Ionizing Radiation Causes a Dose-Dependent Release of Transforming Growth Factor α In vitro from Irradiated Xenografts and during Palliative Treatment of Hormone-Refractory Prostate Carcinoma

GZ17-6.02 and Doxorubicin Interact to Kill Sarcoma Cells via Autophagy and Death Receptor Signaling

GZ17-6.02 (602) is presently under phase I clinical evaluation (NCT03775525). We defined the mechanisms by which it interacted with a standard of care therapeutic doxorubicin to kill sarcoma cells. Doxorubicin and 602 interacted to rapidly activate ATM and c-MET, inactivate mTOR, AKT, and p70 S6K, enhance the expression of Beclin1 and reduce the levels of K-RAS and N-RAS. This was followed later by the drugs interacting to reduce expression of MCL-1, BCL-XL, and HDAC6. Knock down of ATM prevented the drugs alone or in combination inactivating mTOR or activating ULK1. Knock down of c-MET significantly enhanced [doxorubicin + 602] lethality. Knock down of ATM and to a greater extent ULK1, Beclin1, or ATG5 significantly reduced killing by 602 alone or when combined with doxorubicin. Expression of an activated mTOR mutant suppressed killing, autophagosome formation and prevented autophagic flux. In the absence of Beclin1, knock down of CD95, or FADD, or over-expression of c-FLIP-s or BCL-XL abolished tumor cell killing. We conclude that 602 and doxorubicin interact to increase autophagosome formation and autophagic flux as well as causing elevated death receptor signaling resulting in mitochondrial dysfunction and tumor cell death.

Signaling alterations caused by drugs and autophagy

Autophagy is an evolutionary conserved process that recycles cellular materials in times of nutrient restriction to maintain viability. In cancer therapeutics, the role of autophagy in response to multi-kinase inhibitors, alone or when combined with histone deacetylase (HDAC) inhibitors acts, generally, to facilitate the killing of tumor cells. Furthermore, the formation of autophagosomes and subsequent degradation of their contents can reduce the expression of HDAC proteins themselves as well as of other signaling regulatory molecules such as protein chaperones and mutated RAS proteins. Reduced levels of HDAC6 causes the acetylation and inactivation of heat shock protein 90, and, together with reduced expression of the chaperones HSP70 and GRP78, generates a strong endoplasmic reticulum (ER) stress response. Prolonged intense ER stress signaling causes tumor cell death. Reduced expression of HDACs 1, 2 and 3 causes the levels of programed death ligand 1 (PD-L1) to decline and the expression of Class I MHCA to increase which correlates with elevated immunogenicity of the tumor cells in vivo. This review will specifically focus on the downstream implications that result from autophagic-degradation of HDACs, RAS and protein chaperones.

Targeted and Off-Target (Bystander and Abscopal) Effects of Radiation Therapy: Redox Mechanisms and Risk/Benefit Analysis

SIGNIFICANCE

Radiation therapy (from external beams to unsealed and sealed radionuclide sources) takes advantage of the detrimental effects of the clustered production of radicals and reactive oxygen species (ROS). Research has mainly focused on the interaction of radiation with water, which is the major constituent of living beings, and with nuclear DNA, which contains the genetic information. This led to the so-called target theory according to which cells have to be hit by ionizing particles to elicit an important biological response, including cell death. In cancer therapy, the Poisson law and linear quadratic mathematical models have been used to describe the probability of hits per cell as a function of the radiation dose. Recent Advances: However, in the last 20 years, many studies have shown that radiation generates "danger" signals that propagate from irradiated to nonirradiated cells, leading to bystander and other off-target effects.

CRITICAL ISSUES

Like for targeted effects, redox mechanisms play a key role also in off-target effects through transmission of ROS and reactive nitrogen species (RNS), and also of cytokines, ATP, and extracellular DNA. Particularly, nuclear factor kappa B is essential for triggering self-sustained production of ROS and RNS, thus making the bystander response similar to inflammation. In some therapeutic cases, this phenomenon is associated with recruitment of immune cells that are involved in distant irradiation effects (called "away-from-target" i.e., abscopal effects).

FUTURE DIRECTIONS

Determining the contribution of targeted and off-target effects in the clinic is still challenging. This has important consequences not only in radiotherapy but also possibly in diagnostic procedures and in radiation protection.

Immunological Markers of Chronic Occupational Radiation Exposure

This study aimed to identify immunological biomarkers for prolonged occupational radiation exposure and thus studied a random sample of the Mayak Production Association worker cohort (91 individuals). The control group included 43 local individuals never employed at the Mayak Production Association. To identify biomarkers, two groups of workers were formed: the first one included workers chronically exposed to external gamma rays at cumulative doses of 0.5-3.0 Gy (14 individuals); the second one included workers exposed to combined radiation-external gamma rays at doses ranging from 0.7 to 5.1 Gy and internal alpha radiation from incorporated plutonium with 0.3-16.4 kBq body burden (77 individuals). The age range of the study individuals was 66-91 y. Peripheral blood serum protein concentrations of cytokines, immunoglobulins, and matrix metalloproteinase-9 were analyzed using enzyme-linked immunoassay following the manufacturer's protocol. Flow cytometry was used to analyze levels of various lymphocyte subpopulations. The findings of the current study demonstrate that some immunological characteristics may be considered as biomarkers of prolonged chronic radiation exposure for any radiation type (in the delayed period after the exposure) based on fold differences from controls: M immunoglobulin fold differences were 1.75 ± 0.27 (p = 0.0001) for external gamma-ray exposure and 1.50 ± 0.27 (p = 0.0003) for combined radiation exposure; matrix metalloproteinase-9 fold differences were 1.5 ± 0.22 (p = 0.008) for external gamma-ray exposure and 1.69 ± 0.24 (p = 0.00007) for combined radiation exposure; A immunoglobulin fold differences were 1.61 ± 0.27 (p = 0.002) for external gamma-ray exposure and 1.56 ± 0.27 (p = 0.00002) for combined radiation exposure; relative concentration of natural killer cell fold differences were 1.53 ± 0.23 (p = 0.01) for external gamma-ray exposure and 1.35 ± 0.22 (p = 0.001) for combined radiation exposure; and relative concentration of T-lymphocytes fold differences were 0.89 ± 0.04 (p = 0.01) for external gamma-ray exposure and 0.95 ± 0.05 (p = 0.003) for combined radiation exposure. Based on fold differences from controls, interferon-gamma (3.50 ± 0.65, p = 0.031), transforming growth factor-beta (2.91 ± 0.389, p = 0.026), and relative blood serum levels of T-helper cells (0.90 ± 0.065, p = 0.02) may be used as immunological markers of chronic external gamma-ray exposure. Moreover, there was a significant inverse linear association of relative concentration of T-helper cells with dose from external gamma rays accumulated over an extended period.

