Improving tumor response to radiotherapy by targeting angiogenesis signaling pathways

Dodecafluoropentane Emulsion as a Radiosensitizer in Glioblastoma Multiforme

Purpose

Glioblastoma multiforme (GBM) is a hypoxic tumor resistant to radiotherapy. The purpose of this study was to assess the safety and efficacy of a novel oxygen therapeutic, dodecafluoropentane emulsion (DDFPe), in chemoradiation treatment of GBM.

Experimental Design

In this multicenter phase Ib/II dose-escalation study, patients were administered DDFPe via intravenous infusion (0.05, 0.10, or 0.17 mL/kg) while breathing supplemental oxygen prior to each 2 Gy fraction of radiotherapy (30 fractions over 6 weeks). Patients also received standard-of-care chemotherapy [temozolomide (TMZ)]. Serial MRI scans were taken to monitor disease response. Adverse events were recorded and graded. TOLD (tissue oxygenation level-dependent) contrast MRI was obtained to validate modulation of tumor hypoxia.

Results

Eleven patients were enrolled. DDFPe combined with radiotherapy and TMZ was well tolerated in most patients. Two patients developed delayed grade 3 radiation necrosis during dose escalation, one each at 0.1 and 0.17 mL/kg of DDFPe. Subsequent patients were treated at the 0.1 mL/kg dose level. Kaplan-Meier analysis showed a median overall survival of 19.4 months and a median progression-free survival of 9.6 months, which compares favorably to historical controls. Among 6 patients evaluable for TOLD MRI, a statistically significant reduction in tumor T1 was observed after DDFPe treatment.

Conclusions

This trial, although small, showed that the use of DDFPe as a radiosensitizer in patients with GBM was generally safe and may provide a survival benefit. This is also the first time than TOLD MRI has shown reversal of tumor hypoxia in a clinical trial in patients. The recommended dose for phase II evaluation is 0.1 mL/kg DDFPe.Trial Registration: NCT02189109.

Significance

This study shows that DDFPe can be safely administered to patients, and it is the first-in-human study to show reversal of hypoxia in GBM as measured by TOLD MRI. This strategy is being used in a larger phase II/III trial which will hopefully show a survival benefit by adding DDFPe during the course of fractionated radiation and concurrent chemotherapy.

Overcoming tumor hypoxia as a barrier to radiotherapy, chemotherapy and immunotherapy in cancer treatment

Hypoxia exists to some degree in most solid tumors due to inadequate oxygen delivery of the abnormal vasculature which cannot meet the demands of the rapidly proliferating cancer cells. The levels of oxygenation within the same tumor are highly variable from one area to another and can change over time. Tumor hypoxia is an important impediment to effective cancer therapy. In radiotherapy, the primary mechanism is the creation of reactive oxygen species; hypoxic tumors are therefore radiation resistant. A number of chemotherapeutic drugs have been shown to be less effective when exposed to a hypoxic environment which can lead to further disease progression. Hypoxia is also a potent barrier to effective immunotherapy in cancer treatment. Because of the recognition of hypoxia as an important barrier to cancer treatment, a variety of approaches have been undertaken to overcome or reverse tumor hypoxia. Such approaches have included breathing hyperbaric oxygen, artificial hemoglobins, allosteric hemoglobin modifiers, hypoxia activated prodrugs and fluorocarbons (FCs). These approaches have largely failed due to limited efficacy and/or adverse side effects. Oxygen therapeutics, based on liquid FCs, can potentially increase the oxygen-carrying capacity of the blood to reverse tumor hypoxia. Currently, at least two drugs are in clinical trials to reverse tumor hypoxia; one of these is designed to improve permeability of oxygen into the tumor tissue and the other is based upon a low boiling point FC that transports higher amounts of oxygen per gram than previously tested FCs.

A pilot study of hypofractionated stereotactic radiation therapy and sunitinib in previously irradiated patients with recurrent high-grade glioma

PURPOSE/OBJECTIVE(S)

Angiogenic blockade with irradiation may enhance the therapeutic ratio of radiation therapy (RT) through vascular normalization. We sought to determine the safety and toxicity profile of continuous daily-dosed sunitinib when combined with hypofractionated stereotactic RT (fSRT) for recurrent high-grade gliomas (rHGG).

