Biomedical subjects

Klaus Strebhardt

Publications and source records attributed to Klaus Strebhardt.

31 records · Page 2Linked to original sources

PubMed2004

Highly specific HER2-mediated cellular uptake of antibody-modified nanoparticles in tumour cells.

Nanoparticles represent useful drug delivery systems for the specific transport of drugs to tumour cells. In the present study biodegradable nanoparticles based on gelatin and human serum albumin (HSA) were developed. The surface of the nanoparticles was modified by covalent attachment of the biotin-binding protein NeutrAvidin enabling the binding of biotinylated drug targeting ligands by avidin-biotin-complex formation. Using the HER2 receptor specific antibody trastuzumab (Herceptin) conjugated to the surface of these nanoparticles, a specific targeting to HER2-overexpressing cells could be shown. Attachment of the antibody-conjugated nanoparticles to the surface of HER2-overexpressing cells was time and dose dependent. Confocal laser scanning microscopy demonstrated an effective internalisation of the nanoparticles by HER2-overexpressing cells via receptor-mediated endocytosis. The results indicate that nanoparticles conjugated with an antibody against a specific tumour antigen holds promise, as selective drug delivery systems for the treatment of tumours expressing a specific tumour antigen. To our knowledge, this is the first study that demonstrates the effective and specific targeting of protein-based nanoparticles as drug delivery systems.

Antibodies, Monoclonal↗

PubMed2002

Effect of RNA silencing of polo-like kinase-1 (PLK1) on apoptosis and spindle formation in human cancer cells.

BACKGROUND: Expression of polo-like kinase-1 (PLK1), which has several functions in mitotic progression, is elevated in a broad range of human tumors. To investigate the role of PLK1 in neoplastic proliferation, we used the technique of RNA interference. METHODS: Cells from several different cancer cell lines (MCF-7 breast cancer cells, HeLa S3 cervical cancer cells, SW-480 colon cancer cells, and A549 lung cancer cells) were transfected with small interfering (si) RNAs targeted against the human PLK1 or lamin genes. Northern and western blot analyses were used to examine PLK1 gene expression in transfected cancer cells and normal cells (human mammary epithelial cells [HMECs]). The phenotype, proliferation, and cell cycle distribution of cells transfected with siRNAs were also monitored by fluorescence microscopy and fluorescence-activated cell sorting analysis. RESULTS: All cancer cell lines transfected with low doses of siRNAs targeted to PLK1 had greatly decreased levels of PLK1 mRNA and protein. siRNA4, which had the strongest inhibitory effect, reduced PLK1 mRNA in MCF-7 cells by 70% and PLK1 protein in MCF-7 cells by 95% 24 hours after transfection. Cell proliferation was reduced by between 66% and 99% 48 hours after transfection, and apoptosis was increased from 1%-5% to 13%-50% in transfected cells. Transfected SW-480 cells were mitotically arrested, and their centrosomes had lost the ability to nucleate microtubules. HMECs took up siRNAs less efficiently than cancer cells, and transfection with siRNAs targeted to PLK1 did not inhibit their proliferation. CONCLUSIONS: PLK1 function appears to be essential for centrosome-mediated microtubule events and, consequently, for spindle assembly. siRNAs targeted against human PLK1 may be valuable tools as antiproliferative agents that display activity against a broad spectrum of neoplastic cells at very low doses.

Antibodies, Monoclonal↗

PubMed2002

Cooperative phosphorylation including the activity of polo-like kinase 1 regulates the subcellular localization of cyclin B1.

