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T Efferth

Publications and source records attributed to T Efferth.

At least 37 records · Page 2Linked to original sources
PubMed1999

Testing for tumor drug resistance in the age of molecular medicine. A contribution to the Debate Round-Table on Phenotypic and Genotypic Analyses of Multidrug Resistance (MDR) in Clinical Hospital Practice.

The detection of multidrug resistance (MDR) in clinical hospital practice represents an important strategy to combat clinical tumor drug resistance. Predicting the response of tumors to cytostatic drugs is of prognostic value. The 'Debate Round-Table on Phenotypic and Genotypic Analyses of Multidrug Resistance (MDR) in Clinical Hospital Practice' was launched in 1997 to address specific questions on this topic. The results published thus far are a rich source to learn about the promises and pitfalls of methods, eg surrogate and functional tests and protein or mRNA expression assays as well. In the present paper, some requirements are discussed for applications of drug resistance testing in clinical routine diagnostics. To improve the detection of low-level resistance, established methodologies may be strengthened with respect to: (1) standardization of sample handling, antibodies, PCR primers, and detection reagents; (2) standardization of protocols and far reaching automation in performance and evaluation of results to ensure high quality control criteria. Sophisticated new techniques will feature: (1) high-throughput analyses for the 'horizontal screening' of single drug resistance genes in large numbers of patient samples at economically fair costs; (2) 'vertical screening' of a large number of resistance mechanisms operating upstream or downstream of the actual drug-target interaction sites, in order to detect more complex and multifaceted genotypes and phenotypes of multidrug resistance.

Drug Resistance, Multiple↗
PubMed1997

Apoptosis and resistance to daunorubicin in human leukemic cells.

We compared test methods based on specific mechanisms of daunorubicin (DNR) resistance to more global procedures. Assessment of P-glycoprotein (P-gp) expression and function by means of immunocytochemistry, DNR accumulation, and modulation of resistance and accumulation by the P-gp inhibitor cyclosporin A (CsA) were selected as parameters for multidrug resistance (MDR). On the other hand, we used the MTT assay and measured apoptosis and proliferative activity (S- and G2M-phases of the cell cycle) by flow cytometry. Validation of test methods was achieved for four leukemic cell lines (HL-60, KG-1a, K562/WT, K562/ADM). This battery of tests was then applied to mononuclear cells (MNC) from 18 leukemic patients. Low proficiency of MNC to undergo apoptosis and low proliferative activity rather than P-gp-mediated MDR correlated with DNR resistance as measured by the MTT assay. Bell-shaped dose-response curves for apoptosis, however, which reflect a switch from the apoptotic to the necrotic death mode with increasing cellular damage tend to limit practicability in clinical testing, because appropriate dose range and time points need to be explored. Thus, measurement of apoptosis by flow cytometry may be less convenient than the MTT assay for determination of chemosensitivity, if clinical samples with unknown patterns of responsiveness are to be tested. Spontaneous apoptosis in untreated MNC following 24 h incubation in vitro correlated significantly with DNR sensitivity in the MTT assay. A lack of essential viability factors (eg growth factors or cytokines) in vitro which are known to prevent apoptosis may contribute to DNR sensitivity.

Antibiotics, Antineoplastic↗
PubMed1996

Anti-Fas/Apo-1 monoclonal antibody CH-11 depletes glutathione and kills multidrug-resistant human leukemic cells.

Apoptosis is a common pathway by which cells respond to noxious insults or growth regulatory factors. Since cellular glutathione (GSH) content has long been known to govern response to antineoplastic treatment we have compared induction of apoptosis in drug sensitive (HL-60 and K562/WT) and drug resistant (KG-1a and K562/ADM) human leukemic cell lines by the monoclonal antibody CH-11 (anti-Fas/Apo-1). Fraction of apoptotic cells and cellular GSH were determined by flow cytometry. All cell lines were induced to undergo apoptosis by exposure to mAb CH-11 independent of resistance to conventional antineoplastic treatment. In conjunction with exposure to daunorubicin, vincristine, carboplatin, cytosine arabinoside, dexamethasone, or ionizing irradiation the effect of mAb CH-11 on induction of apoptosis was no more than additive. In contrast, preincubation with IFN-gamma markedly enhanced the induction of apoptosis by mAb CH-11 due to an increase of Fas-receptor expression. In each instance, GSH content decreased with increasing fraction of apoptotic cells indicating a crucial role of GSH in the apoptotic pathway.

