhibition of monocarboxylate transporter-1 (MCT1) by AZD3965 enhances radiosensitivity by reducing lactate transport

Inhibition of the monocarboxylate transporter MCT1 by AZD3965 results in an increase in glycolysis in human tumor cell lines and xenografts. This is indicated by changes in the levels of specific glycolytic metabolites and in changes in glycolytic enzyme kinetics. These drug-induced metabolic changes translate into an inhibition of tumor growth in vivo. Thus, we combined AZD3965 with fractionated radiation to treat small cell lung cancer (SCLC) xenografts and showed that the combination provided a significantly greater therapeutic effect than the use of either modality alone. These results strongly support the notion of combining MCT1 inhibition with radiotherapy in the treatment of SCLC and other solid tumors.

Optimization of the dorsal skinfold window chamber model and multi-parametric characterization of tumor-associated vasculature

The dorsal skinfold window chamber (DSWC) model is a unique tool that enables analysis of various aspects of tumor biology and therapeutic response. Although the protocol for the murine DSWC model is standardized, certain tumors fail to grow or require a particular environment to promote growth. Given such limitations, we optimized the DSWC model for a slow-growing tumor that regresses spontaneously in the standard protocol. We further characterized the vascular network in the tumor model compared with that of non-tumor-bearing mice and observed significant differences in multiple parameters related to vascular structure and function.

Inhibiting the phosphatidylinositide 3-kinase pathway blocks radiation-induced metastasis associated with Rho-GTPase and Hypoxia-inducible factor-1 activity

BACKGROUND AND PURPOSE

Undifferentiated follicular and anaplastic thyroid tumours often respond poorly to radiotherapy and show increased metastatic potential. We evaluated radiation-induced effects on metastasis in thyroid carcinoma cells and tumours, mechanistically focusing on phosphatidylinositide 3-kinase (PI3K) and associated pathways.

MATERIAL AND METHODS

Migration was analysed in follicular (FTC133) and anaplastic (8505c) cells following radiotherapy (0-6 Gray) with concomitant pharmacological (GDC-0941) or genetic inhibition of PI3K. Hypoxia-inducible factor-1 (HIF-1)-activity was measured using luciferase reporter assays and was inhibited using a dominant-negative variant. Activation and subcellular localisation of target proteins were assessed via Western blot and immunofluorescence. In vivo studies used FTC133 xenografts with metastatic lung dissemination assessed ex vivo.

RESULTS

Radiation induced migration in a HIF-dependent manner in FTC133 cells but decreased migration in 8505c's. Post-radiation HIF-activity correlated with migratory phenotype. PI3K-targeting inhibited migration under basal and irradiated conditions through inhibition of HIF-1α, Rho-GTPase expression/activity and localisation whilst having little effect on src/FAK. In vivo, radiation induced PI3K, HIF, Rho-GTPases and src but only PI3K, HIF and Rho-GTPases were inhibited by GDC-0941. Co-treatment with GDC-0941 and radiation significantly reduced metastatic dissemination versus radiotherapy alone.

CONCLUSIONS

Radiation modifies metastatic characteristics of thyroid carcinoma cells, which can be successfully inhibited by targeting PI3K using GDC-0941 in vitro and in vivo.

Targeting hypoxia, HIF-1, and tumor glucose metabolism to improve radiotherapy efficacy

Radiotherapy, an important treatment modality in oncology, kills cells through induction of oxidative stress. However, malignant tumors vary in their response to irradiation as a consequence of resistance mechanisms taking place at the molecular level. It is important to understand these mechanisms of radioresistance, as counteracting them may improve the efficacy of radiotherapy. In this review, we describe how the hypoxia-inducible factor 1 (HIF-1) pathway has a profound effect on the response to radiotherapy. The main focus will be on HIF-1-controlled protection of the vasculature postirradiation and on HIF-1 regulation of glycolysis and the pentose phosphate pathway. This aberrant cellular metabolism increases the antioxidant capacity of tumors, thereby countering the oxidative stress caused by irradiation. From the results of translational studies and the first clinical phase I/II trials, it can be concluded that targeting HIF-1 and tumor glucose metabolism at several levels reduces the antioxidant capacity of tumors, affects the tumor microenvironment, and sensitizes various solid tumors to irradiation.