The cyclin-dependent kinase 1 (Cdc2)/cyclin B1 complex performs cardinal roles for eukaryotic mitotic progression. Phosphorylation of four serine residues within cyclin B1 promotes the rapid nuclear translocation of Cdc2/cyclin B1 at the G(2)/M transition. Still, the role of individual phosphorylation sites and their corresponding kinases remain to be elucidated. Polo-like kinase 1 (Plk1) shows a spatial and temporal distribution which makes it a candidate kinase for the phosphorylation of cyclin B1. We could demonstrate the interaction of both proteins in mammalian cells. Plk1 phosphorylated wild-type cyclin B1 expressed in bacteria and in mammalian cells. Ser-133 within the cytoplasmic retention signal (CRS) of cyclin B1, which regulates the nuclear entry of the heterodimeric complex during prophase, is a target of Plk1. In contrast, MAPK (Erk2) and MPF phosphorylate Ser-126 and Ser-128 within the CRS. Phosphorylation of CRS by MAPK (Erk2) prior to Plk1 treatment induced enhanced phosphorylation of cyclin B1 by Plk 1 suggesting a synergistic action of both enzymes towards cyclin B1. In addition, pretreatment of cyclin B1 by MAPK (Erk2) altered the phosphorylation pattern of Plk 1. Mutation of Ser-133 to Ala decreased the phosphorylation of cyclin B1 in vivo. An immunofluorescence study revealed that a mutation of Ser-133 reduced the nuclear import rate of cyclin B1. Still, multiple serine mutations are required to prevent nuclear translocation completely indicating that orchestrated phosphorylation within the CRS triggers rapid import of cyclin B1.

Bacteria↗

PubMed2002

Expression of endothelial and inducible nitric oxide synthase in benign and malignant lesions of the breast and measurement of nitric oxide using electron paramagnetic resonance spectroscopy.

BACKGROUND: Nitric oxide (NO) is present in various human solid tumors and tumor cell lines, and it is believed that NO plays an important role in tumor growth. An increased NO concentration catalyzed by NO synthase (NOS) is cytotoxic and can promote apoptosis. The expression of endothelial NOS (e-NOS) and induced NOS (i-NOS) was examined in various breast tumors. METHODS: Immunohistochemical staining with a monoclonal antibody (Ab) against e-NOS and a polyclonal Ab against i-NOS was performed on paraffin embedded tissues from 41 benign breast lesions, 9 in situ breast lesions, and 54 invasive breast lesions. Functionality was confirmed by detection of NO using spin-trapping electron paramagnetic resonance (EPR) spectroscopy. RESULTS: e-NOS expression was found in 2 benign lesions (5%; 1 fibroadenoma and 1 proliferative mastopathy), in 5 in situ lesions (56%), and in 33 invasive lesions (61%). None of the benign lesions was positive for i-NOS, but 6 in situ lesions (67%) and 33 invasive lesions (61%) showed tumor cell staining. In particular, capillaries that were embedded in lymphocytic stroma showed a positive reaction for e-NOS. The functionality of NOS was demonstrated by direct NO formation using the EPR spin-trapping method. Tumors that were positive for e-NOS were observed more often in younger patients (P = 0.05). These tumors more frequently were highly differentiated or moderately differentiated and more often showed invasive ductal subtypes and a lower proliferation rate. Tumors that were positive for both e-NOS and i-NOS were more likely to be lymph node negative tumors. Both i-NOS-expressing lesions and e-NOS-expressing lesions showed strong coexpression (P = 0.00001). CONCLUSIONS: NOS is detected predominantly in in situ lesions and invasive breast lesions but rarely in benign lesions. NOS is found more frequently in invasive carcinomas with low malignancy. Using the spin-trapping EPR method, this study demonstrates direct NO formation in human breast tumors for the first time.

Breast Diseases↗

PubMed2002

Efficient internalization of the polo-box of polo-like kinase 1 fused to an Antennapedia peptide results in inhibition of cancer cell proliferation.

Polo-like kinases (Plk) regulate multiple stages in mitosis. Plk1 is overexpressed in tumors. The COOH-terminal regions of Plks contain a conserved domain, termed polo-box, which is required for subcellular localization and for physical interaction with substrates. We linked the polo-box (amino acids 410-429) of Plk1 to an Antennapedia peptide and studied its impact on tumor cells. Whereas the wild-type polo-box inhibited the proliferation of tumor cells associated with induction of apoptosis, a mutated derivative was much less effective. The treatment caused mitotic arrest, misaligned chromosomes, and multiple centrosomes. Taken together, membrane-permeable polo-box peptides inhibit cancer cell proliferation efficiently.

Amino Acid Sequence↗

PubMed2002

Downregulation of human polo-like kinase activity by antisense oligonucleotides induces growth inhibition in cancer cells.