Bystander signaling via oxidative metabolism

The radiation-induced bystander effect (RIBE) is the initiation of biological end points in cells (bystander cells) that are not directly traversed by an incident-radiation track, but are in close proximity to cells that are receiving the radiation. RIBE has been indicted of causing DNA damage via oxidative stress, besides causing direct damage, inducing tumorigenesis, producing micronuclei, and causing apoptosis. RIBE is regulated by signaling proteins that are either endogenous or secreted by cells as a means of communication between cells, and can activate intracellular or intercellular oxidative metabolism that can further trigger signaling pathways of inflammation. Bystander signals can pass through gap junctions in attached cell lines, while the suspended cell lines transmit these signals via hormones and soluble proteins. This review provides the background information on how reactive oxygen species (ROS) act as bystander signals. Although ROS have a very short half-life and have a nanometer-scale sphere of influence, the wide variety of ROS produced via various sources can exert a cumulative effect, not only in forming DNA adducts but also setting up signaling pathways of inflammation, apoptosis, cell-cycle arrest, aging, and even tumorigenesis. This review outlines the sources of the bystander effect linked to ROS in a cell, and provides methods of investigation for researchers who would like to pursue this field of science.

Secretome Signature Identifies ADAM17 as Novel Target for Radiosensitization of Non-Small Cell Lung Cancer

PURPOSE

Ionizing radiation (IR) induces intracellular signaling processes as part of a treatment-induced stress response. Here we investigate IR-induced ADAM17 activation and the role of ADAM17-shed factors for radiation resistance in non-small cell lung cancer.

EXPERIMENTAL DESIGN

Large-scale secretome profiling was performed using antibody arrays. Secretion kinetics of ADAM17 substrates was determined using ELISA across multiple in vitro and in vivo models of non-small cell lung cancer. Clonogenic survival and tumor xenograft assays were performed to determine radiosensitization by ADAM17 inhibition.

RESULTS

On the basis of a large-scale secretome screening, we investigated secretion of auto- or paracrine factors in non-small cell lung cancer in response to irradiation and discovered the ADAM17 network as a crucial mediator of resistance to IR. Irradiation induced a dose-dependent increase of furin-mediated cleavage of the ADAM17 proform to active ADAM17, which resulted in enhanced ADAM17 activity in vitro and in vivo Genetic or pharmacologic targeting of ADAM17 suppressed IR-induced shedding of secreted factors, downregulated ErbB signaling in otherwise cetuximab-resistant target cells, and enhanced IR-induced cytotoxicity. The combined treatment modality of IR with the ADAM17 inhibitor TMI-005 resulted in a supra-additive antitumor response in vivo demonstrating the potential of ADAM17 targeting in combination with radiotherapy.

CONCLUSIONS

Radiotherapy activates ADAM17 in non-small cell lung cancer, which results in shedding of multiple survival factors, growth factor pathway activation, and IR-induced treatment resistance. We provide a sound rationale for repositioning ADAM17 inhibitors as short-term adjuvants to improve the radiotherapy outcome of non-small cell lung cancer. Clin Cancer Res; 22(17); 4428-39. ©2016 AACR.

Resveratrol Enhances Etoposide-Induced Cytotoxicity through Down-Regulating ERK1/2 and AKT-Mediated X-ray Repair Cross-Complement Group 1 (XRCC1) Protein Expression in Human Non-Small-Cell Lung Cancer Cells

Etoposide (VP-16), a topoisomerase II inhibitor, is an effective anti-cancer drug used for the treatment of non-small-cell lung cancer (NSCLC). Resveratrol is a naturally occurring polyphenolic compound that has been proved to have anti-cancer activity. XRCC1 is an important scaffold protein involved in base excision repair that is regulated by ERK1/2 and AKT signals and plays an important role in the development of lung cancer. However, the role of ERK1/2 and AKT-mediated XRCC1 expression in etoposide treatment alone or combined with resveratrol-induced cytotoxicity in NSCLC cells has not been identified. In this study, etoposide treatment increased XRCC1 mRNA and protein expression through AKT and ERK1/2 activation in two NSCLC cells, H1703 and H1975. Knockdown of XRCC1 in NSCLC cells by transfection of XRCC1 siRNA or inactivation of ERK1/2 and AKT resulted in enhancing cytotoxicity and cell growth inhibition induced by etoposide. Resveratrol inhibited the expression of XRCC1 and enhanced the etoposide-induced cell death and anti-proliferation effect in NSCLC cells. Furthermore, transfection with constitutive active MKK1 or AKT vectors could rescue the XRCC1 protein level and also the cell survival suppressed by co-treatment with etoposide and resveratrol. These findings suggested that down-regulation of XRCC1 expression by resveratrol can enhance the chemosensitivity of etoposide in NSCLC cells.

MEK1/2 inhibition enhances the radiosensitivity of cancer cells by downregulating survival and growth signals mediated by EGFR ligands

The inhibition of the Ras/mitogen-activated protein kinase (Ras/MAPK) pathway through the suppression of mutated Ras or MAPK/extracellular signal-regulated kinase 1/2 (MEK1/2) has been shown to sensitize tumor cells to ionizing radiation (IR). The molecular mechanisms of this sensitization however, are not yet fully understood. In this study, we investigated the role of transforming growth factor-α (TGF-α) in the radiosensitizing effects of selumetinib, a selective inhibitor of MEK1/2. The expression of epidermal growth factor receptor (EGFR) ligands was assessed by ELISA in both Ras wild-type and Ras mutant cells that were exposed to radiation with or without selumetinib. The effects of selumetinib on the TGF-α/EGFR signaling cascade in response to radiation were examined by western blot analysis, clonogenic assay and by determing the yield of mitotic catastrophe. The treatment of cells with selumetinib reduced the basal and IR-induced secretion of TGF-α in both Ras wild-type and Ras mutant cell lines in vitro and in vivo. The reduction of TGF-α secretion was accompanied with a reduction in phosphorylated tumor necrosis factor-α converting enzyme (TACE) in the cells treated with selumetinib with or without IR. The treatment of cells with selumetinib with or without IR inhibited the phosphorylation of EGFR and check-point kinase 2 (Chk2), and reduced the expression of survivin. Supplementation with exogenous TGF-α partially rescued the selumetinib-treated cells from IR-induced cell death, restored EGFR and Chk2 phosphorylation and increased survivin expression. These data suggest that the inhibition of MEK1/2 with selumetinib may provide a mechanism to sensitize tumor cells to IR in a fashion that prevents the activation of the TGF-α autocrine loop following IR.

Metformin-mediated downregulation of p38 mitogen-activated protein kinase-dependent excision repair cross-complementing 1 decreases DNA repair capacity and sensitizes human lung cancer cells to paclitaxel

Metformin, an extensively used and well-tolerated drug for treating individuals with type 2 diabetes, has recently gained significant attention as an anticancer drug. On the other hand, paclitaxel (Taxol) is a new antineoplastic drug that has shown promise in the treatment of non-small cell lung cancer (NSCLC). High expression levels of excision repair cross-complementary 1 (ERCC1) in cancers have been positively associated with the DNA repair capacity and a poor prognosis in NSCLC patients treated with platinum-containing chemotherapy. In this current study, paclitaxel was found to increase phosphorylation of mitogen-activated protein kinase (MAPK) kinase 3/6 (MKK3/6)-p38 MAPK as well as protein and mRNA levels of ERCC1 in H1650 and H1703 cells. Moreover, paclitaxel-induced ERCC1 protein and mRNA levels significantly decreased via the downregulation of p38 activity by either a p38 MAPK inhibitor SB202190 or p38 knockdown with specific small interfering RNA (siRNA). Specific inhibition of ERCC1 with siRNA was found to enhance the paclitaxel-induced cytotoxic effect and growth inhibition. Furthermore, metformin was able to not only decrease the paclitaxel-induced p38 MAPK-mediated ERCC1 expression, but also augment the cytotoxic effect induced by paclitaxel. Finally, expression of constitutive activate MKK6 or HA-p38 MAPK vectors in lung cancer cells was able to abrogate ERCC1 downregulation by metformin and paclitaxel as well as cell viability and DNA repair capacity. Overall, our results suggest that inhibition of the p38 MAPK signaling by metformin coupled with paclitaxel therapy in human NSCLC cells may be a clinically useful combination, which however will require further validation.

