Potential of a Cetuximab-based radioimmunotherapy combined with external irradiation manifests in a 3-D cell assay.

Targeting epidermal growth factor receptor (EGFR)-overexpressing tumors with radiolabeled anti-EGFR antibodies is a promising strategy for combination with external radiotherapy. In this study, we evaluated the potential of external plus internal irradiation by [(90) Y]Y-CHX-A″-DTPA-C225 (Y-90-C225) in a 3-D environment using FaDu and SAS head and neck squamous cell carcinoma (HNSCC) spheroid models and clinically relevant endpoints such as spheroid control probability (SCP) and spheroid control dose 50% (SCD50 , external irradiation dose inducing 50% loss of spheroid regrowth). Spheroids were cultured using a standardized platform. Therapy response after treatment with C225, CHX-A"-DTPA-C225 (DTPA-C225), [(90) Y]Y-CHX-A"-DTPA (Y-90-DTPA) and Y-90-C225 alone or in combination with X-ray was evaluated by long-term monitoring (60 days) of spheroid integrity and volume growth. Penetration kinetics into spheroids and EGFR binding capacities on spheroid cells were identical for unconjugated C225 and Y-90-C225. Spheroid-associated radioactivity upon exposure to the antibody-free control conjugate Y-90-DTPA was negligible. Determination of the SCD50 demonstrated higher intrinsic radiosensitivity of FaDu as compared with SAS spheroids. Treatment with unconjugated C225 alone did not affect spheroid growth and cell viability. Also, C225 treatment after external irradiation showed no additive effect. However, the combination of external irradiation with Y-90-C225 (1 µg/ml, 24 hr) resulted in a considerable benefit as reflected by a pronounced reduction of the SCD50 from 16 Gy to 9 Gy for SAS spheroids and a complete loss of regrowth for FaDu spheroids due to the pronounced accumulation of internal dose caused by the continuous exposure to cell-bound radionuclide upon Y-90-C225-EGFR interaction.

Flow cytometric cell-based assay to preselect antibody constructs for radionuclide conjugation.

Radiolabeled antibodies (Abs) are an attractive tool for targeting and delivering particle emitters for therapy or imaging applications. The labeling of Abs with metal radionuclides requires chelating agents and can cause loss of binding to their ligands. The aim of the present approach was to design an easy-handling flow cytometric cell-based assay to evaluate Ab-binding capacity of conjugates of the therapeutic Ab Cetuximab and to verify the most promising candidate in a competitive radioactive binding experiment. The final setup for flow cytometric assessment of cellular binding capacities of epidermal growth factor receptor (EGFR)/ErbB1-directed Ab conjugates is based on (a) the selection of a robust cell line model (b) the definition of nonsaturated staining concentrations for the unconjugated reference Ab Cetuximab plus implementation of a reasonable isotype control, and (c) the calculation of relative Ab affinities based on the flow cytometric data. Two (FaDu, SAS) out of the three cell lines with different total and cell surface expression levels of EGFR turned out to be adequate models but the application of one cell line was sufficient to estimate reduced binding capacities of conjugates relative to Cetuximab. Only 1/11 conjugate Abs exhibited a fluorescence signal comparable to unconjugated Cetuximab and was applied for radiolabeling with Yttrium-90. Unaltered binding affinity of this conjugate was proven in a competitive radioactive Ab-binding study. We conclude that the flow cytometric assay is reliable and that the relative binding capacity of Cetuximab is neither affected by covalent modification with CHX-A"-DTPA (N-[(R)-2-Amino-3-(p-isothiocyanato-phenyl) propyl]-trans-(S,S)-cyclohexane-1,2-diamine-N,N,N',N",N"-pentaacetic acid) with a final chelator-to-Ab ratio of 5 nor by subsequent radiolabeling. [(90)Y]Y-CHX-A"-DTPA-Cetuximab thus qualifies for preclinical treatment testing as a prerequisite for therapeutic application.

[Molecular signaling pathways. Mechanisms and clinical use]. / Molekulare Signalwege. Mechanismen und klinische Anwendung.

This brief summary on the role of experimental radiation oncology highlights several new research topics and research approaches that offer great potential for the optimization of modern radiation oncology. In addition, many areas of research, such as hypoxia, angiogenesis, the immune system, and metabolism, to name a few, comprise a substantial part of our current knowledge of tumor and radiation biology. Which new insights and therapeutic possibilities via the Human Cancer Genome Project or new processes, such as next generation sequencing may offer, cannot be easily foreseen at present. However, we do know for certain: radiation biology has and will continue to contribute to improvements in radiation oncology.