A central role for polo-like kinases (PLK) in regulating several stages of mitotic progression has been born out in several species. Overexpression of PLK1 is observed in the majority of hitherto analysed human tumors. PLK1 overexpression is a negative prognostic factor in patients suffering from non-small cell lung cancer, head and neck tumors, esophageal carcinomas and melanomas. In order to define the role of PLK1 for mitotic progression of human cells and for neoplastic cell growth, phosphorothioate antisense oligonucleotides (ASOs) were tested to selectively downregulate PLK1 expression in MDA-MB-435 (breast cancer), HeLa S3 (cervical carcinoma) and A549 (non-small cell lung cancer) cells. ASOs were identified which suppress PLK1 mRNA and protein in a dose-dependent and sequence-specific manner. This approach also led to reduced PLK1 serine/threonine kinase activity. Downregulation of cellular PLK1 levels in cancer cells altered cell cycle progression moderately with an elevated percentage (20-30%) of cells in G(2)/M. Furthermore, cells with reduced PLK1 protein gained a rounded phenotype with multiple centrosomes. Moreover, ASO treatment resulted in potent antiproliferative effects in cell culture. Considerable antitumor activity was observed in vivo against A549 cells. This study suggests that antisense inhibitors targeted against PLK1 at well tolerated doses may be considered as a cancer therapeutic agent.

Adenocarcinoma↗

PubMed2002

Identification of high risk breast-cancer patients by gene expression profiling.

We previously used DNA array analyses in the molecular profiling of breast cancers. By cluster analysis of 55 patients, we identified a subpopulation of breast cancers-designated class A-that contained a high number of nodal-positive tumours and that had frequently developed distant metastases at the time of diagnosis. We have now analysed follow-up data from these patients. We found that, despite a median of only 23.5 months of follow-up, 11 of 22 patients in class A progressed to metastatic disease, and three of five patients classified as having a nodal status of N0 in this subpopulation developed distant metastases. Our analysis identifies breast-cancer patients with a high risk of disease recurrence, and could act as a first step towards improved patient-adapted therapy.

Biomarkers, Tumor↗

PubMed2002

Expression of polo-like kinase (PLK1) in thin melanomas: a novel marker of metastatic disease.

BACKGROUND: The maximum thickness of a primary malignant melanoma as measured by Breslow's method is currently the most important prognostic factor. However, some thin melanomas (< or= 0.75 mm), which should have an excellent prognosis according to Breslow, can be lethal due to their ability to metastasize. METHODS: In our study, thin malignant melanomas (< or= 0.75 mm) from 36 patients were analyzed with immunohistochemical techniques using monoclonal antibodies directed against PLK1 and Ki-67. The immunoreactivity of 22 melanomas which developed metastases within 5 years of follow-up was compared with a group of 14 non-metastasized melanomas. Two independent investigators evaluated stained sections. Differences of PLK1 and Ki-67 indices between melanomas with and without metastases were tested statistically using the Mann-Whitney U-test. RESULTS: Malignant melanomas with metastases expressed PLK1 at markedly elevated levels compared to melanomas without metastases (median, 60.00% vs. 37.98%; p = 0.000053). The difference of the Ki-67 index between both groups was not significant (median, 6.35% vs. 4.53%; p = 0.150473). CONCLUSIONS: Our results suggest that PLK1 expression in thin melanomas is a reliable marker to identify patients at high risk for metastases.

Cell Cycle Proteins↗

PubMed1996

Eph receptors and ligands comprise two major specificity subclasses and are reciprocally compartmentalized during embryogenesis.

We report that the many Eph-related receptor tyrosine kinases, and their numerous membrane-bound ligands, can each be grouped into only two major specificity subclasses. Receptors in a given subclass bind most members of a corresponding ligand subclass. The physiological relevance of these groupings is suggested by viewing the collective distributions of all members of a subclass. These composite distributions, in contrast with less informative patterns seen with individual members of the family, reveal that the developing embryo is subdivided into domains defined by reciprocal and apparently mutually exclusive expression of a receptor subclass and its corresponding ligands. Receptors seem to encounter their ligands only at the interface between these domains. This reciprocal compartmentalization implicates the Eph family in the formation of spatial boundaries that may help to organize the developing body plan.

Animals↗

PubMedDate not supplied

Silencing of the HER2/neu gene by siRNA inhibits proliferation and induces apoptosis in HER2/neu-overexpressing breast cancer cells.