Response of HT29 colorectal xenograft model to cediranib assessed with 18 F-fluoromisonidazole positron emission tomography, dynamic contrast-enhanced and diffusion-weighted MRI

Cediranib is a small-molecule pan-vascular endothelial growth factor receptor inhibitor. The tumor response to short-term cediranib treatment was studied using dynamic contrast-enhanced and diffusion-weighted MRI at 7 T, as well as (18) F-fluoromisonidazole positron emission tomography and histological markers. Rats bearing subcutaneous HT29 human colorectal tumors were imaged at baseline; they then received three doses of cediranib (3 mg/kg per dose daily) or vehicle (dosed daily), with follow-up imaging performed 2 h after the final cediranib or vehicle dose. Tumors were excised and evaluated for the perfusion marker Hoechst 33342, the endothelial cell marker CD31, smooth muscle actin, intercapillary distance and tumor necrosis. Dynamic contrast-enhanced MRI-derived parameters decreased significantly in cediranib-treated tumors relative to pretreatment values [the muscle-normalized initial area under the gadolinium concentration curve decreased by 48% (p=0.002), the enhancing fraction by 43% (p=0.003) and K(trans) by 57% (p=0.003)], but remained unchanged in controls. No change between the pre- and post-treatment tumor apparent diffusion coefficients in either the cediranib- or vehicle-treated group was observed over the course of this study. The (18) F-fluoromisonidazole mean standardized uptake value decreased by 33% (p=0.008) in the cediranib group, but showed no significant change in the control group. Histological analysis showed that the number of CD31-positive vessels (59 per mm(2) ), the fraction of smooth muscle actin-positive vessels (80-87%) and the intercapillary distance (0.17 mm) were similar in cediranib- and vehicle-treated groups. The fraction of perfused blood vessels in cediranib-treated tumors (81 ± 7%) was lower than that in vehicle controls (91 ± 3%, p=0.02). The necrotic fraction was slightly higher in cediranib-treated rats (34 ± 12%) than in controls (26 ± 10%, p=0.23). These findings suggest that short-term treatment with cediranib causes a decrease in tumor perfusion/permeability across the tumor cross-section, but changes in vascular morphology, vessel density or tumor cellularity are not manifested at this early time point.

Microenvironment and radiation therapy

Dependency on tumor oxygenation is one of the major features of radiation therapy and this has led many radiation biologists and oncologists to focus on tumor hypoxia. The first approach to overcome tumor hypoxia was to improve tumor oxygenation by increasing oxygen delivery and a subsequent approach was the use of radiosensitizers in combination with radiation therapy. Clinical use of some of these approaches was promising, but they are not widely used due to several limitations. Hypoxia-inducible factor 1 (HIF-1) is a transcription factor that is activated by hypoxia and induces the expression of various genes related to the adaptation of cellular metabolism to hypoxia, invasion and metastasis of cancer cells and angiogenesis, and so forth. HIF-1 is a potent target to enhance the therapeutic effects of radiation therapy. Another approach is antiangiogenic therapy. The combination with radiation therapy is promising, but several factors including surrogate markers, timing and duration, and so forth have to be optimized before introducing it into clinics. In this review, we examined how the tumor microenvironment influences the effects of radiation and how we can enhance the antitumor effects of radiation therapy by modifying the tumor microenvironment.

Molecular biology of lung cancer: clinical implications

Lung cancer is a heterogeneous disease clinically, biologically, histologically, and molecularly. Understanding the molecular causes of this heterogeneity, which might reflect changes occurring in different classes of epithelial cells or different molecular changes occurring in the same target lung epithelial cells, is the focus of current research. Identifying the genes and pathways involved, determining how they relate to the biological behavior of lung cancer, and their utility as diagnostic and therapeutic targets are important basic and translational research issues. This article reviews current information on the key molecular steps in lung cancer pathogenesis, their timing, and clinical implications.

The clinically active PARP inhibitor AG014699 ameliorates cardiotoxicity but does not enhance the efficacy of doxorubicin, despite improving tumor perfusion and radiation response in mice

AG014699 was the first inhibitor of the DNA repair enzyme PARP-1 to enter clinical trial in cancer patients. In addition to enhancing the cytotoxic effect of DNA-damaging chemotherapies, we have previously shown that AG014699 is vasoactive, thereby having the potential to improve drug biodistribution. The effectiveness of the clinical agent doxorubicin is confounded both by poor tumor penetration and cardiotoxicity elicited via PARP hyperactivation. In this study, we analyzed the impact of AG014699 on doxorubicin tolerance and response in breast (MDA-MB-231) and colorectal (SW620, LoVo) tumor models in vitro and in vivo. As anticipated, AG014699 did not potentiate the response to doxorubicin in vitro. In vivo, AG014699 did not influence the pharmacokinetics of doxorubicin; however, it did ameliorate cardiotoxicity. Both toxicity and extent of amelioration were more pronounced in male than in female mice. AG014699 improved vessel perfusion in both MDA-MB-231 and SW620 tumors; however, this neither led to improved tumor-accumulation of doxorubicin nor enhanced therapeutic response. In contrast, when combined with radiotherapy, AG014699 significantly enhanced response both in vitro and in vivo. Real-time assessment of tumor vessel function and companion histologic studies indicate that doxorubicin causes a profound antivascular effect that counters the positive effect of AG014699 on perfusion. These data indicate that although AG014699 can enhance response to some chemotherapeutic drugs via improved delivery, this does not apply to doxorubicin. PARP inhibitors may still be of use to counter doxorubicin toxicity, and if the gender effect translates from rodents to humans, this would have greater effect in males.

