Repurposing cephalosporin antibiotics as pro-senescent radiosensitizers

Radiation therapy remains a significant therapeutic modality in the treatment of cancer. An attractive strategy would be to enhance the benefits of ionizing radiation (IR)with radiosensitizers. A high-content drug repurposing screen of approved and investigational agents, natural products and other small molecules has identified multiple candidates that blocked repair of IR damage in vitro. Here, we validated a subset of these hits in vitro and then examined effects on tumor growth after IR in a murine tumor model. Based on robust radiosensitization in vivo and other favorable properties of cephalexin, we conducted additional studies with other beta-lactam antibiotics. When combined with IR, each cephalosporin tested increased DNA damage and slowed tumor growth without affecting normal tissue toxicity. Our data implicate reactive oxygen species in the mechanism by which cephalosporins augment the effects of IR. This work provides a rationale for using commonly prescribed beta-lactam antibiotics as non-toxic radiosensitizers to enhance the therapeutic ratio of radiotherapy.

HMG-CoA Reductase Inhibition Delays DNA Repair and Promotes Senescence After Tumor Irradiation

Despite significant advances in combinations of radiotherapy and chemotherapy, altered fractionation schedules and image-guided radiotherapy, many cancer patients fail to benefit from radiation. A prevailing hypothesis is that targeting repair of DNA double strand breaks (DSB) can enhance radiation effects in the tumor and overcome therapeutic resistance without incurring off-target toxicities. Unrepaired DSBs can block cancer cell proliferation, promote cancer cell death, and induce cellular senescence. Given the slow progress to date translating novel DSB repair inhibitors as radiosensitizers, we have explored drug repurposing, a proven route to improving speed, costs, and success rates of drug development. In a prior screen where we tracked resolution of ionizing radiation-induced foci (IRIF) as a proxy for DSB repair, we had identified pitavastatin (Livalo), an HMG-CoA reductase inhibitor commonly used for lipid lowering, as a candidate radiosensitizer. Here, we report that pitavastatin and other lipophilic statins are potent inhibitors of DSB repair in breast and melanoma models both in vitro and in vivo When combined with ionizing radiation, pitavastatin increased persistent DSBs, induced senescence, and enhanced acute effects of radiation on radioresistant melanoma tumors. shRNA knockdown implicated HMG-CoA reductase, farnesyl diphosphate synthase, and protein farnesyl transferase in IRIF resolution, DSB repair, and senescence. These data confirm on-target activity of statins, although via inhibition of protein prenylation rather than cholesterol biosynthesis. In light of prior studies demonstrating enhanced efficacy of radiotherapy in patients taking statins, this work argues for clinical evaluation of lipophilic statins as nontoxic radiosensitizers to enhance the benefits of image-guided radiotherapy. Mol Cancer Ther; 17(2); 407-18. ©2017 AACRSee all articles in this MCT Focus section, "Developmental Therapeutics in Radiation Oncology."

Abstract LB-178: In vivo validation of candidate radiosensitizers that target ionizing radiation induced foci

Even after several decades of use, radiation therapy (RT) remains an important tool in the treatment of different types of cancers. Discovery of novel non-toxic radiosensitizers that halt tumor growth and/or restore senescence checkpoint growth arrest are highly desirable. Our work, along with other studies, has revealed that disrupting the repair of DNA double strand breaks (DSBs) can sensitize cancer cells to genotoxic stress. In our prior work we used GFP-53BP1 expressed in the MCF-7 breast cancer cell line as a sensor to screen small molecules that affect radiation-induced foci (IRIF) persistence. The screening of libraries of approved and investigational drugs identified several “hits”, a surprising number of which were compounds without known connections to the DNA damage response or to chromatin alteration. Significantly, several compounds that promote IRIF persistence also restore the senescence checkpoint in irradiated cancer cells. To validate the candidate radiosensitizers we demonstrated that selected hits induced IRIF persistence and senescence in a variety of different cell lines, including HNSCC, and pancreatic and melanoma cells. Based on in vitro analysis, we identified the most promising compounds/”hits” for testing in tumor growth studies. Combining selected “hits” with radiation treatment (RT) induced IRIF persistence and increased senescence induction in MCF7-GFP-53BP1 xenografts growing in nude mice. We report that drug “hits” combined with RT induced senescence and suppressed tumor regrowth in highly radioresistant B16-SIY melanoma tumors growing in syngeneic C57BL/6 mice. Our data suggest that the use of nontoxic radiation sensitizers which enhance the effects of DNA damage and overcome intrinsic tumor radioresistance may be employed to enhance the therapeutic ratio of radiotherapy.

Citation Format: Elena V. Efimova, Helena J. Mauceri, Edwardine Labay, Harold Sutton, Ashly Haraf, Stehen J. Kron, Ralph Weichselbaum. In vivo validation of candidate radiosensitizers that target ionizing radiation induced foci. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr LB-178. doi:10.1158/1538-7445.AM2014-LB-178

A survivin-associated adaptive response in radiation therapy

Adaptive responses can be induced in cells by very low doses of ionizing radiation resulting in an enhanced resistance to much larger exposures. The inhibitor of apoptosis protein, survivin, has been implicated in many adaptive responses to cellular stress. Computerized axial tomography used in image-guided radiotherapy to position and monitor tumor response uses very low radiation doses ranging from 0.5 to 100 mGy. We investigated the ability of these very low radiation doses administered along with two 2 Gy doses separated by 24 hours, a standard conventional radiotherapy dosing schedule, to initiate adaptive responses resulting in the elevation of radiation resistance in exposed cells. Human colon carcinoma (RKO36), mouse sarcoma (SA-NH), along with transformed mouse embryo fibroblasts, wild type or cells lacking functional tumor necrosis factor receptors 1 and 2 were used to assess their relative ability to express an adaptive response when grown either to confluence in vitro or as tumors in the flank of C57BL/6 mice. The survival of each of these cells was elevated from 5% to 20% (P ≤ 0.05) as compared to cells not receiving a 100 mGy or lesser dose. In addition, the cells exposed to 100 mGy exhibited elevations in survivin levels, reductions in apoptosis frequencies, and loss of an adaptive response if transfected with survivin siRNA. This survivin-mediated adaptive response has the potential for affecting outcomes if regularly induced throughout a course of image guided radiation therapy.

Abstract 67: A novel survivin-mediated adaptive response induced by very low dose imaging-level exposures and radiation therapy

Exposure of cells to a very low dose of ionizing radiation can induce an enhanced resistance or adaptive response to a subsequent larger radiation dose as evidenced by an increase in cell survival. This expression of an adaptive response has been attributed to the result of signaling processes induced by very low radiation doses in the range of 0.5 to 100 mGy. The radiation-induced adaptive response is garnering considerable attention now due in part to the burgeoning increase in the use of imaging technologies such as computerized axial tomography and portal imaging to monitor tumor response and positioning during multi-dose standard radiation therapy protocols. The focus of this study was to investigate whether this process could occur when the delivery of the very small radiation dose was administered before or in between the administration of two typically used radiation therapy level doses. Specifically, could this signaling process be perturbed by the addition of a second 2 Gy dose of ionizing radiation delivered at a relatively short time interval from the exposure of cells to the very low dose? A human colon carcinoma cell line (RKO36) along with transformed mouse embryo fibroblasts (MEF), both wild type (WT) or tumor necrosis factor receptor 1 and 2 knockout cells (TNFR1−2−) were grown to confluence in vitro or as MEF tumors in the flank of C57BL/6 mice. Changes in SOD2 enzymatic activity, survivin protein, apoptosis, and cell survival as a function of radiation conditions and transfection of cells with SOD2-or survivin siRNA were determined. An adaptive response was induced in cells at all doses tested from 5 to 100 mGy. The adaptive responses measured in all three cell lines were associated with a reduction in apoptosis frequencies, a 5 to 20% increase in cell survival, and a rapid 2 to 3 fold elevation in survivin protein levels. Very low dose radiation-induced elevation in survivin levels was completely inhibited by transfection of cells with survivin siRNA. This was accompanied by an increase in apoptosis and a loss of the expression of these survival related adaptive responses. We have identified a very low radiation dose-induced survivin-mediated adaptive response that may affect therapeutic outcomes associated with increased usage of imaging procedures in radiation therapy. This work was supported by NIH/NCI grant R01 CA132998 and DOE Low Dose Program/Project Grant DE-SC0001271 (D.J.G.)