Antibodies, Monoclonal↗
PubMed1996

Detection of apoptosis in KG-1a leukemic cells treated with investigational drugs.

Four investigational drugs, p-benzoquinone, primine, miconidine acetate, and artesunate (dihydroqinghaosusuccinate), with growth inhibitory activity against flagellatae (e.g. trypanosoma, leptomonas, plasmodium) were investigated for their capability to induce programmed cell death (apoptosis) in human KG-1a leukemic cells. The results were compared with those of three well established cytostatic agents (cisplatin, daunorubicin, cytosine-arabinoside) and ionizing radiation. The antitumor activity of the drugs was validated by a cellular growth inhibition assay. The depletion of glutathione by these four investigational drugs favours the hypothesis that formation of free radicals and subsequent DNA strand breaks may be critical mechanisms of action and that the glutathione redox cycle is involved in detoxification of these reactive molecules.

Antineoplastic Agents↗
PubMed1995

Increased induction of apoptosis in mononuclear cells of a glucose-6-phosphate dehydrogenase deficient patient.

Glucose-6-phosphate dehydrogenase (G6PD) deficiency belongs to the most common human disorders of metabolism. In affected patients generation of free radicals causes life-threatening hemolytic crises, for example, after consumption of certain drugs and foods or after infections. Rather than erythrocytes we analyzed mononuclear white blood cells of a patient suffering from G6PD deficiency with respect to their ability to enter apoptosis after treatment with daunorubicin, ionizing radiation, or dexamethasone. The induction of apoptosis was increased in G6PD-deficient cells compared to cells from eight normal donors. In parallel, the glutathione content of mononuclear cells from the G6PD-deficient patient was significantly decreased. While in affected patients decreased life span of erythrocytes damaged by oxidative stress has long been recognized as the mechanism underlying hemolysis, peripheral leukocytes have not received similar attention. Induction of apoptosis is a relatively complex process that has been linked to cellular glutathione content. This is the first report investigating G6PD deficiency and apoptosis.

Adult↗
PubMed1995

Sister chromatid exchange-inducing DNA lesions and depression of activation markers on the surface of cultured peripheral blood mononuclear cells after the addition of streptococcal pyrogenic exotoxins A and C.

Cultivation of peripheral blood mononuclear cells (PBMC) in the presence of streptococcal pyrogenic exotoxins (SPE) A and C resulted in a significant induction of sister chromatid exchange (SCE)-inducing DNA lesions. Concomitantly, the expression of interleukin-2 receptor alpha chain (IL-2R alpha chain), transferrin receptor (TfR), and major histocompatibility complex class II molecule HLA-DR on the surface of phytohemagglutinin-activated T cells from whole blood culture cells (WBCC) significantly decreased within 72 h, that is at least two cell cycles, whereas unstimulated T cells from WBCC did not express these markers but had lost their CD3 molecules, an effect reported to precede apoptosis as part of a T cell inactivation pathway. However, no apoptotic cells were observed within a cultivation period of 120 h. We observed clearcut differences in the responses towards SPE A in WBCC and isolated lymphocytes, since SPE A-treated lymphocytes showed an increase in the [3H]thymidine incorporation and did express IL-2R alpha chain and TfR on their cell surface. Regardless of the precise underlying mechanism, T cells from WBCC seem to be in a state of functional incompetence. The data presented here are the first to provide strong evidence that streptococcal toxins produce SCE-inducing DNA lesions in PBMC, an effect that might contribute to the process of immune cell lethality in streptococcal toxic shock-like syndrome and could be of pivotal importance in the pathogenesis of severe streptococcal disease.

