Expression of Oestrogen Receptor and Transforming Growth Factor-α in MCF-7 Cells after Exposure to Fractionated Irradiation

Radiation-Induced Gene Expression Changes in High and Low Grade Breast Cancer Cell Types

BACKGROUND

There is extensive scientific evidence that radiation therapy (RT) is a crucial treatment, either alone or in combination with other treatment modalities, for many types of cancer, including breast cancer (BC). BC is a heterogeneous disease at both clinical and molecular levels, presenting distinct subtypes linked to the hormone receptor (HR) status and associated with different clinical outcomes. The aim of this study was to assess the molecular changes induced by high doses of ionizing radiation (IR) on immortalized and primary BC cell lines grouped according to Human epidermal growth factor receptor (HER2), estrogen, and progesterone receptors, to study how HR status influences the radiation response. Our genomic approach using in vitro and ex-vivo models (e.g., primary cells) is a necessary first step for a translational study to describe the common driven radio-resistance features associated with HR status. This information will eventually allow clinicians to prescribe more personalized total doses or associated targeted therapies for specific tumor subtypes, thus enhancing cancer radio-sensitivity.

METHODS

Nontumorigenic (MCF10A) and BC (MCF7 and MDA-MB-231) immortalized cell lines, as well as healthy (HMEC) and BC (BCpc7 and BCpcEMT) primary cultures, were divided into low grade, high grade, and healthy groups according to their HR status. At 24 h post-treatment, the gene expression profiles induced by two doses of IR treatment with 9 and 23 Gy were analyzed by cDNA microarray technology to select and compare the differential gene and pathway expressions among the experimental groups.

RESULTS

We present a descriptive report of the substantial alterations in gene expression levels and pathways after IR treatment in both immortalized and primary cell cultures. Overall, the IR-induced gene expression profiles and pathways appear to be cell-line dependent. The data suggest that some specific gene and pathway signatures seem to be linked to HR status.

CONCLUSIONS

Genomic biomarkers and gene-signatures of specific tumor subtypes, selected according to their HR status and molecular features, could facilitate personalized biological-driven RT treatment planning alone and in combination with targeted therapies.

Key mechanisms involved in ionizing radiation-induced systemic effects. A current review

Organisms respond to physical, chemical and biological threats by a potent inflammatory response, aimed at preserving tissue integrity and restoring tissue homeostasis and function. Systemic effects in an organism refer to an effect or phenomenon which originates at a specific point and can spread throughout the body affecting a group of organs or tissues. Ionizing radiation (IR)-induced systemic effects arise usually from a local exposure of an organ or part of the body. This stress induces a variety of responses in the irradiated cells/tissues, initiated by the DNA damage response and DNA repair (DDR/R), apoptosis or immune response, including inflammation. Activation of this IR-response (IRR) system, especially at the organism level, consists of several subsystems and exerts a variety of targeted and non-targeted effects. Based on the above, we believe that in order to understand this complex response system better one should follow a 'holistic' approach including all possible mechanisms and at all organization levels. In this review, we describe the current status of knowledge on the topic, as well as the key molecules and main mechanisms involved in the 'spreading' of the message throughout the body or cells. Last but not least, we discuss the danger-signal mediated systemic immune effects of radiotherapy for the clinical setup.

Biochemical signatures of in vitro radiation response in human lung, breast and prostate tumour cells observed with Raman spectroscopy

This work applies noninvasive single-cell Raman spectroscopy (RS) and principal component analysis (PCA) to analyze and correlate radiation-induced biochemical changes in a panel of human tumour cell lines that vary by tissue of origin, p53 status and intrinsic radiosensitivity. Six human tumour cell lines, derived from prostate (DU145, PC3 and LNCaP), breast (MDA-MB-231 and MCF7) and lung (H460), were irradiated in vitro with single fractions (15, 30 or 50 Gy) of 6 MV photons. Remaining live cells were harvested for RS analysis at 0, 24, 48 and 72 h post-irradiation, along with unirradiated controls. Single-cell Raman spectra were acquired from 20 cells per sample utilizing a 785 nm excitation laser. All spectra (200 per cell line) were individually post-processed using established methods and the total data set for each cell line was analyzed with PCA using standard algorithms. One radiation-induced PCA component was detected for each cell line by identification of statistically significant changes in the PCA score distributions for irradiated samples, as compared to unirradiated samples, in the first 24-72 h post-irradiation. These RS response signatures arise from radiation-induced changes in cellular concentrations of aromatic amino acids, conformational protein structures and certain nucleic acid and lipid functional groups. Correlation analysis between the radiation-induced PCA components separates the cell lines into three distinct RS response categories: R1 (H460 and MCF7), R2 (MDA-MB-231 and PC3) and R3 (DU145 and LNCaP). These RS categories partially segregate according to radiosensitivity, as the R1 and R2 cell lines are radioresistant (SF(2) > 0.6) and the R3 cell lines are radiosensitive (SF(2) < 0.5). The R1 and R2 cell lines further segregate according to p53 gene status, corroborated by cell cycle analysis post-irradiation. Potential radiation-induced biochemical response mechanisms underlying our RS observations are proposed, such as (1) the regulated synthesis and degradation of structured proteins and (2) the expression of anti-apoptosis factors or other survival signals. This study demonstrates the utility of RS for noninvasive radiobiological analysis of tumour cell radiation response, and indicates the potential for future RS studies designed to investigate, monitor or predict radiation response.

Molecular mechanism of the schedule-dependent synergistic interaction in EGFR-mutant non-small cell lung cancer cell lines treated with paclitaxel and gefitinib

Background

Chemotherapy combined concurrently with TKIs produced a negative interaction and failed to improve survival when compared with chemotherapy or TKIs alone in the treatment of non-small cell lung cancer (NSCLC). The present study investigated the sequence-dependent interaction between paclitaxel and gefitinib and clarified the underlying mechanism.

Methods

The effects on cell proliferation, EGFR signaling pathway, and TGFα expression were evaluated in a panel of human NSCLC cell lines harboring EGFR mutations with three different combination sequences: sequential treatment with paclitaxel followed by gefitinib (T→G), sequential treatment with gefitinib followed by paclitaxel (G→T), or concomitant treatment (T + G).

