Biomedical subjects

Martin Pruschy

Publications and source records attributed to Martin Pruschy.

8 recordsLinked to original sources

PubMed2006

Ionizing radiation antagonizes tumor hypoxia induced by antiangiogenic treatment.

PURPOSE: The combined treatment modality of ionizing radiation with inhibitors of angiogenesis is effective despite the supposition that inhibition of angiogenesis might increase tumor hypoxia and thereby negatively affect radiation sensitivity. To directly assess this still controversial issue, we analyzed treatment-dependent alterations of tumor oxygenation in response to inhibition of angiogenesis alone, ionizing radiation, and combined treatment. EXPERIMENTAL DESIGN: Serial measurements with high-resolution [18F]fluoromisonidazole positron emission tomography and immunohistochemical detection of the endogenous hypoxia marker glucose transporter-1 were done to determine tumor hypoxia in a murine mammary carcinoma allograft model. RESULTS: Inhibition of angiogenesis with the clinically relevant vascular endothelial growth factor receptor tyrosine kinase inhibitor PTK787/ZK222584 reduced microvessel density but had only minimal effects on tumor growth, tumor cell apoptosis, and proliferation. However, PTK787/ZK222584 treatment increased overall and local tumor hypoxia as revealed by extended expression of the hypoxia marker glucose transporter-1 and increased uptake of [18F]fluoromisonidazole. Fractionated irradiation induced a strong growth delay, which was associated with enhanced apoptosis and reduced proliferation of tumor cells but only minor effects on microvessel density and allograft oxygenation. Combined treatment with fractionated irradiation resulted in extended tumor growth delay and tumor cell apoptosis but no increase in tumor hypoxia. CONCLUSIONS: These results show that irradiation antagonizes the increase of hypoxia by vascular endothelial growth factor receptor tyrosine kinase inhibition and abrogates the potential negative effect on tumor hypoxia. Thus, the risk of treatment-induced hypoxia by inhibitors of angiogenesis exists but is kept minimal when combined with a cytotoxic treatment modality.

Animals↗

PubMed2005

G2/M cell cycle checkpoint is functional in cervical cancer patients after initiation of external beam radiotherapy.

PURPOSE: To investigate changes in cancer of the uterine cervix during radiotherapy (RT) with respect to G2/M transition in relation to tumor cell apoptosis and changes in the tumor vasculature in cervical carcinoma. METHODS AND MATERIALS: A total of 40 consecutive patients with Stage IIA-IIIB cervical cancer underwent RT without any chemotherapy. Tumor biopsy was obtained before RT and after five fractions of 1.8 Gy. The tumor samples were stained for cyclin B1, cdc2, and Ki-67, the apoptotic index, using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling staining. The tumor vasculature density was assessed. In 38 cases, the tissue samples were informative. RESULTS: Cyclin B1 was positive in all biopsies before and after initiation of RT, and staining for cdc2 was positive in 35 (92%) of 38 biopsies before and 33 (87%) of 38 after 1 week of RT. Nuclear staining for cyclin B1 was observed in 92% of patients, staining an average of 15% of cells before RT. After initiating RT, 73% of patients showed positive staining on about 5% of tumor cells (p < 0.01). Nuclear staining for cdc2 was detected in 89% of patients, staining an average of 21% of cells before RT. After initiating RT, 79% of patients showed positive staining on 9% of cells (p < 0.01). The apoptotic index of the tumor cells increased after initiating RT, and a slight decrease in the vascular density after 1 week of RT was noted (p = 0.08). Changes in G2/M were associated with the clinical response, but changes in apoptosis or tumor vasculature were not. CONCLUSION: RT leads to significant changes in the cell cycle in cervical cancer indicating intact G2/M checkpoint function. Targeting G2/M with compounds interfering with G2/M transition may further enhance the effect of RT in cervical cancer patients.

Adult↗

PubMed2005

Patupilone acts as radiosensitizing agent in multidrug-resistant cancer cells in vitro and in vivo.