Inhibition of PARP-1 by olaparib (AZD2281) increases the radiosensitivity of a lung tumor xenograft

PARP-1 is a critical enzyme in the repair of DNA strand breaks. Inhibition of PARP-1 increases the effectiveness of radiation in killing tumor cells. However, although the mechanism(s) are well understood for these radiosensitizing effects in vitro, the underlying mechanism(s) in vivo are less clear. Nicotinamide, a drug structurally related to the first generation PARP-1 inhibitor, 3-aminobenzamide, reduces tumor hypoxia by preventing transient cessations in tumor blood flow, thus improving tumor oxygenation and sensitivity to radiotherapy. Here, we investigate whether olaparib, a potent PARP-1 inhibitor, enhances radiotherapy, not only by inhibiting DNA repair but also by changing tumor vascular hemodynamics in non-small cell lung carcinoma (NSCLC). In irradiated Calu-6 and A549 cells, olaparib enhanced the cytotoxic effects of radiation (sensitizer enhancement ratio at 10% survival = 1.5 and 1.3) and DNA double-strand breaks persisted for at least 24 hours after treatment. Combination treatment of Calu-6 xenografts with olaparib and fractionated radiotherapy caused significant tumor regression (P = 0.007) relative to radiotherapy alone. To determine whether this radiosensitization was solely due to effects on DNA repair, we used a dorsal window chamber model to establish the drug/radiation effects on vessel dynamics. Olaparib alone, when given as single or multiple daily doses, or in combination with fractionated radiotherapy, increased the perfusion of tumor blood vessels. Furthermore, an ex vivo assay in phenylephrine preconstricted arteries confirmed olaparib to have higher vasodilatory properties than nicotinamide. This study suggests that olaparib warrants consideration for further development in combination with radiotherapy in clinical oncology settings such as NSCLC.

Cediranib enhances control of wild type EGFR and EGFRvIII-expressing gliomas through potentiating temozolomide, but not through radiosensitization: implications for the clinic

Glioblastomas (GBM) frequently overexpress the epidermal growth factor receptor (wtEGFR) or its mutant, EGFRvIII, contributing to chemo- and radioresistance. The current standard of care is surgery followed by radiation therapy with concurrent temozolomide (TMZ) followed by adjuvant TMZ. New treatment strategies for GBM include blockade of EGFR signaling and angiogenesis. Cediranib is a highly potent receptor tyrosine kinase inhibitor that inhibits all three VEGF receptors. This study investigated the radiosensitizing potential of cediranib in combination with TMZ in U87 GBM xenografts expressing wtEGFR or EGFRvIII. U87 GBM cells stably transfected with either wtEGFR or EGFRvIII were injected into the hind limbs of nude mice. Cediranib was dosed at 3 mg/kg daily five times a week orally for 2 weeks. TMZ was dosed at 10 mg/kg once only on day 0. Radiotherapy (RT) consisted of 3 fractions of 5 Gy (days 0-2). Cediranib did not radiosensitize either tumor type; however, cediranib did enhance the effectiveness of TMZ in both transfectants. Our results suggest that combining cediranib with temozolomide in the clinic will lead to improved tumor control.

