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Biomedical subjects

J Denekamp

Publications and source records attributed to J Denekamp.

At least 73 records · Page 4Linked to original sources
PubMed1991

Selective induction of endothelial cell tissue factor in the presence of a tumour-derived mediator: a potential mechanism of flavone acetic acid action in tumour vasculature.

Flavone acetic acid (FAA) is a potentially useful anti-tumour agent which has been reported to induce changes in tumour vasculature, in particular loss of bloodflow. This led us to examine whether endothelium could be a cellular target of FAA action, with resultant modulation of cell-surface coagulant properties leading to activation of coagulation and blockade of tumour blood flow. Incubation of endothelium with FAA led to the expression of functional tissue factor on the cell surface, in a time-dependent and dose-dependent (half-maximal at 0.6-0.7 mg/ml) manner. Induction of tissue-factor activity resulted from de novo translation of the tissue factor message. To explain the selectivity of FAA's action on tumour vasculature in vivo, we considered its interaction with tumour-derived factors. Starting with serum-free FO-I-melanoma cell-conditioned medium, a co-factor enhancing FAA-mediated induction of endothelial tissue factor (FO-I factor) was partially purified by sequential ion exchange and reverse phase chromatography, followed by preparative SDS-PAGE. The FO-I factor migrates with an apparent Mr of approx. 20 to 25,000 on non-reduced SDS-PAGE, is sensitive to protease K, and augments the effect of FAA on endothelial-cell-tissue factor. This activity is not found in supernatants from non-neoplastically transformed cell lines. These data lead us to hypothesize that FAA exerts its action, at least in part, by promoting activation of coagulation on the endothelial surface, and this effect is selective for the tumour bed by virtue of its interaction with a tumour-derived factor. The interaction of FAA with host factors may be important for optimizing its therapeutic efficacy for a particular tumour.

Blood Coagulation Factors↗
PubMed1991

Early detection of damage following bilateral renal irradiation in the mouse.

The rate and early pattern of development of radiation-induced renal damage has been determined in the mouse by measuring reductions in both haematocrit and excretion of 51Cr-EDTA, and increases in both urination frequency and urine volume. Kidneys of CBA mice were irradiated bilaterally with 2 fractions of X-rays, one week apart. Renal function was determined immediately prior to irradiation and at 3-4 weekly intervals to 22 weeks post-irradiation. Onset of damage was detected as early as 3-6 weeks using the urination frequency assay. This was confirmed by estimating the volume of urine excreted. A significant fall in haematocrit was not detected until 6-9 weeks post-treatment and a fall in isotope clearance was not detected significantly until 12 weeks. This early detection of damage was consistent with reports using both mouse and other species. The time at which damage was detected first was independent of radiation dose for the frequency and haematocrit assays. For 51Cr-EDTA clearance, there was the suggestion of earlier functional loss for the higher doses. Following the onset of damage, a steady, dose-dependent decline in renal function was measured by all assays. The latency period is defined as the time required to reach a given level of functional damage. This time decreased with increasing radiation dose, to a minimum value set by the time of onset of damage, which varied from 3 to 12 weeks, depending on the assay used. The differences in response measured prior to 12 weeks post-irradiation represent the first occasion on which a dissociation between these 3 assays has been detected.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Vascular attack as a therapeutic strategy for cancer.

The blood supply to all solid tumours consists of parasitized normal vessels and new vessels which have been induced to grow by the presence of the tumour. These vessels are inadequate in many respects, being tortuous, thin-walled, chaotically arranged, lacking innervation and with no predetermined direction of flow. The walls consist of a basement membrane lined with rapidly proliferating immature endothelial cells, and are more permeable than normal vessels. The spacing of the vessels and their average diameters are not optimal for nutrient provision. This paper focuses on the evidence that many existing therapies may already have, as part of their action, a vascular mediated process of killing tumour cells. This may result from local changes within individual vessels or from systemic alterations in blood pressure, viscosity, coagulability etc. The hallmarks of vascular injury are identified and the dangers of discarding useful anticancer agent by failing to understand their mechanism of action are highlighted.

Animals↗
PubMed1990

Preclinical evaluation of pions in vivo: experience at TRIUMF.

