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G Steger

Publications and source records attributed to G Steger.

At least 91 records · Page 5Linked to original sources
PubMed1988

Nucleotide sequence predicts circularity and self-cleavage of 300-ribonucleotide satellite of arabis mosaic virus.

The nucleotide sequence of the satellite of arabis mosaic virus was determined using the satellite RNA encapsidated in virions. The 300-nucleotide long sequence showed extensive homology (50%) with that of the 359-nucleotide satellite RNA of tobacco ringspot virus, which occurs both in a linear and a circular form. This homology also revealed the presence of conceived sequences believed to mediate self-cleavage of the latter as well as other viral satellite RNAs. A circular form of the arabis mosaic virus satellite can be isolated from infected tissues and partially converts to the linear form upon elution from denaturing gels.

Base Sequence↗
PubMed1988

Escalating dose regimen of intraperitoneal mitoxantrone: phase I study--clinical and pharmacokinetic evaluation.

Mitoxantrone, a recent anthracenedione derivative, is a potentially useful drug for direct intraperitoneal (i.p.) application because of its high tissue binding and therapeutic index. We have carried out studies to establish maximum tolerated doses as well as pharmacokinetic studies with i.p. mitoxantrone in 21 patients (5 male, 16 female) with gastrointestinal (9), ovarian (6), unknown (2) and other (4) primary cancers and peritoneal carcinomatosis. Increasing doses (10-40 mg/m2) were given i.p. every 4 weeks. Five partial remissions (2-8+ months) and 7 stable disease courses (2-6+ months) were achieved. A reduction or disappearance of ascites was seen in an additional 3 patients. Severe toxicity (leucopenia) was observed in 4 patients only after 35 and 40 mg/m2 i.p. Pharmacokinetic analysis using high performance liquid chromatography yielded the following data: The mean ratio of area under curve peritoneal fluid to plasma was 1109. The peritoneal clearance rate was 680 ml/min and the mean disappearance half life was 13.1 h. Mean urinary excretion within 24 h was 0.42% of the i.p. dose. These data indicate that mitoxantrone is sequestered in the intraperitoneal tissue compartment and only slowly released. Based on the outcome of this phase I study we recommend phase II studies at a dose of 30 mg/m2 i.p., repeated every 3-4 weeks.

Adult↗
PubMed1988

Human papillomavirus 8-L1 immune serum: a new diagnostic possibility for Epidermodysplasia verruciformis-specific HPVs.

Human papillomavirus (HPV) 8 induces flat macular skin lesions with a high risk of malignant conversion. A 600-bp fragment from the center of the major structural protein gene L1 was cloned into pEX2 to produce a beta-galactosidase-L1 fusion protein. The expressed part of L1 is masked in intact virions and not detected by sera of infected patients. Immunization of guinea pigs with purified fusion protein raised high-titer antisera, which reacted with capsid proteins of HPV8 and closely related viruses in Western blot and indirect immunofluorescence tests. Structural proteins of HPV1, 2, and 3 were not detected, indicating specificity for the subgroup of ev-specific HPVs. The sera present themselves as convenient diagnostic reagents for the demonstration of infections with potentially oncogenic HPVs using routine immunofluorescence procedures.

Antibody Specificity↗
PubMed1987

Double-stranded cucumovirus associated RNA 5: experimental analysis of necrogenic and non-necrogenic variants by temperature-gradient gel electrophoresis.

Cucumber mosaic virus (CMV) and peanut stunt virus (PSV) each contain a fifth major RNA in the size range of 334 to 393 nucleotides. This fifth RNA is a satellite capable of modulating the expression of viral disease symptoms. It is present in infected tissue in single-stranded and double-stranded form. Nucleotide sequence variants of the double-stranded CMV-associated RNA 5 (dsCARNA 5) and PSV-associated RNA 5 (dsPARNA 5) were analysed by temperature-gradient gel electrophoresis. Gels were 5% polyacrylamide, containing 8 M urea in 8.9 mM Tris-borate buffer, with temperature differences of 25-40 degrees C establishing gradients either perpendicular or parallel to the direction of the electric field. For dsCARNA 5 two characteristic transitions were detected with increasing temperature: at temperatures between 40 degrees C and 46 degrees C a drastic retardation in electrophoretic mobility induced by partial dissociation of the duplex structure from the ends and at temperatures above 52 degrees C an abrupt increase in mobility due to complete strand dissociation. dsPARNA 5 exhibited both transitions at up to 10 degrees C higher temperatures and an additional retardation between the transitions mentioned. Seven different variants of dsCARNA 5, 4 necrogenic and 3 non-necrogenic, were analysed. Some showed only one single band, others gave rise to up to six well separated bands corresponding to six molecular species. From all experimental results a correlation between the temperature of the retardation transition and the necrogenicity of CARNA 5 was derived. The diagnostic application of the temperature-gradient gel analysis in agriculture, particularly for the use of non-necrogenic variants as biological control agents to impede CMV-infections, is discussed.