Reversion of the ErbB malignant phenotype and the DNA damage response

The ErbB or HER family is a group of membrane bound tyrosine kinase receptors that initiate signal transduction cascades, which are critical to a wide range of biological processes. When over-expressed or mutated, members of this kinase family form homomeric or heteromeric kinase assemblies that are involved in certain human malignancies. Targeted therapy evolved from studies showing that monoclonal antibodies to the ectodomain of ErbB2/neu would reverse the malignant phenotype. Unfortunately, tumors develop resistance to targeted therapies even when coupled with genotoxic insults such as radiation. Radiation treatment predominantly induces double strand DNA breaks, which, if not repaired, are potentially lethal to the cell. Some tumors are resistant to radiation treatment because they effectively repair double strand breaks. We and others have shown that even in the presence of ionizing radiation, active ErbB kinase signaling apparently enhances the repair process, such that transformed cells resist genotoxic signal induced cell death. We review here the current understanding of ErbB signaling and DNA double strand break repair. Some studies have identified a mechanism by which DNA damage is coordinated to assemblies of proteins that associate with SUN domain containing proteins. These assemblies represent a new target for therapy of resistant tumor cells.

ERCC1: impact in multimodality treatment of upper gastrointestinal cancer

Platinum-based drugs and radiation are key elements of multimodality treatment in a wide variety of solid tumors and especially tumors of the upper gastrointestinal tract. Cytotoxicity is directly related to their ability to cause DNA damage. This event consecutively triggers the nucleotide excision repair (NER) complex. The NER capacity has a major impact on chemo and radiation sensitivity, emergence of resistance and patient outcome. Excision repair cross-complementing group 1 (ERCC1) is a key molecule in NER. This review provides an overview of the NER complex with a focus on ERCC1. Recent literature has been analyzed and provides information regarding the potential role of ERCC1 as a prognostic factor in multimodality treatment of upper gastrointestinal cancer and cancer risk. To date, the role of ERCC1 as a predictive marker for individual multimodality treatment is far from being firmly established for routine use. However, with reliable methods, established cut-off values and validation in large, prospective, randomized trials, ERCC1 may possibly prove to play an important role as a tumor marker in individualized treatment for upper gastrointestinal cancer.

The combi-targeting concept: mechanism of action of the pleiotropic combi-molecule RB24 and discovery of a novel cell signaling-based combination principle

RB24 (NSC 741279), a 3-methyltriazene termed "combi-molecule" designed to possess mixed epidermal growth factor receptor (EGFR) targeting and DNA methylating properties showed over a 100-fold greater antiproliferative activity than Temodal(®) (TEM), a 4-fold greater potency than gefitinib and a 5-fold stronger activity than an equi-effective combination of gefitinib+TEM against the O(6)-alkylguanine transferase (AGT)-proficient DU145 cell line that co-expresses EGFR. Investigation of the mechanisms underlying the unique potency of RB24 revealed that cell exposure to TEM was accompanied by activation of p38MAPK and concomitant elevation of the levels of X-ray repair cross-complementing group 1 (XRCC1) protein. Levels of phospho-p38MAPK and XRCC1 were increased by 2-fold in EGF-stimulated cells. In contrast, EGF-stimulation did not alter the status of these proteins in RB24-treated cells and this translated into a 2-fold lower level of XRCC1 when compared with those exposed to TEM+EGF. These effects correlated with significantly delayed DNA repair activity in combi-molecule-treated cells when compared with TEM-exposed ones. Further analysis demonstrated that in contrast to TEM, RB24 could block Bad phosphorylation at serine 136 in a dose-dependent manner and induced significantly higher levels of apoptosis than the former molecule. Tandem depletion of XRCC1 and Bad activation through alternative pathways using the MEK1 inhibitor, PD98059, led to substantial levels of apoptosis in RB24-treated cells. The results in toto indicate that the superior activity of the combi-molecule may be attributed to its ability to down-regulate DNA repair proteins such as XRCC1 and to alleviate anti-apoptotic signaling through blockade of EGFR-mediated signaling while inflicting high levels of DNA lesions to the cells.

EGFR inhibitor C225 increases the radiosensitivity of human lung squamous cancer cells

Background

The purpose of the present study is to investigate the direct biological effects of the epidermal growth factor receptor (EGFR) inhibitor C225 on the radiosensitivity of human lung squamous cancer cell-H520. H520 cells were treated with different dosage of ⁶⁰Co γ ray irradiation (1.953 Gy/min) in the presence or absence of C225. The cellular proliferation, colony forming capacity, apoptosis, the cell cycle distribution as well as caspase-3 were analyzed in vitro.

Results

We found that C225 treatment significantly increased radiosensitivity of H-520 cells to irradiation, and led to cell cycle arrest in G₁ phase, whereas ⁶⁰Co γ ray irradiation mainly caused G₂ phase arrest. H-520 cells thus displayed both the G₁ and G₂ phase arrest upon treatment with C225 in combination with ⁶⁰Co γ ray irradiation. Moreover, C225 treatment significantly increased the apoptosis percentage of H-520 cells (13.91% ± 1.88%) compared with the control group (5.75% ± 0.64%, P < 0.05).

Conclusion

In this regard, C225 treatment may make H-520 cells more sensitive to irradiation through the enhancement of caspase-3 mediated tumor cell apoptosis and cell cycle arrest.

Chemotherapy-induced activation of ADAM-17: a novel mechanism of drug resistance in colorectal cancer

PURPOSE

We have shown previously that exposure to anticancer drugs can trigger the activation of human epidermal receptor survival pathways in colorectal cancer (CRC). In this study, we examined the role of ADAMs (a disintegrin and metalloproteinases) and soluble growth factors in this acute drug resistance mechanism.

EXPERIMENTAL DESIGN

In vitro and in vivo models of CRC were assessed. ADAM-17 activity was measured using a fluorometric assay. Ligand shedding was assessed by ELISA or Western blotting. Apoptosis was assessed by flow cytometry and Western blotting.

RESULTS

Chemotherapy (5-fluorouracil) treatment resulted in acute increases in transforming growth factor-alpha, amphiregulin, and heregulin ligand shedding in vitro and in vivo that correlated with significantly increased ADAM-17 activity. Small interfering RNA-mediated silencing and pharmacologic inhibition confirmed that ADAM-17 was the principal ADAM involved in this prosurvival response. Furthermore, overexpression of ADAM-17 significantly decreased the effect of chemotherapy on tumor growth and apoptosis. Mechanistically, we found that ADAM-17 not only regulated phosphorylation of human epidermal receptors but also increased the activity of a number of other growth factor receptors, such as insulin-like growth factor-I receptor and vascular endothelial growth factor receptor.