A 3' UTR transition within DEFB1 is associated with chronic and aggressive periodontitis.

Periodontal diseases are complex inflammatory diseases and affect up to 20% of the worldwide population. An unbalanced reaction of the immune system toward microbial pathogens is considered as the key factor in the development of periodontitis. Defensins have a strong antimicrobial function and are important contributors of the immune system toward maintaining health. Here, we present the first systematic association study of DEFB1. Using a haplotype-tagging single nucleotide polymorphism (SNP) approach, including described promoter SNPs of DEFB1, we investigated the associations of the selected variants in a large population (N=1337 cases and 2887 ethnically matched controls). The 3' untranslated region SNP, rs1047031, showed the most significant association signal for homozygous carriers of the rare A allele (P=0.002) with an increased genetic risk of 1.3 (95% confidence interval: 1.11-1.57). The association was consistent with the specific periodontitis forms: chronic periodontitis (odds ratio=2.2 (95% confidence interval: 1.16-4.35), P=0.02), and aggressive periodontitis (odds ratio=1.3 (95% confidence interval 1.04-1.68), P=0.02). Sequencing of regulatory and exonic regions of DEFB1 identified no other associated variant, pointing toward rs1047031 as likely being the causative variant. Prediction of microRNA targets identified a potential microRNA-binding site at the position of rs1047031.

Integrin-linked kinase interacts with caspase-9 and -8 in an adhesion-dependent manner for promoting radiation-induced apoptosis in human leukemia cells.

Integrin-mediated adhesion of leukemia cells to extracellular matrix proteins reduces apoptosis following radiation-induced genotoxic injury. To evaluate the role of integrin-linked kinase (ILK) in this process, HL60 human acute promyelocytic leukemia cells were stably transfected with ILK wild-type or kinase-hyperactive overexpression vectors. Suspension or fibronectin (FN) adhesion cultures were irradiated with X-rays and processed for measurement of apoptosis, mitochondrial transmembrane potential and caspase activation. Adhesion to FN pronouncedly reduced radiation-induced apoptosis of HL60 cells and vector controls. Intriguingly, overexpressed ILK enhanced apoptosis after irradiation by combined activation of caspase-3 through caspase-8 and -9 in irradiated FN cultures. Irradiation of ILK suspension cultures lacked caspase-8 activation, but showed serial cleavage of caspase-9, -3 and poly (ADP-ribose) polymerase. These findings further characterize the cell death-promoting function of ILK in DNA-damaged cells. Moreover, ILK might represent a potential therapeutic target for innovative chemo- and radiooncological approaches in hematological malignancies.

Human pancreatic tumor cells are sensitized to ionizing radiation by knockdown of caveolin-1.

Caveolin-1 (Cav-1) is an integral transmembrane protein and a critical component in interactions of integrin receptors with cytoskeleton-associated and signaling molecules. Since integrin-mediated cell adhesion generates signals conferring radiation resistance, we examined the effects of small interfering RNA-mediated knockdown of Cav-1 alone or in combination with beta1-integrin or focal adhesion kinase (FAK) on radiation survival and proliferation of pancreatic carcinoma cell lines. Irradiation induced Cav-1 expression in PATU8902, MiaPaCa2 and Panc1 cell lines. The cell lines showed significant radiosensitization after knockdown of Cav-1, beta1-integrin or FAK and cholesterol depletion by beta-cyclodextrin relative to nonspecific controls. Under knockdown conditions, proliferation of non-irradiated and irradiated cells was significantly attenuated relative to controls. These findings correlated with changes in expression or phosphorylation of Akt, glycogen synthase kinase 3beta, Paxillin, Src, c-Jun N-terminal kinase and mitogen-activated protein kinase. Analysis of DNA microarray data revealed a Cav-1 overexpression in a subset of pancreatic ductal adenocarcinoma samples. The data presented show, for the first time, that disruption of interactions of Cav-1 with beta1-integrin or FAK affects radiation survival and proliferation of pancreatic carcinoma cells and suggest that Cav-1 is critical to these processes. These results indicate that strategies targeting Cav-1 may be useful as an approach to improve conventional therapies, including radiotherapy, for pancreatic cancer.

beta1-integrin-mediated signaling essentially contributes to cell survival after radiation-induced genotoxic injury.