This paper describes the results obtained from in vivo studies of the pion beam at the TRI University Meson Facility (TRIUMF). The studies encompass work (from 1978 to 1986), designed to evaluate the RBE for early and late effects and to assess the importance of X-ray dose rate and treatment volume on these values. Results with early responding tissues, i.e. mouse and pig skin and mouse intestine indicate a pion RBE of about 1.5 in the clinically relevant dose per fraction range of 2-3 Gy. At these doses, RBE appears to be independent of the reference X-ray dose rate. However, at high doses per fraction, the RBE values become increasingly X-ray dose rate dependent. The induction of late effects by pions has been assessed by monitoring the late dermal response of pig skin; late fibrosis was not assessed in this study. The values obtained using the chosen endpoint indicate that the RBE is not significantly higher than that seen in any of the early responding tissues for pion doses as low as 2-3 Gy per fraction. The effect of increasing the treatment volume for pion therapy has been assessed using mouse intestine. The results show that for a constant field size, RBE decreases with increasing peak width. However, if peak width is held constant and field size increased, there is evidence for an increased RBE.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Leukocyte antigen CD34 is expressed by a subset of cultured endothelial cells and on endothelial abluminal microprocesses in the tumor stroma.

It has been reported that the human haemopoietic progenitor cell antigen CD34 is also expressed by vascular structures. To investigate its precise vascular localization, we have studied the cellular and subcellular distribution of CD34 in normal tissues and pathologic tissues with neovascularization. In normal resting tissues, anti-CD34 antibodies, ICH3 and QBEND-10 predominantly stain the luminal endothelial membrane, whereas the abluminal membrane is negative or weakly positive. In contrast, a striking staining of endothelial abluminal microprocesses (EAM) was found in the tumor stroma. These structures, measuring up to 20 microns in length, could be observed in thick vibratome sections both at the tips of vascular sprouts and, also frequently, on fully formed microvessels. The number of vascular sprouts and EAM varied widely between different tumors. CD34-stained EAM were sparsely present in fetal tissue of 10 weeks gestation, but they could not be demonstrated in granulation tissue of wound healing. By immunoelectron microscopy, the EAM were continuous with the cytoplasm of endothelial cells showing an immature phenotype as seen in regeneration. In cultured human umbilical vein endothelium, CD34 was preferentially found on a small subset of cells with the morphologic appearance of migrating cells. These findings suggest that CD34 is an endothelial marker for EAM present during angiogenesis.

Antibodies, Monoclonal↗
PubMed1989

The fractionated response of mouse stroma after X-rays and neutrons: influence of early vs late expression of damage.

The sparing effect of dividing a radiation treatment into many small fractions is different for acutely responding tissues and those which have delayed expression of injury. We have used the Tumour Bed Effect assay (TBE) to investigate the influence of the time of damage expression on the response of the normally quiescent subcutaneous stroma. Implanted tumour cells provide an angiogenic stimulus which forces the vasculature to proliferate. The subcutaneous stroma of the mouse dorsum was irradiated with one to 32 equal fractions of X-rays, followed by a top-up dose of neutrons. CaNT cells were implanted into the treated site either within 3 days or not until 6 months after irradiation, to stimulate the expression of latent injury. The dose-response curves obtained for tumour growth in irradiated sites were much steeper at 1 to 3 days than at 6 months, suggesting some sort of repair of damage during this period. There was no suggestion that repair occurred preferentially after low doses per fraction and the alpha/beta ratio remained unchanged when the expression of stromal injury was delayed. The time of damage expression therefore seems unlikely to explain the difference in the alpha/beta ratios measured for early and late responding tissues. Rather, it seems to be determined by the proliferative status of the tissue at the time of irradiation.

Animals↗
PubMed1989

An experimental study of tumour size and radiosensitivity: analysis by regrowth delay.

When designing experimental studies of tumours, it is considered important to control all variables that might alter the radiosensitivity and hence influence the variability of the data. One such variable is tumour size. We have studied the regrowth delay of a mammary carcinoma treated at 2-10 mm mean diameter (a 125-fold change of volume) with X-rays alone or X-rays plus misonidazole (MISO). The data were analysed to give dose-response curves, using four endpoints. Regrowth to a fixed size (4.5 mm larger than treatment size), or by a fixed increment (4 times the original volume) was expressed either as absolute delay, or as specific growth delay to allow for the changes in volume doubling time as the tumour grows. The method of analysis made no difference to the measured sensitizer enhancement ratio (SER) for MISO. The SER was dose-dependent, being higher at higher doses, but was not different in tumours of 2 or 10 mm diameter. However, when comparing response to X-rays alone, the method of analysis made a very big difference to the conclusions. Regrowth to R + 4.5 mm showed no change in radiosensitivity with tumour size, but regrowth to 4 times the original volume (the most logical endpoint) indicated that large tumours were more sensitive than small. We conclude that regrowth delay may be an inappropriate method for comparing absolute sensitivities of tumours of different sizes. However, for studying the effectiveness of a radiomodifier the constraints of tumour size at irradiation seem to be less severe than previously believed.

Animals↗
PubMed1989

Vascular collapse after flavone acetic acid: a possible mechanism of its anti-tumour action.