Results

The sequence-dependent anti-proliferative effects differed between EGFR-TKI-sensitive and -resistant cell lines carrying EGFR mutations. A synergistic anti-proliferative activity was obtained with paclitaxel treatment followed by gefitinib in all cell lines, with mean CI values of 0.63 in Hcc827, 0.54 in PC-9, 0.81 in PC-9/GR, and 0.77 in H1650 cells for the T→G sequence. The mean CI values for the G→T sequence were 1.29 in Hcc827, 1.16 in PC-9, 1.52 in PC-9/GR, and 1.5 in H1650 cells. The mean CI values for T+G concomitant treatment were 0.88 in Hcc827, 0.91 in PC-9, 1.05 in PC-9/GR, and 1.18 in H1650 cells. Paclitaxel produced a dose-dependent increase in EGFR phosphorylation. Paclitaxel significantly increased EGFR phosphorylation compared with that in untreated controls (mean differences: +50% in Hcc827, + 56% in PC-9, + 39% in PC-9/GR, and + 69% in H1650 cells; p < 0.05). The T→G sequence produced significantly greater inhibition of EGFR phosphorylation compared with the opposite sequence (mean differences: -58% in Hcc827, -38% in PC-9, -35% in PC-9/GR, and -30% in H1650 cells; p < 0.05). Addition of a neutralizing anti-TGFα antibody abolished paclitaxel-induced activation of the EGFR pathway in PC-9 and H1650 cells. Sequence-dependent TGFα expression and release are responsible for the sequence-dependent EGFR pathway modulation.

Conclusion

The data suggest that the sequence of paclitaxel followed by gefitinib is an appropriate treatment combination for NSCLC cell lines harboring EGFR mutations. Our results provide molecular evidence to support clinical treatment strategies for patients with lung cancer.

Induction of bystander response in human glioma cells using high-energy electrons: a role for TGF-beta1

We examined bystander cell death produced in T98G cells by exposure to irradiated cell conditioned medium (ICCM) produced by high-energy 20 MeV electrons at a dose rate of 10 Gy min(-1) and doses up to 20 Gy. ICCM induced a bystander response in T98G glioma cells, reducing recipient cell survival by more than 25% below controls at 5 and 10 Gy. Higher doses increased survival to near control levels. ICCM was analyzed for the presence of transforming growth factor alpha (TGF-alpha) and transforming growth factor beta1 (TGF-beta1). Monoclonal antibodies for TGF-alpha (mAb TGF-alpha) and TGF-beta1 (mAb TGF-beta1) were added to the ICCM to neutralize any potential effect of the cytokines. The results indicate that TGF-alpha was not present in the ICCM and addition of mAb TGF-alpha to the ICCM had no effect on bystander cell survival. No active TGF-beta1 was present in the ICCM; however, addition of mAb TGF-beta1 completely abolished bystander death of reporter cells at all doses. These results indicate that bystander cell death can be induced in T98G glioma if a large enough radiation stress is applied and that TGF-beta1 plays a downstream role in this response.

Concurrent hormone and radiation therapy in patients with breast cancer: what is the rationale?

Endocrine therapy is often given together with postoperative radiotherapy in patients with breast cancer and positive hormone-receptor status. However, few experimental or clinical studies address the combined effects of hormone and radiation therapy. Preclinical models have shown changes in tumour cell kinetics with the addition of tamoxifen, and some show reduced tumour cell death with concurrent anti-oestrogen treatment and radiotherapy. Although data from in-vitro studies support the notion of antagonistic effects of concurrent tamoxifen and radiotherapy on tumour cells, in-vivo research suggests a synergistic effect that could be attributable to micro-environmental changes in tumour responsiveness to ionising radiation and hormone therapy. Retrospective studies suggest that in practical application, concurrent administration of tamoxifen with radiotherapy does not compromise local control but might increase toxicity. Preliminary results from simultaneous treatment with aromatase inhibitors and radiation indicate that this combination of endocrine and radiation therapy could enhance cytotoxicity and improve tumour response. Further studies are needed to clarify the physiological mechanisms activated by oestrogens, which will allow a more thorough understanding of the complex interactions between 17beta-oestradiol and P53/P21(WAF1/CIP1)/Rb pathways and of the interaction between endocrine therapy and radiotherapy.

Combination of radiotherapy with EGFR antagonists for head and neck carcinoma

The introduction of biologically sound radiation fractionation regimens and combinations of radiotherapy with chemotherapy have gradually improved both the survival of patients with locally advanced head and neck squamous cell carcinoma (HNSCC) and the prospect of organ preservation. Long-term follow-up, however, has shown that some of the radiation-chemotherapy combinations are associated with increased late toxicity. This observation, in conjunction with advances in tumor biology, has led to the launch of investigations into molecular markers and targets for therapeutic interventions. Research on the epidermal growth factor receptor (EGFR)-mediated signaling pathway has enriched our understanding of the biology of HNSCC, in terms of carcinogenesis and cellular processes governing tumor response to therapy. The finding that the addition of an antibody-based inhibitor of the EGFR pathway to radiotherapy significantly improves locoregional control and overall survival rates in patients with locally advanced HNSCC, without increasing radiation-induced toxicity, has resulted in the growing acceptance of such combined regimens as a frontline therapy option for locally advanced HNSCC. Because such therapy has benefited only an additional 10%-15% of patients, studies are being undertaken to identify markers and mechanisms of resistance to EGFR antagonists that are essential for the further refinement of therapy. Overall, preclinical and clinical studies on EGFR have validated the concept that selective tumor radiation sensitization can be achieved by modulating a specific perturbed signaling pathway, and these studies have increased the enthusiasm for developing and investigating other novel agents targeting other cellular processes.

