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S Lehnert

Publications and source records attributed to S Lehnert.

At least 19 recordsLinked to original sources
PubMed2005

A novel non-toxic camptothecin formulation for cancer chemotherapy.

The use of a novel injectable biocompatible and biodegradable camptothecin-polymer implant for sustained intra-tumoral release of high concentrations of camptothecin is described. The drug delivery vehicle is an in situ thermogelling formulation, which is based on the natural biopolymer chitosan. This formulation, containing homogeneously dispersed camptothecin, was implanted intra-tumorally into a sub-cutaneous mouse tumor model (RIF-l). The effectiveness of treatment was measured in terms of tumor growth delay (TGD). Animals treated with the polymer implants containing camptothecin had significantly longer TGDs compared to untreated animals as well as to animals treated systemically with camptothecin by intra-peritoneal injection with no evidence of toxicity in terms of loss of body weight. The results indicate that this novel biodegradable polymer implant is an effective vehicle for the sustained intra-tumoral delivery of camptothecin which might also be suitable to deliver other insoluble anti-cancer drugs such as taxol.

Absorbable Implants↗
PubMed2004

[Airbag associated deceleration trauma with complete infradiaphragmatic dissection of the inferior vena cava (IVC) and tear of liver veins].

Numerous investigations have demonstrated that the ability of passenger airbag systems to reduce both injury severity and mortality in car accidents is restricted to the simultaneous application of seatbelts and airbags. Depending on the impact force during the accident and also on the driver's position to the airbag an isolated airbag deployment can even produce severe injuries. We describe a complete infradiaphragmatic dissection of the IVC and a tear of liver veins after an airbag deployment without seatbelt use. We discuss different airbag associated injuries, the possible pathomechanism of the described injury, frequency and prognosis of abdominal vascular injuries and their emergency treatment. In the presented case the isolated severe vascular injury resulted in an intraoperative death caused by exsanguination. In blunt trauma with accompanying hypotension pre-arrival alarming of the ER, rapid transport to the hospital and immediate surgery are most important for the outcome.

Accidents, Traffic↗
PubMed2002

Implication of PBP74/mortalin/GRP75 in the radio-adaptive response.

PURPOSE: To investigate the relationship between expression of the human peptide-binding protein PBP74 and the occurrence of an adaptive response to ionizing radiation. MATERIALS AND METHODS: Human tumour cell lines HT29 and MCF-7 were transfected with a PBP74 or PBP74 antisense construct. For demonstration of an adaptive response, cells lines were irradiated with a conditioning dose of 0.25 Gy cobalt-60 gamma-rays followed by a second dose of 4.0 Gy after an interval of 4.5 h. Response was measured in terms of clonogenic survival. RESULTS: Transfection of a PBP74 plasmid caused transient overexpression of PBP74 mRNA in both cell lines. The optimal dose for the induction of PBP74 in the cell lines investigated was 0.1-0.25Gy and PBP74 induction occurred within 30 min of irradiation. For both cell lines, the adaptive response was repressed when cells were transfected with the anti-PBP plasmid. However, the converse, an enhancement of the adaptive response in cell lines transfected with the PBP74 construct, was seen only for HT29 cells under certain experimental conditions. CONCLUSIONS: The results support the view that while PBP74 is necessary to the adaptive response, it may not by itself be sufficient for the adaptive response to occur.

Adaptation, Physiological↗
PubMed2000

In vitro response of human and porcine vascular cells exposed to high dose-rate gamma-irradiation.

AIM: The objective of this study was to compare the in vitro response of human and pig endothelial cells, smooth muscle cells and fibroblasts exposed to conventional high dose-rate gamma-irradiation. MATERIALS AND METHODS: Clonogenic cell survival and growth responses were obtained after irradiation of plateau-phase cells with a 60Co source at a dose-rate of 1.5 Gy/min. DNA single-strand breaks were also evaluated using an alkaline filter elution technique. RESULTS: Overall, both the pig and human cell lines showed a similar response to conventional high dose-rate irradiation. Using clonogenic assays, the human aortic smooth muscle cell line was more sensitive than the fibroblast and endothelial cell lines, whereas the pig endothelial cell line was more sensitive than smooth muscle cells and fibroblasts. Shortly after irradiation (10 days) there was a temporary growth arrest, which was similar for endothelial, smooth muscle cells and fibroblasts with doses above 6 Gy. There was also a non-linear, dose-dependent growth delay up to 4 weeks after irradiation. This effect was also consistent between the different cell lines. Using alkaline filter elution, there was no significant difference in relative elution between endothelial cells, smooth muscle cells and fibroblasts, indicating similar DNA damage among the different cell lines. CONCLUSION: The in vitro response of human and pig endothelial cells, smooth muscle cells and fibroblasts exposed to high dose-rate irradiation appeared similar. The pig model seems well suited to evaluate the short- and long-term effects of ionizing radiation in the prevention of restenosis after vessel injury.