Citation Format: Jeffrey S. Murley, Richard C. Miller, Helena J. Mauceri, Harold G. Sutton, Ralph R. Weichselbaum, David J. Grdina. A novel survivin-mediated adaptive response induced by very low dose imaging-level exposures and radiation therapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 67. doi:10.1158/1538-7445.AM2013-67

A manganese superoxide dismutase (SOD2)-mediated adaptive response

Very low doses of ionizing radiation, 5 to 100 mGy, can induce adaptive responses characterized by elevation in cell survival and reduction in micronuclei formation. Utilizing these end points, RKO human colon carcinoma and transformed mouse embryo fibroblasts (MEF), wild-type or knockout cells missing TNF receptors 1 and 2 (TNFR1(-)R2(-)), and C57BL/6 and TNFR1(-)R2(-) knockout mice, we demonstrate that intact TNF signaling is required for induction of elevated manganese superoxide dismutase (SOD2) activity (P < 0.001) and the subsequent expression of these SOD2-mediated adaptive responses when cells are challenged at a later time with 2 Gy. In contrast, amifostine's free thiol form WR1065 can directly activate NF-κB giving rise to elevated SOD2 activity 24 h later and induce an adaptive response in both MEF wild-type and TNF signaling defective TNFR1(-)R2(-) cells. Transfection of cells with SOD2 siRNA completely abolishes both the elevation in SOD2 activity and expression of the adaptive responses. These results were confirmed in vivo using a micronucleus assay in splenocytes derived from C57BL/6 and TNFR1(-)R2(-) knockout mice that were exposed to 100 mGy or 400 mg/kg amifostine 24 h prior to exposure to a 2 Gy whole-body dose. A dose of 100 mGy also conferred enhanced protection to C57BL/6 mice exposed 24 h later to 100 mg/kg of N-Ethyl-N-nitrosourea (ENU). While very low radiation doses require an intact TNF signaling process to induce a SOD2-mediated adaptive response, amifostine can induce a similar adaptive response in both TNF receptor competent and knockout cells, respectively.

Tumor endothelial inflammation predicts clinical outcome in diverse human cancers

BACKGROUND

Vascular endothelial cells contribute to the pathogenesis of numerous human diseases by actively regulating the stromal inflammatory response; however, little is known regarding the role of endothelial inflammation in the growth of human tumors and its influence on the prognosis of human cancers.

METHODS

Using an experimental model of tumor necrosis factor-alpha (TNF-α)-mediated inflammation, we characterized inflammatory gene expression in immunopurified tumor-associated endothelial cells. These genes formed the basis of a multivariate molecular predictor of overall survival that was trained and validated in four types of human cancer.

RESULTS

We report that expression of experimentally derived tumor endothelial genes distinguished pathologic tissue specimens from normal controls in several human diseases associated with chronic inflammation. We trained these genes in human cancer datasets and defined a six-gene inflammatory signature that predicted significantly reduced overall survival in breast cancer, colon cancer, lung cancer, and glioma. This endothelial-derived signature predicted outcome independently of, but cooperatively with, standard clinical and pathological prognostic factors. Consistent with these findings, conditioned culture media from human endothelial cells stimulated by pro-inflammatory cytokines accelerated the growth of human colon and breast tumors in immunodeficient mice as compared with conditioned media from untreated endothelial cells.

CONCLUSIONS

This study provides the first prognostic cancer gene signature derived from an experimental model of tumor-associated endothelial inflammation. These findings support the notion that activation of inflammatory pathways in non-malignant tumor-infiltrating endothelial cells contributes to tumor growth and progression in multiple human cancers. Importantly, these results identify endothelial-derived factors that could serve as potential targets for therapy in diverse human cancers.

Abstract LB-162: DNA-damage foci persistence and accelerated senescence as determinants of radiosensitization by glycolysis inhibitors

One of the most striking characteristics of cancer cells is their altered glucose metabolism. Many cancer cells display a dramatic elevation in glucose utilization, independent of the availability of oxygen or the activity of oxidative phosphorylation. Cancers often display the Warburg effect, wherein glycolysis drives fermentation of pyruvate to lactate even under aerobic conditions. Aerobic glycolysis has been widely investigated and it is now considered a metabolic hallmark of transformation and a key driver for cancer cell proliferation, malignancy, metastasis, and therapeutic resistance. En route to cancer, pre-malignant cancer cells have to overcome cellular senescence which is recognized as a barrier for tumorigenesis. Recent data link both replicative and accelerated senescence to persistent DNA damage signals that arise from domains of modified chromatin at sites of un-repairable double strand breaks. Our prior work has established the kinetics of resolution of these chromatin domains, dubbed ionizing radiation induced foci (IRIF), and resulting effects on accelerated senescence as determinants of radiation sensitivity and as a target that can sensitize cancer cells to genotoxic therapy. To obtain probes that impinge on the DNA damage response and senescence, we developed a cell based assay for high throughput, high content screening based on the detection of IRIF persistence. Screening over 2500 drugs, including natural products and drug-like compounds identified known DNA damaging agents as well as novel candidates. To gain mechanistic insight, we tested these “hits” in combination with the mitochondrial inhibitor antimycin A and discovered several that blocked ATP synthesis. Combining bona fide glycolytic pathway inhibitors with radiation enhanced IRIF persistence and accelerated senescence in vitro. The glucokinase inhibitor 2-DG increased IRIF persistence and senescence after irradiation of tumor xenografts. These data suggest a critical role for aerobic glycolysis in the proliferation and survival of cancer cells to prevent stress-induced premature senescence, specifically by blocking the formation of DNA damage foci and/or preventing their persistence. Rather than simply satisfying energy needs, aerobic glycolysis likely serves an important survival and immortalization function for cancer cells. As such, targeting the Warburg effect to promote cancer cell senescence appears to be an attractive strategy for therapeutic intervention, particularly in combination with genotoxic therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-162. doi:1538-7445.AM2012-LB-162

Everolimus exhibits efficacy as a radiosensitizer in a model of non-small cell lung cancer

Signaling pathways that activate mTOR (mammalian target of rapamycin) are altered in many human cancers and these alterations are associated with prognosis and treatment response. mTOR inhibition can restore sensitivity to DNA damaging agents such as cisplatin. The rapamycin derivative everolimus exhibits antitumor activity and is approved for patients with renal cell cancer. Clinically, everolimus has also been evaluated in patients with advanced non-small cell lung cancer (NSCLC) that were refractory to chemotherapy and epidermal growth factor receptor tyrosine kinase inhibitors. We tested the effects of combined treatment with everolimus (RAD001) and fractionated radiation using a xenograft model of human NSCLC (A549 cells). In growth studies, mean tumor volume was reduced in the everolimus plus 30 Gy cohort with significant tumor growth suppression compared to 30 Gy alone (p=0015), or everolimus alone (p<0.001, ANOVA). everolimus (20 nM) significantly reduced protein levels of the mTOR downstream effector p70-S6K compared with radiation and vehicle (p=0.05, ANOVA) and significantly suppressed phospho-p70-S6K levels compared with all other treatments (p<0.001, ANOVA). We also evaluated everolimus and radiation effects on gene expression in A549 cells. Everolimus ± 5 Gy suppressed endothelin 1 and lactate dehydrogenase expression and increased VEGFA, p21, hypoxia-inducible factor-1α and SLC2A1 (facilitated glucose transporter 1). mTOR mRNA levels were unaffected while TNF-α levels were increased with everolimus + 5 Gy compared to either treatment alone. These findings suggest that everolimus increases the antitumor activity of radiation. Clinical trials combining everolimus with fractionated radiation in patients with NSCLC are warranted.

Response of human prostate cancer cells and tumors to combining PARP inhibition with ionizing radiation

Radiation therapy remains a promising modality for curative treatment of localized prostate cancer, but dose-limiting toxicities significantly limit its effectiveness. Agents that enhance efficacy at lower radiation doses might have considerable value in increasing tumor control without compromising organ function. Here, we tested the hypothesis that the PARP inhibitor ABT-888 (veliparib) can enhance the response of prostate cancer cells and tumors to ionizing radiation (IR). Following exposure of DU-145 and PC-3 prostate cancer cell lines to the combination of 10 μmol/L ABT-888 and 6 Gy, we observed similar persistence between both cell lines of DNA damage foci and in vitro radiosensitization. We have previously observed that persistent DNA damage foci formed after ABT-888 plus IR efficiently promote accelerated cell senescence, but only PC-3 cells displayed the expected senescent response of G(2)-M arrest, induction of p21 and β-galactosidase expression, and accumulation as large flat cells. In turn, combining ABT-888 with 6 Gy resulted in delayed tumor regrowth compared with either agent alone only in PC-3 xenograft tumors, whereas DU-145 tumors continued to grow. By 7 days after treatment with ABT-888 plus IR, PC-3 tumors contained abundant senescent cells displaying persistent DNA damage foci, but no evidence of senescence was noted in the DU-145 tumors. That equivalent radiosensitization by ABT-888 plus IR in vitro failed to predict comparable results with tumors in vivo suggests that the efficacy of PARP inhibitors may partially depend on a competent senescence response to accumulated DNA damage.