Radiation-induced cell signaling: inside-out and outside-in

Exposure of tumor cells to clinically relevant doses of ionizing radiation causes DNA damage as well as mitochondria-dependent generation of reactive oxygen species. DNA damage causes activation of ataxia telangiectasia mutated and ataxia telangiectasia mutated and Rad3-related protein, which induce cell cycle checkpoints and also modulate the activation of prosurvival and proapoptotic signaling pathways, such as extracellular signal-regulated kinase 1/2 (ERK1/2) and c-Jun NH(2)-terminal kinase 1/2, respectively. Radiation causes a rapid reactive oxygen species-dependent activation of ERBB family and other tyrosine kinases, leading to activation of RAS proteins and multiple protective downstream signaling pathways (e.g., AKT and ERK1/2), which alter transcription factor function and the apoptotic threshold of cells. The initial radiation-induced activation of ERK1/2 can promote the cleavage and release of paracrine ligands, which cause a temporally delayed reactivation of receptors and intracellular signaling pathways in irradiated and unirradiated bystander cells. Hence, signals from within the cell can promote activation of membrane-associated receptors, which signal back into the cytosol: signaling from inside the cell outward to receptors and then inward again via kinase pathways. However, cytosolic signaling can also cause release of membrane-associated paracrine factors, and thus, paracrine signals from outside of the cell can promote activation of growth factor receptors: signaling from the outside inward. The ultimate consequence of these signaling events after multiple exposures may be to reprogram the irradiated and affected bystander cells in terms of their expression levels of growth-regulatory and cell survival proteins, resulting in altered mitogenic rates and thresholds at which genotoxic stresses cause cell death. Inhibition of signaling in one and/or multiple survival pathways enhances radiosensitivity. Prolonged inhibition of any one of these pathways, however, gives rise to lineages of cells, which have become resistant to the inhibitor drug, by evolutionary selection for the clonal outgrowth of cells with point mutations in the specific targeted protein that make the target protein drug resistant or by the reprogramming of multiple signaling processes within all cells, to maintain viability. Thus, tumor cells are dynamic with respect to their reliance on specific cell signaling pathways to exist and rapidly adapt to repeated toxic challenges in an attempt to maintain tumor cell survival.

Isolation and characterization of highly radioresistant malignant hamster fibroblasts that survive acute gamma irradiation with 20 Gy

To study the acquired radioresistance of tumor cells, a model system of two cell lines, Djungarian hamster fibroblasts (DH-TK-) and their radioresistant progeny, was established. The progeny of irradiated cells were isolated by treating the parental cell monolayer with a single dose of 20 Gy (PIC-20). The genetic and morphological features, clonogenic ability, radiosensitivity, cell growth kinetics, ability to grow in methylcellulose, and tumorigenicity of these cell lines were compared. The plating efficiency of PIC-20 cells exceeded that of DH-TK- cells. The progeny of irradiated cells were more radioresistant than parental cells. The average D0 for PIC-20 cells was 7.4 +/- 0.2 Gy, which is three times higher than that for parental cells (2.5 +/- 0.1 Gy). Progeny cell survival in methylcellulose after irradiation with a dose of 10 Gy was 15 times higher than that of DH-TK- cells. In contrast to parental cells, the progeny of irradiated cells showed fast and effective repopulation after irradiation with doses of 12.5 and 15 Gy. The tumor formation ability of irradiated progeny cells was higher than that of parental cells; after 15 Gy irradiation, PIC-20 cells produced tumors as large as unirradiated progeny of irradiated cells, whereas the tumor development of DH-TK- cells diminished by 70%. High radioresistance of progeny of irradiated cells was reproduced during the long period of cultivation (more than 80 passages). The stability of the radioresistant phenotype of PIC-20 cells allows us to investigate the possible mechanisms of acquired tumor radioresistance.

Sequence of radiotherapy with tamoxifen in conservatively managed breast cancer does not affect local relapse rates

PURPOSE

To evaluate whether the sequencing of tamoxifen (TAM) relative to radiation (RT) affects outcome in breast cancer patients treated with conservative surgery (CS) plus RT (lumpectomy with RT).

METHODS

Between 1976 and 1999, 1,649 patients with stage I or II breast cancer were treated with CS plus RT at Yale-New Haven Hospital (New Haven, CT). TAM was administered to 500 patients. The timing of TAM relative to RT was documented for each patient. Of the 500 patients, the timing of TAM was unclear in five patients, was administered concurrently with RT in 254 patients (CON-TAM), and was administered sequentially after completion of RT in 241 patients (SEQ-TAM).

RESULTS

There were no differences between the CON-TAM and SEQ-TAM group in T stage, estrogen and progesterone status, nodal status, histology, or margin status. The CON-TAM group was slightly older than the SEQ-TAM group (62 v 58 years) and received chemotherapy in addition to TAM less frequently (14% v 38%). As of September 2002, with a median follow-up of 10.0 years, there were no significant differences between the CON-TAM and SEQ-TAM groups in overall survival (84% v 82%; hazard ratio [HR], 1.234; 95% CI, 0.42 to 2.05; P = .45), distant-metastasis-free rate (82% v 78%; HR, 1.55; 95% CI, 0.89 to 2.68; P = .12), ipsilateral breast-relapse-free rate (90% v 86%; HR, 0.932; 95% CI, 0.42 to 2.05; P = .86), or contralateral breast-relapse-free rate (95% v 93%; HR, 0.892; 95% CI, 0.53 to 1.48; P = .66).

CONCLUSION

Although the concurrent use of TAM with RT may theoretically render cancer cells less responsive to RT, this retrospective study suggests that in practical application, concurrent administration of TAM with RT does not compromise local control.

Hormonoradiothérapie adjuvante concomitante des cancers du sein : état de l'art

Combining radiation and hormone therapy has become common clinical practice in recent years for locally advanced prostate cancer. The use of such concomitant therapy in the treatment of breast disease has been very infrequently reported in the literature, but such an application seems justified given the common hormonal dependence of breast cancer and the potential synergetic effect of these two treatment modalities. As adjuvant therapy, tamoxifen is the key drug in the hormonal treatment arsenal, providing a significant improvement in both local control and global survival rates. Aromatase inhibitors are currently being evaluated in this setting, and initial results are promising. In vitro, tamoxifen does not seem to offer a protective effect against radiation. In clinical use, the few available published studies confirm the superiority of the association of radiation with tamoxifen as opposed to radiation therapy alone in decreasing local recurrences of surgically removed breast tumors. Toxicity associated with such concomitant therapy includes mainly subcutaneous and pulmonary fibroses. However, subcutaneous fibrosis and its cosmetic impact on the treated breast are frequently described side effects of radiation therapy, and their incidence may actually be reduced when tamoxifen is associated. The evidence is less controversial for pulmonary fibrosis, which is more common with the concomitant therapy. The association of radiation and aromatase inhibitors has as of yet rarely been reported. Letrozole (Femara) has a radiosensitizing effect on breast-cancer cell lines transfected with the aromatase gene. Clinical data assessing this effect in vivo are not available. The FEMTABIG study (letrozole vs. tamoxifen vs. sequential treatment) did not specify the sequence of radiation and hormonal therapy. The ATAC study comparing the adjuvant use of anastrozole (Arimidex) and tamoxifen does not provide any information on the number of patients receiving radiation concomitant with the hormonal treatment, and in addition also does not specify the sequence of radiation and hormonal treatment. The TEAM study compared exemestane (Aromasine) and tamoxifen, but specified that hormonal treatment follow the completion of radiation therapy.