In eukaryotes, double-stranded (ds) RNA induces sequence-specific inhibition of gene expression referred to as RNA interference (RNAi). We exploited RNAi to define the role of HER2/neu in the neoplastic proliferation of human breast cancer cells. We transfected SK-BR-3, BT-474, MCF-7, and MDA-MB-468 breast cancer cells with short interfering RNA (siRNA) targeted against human HER2/neu and analyzed the specific inhibition of HER2/neu expression by Northern and Western blots. Transfection with HER2/neu-specific siRNA resulted in a sequence-specific decrease in HER2/neu mRNA and protein levels. Moreover, transfection with HER2/neu siRNA caused cell cycle arrest at G0/G1 in the breast cancer cell lines SK-BR-3 and BT-474, consistent with a powerful RNA silencing effect. siRNA treatment resulted in an antiproliferative and apoptotic response in cells overexpressing HER2/neu, but had no influence in cells with almost no expression of HER2/neu proteins like MDA-MB-468 cells. These data indicate that HER2/neu function is essential for the proliferation of HER2/neu-overexpressing breast cancer cells. Our observations suggest that siRNA targeted against human HER2/neu may be valuable tools as antiproliferative agents that display activity against neoplastic cells at very low doses.

Apoptosis↗

PubMedDate not supplied

STAT 3 activation in head and neck squamous cell carcinomas is controlled by the EGFR.

Proliferation of squamous cell carcinoma of the head and neck (SCCHN) depends on epidermal growth factor receptor (EGFR) expression. As STAT 3 activation as well contributes to the cell growth in SCCHN, the interaction of STAT 3 and the EGFR is of great interest when considering treatment options through inhibition of STAT 3. We, therefore, evaluated the influence of blocking or activating the EGFR in human SCCHN cell lines and in vivo tumors on STAT 3 activation. We compared the effects on STAT 3 activation with the regulation of MAP Kinase under these conditions. We found that STAT 3 can be strongly inhibited via EGFR blocking in vitro as well as in vivo. However, the influence of EGFR regulation on the MAP Kinase pathway seemed to be very slight. These findings provide evidence that STAT 3 signal activity in head and neck carcinomas, which is partially responsible for proliferative activity, can be controlled via the EGFR.

Animals↗

PubMedDate not supplied

Iressa (ZD 1839) inhibits phosphorylation of three different downstream signal transducers in head and neck cancer (SCCHN).

Proliferation of squamous cell carcinoma of the head and neck (SCCHN) depends on epidermal growth factor receptor (EGFR) expression. The EGFR activates different signal pathways leading to gene transcription in the nucleus due to cell cycle progression and proliferation of tumor cells. AKT, STAT3 and MAPK play central roles in these pathways. However, they are not only regulated by the EGFR. We therefore investigated whether a specific inhibitor of the EGFR tyrosine kinase (ZD 1839 or Iressa) is able to inhibit phosphorylation of these three signals at the same time. Western blot analysis of pretreated SCCHN cells revealed that ZD 1839 greatly reduces the amount of phosphorylated AKT, STAT3 as well as MAPK Surprisingly, this effect was not dose-dependent between the concentration range of 5.15 to 41.2 microM/ml. We conclude that Iressa has a high potency to inhibit nuclear gene transcription responsible for cell cycle progression. Furthermore, dose reduction of Iressa in the case of toxicity may not severely influence the response to treatment.

Antineoplastic Agents↗

PubMedDate not supplied

Reduction of cisplatin dosage by ZD 1839.

Cisplatin (CDDP) is the main chemotherapeutic drug in the treatment of recurrent or metastatic squamous cell carcinoma of the head and neck (SCCHN), but its nephrotoxicity often limits the treatment. ZD 1839 is an orally-applicable, selective EGFR tyrosine kinase inhibitor. This investigation explored whether the cisplatin dose can be reduced by the additional application of ZD 1839. Four different SCCHN cell lines were treated with descending doses of CDDP alone or in combination with ZD 1839. Proliferation was measured by the MTT assay; tumor cell toxicity was measured by using the lactate dehydrogenase approach. ZD 1839 augments CDDP-dependent antiproliferative effects. By adding ZD 1839 to the treatment regimen, the CDDP dose could be reduced by up to 25% of the CDDP IC50 dose without compromising the antiproliferative effect. Adding ZD 1839 to CDDP may therefore enable CDDP treatment at a lower dose without compromising antiproliferative effects.

Antineoplastic Combined Chemotherapy Protocols↗