Abstract LB-363: DNA-damage foci persistence and accelerated senescence as determinants of radiosensitization by PARP inhibitors

Along with apoptosis and necrosis, accelerated senescence may be a desirable outcome when replicative cancer cells undergo unrepairable DNA double strand breaks (DSBs) after treatment with ionizing radiation (IR) or chemotherapy. In both normal and cancer cells, DSBs promote the assembly of Ionizing radiation induced foci (IRIF), domains of modified chromatin that serve a key role in DNA damage signaling and DNA repair. IRIF persistence is a critical determinant of accelerated senescence, making targeting IRIF resolution an attractive strategy to sensitize cancer cells to genotoxic therapy. As an IRIF reporter, we constructed an inducible GFP fusion to the IRIF-binding domain of 53BP1 (GFP-IBD) which we have expressed in breast, head and neck, prostate, glioma and pancreatic cancer cell lines. Typically, within minutes after IR exposure, GFP-IBD relocalizes to form fluorescent nuclear foci, which disperse over several hours. Anti-GFP immunoprecipitation and proteomic analysis of IRIF revealed chromatin modifiers and DNA damage response proteins at DSBs including the poly(ADP-ribose) polymerase PARP1. To block DSB repair in cancer cells and tumors, we treated cells with veliparib (ABT-888), one of several PARP inhibitors currently in clinical trials. Veliparib markedly enhanced IRIF persistence and increased cell senescence in the majority of cancer cell lines tested. Treatment of tumor xenografts in nude mice with veliparib and IR induced persistent foci, increased senescence in tumor and stroma, and delayed tumor regrowth. Our results suggest that the efficacy of PARP inhibitors may partially depend on a competent senescence response to accumulated DNA damage, validating this response as a desirable outcome of genotoxic therapy.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-363. doi:10.1158/1538-7445.AM2011-LB-363

Poly(ADP-ribose) polymerase inhibitor induces accelerated senescence in irradiated breast cancer cells and tumors

Persistent DNA double-strand breaks (DSB) may determine the antitumor effects of ionizing radiation (IR) by inducing apoptosis, necrosis, mitotic catastrophe, or permanent growth arrest. IR induces rapid modification of megabase chromatin domains surrounding DSBs via poly-ADP-ribosylation, phosphorylation, acetylation, and protein assembly. The dynamics of these IR-induced foci (IRIF) have been implicated in DNA damage signaling and DNA repair. As an IRIF reporter, we tracked the relocalization of green fluorescent protein fused to a chromatin binding domain of the checkpoint adapter protein 53BP1 after IR of breast cancer cells and tumors. To block DSB repair in breast cancer cells and tumors, we targeted poly(ADP-ribose) polymerase (PARP) with ABT-888 (veliparib), one of several PARP inhibitors currently in clinical trials. PARP inhibition markedly enhanced IRIF persistence and increased breast cancer cell senescence both in vitro and in vivo, arguing for targeting IRIF resolution as a novel therapeutic strategy.

Abstract 44: STAT1-dependent expression of genes and proteins involved in energy metabolism links tumor growth and radioresistance to the Warburg effect and predicts poor prognosis in cancer patients

Signal Transducer and Activator of Transcription 1 (STAT1) has traditionally been regarded as a transmitter of interferon signaling and a pro-apoptotic tumor suppressor. Recent data have identified new functions of STAT1 associated with tumorigenesis and resistance to genotoxic stress, including ionizing radiation (IR) and chemotherapy. To investigate the mechanisms contributing to the tumorigenic functions of STAT1, we performed a combined transcriptomic-proteomic expressional analysis of tumor xenografts with stable Stat1 knock-down (KD) relative to tumors with wild type (wt) Stat1. We also compared previously described SCC61 and nu61 isologous tumors, where SCC61 is radiosensitive and nu61 is radioresistant counterparts with different expression of IFN/Stat1 pathway. Transcriptional profiling was based on Affymetrix Human GeneChip® Gene 1.0 ST microarrays. Proteomes were determined from the MS/MS data by searching against the human subset of the UniProt database. Knockdown of STAT1 led to significant growth suppression in untreated tumors and radiosensitization of irradiated tumors. These changes were accompanied by alterations in the expression of genes and proteins of glycolysis/gluconeogenesis (GG), the citrate cycle (CC), and oxidative phosphorylation (OP). Of these pathways, GG had the most concordant changes in gene and protein expression and demonstrated a STAT1-dependent expression of genes and proteins consistent with tumor-specific glycolysis. IR drastically suppressed the GG pathway in STAT1 KD tumors without significant change in STAT1 WT tumors. Using 18F-FDG-PET we observed significantly higher glucose uptake in nu61 compared to SCC61 post-irradiation (6Gy). The STAT1 and glycolytic pathways were co-expressed in human breast tumors, and expression of STAT1-linked glycolytic genes was highly predictive of poor prognosis. Our results identify a previously uncharacterized function of STAT1 in tumors: expressional regulation of genes and enzymes involved in glycolysis, the citrate cycle, and mitochondrial oxidative phosphorylation, with predominant regulation of glycolysis. STAT1-dependent transcriptional and translational regulation of glycolysis suggests a potential role for STAT1 as a transcriptional modulator of genes responsible for the Warburg effect.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 44.

Characterization of response to radiation mediated gene therapy by means of multimodality imaging

Imaging techniques are under development to facilitate early analysis of spatial patterns of tumor response to combined radiation and antivascular gene therapy. A genetically modified, replication defective adenoviral vector (Ad.EGR-TNFalpha), injected intratumorally, mediates infected cells to express tumor necrosis factor alpha (TNFalpha), which is increased after exposure to radiation. The goal of this study was to characterize an image based "signature" for response to this combined radiation and gene therapy in mice with human prostate xenografts. This study is part of an imaged guided therapy project where such a signature would be useful in guiding subsequent treatments. Changes in the tumor micro-environment were assessed using MRI registered with electron paramagnetic resonance imaging which provides images of tissue oxygenation. Dynamic contrast-enhanced MRI was used to assess tissue perfusion. When compared with null vector (control) treatment, the ratio of contrast agent (Gd-DTPA-BMA) washout rate to uptake rate was lower (P = 0.001) after treatment, suggesting a more balanced perfusion. Concomitantly, oxygenation significantly increased in the treated animals and decreased or did not change in the control animals (P < 0.025). This is the first report of minimally invasive, quantitative, absolute oxygen measurements correlated with tissue perfusion in vivo.

STAT1 pathway mediates amplification of metastatic potential and resistance to therapy

Background

Traditionally IFN/STAT1 signaling is connected with an anti-viral response and pro-apoptotic tumor-suppressor functions. Emerging functions of a constitutively activated IFN/STAT1 pathway suggest an association with an aggressive tumor phenotype. We hypothesized that tumor clones that constitutively overexpress this pathway are preferentially selected by the host microenvironment due to a resistance to STAT1-dependent cytotoxicity and demonstrate increased metastatic ability combined with increased resistance to genotoxic stress.

Methodology/Principal Findings

Here we report that clones of B16F1 tumors grown in the lungs of syngeneic C57BL/6 mice demonstrate variable transcriptional levels of IFN/STAT1 pathway expression. Tumor cells that constitutively overexpress the IFN/STAT1 pathway (STAT1^H genotype) are selected by the lung microenvironment. STAT1^H tumor cells also demonstrate resistance to IFN-gamma (IFNγ), ionizing radiation (IR), and doxorubicin relative to parental B16F1 and low expressors of the IFN/STAT1 pathway (STAT1^L genotype). Stable knockdown of STAT1 reversed the aggressive phenotype and decreased both lung colonization and resistance to genotoxic stress.

Conclusions

Our results identify a pathway activated by tumor-stromal interactions thereby selecting for pro-metastatic and therapy-resistant tumor clones. New therapies targeted against the IFN/STAT1 signaling pathway may provide an effective strategy to treat or sensitize aggressive tumor clones to conventional cancer therapies and potentially prevent distant organ colonization.