Electrophoresis↗
PubMed1987

Double-stranded cucumovirus associated RNA 5: which sequence variations may be detected by optical melting and temperature-gradient gel electrophoresis?

Sequence variants of the double-stranded form of satellite RNAs of cucumber mosaic virus (dsCARNA 5) were analyzed for the possibility to experimentally detect minor nucleotide sequence changes. Denaturation maps (helix-probability versus position of the nucleotide in the sequence versus temperature) were calculated applying the Poland algorithm. Optical denaturation curves and temperature-gradient gel mobility curves were simulated using the denaturation maps and were compared with experimental results from optical melting and temperature-gradient gel electrophoresis (Tien Po et al., accompanying paper). Melting of the dsRNAs starts from both ends of the molecule in two transitions of low co-operativity, continues in the right part in a highly co-operative transition, and is finished in another highly co-operative transition including strand-separation. Whereas all parts of the molecule contribute uniformly to the optical melting curve, opening of the ends predominates in the retardation transition in gel electrophoresis. Detailed discussion of the influence of base pair changes in the sequence shows that a single base pair change may be detected by temperature-gradient gel electrophoresis, if it is located in certain favorable locations, whereas its detection in optical melting curves is possible only in very special cases. The systematic differences found in the accompanying paper between necrogenic and non-necrogenic dsCARNA 5 could be interpreted on the basis of such nucleotide sequence differences.

Base Composition↗
PubMed1987

[Reversible opening of the blood-brain barrier in the chemotherapy of malignant gliomas].

The concept of a blood brain or blood tumour barrier blocking the passage of lipid insoluble cytoreductive drugs from blood into brain-tumor, leads to a protocol of intraarterial injection of high dose methotrexate (MTX) during reversible, osmotic blood brain barrier disruption (BBBD). Malignant Gliomas of grades III and IV in 9 patients and one primary CNS-lymphoma in one patient have been treated in 2 to 5 sessions per patient with BBBD plus polychemotherapy (MTX, cyclophosphamide, procarbazine). Median progression free intervals (PFI) which are still in continuation are 12.2 months. Median PFI which had been terminated by tumour recurrence are 7.75 months.

Antineoplastic Agents↗
PubMed1987

[Interferon alpha 2C in the treatment of 2 patients with AIDS-associated Kaposi sarcoma].

Two patients with AIDS and histologically confirmed Kaposi's sarcoma were treated with 3 X 10(6) U/m2 interferon alpha 2C (rIFN alpha 2C) subcutaneously three times a week. In both cases remissions (7 weeks and more than 9 months) of the tumour lesions were achieved and in one case pretherapeutic moderate thrombocytopenia improved. The positive serum antibody titres to HTLV III-virus showed no conversion. Except for fever (below 39 degrees C) during the first two weeks of IFN treatment in both patients, therapy-requiring hypotonia, mild depression, leucopenia (WHO grade 1) and thrombocytopenia (WHO grade 2) in one patient, no side effects were observed. All the above-mentioned features were reversible after termination of treatment. Further studies to optimize the dosage of rIFN alpha 2C and its time schedule in the treatment of Kaposi's sarcoma in patients with AIDS are recommended.

Acquired Immunodeficiency Syndrome↗
PubMed1987

Poly(I).poly(C), a potential drug carrier for the antitumor agent mitoxantrone: in vitro drug binding study.

Coupling of mitoxantrone, a new antitumor agent, to a macromolecular carrier system may improve the drug's selectivity of action and pharmacokinetic properties. We have studied in vitro binding of mitoxantrone to poly(I).poly(C), a macromolecular, double-stranded homoribopolymer, by equilibrium dialysis and high-performance liquid chromatography (HPLC). Results showed high binding affinity for mitoxantrone to poly(I).poly(C) (Kd = 1.05 X 10(-6) M), the calculated number of mitoxantrone-binding sites is 60 per molecule poly(I).poly(C). In view of the good tolerance in clinical studies, poly(I).poly(C) may thus be a useful drug carrier for mitoxantrone. A mitoxantrone:poly(I).poly(C) ratio of 1:30 (w/w) is recommended for therapeutic studies.