METHODS AND MATERIALS

Eligible patients had malignant high-grade glioma that recurred or progressed after primary surgery and RT. All patients received a minimum of a 10-day course of fSRT, had World Health Organization performance status of 0 to 1, and a life expectancy of >3 months. During fSRT, sunitinib was administered at 37.5 mg daily. The primary endpoint was acute toxicity, and response was assessed via serial magnetic resonance imaging.

RESULTS

Eleven patients with rHGG were enrolled. The fSRT doses delivered ranged from 30 to 42 Gy in 2.5- to 3.75-Gy fractions. The median follow-up time was 40 months. Common acute toxicities included hematologic disorders, fatigue, hypertension, and elevated liver transaminases. Sunitinib and fSRT were well tolerated. One grade 4 mucositis toxicity occurred, and no grade 4 or 5 hypertensive events or intracerebral hemorrhages occurred. One patient had a nearly complete response, and 4 patients had stable disease for >9 months. Two patients (18%) remain alive and progression-free >3 years from enrollment. The 6-month progression-free survival was 45%.

CONCLUSIONS

Sunitinib at a daily dose of 37.5 mg given concurrently with hypofractionated stereotactic reirradiation for rHGG yields acceptable toxicities and an encouraging 6-month progression-free survival.

The addition of Sunitinib to radiation delays tumor growth in a murine model of glioblastoma

OBJECTIVES

Recent preclinical studies suggest that treating glioblastoma (GBM) with a combination of targeted chemotherapy and radiotherapy may enhance the anti-tumor effects of both therapies. However, the effects of these treatments on glioma growth and progression are poorly understood.

METHODS

In this study, we have tested the effects of combination therapy in a mouse glioma model that utilizes a PDGF-IRES-Cre-expressing retrovirus to infect adult glial progenitors in mice carrying conditional deletions of Pten and p53. This model produces tumors with the histological features of GBM with 100% penetrance, making it a powerful system to test novel treatments. Sunitinib is an orally active, small molecule inhibitor of multiple receptor tyrosine kinases critical for tumor growth and angiogenesis, including PDGF receptors. We investigate the addition of Sunitinib to radiotherapy, and use bioluminescence imaging to characterize the effects of treatment on glioma growth and progression.

RESULTS

Treating our PDGF-driven mouse model with either Sunitinib or high-dose radiation alone delayed tumor growth and had a modest but significant effect on survival, while treating with low-dose radiation alone failed to control glioma growth and progression. The addition of Sunitinib to low-dose radiation caused a modest, but significant delay in tumor growth. However, no significant survival benefit was seen as tumors progressed in 100% of animals. Histological analysis revealed a reduction in vascular proliferation and a marked increase in brain invasion. An additional study combining Sunitinib with high-dose radiation revealed a fatal toxicity despite individual monotherapies being well tolerated.

DISCUSSION

These results show that the addition of Sunitinib to radiotherapy fails to significantly alter survival in GBM despite enhancement of the effects of radiation. Furthermore, an enhanced risk of toxicity associated with combined therapy must be considered in the design of future clinical studies.

A phase 1b trial of the combination of the antiangiogenic agent sunitinib and radiation therapy for patients with primary and metastatic central nervous system malignancies

BACKGROUND

In this phase 1 trial, the authors evaluated sunitinib combined with radiation therapy (RT) for the treatment of primary or metastatic central nervous system (CNS) malignancies.

METHODS

Eligible patients had CNS malignancies that required a (minimum) 2-week course of RT. Sunitinib (37.5 mg) was administered daily for the duration of RT with optional treatment extension of 1 month. Urine was collected at 3 time points for correlative biomarker studies. The primary endpoint was acute toxicity defined according to Common Toxicity Criteria version 3.