Integrin-mediated adhesion to extracellular matrix proteins confers resistance to radiation- or drug-induced genotoxic injury. To analyse the underlying mechanisms specific for beta1-integrins, wild-type beta1A-integrin-expressing GD25beta1A cells were compared to GD25beta1B cells, which express signaling-incompetent beta1B variants. Cells grown on fibronectin, collagen-III, beta1-integrin-IgG or poly-l-lysine were exposed to 0-6 Gy X-rays in presence or depletion of growth factors and phosphatidylinositol-3 kinase (PI3K) inhibitors (LY294002, wortmannin). In order to test the relevance of these findings in tumor cells, human A-172 glioma cells were examined under the same conditions after siRNA-mediated silencing of beta1-integrins. We found that beta1A-integrin-mediated adhesion to fibronectin, collagen-III or beta1-IgG was essential for cell survival after radiation-induced genotoxic injury. Mediated by PI3K, pro-survival beta1A-integrin/Akt signaling was critically involved in this process. Additionally, the beta1-integrin downstream targets p130Cas and paxillin-impaired survival-regulating PI3K-dependent JNK. In A-172 glioma cells, beta1-integrin knockdown and PI3K inhibition confirmed the central role of beta1-integrins in Akt- and p130Cas/paxillin-mediated prosurvival signaling. These findings suggest beta1-integrins as critical regulators of cell survival after radiation-induced genotoxic injury. Elucidation of the molecular circuitry of prosurvival beta1-integrin-mediated signaling in tumor cells may promote the development of innovative molecular-targeted therapeutic antitumor strategies.

Cell adhesion-mediated radioresistance revisited.

PURPOSE: Integrin-mediated adhesion of cells to proteins of the extracellular matrix modulates the cellular response to ionizing radiation in vitro. This mechanism might be in part causative for radiation and chemoresistance phenotypes in tumor cells. MATERIALS AND METHODS: A PubMed database search was performed and the data were summarized with a focus on cell adhesion-mediated radioresistance (CAM-RR). RESULTS: Integrins and their associated downstream signaling pathways as well as cooperative interactions of integrins with receptor tyrosine kinases mediate defensive mechanisms that aggravate the therapeutic eradication of tumor cells by radiotherapy. CONCLUSIONS: A better knowledge of the molecular composition and function of the multiprotein, multifunctional cell-matrix interactions mediating complexes termed focal adhesions may point at significant differences between normal and tumor cells, which could foster the development of novel targeted therapies in radiotherapy.

Targeting of ß1 integrins impairs DNA repair for radiosensitization of head and neck cancer cells.

ß1 Integrin-mediated cell-extracellular matrix interactions allow cancer cell survival and confer therapy resistance. It was shown that inhibition of ß1 integrins sensitizes cells to radiotherapy. Here, we examined the impact of ß1 integrin targeting on the repair of radiation-induced DNA double-strand breaks (DSBs). ß1 Integrin inhibition was accomplished using the monoclonal antibody AIIB2 and experiments were performed in three-dimensional cell cultures and tumor xenografts of human head and neck squamous cell carcinoma (HNSCC) cell lines. AIIB2, X-ray irradiation, small interfering RNA-mediated knockdown and Olaparib treatment were performed and residual DSB number, protein and gene expression, non-homologous end joining (NHEJ) activity as well as clonogenic survival were determined. ß1 Integrin targeting impaired repair of radiogenic DSB (γH2AX/53BP1, pDNA-PKcs T2609 foci) in vitro and in vivo and reduced the protein expression of Ku70, Rad50 and Nbs1. Further, we identified Ku70, Ku80 and DNA-PKcs but not poly(ADP-ribose) polymerase (PARP)-1 to reside in the ß1 integrin pathway. Intriguingly, combined inhibition of ß1 integrin and PARP using Olaparib was significantly more effective than either treatment alone in non-irradiated and irradiated HNSCC cells. Here, we support ß1 integrins as potential cancer targets and highlight a regulatory role for ß1 integrins in the repair of radiogenic DNA damage via classical NHEJ. Further, the data suggest combined targeting of ß1 integrin and PARP as promising approach for radiosensitization of HNSCC.

Fibronectin alters cell survival and intracellular signaling of confluent A549 cultures after irradiation.