Binding Sites↗
PubMed1987

Possible adverse effect of failed adjuvant chemotherapy on the prognosis of women receiving consecutive chemotherapy for recurrent breast cancer.

This study tried to evaluate the impact of adjuvant chemotherapy on the induction of chemoresistance in radically operated upon breast cancer patients. Remission rate, remission duration and survival of a group of women (n = 22) treated with combination chemotherapy (adriamycin and cyclophosphamide, AC) for recurrent breast cancer after failed adjuvant therapy (cyclophosphamide, methotrexate, fluorouracil, vinblastine) were retrospectively compared with the clinical data of non-pre-treated patients (n = 28) receiving the same regimen (AC). The two groups of patients were comparable with regard to their risk factors. In the group of women with prior adjuvant chemotherapy only 3 out of 22 had a partial response, lasting 3, 8, and 16 months; the median survival was 50 months. In the group without prior adjuvant therapy 3 complete and 7 partial remissions with a median remission duration of 15.5 months (range 2-54 months) were found; the median survival was 104 months. The percentage of objective responses among the non-pre-treated patients at 36% was almost significantly higher than that of the pretreated women with 14% (p less than 0.1). Responders to chemotherapy after relapse profited in terms of survival within the first 3 years after radical mastectomy, although no statistically significant difference was observed. The survival data shown assume a "shifting" of women from a group with better prognosis to a group with unfavourable prognosis following failed adjuvant chemotherapy.

Antineoplastic Combined Chemotherapy Protocols↗
PubMed1987

Phase-I study of intraperitoneal mitoxantrone--clinical and pharmacokinetic evaluation.

Mitoxantrone, a recent anthracenedione derivative is a potentially useful drug for direct intraperitoneal (i.p.) application because of its high tissue-binding and therapeutic index. We have carried out studies to establish maximum tolerated doses as well as pharmacokinetic studies with i.p. mitoxantrone in 21 patients (5 male, 16 female) with gastrointestinal (9), ovarian (6), unknown (2) and other (4) primary cancers and peritoneal carcinomatosis. Increasing doses (10-40 mg/m2) were given i.p. every 4 weeks. Five partial remissions (2-8+ months) and 7 stable disease courses (2-6+ months) were achieved. A reduction or disappearance of ascites was seen in an additional 3 patients. Severe toxicity (leukopenia) was observed in 4 patients only after 35 mg/m2 and 40 mg/m2 i.p. Pharmacokinetic analysis using high-performance liquid chromatography yielded the following data: The mean ratio of area under curve peritoneal fluid to serum was 1,108. The peritoneal clearance ranged from 2 ml/min to 9,617 ml/min and the disappearance half-life from 0.6-28.9 h. Mean urinary excretion within 24 h was 0.42% of the i.p. dose. These data indicate that mitoxantrone is sequestered in the intraperitoneal tissue compartment and only slowly released. Based on the outcome of this phase-I study we recommend phase-II studies at a dose of 30 mg/m2 i.p., repeated every 3-4 weeks.

Drug Evaluation↗
PubMed1987

Coupling of mitoxantrone to poly(I).poly(C) reduces absorption after intraperitoneal administration.

Coupling of mitoxantrone (M), an intercalating cytostatic, to macromolecular polynucleotides may reduce side effects after direct intraperitoneal chemotherapy by interfering with systemic absorption of M. We have administered free M (30 mg/m2) or M mixed with poly(I).poly(C) (90 mg/m2) intraperitoneally to 5 patients with peritoneal carcinosis (cross-over study): peak plasma levels (HPLC assay) were 62 +/- 12 versus 28 +/- 4 ng/ml (p less than 0.0025), AUC0-24h were 583 +/- 126 versus 481 +/- 57 ng X h/ml (p less than 0.025). Coupling of M to poly(I).poly(C) seems to reduce M absorption after intraperitoneal administration.

Absorption↗
PubMed1986

Structure of viroid replicative intermediates: physico-chemical studies on SP6 transcripts of cloned oligomeric potato spindle tuber viroid.