RESULTS

Fifteen patients were enrolled (12 with CNS metastasis and 3 with primary tumors). RT doses ranged from 14 Gray (Gy) to 70 Gy (1.8-3.5 Gy per fraction). Acute toxicities included hematologic, nausea, hyperglycemia, fatigue, hypocalcemia, and diarrhea. Six patients (40%) developed grade ≤ 2 toxicities. Grade 3 toxicities occurred in 7 patients (47%) and included hematologic toxicity, fatigue, deep vein thrombosis, dysphasia, hyperglycemia, and hyponatremia. No grade 3 through 5 hypertensive events or intracerebral hemorrhages occurred. Two grade 5 adverse events attributed to disease progression occurred. The median follow-up was 34.2 months. Two patients (13%) achieved a partial response, 9 patients (60%) had stable disease, and 2 patients (13%) patients had progressive disease. The 6-month progression-free survival rate for patients who had brain metastasis was 58%. Grade 3 hematologic toxicity was correlated with greater changes in vascular endothelial growth factor levels changes between baseline and the completion of RT.

CONCLUSIONS

Continuous 37.5-mg sunitinib combined with RT in patients who had CNS malignancies yielded acceptable toxicities and adverse events. The current results indicated that changes in urine vascular endothelial growth factor levels are associated with hematologic toxicity, and this association should be analyzed in a larger cohort. The feasibility, safety, and early response results warrant a phase 2 trial.

Epidermal growth factor receptor expression modulates antitumor efficacy of vandetanib or cediranib combined with radiotherapy in human glioblastoma xenografts

PURPOSE

The purpose of this study was to determine the ability of radiation therapy (RT) combined with the tyrosine kinase inhibitors (TKI) vandetanib (antiepidermal growth factor receptor [EGFR] plus antivascular endothelial growth factor receptor [anti-VEGFR]) and cediranib (anti-VEGFR) to inhibit glioblastoma multiforme (GBM) growth. A secondary aim was to investigate how this regimen is modulated by tumor EGFR expression.

METHODS AND MATERIALS

Radiosensitivity was assessed by clonogenic cell survival assay. VEGF secretion was quantified by enzyme-linked immunosorbent assay. GBM (U87MG wild-type EGFR [wtEGFR] and U87MG EGFR-null) xenografts were treated with vandetanib, cediranib, and RT, alone or in combinations. Excised tumor sections were stained for proliferative and survival biomarkers.

RESULTS

In vitro, U87MG wtEGFR and U87 EGFR-null cells had similar growth kinetics. Neither TKI affected clonogenic cell survival following RT. However, in vivo, exogenous overexpression of wtEGFR decreased tumor doubling time (T2x) in U87MG xenografts (2.70 vs. 4.41 days for U87MG wtEGFR vs. U87MG vector, respectively). In U87MG EGFR-null cells, TKI combined with radiation was no better than radiation therapy alone. In U87MG wtEGFR, RT in combination with vandetanib (but not with cediranib) significantly increased tumor T2x compared with RT alone (T2x, 10.4 days vs. 4.8 days; p < 0.001). In vivo, growth delay correlated with suppression of pAkt, survivin, and Ki67 expression in tumor samples. The presence of EGFR augmented RT-stimulated VEGF release; this effect was inhibited by vandetanib.

CONCLUSIONS

EGFR expression promoted tumor growth in vivo but not in vitro, suggesting a microenvironmental effect. GBM xenografts expressing EGFR exhibited greater sensitivity to both cediranib and vandetanib than EGFR-null tumors. Hence EGFR status plays a major role in determining a tumor's in vivo response to radiation combined with TKI, supporting a "personalized" approach to GBM management.

Decreasing the adverse effects of cancer therapy: National Cancer Institute guidance for the clinical development of radiation injury mitigators

Recently, many agents have been identified that target molecular pathways that can mitigate radiation toxicity. To date, no drugs have been approved as radiation injury mitigators, which are defined as agents administered after irradiation but before toxicity is manifest. In order to accelerate the application of potential mitigators for cancer patients, a meeting sponsored by the National Cancer Institute (NCI) and National Institute of Allergy and Infectious Diseases (NIAID) was held in January 2010. This article presents an algorithm to guide clinical trials for such agents in patients receiving radiotherapy or radiochemotherapy. It reviews the mechanisms of radiation injury, the clinical problem, the preclinical and clinical development of candidate agents, and the design and conduct of clinical trials. The central role of patient reported outcomes is outlined, as well as key lessons learned from prior clinical trials. Ultimately, the goal is to be able to apply such promising agents to improve the quality of life for patients receiving radiotherapy or chemoradiotherapy for cancer.