Cell-cell and cell-extracellular matrix contacts influence cellular sensitivity to ionizing radiation. To further define the influence of these interactions on tumor cell survival and cell cycle progression after irradiation without or in combination with the phorbol ester phorbol-12-myristate-13-acetate (PMA), the radiation response of p53 wild-type A549 lung cancer cells grown on polystyrene, fibronectin (FN) or BSA was examined. Confluently growing and log-phase A549 cell cultures irradiated on FN showed significantly greater survival compared to cells irradiated on polystyrene or BSA. There was a significantly greater elevation of G(2)/M cells in FN cultures after irradiation compared to other culture conditions. PMA reduced radiation survival on all three substrata and under both log-phase and confluent culture conditions, but had no effect on the elevation of G(2)/M cells in FN cultures. Induction of Chk1 phosphorylation by irradiation was only seen in FN cultures. Chk2 and Cdk1 phosphorylation and Cdc25C expression also differed between FN and polystyrene cultures. Induction of p53 and p21 by irradiation was modulated but not inhibited by PMA, as were changes in cyclin D1 and pRb. Changes in protein expression and phosphorylation of these cell cycle regulatory proteins coincided tightly with accumulation of cells in G(2)/M after irradiation. These findings clearly demonstrate the influence of both intercellular and cell-substratum interactions on the radiation response without or in combination with PMA and differentiate between the cell survival and cell cycle effects of FN attachment.

Investigation of microvessel density after irradiation.

It is believed that malignant cell populations need the development of microvessels to grow and metastasize. The aim of our investigation was to find out whether gamma irradiation can affect proliferation of endothelial cells and thus can affect microvessel density in vivo. We used fertilized chicken eggs. The vascularized part of the yolk sac membrane (area vasculosa) of the eggs received single doses of 2 to 10 Gy. Forty-eight hours after irradiation, the area vasculosa was photographed in vivo, and prints of known magnification were evaluated to determine the density of the blood vessels. Microvessel count is the well-established marker used to determine vascular density. In addition, the proliferative activity of endothelial cells in the yolk sac membrane was determined by estimating the expression of proliferating cell nuclear antigen (PCNA). PCNA immunostaining was assessed immunohistochemically. After a single dose of 10 Gy, a statistically significant increase in vascular density was found compared to values determined at 0, 2, 4 and 8 Gy (P < 0.05). Twenty-four hours after 10 Gy irradiation, 44.8% (mean) of the endothelial cells were PCNA-positive. This was significantly higher (P < 0.05) compared to the results 24 h after 4.0 Gy (22.7%) and compared to control (19.4%). Twenty-four hours later, i.e. 48 h after irradiation with 10 Gy, the endothelial cells also showed a significantly (P < 0.05) higher PCNA positivity with a mean of 34.1% compared to the nonirradiated area vasculosa (18.1%) and compared to the results after 4.0 Gy irradiation (12.0%). The prerequisite for blood vessel formation is the proliferation of endothelial cells. Thus a single-dose irradiation with 10 Gy induces endothelial cell proliferation and subsequent neovascularization in the area vasculosa of the fertilized egg.

Cell line and schedule-dependent cytotoxicity of paclitaxel (Taxol): role of the solvent Cremophor EL/ethanol.

BACKGROUND: Paclitaxel's optimal dosage and scheduling is currently not determined. To compare paclitaxel (PTX) cytotoxicity in vitro, three cell lines were chosen for investigation by single versus fractionated exposure to Taxol and the diluent Cremophor EL/ethanol (CEL/eth). METHODS: An exponentially growing human lung-carcinoma (SK-LU-1), human glioblastoma (U-138 MG) and mammalian fibroblast cell line (HyB14FAF28) were used for colony forming assay examining cell survival, and flow cytometric DNA analysis by measuring cell cycle development. Tested concentrations varied from 2-50 microM and were incubated for 3 and 15 hours. Single (2-50 microM/d, especially 10 microM/d), versus fractionated (2 microM/d, day 1-5) exposure of Taxol and CEL/eth was investigated. As the control population, cells were exposed to a phosphate buffered solution (PBS). RESULTS: Control populations demonstrated an average survival of 90, 99 and 93% for SK-LU-1, U-138 MG, B14, respectively. Single Taxol exposure at 10 microM showed average survival of 54, 50 and 84% after 3 hours and 9, 48 and 82% after 15 hours for the above cell lines. Fractionated Taxol exposure with 2 microM/d, days 1-5 led to average survival of 55, 86 and 63%, respectively. Single CEL/eth exposure showed a cytotoxic effect with average survival of 94, 126 and 91% after 3 hours and 47, 63 and 88% after 15 hours respectively. Fractionated CEL/eth exposure showed an average survival of 67, 94 and 65% respectively. Flow cytometric analysis detected cell cycle shift concerning S- and G2/M-phase after Taxol exposure only in the two tumour cell lines, and not in the fibroblastic cells. CEL/eth was without significant effect on cell cycle distribution in all three cell lines. CONCLUSIONS: In the two human tumour cell lines cytotoxicity was more pronounced after prolonged Taxol exposure. The fibroblast cell line was not sensitive to single treatment, and was without cell cycle changes. Comparable to Taxol the diluent CEL/eth had a significant but less pronounced cytotoxic effect. Therefore, the cytotoxic mechanisms of paclitaxel's and CEL/eth's are worthy of further investigation.