ABT-869, a multitargeted receptor tyrosine kinase inhibitor, reduces tumor microvascularity and improves vascular wall integrity in preclinical tumor models

N-[4-(3-amino-1H-indazol-4-yl)phenyl]-N1-(2-fluoro-5-methyl phenyl)-urea (ABT-869) is a novel multitargeted receptor tyrosine kinase inhibitor that demonstrates single-agent activity in preclinical studies and has undergone phase I and II clinical trials. We characterized the mechanism of action of ABT-869 by examining vascular changes after treatment (25 mg/kg per day) in HT1080 fibrosarcoma and SW620 colon carcinoma cells, using immunohistochemistry, dynamic contrast enhanced-magnetic resonance imaging (DCE-MRI), and hypoxic protein detection. We observed the inhibition of vascular endothelial growth factor receptor 2 and platelet-derived growth factor receptor β phosphorylation in both tumors and changes in tumor vasculature. Reductions in microvessel density and diameter were observed. Vascular-wall integrity was assessed by colocalization of pericytes and basement membrane. Although both microvessel density and total number of pericytes decreased with treatment, the percentage of pericyte coverage on remaining vessels significantly increased. These data suggest the selective ablation of microvessels lacking pericyte coverage. Functional vascular measures DCE-MRI and hypoxia formation were also tested. After 2 days of treatment on the HT1080 model, vascular permeability, K(trans), was reduced by >60% and hypoxic tumor fraction was significantly decreased, which was also seen in the SW620 tumors after 4 days of treatment. Taken together, decreases in vascular permeability and changes in vascular integrity observed in these studies define the mode of action of ABT-869 and may aid in optimizing the timing of therapeutic window for combination therapies.

The tumor microenvironment in non-small-cell lung cancer

The tumor microenvironment (TME) of NSCLC is heterogeneous with variable blood flow through leaky immature vessels resulting in regions of acidosis and hypoxia. Hypoxia has been documented in NSCLC directly by polarographic needle electrodes and indirectly by assessing tissue and plasma hypoxia markers. In general, elevated expression of these markers portends poorer outcomes in NSCLC. Impaired vascularity and hypoxia can lead to increased metastasis and treatment resistance. Compounds that directly target hypoxic cells such as tirapazamine have been tested in clinical trials for NSCLC with mixed results. Preclinical data, however, suggest other ways of exploiting the abnormal TME in NSCLC for therapeutic gain. The inhibition of hypoxia-inducible factor-1alpha or vascular endothelial growth factor may increase local control after radiation. Inhibitors of the epidermal growth factor receptor (EGFR)/phosphatidylinositol 3-kinase (PI3K)/Akt pathway, such as erlotinib or PI-103, may "normalize" tumor vessels, allowing for increased chemotherapy delivery or improved oxygenation and radiation response. To select patients who may respond to these therapies and to evaluate the effects of these agents, a noninvasive means of imaging the TME is critical. Presently, there are several promising modalities to image hypoxia and the tumor vasculature; these include dynamic perfusion imaging and positron emission tomography scanning with radiolabled nitroimidazoles.

The hypoxia-selective cytotoxin NLCQ-1 (NSC 709257) controls metastatic disease when used as an adjuvant to radiotherapy

BACKGROUND

Metastases cause most cancer-related deaths. We investigated the use of hypoxia-selective cytotoxins as adjuvants to radiotherapy in the control of metastatic tumour growth.

METHODS

The NLCQ-1, RB6145 and tirapazamine were assessed against the spontaneously metastasising KHT model. Subcutaneous KHT tumours (250 mm(3)) were irradiated with 25 Gy (single fraction) to control primary growth. Equitoxic drug treatments (NLCQ-1 (10 mg kg(-1)) once daily; RB6145 (75 mg kg(-1)) and tirapazamine (13 mg kg(-1)) twice daily) were administered 3-6 days post-radiotherapy when hypoxic cells were evident in lung micrometastases. Mice were culled when 50% of controls exhibited detrimental signs of lung metastases.

RESULTS

In total, 95% of control mice presented with lung disease. This was significantly reduced by NLCQ-1 (33%; P=0.0002) and RB6145 (60%; P=0.02). Semi-quantitative grading of lung disease revealed a significant improvement with all treatments, with NLCQ-1 proving most efficacious (median grades: control, 4; NLCQ, 0 (P<0.0001); RB6145, 1 (P<0.001), tirapazamine, 3 (P=0.007)). Positron emission tomography (PET) was evaluated as a non-invasive means of assessing metastatic development. Primary and metastatic KHT tumours showed robust uptake of [(18)F]fluorodeoxyglucose ([(18)F]FDG). Metastatic burden discernable by [(18)F]FDG PET correlated well with macroscopic and histological lung analysis.

CONCLUSION

The hypoxia-selective cytotoxin NLCQ-1 controls metastatic disease and may be a successful adjuvant to radiotherapy in the clinical setting.