Resveratrol is an effective inducer of CArG-driven TNF-alpha gene therapy

We report the anticarcinogenic, anti-aging polyphenol resveratrol activates the radio- and chemo-inducible cancer gene therapy vector Ad.Egr.TNF, a replication-deficient adenovirus that expresses human tumor necrosis factor alpha (TNF-alpha) under control of the Egr-1 promoter. Like ionizing radiation or chemotherapeutic agents previously shown to activate Ad.Egr.TNF, resveratrol also induces Egr-1 expression from its chromosomal locus with a possible role for Egr-1 promoter CC(A+T)richGG sequences in the expression of TNF-alpha. Resveratrol induction of TNF-alpha in Ad.Egr.TNF-infected tumor xenografts demonstrated antitumor response in human and rat tumor models comparable to that of radio- or chemotherapy-induced TNF-alpha. Although sirtuins are known targets of resveratrol, in vitro inhibition of SIRT1 activity did not abrogate resveratrol induction of Egr-1 expression. This suggests that SIRT1 is not essential to mediate resveratrol induction of Egr-1. Nevertheless, control of transgene expression via resveratrol activation of Egr-1 may extend use of Ad.Egr.TNF to patients intolerant of radiation or cytotoxic therapy and offer a novel tool for development of other inducible gene therapies.

Signal transducer and activator of transcription 1 regulates both cytotoxic and prosurvival functions in tumor cells

Elsewhere, we reported that multiple serial in vivo passage of a squamous cell carcinoma cells (SCC61) concurrent with ionizing radiation (IR) treatment resulted in the selection of radioresistant tumor (nu61) that overexpresses the signal transducer and activator of transcription 1 (Stat1)/IFN-dependent pathway. Here, we report that (a) the Stat1 pathway is induced by IR, (b) constitutive overexpression of Stat1 is linked with failure to transmit a cytotoxic signal by radiation or IFNs, (c) selection of parental cell line SCC61 against IFN-alpha and IFN-gamma leads to the same IR- and IFN-resistant phenotype as was obtained by IR selection, and (d) suppression of Stat1 by short hairpin RNA renders the IR-resistant nu61 cells radiosensitive to IR. We propose a model that transient induction of Stat1 by IFN, IR, or other stress signals activates cytotoxic genes and cytotoxic response. Constitutive overexpression of Stat1 on the other hand leads to the suppression of the cytotoxic response and induces prosurvival genes that, at high levels of Stat1, render the cells resistant to IR or other inducers of cell death.

Local gene delivery of tumor necrosis factor alpha can impact primary tumor growth and metastases through a host-mediated response

TNFerade is a replication incompetent adenovector designed to express human TNFalpha under control of the Egr-1 radiation and chemotherapy enhanced promoter, and is currently in Phase II/III clinical testing. Data from Phase I clinical testing of TNFerade in a limited set of melanoma patients suggested the potential to impact distal metastases following intratumoral injections of TNFerade. These clinical observations and the multiple potential mechanisms of TNFerade led us to hypothesize local treatment with TNFerade + radiation may impact metastatic disease. We explored this hypothesis in preclinical models using the spontaneously metastatic, syngeneic B16F10 murine melanoma model. Established subcutaneous B16F10 tumors were treated with intratumoral injections of TNFerade and localized 2 Gy fractionated radiation therapy, modeling the clinical treatment regimen. Following 10-14 days of treatment, mice were evaluated for metastases development in the iliac and axillary lymph nodes. Comparisons of metastatic burden to control groups indicated TNFerade +/- radiation suppressed the formation of metastases in the lymph nodes. Additional experiments in TNF receptor knockout mice, where the only possible effects are on tumor cells containing the TNFalpha receptor, indicate TNFerade's local and distal activities are critically dependent on a host-mediated response. These data provide direct preclinical evidence local therapy of a solid tumor with TNFerade can also reduce metastatic disease, in addition to effects on the treated lesion. Furthermore, our finding of a host dependant response(s) for TNFerade at both the treated tumor and on lymph node metastases suggest the potential for broad activity independent of tumor histology.

Establishment of a syngeneic model of hepatic colorectal oligometastases

BACKGROUND

Regional and systemic therapies aimed at improving the outcome for patients with colorectal hepatic metastases have met with modest yet tangible success. Currently, liver resection remains the only curative treatment, but only a minority of patients are candidates for surgery. Animal models are an ideal way to study new treatments for patients with metastatic colorectal cancer. We propose a syngeneic animal model of hepatic colorectal metastases that simulates oligometastases, which is a clinical state considered amenable to regional therapeutic strategies.

MATERIALS AND METHODS

BDIX (BD-9) rats underwent intrasplenic injection of DHD/K12/TRb (Prob/K12) cells to create hepatic metastases via the portal system. After injection of 5 x 10(6) cells, rats underwent laparotomy to determine metastatic burden. Histological analysis confirmed the presence of metastases from resected tumors.

RESULTS

Fifty-three animals were prospectively treated and observed for the development of oligometastases defined as between 1 and 10 hepatic lesions. Thirty-six (68%) of the animals developed detectable metastases while 32 (60%) developed oligometastases (average = 4.40 +/- 2.67). Four animals had overwhelming metastatic liver and peritoneal disease. All animals underwent peritoneal examination and thoracotomy to ensure localized disease. Histological analysis of five hepatectomy specimens confirmed the presence of metastatic cancer. Animals with oligometastases were healthy as evidenced by normal feeding and grooming behavior.

CONCLUSIONS

An animal model of oligometastatic colorectal cancer to the liver can reproducibly mimic the stage IV state in humans conducive to regional therapy and can be used reliably to test novel treatments and mechanisms of metastatic colorectal cancer.

Forphenicinol enhances the antitumor effects of cyclophosphamide in a model of squamous cell carcinoma

We examined the interaction between forphenicinol (FPL) and cyclophosphamide (CPA) or ionizing radiation (IR) on the growth of murine squamous cell carcinoma tumors SCCVII. Primary tumors were established in C3H mice by injecting SCCVII tumor cells subcutaneously into the right hind limb. FPL (100 mg/kg for 8 days) and/or CPA (25 mg/kg twice) were administered by intraperitoneal injection. Tumors were irradiated to a total dose of 40 Gy (eight 5-Gy fractions). SCCVII tumor growth was inhibited by FPL (P=0.054), IR (P=0.003) and CPA (P<0.001) compared with control. The combination of FPL and CPA inhibited tumor growth additively compared with either treatment alone in both small- and large-volume tumors. FPL did not significantly enhance the antitumor effects of IR, however, when CPA+FPL were combined with IR, significant tumor growth inhibition was observed compared with FPL alone (P<0.001), CPA alone (P=0.002) and IR alone (P=0.002). Due to its low toxicity profile, FPL may be combined with CPA, IR and other cytotoxic therapies to potentially enhance the therapeutic ratio.

Chemoinducible gene therapy: a strategy to enhance doxorubicin antitumor activity

A replication-defective adenoviral vector, Ad.Egr-TNF.11D, was engineered by ligating the CArG (CC(A/T)6GG) elements of the Egr-1 gene promoter upstream to a cDNA encoding human tumor necrosis factor-alpha. We report here that Ad.Egr-TNF.11D is activated by the clinically important anticancer agents cisplatin, cyclophosphamide, doxorubicin, 5-fluorouracil, gemcitabine, and paclitaxel. N-acetylcysteine, a free radical scavenger, blocked induction of tumor necrosis factor-alpha by anticancer agents, supporting a role for reactive oxygen intermediates in activation of the CArG sequences. Importantly, resistance of PC-3 human prostate carcinoma and PROb rat colon carcinoma tumors to doxorubicin in vivo was reversed by combining doxorubicin with Ad.Egr-TNF and resulted in significant antitumor effects. Treatment with Ad.Egr-TNF.11D has been associated with inhibition of tumor angiogenesis. In this context, a significant decrease in tumor microvessel density was observed following combined treatment with doxorubicin and Ad.Egr-TNF.11D as compared with either agent alone. These data show that Ad.Egr-TNF.11D is activated by diverse anticancer drugs.