CONCLUSIONS

Chemotherapy acutely activates ADAM-17, which results in growth factor shedding, growth factor receptor activation, and drug resistance in CRC tumors. Thus, pharmacologic inhibition of ADAM-17 in conjunction with chemotherapy may have therapeutic potential for the treatment of CRC.

2,3,7,8-Tetrachlorodibenzo-p-dioxin inhibits fibroblast growth factor 10-induced prostatic bud formation in mouse urogenital sinus

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) dorsalizes the pattern of prostatic buds developing from the urogenital sinus (UGS) of male fetal mice, causing some buds to form in inappropriate positions while blocking formation of others. This teratogenic TCDD action significantly reduces prostate main duct number and causes ventral prostate agenesis in exposed males. The purpose of this study was to determine whether inhibition of fibroblast growth factor 10 (FGF10) signaling is mechanistically linked to mouse prostatic budding impairment by TCDD. In utero TCDD exposure induced aryl hydrocarbon receptor-responsive cytochrome P450 1b1 messenger RNA (mRNA) in ventral UGS regions where Fgf10 and fibroblast growth factor receptor 2 (Fgfr2) mRNA were expressed and where budding was most severely inhibited by TCDD. However, TCDD exposure did not reduce Fgf10 or Fgfr2 mRNA abundance in the UGS or alter their distribution. Addition of FGF10 protein to UGS organ culture media increased the abundance of UGS basal epithelial cells immunopositive for phosphorylated extracellular signal-regulated kinase (ERK). FGF10 also increased the number of 5-bromo-2'-deoxyuridine (BrdU)-labeled UGS epithelial cells and increased the number of prostatic buds formed per UGS. Addition of TCDD to UGS organ culture media did not alter FGF10-induced ERK activation in UGS basal epithelium but prevented FGF10-induced BrdU incorporation and blocked FGF10-induced prostatic bud formation. These results identify basal urogenital sinus epithelium cells as the key site of FGF10 action during fetal prostate development and suggest that TCDD likely acts downstream of FGFR2 and ERK to restrict UGS epithelial cell proliferation and prevent prostatic bud formation.

MicroRNA-17-3p is a prostate tumor suppressor in vitro and in vivo, and is decreased in high grade prostate tumors analyzed by laser capture microdissection

MicroRNAs (miRs) are a novel class of RNAs with important roles in regulating gene expression. To identify miRs controlling prostate tumor progression, we utilized unique human prostate sublines derived from the parental P69 cell line, which differ in their tumorigenic properties in vivo. Grown embedded in laminin-rich extracellular matrix (lrECM) gels these genetically-related sublines displayed drastically different morphologies correlating with their behaviour in vivo. The non-tumorigenic P69 subline grew as multicellular acini with a defined lumen and basal/polar expression of relevant marker proteins. M12, a highly tumorigenic, metastatic derivative, grew as a disorganized mass of cells with no polarization, whereas the F6 subline, a weakly tumorigenic, non-metastatic M12 variant, reverted to acini formation akin to the P69 cell line. These sublines also differed in expression of vimentin, which was high in M12, but low in F6 and P69 sublines. Analysis of vimentin's conserved 3'-UTR suggested several miRs that could regulate vimentin expression. The lack of miR-17-3p expression correlated with an increase in vimentin synthesis and tumorigenicity. Stable expression of miR-17-3p in the M12 subline reduced vimentin levels 85% and reverted growth to organized, polarized acini in lrECM gels. In vitro motility and invasion assays suggested a decrease in tumorigenic behaviour, confirmed by reduced tumor growth in male athymic, nude mice dependent on miR-17-3p expression. Analysis of LCM-purified clinical human prostatectomy specimens confirmed that miR-17-3p levels were reduced in tumor cells. These results suggest that miR-17-3p functions as a tumor suppressor, representing a novel target to block prostate tumor progression.

Inhibition of vimentin or beta1 integrin reverts morphology of prostate tumor cells grown in laminin-rich extracellular matrix gels and reduces tumor growth in vivo

Prostate epithelial cells grown embedded in laminin-rich extracellular matrix (lrECM) undergo morphologic changes that closely resemble their architecture in vivo. In this study, growth characteristics of three human prostate epithelial sublines derived from the same cellular lineage, but displaying different tumorigenic and metastatic properties in vivo, were assessed in three-dimensional lrECM gels. M12, a highly tumorigenic and metastatic subline, was derived from the immortalized, prostate epithelial P69 cell line by selection in athymic, nude mice and found to contain a deletion of 19p-q13.1. The stable reintroduction of an intact human chromosome 19 into M12 resulted in a poorly tumorigenic subline, designated F6. When embedded in lrECM gels, the parental, nontumorigenic P69 line produced acini with clearly defined lumena. Immunostaining with antibodies to beta-catenin, E-cadherin, or alpha6 and beta1 integrins showed polarization typical of glandular epithelium. In contrast, the metastatic M12 subline produced highly disorganized cells with no evidence of polarization. The F6 subline reverted to acini-like structures exhibiting basal polarity marked with integrins. Reducing either vimentin levels via small interfering RNA interference or the expression of alpha6 and beta1integrins by the addition of blocking antibodies, reorganized the M12 subline into forming polarized acini. The loss of vimentin significantly reduced M12-Vim tumor growth when assessed by s.c. injection in athymic mice. Thus, tumorigenicity in vivo correlated with disorganized growth in three-dimensional lrECM gels. These studies suggest that the levels of vimentin and beta1 integrin play a key role in the homeostasis of the normal acinus in prostate and that their dysregulation may lead to tumorigenesis.

Therapeutic efficacy of 177Lu-CHX-A''-DTPA-hu3S193 radioimmunotherapy in prostate cancer is enhanced by EGFR inhibition or docetaxel chemotherapy

BACKGROUND

This study investigated the biodistribution and therapeutic efficacy of Lutetium-177 (177Lu) radiolabeled anti-Lewis Y monoclonal antibody hu3S193 radioimmunotherapy (RIT) in mice bearing prostate cancer xenografts. The ability of epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor AG1478 and docetaxel chemotherapy to enhance the efficacy of RIT was also assessed in vivo.

METHODS

The in vitro cytotoxicity of 177Lu labeled hu3S193 on Le(y) positive DU145 prostate cancer cells was assessed using proliferation assays, with induction of apoptosis measured by ELISA. The in vivo biodistribution and tumor localization of 177Lu-hu3S193 was assessed in mice bearing established DU145 tumor xenografts. The efficacy and maximum tolerated dose of 177Lu-hu3S193 RIT in vivo was determined by a dose escalation study. EGFR inhibitor AG1478 or docetaxel chemotherapy was administered at sub-therapeutic doses in conjunction with RIT in vivo.

RESULTS

177Lu-hu3S193 mediated significant induction of cytotoxicity and apoptosis in vitro. In vivo analysis of 177Lu-hu3S193 biodistribution demonstrated specific targeting of DU145 prostate cancer xenografts, with maximal tumor uptake of 33.2 +/- 3.9%ID/g observed at 120 hr post-injection. In RIT studies, 177Lu-hu3S193 caused specific and dose-dependent inhibition of prostate cancer tumor growth. A maximum tolerated dose of 350 microCi was determined for 177Lu-hu3S193. Combination of 177Lu-hu3S193 RIT with EGFR inhibitor AG1478 or docetaxel chemotherapy both significantly improved efficacy.