Effet radiosensibilisateur de l'acide linoléique conjugué chez les cellules cancéreuses du sein MCF-7 et MDA-MB-231

Apoptotic pathways in breast cancer cells are frequently altered, reducing the efficiency of radiotherapy. Conjugated linoleic acid (CLA), known to trigger apoptosis, was tested as radiosensitizer in breast cancer cells MCF-7 and MDA-MB-231. The CLA-mix, made up of the isomers CLA-9cis 11trans and CLA-10trans 12cis, was compared to three purified isomers, i.e., the CLA-9cis 11cis, CLA-9cis 11trans, and CLA-10trans 12cis. Using the apoptotic marker YO-PRO®-1, the CLA-9cis 11cis at 50 µmol/L turned out to be the best apoptotic inducer leading to a 10-fold increase in MCF-7 cells and a 2,5-fold increase in MDA-MB-231 cells, comparatively to the CLA-mix. Contrary to previous studies on colorectal and prostate cancer cells, CLA-10trans 12cis does not lead to an apoptotic response on breast cancer cell lines MCF-7 and MDA-MB-231. Our results also suggest that the main components of the CLA-mix (CLA-9cis 11trans and CLA-10trans 12cis) are not involved in the induction of apoptosis in the breast cancer cells studied. A dose of 5 Gy did not induce apoptosis in MCF-7 and MDA-MB-231 cells. The addition of CLA-9cis 11cis or CLA-mix has allowed us to observe a radiation-induced apoptosis, with the CLA-9cis 11cis being about 8-fold better than the CLA-mix. CLA-9cis 11cis turned out to be the best radiosensitizer, although the isomers CLA-9cis 11trans and CLA-10trans 12cis have also reduced the cell survival following irradiation, but using a mechanism not related to apoptosis. In conclusion, the radiosensitizing property of CLA-9cis 11cis supports its potential as an agent to improve radiotherapy against breast carcinoma.Key words: breast cancer, conjugated linoleic acid (CLA), radiotherapy, apoptosis.

Targeting the over-expressed urokinase-type plasminogen activator receptor on glioblastoma multiforme

A recombinant fusion protein targeting the urokinase-type plasminogen activator receptor (uPAR) and delivering a potent catalytic toxin has the advantage of simultaneously targeting both over-expressed uPAR on glioblastoma cells and on the tumor neovasculature. Such a hybrid protein was synthesized consisting of the noninternalizing amino-terminal fragment (ATF) of urokinase-type plasminogen activator (uPA) for binding, and the catalytic portion of diphtheria toxin (DT) for killing, and the translocation enhancing region (TER) of DT for internalization. The protein was highly selective for human glioblastoma in vitro and in vivo. In vivo, this DT/ATF hybrid called DTAT caused the regression of small subcutaneous uPAR-expressing tumors with minimal toxicity to critical organs. In vitro, DTAT killed only uPAR-positive glioblastoma cell lines and human endothelial cells in the form of the HUVEC cell line. Killing was selective and blockable with specific antibody. DTAT was highly effective against tumor cells cultured from glioblastoma multiforme patients and in vitro mixing experiments combining DTAT with DTIL13 another highly effective anti-glioblastoma agent showed that the mixture was as toxic as the most potent immunotoxin. In this article, we review our progress to date with DTAT.

An in vitro model of epithelial cell growth stimulation in the rodent mammary gland

Mouse mammary epithelial cell cultures previously described bring about extensive proliferation and a cell population with the appropriate markers for luminal ductal epithelial cells, and also the ability to form normal tissue after implantation into mice. This success may result from a culture environment that resembles certain aspects of the environment in the mammary gland. Mouse mammary epithelial cells, whose proliferation is limited when plated alone, can be stimulated to multiply by contact with lethally irradiated cells of the LA7 rat mammary tumour line. Most of the proliferative stimulus is imparted by direct cell contact between LA7 and mouse mammary cells. Junctions, including adherens junctions, form among all cells in the culture, much as junctions form in the mammary gland. LA7 cells secrete TGFalpha and bFGF, factors found in the mammary gland, and factors to which mouse mammary cells respond in culture. Mouse mammary cells express keratins 8 and 18, markers for luminal cells of the mammary duct. LA7 cells express keratin 14 and vimentin, markers for myoepithelial cells. These facts, taken together, fit a model of cell replacement in an epithelial tissue and also imitate the relationship between luminal ductal cells and myoepithelial cells in the mammary gland. This method of culturing cells is useful, not only for in vitro-in vivo carcinogenesis studies, but also for the study of mechanisms by which growth signals are imparted from one cell to another.

Immunotoxin therapy for CNS tumor

Surgery, chemotherapy, and radiation therapy have become standard of practice in treating malignant brain tumors. Unfortunately, the prognosis of these malignant tumors still remains poor. Immunotoxins are a relatively new adjuvant treatment for brain tumors. Within the last few years an increased amount of clinically-oriented research involving immunotoxins has been published. This has led to numerous clinical trials which although encouraging have not yet born out the "magic bullet" concept envisioned for immunotoxins. In this review article the history, design, toxicity, and pharmokinetics of immunotoxins will be discussed in detail.