Adult↗
PubMed1995

Expression of apoptosis-related oncoproteins and modulation of apoptosis by caffeine in human leukemic cells.

We investigated the modulation of radio- and chemoresistance by caffeine and mechanisms of resistance in human leukemic cell lines and mononuclear cells from 18 leukemic patients. Caffeine synergistically potentiated cytotoxicity and apoptosis induced by ionizing radiation or carboplatin (CPt), but attenuated induction of apoptosis by daunorubicin (DNR) in KG-1a cells. Since caffeine released irradiated as well as DNR-treated KG-1a cells from G2M cell cycle arrest and CPt-treated cells from S-phase arrest, this release does not fully explain the different effects of caffeine. Caffeine synergistically reduced the level of the apoptosis inhibitor glutathione after irradiation or CPt treatment. In contrast, treatment with DNR plus caffeine diminished glutathione levels to a lesser extent than DNR alone. We conclude that the effect of caffeine on glutathione depletion represents a mechanism of action by which caffeine can modulate apoptosis. Caffeine increased CPt cytotoxicity in K562 cells and its doxorubicin-resistant subline (K562/ADM), but little effect was seen in HL-60 cells or mononuclear cells from leukemic patients. Multivariate cluster analysis revealed an association of CPt resistance with the expression of c-Fos, c-N-Ras, and p53 oncoproteins and with proliferative activity (S-phase of cell cycle), but not with Bcl-2 expression.

Apoptosis↗
PubMed1993

Reversal of doxorubicin-resistance in sarcoma 180 tumor cells by inhibition of different resistance mechanisms.

Resistance of tumor cells to doxorubicin is a multifactorial phenomenon. In the present investigation, the ability of resistance modifiers against different resistance mechanisms was analysed. Substances which block P-glycoprotein (P-170) function circumvented resistance of doxorubicin-resistant sarcoma 180 (S180) cells completely (verapamil, thioridazine) or partially (hycanthone), whereas inhibitors of glutathione S-transferase (ethacrynic acid, N-ethylmaleimide, buthionine sulfoximine), and protein kinase C (staurosporine, acridine orange) caused only a partial reversion of resistance. In contrast, an inhibitor of alkaline phosphatase (levamisole) did not overcome doxorubicin-resistance. These results indicate that P-glycoprotein blockers might be more effective to modulate doxorubicin-resistance of S180 cells as compared to other modifiers. Further investigations using other MDR cell lines are required to clarify the generality of these findings.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

Expression of resistance factors (P-glycoprotein, glutathione S-transferase-pi, and topoisomerase II) and their interrelationship to proto-oncogene products in renal cell carcinomas.

BACKGROUND: This study investigates whether or not an interrelationship exists between the expression of resistance-related proteins (P-glycoprotein, glutathione S-transferase, topoisomerase II) and proto-oncogene products (c-fos, c-myc, c-K-ras, epidermal growth factor receptor [EGF-R], and c-neu proteins.) METHODS: Thirty-eight human renal cell carcinomas of previously untreated patients were analyzed for expression of P-glycoprotein (P-170), glutathione S-transferase-pi (GST-pi), topoisomerase II (Topo II) and proto-oncogene proteins by means of immunohistochemistry. Because of significant heterogeneity in most tumor biopsies, all analyses were done on tumor-derived primary cell culture lines on the third or fourth passage. RESULTS: An interrelationship between increased expression of P-170 and GST-pi and down-regulation of Topo II was found. Expression of the c-fos protein was seen in 66% of the tumors; expression of the c-myc protein, in 50%; of the c-K-ras protein, in 16%; of the EGF-R protein, in 61%; and of the c-neu protein, in 54% of the tumors. A significant correlation between the resistance factors and the c-fos, EGF-R, and c neu-proteins was observed (GST/c-fos, P = 0.012; Topo II/c-fos, P = 0.024; P-170/EGF-R, P < 0.001; GST/EGF-R, P = 0.018; Topo II/EGF-R, P = 0.027; P-170/c-neu, P = 0.005; GST/c-neu, P = 0.018; Topo II/EGF-R, P = 0.027; P-170/c-neu, P = 0.005; GST/c-neu, P = 0.008; Topo II/c-neu, P = 0.05). In contrast, interrelationships between resistance proteins and c-myc and c-K-ras proteins were not found. A significant interrelationship between the investigated resistance-related proteins or proto-oncogene proteins and the stage or grading of the tumors was not observed. CONCLUSIONS: The results demonstrate that in renal cell carcinomas a significant relationship exists between resistance-related proteins, such as P-170, GST-pi, or Topo II, and proto-oncogenes, such as c-fos, c-erbB1, and c-neu.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