CONCLUSIONS

177Lu-hu3S193 RIT is effective as a single agent in the treatment of Le(y) positive prostate cancer models. The enhancement of RIT by AG1478 or docetaxel indicates the promise of combined modality strategies.

Practical approaches to proteomic biomarkers within prostate cancer radiotherapy trials

INTRODUCTION

Proteomic biomarkers may be useful for monitoring therapeutic response and to triage cancer patients to best therapy.

OBJECTIVES

In this review, we highlight the importance of specimen acquisition, preparation and analysis in radiotherapy proteomic studies. We also discuss practical approaches for the design and execution of clinical proteomic studies using our recent experience based on specimens accrued during prostate cancer radiation therapy.

DISCUSSION AND CONCLUSIONS

Numerous proteomic methods are being employed, including high-throughput mass spectrometry and immunoassays, and using solid tissues, blood and urine for analysis. Given the potential complexity of cytokine and other protein responses, there is a need to assess proteomic signatures within serial samples as longitudinal studies during a course of fractionated radiotherapy (RT).

Noninvasive imaging and quantification of epidermal growth factor receptor kinase activation in vivo

Epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase (RTK) critical in tumor growth and a major target for anticancer drug development. However, thus far, there is no effective system to monitor its activities in vivo. Here, we report a novel approach to monitor EGFR activation based on the bifragment luciferase reconstitution system. The EGFR receptor and its interacting partner proteins (EGFR, growth factor receptor binding protein 2, and Src homology 2 domain-containing) were fused to NH(2) terminal and COOH terminal fragments of the firefly luciferase. After establishing tumor xenograft from cells transduced with the reporter genes, we show that the activation of EGFR and its downstream factors could be quantified through optical imaging of reconstituted luciferase. Changes in EGFR activation could be visualized after radiotherapy or EGFR inhibitor treatment. Rapid and sustained radiation-induced EGFR activation and inhibitor-mediated signal suppression were observed in the same xenograft tumors over a period of weeks. Our data therefore suggest a new methodology where activities of RTKs can be imaged and quantified optically in mice. This approach should be generally applicable to study biological regulation of RTK, as well as to develop and evaluate novel RTK-targeted therapeutics.

Radiation-induced PARP activation is enhanced through EGFR-ERK signaling

We examined the impact of EGFR-ERK signaling on poly (ADP-ribose) polymerase (PARP) activation following ionizing irradiation of human prostate cancer (PCa) cell lines displaying marked differences in ERK dependence. PARP activation was indicated by the appearance of polyADP-ribose, the incorporation of P32-labelled NADH, and by cellular NADH. EGFR-ERK signaling was manipulated through ligand activation or signal interruption using the tyrphostin AG1478, or MEK inhibitor PD 184352. EGF activation of ERK prior to irradiation was associated with a marked increase in PARP activation and decreased survival in both cell lines. Prior inactivation of PARP protected both cell lines from the initial decrease in NAD+ and improved the survival of LNCaP cells following combined EGF and IR treatment. MEK inhibitor PD 184352 also reduced PARP activation and improved LNCaP survival following EGF and IR treatment. These data imply that PARP activation following exposure to ionizing radiation is enhanced through EGFR-ERK signaling.

Silibinin impairs constitutively active TGFalpha-EGFR autocrine loop in advanced human prostate carcinoma cells

PURPOSE

Epidermal growth factor (EGF) and transformation growth factor-alpha (TGFalpha) are potent mitogens that regulate proliferation of prostate cancer cells via autocrine and paracrine loops, and promote tumor metastasis. They exert their action through binding to the cell surface receptor, epidermal growth factor receptor (EGFR), and cause activation of Erk1/2 mediated mitogenic signaling in human prostate cancer (PCA) at both advanced and androgen-independent stages. Thus, we rationalized that inhibiting this mitogenic pathway could be useful in controlling advanced PCA growth.

METHODS

LNCaP and DU145 human PCA cells were treated with silibinin (100-200 microM) for different time points, and the levels of TGFalpha, activated signaling molecules (EGFR, Erk1/2 and Jnk1/2) and Erk1/2 kinase activity were analyzed employing ELISA, immunoprecipitation and/or immunoblotting techniques. The mRNA levels of TGFalpha were analyzed by RT-PCR.

RESULTS

Treatment of cells (LNCaP and DU145) with silibinin resulted in a decrease in TGFalpha protein at both secreted and cellular levels together with a decrease in its mRNA level. Silibinin also caused an inhibition of EGFR activation followed by that of Erk1/2 without any change in their protein levels. The kinase activity of Erk1/2 to Elk1 was also inhibited by silibinin at least in DU145 cells. In other study, silibinin caused strong inhibition of Jnk1/2 activation in LNCaP cells while in DU145 cells, a strong induction in Jnk1/2 activation was observed. These results suggest that silibinin impairs TGFalpha-EGFR-Erk1/2 signaling in both androgen-dependent (LNCaP) and -independent (DU145) advanced human prostate carcinoma cells.

CONCLUSIONS

This study, for the first time, identifies the inhibitory effect of silibinin on constitutively active TGFalpha-EGFR autocrine loop in advanced human PCA cells, which plausible contributes to the strong efficacy of silibinin in PCA prevention and intervention, as reported in recent studies.

Gene expression profiles in mouse liver cells after exposure to different types of radiation

The liver is one of the target organs of radiation-induced cancers by internal exposures. In order to elucidate radiation-induced liver cancers including Thorotrast, we present a new approach to investigate in vivo effects of internal exposure to alpha-particles. Adopting boron neutron capture, we separately irradiated Kupffer cells and endothelial cells in mouse liver in vivo and analyzed the changes in gene transcriptions by an oligonucleotide microarray. Differential expression was defined as more than 3-fold for up-regulation and less than 1/3 for under-regulation, compared with non-irradiated controls. Of 6,050 genes examined, 68 showed differential expression compared with non-irradiated mice. Real-time polymerase chain reaction validated the results of the microarray analysis. Exposure to alpha-particles and gamma-rays produced different patterns of altered gene expression. Gene expression profiles revealed that the liver was in an inflammatory state characterized by up-regulation of positive acute phase protein genes, irrespective of the target cells exposed to radiation. In comparison with chemical and biological hepatotoxicants, inductions of Metallothionein 1 and Hemopexin, and suppressions of cytochrome P450s are characteristic of radiation exposure. Anti-inflammatory treatment could be helpful for the prevention and protection of radiation-induced hepatic injury.

Molecular Biology for the Radiation Oncologist: the 5Rs of Radiobiology meet the Hallmarks of Cancer

Recent advances in our understanding of the biology of cancer have provided enormous opportunities for the development of novel therapies against specific molecular targets. It is likely that most of these targeted therapies will have only modest single agent activities but may have the potential to accentuate the therapeutic effects of ionising radiation. In this introductory review, the 5Rs of classical radiobiology are interpreted in terms of their relationship to the hallmarks of cancer. Future articles will focus on the specific hallmarks of cancer and will highlight the opportunities that exist for designing new combination treatment regimens.