Microvessel density and endothelial cell proliferation after amifostine (Ethyol) administration in vivo.

BACKGROUND: As amifostine is rapidly metabolised by the membrane-bound and capillary alkaline phosphatase to the active metabolite WR-1065, microvessel density in normal and cancer tissue may influence the therapeutic potential of the pro-drug WR-2721. Thus, it is of interest how the administration of amifostine itself alters vascular density. MATERIALS AND METHOD: For this study fertilized eggs were used and 0.05 ml amifostine (25.7 micrograms) was injected into the area vasculosa. As controls untreated area vasculosa were examined as well as eggs treated with 0.05 ml NaCl 0.9%, 48 hr after injection the vascular density was determined by histometrical methods. Applying the LAB method we performed immunohistochemical analysis of the proliferating cell nuclear antigen of endothelial cells. RESULTS: There was a significant (p < 0.001) difference in vascular density with a mean microvessel count of 25.08 (+/- 8.45 SD) vascular intersections/mm2 in the untreated control, 30.40 (+/- 12.84 SD) in the NaCl control and 53.69 (+/- 24.56 SD) in the amifostine treated area. There was also a significant (p < 0.001) difference in endothelial cell proliferation (PCNA) between untreated controls with a mean PCNA positivity of 14.05 (+/- 5.28 SD) and amifostine treated area vasculosa with a mean PCNA positivity of 32.22 (+/- 18.14 SD). CONCLUSION: A single dose administration of 25.7 micrograms amifostine induces endothelial cell proliferation and subsequent neovascularisation in the area vasculosa of the fertilised egg.

Ionizing radiation modules of the expression and tyrosine phosphorylation of the focal adhesion-associated proteins focal adhesion kinase (FAK) and its substrates p130cas and paxillin in A549 human lung carcinoma cells in vitro.

PURPOSE: Focal adhesion kinase (FAK) is involved in the regulation of many cellular processes, including cell survival and death, proliferation and migration. The same endpoints are influenced by ionizing radiation (IR). Therefore, study was performed to determine the effect of IR on the expression and phosphorylation of FAK and two of its substrates, p130cas and paxillin, in vitro. MATERIALS AND METHODS: Exponentially growing A549 lung carcinoma cells were exposed to 6 Gy X-rays. Protein expression and the extent of tyrosine phosphorylation were investigated by immunoprecipitation experiments and Western blotting analysis using specific or unspecific phosphotyrosine antibodies. Immunofluorescence staining in combination with confocal laser scanning microscopy was done to localize the proteins within the cell. RESULTS: Tyrosine phosphorylation, of Mr 110 000 150 000 and 65 000-75 000 protein bands, was induced within 30 min after exposure to IR. Three of these proteins were identified as FAK, p130cas and paxillin. IR induced phosphorylation of FAK (tyr397 and tyr925) but did not change FAK expression. Additionally, IR induced phosphorylation of paxillin (tyr31 and tyr181) within 30 min and an up-regulation of paxillin expression 2-6 h after exposure. Furthermore, a higher amount of phosphorylated p130cas was found in irradiated cells. Immunofluorescence staining demonstrated that in A549 cells, all three proteins colocalize at sites of focal adhesions at the cytoplasmic face of the cell membrane and to lamellopodia. CONCLUSIONS: The data indicate that these focal adhesion-associated proteins are modulated by IR and thus are likely to play a role in the cellular response to IR. These proteins might represent attractive targets to modulate FAK-initiated signalling pathways, which may be involved in improved radioresistance and, furthermore, in important pathological phenomena such as tumour growth and metastatic phenotypes.

Ukrain, an alkaloid thiophosphoric acid derivative of Chelidonium majus L. protects human fibroblasts but not human tumour cells in vitro against ionizing radiation.