Targeting integrins in malignant glioma

The integrin family of cell adhesion receptors is emerging as a promising target of anticancer therapy. AlphaVbeta3 and alphaVbeta5 integrins are overexpressed on both glioma cells and tumor vasculature. Cilengitide, the most advanced specific integrin inhibitor in oncology, has shown antitumor activity against glioma in early clinical trials. Durable remissions have been observed in phase I and phase II trials for recurrent glioblastoma (GBM) with both lower and higher doses of cilengitide. Pilot trials in newly diagnosed glioblastoma in conjunction with standard chemoradiotherapy have been encouraging. Preclinical data suggest synergy with concomitant chemo- and radiation therapy. A pivotal phase III study (CENTRIC) in newly diagnosed GBM patients is currently recruiting. This paper summarizes the current understanding of the role of integrins and their inhibition in gliomagenesis. The background and design of ongoing trials are outlined.

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.

Interstitial fluid pressure as a prognostic factor in cervical cancer following radiation therapy

PURPOSE

To investigate tumor interstitial fluid pressure as a prognostic factor for recurrence-free survival in patients with cervical cancer following radiation therapy.

EXPERIMENTAL DESIGN

Tumor interstitial fluid pressure was measured in 55 cervical cancer patients who received radiation therapy between August 1998 and September 2002. Interstitial fluid pressure measurements were made before radiation therapy (pre-radiation therapy interstitial fluid pressure) and after a median of 28.8 Gy in 16 fractions (range, 25.2-30.6 Gy in 14-17 fractions) of radiation therapy (mid-radiation therapy interstitial fluid pressure), using a modified wick-in-needle technique. Median follow-up was 74 months (range, 2-118 months). The Kaplan-Meier method with the log-rank test and Cox's proportional hazard model were used in univariate and multivariate analyses, respectively, of prognostic factors for recurrence-free survival.

RESULTS

Median pre-radiation therapy and mid-radiation therapy interstitial fluid pressure were 29.0 mm Hg (range, 4.0-93.9 mm Hg) and 20.0 mm Hg (range, -1.2 to 29.6 mm Hg), respectively (P = 0.001). Pre-radiation therapy interstitial fluid pressure was significantly higher in adenocarcinomas than squamous cell carcinomas (P = 0.028). Significant reduction of interstitial fluid pressure was noted only in patients with complete responses (P = 0.002), and mid-radiation therapy interstitial fluid pressure was significantly lower in patients with complete responses (P = 0.036). In the multivariate analysis including interstitial fluid pressures and clinical variables, pre-radiation therapy interstitial fluid pressure was an independent prognostic factor for local and distant recurrence-free survival (P = 0.001 and 0.027, respectively).

CONCLUSIONS

Mid-radiation therapy interstitial fluid pressure measurement may be useful in predicting radiation therapy responses, and pre-radiation therapy interstitial fluid pressure was a significant prognostic factor for local and distant relapse-free survival in patients with cervical cancer after radiation therapy.

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.

Optical clearing of unsectioned specimens for three-dimensional imaging via optical transmission and emission tomography

Optical computed tomography (optical-CT) and optical emission computed tomography (optical-ECT) are new techniques that enable unprecedented high-resolution 3-D multimodal imaging of tissue structure and function. Applications include imaging macroscopic gene expression and microvasculature structure in unsectioned biological specimens up to 8 cm(3). A key requisite for these imaging techniques is effective sample preparation including optical clearing, which enables light transport through the sample while preserving the signal (either light absorbing stain or fluorescent proteins) in representative form. We review recent developments in optical-CT and optical-ECT, and compatible "fluorescence-friendly" optical clearing protocols.