Flavone acetic acid (FAA, LM 975) causes regression and growth retardation in several solid murine tumours. The mechanism of action is unknown, although various lines of evidence suggest an indirect cytotoxic effect. We have carried out preliminary studies on the effect of FAA on relative blood flow in six experimental murine tumours using 86RbCl extraction. We have also measured growth delay after treatment with the same dose of FAA (200 mg/kg). The data show that the drug induces a drop in tumour perfusion within 6 h of treatment in all of the tumours, and that this can be correlated with the growth delay measured. We conclude that vascular collapse may be an important component of the action of this drug, and that further investigation of this phenomenon is warranted.

Animals↗
PubMed1989

Radioprotection of normal tissues of the mouse by hypoxic breathing.

Hypoxic breathing during irradiation has been advocated as a therapeutic modality, to increase the efficacy of radiotherapy. In this form of treatment, the total and daily X-ray dose is increased by a factor of 1.25, on the assumption that all normal tissues in the beam will be protected to a similar extent by breathing gas containing a reduced oxygen concentration (usually 10%). To test this concept, we have determined the effect of varying the inspired oxygen tension on the radiosensitivity of 3 normal tissues in the mouse (kidney, jejunum and skin), and have compared these results with data from the literature for mouse lung. Reduction of the inspired oxygen tension from 21% (air) to 7-8% led to much greater radioprotection of skin (protection factor 1.37) than of lung (1.09). Protection factors for jejunum and kidney were 1.16 and 1.36 respectively. The results show that the extent of radioprotection afforded by hypoxic breathing is tissue dependent, and that great care must be taken clinically in choosing the increased radiation dose to be used in conjunction with hypoxic breathing.

Animals↗
PubMed1989

Biphasic survival curves for XRS radiosensitive cells: subpopulations or transient expression of repair competence?

Four of the most radiosensitive xrs variants of CHO-K1 cells, obtained after mutagenizing treatment with EMS, have been studied in detail over three to five decades of cell survival. Although these lines were initially reported to have very steep exponential survival curves, and to vary in sensitivity between themselves by a factor of two, we found in each case a similar biphasic response. The initial sensitivity was similar for all four lines, with a D0 of 0.5-0.7 Gy. A subpopulation, representing between 0.4 and 12 per cent of the cells, showed a resistant response, characterized by a D0 of 1.5-2.0 Gy. The previously reported variation in sensitivity seems to result from differences in the fraction of resistant cells rather than from differences in the D0. The consequence of such phenotypic variants within each cloned line is considerable, both for radiobiological studies of repair, and for molecular biology studies of the repair genes. Attempts were made to clone the sensitive and resistant subpopulations from each xrs cell line. Simple cloning from an untreated population was expected to yield pure sensitive cells, but these cells also gave biphasic responses in most cases. Only the cell line with the lowest resistant fraction (xrs5) gave a completely sensitive response in two of its subclones. Cells selected as survivors after high radiation doses were expected to yield resistant populations. However, for xrs4, 5 and 7 these subclones all gave biphasic responses. Three of the subclones from xrs6 gave biphasic responses but others gave a resistant response close to the wild type. We present a model in which transient gene expression may be seen in each individual cell if the silent copy of the xrs repair gene is temporarily hemimethylated. This transient gene transcription should occur during DNA synthesis, in the interval between synthesis of the gene and maintenance methylation. This interval may vary from cell line to cell line, resulting in different fractions of resistant cells.

Animals↗
PubMed1988

Validation of the fluorescent dye Hoechst 33342 as a vascular space marker in tumours.

The DNA-binding fluorescent dye Hoechst 33342 (H33342) has been used in a series of investigations of the vascular parameters of two murine tumours. This dye has been shown, to have a short half-life in the circulation (T1/2 less than 2 min), but is stably bound for at least 2 h after it enters cells. It can be used in morphometric studies on frozen sections to determine the effective vascular volume, the capillary fraction and the size distribution of blood vessels in each tumour. These latter two parameters cannot be deduced from the less labour intensive techniques using radioactive isotopes. The effective vascular volume perfused in 1 min by H33342 was compared with the volume perfused in 30 min with 51Cr labelled erythrocytes. Similar volumes were estimated with the two techniques in a murine carcinoma and in a sarcoma. Both techniques showed that the vascular volume decreased in larger tumours. The H33342 analysis of vessel size showed the decrease in capillary vessels in the carcinomas was even greater, falling from 70% in small tumours to 20% in larger tumours. The deteriorating vascular network in larger tumours is associated with an increasing fraction of necrotic tissue. Experiments in which the isotopes and dye were co-injected suggest that at 40 mgkg-1 the dye may rapidly lead to a partial shutdown of the tumour vascular bed. This is less marked with 20 mg kg-1. In spite of this effect there is in general a close correlation between the volumes perfused by labelled red blood cells and the fluorescent dye.

Adenocarcinoma↗