PURPOSE: Ukrain, an alkaloid thiophosphoric acid derivative of Chelidonium majus L., has demonstrated a promising impact on chemotherapy in a variety of malignancies. The effects of the drug on cell survival, alteration of the cell cycle and induction of apoptosis were examined without and in combination with ionizing radiation (IR). The TP53 status of the cell lines used was also investigated. MATERIALS AND METHODS: Exponentially growing human tumour cell lines MDA-MB-231 (breast), PA-TU-8902 (pancreas), CCL-221 (colorectal), U-138MG (glioblastoma), and human skin and lung fibroblastic cells, HSF1, HSF2 and CCD32-LU were studied by colony assay, flow cytometry (cell-cycle, annexin-V staining for apoptosis) and Western blotting. Ukrain was used in concentrations from 0.1 to 50 microg ml(-1) for 1, 3 and 24 h and radiation as single doses of 1-10Gy. Combined drug-radiation exposure employed 1 microg ml(-1) Ukrain for 24h plus 2-8 Gy. RESULTS: Ukrain cytotoxicity was time- and dose-dependent. The combination of Ukrain plus IR gave enhanced toxicity in CCL-221 and U-138MG cells, but not in MDA-MB-231 and PA-TU-8902 cells. Most strikingly, a radioprotective effect was found in normal human skin and lung fibroblasts. Flow-cytometry analyses supported the differential and cell line-specific cytotoxicity of Ukrain. CCL-221 and U-138MG cells accumulated in G2 after 24-h Ukrain treatment, whereas no alterations were detected in the other tumour cells and normal fibroblasts tested. Western blotting of TP53 demonstrated non-functional overexpression in all tumour cell lines without affecting p21. HSF1 presented wild-type TP53 and a p21 response after IR. Flowcytometric analyses of annexin-V staining showed no induction of apoptosis after Ukrain treatment in comparison with untreated controls. CONCLUSIONS: Differential effects of Ukrain in modulating radiation toxicity of human cancer cell lines and its protective effect in normal human fibroblasts suggest that this alkaloid may have potential properties for clinical radiochemotherapy.

Ionizing radiation induces up-regulation of functional beta1-integrin in human lung tumour cell lines in vitro.

PURPOSE: Cell-matrix interactions are in part mediated through the beta1-integrin pathway regulating cell survival, proliferation, adhesion and migration. This study was performed to elucidate alterations of expression of the beta1-integrin and its co-localized protein kinase, integrin-linked kinase (ILK), after exposure to ionizing radiation in two lung carcinoma cell lines in the presence or absence of different beta1-integrin-dependent matrix proteins. MATERIALS AND METHODS: Exponentially growing A549 and SKMES1 cells grown on fibronectin, laminin, BSA or plastic were exposed to 2 Gy or 6 Gy. Besides colony formation assays (0.5-8 Gy) and immediate plating experiments, flow cytometry (for beta1-integrin) and immunoblotting (for beta1-integrin and ILK) were carried out to analyze the protein expression. The localization of both proteins plus filamentous (f-) actin was further examined by immunofluorescence staining and laser confocal scanning microscopy. Functionality of the beta1 receptor subunit after irradiation was investigated in adhesion assays. RESULTS: A549 and SKMES1 cells grown on fibronectin or laminin demonstrated a significant increase in cell survival after irradiation compared to cells grown on BSA or plastic. Immediate plating of cells after irradiation on fibronectin did not show an improved survival. Flow cytometric and Western blot data showed a dose- and matrix-dependent induction of beta1-integrin and ILK expression after irradiation within 48 h. Adhesion to fibronectin or laminin compared to BSA or plastic was increased by 10-fold after irradiation, demonstrating these specific cell surface receptors to be functional. The staining of beta1-integrin and ILK in A549 cells confirmed the radiation-induced up-regulation of both proteins. Additionally, beta1-integrin and ILK co-localized with accumulated actin fibers at the cytoplasmic face of the cell membrane at confined areas. CONCLUSIONS: Ionizing radiation strongly induced the expression of functional beta1-integrin and ILK in the two lung cancer cell lines, A549 and SKMES1, dependent on different matrices used. Additionally, the subcellular localization of both proteins was altered by irradiation, and the individual cellular radiosensitivity was reduced in the presence of an extracellular matrix. On the one hand, this may result in aggravated therapeutic approaches and on the other hand, cells could adhere more strongly in their environment by the increase in functional surface receptor density preventing metastasis. Concerning intravascular located tumour cells, beta1-integrin up-regulation might enable these cells to adhere to the endothelium, which represents a prerequisite for metastatic disease. Identification of such mechanisms will provide considerable insights into the understanding of tumorigenicity and metastatic phenotypes, possibly leading to new, optimized radiochemotherapeutic regimens.