Chemoinducible gene therapy: A strategy to enhance doxorubicin antitumor activity

A replication-defective adenoviral vector, Ad.Egr-TNF.11D, was engineered by ligating the CArG (CC(A/T)6GG) elements of the Egr-1 gene promoter upstream to a cDNA encoding human tumor necrosis factor-α. We report here that Ad.Egr-TNF.11D is activated by the clinically important anticancer agents cisplatin, cyclophosphamide, doxorubicin, 5-fluorouracil, gemcitabine, and paclitaxel. N-acetylcysteine, a free radical scavenger, blocked induction of tumor necrosis factor-α by anticancer agents, supporting a role for reactive oxygen intermediates in activation of the CArG sequences. Importantly, resistance of PC-3 human prostate carcinoma and PROb rat colon carcinoma tumors to doxorubicin in vivo was reversed by combining doxorubicin with Ad.Egr-TNF and resulted in significant antitumor effects. Treatment with Ad.Egr-TNF.11D has been associated with inhibition of tumor angiogenesis. In this context, a significant decrease in tumor microvessel density was observed following combined treatment with doxorubicin and Ad.Egr-TNF.11D as compared with either agent alone. These data show that Ad.Egr-TNF.11D is activated by diverse anticancer drugs.

Glioblastoma cells block radiation-induced programmed cell death of endothelial cells

We demonstrate that human umbilical vein endothelial cells (HUVEC) grown in co-culture (CC) with U87 glioblastoma cells transfected with green fluorescent protein (GFP-U87) exhibit resistance to radiation-mediated apoptosis. cDNA macroarray analysis reveals increases in the accumulation of RNAs for HUVEC genes encoding cell adhesion molecules, growth factor-related proteins, and cell cycle regulatory/DNA repair proteins. An increase in protein expression of integrin alphav, integrin beta1, MAPK(p42), Rad51, DNA-PK(CS), and ataxia telangiectasia gene (ATM) was detected in HUVEC grown in CC with GFP-U87 cells compared with HUVEC grown in mono-culture. Treatment with anti-VEGF antibody decreases the expression of integrin alphav, integrin beta1, DNA-PK(CS) and ATM with a corresponding increase in ionizing radiation (IR)-induced apoptosis. These data support the concept that endothelial cells growing in the tumor microenvironment may develop resistance to cytotoxic therapies due to the up-regulation by tumor cells of endothelial cells genes associated with survival.

Control of gene therapy by MDR1 and EGR1 promoter sequences in transcriptional targeting by chemotherapy (Review)

The promising benefits of cancer gene therapy have been limited by the inability to deliver therapeutic genes homogeneously throughout the tumor mass and to control gene expression within the tumor cells. Transcriptional targeting, the use of DNA regulatory promoter sequences to localize transgene expression, has been employed as a solution to circumvent these limitations. TNF-alpha is a cytokine that exhibits potent anticancer properties, but its utility following systemic administration is limited by toxicity. We review a strategy whereby ligating TNF-alpha to segments of the chemo-inducible EGR1 or MDR1 promoters activates expression of TNF-alpha cDNA and enhances effectiveness of gene therapy and chemotherapy.

Tumour-endothelium interactions in co-culture: coordinated changes of gene expression profiles and phenotypic properties of endothelial cells

Tumour angiogenesis is a complex process based upon a sequence of interactions between tumour cells and endothelial cells. To model tumour/endothelial-cell interactions, we co-cultured U87 human glioma cells with human umbilical vein endothelial cells (HUVECs). U87 cells induced an 'activated' phenotype in HUVECs, including an increase in proliferation, migration and net-like formation. Activation was observed in co-cultures where cells were in direct contact and physically separated, suggesting an important role for soluble factor(s) in the phenotypic and genotypic changes observed. Expressional profiling of tumour-activated endothelial cells was evaluated using cDNA arrays and confirmed by quantitative PCR. Matching pairs of receptors/ligands were found to be coordinately expressed, including TGFbetaRII with TGFbeta3, FGFRII and cysteine-rich fibroblast growth factor receptor (CRF-1) with FGF7 and FGF12, CCR1, CCR3, CCR5 with RANTES and calcitronin receptor-like gene (CALCRL) with adrenomedullin. Consistent with cDNA array data, immunohistochemical staining of expressed proteins revealed the upregulation of Tie-2 receptor in vitro and in vivo. Our data suggest that tumour-induced activation of quiescent endothelial cells involves the expression of angiogenesis-related receptors and the induction of autocrine growth loops. We suggest that tumour cells release growth factors that induce endothelial cells to express specific ligands and their cognate receptors coordinately.

Selective gene expression using a DF3/MUC1 promoter in a human esophageal adenocarcinoma model

The efficacy of replication-deficient adenoviral vectors in gene therapy is confined to the number of tumor cells the vector infects. To focus and enhance the therapeutic efficacy, we employed a conditionally replication-competent adenoviral vector with a tissue-specific promoter, DF3/MUC1, in a human esophageal adenocarcinoma model. Our results demonstrate that Ad.DF3.E1A.CMV.TNF (Ad.DF3.TNF) specifically replicates in Bic-1 (DF3-producing cells) and mediates an enhanced biologic effect due to increased TNF-alpha in the same DF3-producing cells. We also show that the increased TNF-alpha interacts with ionizing radiation to produce greater tumor regression and a greater delay in tumor regrowth in Bic-1 (DF3-producing cells) compared to Seg-1 (DF3 non-producers). Tumor cell targeting using conditionally replication-competent adenoviral vectors with tumor-specific promoters to drive viral replication and deliver TNF-alpha provides a novel approach to enhancing tumor radiosensitivity.

Prolonged treatment with angiostatin reduces metastatic burden during radiation therapy

Ionizing radiation (IR) and concomitant angiostatin (AS) produce greater than additive local antitumor effects. We examined whether prolonged AS treatment added to IR reduces proliferation of lung metastases from LLC primary tumors. Flank tumors were treated with 40 Gy with or without AS (25 mg/kg/day). IR plus a 14-day course of AS improved local tumor control and blocked the increase in lung weights observed in the group receiving IR plus a 2-day course of AS group. Animals treated with prolonged AS exhibited no increase in lung weight and no macrometastases. These findings suggest that long-term treatment with antiangiogenic compounds may be effective in preventing metastases from IR-treated tumors as well as increasing the local antitumor effects of radiotherapy.

Dual induction of the Epo-Egr-TNF-alpha- plasmid in hypoxic human colon adenocarcinoma produces tumor growth delay

Gene therapy is a modality for the treatment of solid tumors that involves the introduction of a suicide gene into the tumor cells. Genetic radiotherapy involves the placement of a radiation-sensitive promoter upstream from a suicide gene. Because of their irregular vasculature some solid tumors are chronically hypoxic and hence are resistant to conventional treatment with chemotherapy and ionizing radiation (IR). The purpose of this study was to demonstrate that regional tumor hypoxia could be exploited to improve local tumor control. The cDNA coding the erythropoietin hypoxia-responsive element (EPO) was placed upstream from the Egr-TNF-alpha construct. WIDR human colon adenocarcinoma cells were injected into the right hind limb of nude mice and treated with Epo-Egr-TNF-alpha plasmid with or without IR. Tumor volumes were measured by calipers and tumor necrosis factor (TNF)-alpha content of the tumor was determined by enzyme-linked immunosorbent assay. Treatment with the combined regimen of Epo-Egr-TNF-alpha plasmid + IR resulted in significant tumor growth delay. Tumor TNF-alpha content was increased by 30 per cent in the combined treatment group compared with each treatment alone. Regional tumor hypoxia can be exploited successfully to induce tumor growth delay, enhance local control, and enhance the therapeutic ratio.

Dual Induction of the Epo-Egr-TNF-α Plasmid in Hypoxic Human Colon Adenocarcinoma Produces Tumor Growth Delay

Gene therapy is a modality for the treatment of solid tumors that involves the introduction of a suicide gene into the tumor cells. Genetic radiotherapy involves the placement of a radiation-sensitive promoter upstream from a suicide gene. Because of their irregular vasculature some solid tumors are chronically hypoxic and hence are resistant to conventional treatment with chemotherapy and ionizing radiation (IR). The purpose of this study was to demonstrate that regional tumor hypoxia could be exploited to improve local tumor control. The cDNA coding the erythropoietin hypoxia-responsive element (EPO) was placed upstream from the Egr-TNF-α construct. WIDR human colon adenocarcinoma cells were injected into the right hind limb of nude mice and treated with Epo-Egr-TNF-α plasmid with or without IR. Tumor volumes were measured by calipers and tumor necrosis factor (TNF)-α content of the tumor was determined by enzyme-linked immunosorbent assay. Treatment with the combined regimen of Epo-Egr-TNF-α plasmid + IR resulted in significant tumor growth delay. Tumor TNF-α content was increased by 30 per cent in the combined treatment group compared with each treatment alone. Regional tumor hypoxia can be exploited successfully to induce tumor growth delay, enhance local control, and enhance the therapeutic ratio.