Adult↗
PubMed1999

Tumor radiosensitization by sustained intratumoral release of bromodeoxyuridine.

We have previously reported that the use of the polymer bis(p-carboxyphenoxy)propane-sebacic acid (20:80) for intratumoral delivery of cis-platinum in a mouse tumor model (RIF-1) potentiated the effects of acute and fractionated radiation. This mode of drug delivery seems particularly applicable to the administration of radiosensitizing drugs because an optimum concentration of radiosensitizer can be maintained in the tumor over the prolonged period required for fractionated radiation treatment. We have now investigated, in the same tumor model, radiosensitization by the thymidine analogue bromodeoxyuridine (BrdUrd). BrdUrd (20%, w/w) was incorporated into bis(p-carboxyphenoxy)propane-sebacic acid (20:80) and polymer rods containing the drug implanted in the RIF-1 tumor. Preliminary in vitro studies of the rate of release of BrdUrd from the polymer showed an initial rapid loss over 24 h, followed by a slower release extending over the next 5 days. In experiments in which tumor cells, which had incorporated BrdUrd in vivo from implanted polymer, were excised and a single cell suspension irradiated in vitro radiosensitization indicative of BrdUrd incorporation was associated mainly with an increase in the alpha constant for the linear quadratic model of cell survival. Radiosensitization was seen for tumor cells harvested between 5 and 10 days after polymer implant, a finding that is consistent with results of experiments in which the percentage of cells that had incorporated BrdUrd were measured by flow cytometry at various times after polymer/BrdUrd implant. The proportion of tumor cells positive for BrdUrd was 40-50% between 3 and 8 days after polymer implant. When tumors were irradiated in situ and response measured in terms of tumor growth delay (TGD), radiosensitization was not seen for an acute dose of 16.5 Gy. In contrast, significant radiosensitization was seen for fractionated treatments when polymer/BrdUrd was implanted 3 days before the first radiation dose. For a dose of 5 x 6 Gy, TGD was increased from 22 days for radiation alone to 27 days for radiation plus polymer implant. For 10 x 6 Gy fractions, TGD increased from 45-77 days for those mice in whom the tumor eventually regrew, whereas for 25% of the mice in this group the tumor volume was reduced to a point where it was no longer detectable and there was no recurrence for at least 120 days after treatment.

Animals↗
PubMed1999

Radiosensitization of a mouse tumor model by sustained intra-tumoral release of etanidazole and tirapazamine using a biodegradable polymer implant device.

BACKGROUND AND PURPOSE: Drug toxicities are often a limiting factor in long term treatment regimes used in conjunction with radiotherapy. If the drug could be localized to the tumor site and released slowly, then optimal, intra-tumoral drug concentrations could be achieved without the cumulative toxicity associated with repeated systemic drug dosage. In this paper we describe the use of a biodegradable polymer implant for sustained intra-tumoral release of high concentrations of drugs targeting hypoxic cells. MATERIALS AND METHODS: The RIF-1 tumor was implanted subcutaneously or intramuscularly in C3H mice and irradiated with 60Co gamma rays. The drug delivery device was the co-polymer CPP-SA;20:80 into which the drug was homogeneously incorporated. The hypoxic radiosensitizer Etanidazole or the bioreductive drug Tirapazamine were delivered intra-tumorally by means of implanted polymer rods containing the drugs. Tumor growth delay (TGD) was used as the end point in these experiments. RESULTS: Both Etanidazole and Tirapazamine potentiated the effects of acute and fractionated radiation in the intra-muscular tumors but neither drug was effective in sub-cutaneous tumors. Since both drugs target hypoxic cells we hypothesized that the lack of effect in the subcutaneous tumor was attributable to the smaller size of the hypoxic fraction in this tumor model. This was confirmed using the hypoxia marker EF5. CONCLUSIONS: These results indicate that the biodegradable polymer implant is an effective vehicle for the intra-tumoral delivery of Etanidazole and Tirapazamine and that, in conjunction with radiation, this approach could improve treatment outcome in tumors which contain a sub-population of hypoxic, radioresistant cells.

Animals↗
PubMed1998

Genetic analysis of the yeast NUD1 endo-exonuclease: a role in the repair of DNA double-strand breaks.