Radiotherapy in combination with vascular-targeted therapies

BACKGROUND

Given the critical role of tumor vasculature in tumor development, considerable efforts have been spent on developing therapeutic strategies targeting the tumor vascular network. A variety of agents have been developed, with two general approaches being pursued. Antiangiogenic agents (AAs) aim to interfere with the process of angiogenesis, preventing new tumor blood vessel formation. Vascular-disrupting agents (VDAs) target existing tumor vessels causing tumor ischemia and necrosis. Despite their great therapeutic potential, it has become clear that their greatest clinical utility may lie in combination with conventional anticancer therapies. Radiotherapy is a widely used treatment modality for cancer with its distinct therapeutic challenges. Thus, combining the two approaches seems reasonable.

CONCLUSIONS

Strong biological rationale exist for combining vascular-targeted therapies with radiation. AAs and VDAs were shown to alter the tumor microenvironment in such a way as to enhance responses to radiation. The results of preclinical and early clinical studies have confirmed the therapeutic potential of this new treatment strategy in the clinical setting. However, concerns about increased normal tissue toxicity, have been raised.

Antiangiogenics and radiotherapy

Antiangiogenic therapies are one of the fore-runners of the new generation of anticancer drugs aimed at tumour-specific molecular targets. Up until the beginning of this century, the general opinion was that targeted agents should show antitumour activity when used as single agents. However, it has now become clear that much greater improvements in therapeutic activity may be achieved by combining the novel agents with conventional cytotoxic therapies already in use in the clinic. Radiotherapy is currently used to treat half of all cancer patients at some stage in their therapy, although the development of radioresistance is an ongoing problem. It is therefore reasonable to expect that any novel molecularly-targeted agent which reaches the clinic will be used in combination with radiotherapy. The rationale for combining antiangiogenics in particular with radiotherapy exists, as radiotherapy has been shown to kill proliferating endothelial cells, suggesting that inhibiting angiogenesis may sensitise endothelial cells to the effects of radiation. Furthermore, targeting the vasculature may paradoxically increase oxygenation within tumours, thereby enhancing radiotherapy efficacy. In this review we present an update on the use of antiangiogenic methods in combination with radiotherapy.

Application of intravital microscopy in studies of tumor microcirculation

To grow and progress, solid tumors develop a vascular network through co-option and angiogenesis that is characterized by multiple structural and functional abnormalities, which negatively influence therapeutic outcome through direct and indirect mechanisms. As such, the morphology and function of tumor blood vessels, plus their response to different treatments, are a vital and active area of biological research. Intravital microscopy (IVM) has played a key role in studies of tumor angiogenesis, and ongoing developments in molecular probes, imaging techniques, and postimage analysis methods have ensured its continued and widespread use. In this review we discuss some of the primary advantages and disadvantages of IVM approaches and describe recent technological advances in optical microscopy (e.g., confocal microscopy, multiphoton microscopy, hyperspectral imaging, and optical coherence tomography) with examples of their application to studies of tumor angiogenesis.

Modulating the tumor microenvironment to increase radiation responsiveness

Radiosensitivity can be influenced both by factors intrinsic and extrinsic to the cancer cell. One of the factors in the tumor microenvironment (TME) extrinsic to the cancer cell that can affect radiosensitivity is oxygenation. Severely hypoxic cells require a 2-3 fold higher dose of radiation to achieve the same level of cell killing as do well-oxygenated cells. Other elements in the microenvironment that may influence tumor radiosensitivity are the response of stromal cells to radiation and the expression of factors such as vascular endothelial growth factor (VEGF) and hypoxia inducible factor-1 (HIF-1). There are currently several classes of agents that may increase tumor radiosensitivity by modulating the TME. Pre-clinical evidence indicates that inhibition of VEGF may increase local control after radiation. Several mechanisms have been postulated to explain this including radiosensitization of tumor endothelial cells, prevention of the establishment of new vasculature post-radiation, and increased oxygenation secondary to vascular normalization. Agents targeting HIF-1 also increase local control after radiation in pre-clinical models. This may occur via indirect inhibition of VEGF, which is a downstream target of HIF-1, or by VEGF-independent means. When combined with radiation, the EGFR inhibitor cetuximab improves local control and survival in patients with head and neck cancer. Pre-clinical data indicate that EGFR inhibitors can increase the intrinsic radiosensitivity of cancer cells. They can also improve tumor blood flow and oxygenation, which may increase extrinsic radiosensitivity. One of the pathways downstream of EGFR that may contribute to this effect is the PI3K/Akt pathway. Agents that directly inhibit this pathway improve blood flow and increase tumor oxygenation in pre-clinical models. The challenge remains to obtain clinical data from patients showing that modulation of the TME is an important mechanism by which biological agents can radiosensitize tumors and then to utilize this information to optimize therapy.