Fibronectin and laminin increase resistance to ionizing radiation and the cytotoxic drug Ukrain in human tumour and normal cells in vitro.

PURPOSE: Cell-extracellular matrix (ECM) interactions are thought to mediate drug and radiation resistance. Dependence of cell survival, beta1-integrin expression and cell cycling on the ECM proteins and beta1-integrin ligands fibronectin (FN) and laminin (LA) were examined in malignant and normal cells exposed to the cytotoxic drug Ukrain plus/minus irradiation. MATERIALS AND METHODS: Human A549 lung cancer and MDAMB231 (MDA231) breast cancer cells and normal fibroblasts (HSF1) grown on FN, LA, bovine serum albumin (BSA) or polystyrene were treated with Ukrain (1 microg ml(-1), 24 h) plus/minus irradiation (2-8 Gy) and the effects studied using colony formation assays, flow cytometry (beta1-integrin, DNA analysis) and adhesion assays. RESULTS: FN and LA reduced the cytotoxic effect of single Ukrain treatment compared with polystyrene and BSA. FN and LA also abolished Ukrain-dependent radiosensitization in A549 cells and decreased the radiosensitivity of MDA231 and HSF1 cells. Single Ukrain exposure on polystyrene significantly reduced beta1-integrin expression and promoted G2-phase accumulation of A549 cells. In contrast, Ukrain-treated MDA231 and HSF1 cells showed elevated beta1-integrin expression and no Ukrain-specific cell cycle effect. Under Ukrain-radiation exposure, irradiation, FN or LA abolished Ukrain-mediated reduction of beta1-integrin expression and G2-phase accumulation in A549 cells, whereas in MDA231 cells and fibroblasts beta1-integrin expression and cell cycle distribution were stabilized. Cell adhesion to FN or LA was significantly impaired (A549) or improved (MDA231, HSF1) upon Ukrain treatment. CONCLUSIONS: The data corroborate the findings of other groups that cell adhesion-mediated resistance to either single or combined drug and radiation exposure is tightly correlated to specific ECM proteins. By demonstrating a strong modulatory impact of FN and LA on the radiosensitivity-modifying activity of the drug Ukrain, the set findings are also highly important for the assessment of drug and radiation effects within in vitro cytotoxicity studies. The data give the first mechanistic insights into specific FN- and LA-modulated cellular resistance mechanisms as well as into the important role for beta1-integrins using the unique cytotoxic and radiosensitivity-modifying drug Ukrain.

APPL proteins modulate DNA repair and radiation survival of pancreatic carcinoma cells by regulating ATM.

Despite intensive multimodal therapies, the overall survival rate of patients with ductal adenocarcinoma of the pancreas is still poor. The chemo- and radioresistance mechanisms of this tumor entity remain to be determined in order to develop novel treatment strategies. In cancer, endocytosis and membrane trafficking proteins are known to be utilized and they also critically regulate essential cell functions like survival and proliferation. On the basis of these data, we evaluated the role of the endosomal proteins adaptor proteins containing pleckstrin homology domain, phosphotyrosine binding domain and a leucine zipper motif (APPL)1 and 2 for the radioresistance of pancreatic carcinoma cells. Here, we show that APPL2 expression in pancreatic cancer cells is upregulated after irradiation and that depletion of APPL proteins by small interfering RNA (siRNA) significantly reduced radiation survival in parallel to impairing DNA double strand break (DSB) repair. In addition, APPL knockdown diminished radiogenic hyperphosphorylation of ataxia telangiectasia mutated (ATM). Activated ATM and APPL1 were also shown to interact after irradiation, suggesting that APPL has a more direct role in the phosphorylation of ATM. Double targeting of APPL proteins and ATM caused similar radiosensitization and concomitant DSB repair perturbation to that observed after depletion of single proteins, indicating that ATM is the central modulator of APPL-mediated effects on radiosensitivity and DNA repair. These data strongly suggest that endosomal APPL proteins contribute to the DNA damage response. Whether targeting of APPL proteins is beneficial for the survival of patients with pancreatic adenocarcinoma remains to be elucidated.

Cell adhesion to the extracellular matrix protein fibronectin modulates radiation-dependent G2 phase arrest involving integrin-linked kinase (ILK) and glycogen synthase kinase-3beta (GSK-3beta) in vitro.