Radiation-induced tumour necrosis factor-alpha expression: clinical application of transcriptional and physical targeting of gene therapy

Promising data are emerging on a new anticancer agent, Ad.EGR-TNF, an adenoviral vector, which contains radio-inducible DNA sequences from the early growth response (EGR1) gene promoter and cDNA for the gene encoding human tumour necrosis factor-alpha. Ad.EGR-TNF combines the well-documented broad-spectrum anticancer activity of TNFalpha with the proven clinical usefulness of radiotherapy. Systemic delivery of the TNFalpha protein has had limited success clinically because of severe dose-limiting toxic effects. This limitation has been overcome by the use of a gene delivery approach, combined with a radiation-inducible promoter to express the TNFalpha protein in the irradiated tumour tissue. Preclinical and early phase I clinical testing indicates that effective concentrations of TNFalpha can be delivered to the tumour site without significant systemic exposure or toxic effects. The combination of radiation and TNFalpha gene delivery has produced striking antitumour effects in model systems in animals. In the clinical setting, potent anticancer activity has been observed with a high rate of complete and partial objective tumour responses. A novel mechanism of destruction of the tumour vasculature seems to be central to this distinct antitumour activity. This review summarises the rationale, mechanistic basis, preclinical data, and preliminary clinical findings for this new treatment model.

Angiostatin potentiates cyclophosphamide treatment of metastatic disease

PURPOSE

We examined the interaction between cyclophosphamide (CPA) and angiostatin (AS) on the growth of primary Lewis lung carcinoma (LLC) tumors and on the development of LLC pulmonary metastases. We studied the effects of AS and CPA on the stages of angiogenesis employing in vitro assays.

METHODS

Primary tumor growth and pulmonary metastases were measured to evaluate the effects of treatment with AS alone, CPA alone or the combination of CPA and AS. We examined the effects of CPA plus AS on endothelial cell (HUVEC) survival, migration and tube formation.

RESULTS

Combined treatment with CPA and AS did not significantly affect primary tumor growth when compared with CPA treatment alone. However, a significant decrease in the number of pulmonary metastases was observed following CPA plus AS treatment when compared with CPA treatment alone ( P<0.001). AS did not enhance CPA-mediated HUVEC cytotoxicity, and CPA failed to enhance AS-mediated inhibition of migration. However, tube formation was inhibited following combined treatment with CPA and AS when compared with either treatment alone.

CONCLUSIONS

AS enhanced the antimetastatic effects of CPA without significantly influencing the effects of CPA on primary tumor growth. CPA plus AS inhibited tube formation, suggesting that interrupting specific steps in the angiogenesis process might be an effective approach to the treatment of subclinical distant metastases.

Transcriptional control of viral gene therapy by cisplatin

Ionizing radiation (IR) and radical oxygen intermediates (ROIs) activate the early growth response-1 (Egr1) promoter through specific cis-acting sequences termed CArG elements. Ad.Egr.TNF.11D, a replication-deficient adenoviral vector containing CArG elements cloned upstream of the cDNA for human recombinant TNF-alpha was used to treat human esophageal adenocarcinoma and rat colon adenocarcinoma cells in culture and as xenografts in athymic nude mice. Cisplatin, a commonly used chemotherapeutic agent, causes tumor cell death by producing DNA damage and generating ROIs. The present studies demonstrate induction of TNF-alpha production in tumor cells and xenografts treated with the combination of Ad.Egr.TNF.11D and cisplatin. The results show that the Egr1 promoter is induced by cisplatin and that this induction is mediated in part through the CArG elements. These studies also demonstrate an enhanced antitumor response without an increase in toxicity following treatment with Ad.Egr.TNF.11D and cisplatin, compared with either agent alone. Chemo-inducible cancer gene therapy thus provides a means to control transgene expression while enhancing the effectiveness of commonly used chemotherapeutic agents.

Combined gene therapy and ionizing radiation is a novel approach to treat human esophageal adenocarcinoma

BACKGROUND

The ability to infect tumor cells limits the antitumor effects of gene therapy. The addition of radiotherapy to treatment with Ad.Egr.TNF.11D, a replication-deficient adenovirus containing a radiation-inducible promoter, early growth response-1, and the tumor necrosis factor-alpha (TNFalpha) complementary DNA may enhance the therapeutic ratio.

METHODS

Seg-1 human esophageal adenocarcinoma cells were treated with Ad.Egr.TNF.11D with or without radiation. TNFalpha levels were quantified with enzyme-linked immunosorbent assay. Athymic nude mice bearing Seg-1 tumors were randomized to buffer, ionizing radiation, Ad.Egr.TNF.11D, and combination therapy. Tumor growth delay was used to compare treatment regimens. TNFalpha levels were measured in tumor homogenates and plasma.

RESULTS

Seg-1 cells treated with Ad.Egr.TNF.11D and ionizing radiation demonstrated increased TNFalpha levels at 72 hours compared with cells exposed to vector alone (124 +/- 0 pg/mL vs. 31.11 +/- 22 pg/mL; P =.008). In vivo, Ad.Egr.TNF.11D-treated tumors expressed low TNFalpha levels (151.5 +/- 107.11 pg/mg protein) compared with tumors receiving combined treatment (793.92 +/- 489.13 pg/mg protein; P =.067). Increased TNFalpha levels were associated with increased tumor growth delay after combined treatment (P <.05).

CONCLUSIONS

Radiotherapy enables focal stimulation of TNFalpha expression in Ad.Egr.TNF.11D-infected cells and thus improves local tumor control.

Tumor production of angiostatin is enhanced after exposure to TNF-alpha

Infection of tumors with an adenoviral vector expressing a chimeric gene composed of the CArG elements of the Egr-1 promoter and a cDNA encoding TNF-alpha (Ad.Egr-TNF) has previously been shown to result in the production of high intratumoral levels of TNF-alpha and thereby tumor regression. The antitumor effects of TNF-alpha were ascribed to vascular thrombosis. We and others, have reported that inhibition of tumor vessel thrombosis using anticoagulation therapy does not abrogate the antitumor effects after TNF-alpha treatment. To investigate the potential antiangiogenic effects of TNF-alpha, we studied the generation of angiostatin after intratumoral injection of Ad.Egr-TNF. We report an increase in plasma angiostatin levels both during and after treatment with Ad.Egr-TNF that parallel tumor regression. We also report that TNF-alpha enhances angiostatin production by inducing the activity of plasminogen activator and the release of MMP-9 by tumor cells. These studies support a model in which the antiangiogenic effects of TNF-alpha on the tumor microvasculature are mediated by generation of angiostatin.

Vascular endothelial growth factor enhances endothelial cell survival and tumor radioresistance

PURPOSE

Vascular endothelial growth factor (VEGF) is an important mediator of endothelial cell proliferation and survival. The purpose of the present studies was to investigate the role of VEGF in the tumor response to ionizing radiation.

METHODS

Two ras-transformed murine fibrosarcoma cell lines, VEGF+/+ and VEGF-/- were exposed to ionizing radiation (0, 1, 3, 5, 7 or 9 Gy) in vitro, and clonogenic survival was determined. VEGF+/+ and VEGF-/- xenografts were generated in athymic nude mice and then treated with ionizing radiation (ten 5-Gy fractions = 50 Gy). Mean fractional tumor volume was used to evaluate treatment efficacy. To determine whether VEGF enhances tumor radioresistance by targeting endothelial cells, we performed clonogenic survival assays with human umbilical vein endothelial cells. Surviving fractions were calculated after treatment with ionizing radiation (5 Gy) and recombinant hVEGF165 (0, 1, 10, and 100 ng/mL). To determine whether VEGF neutralization enhances tumor radiosensitivity, we employed anti-VEGF165 monoclonal antibody to treat human tumor xenografts. Tumors were exposed to ionizing radiation (four 5-Gy fractions = 20 Gy) and treated with anti-VEGF antibody (0, 5, and 25 microg/kg in four intraperitoneal doses). Mean fractional tumor volume was used to evaluate treatment efficacy. To elucidate the molecular mechanism contributing to the observed anti-VEGF/ionizing radiation interaction, we exposed human umbilical vein endothelial cells to ionizing radiation (5 Gy) in the presence of anti-VEGF antibody (1 microg/mL). Sodium dodecyl sulfate polyacrylamide gel electrophoresis of cell lysates was probed for mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK1/MEK2).