The deoxyribonucleases (DNases) have been shown genetically to be important in the vital processes of DNA repair and recombination. The NUD1 gene, which codes for an endo-exonuclease of Saccharomyces cerevisiae, was analyzed for its role in the DNA double-strand break (DSB) repair processes. While the nud1 strain is only slightly sensitive to ionizing radiation, expression of the HO-endonuclease to introduce a DSB at the MAT locus in that strain results in cell death. Cell survival is inversely proportional to the duration of HO-endonuclease expression. Analysis of the surviving colonies from the nud1 strain indicated that many of the survivors are sterile and that the proportion of these sterile survivors increases with the time of HO-endonuclease expression. On the other hand, the surviving colonies from the isogenic NUD1 strain are mating-proficient. Interestingly, double mutants of nud1 rad52 are more resistant to ionizing irradiation than the rad52 strain and have a cell-survival fraction of 32% for rad52-1 nud1 and 9% for rad52::URA3 nud1 following prolonged HO-endonuclease expression, indicating that nud1 has a suppressor effect on the DSB-induced lethality in rad52. Polymerase chain reaction analysis showed that many of the nud1 survivors contained small alterations within theMAT locus, suggesting that the survivors arose through the process of non-homologous end-joining. These results suggest that the endo-exonuclease acts at a DSB to promote DNA repair via the homologous recombination pathway.

DNA↗
PubMed1997

Low doses of ionizing radiation induce nuclear activity in human tumour cell lines which catalyzes homologous double-strand recombination.

Activity catalysing double-strand DNA recombination has been investigated in human tumour cell lines using an in vitro assay in which nuclear extracts from tumour cells are used to catalyse homologous recombination between deletion plasmids. The cell lines investigated showed comparable constitutive levels of recombination activity. In several cell lines a two- fold to fourfold increase in the frequency of double-strand recombinational events catalysed by nuclear extracts was observed if the cells were exposed to low doses of ionizing radiation. The response was greatest for cells harvested at 6 h after radiation exposure, and the dose to produce an optimal effect was 25 cGy. Cell lines showing this response included a relatively radioresistant human colon cancer line and two cis-DDP (cis-diamminedichloroplatinum II) resistant ovarian tumour cell lines which are cross-resistant to radiation. Sub-lethal doses of cis-DDP were also effective in inducing upregulation of recombinational activity in the cis-DDP resistant cell lines. No change in recombinational activity was seen for radiation/drug-sensitive ovarian cell line following exposure to low drug or radiation doses. These findings are of particular interest since they involve a radiation-induced process with potential for direct involvement in DNA repair. Further studies will be aimed at determining if the extent of resistance to cytotoxic agents is causally related to the degree of inducible recombination activity.

Antineoplastic Agents↗
PubMed1997

Induction of PBP74/mortalin/Grp75, a member of the hsp70 family, by low doses of ionizing radiation: a possible role in induced radioresistance.

The identification of genes whose expression is altered following exposure to a low dose of ionizing radiation (IR) is an important step in understanding the phenomenon of the adaptive response. Using the differential mRNA display method we have identified a gene whose expression is up-regulated following exposure to 0.25 Gy IR. Partial DNA sequence and restriction endonuclease analysis of this gene showed that it is identical to the gene encoding for the human peptide-binding protein 74 (PBP74/mortalin/Grp75), a member of the heat shock 70 protein family. Time-course measurement of the PBP74/mortalin/Grp75 mRNA showed that its level was elevated after a lag of at least 15 min. The maximum induction appears to be at 30 min following gamma-irradiation and there is then a steady decline to control levels within 5 h in the HT29 cell line. On the other hand, the level of the PBP74/mortalin/Grp75 mRNA in the human breast adenocarcinoma cell line MCF-7 is consistently elevated after gamma-irradiation for up to 6 h post-irradiation. Furthermore, a cell line that does not demonstrate the induced radioresistance phenomenon (SW48) shows no induction of the PBP74/mortalin/Grp75 mRNA in contrast with HT29 or MCF-7. Treatment of the HT29 cells with antisense oligonucleotide directed towards the initiation codon of PBP74 sensitized cells to ionizing radiation.

Base Sequence↗
PubMed1995

Mammalian endo-exonuclease activity and its level in various radiation sensitive cell lines.

The levels of endo-exonuclease in various mammalian cell lines were examined. While the expression of the endo-exonuclease during cell growth behaved exactly the same as the pattern observed in lower eukaryotes, the amount of activity was found to be reduced in the radiosensitive Chinese hamster ovary (CHO) xrs-5 and various human AT, AT-5 and NE-1 cells when compared to the radionormal CHO K1 and human HeLa cell lines. The reduced endo-exonuclease activity in these cells was due to a decreased amount of protein as demonstrated with the immuno-blot method. The results presented here suggest that endo-exonuclease may be one of the many proteins whose expression is regulated by genes coding for xrs-5 in CHO and AT in humans.

Animals↗
PubMed1994

Amplification of the graft-versus-host reaction by cyclophosphamide: dependence on timing of drug administration.