The mitogen-activated protein/extracellular signal-regulated kinase kinase 1/2 inhibitor AZD6244 (ARRY-142886) enhances the radiation responsiveness of lung and colorectal tumor xenografts

PURPOSE

Novel molecularly targeted agents, given in combination with radiotherapy, have the potential to increase tumor response rates and the survival of patients with lung cancer. AZD6244 is a potent and selective inhibitor of mitogen-activated protein kinase (MAPK) kinase 1/2 (MEK1/2), a critical enzyme within the MAPK/extracellular signal-regulated kinase (ERK) signaling pathway that regulates the proliferation and survival of tumor cells.

EXPERIMENTAL DESIGN

This study examined the potential benefit of combining AZD6244 with fractionated radiotherapy using human lung and colon carcinoma xenograft models.

RESULTS

AZD6244 reduced ERK phosphorylation in Calu-6 lung cancer cells in vitro. Administration of AZD6244 for 10 days (25 mg/kg twice daily p.o.) inhibited the tumor growth of Calu-6 xenografts, with regrowth occurring on cessation of drug treatment. When fractionated tumor-localized radiotherapy (5 x 2 Gy) was combined with AZD6244 treatment, the tumor growth delay was enhanced significantly when compared with either modality alone, and this effect was also seen in a colon tumor model. We examined the effect of inhibiting MEK1/2 on the molecular responses to hypoxia, a potential interaction that could contribute to radioresponsiveness. AZD6244 reduced hypoxia-inducible factor-specific transactivation in vivo, shown using Calu-6 dual clone cells that stably express a Firefly luciferase gene under the control of a hypoxia-driven promoter. Furthermore, hypoxia-inducible factor-1 alpha, GLUT-1, and vascular endothelial growth factor levels were reduced by AZD6244, and there was a significant decrease in vascular perfusion in the tumors given combination treatment when compared with the other treatment groups.

CONCLUSIONS

These data provide support for the clinical development of AZD6244 in combination with radiotherapy and indicate a potential role for AZD6244 in inhibiting the tumor hypoxia response.

Vasoactivity of AG014699, a clinically active small molecule inhibitor of poly(ADP-ribose) polymerase: a contributory factor to chemopotentiation in vivo?

PURPOSE

Poly(ADP-ribose) polymerase (PARP) plays an important role in DNA repair, and PARP inhibitors can enhance the activity of DNA-damaging agents in vitro and in vivo. AG014699 is a potent PARP inhibitor in phase II clinical development. However, the range of therapeutics with which AG014699 could interact via a DNA-repair based mechanism is limited. We aimed to investigate a novel, vascular-based activity of AG014699, underlying in vivo chemosensitization, which could widen its clinical application.

EXPERIMENTAL DESIGN

Temozolomide response was analyzed in vitro and in vivo. Vessel dynamics were monitored using "mismatch" following the administration of perfusion markers and real-time analysis of fluorescently labeled albumin uptake in to tumors established in dorsal window chambers. Further mechanistic investigations used ex vivo assays of vascular smooth muscle relaxation, gut motility, and myosin light chain kinase (MLCK) inhibition.

RESULTS

AG014699 failed to sensitize SW620 cells to temozolomide in vitro but induced pronounced enhancement in vivo. AG014699 (1 mg/kg) improved tumor perfusion comparably with the control agents nicotinamide (1 g/kg) and AG14361 (forerunner to AG014699; 10 mg/kg). AG014699 and AG14361 relaxed preconstricted vascular smooth muscle more potently than the standard agent, hydralazine, with no impact on gut motility. AG014699 inhibited MLCK at concentrations that relaxed isolated arteries, whereas AG14361 had no effect.

CONCLUSION

Increased vessel perfusion elicited by AG014699 could increase tumor drug accumulation and therapeutic response. Vasoactive concentrations of AG014699 do not cause detrimental side effects to gut motility and may increase the range of therapeutics with which AG014699 could be combined with for clinical benefit.

Radiosensitising agents for the radiotherapy of cancer: novel molecularly targeted approaches

BACKGROUND

The efficacy of radiotherapy (RT) for cancer treatment is limited by normal tissue toxicity and by the intrinsic or acquired radioresistance of many tumours. Therefore, continuing efforts are conducted to identify radiosensitising agents that preferentially sensitise tumour cells to the cytotoxic action of RT. Recent progresses in molecular oncology have uncovered an array of novel targets, which may be exploited for RT enhancement.

OBJECTIVE

To survey the patent literature of the past 4 years pertaining to the development of molecularly targeted agents as potential tumour radiosensitisers.