RESULTS

The in vitro radiosensitivities of the VEGF+/+ and VEGF-/- clones were equivalent (D0 = 146 vs 149). However, the VEGF+/+ xenografts were more resistant to the cytotoxic effects of ionizing radiation than the VEGF-/- xenografts. VEGF+/+ xenografts demonstrated a faster doubling time (4.5 vs 6.0 days) and a shorter growth delay (15 vs 23 days) than VEGF-/- xenografts. The surviving fraction of human umbilical vein endothelial cells after exposure to ionizing radiation was significantly enhanced in the presence of VEGF (6.4% vs 12.5%). Western blot analysis demonstrated that stimulation of MAPK and MEK1/MEK2 was abrogated after exposure to anti-VEGF antibody.

DISCUSSION

These findings represent the first genetic evidence that factors other than inherent tumor cell radiosensitivity are important determinants of radiocurability. Antitumor strategies targeting VEGF and other endothelial cell survival mechanisms may be used to enhance the cytotoxic effects of radiotherapy.

Prevention of restenosis by a herpes simplex virus mutant capable of controlled long-term expression in vascular tissue in vivo

Neointimal hyperplasia resulting from vascular smooth muscle cell (SMC) proliferation and luminal migration is the major cause of autologous vein graft failure following vascular coronary or peripheral bypass surgery. Strategies to attenuate SMC proliferation by the delivery of oligonucleotides or genes controlling cell division rely on the use of high concentrations of vectors, and require pre-emptive disruption of the endothelial cell layer. We report a genetically engineered herpes simplex virus (HSV-1) mutant that, in an in vivo rabbit model system, infects all vascular layers without prior injury to the endothelium; expresses a reporter gene driven by a viral promoter with high efficiency for at least 4 weeks; exhibits no systemic toxicity; can be eliminated at will by administration of the antiviral drug acyclovir; and significantly reduces SMC proliferation and restenosis in vein grafts in immunocompetent hosts.

Treatment of head and neck and esophageal xenografts employing Alimta and concurrent ionizing radiation

We examined the interaction between Alimta and ionizing radiation (IR) as a potential strategy to enhance the therapeutic ratio of combined-modality cancer treatment. Mice bearing human esophageal adenocarcinoma xenografts (Seg-1) or squamous cell carcinoma xenografts (SQ-20B) were treated with Alimta and IR employing a fractionated treatment schedule. Treatment with Alimta alone slowed the growth of Seg-1 but not SQ-20B tumors compared with control tumors. In Seg-1 xenografts combined treatment with Alimta and IR produced significant tumor growth inhibition compared with Alimta alone or IR alone. In SQ-20B xenografts, treatment with Alimta did not enhance IR-mediated tumor growth inhibition suggesting that sensitivity to Alimta is necessary for an interactive cytotoxic effect with IR. The present data suggest the potential clinical efficacy of combining Alimta administration with radiotherapy for Alimta-sensitive cells and indicate that further testing needs to be conducted to optimize the dosing schedule to enhance the interaction between the therapeutic agents.

NM-3, an isocoumarin, increases the antitumor effects of radiotherapy without toxicity

We examined the effects of a new antiangiogenic isocoumarin, NM-3, as a radiation modifier in vitro and in vivo. The present studies demonstrate that NM-3 is cytotoxic to human umbilical vein endothelial cells (HUVECs) but not to Lewis lung carcinoma (LLC) cells nor Seg-1, esophageal adenocarcinoma cells, in clonogenic survival assays. When HUVEC cultures are treated with NM-3 combined with ionizing radiation (IR), additive cytotoxicity is observed. In addition, the combination of NM-3 and IR inhibits HUVEC migration to a greater extent than either treatment alone. The effects of treatment with NM-3 and IR were also evaluated in tumor model systems. C57BL/6 female mice bearing LLC tumors were given injections for 4 consecutive days with NM-3 (25 mg/kg/day) and treated with IR (20 Gy) for 2 consecutive days. Combined treatment with NM-3 and IR significantly reduced mean tumor volume compared with either treatment alone. An increase in local tumor control was also observed in LLC tumors in mice receiving NM-3/IR therapy. When athymic nude mice bearing Seg-1 tumor xenografts were treated with NM-3 (100 mg/kg/day for 4 days) and 20 Gy (four 5 Gy fractions), significant tumor regression was observed after combined treatment (NM-3 and IR) compared with IR alone. Importantly, no increase in systemic or local tissue toxicity was observed after combined treatment (NM-3 and IR) when compared with IR alone. The bioavailability and nontoxic profile of NM-3 suggests that the efficacy of this agent should be tested in clinical radiotherapy.

Antitumor interaction of short-course endostatin and ionizing radiation

PURPOSE

The purpose of this study was to evaluate whether endostatin, an antiangiogenic cleavage fragment of collagen XVIII, enhances the antitumor effects of ionizing radiation (IR). Endostatin was injected to coincide with fractionated radiotherapy.

METHODS

Xenografts of radioresistant SQ-20B tumor cells were established in athymic nude mice. Lewis lung carcinoma cells were injected into C57BI/6 mice. Mice bearing SQ-20B xenografts were injected intraperitoneally with 2.5 mg/kg/day of murine recombinant endostatin 5 times per week for 2 weeks 3 hours before IR treatment (50 Gy total dose). Mice bearing Lewis lung carcinoma tumors were injected intraperitoneally with endostatin (2.5 mg/kg/day) four times; the first injection was given 24 hours before the first IR dose (15 Gy) and then 3 hours before IR (15 Gy/day) for 3 consecutive days. Microvascular density was assessed on tumor tissue sections by use of CD31 immunohistochemistry and light microscopy. Endothelial cell survival analyses were employed to evaluate endostatin effects on human aortic endothelial cells and human umbilical vein endothelial cells. Endothelial cell apoptosis was examined by use of FACS analysis and DAPI microscopy.

RESULTS

In SQ-20B xenografts, combined treatment with endostatin and IR produced tumor growth inhibition that was most pronounced at the nadir of regression (day 21). By day 35, tumors receiving combined treatment with endostatin and IR were 47% smaller than tumors treated with endostatin alone. Interactive cytotoxic treatment effects between endostatin and IR were also demonstrated in mice bearing Lewis lung carcinoma tumors. Significant tumor growth inhibition was observed in the endostatin/IR group at days 11 and 13 compared with IR alone. Histologic analyses demonstrated a reduction in microvascular density after combined treatment with endostatin and IR compared with endostatin treatment alone. Survival analyses confirmed interactive cytotoxicity between endostatin and IR in both human aortic endothelial cells and human umbilical vein endothelial cells but not in SQ-20B tumor cells. Combined treatment with endostatin and IR produced an increase in cow pulmonary artery endothelial apoptosis compared with either treatment alone.

DISCUSSION

The tumor regression observed after combined treatment with endostatin and IR suggests additive antitumor effects in both human and murine tumors. Importantly, the concentrations of endostatin employed produced little tumor regression when endostatin was employed as a single agent. The results from the clonogenic and apoptosis assays support the hypothesis that the endothelial compartment is the target for the endostatin/IR interaction.

Angiostatin induces mitotic cell death of proliferating endothelial cells

Angiostatin is an inhibitor of tumor angiogenesis that induces regression of experimental tumors and enhances the antitumor effects of radiation therapy. We report that the cytotoxic effects of angiostatin are restricted to the proliferating endothelial cell population. In addition, angiostatin and ionizing radiation (IR) interact by inducing death of dividing endothelial cells. We also show that angiostatin and IR interact to inhibit endothelial cell migration. These findings demonstrate that angiostatin targets the proliferating tumor vasculature and provide a mechanistic basis for the cytotoxic interaction of angiostatin and IR.

Gene therapy enhances the antiproliferative effect of radiation in intimal hyperplasia

BACKGROUND

Although ionizing radiation (IR) has been demonstrated to attenuate vessel wall restenosis and intimal hyperplasia (IH), dose-related mural injury and atrophy are possible deleterious side effects. We tested the hypothesis that a radiosensitizing strategy may improve IR-induced inhibition of in vivo vascular smooth muscle cells (VSMCs) without influencing apoptotic cell death.

METHODS

In 28 New Zealand White rabbits, the right common carotid artery (CCA) was injured and subjected to low-flow conditions to promote IH. The CCA was transfected with an adenoviral vector incorporating the cytosine deaminase (CD) gene (1 x 10(9) PFU/ml). 5-Fluorocytosine (5-FC), a prodrug that is converted to the radiosensitizing agent 5-fluorouracil (5-FU) by CD, was thereafter administered intravenously. The CCA was exposed to 5 Gy IR at 24 h. Intimal/medial (I/M) area and thickness ratios were determined in the harvested CCAs at 14 days. VSMC proliferative and apoptotic indices were assessed with immunohistochemistry.