An experimental model, previously developed to study the combined effect of partial body irradiation and the graft-versus-host (GVH) reaction, has been adapted to assay the amplification of the GVH reaction by cyclophosphamide (CY). The system has proved sensitive enough to detect differences in the level of the GVH reaction produced by relatively small changes in pre-transplant conditioning. F1 hybrid mice treated with either CY 60 mg/kg or allogeneic (parental) lymphoid cells (ALC, 20 x 10(6)) had 100% survival. In contrast, ALC given 24 h after CY injection resulted in 84% GVHD-related mortality with a mean survival time of 18 days. Amplification of the GVH reaction by CY was also seen in terms of splenomegaly and immunosuppression. Separation of CY and ALC injection by an interval longer that 24 h reduced the severity of GVH reaction but some amplification was still observed. Based on several GVHD-related criteria, experimental groups with a 2 or 4 day interval between CY and ALC injection had approximately the same response, an effect was still detectable for an interval of 7 days between injections but was no longer apparent when the interval was extended to 12 days.

Animals↗
PubMed1994

Radiation resistance in a melphalan-resistant subline of a rat mammary carcinoma.

A subline of a rat mammary carcinoma (MATB 13762), selected for resistance to melphalan, is cross-resistant to other alkylating drugs, to unrelated drugs and to ionizing radiation. The difference in radioresponse between the sensitive wild-type cell line and the melphalan- and radiation-resistant line (MLNr) is related to the size of the alpha component in the linear-quadratic model. Reduction of dose rate does not affect the response of MLNr cells but does increase survival for wild-type cells. MLNr cells have elevated levels of reduced glutathione (GSH) and overexpress redox enzyme glutathione-S-transferase and glutathione peroxidase. Modest depletion of GSH (to 50% of control) radiosensitizes MLNr cells but not wild-type cells. On the basis of the results of an excision assay, growth delay and tumor control experiments, MATB MLNr tumors are also more radioresistant than wild-type cells when irradiated in situ. However, wild-type cells irradiated shortly after excision of the tumor are much more radioresistant than the same cells irradiated 24 h after excision or maintained in culture, and their response resembles that of MLNr cells irradiated under the same conditions. These results suggest that, in spite of some similarity between in vivo and in vitro observations, intrinsic radioresistance is not the most important factor influencing the response of MLNr cells in vivo.

Animals↗
PubMed1993

Factors influencing lung density in experimental models: results of studies using CT densitometry.

Lung density measurements using computed tomography have been made in mice, rats, and pure-bred beagles and mongrel dogs. Density was found to be dependent on a number of factors including the location of the area scanned, and the age and species of the animal. Lung density was found to decrease by approximately 40% from initial values in a group of rats scanned at intervals between 30 and 800 days old. Age-related density changes were not seen for the lungs of mice or dogs; however measurements were not made over a prolonged period. A gradient of increasing density from the base to apex of the lung was seen for 30 and 175-day-old rats (scanned in the prone position) while an apex to base density gradient was seen for both types of dog studied (scanned in the supine position). In none of the species studied was there a systematic difference in density of the right and left lungs. Differences in average lung density between the mice, rats and dogs reported here are consistent with the relationship between lung morphology, metabolic rate and body size which obtains for a range of mammalian species.

Absorptiometry, Photon↗
PubMed1993

In vivo reversal of doxorubicin resistance by a new tiapamil analog Ro11-2933.

The effectiveness of a calcium antagonist analog Ro11-2933 to modulate doxorubicin (DOX) response in DOX-sensitive (WT) and -resistant (DOXr, 200-fold) cell lines was investigated and compared to verapamil (VP) in vitro and in vivo in rats bearing mammary carcinoma using equivalent nontoxic doses. In vitro exposure to a nontoxic concentration of Ro11-2933 (2 microM) normalizes the DOX accumulation defect observed in DOXr cells, increases DOX-induced DNA single-strand breaks and effectively sensitizes DOXr cells to DOX. Ten microM VP was required to obtain an effect equivalent to that seen with 2 microM Ro11-2933. Intravenous administration of DOX at 5 mg/kg to the rat bearing the DOXr tumors has no significant therapeutic effect on tumor growth (P > .5), whereas it was found effective in inhibiting the growth of WT tumors (P < .05). Ro11-2933 or VP administered alone has no significant effect on tumor growth as compared to a saline-treated group (P > .1). Combination of Ro11-2933 with DOX effectively inhibits DOXr tumor growth as compared to DOX alone. Combination of DOX with VP was found less effective than Ro11-2933 and the results were not statistically significant from DOX treatment alone (P > .5). Our data demonstrate that Ro11-2933 is well tolerated after i.v. administration and an effective modulator of DOX resistance in a solid tumor model.

Animals↗