Sensing radiosensitivity of human epidermal stem cells

PURPOSE

Radiosensitivity of stem cells is a matter of debate. For mouse somatic stem cells, both radiosensitive and radioresistant stem cells have been described. By contrast, the response of human stem cells to radiation has been poorly studied. As epidermis is a radiosensitive tissue, we evaluated in the present work the radiosensitivity of cell populations enriched for epithelial stem cells of human epidermis.

METHODS AND MATERIALS

The total keratinocyte population was enzymatically isolated from normal human skin. We used flow cytometry and antibodies against cell surface markers to isolate basal cell populations from human foreskin. Cell survival was measured after a dose of 2Gy with the XTT assay at 72h after exposure and with a clonogenic assay at 2 weeks. Transcriptome analysis using oligonucleotide microarrays was performed to assess the genomic cell responses to radiation.

RESULTS

Cell sorting based on two membrane proteins, alpha6 integrin and the transferrin receptor CD71, allowed isolation of keratinocyte populations enriched for the two types of cells found in the basal layer of epidermis: stem cells and progenitors. Both the XTT assay and the clonogenic assay showed that the stem cells were radioresistant whereas the progenitors were radiosensitive. We made the hypothesis that upstream DNA damage signalling might be different in the stem cells and used microarray technology to test this hypothesis. The stem cells exhibited a much more reduced gene response to a dose of 2Gy than the progenitors, as we found that 6% of the spotted genes were regulated in the stem cells and 20% in the progenitors. Using Ingenuity Pathway Analysis software, we found that radiation exposure induced very specific pathways in the stem cells. The most striking responses were the repression of a network of genes involved in apoptosis and the induction of a network of cytokines and growth factors.

CONCLUSION

These results show for the first time that keratinocyte populations enriched for stem cells from human epidermis are radioresistant. Based on both repressed and induced genes, we found that the major response of the irradiated stem cell population was the regulation of genes functionally related to cell death, cell survival and apoptosis.

Conjugated bile acids regulate hepatocyte glycogen synthase activity in vitro and in vivo via Galphai signaling

The regulation of glycogen synthase activity by bile acids in primary hepatocytes and in the intact liver was investigated. Bile acids (deoxycholic acid, DCA; taurocholic acid, TCA) activated AKT and glycogen synthase (GS) in primary rat hepatocytes. Incubation with a phosphatidyl inositol-3 kinase inhibitor or expression of dominant-negative AKT in primary rat hepatocytes abolished activation of AKT and GS by DCA and TCA. TCA, but not DCA, activated Galpha(i) proteins in primary rat hepatocytes. Treatment of cells with pertussis toxin or expression of dominant-negative Galpha(i) blocked TCA-induced activation of AKT and of GS but did not alter AKT or GS activation caused by DCA. TCA caused activation of AKT and GS in intact rat liver. Expression of dominant-negative Galpha(i) reduced TCA-induced activation of AKT and of GS in intact rat liver. Together, our findings demonstrate that bile acids are physiological regulators of glycogen synthase in rat liver and that conjugated bile acids use a Galpha(i)-coupled G protein-coupled receptor to regulate GS activity in vitro and in vivo.

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.

Molecular staging of prostate cancer in the year 2007

Numerous attempts towards improving patient management by molecular staging have been fruitless so far. No single molecular parameter is routinely analyzed in prostate cancer tissue. This may be partly due to genuine properties of prostate cancer that may make this tumor a difficult target. Furthermore, inherent logistical problems result in a shortage of prostate cancer tissue for research purposes. For the future, it can be hoped that the availability of more powerful molecular techniques in combination with better tissue archives will allow more rapid progress. Powerful DNA array and proteomics methods allow the systematic analysis of virtually all genes of a cancer on the DNA, RNA, and protein level. Although such approaches are sometimes labeled as "fishing expeditions," it cannot be totally disregarded that the simultaneous analysis of all genes has a high likelihood of identifying significant new information. In future, one of the major scientific challenges will be the validation of several potential biomarkers in large enough and clinically well-characterized patient cohorts. In particular, studies on needle core biopsies and hormone refractory cancers are imperatively needed for investigating the natural history of the disease or to discover potential predictive markers for radiation therapy and new therapeutic target genes to answer the clinically most important questions for optimal clinical decision making in prostate cancer patients: which patients will not require local therapy? If local therapy is needed, what is the treatment of choice? What medications should be given if metastases are present?

Intercellular and intracellular signaling pathways mediating ionizing radiation-induced bystander effects

A rapidly growing body of experimental evidence indicates that ionizing radiation induces biological effects in non-irradiated bystander cells that have received signals from adjacent or distant irradiated cells. This phenomenon, which has been termed the ionizing radiation-induced bystander effect, challenges the long-standing paradigm that radiation traversal through the nucleus of a cell is a prerequisite to elicit genetic damage or a biological response. Bystander effects have been observed in a number of experimental systems, and cells whose nucleus or cytoplasm is irradiated exert bystander responses. Bystander cells manifest a multitude of biological consequences, such as genetic and epigenetic changes, alterations in gene expression, activation of signal transduction pathways, and delayed effects in their progeny. Several mediating mechanisms have been proposed. These involve gap junction-mediated intercellular communication, secreted soluble factors, oxidative metabolism, plasma membrane-bound lipid rafts, and calcium fluxes. This paper reviews briefly the current knowledge of the bystander effect with a focus on proposed mechanisms. The potential benefit of bystander effects to cancer radiotherapy will also be discussed.

Type II combi-molecules: design and binary targeting properties of the novel triazolinium-containing molecules JDD36 and JDE05

We recently designed molecules termed "type II combi-molecules" to block the epidermal growth factor receptor and to damage DNA without the requirement for hydrolytic cleavage. Here, we studied two such combi-molecules (JDD36 and JDE05), containing a novel quinazoline-linked chloroethyltriazolinium system. The epidermal growth factor receptor-targeting potential of these novel structures was studied by ELISA for isolated epidermal growth factor receptor and by Western blotting for whole-cell assays. DNA damage was analyzed using the single-cell microelectrophoresis comet assay. Antiproliferative effects were determined by the sulforhodamine B assay. JDD36 showed an IC50 of 0.6 micromol/l in the ELISA for epidermal growth factor receptor tyrosine kinase, a dose-dependent inhibition of epidermal growth factor receptor phosphorylation and significant levels of DNA damage in the human DU145 prostate cancer cell line. JDD36 was an overall 2- to 15-fold stronger antiproliferative agent than JDE05 that showed potent epidermal growth factor receptor inhibitory activity (IC50 epidermal growth factor receptor, 0.035 micromol/l) but weak DNA-damaging potential. In a panel of LNCaP erbB transfectants, in contrast to JDE05, JDD36 showed remarkable and selective potency against the LNCaPerbB2 transfectant. The results in toto suggest that the overall superior potency of JDD36 when compared with JDE05 may be imputed to its balanced binary epidermal growth factor receptor-DNA-targeting properties that may induce a tandem blockade of epidermal growth factor receptor-mediated mitogenic signaling while depleting alternative survival mechanism by damaging DNA.

The Combi-Targeting Concept: In vitro and In vivo Fragmentation of a Stable Combi-Nitrosourea Engineered to Interact with the Epidermal Growth Factor Receptor while Remaining DNA Reactive

PURPOSE

JDA58 (NSC 741282), a "combi-molecule" optimized in the context of the "combi-targeting concept," is a nitrosourea moiety tethered to an anilinoquinazoline. Here, we sought to show its binary epidermal growth factor receptor (EGFR)/DNA targeting property and to study its fragmentation in vitro and in vivo.