High rate of expression of multidrug resistance-associated P-glycoprotein in human endometrial carcinoma and normal endometrial tissue.

The overexpression of P-glycoprotein was studied in 10 normal endometrial controls (five from the proliferative and five from the secretory phase of the menstrual cycle) and in 23 endometrial carcinomas of different histological varieties, using the C219 and JSB-1 monoclonal antibodies. Three of the tumours had been previously treated with combination chemotherapy containing doxorubicin. All endometrial carcinomas, whether treated or untreated, as well as the normal endometrial controls from both the proliferative and the secretory phase of the menstrual cycle, overexpressed P-glycoprotein. This puts endometrial carcinoma into the same category as other tumours arising in organs which normally overexpress P-glycoprotein, all of which tend to be intrinsically resistant to chemotherapy.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

Increase of alkaline phosphatase in multidrug-resistant tumor cells and their cross-resistance to 6-thioguanine.

The expression of alkaline phosphatase (AP) was analyzed in multidrug-resistant (MDR) tumor cells (sarcoma 180, lung carcinoma, and renal cell carcinoma cell lines) by means of immunocytochemistry. MDR cell cultures showed an overexpression of AP and a cross-resistance to 6-thioguanine (6-TG, CAS 154-42-7). Significant correlations between AP expression and doxorubicin or vincristine resistance and P-glycoprotein (P-170) expression were found in these cell cultures. A specific AP inhibitor, levamisole, reversed resistance to 6-TG, but not to doxorubicin. This indicates that 6-TG resistance is certainly associated to P-170 but a causal function of AP for the development of MDR does not exist.

Alkaline Phosphatase↗
PubMed1992

Antibody-directed therapy of multidrug-resistant tumor cells.

The major obstacle to effective cancer chemotherapy is the resistance of tumor cells to cytostatic agents. Tumor cells frequently express a multidrug-resistance (MDR) phenotype. In an effort to devise new strategies to overcome MDR, antibody-directed approaches for the eradication of MDR cells have been developed. Experimental data have shown that multidrug-resistant tumor cells can be efficiently killed by monoclonal antibodies, immunotoxins, or bispecific antibodies. The current experimental results indicate that an antibody-directed therapeutic approach to eradication of MDR cells might be a promising adjunct to conventional chemotherapy of cancer patients.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

Immunohistochemical detection of the multi-drug-resistance marker P-glycoprotein in uterine cervical carcinomas and normal cervical tissue.

Uterine cervical carcinomas and normal cervical tissue (controls) were investigated for the presence of the multi-drug-resistance gene product P-glycoprotein by means of immunohistochemistry, with the C219 monoclonal antibody and the streptavidin-biotin-peroxidase technique. Ten of 11 cervical carcinomas, 2 of which were previously treated with chemotherapeutic agents of the multi-drug-resistance group, showed a positive reaction of tumor cells. All normal controls showed a positive reaction of the ectocervical and endocervical epithelial cells. P-glycoprotein seems to be implicated at least in part in resistance to chemotherapy of cervical carcinoma.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

Immunohistochemical detection of P glycoprotein, glutathione S transferase and DNA topoisomerase II in human tumors.