RESULTS

A 50% reduction in I/M area was found in rabbits treated with IR and IR + CD/5-FC (0.19 +/- 0.03 and 0.18 +/- 0.02) when compared with untreated controls (UC) (0.37 +/- 0.06) (P = 0.005). This finding was substantiated by attenuation of I/M thickness in the IR groups [0.47 +/- 0.13 (IR), 0.41 +/- 0.11 (IR + CD/5-FC), 0.61 +/- 0.17 (UC)] (P = 0.007). The number of proliferating VSMCs was notably smaller when IR was combined with CD/5-FC (4.17 +/- 1.16 vs 2.97 +/- 1.09 log transformed cells/mm(2), P < 0.07). Apoptosis was similar in all groups.

CONCLUSIONS

Both IR alone and IR combined with a radiosensitizing agent are effective in attenuating experimental IH. However, combination therapy is synergistic and achieves greater inhibition of VSMC proliferation and may involve selective killing of radioresistant S-phase VSMCs. IR + CD/5-FC represents a novel therapeutic strategy that offers potential for long-term control of IH.

In vitro and in vivo activity of protein kinase C inhibitor chelerythrine chloride induces tumor cell toxicity and growth delay in vivo

Although clonogenic or divisional death is the main mechanism by which DNA-damaging agents demonstrate antitumor activity, recent data indicate that strategies specifically designed to trigger apoptosis may also prove to be useful antitumor agents. Protein kinase C (PKC) isoenzymes are involved in the regulation of cell proliferation, differentiation, and survival. Whereas pharmacological inhibition of PKC activity triggers apoptosis in most mammalian cells, cell line and tissue differences in sensitivities to these inhibitors remain. Whereas PKC inhibitors have potential as antitumor agents, issue of kinase specificity and solubility have remained obstacles to their clinical use. In this report, we investigated the antitumor activity of the PKC inhibitor chelerythrine chloride (chelerythrine), a selective inhibitor of group A and B PKC isoforms. Chelerythrine exhibited cytotoxic activity against nine human tumor cell lines tested in vitro. On the basis of the finding that radioresistant and chemoresistant squamous cell carcinoma lines (HNSCC) undergo apoptosis rapidly after treatment with chelerythrine in vitro, we assessed the effects of this agent on p53-deficient SQ-20B HNSCC cells in vivo. The results demonstrate that chelerythrine treatment of nude mice bearing SQ-20B is associated with significant tumor growth delay. Significantly, treatment with chelerythrine resulted in minimal toxicity. These findings demonstrate a potential for chelerythrine as an antitumor drug against squamous cell carcinoma.

Blockage of the vascular endothelial growth factor stress response increases the antitumor effects of ionizing radiation

The family of vascular endothelial growth factor (VEGF) proteins include potent and specific mitogens for vascular endothelial cells that function in the lation of angiogenesis Inhibition of VEGF-induced angiogenesis either by neutralizing antibodies or dominant-negative soluble receptor, blocks the growth of primary and metastatic experimental tumors Here we report that VEGF expression is induced in Lewis lung carcinomas (LLCs) both in vitro and vivo after exposure to ionizing radiation (IR) and in human tumor cell lines (Seg-1 esophageal adenocarcinoma, SQ20B squamous cell carcinoma, T98 and U87 glioblastomas, and U1 melanoma) in vitro. The biological significance of IR-induced VEGF production is supported by our finding that treatment of tumor-bearing mice (LLC, Seg-1, SQ20B, and U87) with a neutralizing antibody to VEGF-165 before irradiation is associated with a greater than additive antitumor effect. In vitro, the addition of VEGF decreases IR-induced killing of human umbilical vein endothelial cells, and the anti-VEGF treatment potentiates IR-induced lethality of human umbilical vein endothelial cells. Neither recombinant VEGF protein nor neutralizing antibody to VEGF affects the radiosensitivity of tumor cells These findings support a model in which induction of VEGF by IR contributes to the protection of tumor blood vessels from radiation-mediated cytotoxicity and thereby to tumor radioresistance.

Radiation-inducible gene therapy

The radiation-inducible chimeric genetic construct Egr-TNF alpha introduced into human xenografts produces cytotoxicity of infected tumor cells resulting in tumor growth inhibition. The interaction between Egr-TNF and radiation is selectively cytotoxic for the tumor microvasculature resulting in vascular thrombosis and tumor necrosis. Gene therapy combined with radiation therapy offers great potential for the treatment of localized human cancers.

Potentiation of the antitumor effect of ionizing radiation by brief concomitant exposures to angiostatin

Angiostatin, a proteolytic fragment of plasminogen, inhibits the growth of primary and metastatic tumors by suppressing angiogenesis. When used in combination with ionizing radiation (IR), angiostatin demonstrates potent antitumor synergism, largely caused by inhibition of the tumor microvasculature. We report here the temporal interaction of angiostatin and IR in Lewis lung carcinoma (LLC) tumors growing in the hind limbs of syngeneic mice. Tumors with an initial mean volume of 510 +/- 151 mm3 were treated with IR alone (20 Gy x 2 doses on days 0 and 1), angiostatin alone (25 mg/kg/day divided twice daily) on days 0 through 13, or a combination of the two as follows: (a) IR plus angiostatin (days 0 through 13); (b) IR plus angiostatin (days 0 and 1); and (c) IR followed by angiostatin beginning on the day after IR completion and given daily thereafter (days 2 through 13). By day 14, tumors in untreated control mice had grown to 6110 +/- 582 mm3, whereas in mice treated with: (a) IR alone, tumors had grown to 2854 +/- 338 mm3 (P < 0.05 compared with untreated controls); and (b) angiostatin alone, tumors had grown to 3666 +/- 453 mm3 (P < 0.05 compared with untreated controls). In combined-treatment groups, in mice treated with: (a) IR plus longer-course angiostatin, tumors reached 2022 +/- 282 mm3 (P = 0.036 compared with IR alone); (b) IR followed by angiostatin, tumors reached 2677 +/- 469 mm3 (P > 0.05 compared with IR alone); and (c) IR plus short-course angiostatin, tumors reached 1032 +/- 78 mm3 (P < 0.001 compared with IR alone). These findings demonstrate that the efficacy of experimental radiation therapy is potentiated by brief concomitant exposure of the tumor vasculature to angiostatin.

Tumor necrosis factor-alpha-based gene therapy enhances radiation cytotoxicity in human prostate cancer

The purpose of the present study was to determine the therapeutic potential of combining radiotherapy with tumor necrosis factor (TNF)-alpha-based gene therapy in the human prostate cancer PC-3 xenograft. PC-3 cells are highly resistant to TNF-alpha-induced cytotoxicity in vitro. A modest enhancement of radiation killing was observed with the addition of TNF-alpha in clonogenic survival assays. Combined treatment with Ad.Egr-TNF, a replication-deficient adenovirus modified to express TNF-alpha following the exposure of infected cells to ionizing radiation (40 Gy administered at 5 Gy per fraction) in vivo, resulted in increased tumor control, as defined by a reduction of tumor volume, when compared with treatment with Ad.Egr-TNF alone or with radiation alone (P < .03). The improvement in tumor control was achieved without increasing acute normal tissue damage when compared with tissue injury from radiation alone. The results of these studies support further development and clinical application of genetic radiotherapy for human prostate cancer.

Combined effects of angiostatin and ionizing radiation in antitumour therapy

Angiogenesis, the formation of new capillaries from pre-existing vessels, is essential for tumour progression. Angiostatin, a proteolytic fragment of plasminogen that was first isolated from the serum and urine of tumour-bearing mice, inhibits angiogenesis and thereby growth of primary and metastatic tumours. Radiotherapy is important in the treatment of many human cancers, but is often unsuccessful because of tumour cell radiation resistance. Here we combine radiation with angiostatin to target tumour vasculature that is genetically stable and therefore less likely to develop resistance. The results show an antitumour interaction between ionizing radiation and angiostatin for four distinct tumour types, at doses of radiation that are used in radiotherapy. The combination produced no increase in toxicity towards normal tissue. In vitro studies show that radiation and angiostatin have combined cytotoxic effects on endothelial cells, but not tumour cells. In vivo studies show that these agents, in combination, target the tumour vasculature. Our results provide support for combining ionizing radiation with angiostatin to improve tumour eradication without increasing deleterious effects.