Integration of systemic therapy and radiation therapy for patients with early-stage breast cancer treated with conservative surgery

There is no consensus on the optimal combination of systemic therapy and radiation therapy for patients with early-stage breast cancer treated with conservative surgery. This article reviews prospective and retrospective studies that shed light on this topic. Patients with positive, close, or unknown microscopic margins appear to benefit from relatively early initiation of radiation therapy, whereas those with wider tumor-free margin widths do not. For patients at high risk of distant failure (such as those with = 4 positive axillary nodes), chemotherapy may be more effective when it begins before radiation therapy rather than after. Regimens of concurrent radiation therapy and chemotherapy tend to have higher acute and subacute complication rates than sequential regimens, but the actual rates vary substantially with the exact details of the overall treatment program. There are no data on the impact of the timing of tamoxifen administration on the effectiveness of radiation therapy. Tamoxifen does not appear to increase complication rates relative to the use of radiation therapy alone. Thus, the best way of giving combined-modality therapy is uncertain. Further retrospective and prospective studies to investigate the issues discussed herein should be performed.

Stress and radiation-induced activation of multiple intracellular signaling pathways

Exposure of cells to a variety of stresses induces compensatory activations of multiple intracellular signaling pathways. These activations can play critical roles in controlling cell survival and repopulation effects in a stress-specific and cell type-dependent manner. Some stress-induced signaling pathways are those normally activated by mitogens such as the EGFR/RAS/PI3K-MAPK pathway. Other pathways activated by stresses such as ionizing radiation include those downstream of death receptors, including pro-caspases and the transcription factor NFKB. This review will attempt to describe some of the complex network of signals induced by ionizing radiation and other cellular stresses in animal cells, with particular attention to signaling by growth factor and death receptors. This includes radiation-induced signaling via the EGFR and IGFI-R to the PI3K, MAPK, JNK, and p38 pathways as well as FAS-R and TNF-R signaling to pro-caspases and NFKB. The roles of autocrine ligands in the responses of cells and bystander cells to radiation and cellular stresses will also be discussed. Based on the data currently available, it appears that radiation can simultaneously activate multiple signaling pathways in cells. Reactive oxygen and nitrogen species may play an important role in this process by inhibiting protein tyrosine phosphatase activity. The ability of radiation to activate signaling pathways may depend on the expression of growth factor receptors, autocrine factors, RAS mutation, and PTEN expression. In other words, just because pathway X is activated by radiation in one cell type does not mean that pathway X will be activated in a different cell type. Radiation-induced signaling through growth factor receptors such as the EGFR may provide radioprotective signals through multiple downstream pathways. In some cell types, enhanced basal signaling by proto-oncogenes such as RAS may provide a radioprotective signal. In many cell types, this may be through PI3K, in others potentially by NFKB or MAPK. Receptor signaling is often dependent on autocrine factors, and synthesis of autocrine factors will have an impact on the amount of radiation-induced pathway activity. For example, cells expressing TGFalpha and HB-EGF will generate protection primarily through EGFR. Heregulin and neuregulins will generate protective signals through ERBB4/ERBB3. The impact on radiation-induced signaling of other autocrine and paracrine ligands such as TGFbeta and interleukin 6 is likely to be as complicated as described above for the ERBB receptors.

Ionizing radiation modulates vascular endothelial growth factor (VEGF) expression through multiple mitogen activated protein kinase dependent pathways

We investigated the role of radiation-induced mitogen activated protein kinase (MAPK) pathway activity in the regulation of proliferation, cell survival and vascular endothelial growth factor (VEGF) production in primary astrocytes and in T9 and RT2 glioblastoma cells derived from Fisher 344 rats. In these cells, ionizing radiation (2 Gy) caused activation of the MAPK pathway which was blocked by specific inhibitor drugs. Blunting of radiation-induced MAPK activity weakly enhanced radiation-induced apoptosis 24 h after exposure in RT2 cells. Furthermore, blunting of MAPK activation weakly enhanced the ability of radiation to reduce RT2 cell growth in clonogenic growth assays. These findings argue that inhibition of MAPK signaling reduces proliferation and enhances cell killing by ionizing radiation in transformed astrocytes. Proliferation and survival of cancer cells has been linked in vivo to enhanced expression of angiogenic growth factors. Recently we demonstrated that the gene product of a novel rodent radiation-responsive gene, progression elevated gene 3 (PEG-3), could enhance vascular endothelial growth factor (VEGF) promoter activity in rodent fibroblasts, leading to increased VEGF protein levels and tumorigenic behavior in vivo. Thus PEG-3 and VEGF expression could be expected to directly correlate with the oncogenic potential of transformed cells. RT2 cells expressed more PEG-3 and VEGF protein than T9 cells, and were more tumorigenic in vivo than T9 cells. Radiation activated the PEG-3 promoter via MAPK signaling and ectopic over-expression of PEG-3 enhanced both basal MAPK activity and basal VEGF promoter activity. Basal MAPK activity partially correlated with basal VEGF promoter activity and VEGF protein levels in primary astrocytes, T9 and RT2 cells. Radiation increased the activity of the VEGF promoter and VEGF protein levels in primary astrocytes, T9 and RT2 cells which were dependent upon MAPK function. Furthermore, inhibition of AP-1 transcription factor signaling by dominant negative c-Jun (TAM67) also significantly reduced basal, and to a lesser extent radiation-induced, VEGF promoter function in RT2 cells. Collectively, our data demonstrate that radiation-induced MAPK signaling can both protect cells from radiation-induced cell death as well as enhance protein levels of pro-angiogenic factors such as VEGF. Enhanced VEGF expression in RT2 cells may be mediated via MAPK and JNK pathway signaling which converges upon the AP-1 transcription factor complex.

Effect of low dose irradiation on estrogen receptor level in MCF-7 breast cancer cells

Exposure of MCF-7 cells to single and/or repeated low gamma-ray doses (0.5 to 8 Gy) resulted in a decrease in the capacity of these cells to concentrate tritiated estradiol ([3H]E2) (reduction of the number of binding sites). The decrease in the [3H]E2-binding capacity was higher than the survival rate, indicating that it could not be ascribed to cell death. Moreover, such low irradiation doses failed to similarly affect the specific incorporation of [3H]ORG 2058, even when the progesterone receptor was induced by E2, a finding that rejects the hypothesis of a nonspecific effect on all steroid hormone receptors. This loss of [3H]E2 binding was reflected by the elimination of the estrogen receptor alpha (ER) when the latter was assessed by immunocytochemistry. However, additional immunochemical studies (Western blot data) performed on cell extracts under denaturing conditions failed to show any similar elimination of the ER peptide, suggesting that the loss of E2-binding capacity would be relevant to subtle changes in the ER structure and/or ER-associated proteins. The loss of binding capacity, produced by a 3-Gy irradiation, failed to decrease the sensitivity of the cells to E2, since progesterone receptor induction and growth stimulation were maintained. Insufficient ER diminution may explain this observation.