EXPERIMENTAL DESIGN

The fragmentation of JDA58 was detected in cells in vitro and in vivo by fluorescence microscopy and tandem mass spectrometry. EGFR phosphorylation and DNA damage were determined by Western blotting and comet assay, respectively. Tumor data were examined for statistical significance using the Student's t test.

RESULTS

JDA58 inhibited EGFR tyrosine kinase (IC(50), 0.2 micromol/L) and blocked EGFR phosphorylation in human DU145 prostate cancer cells. It induced significant levels of DNA damage in DU145 cells in vitro or in vivo and showed potent antiproliferative activity both in vitro and in a DU145 xenograft model. In cell-free medium, JDA58 was hydrolyzed to JDA35, a fluorescent amine that could be observed in tumor cells both in vitro and in vivo. In tumor cells in vitro or in vivo, or in plasma collected from mice, the denitrosated species JDA41 was the predominant metabolite. However, mass spectrometric analysis revealed detectable levels of the hydrolytic product JDA35 in tumor cells both in vitro and in vivo.

CONCLUSIONS

The results in toto suggest that growth inhibition in vitro and in vivo may be sustained by the intact combi-molecule plus JDA35 plus JDA41, three inhibitors of EGFR, and the concomitantly released DNA-damaging species. This leads to a model wherein a single molecule carries a complex multitargeted-multidrug combination.

Radiation-induced bystander effects and adaptive response in murine lymphocytes

PURPOSE

To study the bystander effects of gamma-radiation in murine lymphocytes using irradiated conditioned medium (ICM) generated from irradiated lymphocytes.

METHODS

Proliferation response of unirradiated lymphocytes to mitogen concanavalin A (con A) in presence of ICM, collected from gamma-irradiated lymphocytes (60Co source; 0.35 Gy/min; 0.1-1 Gy), was studied by 3H-thymidine incorporation and also by dye dilution using carboxyfluorescein succinimidyl ester (CFSE). Expression of proliferation markers, interleukin 2 receptor alpha chain (CD25) and cyclin D in ICM treated lymphocytes was analyzed by labeling with specific antibodies. Intracellular reactive oxygen species (ROS) and apoptosis were estimated by flow cytometry using dichlorodihydrofluorescein diacetate (H2DCFDA) and propidium iodide, respectively. Nitric oxide (NO) was measured using Griess reagent.

RESULTS

Proliferation response to con A in unirradiated lymphocytes was enhanced in the presence of ICM with maximum enhancement observed in the presence of 0.5 Gy ICM. Augmentation of proliferation in the presence of ICM was accompanied by an increase in CD25 and cyclin D expression, enhanced ROS and NO generation. ICM pretreated lymphocytes showed adaptive response to radiation which was not abrogated by wortmannin, a phosphatidyl inositol 3-kinase (PI3K) inhibitor.

CONCLUSION

Soluble factors released from irradiated lymphocytes initiate a signaling cascade in unirradiated lymphocytes resulting in increased response to mitogen and radioresistance which may have an important role in radiation-induced immunomodulation.

Integration of EGFR inhibitors with radiochemotherapy

Laboratory studies that led to the development of epidermal growth factor receptor (EGFR) inhibitors indicated that such inhibitors would be effective when given to patients with tumours that are driven by activated EGFR. However, initial clinical studies have shown modest responses to EGFR inhibitors when used alone, and it has not yet been possible to clearly identify which tumours will respond to this therapy. As a result, EGFR inhibitors are now used in combination with radiation therapy, chemotherapy and, more recently, with concurrent radiochemotherapy. In general, these clinical trials have been designed without much preclinical data. What do we need to know to make these combinations successful in the clinic?

Human chorionic gonadotropin modulates prostate cancer cell survival after irradiation or HMG CoA reductase inhibitor treatment

The impact of human chorionic gonadotropin (hCG) on prostate carcinoma viability was investigated. Treatment of LNCaP and PC-3 cells with hCG modestly reduced cell viability within 96 h. Treatment of cells with hCG followed by exposure to ionizing radiation enhanced radiosensitivity. Exposure of LNCaP cells to hCG promoted activation of epidermal growth factor receptor (ERBB1) via a Galpha(i)-, mitogen-activated protein kinase kinase (MEK)1/2-, and metalloprotease-dependent paracrine mechanism, effects that were further enhanced after radiation exposure, and that were causal in prolonged intense activation of poly(ADP-ribose) polymerase (PARP). Inhibition of ERBB1, MEK1, or PARP1 function suppressed the radiosensitizing properties of hCG. Radiosensitization was also, in part, dependent upon c-Jun NH2-terminal kinase 1/2 signaling. PARP1-dependent radiosensitization was suppressed by a pan-caspase inhibitor and by knockdown of apoptosis-inducing factor expression. Inhibition of phosphatidylinositol 3-kinase, expression of dominant-negative AKT, or treatment with the HMG CoA reductase inhibitor lovastatin suppressed AKT phosphorylation and enhanced the cytotoxic effects of hCG. The enhancing effect of lovastatin was reproduced by incubation with a geranylgeranyl transferase inhibitor and blocked by coexposure to geranylgeranyl pyrophosphate. Treatment with hCG and lovastatin decreased expression of BCL-(XL) and XIAP, and increased expression of IkappaB. The cytotoxic effects of hCG were enhanced by expression of dominant-negative IkappaB, and they were abolished by coexpression of activated AKT. Expression of activated AKT maintained BCL-(XL) levels in cells expressing dominant-negative IkappaB. The promotion of hCG lethality by lovastatin was abolished by overexpression of BCL-(XL), and was dependent upon activation of caspase-9. Thus, hCG, in combination with radiation and lovastatin, may represent a novel approach to kill prostate cancer cells.

The involvement of calcium and MAP kinase signaling pathways in the production of radiation-induced bystander effects

Much evidence now exists regarding radiation-induced bystander effects, but the mechanisms involved in the transduction of the signal are still unclear. The mitogen-activated protein kinase (MAPK) pathways have been linked to growth factor-mediated regulation of cellular events such as proliferation, senescence, differentiation and apoptosis. Activation of multiple MAPK pathways such as the ERK, JNK and p38 pathways have been shown to occur after exposure of cells to radiation and a variety of other toxic stresses. Previous studies have shown oxidative stress and calcium signaling to be important in radiation-induced bystander effects. The aim of the present study was to investigate MAPK signaling pathways in bystander cells exposed to irradiated cell conditioned medium (ICCM) and the role of oxidative metabolism and calcium signaling in the induction of bystander responses. Human keratinocytes (HPV-G cell line) were irradiated (0.005-5 Gy) using a cobalt-60 teletherapy unit. The medium was harvested 1 h postirradiation and transferred to recipient HPV-G cells. Phosphorylated forms of p38, JNK and ERK were studied by immunofluorescence 30 min-24 h after exposure to ICCM. Inhibitors of the ERK pathway (PD98059 and U0126), the JNK pathway (SP600125), and the p38 pathway (SB203580) were used to investigate whether bystander-induced cell death could be blocked. Cells were also incubated with ICCM in the presence of superoxide dismutase, catalase, EGTA, verapamil, nifedipine and thapsigargin to investigate whether bystander effects could be inhibited because of the known effects on calcium homeostasis. Activated forms of JNK and ERK proteins were observed after exposure to ICCM. Inhibition of the ERK pathway appeared to increase bystander-induced apoptosis, while inhibition of the JNK pathway appeared to decrease apoptosis. In addition, reactive oxygen species, such as superoxide and hydrogen peroxide, and calcium signaling were found to be important modulators of bystander responses. Further investigations of these signaling pathways may aid in the identification of novel therapeutic targets.