METHODS

Patents were searched with a set of relevant keywords using several search engines. A Medline search on the same topics was performed in parallel.

RESULTS/CONCLUSION

A total of 48 patents/applications were selected. These concerned agents target molecular components of pathways involved in DNA damage repair, cell growth and survival signalling, apoptosis modulation and tumour angiogenesis. Current trials of some of these agents may reveal their value as clinical radiosensitisers.

Current status of cediranib: the rapid development of a novel anti-angiogenic therapy

Angiogenesis, the process whereby tumors develop new blood vessels to facilitate growth and metastasis, is a pivotal event in tumorigenesis. It is tightly regulated by the VEGF system. Cediranib (AZD2171, Recentin; AstraZeneca, London, UK) is a novel and potent small-molecule inhibitor of VEGF signaling, with activity against the three VEGF receptors, as well as other targets. This article provides a comprehensive and up-to-date synopsis of all pertinent preclinical and clinical studies detailing this promising new therapy.

The vascular endothelial growth factor receptor-2 tyrosine kinase inhibitor cediranib (Recentin; AZD2171) inhibits endothelial cell function and growth of human renal tumor xenografts

PURPOSE

The goal of this study was to examine the therapeutic potential of the vascular endothelial growth factor (VEGF) signaling inhibitor cediranib in a human model of renal cell carcinoma (Caki-1).

METHODS AND MATERIALS

The effects of cediranib treatment on in vitro endothelial cell function (proliferation, migration, and tube formation), as well as in vivo angiogenesis and tumor growth, were determined.

RESULTS

In vitro, cediranib significantly impaired the proliferation and migration of endothelial cells and their ability to form tubes, but had no effect on the proliferation of Caki-1 tumor cells. In vivo, cediranib significantly reduced Caki-1 tumor cell-induced angiogenesis, reduced tumor perfusion, and inhibited the growth of Caki-1 tumor xenografts.

CONCLUSIONS

The present results are consistent with the notion that inhibition of VEGF signaling leads to an indirect (i.e., antiangiogenic) antitumor effect, rather than a direct effect on tumor cells. These results further suggest that inhibition of VEGF signaling with cediranib may impair the growth of renal cell carcinoma.

Inhibition of vascular endothelial growth factor signalling using cediranib (RECENTIN; AZD2171) enhances radiation response and causes substantial physiological changes in lung tumour xenografts

A number of pre-clinical studies have suggested that blocking vascular endothelial growth factor (VEGF) signalling can be beneficial in combination with radiotherapy. This study investigated the effects of cediranib, a highly potent orally available inhibitor of VEGF receptor tyrosine kinase activity in combination with radiation in Calu-6 lung xenografts. In nude mice, Calu-6 tumours were established and treatments initiated at a volume of 250 mm(3). Tumour-localized radiotherapy was given as three or five daily fractions of 2 Gy. Cediranib (3 mg kg(-1)) was administered 2 h prior to each fraction and continued post radiotherapy (concomitant regimen) or was initiated immediately after the completion of radiotherapy (sequential regimen). The endpoint was the time taken for tumour volume to quadruple (RTV4). Combined treatments resulted in a significantly enhanced growth delay compared with either modality alone. The therapeutic benefit was the same irrespective of the scheduling regimen. Tumour regression was observed post radiotherapy, which was associated with high levels of apoptosis and necrosis, and pronounced antivascular effects in histological samples. The amplified antivascular effect of cediranib when given after radiation suggests that pre-irradiated endothelium is sensitized to cediranib. Concomitant 5-day treatment with both cediranib and radiation reduced vessel density, perfusion and increased in tumour hypoxia. This was not associated with an acquired radioresistance suggesting that the maintenance of cediranib treatment post radiotherapy prevents the contribution of hypoxic cells to tumour regrowth. Collectively, these data support the contention that VEGFR inhibition can enhance radiation response in pre-clinical models and provide a rationale to develop cediranib in combination with radiotherapy in the clinical setting.

Initial testing (stage 1) of sunitinib by the pediatric preclinical testing program

BACKGROUND

Sunitinib is an orally bioavailable, multi-targeted tyrosine kinase inhibitor with selectivity for PDGF receptors, VEGF receptors, FLT3, and KIT.

PROCEDURES

Sunitinib was tested at concentrations ranging from 0.1 nM to 1.0 microM against 23 cell lines from the PPTP in vitro panel. We also compared sunitinib (53.5 mg/kg) or vehicle administered for 28 days by oral gavage in 46 murine xenograft models representing 9 distinct pediatric cancer histologies.