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

AZD2171 is a highly potent, orally active inhibitor of vascular endothelial growth factor receptor signaling. The potential for AZD2171 to enhance the antitumor effects of radiotherapy was investigated in lung (Calu-6) and colon (LoVo) human tumor xenograft models. Combined treatment resulted in a significantly enhanced growth delay compared with either modality alone. The enhancement was independent of whether chronic once daily AZD2171 treatment was given 2 h prior to each radiation fraction (2 Gy daily for 3 or 5 consecutive days), and daily thereafter, or commenced immediately following the course of radiotherapy. Histologic assessments revealed that 5 days of radiation (2 Gy) or AZD2171 (3 or 6 mg/kg/d) reduced vessel density and perfusion. Concomitant AZD2171 and radiation enhanced this effect and produced a significant increase in tumor hypoxia. Concomitant AZD2171 (6 mg/kg/d) was also found to reduce tumor growth significantly during the course of radiotherapy (5 x 2 Gy). However, the extent and duration of tumor regression observed postradiotherapy was similar to sequentially treated tumors, suggesting that preirradiated tumors were sensitized to AZD2171 treatment. An enhanced antivascular effect of administering AZD2171 postradiotherapy was observed in real-time in Calu-6 tumors grown in dorsal window chambers. Collectively, these data support the clinical development of AZD2171 in combination with radiotherapy.

Application of radiotherapy and chemotherapy protocols to pre-clinical tumor models

This unit (1) provides background into understanding how agents that target specific molecules or receptors (molecular-targeted agents), in particular, agents affecting the tumor vasculature (perivasculature network in tumors), interact with and modify radiation therapy; (2) details factors affecting interpretation of results in murine tumor model experiments utilizing radiation therapy and drug combinations; and (3) provides specific protocols for the application of radiation therapy, both alone and in combination with chemotherapy and/or molecular-targeted agents.

Targeting Integrins and PI3K/Akt-Mediated Signal Transduction Pathways Enhances Radiation-Induced Anti-angiogenesis

The integrins and PI3K/Akt are important mediators of the signal transduction pathways involved in tumor angiogenesis and cell survival after exposure to ionizing radiation. Selective targeting of either integrins or PI3K/Akt can radiosensitize tumors. In this study, we tested the hypothesis that the combined inhibition of integrin alphanubeta3 by cRGD and PI3K/Akt by LY294002 would significantly enhance radiation-induced inhibition of angiogenesis by vascular endothelial cells. Treatment with cRGD inhibited the adhesion and tube formation of human umbilical vein endothelial cells (HUVECs). The inhibitory effect was further increased when cRGD and LY294002 were applied simultaneously. Both radiation and cRGD induced Akt phosphorylation, up-regulated COX2 expression, and increased PGE2 production in HUVECs. Treatment with LY294002 effectively inhibited radiation- and cRGD-induced Akt phosphorylation and up-regulation of COX2 and increased apoptosis of HUVECs. The combined use of cRGD and LY294002 enhanced radiation-induced cell killing. The clonogenic survival of HUVECs was decreased from 34% with 2 Gy radiation to 4% with these agents combined. These results demonstrate that combined use of ionizing radiation, cRGD and LY294002 inhibited multiple signaling transduction pathways involved in tumor angiogenesis and enhanced radiation-induced effects on vascular endothelial cells.

VEGF Trap in Combination With Radiotherapy Improves Tumor Control in U87 Glioblastoma

PURPOSE

To determine the effect of vascular endothelial growth factor VEGF Trap (Regeneron Pharmaceuticals, Tarrytown, NY), a humanized soluble vascular endothelial growth factor (VEGF) receptor protein, and radiation (RT) on tumor growth in U87 glioblastoma xenografts in nude mice.

METHODS AND MATERIALS

U87 cell suspensions were implanted subcutaneously into hind limbs of nude mice. VEGF Trap (2.5-25 mg/kg) was administered every 3 days for 3 weeks alone or in combination with a single dose of 10 Gy or fractionated RT (3 x 5 Gy). In addition, three scheduling protocols for VEGF Trap plus fractionated RT were examined.

RESULTS

Improved tumor control was seen when RT (either single dose or fractionated doses) was combined with the lowest dose of VEGF Trap (2.5 mg/kg). Scheduling did not significantly affect the efficacy of combined therapy. Although high-dose VEGF Trap (10 mg/kg or 25 mg/kg) significantly reduced tumor growth over that of RT alone, there was no additional benefit to combining high-dose VEGF Trap with RT.

CONCLUSIONS

Vascular endothelial growth factor Trap plus radiation is clearly better than radiation alone in a U87 subcutaneous xenograft model. Although high doses of VEGF Trap alone are highly efficacious, it is unclear whether such high doses can be used clinically without incurring normal tissue toxicities. Thus, information on lower doses of VEGF Trap and ionizing radiation is of clinical relevance.