Interference with microtubule function is a promising antitumoral concept. Paclitaxel is a clinically validated tubulin-targeting agent; however, treatment with paclitaxel is often limited by taxane-related toxicities and is ineffective in tumors with multidrug-resistant cells. Patupilone (EPO906, epothilone B) is a novel non-taxane-related microtubule-stabilizing natural compound that retains full activity in multidrug-resistant tumors and is clinically less toxic than paclitaxel. Here we have investigated the effect of combined treatment with ionizing radiation and patupilone or paclitaxel in the P-glycoprotein-overexpressing, p53-mutated human colon adenocarcinoma cell line SW480 and in murine, genetically defined E1A/ras-transformed paclitaxel-sensitive embryo fibroblasts. Patupilone and paclitaxel alone and in combination with ionizing radiation reduced the proliferative activity of the E1A/ras-transformed cell line with similar potency in the sub and low nanomolar range. SW480 cells were only sensitive to patupilone, and combined treatment with low-dose patupilone (0.1 nmol/L) followed by clinically relevant doses of ionizing radiation (2 and 5 Gy) resulted in a supra-additive cytotoxic effect. Inhibition of the drug efflux protein P-glycoprotein with verapamil resensitized SW480 cells to treatment with low doses of paclitaxel alone and in combination with IR. In tumor xenografts derived from SW480 cells a minimal treatment regimen with patupilone and fractionated irradiation (1 x 2 mg/kg plus 4 x 3 Gy) resulted in an at least additive tumor response with extended tumor growth arrest. Analysis by flow cytometry in vitro revealed an apoptosis- and G(2)-M-independent mode of radiosensitization by patupilone. Interestingly though, a transient accumulation of cells in S phase was observed on combined treatment.Overall, patupilone might be a promising alternative in paclitaxel-resistant, P-glycoprotein-overexpressing tumors for a combined treatment regimen using ionizing radiation and a microtubule inhibitor.

ATP Binding Cassette Transporter, Subfamily B↗

PubMed2004

Differential activation of the phosphatidylinositol 3'-kinase/Akt survival pathway by ionizing radiation in tumor and primary endothelial cells.

Ionizing radiation induces an intracellular stress response via activation of the phosphatidylinositol 3'-kinase (PI3K)/Akt survival pathway. In tumor cells, the PI3K/Akt pathway is induced through activation of members of ErbB receptor tyrosine kinases. Here, we investigated the receptor dependence of radiation-induced PI3K/Akt activation in tumor cells and in endothelial cells. The integrity of both the ErbB and the vascular endothelial growth factor (VEGF) ligand-activated PI3K/Akt pathway in endothelial cells was demonstrated using specific ErbB and VEGF receptor tyrosine kinase inhibitors. Irradiation of endothelial cells resulted in protein kinase B (PKB)/Akt activation in a similar time course as observed in response to VEGF. More importantly, radiation-induced PKB/Akt phosphorylation in endothelial cells was strongly down-regulated by the VEGF receptor tyrosine kinase inhibitor, whereas the ErbB receptor tyrosine kinase inhibitor did not affect PKB/Akt stimulation in response to irradiation. An opposite receptor dependence for radiation-induced PKB/Akt phosphorylation was observed in ErbB receptor-overexpressing A431 tumor cells. Furthermore, direct VEGF receptor phosphorylation was detected after irradiation in endothelial cells in absence of VEGF, which was almost completely inhibited after irradiation in presence of the VEGF receptor tyrosine kinase inhibitor. These data demonstrate that ionizing radiation induces VEGF ligand-independent but VEGF receptor-dependent PKB/Akt activation in endothelial cells and that PI3K/Akt pathway activation by radiation occurs in a differential cell type and receptor-dependent pattern.

Cell Survival↗

PubMed2004

Degradation of PKB/Akt protein by inhibition of the VEGF receptor/mTOR pathway in endothelial cells.

An intact VEGF receptor/PI3K/PKB/Akt signaling cascade protects endothelial cells from apoptotic stress-stimuli and mediates the formation of new blood vessels in pathological conditions such as cancer. Therefore, downregulation of this signaling cascade is of clinical interest for antiangiogenic cancer therapy. In this report, we demonstrate that VEGF controls the protein stability of the serine-threonine kinase PKB/Akt via inhibition of PKB/Akt protein degradation. VEGF deprivation or blockage of the VEGF signal transduction cascade with the VEGF receptor tyrosine kinase inhibitor PTK787/ZK222584 resulted in a specific decrease of the PKB/Akt protein level and subsequent cellular restimulation with VEGF rescued its stability. Real-time quantitative RT-PCR analysis demonstrated that VEGF does not regulate PKB/Akt gene expression. On the other hand, broad range inhibitors of caspases and the proteasome complex prevented VEGF-dependent downregulation of the PKB/Akt protein level indicating that PKB/Akt protein stability is regulated by VEGF-controlled proteolysis. Inhibition of the VEGF receptor and PKB/Akt-downstream PIK-related mTOR-kinase by rapamycin also neutralized the VEGF-protective effect in an PKB/Akt gene expression-independent way but results in proteolysis-dependent reduction of PKB/Akt protein stability. These results demonstrate a novel regulatory mechanism of the activated VEGF receptor/mTOR-signal transduction pathway to control the protein stability of PKB/Akt and survival threshold in endothelial cells.

Caspase Inhibitors↗

PubMed2004

Novel radiosensitizers for locally advanced epithelial tumors: inhibition of the PI3K/Akt survival pathway in tumor cells and in tumor-associated endothelial cells as a novel treatment strategy?