RESULTS

The leukemia cell line, Kasumi-1 (gain-of-function KIT(Asn822Lys) mutation) was the only line with an in vitro response to sunitinib (IC(50) 75.7 nM). Sunitinib significantly prolonged EFS in 19 of 35 (54%) of the solid tumor, and in 3 of 8 (38%) of the ALL xenografts analyzed. Using the PPTP time to event measure of efficacy, sunitinib had intermediate (13) and high (1) levels of activity against 14 of 34 evaluable solid tumor xenografts, including 4 of 6 rhabdomyosarcoma, 4 of 5 Ewing tumor, and 2 of 3 rhabdoid tumor xenografts. Following cessation of treatment for the 14 solid tumor xenografts without tumor events by day 28, tumor growth rate increased in most. The only regression noted to sunitinib in the solid tumor panels was a complete response in a rhabdoid tumor xenograft.

CONCLUSIONS

Sunitinib demonstrated significant tumor growth inhibition against most of the PPTP's solid tumor panels, but little activity against the neuroblastoma and ALL panel. Antitumor activity was manifested primarily as tumor growth delay, consistent with an anti-angiogenic effect for sunitinib against many of the pediatric preclinical models evaluated. Pediatr Blood Cancer 2008;51:42-48. (c) 2008 Wiley-Liss, Inc.

Blockade of an angiotensin type I receptor enhances effects of radiation on tumor growth and tumor-associated angiogenesis by reducing vascular endothelial growth factor expression

OBJECTIVE

Angiogenesis, the formation of new capillary blood vessels, is essential for tumor progression. We had reported that Type 1 angiotensin receptor (AT1-R) antagonist reduced tumor-associated angiogenesis. Since antiangiogenic agents were reported to enhance efficacy of radiation therapy, we tested here whether or not AT1-R blockade facilitates the effects of radiation.

METHODS

1 x 10(6) LLC cells were injected into the subcutaneous tissue of male C57BL/6 mice, and when the average tumor volume reached around 0.1 cm(3), radiation doses (3, 5, 10, and 15 Gy) were given on day 1.

RESULTS

The mean tumor volumes at day 22 were 6.39 (3 Gy), 6.15 (5 Gy), 5.15 (10 Gy), and 3.07 (15 Gy) cm(3), respectively. Combination of 10 Gy radiation with AT1R antagonist TCV-116 (30 mg/kg) significantly inhibited tumor growth by 83% (1.47 +/- 0.11 cm(3), P < 0.01) in comparison with its inhibition of control tumors (8.81 +/- 0.45 cm(3)). The same was true for mean vessel density, and the combination therapy markedly reduced tumor-associated angiogenesis. This was confirmed by the reduced expression of CD31. LLC tumor growth was blocked by neutralizing antibody against vascular endothelial growth factor (VEGF). Real-time PCR analysis of VEGF disclosed a marked reduction in the mice under combination therapy, compared with control mice.

CONCLUSIONS

These results suggest that combination of radiation with AT1-R blockade markedly reduced the LLC growth rate, and that this was due to reduction of neovascularization by reducing VEGF levels. Combination therapy consisting of radiation and AT1R blockade may become an effective novel strategy for cancer treatment.

Dual inhibition of EGFR and VEGFR pathways in combination with irradiation: antitumour supra-additive effects on human head and neck cancer xenografts

The aim of this study was to investigate the effects of combining antiangiogenic treatment, epidermal growth factor receptor (EGFR) targeting and irradiation (RT). We evaluated AZD2171, a highly potent, orally active, vascular endothelial growth factor (VEGF) signalling inhibitor, gefitinib, an EGFR tyrosine kinase inhibitor and RT. The antitumour efficacy of these treatments, administered alone and in combination for 2 weeks, was assessed in a VEGF-secreting human head and neck tumour cell line, CAL33 that highly expresses EGFR, established as xenografts (250 mm(3)) in nude mice. The median time to reach a tumour volume of 1000 mm(3) was significantly increased for AZD2171 or gefitinib alone compared with the control. Greater inhibition of tumour growth was seen with the combination of AZD2171+gefitinib compared with either drug alone, and the triple combination compared with either AZD2171+gefitinib or RT alone. The intensity of endothelial cell staining was slightly reduced by each agent given alone, and markedly diminished by the double or triple combination. The triple combination almost completely abolished cell proliferation. The marked RT-induced enhancement in the DNA-repair enzyme ERCC1 expression was totally abolished by the triple combination. This observation could help to explain the supra-additive antitumour effect produced by this combination and could provide a basis for future innovative clinical trials.