The expression of the drug resistance markers P glycoprotein (P-170), glutathione S transferase-pi (GST-pi) and DNA topoisomerase II (Topo II) was analyzed in 16 human kidney carcinoma cell lines, 18 hematological malignancies, and 14 human breast carcinomas. We found a tendency for coexpression of increased P-170 and GST-pi and of increased P-170 and decreased Topo II expression in kidney carcinoma cell lines. A similar tendency was found between P-170 and GST-pi expression in breast carcinomas. In contrast, hematological malignancies did not show such a coexpression of resistance markers. Furthermore, we found interrelationships between the expression of resistance markers, resistance to doxorubicin or vincristine, and doubling times of kidney carcinoma cell lines. This indicates that the proliferative activity of tumor cells plays a role for the expression of resistance markers and the development of resistance to cytostatic drugs.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1992

Resistance mechanisms in murine tumors with acquired multidrug resistance.

Mechanisms of multidrug resistance were studied in murine leukemia (L 1210) and sarcoma (Sa 180) tumors after pretreatment with anthracyclines in vivo. Despite identical pretreatment protocols, a considerable difference in the level of resistance between L 1210 and Sa 180 tumors was noted (for doxorubicin: 45-fold versus 340-fold; for daunorubicin: 51-fold versus 275-fold). However, no difference in mdr 1 gene-amplification and the overexpression of mdr 1-RNA or P-glycoprotein was demonstrated. None of these parameters did increase by further treatment with a higher concentration of anthracyclines. Resistant sublines of Sa 180 revealed an overexpression of glutathione S-transferase-pi (GST-pi) in comparison to the parental line, whereas in sensitive and resistant sublines of L 1210 tumors the expression of GST-pi was similar. In order to study whether trifluoperazine can reverse the P-glycoprotein mediated component of multidrug resistance, trifluoperazine and doxorubicin were tested in vitro in L 1210 and Sa 180 cells. In contrast to the complete reversal of resistance in L 1210 tumors, resistance in Sa 180 was only partly circumvented. However, by buthionine sulfoximine treatment, the toxicity of multidrug resistant Sa 180 tumors could be increased. It was possible to reverse the resistance of Sa 180 tumors completely by trifluoperazine plus buthionine sulfoximine. Thus, multidrug-resistant Sa 180 tumors express different defense mechanisms whereas L 1210 tumors express only one defense mechanism (P-glycoprotein).

Animals↗
PubMed1992

Immunocytochemical detection of oncoproteins in animal and human tumor lines with acquired or inherent multidrug resistance.

In this presentation, we analyze the relationship between protein expression of the protooncogenes c-fos, c-erb B1, c-K-ras, and c-myc and acquired or inherent multidrug resistance (MDR) in a panel of animal (CHO, S 180, L 1210) and human (KTCTL 44, KTCTL 18, CX 1, CXF 94) tumor lines by means of immunocytochemistry. Increased expression of c-fos and c-erb B1 proteins is a constant feature of all resistant cell lines except L 1210 cells, which did not reveal any alteration in oncoprotein expression. No apparent relationship between c-K-ras and c-myc proteins and MDR was found. The immunocytochemical results were corroborated by radioimmunoassays (RIAs). The data indicate that c-fos and c-erb B1 might play a role in the development of MDR.

Adenocarcinoma↗
PubMed1991

Circumvention of multi-drug resistance in human kidney and kidney carcinoma in vitro.

This report investigated whether the calmodulin inhibitor, trifluoperazine, can circumvent multi-drug resistance both in primary tissue cultures of human kidney and kidney carcinoma. For detection of inherent multi-drug resistance, the expression of P-glycoprotein was determined by immunofluorescence and immunocytochemistry using the monoclonal antibody C219. For detection of doxorubicin resistance and reversal of this resistance by trifluoperazine, the incorporation of nucleic acid precursor was measured after addition of doxorubicin and trifluoperazine, respectively. Both P-glycoprotein expressing resistant normal and malignant kidney tissue cultures could be modified by trifluoperazine. However, sensitive normal kidney and kidney carcinoma cultures were little affected by trifluoperazine. Thus, circumvention of primary resistance to doxorubicin is not limited to tumor cells. This might have important implications for the use of resistance modifiers in the clinical setting.

ATP Binding Cassette Transporter, Subfamily B, Mem↗