HIV protease inhibitors decrease VEGF/HIF-1alpha expression and angiogenesis in glioblastoma cells

Glioblastomas are malignant brain tumors that are rarely curable, even with aggressive therapy (surgery, chemotherapy, and radiation). Glioblastomas frequently display loss of PTEN and/or epidermal growth factor receptor activation, both of which activate the PI3K pathway. This pathway can increase vascular endothelial growth factor (VEGF) and hypoxia-inducible factor (HIF)-1alpha expression. We examined the effects of two human immunodeficiency virus protease inhibitors, nelfinavir and amprenavir, which inhibit Akt signaling, on VEGF and HIF-1alpha expression and on angiogenesis. Nelfinavir decreased VEGF mRNA expression and VEGF secretion under normoxia. Downregulation of P-Akt decreased VEGF secretion in a manner similar to that of nelfinavir, but the combination of the two had no greater effect, consistent with the idea that nelfinavir decreases VEGF through the PI3K/Akt pathway. Nelfinavir also decreased the hypoxic induction of VEGF and the hypoxic induction of HIF-1alpha, which regulates VEGF promoter. The effect of nelfinavir on HIF-1alpha was most likely mediated by decreased protein translation. Nelfinavir's effect on VEGF expression had the functional consequence of decreasing angiogenesis in in vivo Matrigel plug assays. Similar effects on VEGF and HIF-1alpha expression were seen with a different protease inhibitor, amprenavir. Our results support further research into these protease inhibitors for use in future clinical trials for patients with glioblastoma multiformes.

Noninvasive assessment of tumor vasculature response to radiation-mediated, vasculature-targeted therapy using quantified power Doppler sonography: implications for improvement of therapy schedules

OBJECTIVE

Stereotactic radiotherapy (ablative radiation) is a modality that holds considerable promise for effective treatment of intracranial and extracranial malignancies. Although tumor vasculature is relatively resistant to small fractionated doses of ionizing radiation, large ablative doses of ionizing radiation lead to effective demise of the tumor vasculature. The purpose of this study was (1) to noninvasively monitor and compare tumor physiologic parameters in response to ablative radiation treatments and (2) to use these noninvasive parameters to optimize the schedule of administration of radiation therapy.

METHODS

Lewis lung carcinoma tumors were implanted into C57BL/6 mice and treated with ablative radiation. The kinetics of change in physiologic parameters of a response to single-dose 20-Gy treatments was measured. Parameters studied included tumor blood flow, apoptosis, and proliferation rates. Serial tumor sections were stained to correlate noninvasive Doppler assessment of tumor blood flow with microvasculature histologic findings.

RESULTS

A single administration of 20 Gy led to an incomplete tumor vascular response, with subsequent recovery of tumor blood flow within 4 days after treatment. Sustained reduction of tumor blood flow by administering the successive ablative radiation treatment before tumor blood flow recovery led to a 3-fold tumor growth delay. The difference in tumor volumes at each measurement time point (every 2 days) was statistically significant (P=.016).

CONCLUSIONS

This study suggests a rational design of schedule optimization for radiation-mediated, vasculature-directed treatments guided by noninvasive assessment of tumor blood flow levels to ultimately improve the tumor response.

Three-dimensional imaging of xenograft tumors using optical computed and emission tomography