The structure and structural transitions of transcripts of cloned oligomeric viroid were studied in physico-chemical experiments and stability calculations. Transcripts of (+) and (-) polarity, from unit up to sixfold length, were synthesized from DNA clones of the potato spindle tuber viroid (PSTV) with the SP6 transcription system. Their structural properties were investigated by optical denaturation curves, high performance liquid chromatography (HPLC), electron microscopy, sedimentation-diffusion equilibrium and velocity sedimentation. Secondary structures of the RNAs and theoretical denaturation curves were calculated using an energy optimization program. The secondary structure of lowest free energy for unit length and oligomeric transcripts is a rod-like structure similar to that of the mature circular viroids. When this structure is used as a model for calculations, there is a large degree of agreement between the theoretical and the experimental denaturation curves. At high temperatures, however, (+) strand transcripts exhibited a transition which was more stable than expected from the calculations or than was known from curves of mature viroids. This transition arises from a rearrangement of the central conserved region of viroids to a helical region of 28 stable base pairs either intermolecularly leading to bimolecular complexes, or intramolecularly giving rise to a branched secondary structure. The rearrangement could be detected by electron microscopy, HPLC, and analytical ultracentrifugation. The helical region serves to divide up the oligomeric (+) strand into structural units which may be recognized by cleavage and ligation enzymes which process the oligomeric intermediates to circular mature viroids.

Microscopy, Electron↗
PubMed1986

Mismatches in DNA double strands: thermodynamic parameters and their correlation to repair efficiencies.

The helix-coil transitions of the 16 octadecameric DNA duplexes dCGTCGTTTXACAACGTCG X dCGACGTTGTX1AAACGACG with A, T, G, and C for X and X1 were measured by UV-absorption. This sequence was taken from former studies of in vivo determination of efficiencies of mismatch repair (Kramer, Kramer, and Fritz (1984) Cell 38, 879-887). The thermodynamic parameters for double strand and mismatch formation have been obtained by evaluating the partition function of a stack model which allowed for loop formation. As a result the mismatches could be classified into wobble base pairs (T/G, G/G, C/A, A/A, A/G), open base pairs, i.e. permanent loops (T/T, C/T, T/C, C/C), and intermediate or weak base pairs (G/T, A/C, G/A). There is no correlation between Tm and the biological repair efficiency of X/X1. The structure classes, however, as described above show a close correlation: Open base pairs show the lowest repair efficiencies, whereas mismatches with high repair efficiency always belong to the structural class of wobble base pairs. Because of the palindromic nearest neighbors of the variation site X/X1, the influence of next-nearest neighbor interactions could be detected and be estimated to about 1 kJ/mol for one stack.

Base Sequence↗
PubMed1986

Blood brain barrier modification and chemotherapy. Interventional neuroradiology in the treatment of malignant gliomas.

Postoperative interventional neuroradiology was performed in patients with malignant gliomas to increase target efficacy of chemotherapy. In 8 glioma patients the blood brain or blood tumor barrier was reversibly opened by intraarterial injection of hyperosmolar fluid (Mannitol 25%). One additional patient had primary lymphoma of the central nervous system. During barrier modification chemotherapeutic agents were applied intraarterially and intravenously. A total of 22 blood brain barrier modification procedures have been carried out until now, ranging from one to five per patient. A presently continuing tumor regression or tumor progression free intervals have been noted in 5 patients. Therapeutic effects are being evaluated from repeated computed tomography and single photon emission computed tomography examinations.

Adult↗
PubMed1984

Conformational transitions in viroids and virusoids: comparison of results from energy minimization algorithm and from experimental data.

Viroids are single-stranded circular RNA molecules of 240 to 400 nucleotides which are pathogens of certain higher plants and replicate autonomously in the host cell. Virusoids are similar to viroids in respect to size and circularity but replicate only as genomic part of a plant virus. Their structure and structural transitions have been investigated by thermo-dynamic, kinetic and hydrodynamic methods. The special features of the sequences of these RNAs, which are the basis for their secondary structures and structural flexibility, are investigated with theoretical methods. A set of thermodynamic parameters for helix growth and loop formation is selected from the literature to calculate secondary structures and structural transitions of single-stranded RNAs. Appropriate modifications of the chosen parameter set are discussed. For calculations we used either Tinoco-plots and the model of "cooperative helices" or the Zuker-program based on the exact algorithm of Nussinov et al, or both. Calculations were done for viroids and virusoids. As both are single-stranded, circular RNAs we had to modify the Zuker-program as described in the appendix. Calculations are done for different viroids, i.e. potato spindle tuber, citrus exocortis, chrysanthemum stunt, coconut cadang-cadang, and avocado sunblotch, and for two virusoids, i.e. the circular RNAs of Solanum nodiflorum mottle virus, and velvet tobacco mottle virus. For viroids the calculations confirm our earlier theoretical and experimental results about the extended native structure and the highly cooperative transition into a branched structure. Virusoids show less base pairing, branching in the native secondary structure, and only low cooperativity during denaturation. They resemble more closely the properties of random sequences with length, G:C content, and circularity as in viroids but statistical sequences. The comparison of viroids, virusoids, and circular RNA or random sequences confirms the uniqueness of viroid structure.

Algorithms↗