Radioresistance of K-Ras mutated human tumor cells is mediated through EGFR-dependent activation of PI3K-AKT pathway

BACKGROUND AND PURPOSE

In the context of EGFR-targeting strategies we investigated autocrine/paracrine factors leading to in vitro radioresistance of K-Ras mutated tumor cells through activation of EGFR mediated signal transduction.

PATIENTS AND METHODS

Ras mutated (Rasmt) and normal Ras (Raswt) presenting human tumor cell lines were used to analyze the potential of conditioned media (CM) of both cell types to mediate radioresistance and to activate EGFR-signaling cascades. Therefore, clonogenic assays as well as SDS-PAGE combined with immunoblotting was performed. Additionally, Ras-mutated cells were transfected with K-Ras-siRNA to investigate, how downregulation of mutated K-Ras affects secretion of EGFR-ligands, stimulation of EGFR-signaling and modulation of radiation response.

RESULTS

TGFalpha, Amphiregulin (ARG) and CM from Rasmt cells (Rasmt-CM) resulted in an increased clonogenic survival of irradiated Raswt cells. Both, EGFR ligands as well as Rasmt-CM led to a strong phosphorylation of EGFR and activation of downstream pathways, i.e. PI3K-AKT. However, neutralization of TGFalpha or ARG in Rasmt-CM led to a marked reduction of P-AKT. Furthermore, Rasmt-CM from K-Ras-siRNA transfected Rasmt-cells markedly inhibited phosphorylation of AKT in Raswt cells and enhanced radiation sensitivity of A549 cells transfected with the siRNA.

CONCLUSION

The data suggest that constitutively upregulated autocrine/paracrine secretion of EGF receptor ligands, especially ARG from K-Ras mutated cells, mediates radioresistance in Rasmt-cells through stimulation of EGFR-PI3K-AKT pathway.

Activated forms of H-RAS and K-RAS differentially regulate membrane association of PI3K, PDK-1, and AKT and the effect of therapeutic kinase inhibitors on cell survival

The abilities of mutated active RAS proteins to modulate cell survival following exposure to ionizing radiation and small molecule kinase inhibitors were examined. Homologous recombination in HCT116 cells to delete the single allele of K-RAS D13 resulted in a cell line that exhibited an ∼75% reduction in basal extracellular signal-regulated kinase 1/2, AKT, and c-jun-NH2-kinase 1/2 activity. Transfection of cells lacking K-RAS D13 with H-RAS V12 restored extracellular signal-regulated kinase 1/2 and AKT activity to basal levels but did not restore c-jun-NH2-kinase 1/2 phosphorylation. In cells expressing H-RAS V12, radiation caused prolonged intense activation of AKT. Inhibition of H-RAS V12 function, blockade of phosphatidylinositol 3-kinase (PI3K) function using small interfering RNA/small-molecule inhibitors, or expression of dominant-negative AKT abolished radiation-induced AKT activation, and radiosensitized these cells. Inhibition of PI3K function did not significantly radiosensitize parental HCT116 cells. Inhibitors of the AKT PH domain including perifosine, SH-(5, 23-25) and ml-(14-16) reduced the plating efficiency of H-RAS V12 cells in a dose-dependent fashion. Inhibition of AKT function using perifosine enhanced radiosensitivity in H-RAS V12 cells, whereas the SH and ml series of AKT PH domain inhibitors failed to promote radiation toxicity. In HCT116 H-RAS V12 cells, PI3K, PDK-1, and AKT were membrane associated, whereas in parental cells expressing K-RAS D13, only PDK-1 was membrane bound. In H-RAS V12 cells, membrane associated PDK-1 was phosphorylated at Y373/376, which was abolished by the Src family kinase inhibitor PP2. Inhibition of PDK-1 function using the PH domain inhibitor OSU-03012 or using PP2 reduced the plating efficiency of H-RAS V12 cells and profoundly increased radiosensitivity. OSU-03012 and PP2 did not radiosensitize and had modest inhibitory effects on plating efficiency in parental cells. A small interfering RNA generated against PDK1 also radiosensitized HCT116 cells expressing H-RAS V12. Collectively, our data argue that molecular inhibition of AKT and PDK-1 signaling enhances the radiosensitivity of HCT116 cells expressing H-RAS V12 but not K-RAS D13. Small-molecule inhibitory agents that blocked stimulated and/or basal PDK-1 and AKT function profoundly reduced HCT116 cell survival but had variable effects at enhancing tumor cell radiosensitivity.

H-RAS V12–induced radioresistance in HCT116 colon carcinoma cells is heregulin dependent

The abilities of mutated active K-RAS and H-RAS proteins, in an isogenic human carcinoma cell system, to modulate the activity of signaling pathways following exposure to ionizing radiation is unknown. Loss of K-RAS D13 expression in HCT116 colorectal carcinoma cells blunted basal extracellular signal-regulated kinase 1/2 (ERK1/2), AKT, and c-Jun NH2-terminal kinase 1/2 activity. Deletion of the allele to express K-RAS D13 also enhanced expression of ERBB1, ERBB3, and heregulin but nearly abolished radiation-induced activation of all signaling pathways. Expression of H-RAS V12 in HCT116 cells lacking an activated RAS molecule (H-RAS V12 cells) restored basal ERK1/2 and AKT activity to that observed in parental cells but did not restore or alter basal c-jun NH2-terminal kinase 1/2 activity. In parental cells, radiation caused stronger ERK1/2 pathway activation compared with that of the phosphatidylinositol 3-kinase (PI3K)/AKT pathway, which correlated with constitutive translocation of Raf-1 into the plasma membrane of parental cells. Inhibition of mitogen-activated protein kinase/ERK1/2, but not PI3K, radiosensitized parental cells. In H-RAS V12 cells, radiation caused stronger PI3K/AKT pathway activation compared with that of the ERK1/2 pathway, which correlated with H-RAS V12–dependent translocation of PI3K into the plasma membrane. Inhibition of PI3K, but not mitogen-activated protein kinase/ERK1/2, radiosensitized H-RAS V12 cells. Radiation-induced activation of the PI3K/AKT pathway in H-RAS V12 cells 2 to 24 hours after exposure was dependent on heregulin-stimulated ERBB3 association with membrane-localized PI3K. Neutralization of heregulin function abolished radiation-induced AKT activation and reverted the radiosensitivity of H-RAS V12 cells to those levels found in cells lacking expression of any active RAS protein. These findings show that H-RAS V12 and K-RAS D13 differentially regulate radiation-induced signaling pathway function. In HCT116 cells expressing H-RAS V12, PI3K-dependent radioresistance is mediated by both H-RAS-dependent translocation of PI3K into the plasma membrane and heregulin-induced activation of membrane-localized PI3K via ERBB3.