Ionizing radiation-induced mitogen-activated protein (MAP) kinase activation in DU145 prostate carcinoma cells: MAP kinase inhibition enhances radiation-induced cell killing and G2/M-phase arrest

These studies examine the role(s) played by the mitogen-activated protein kinase (MAPK) pathway after exposure of DU145 prostate carcinoma cells to radiation. Radiation (2 Gy) was found to cause both immediate primary (0-30 min) and prolonged secondary activations (90-1440 min) of the MAPK pathway. These activations of the MAPK pathway were abolished by inhibition of epidermal growth factor receptor (EGFR) function. The secondary activation was also abolished by addition of a neutralizing monoclonal antibody against transforming growth factor alpha (TGFA). Activation of the MAPK pathway could be induced in nonirradiated cells by the transfer of medium from irradiated cultures. Neutralizing antibody to TGFA blocked this effect, indicating that radiation causes secondary activation of the MAPK pathway by release of TGFA in DU145 cells. Radiation induced a transient G(2)/M-phase growth arrest that was prolonged for up to 24 h by inhibition of the MAPK pathway. Inhibition of the MAPK pathway significantly increased the ability of radiation to cause apoptosis 24 h after exposure. The ability of DU145 cells to proliferate after irradiation became dependent on MAPK signaling. When cells were subjected to single doses or fractionated radiation exposure, continuous inhibition of the MAPK pathway significantly decreased clonogenic survival. Only a small fraction of this cell killing could be accounted for by apoptosis within the first 96 h. Thus inhibition of the MAPK pathway increased radiation-induced cell killing likely by both apoptotic and nonapoptotic mechanisms. Collectively, our findings indicate that disruption of the TGFA/EGFR/MAPK pathway may represent a strategy that could be exploited to manipulate prostate carcinoma growth and cell survival after irradiation.

Ionizing radiation stimulates existing signal transduction pathways involving the activation of epidermal growth factor receptor and ERBB-3, and changes of intracellular calcium in A431 human squamous carcinoma cells

Previous studies demonstrated that ionizing radiation activates the epidermal growth factor receptor (EGFR), as measured by Tyr autophosphorylation, and induces transient increases in cytosolic free [Ca2+], [Ca2+]f. The mechanistic linkage between these events has been investigated in A431 squamous carcinoma cells with the EGFR Tyr kinase inhibitor, AG1478. EGFR autophosphorylation induced by radiation at doses of 0.5-5 Gy or EGF concentrations of 1-10 ng/ml is inhibited by >75% at 100 nM AG1478. Activation of EGFR enhances IP3 production as a result of phospholipase C (PLC) activation. At the doses used, radiation stimulates Tyr phosphorylation of both, PLCgamma and erbB-3, and also mediates the association between erbB-3 and PLCgamma not previously described. The increased erbB-3 Tyr phosphorylation is to a significant extent due to transactivation by EGFR as >70% of radiation- and EGF-induced erbB-3 Tyr phosphorylation is inhibited by AG 1478. The radiation-induced changes in [Ca2+]f are dependent upon EGFR, erbB-3 and PLCgamma activation since radiation stimulated IP3 formation and Ca2+ oscillations are inhibited by AG1478, the PLCgamma inhibitor U73122 or neutralizing antibody against an extracellular epitope of erbB-3. These results demonstrate that radiation induces qualitatively and quantitatively similar responses to EGF in stimulation of the plasma membrane-associated receptor Tyr kinases and immediate downstream effectors, such as PLCgamma and Ca2+.

Radiation-induced release of transforming growth factor alpha activates the epidermal growth factor receptor and mitogen-activated protein kinase pathway in carcinoma cells, leading to increased proliferation and protection from radiation-induced cell death

Exposure of A431 squamous and MDA-MB-231 mammary carcinoma cells to ionizing radiation has been associated with short transient increases in epidermal growth factor receptor (EGFR) tyrosine phosphorylation and activation of the mitogen-activated protein kinase (MAPK) and c-Jun NH(2)-terminal kinase (JNK) pathways. Irradiation (2 Gy) of A431 and MDA-MB-231 cells caused immediate primary activations (0-10 min) of the EGFR and the MAPK and JNK pathways, which were surprisingly followed by later prolonged secondary activations (90-240 min). Primary and secondary activation of the EGFR was abolished by molecular inhibition of EGFR function. The primary and secondary activation of the MAPK pathway was abolished by molecular inhibition of either EGFR or Ras function. In contrast, molecular inhibition of EGFR function abolished the secondary but not the primary activation of the JNK pathway. Inhibition of tumor necrosis factor alpha receptor function by use of neutralizing monoclonal antibodies blunted primary activation of the JNK pathway. Addition of a neutralizing monoclonal antibody versus transforming growth factor alpha (TGFalpha) had no effect on the primary activation of either the EGFR or the MAPK and JNK pathways after irradiation but abolished the secondary activation of EGFR, MAPK, and JNK. Irradiation of cells increased pro-TGFalpha cleavage 120-180 min after exposure. In agreement with radiation-induced release of a soluble factor, activation of the EGFR and the MAPK and JNK pathways could be induced in nonirradiated cells by the transfer of media from irradiated cells 120 min after irradiation. The ability of the transferred media to cause MAPK and JNK activation was blocked when media were incubated with a neutralizing antibody to TGFalpha. Thus radiation causes primary and secondary activation of the EGFR and the MAPK and JNK pathways in autocrine-regulated carcinoma cells. Secondary activation of the EGFR and the MAPK and JNK pathways is dependent on radiation-induced cleavage and autocrine action of TGFalpha. Neutralization of TGFalpha function by an anti-TGFalpha antibody or inhibition of MAPK function by MEK1/2 inhibitors (PD98059 and U0126) radiosensitized A431 and MDA-MB-231 cells after irradiation in apoptosis, 3-[4, 5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide (MTT), and clonogenic assays. These data demonstrate that disruption of the TGFalpha-EGFR-MAPK signaling module represents a strategy to decrease carcinoma cell growth and survival after irradiation.