Cell adhesion to extracellular matrix (ECM) is thought to confer resistance against cell-damaging agents, that is, drugs and radiation, in tumour and normal cells in vitro. The dependence of cell survival on beta1-integrin-linked kinase (ILK), protein kinase Balpha/Akt (PKBalpha/Akt) and glycogen synthase kinase-3beta (GSK-3beta) activity, which participate in beta1-integrin signalling and cell cycle progression was investigated as a function of radiation exposure. Colony-formation assays on polystyrene, fibronectin (FN), laminin (LA), bovine serum albumin (BSA) or poly-L-lysine (poly-L) (0-8 Gy), kinase assays, flow cytometric DNA and annexin-V analysis and immunoblotting were performed in nonirradiated and irradiated (2 or 6 Gy) A549 human lung cancer cells and CCD32 normal human lung fibroblasts. Cell contact to FN in contrast to polystyrene elevated basal ILK, PKBalpha/Akt and GSK-3beta kinase activities in A549 and CCD32 cells, as well as the basal amount of A549 G2 phase cells. Irradiation on FN or LA as compared to polystyrene, BSA or poly-L significantly improved cell survival. Following irradiation, kinase activities were stimulated strongly on polystyrene but showed to be less prominent on FN, which was because of the FN-related basal induction. Following irradiation, FN compared to polystyrene enlarged and prolonged G2 arrest in both the cell lines. For the analysis of phosphatidylinositol-3 kinase (PI3-K) dependence of protein kinases and cell cycle transition, the PI3-K inhibitors LY294002 and wortmannin were used showing decreased kinase activities, antiproliferative and radiation-dependent G2 accumulation-abrogating effects accompanied by downregulation of cyclin D1 and phospho-pRb in cells attached to polystyrene. Fibronectin partly abrogated these effects PI3-K-independently. These findings suggest a novel pathway that makes direct phosphorylation of GSK-3beta by ILK feasible after irradiation. Conclusively, the data indicate that ILK, PKBalpha/Akt and GSK-3beta are involved in modulations of the cell cycle after irradiation. These interactions are strictly dependent on ECM components in a cell line-specific manner. Our findings provide molecular insights into mechanisms likely to be important for ECM-dependent cell survival and cellular radioresistance as well as tumour growth.

Interaction of paclitaxel (Taxol) and irradiation. In-vitro differences between tumor and fibroblastic cells.

AIM: Optimal dose and schedule of paclitaxel in combined drug-irradiation treatment could not be determined for most of tumors yet. The aim of this study was to compare in vitro cytotoxicity and radiosensitizing abilities as a function of single paclitaxel (Taxol) exposure in tumor and fibroblastic cells using different drug incubation irradiation intervals. MATERIAL AND METHOD: A lung-carcinoma (SK-LU-1), glioblastoma (U-138 MG) and rodent fibroblast cell line (HyB14FAF28) were used. The clonogenic assay was applied for survival investigation. alpha beta-values were calculated using the linear-quadratic model (log S = -alpha D - beta D2). Cytotoxicity of Taxol was examined at 0 to 50 microM. Combined Taxol-radiotherapy exposure was accomplished with 10 microM Taxol plus 10 Gy irradiation (RT) following after a 1-hour and 9-hour interval. For controls cells were exposed to Cremophor EL/ethanol (CEL/eth) and a phosphate buffered saline (PBS). RESULTS: Single Taxol exposure (10 microM) resulted in 0.54/0.50/0.84 (3-hours incubation) and 0.094/0.48/0.82 (15-hours incubation) survival of SK-LU-1, U-138 MG and HyB14FAF28 cells, respectively. Taxol concentrations from 2 to 50 microM only had cytotoxic effect in tumor cells. Single dose RT (10 Gy) led to cell survival of 0.0006/0.006/0.03. The diluent CEL/eth also showed cytotoxic activity. Taxol plus RT led to cell survival of 0.00025/0.0014/0.042 (1 hour) and 0.0004/0.0019/0.04 (9 hours) without significant difference between chosen time intervals. alpha beta-values showed great variation lacking evidence for definite radiosensitization. alpha increase after Taxol and alpha decrease after CEL/eth exposure were detected. CONCLUSIONS: The data presented demonstrate a potential beneficial effect, described as co-operation, by combining Taxol and RT in human tumor cells and rodent fibroblasts. High intrinsic alpha components of the tumor cells as well as CEL/eth's antagonizing actions could be likely to disturb and influence paclitaxel's abilities leading to radiosensitization.