The physical basis and preliminary applications of optical computed tomography (optical-CT) and optical emission computed tomography (optical-ECT) are introduced, as new techniques with potential to provide unique 3D information on a variety of aspects of tumor structure and function. A particular focus here is imaging tumor micro-vasculature, and the spatial distribution of viable tumor cells, although the techniques have the potential for much wider application. The principle attractiveness of optical-CT and optical-ECT are that high resolution (<20 microm) and high contrast co-registered 3D images of structure and function can be acquired for relatively large intact samples. The unique combination of high contrast and resolution offers advantages over micro-CT and micro-MRI, and the lack of requirement for sectioning offers advantages over confocal microscopy, conventional microscopy, and histological sectioning techniques. Optical-CT/ECT are implemented using in-house custom apparatus and a commercial dissecting microscope capable of both transmission and fluorescence imaging. Basic studies to characterize imaging performance are presented. Negligible geometrical distortion and accurate reconstruction of relative attenuation coefficients was observed. Optical-CT and optical-ECT are investigated here by application to high resolution imaging of HCT116 xenograft tumors, about 1 cc in dimension, which were transfected with constitutive red fluorescent protein (RFP). Tumor microvasculature was stained in vivo by tail vein injection of either passive absorbing dyes or active fluorescent markers (FITC conjugated lectin). Prior to imaging, the tumors were removed (ex vivo) and optically cleared in a key process to make the samples amenable to light transmission. The cleared tumors were imaged in three modes (i) optical-CT to image the 3D distribution of microvasculature as indicated by absorbing dye, (ii) optical-ECT using the FITC excitation and emission filter set, to determine microvasculature as indicated by lectin-endothelial binding, and (iii) optical-ECT using the DSRed2 filter set to determine the 3D distribution of viable tumor as indicated by RFP emission. A clear correlation was observed between the independent vasculature imaging modes (i) and (ii) and postimaging histological sections, providing substantial validation of the optical-CT and optical-ECT techniques. Strong correlation was also observed between the RFP imaging of mode iii, and modes i and ii, supporting the intuitive conclusion that well-perfused regions contain significant viable tumor. In summary, optical-CT and optical-ECT, when combined with new optical clearing techniques, represent powerful new imaging modalities with potential for providing unique information on the structure and function of tumors.

Molecular strategies targeting the host component of cancer to enhance tumor response to radiation therapy

The tumor microenvironment, in particular, the tumor vasculature, as an important target for the cytotoxic effects of radiation therapy is an established paradigm for cancer therapy. We review the evidence that the phosphoinositide 3-kinase (PI3K)/Akt pathway is activated in endothelial cells exposed to ionizing radiation (IR) and is a molecular target for the development of novel radiation sensitizing agents. On the basis of this premise, several promising preclinical studies that targeted the inhibition of the PI3K/Akt activation as a potential method of sensitizing the tumor vasculature to the cytotoxic effects of IR have been conducted. An innovative strategy to guide cytotoxic therapy in tumors treated with radiation and PI3K/Akt inhibitors is presented. The evidence supports a need for further investigation of combined-modality therapy that involves radiation therapy and inhibitors of PI3K/Akt pathway as a promising strategy for improving the treatment of patients with cancer.

Augmentation of radiation response with the vascular targeting agent ZD6126

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 and 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 and 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 and N and lung cancer cells. These results complement recent reports suggesting the potential value of combining radiation with vascular targeting/antiangiogenic agents.

Circadian clock genes as modulators of sensitivity to genotoxic stress

A broad variety of organisms display circadian rhythms (i.e., oscillations with 24-hr periodicities) in many aspects of their behavior, physiology and metabolism. These rhythms are under genetic control and are generated endogenously at the cellular level. In mammals, the core molecular mechanism of the oscillator consists of two transcriptional activators, CLOCK and BMAL1, and their transcriptional targets, CRYPTOCHROMES (CRYS) and PERIODS (PERS). The CRY and PER proteins function as negative regulators of CLOCK/BMAL1 activity, thus forming the major circadian autoregulatory feedback loop. It is believed that the circadian clock system regulates daily variations in output physiology and metabolism through periodic activation/repression of the set of clock-controlled genes that are involved in various metabolic pathways. Importantly, circadian-controlled pathways include those that determine in vivo responses to genotoxic stress. By using circadian mutant mice deficient in different components of the molecular clock system, we have established genetic models that correlate with the two opposite extremes of circadian cycle as reflected by the activity of the CLOCK/BMAL1 transactivation complex. Comparison of the in vivo responses of these mutants to the chemotherapeutic drug, cyclophosphamide (CY), has established a direct correlation between drug toxicity and the functional status of the CLOCK/BMAL1 transcriptional complex. We have also demonstrated that CLOCK/BMAL1 modulates sensitivity to drug-induced toxicity by controlling B cell responses to active CY metabolites. These results suggest that the sensitivity of cells to genotoxic stress induced by anticancer therapy may be modulated by CLOCK/BMAL1 transcriptional activity. Further elucidation of the molecular mechanisms of circadian control as well as identification of specific pharmacological modulators of CLOCK/BMAL1 activity are likely to lead to the development of new anti-cancer treatment schedules with increased therapeutic index and reduced morbidity.