Radiation survival of two human cervical carcinoma cell lines after multifraction irradiation

PURPOSE

Multifraction irradiation may contribute to radiation therapy treatment failure if selection of radiation resistant subpopulations occurs. We sought to determine whether surviving cells following daily fraction irradiation of two human cervical squamous cell carcinoma lines would express different radiation survival characteristics compared to the unirradiated parent.

METHODS AND MATERIALS

A late-passage line (HTB35) and an early-passage line (RECA) received daily 2 Gy x-irradiation. Two new stable HTB35 cell lines were established after 40 and 60 Gy (HTB35-40 and HTB35-60). A single line was established from RECA after 30 Gy (RECA-30). High dose rate (74 cGy/min) acute radiation survival curves were prepared from the three new lines and the unirradiated parents. Potentially lethal damage repair (PLDR) and sublethal damage repair (SLDR) responses were detailed for HTB35, HTB35-40 and HTB35-60. Low dose rate (1.27 cGy/min) survival was measured for HTB35 and HTB35-60. Clones were derived from HTB35 and from HTB35-60 and the surviving fraction at 2 Gy (SF2) values were determined.

RESULTS

The two parent lines (HTB35 and RECA) differed in acute radiation survival. The surviving lines following multifraction irradiation (HTB35-40, HTB35-60, and RECA-30) showed no change in acute radiation response compared to the appropriate parent. HTB35-40 and HTB35-60 were repair proficient, demonstrating similar PLDR and SLDR recovery ratios as the parent. Likewise, acute, low dose rate survival of HTB35 and HTB35-60 was similar. Nine clones derived from HTB35 lacked a consistent difference in SF2 compared to the original culture. A single clone of seven derived from HTB35-60 was consistently radiation resistant (SF2 = 0.81 +/- 0.06) compared to the original culture (SF2 = 0.50 +/- 0.09).

CONCLUSION

No evidence was obtained that cell lines generated following multiple daily fractions of x-irradiation in vitro possessed acute radiation survival or repair characteristics that were different from the unirradiated parent.

Changes in radiation sensitivity and steroid receptor content induced by hormonal agents and ionizing radiation in breast cancer cells in vitro

Possible influences of tamoxifen and estradiol on in vitro radiation sensitivity and cellular receptor content after irradiation and/or tamoxifen treatment were studied in breast cancer cell lines; estrogen receptor (ER) and progesterone receptor (PgR) positive cell lines MCF-7 and MCF-7/TAM(R)-1 and the ER and PgR negative cell line MDA-MB-231. The tamoxifen resistant MCF-7/TAM(R)-1 cells were more resistant to ionizing radiation than the MCF-7 and MDA-MB-231 cells. Exposure to tamoxifen made the MCF-7 cells more radiation resistant, while estradiol made the MDA-MB-231 cells more radiation sensitive. A radiation dose of 6 Gy reduced the ER content in cytosol in both MCF-7 and MCF-7/TAM(R)-1 cells, but brought no alterations to the PgR content. In MCF-7/TAM(R)-1 cells tamoxifen exposure significantly increased the ER and reduced the PgR content, an effect not observed in the MCF-7 cells. To conclude, the present study indicates that irradiation and tamoxifen may modify the ER and PgR content in cytosol in breast cancer cells. Hormonal treatment may alter the radiation sensitivity, even in ER negative cells, suggesting that hormonal agents may act both via receptor and non-receptor binding mechanisms.

Transforming growth factor alpha expression as a potential survival prognosticator in patients with esophageal adenocarcinoma receiving high-dose radiation and chemotherapy

PURPOSE

Transforming growth factor alpha (TGFA) stimulates the growth and proliferation of cells, and its overexpression has been correlated with patient survival in a variety of tumors, including squamous carcinoma of the esophagus. This study was performed to investigate the influence of TGFA in patients with esophageal adenocarcinoma (EA) receiving high-dose radiation and chemotherapy (HDRCT).

METHODS AND MATERIALS

Thirty-one patients with localized esophageal adenocarcinoma were enrolled in a Phase II study involving high dose radiation and concurrent 5-fluorouracil (5-FU)/mitomycin-C with or without esophagectomy. Twenty-seven pretreatment (tumor not available in 4) and 11 posttreatment (insufficient tumor in 20) specimens were immunostained using the avidin-biotin-peroxidase technique.

RESULTS

Fifteen of 27 (56%) pretreatment and 4 out of 11 (36%) postchemoradiation specimens had intense TGFA staining. Eight patients with intense and seven with little or no staining on pretreatment biopsy underwent esophagectomy. Median survival for the eight patients was 28 months, and for the seven patients 19 months (p = 0.4). Transforming growth factor alpha staining of posttreatment specimens that contained residual tumor also did not correlate with overall (p = 0.36) or disease-free (p = 0.17) survival. Among the 10 patients with both pre and posttreatment TGFA specimens, decreasing or negative TGFA expression was associated with a better median disease-free survival (32 vs. 13 months, p = 0.04) than persistently positive or increasing TGFA expression.

CONCLUSION

There is frequent overexpression of TGFA in EA. Although pretreatment TGFA expression was not associated with survival, patients with tumors that persistently expressed or that increased TGFA expression had a worse prognosis. Posttreatment TGFA expression may serve as a prognostic marker in patients with EA treated with HDRCT.

Effect of epidermal growth factor on the growth and radiation sensitivity of human breast cancer cells in vitro

PURPOSE

To study the effect of epidermal growth factor (EGF) on the radiation sensitivity of MCF-7 breast cancer cells.

METHODS AND MATERIALS

Radiation dose survival curves were generated for MCF-7 cells under conditions of hormonal deprivation. Epidermal growth factor and/or a monoclonal antibody to its receptor (mAb-225) were added prior to irradiation. Cell cycle distribution was determined by flow cytometry and cellular glutathione (GSH) levels were measured by a glutathione reductase assay.