In locally advanced epithelial malignancies, local control can be achieved with high doses of radiotherapy (RT). Concurrent chemoradiotherapy can improve tumor control in selected solid epithelial adult tumors; however, treatment-related toxicity is of major concern and the therapeutic window often small. Therefore, novel pharmacologic radiosensitizers with a tumor-specific molecular target and a broad therapeutic window are attractive. Because of clonal heterogeneity and the high mutation rate of these tumors, combined treatment with single molecular target radiosensitizers and RT are unlikely to improve sustained local tumor control substantially. Therefore, radiosensitizers modulating entire tumor cell survival pathways in epithelial tumors are of potential clinical use. We discuss the preclinical efficacy and the mechanism of three different, potential radiosensitizers targeting the PTEN/PI3K/Akt survival pathway. These compounds were initially thought to act as single-target agents against growth factor receptors (PKI 166 and PTK 787) or protein kinase C isoforms (PKC 412). We describe an additional target for these compounds. PKI 166 (an epidermal growth factor [EGF] receptor inhibitor) and PKC 412, target the PTEN/PI3K/Akt pathway mainly in tumor cells, and PTK 787 (a vascular endothelial growth factor [VEGF] receptor inhibitor) in endothelial cells. Even for these broader range molecular radiosensitizers, the benefit could be restricted to human epithelial tumor cell clones with a distinct molecular profile. Therefore, these potential radiosensitizers have to be carefully tested in specific model systems before introduction in early clinical trials.

Cell Survival↗

PubMed2004

Apoptosis-modulating agents in combination with radiotherapy-current status and outlook.

PURPOSE: To increase the therapeutic efficacy of ionizing radiation or to reduce radiation-mediated side effects, diverse research centers for translational radiation oncology have headed for a specific modulation of defined cellular death pathways. In this regard, several signaling systems have proved to be of high potential value. RESULTS: It has previously been shown that apoptotic pathways induced by ionizing radiation are distinct from death pathways triggered by death ligands such as tumor necrosis factor-related apoptosis-inducing ligand (TRAIL). The combination of both radiation and TRAIL was highly efficient in vitro and in preclinical mouse models. However, several aspects of normal tissue toxicity have not been solved, and no Phase I data are available yet. A second approach tested in a Phase I trial is based on the observation that synthetic phospholipid derivatives (alkyllysophospholipids and alkylphosphocholines) strongly enhance apoptotic effects by modulating the balance among the mitogenic, anti-apoptotic MAPK, phosphatidylinositol 3'-kinase (PI3K)/Akt, and the pro-apoptotic SAPK/JNK signaling pathways. Furthermore, others have provided evidence that inhibition of anti-apoptotic signals generated by mitogenic stimuli may increase radiation responses. In this context, controversial data are available regarding the influence of a pharmacologic abrogation of MEK1, Erk1/2 signaling on apoptotic sensitivity but no Phase I trials of MEK inhibitors either alone or in combination with radiation have yet been published. However, inhibition of the PI3K/Akt survival pathway using compounds such as the protein kinase C (PKC) inhibitor PKC412 has been shown to induce apoptosis or to increase the apoptotic sensitivity of tumor cells. Therefore, these drugs may be used alone or in combination with radiation to increase tumor control; however, Phase I data are lacking. Several other drugs, including cyclooxygenase-2 inhibitors, betulinic acid, and proteasome inhibitors, have been shown to interact with apoptotic signal transduction. Again, most of the drugs have not been tested in combination with radiation in vivo or-in the case of cyclooxygenase-2 inhibitors-exert pleiotropic effects. CONCLUSION: Although the examples do not reflect all available strategies, it is clear that several promising approaches targeting defined cell death pathways have been developed and entered into clinical trials. The use of synthetic phospholipid derivatives in a Phase I trial is an important example, proving that basic research in radiation biology finally guides the development of new treatment strategies. This, and other approaches, will hopefully increase tumor control rates and reduce side effects in the future.

Apoptosis↗

PubMed2004

Profiling treatment-specific post-translational modifications in a complex proteome with subtractive substrate phage display.

Proteolytic activation of zymogens or controlled degradation of inhibitory factors is part of a major regulatory system on the post-translational level to regulate treatment induced cellular stress responses. The identification of differential activity based substrates is thus of high interest to prioritize and validate candidate targets for drug discovery. Here we present a novel subtractive substrate phage display screening method for the selection of treatment induced post-translational peptide modifications in complex proteomes. We investigated this approach with tumor cells in response to a protease activating anticancer treatment modality using subtractive and iterative screening of cellular extracts derived from control and treated cells. Specific phage were identified that served as substrates for proteolytic activities in response to treatment related activity changes and could be distinguished from substrates for unspecific proteolytic background activities. Novel, selected peptide substrates were investigated in vitro and in vivo and showed high substrate specificity and functional biological significance.

Amino Acid Sequence↗