RESULTS

Under hormonal deprivation (control), more than 90% of the MCF-7 cells were arrested in G0/G1 phase and the D(o) of their survival curve was 0.66 +/- .01 Gy. The addition of EGF resulted in (a) growth stimulation; (b) increased percentage of cells in the S-phase of the cell cycle; (c) increased radioresistance (D(o) = 0.81 +/- .04 Gy; p < .05, compared with controls); (d) increased cellular GSH level. The EGF effect on radiation response was observed in a time- and dose-dependent manner. The addition of mAb-225 blocked the ability of EGF to enhance growth and radioresistance (D(o) = 0.68 +/- .03 Gy).

CONCLUSION

Epidermal growth factor stimulates the growth and when administered prior to irradiation increases the radioresistance of hormone-deprived MCF-7 cells. These effects are inhibited by a specific antibody to the EGF receptor. Epidermal growth factor concomitantly increased the fraction of S-phase cells and intracellular GSH levels. This system of growth factor-altered radiosensitivity in human breast cancer cells provides a useful model for the study of the radiation response mechanisms in human malignancy.

Altered expression of epidermal growth factor receptor and estrogen receptor in MCF-7 cells after single and repeated radiation exposures

PURPOSE

Studies on radiation-induced changes in gene expression are likely to be very important in developing a better understanding of cellular responses to ionizing radiation. While there is some information on the activation of cellular signal transduction pathways after radiation, few late reacting target genes have been identified. This study focuses on the characterization of expression modulation of two critical growth regulatory genes, estrogen receptor and epidermal growth factor-receptor in malignant mammary epithelial cells in response to single and repeated ionizing radiation exposures.

METHODS AND MATERIALS

MCF-7 cells were used for single radiation exposure (2-50 Gy) experiments and MCF-IR-3 cells, generated by exposure to cumulative doses of 60 Gy in 2 Gy fractions, respectively, were used to study the effects of repeated exposures. Steady-state messenger ribonucleic acid levels for estrogen receptor, epidermal growth factor-receptor, and transforming growth factor-alpha were determined by ribonucleic acid protection experiments. Estrogen receptor and epidermal growth factor-receptor protein expression was quantitated by competitive binding studies with 3H-estradiol and 125I-EGF.

RESULTS

MCF-IR-3 cells showed a permanent three-fold down-regulation of the estrogen receptor messenger ribonucleic acid and protein, while epidermal growth factor-receptor was upregulated about nine-fold. Epidermal growth factor-receptor was substantially up-regulated in MCF-7 cells, at both the mRNA and protein levels, within 24 h of a single 2 Gy exposures, while there was a two-fold concomitant increase in transforming growth factor-alpha messenger ribonucleic acid expression. A decrease in estrogen receptor messenger ribonucleic acid and protein was suggested only after higher doses of single radiation exposures.

CONCLUSION

Single and repeated radiation exposures modulate the expression of two critical growth promoting genes, estrogen receptor and epidermal growth factor-receptor, in MCF-7 cells. The inverse expression of estrogen receptor and epidermal growth factor-receptor established for estrogen receptor-positive malignant mammary epithelial cells is maintained in MCF-7 cells after single and repeated exposures suggesting that radiation acts through common regulatory circuits and may modulate the cellular phenotype.

Effect of metabolic acidosis on the expression of insulin-like growth factor and growth hormone receptor

To further our understanding of the growth failure in metabolic acidosis, we examined the insulin-like growth factor (IGF-I and IGF-II), the IGF binding protein-3 (IGFBP-3), and the hepatic IGF mRNA and growth hormone receptor mRNA in control, pair-fed and acidotic rats. The rats in the last group were made acidotic by using ammonium chloride (1.5%) as their sole fluid intake for eight days. Metabolic acidosis was confirmed by a blood pH of 7.11 +/- 0.10 (mean +/- SD). The mean starting weights for all rats were 167.1 +/- 3.4 grams. Growth impairment was observed in the acidotic rats after one week of ammonium chloride intake. The body weights of the acidotic rats compared to those of the control rats were 155.5 +/- 18.9 g versus 222.8 +/- 9.7 g, P < 0.001; the pair-fed rats weighed 156.8 +/- 19.6 grams. All rats were bled and sacrificed on day 8. Sera and tissue were analyzed with the following results: compared to the ad libitum controls, the same IGF-I concentrations were significantly decreased in the acidotic animals (P < 0.02) as well as pair-fed controls (P < 0.005). The serum IGF-II and IGF-binding protein-3 concentrations were unchanged by acidosis or food restriction. The hepatic IGF-I mRNA was significantly reduced by acidosis (P < 0.01) and pair-feeding (P < 0.01). Compared to control, the mean hepatic IGF mRNA in acidosis was significantly lower (P < 0.01). However, there was no significant difference between the acidotic and the pair-fed groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Alterations in growth phenotype and radiosensitivity after fractionated irradiation of breast carcinoma cells from a single patient

PURPOSE

To investigate growth regulation and radiosensitivity in surviving clonogens after fractionated irradiation.

METHODS AND MATERIALS

Four breast carcinoma cell lines isolated from the primary tumor (21NT, 21PT) and metastases (21MT-1, 21MT-2) of a single patient were exposed to cumulative radiation doses of 30 Gy yielding cell lines designated-IR with respect to their parent. The irradiated lines were then compared to their parent for serum-and growth factor-requirements under defined media conditions, ability to proliferate in soft agar, concentration of TGF-alpha in conditioned medium, and radiosensitivity.

RESULTS

The irradiated lines showed no change in proliferative doubling times under serum- and growth factor-supplemented media conditions. A single line, 21MT-1-IR, acquired a limited ability to proliferate in serum-and growth factor-deplete medium with a day 2-4 doubling time of 44.5 hr. Three lines, 21MT-1-IR, 21MT-2-IR, and 21NT-IR, formed colonies in soft agar in contrast to none of the unirradiated parent lines. There were significant 6-8 fold increases in conditioned media TGF-alpha concentrations for 21MT-2-IR and 21NT-IR cells. The 21MT-1-IR and 21NT-IR cells were significantly less radiosensitive than their respective parent lines. This decrease in radiosensitivity appeared to be at least partially mediated by a released factor as the radiosensitivity of 21MT-1 cells was significantly decreased by pre-incubation with conditioned medium from 21MT-1-IR cells.

CONCLUSION

Radiation-induced changes in growth phenotype vary with respect to clonal origin of the cell line and may influence the radiosensitivity of surviving clonogens after fractionated treatment.