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Biomedical subjects

D J Chaplin

Publications and source records attributed to D J Chaplin.

At least 91 records · Page 5Linked to original sources
PubMed1994

Reducing acute and chronic hypoxia in tumours by combining nicotinamide with carbogen breathing.

The ability of nicotinamide and carbogen breathing to improve the radiation response of a C3H mammary carcinoma by reducing both acute and chronic hypoxia was investigated. Using a tumour growth delay assay the response of 200 mm3 foot tumours to local irradiation was found to be increased by either injecting nicotinamide (100-1,000 mg/kg) 20 min prior to irradiation, or by allowing mice to breathe carbogen for 10 min before and during the radiation treatment. The greatest radiosensitization occurred when nicotinamide and carbogen were combined. With a histological fluorescent staining technique nicotinamide was shown to prevent transient stoppages in microregional blood flow, and also appeared to improve tumour oxygenation as measured with an Eppendorf oxygen electrode, both effects being consistent with its ability to decrease perfusion limited acute hypoxia. Carbogen had no effect on vessel closure, but it significantly improved tumour oxygenation, which was indicative of it reducing diffusion limited chronic hypoxia.

Animals↗
PubMed1993

Vinca alkaloids: anti-vascular effects in a murine tumour.

We have investigated the blood flow modifying effects of the vinca alkaloids, vincristine and vinblastine in the murine carcinoma CaNT. Vinblastine at doses of 7.5 or 10 mg/kg induced profound and chronic reductions in tumour blood flow as measured by 86RbCl extraction. Following the maximum tolerated dose of 10 mg/kg, blood flow was reduced to 10% of pretreatment values after 2 h and remained below 20% of pretreatment values 24 h after drug administration. These findings are consistent with the early induction of necrosis by vinblastine and suggest that vascular-mediated cell death may account for a large part of the 11 day growth delay induced by this drug dose. In contrast to the large reductions in tumour blood flow, in skin, kidney, liver and muscle, blood flow reductions did not, at any time examined, exceed 40%. In all the normal tissues studied, blood flow had fully recovered by 6 h after vinblastine administration. Similar results, albeit less pronounced, have been obtained with vincristine at the maximum tolerated dose of 3 mg/kg. The results clearly show that both vinblastine and vincristine can induce, with some selectivity, a dramatic and prolonged reduction in tumour blood flow and that this may contribute to the anti-tumour effects against the CaNT tumour.

Adenocarcinoma↗
PubMed1993

Further evaluation of nicotinamide and carbogen as a strategy to reoxygenate hypoxic cells in vivo: importance of nicotinamide dose and pre-irradiation breathing time.

The combination of nicotinamide and carbogen breathing is awaiting clinical evaluation as a strategy to overcome tumour hypoxia and thus enhance radiation response. We have continued our evaluation of this approach in the murine SCCVII tumour with the aim of determining the importance of nicotinamide dose and the pre-irradiation breathing time (PIBT) for carbogen. For carbogen breathing alone maximal enhancement of radiation response was observed with PIBT's of between 5 and 30 min. When nicotinamide (1,000 mg kg-1 IP) was administered 60 min prior to irradiation little or no variation in radiation response was observed for all the PIBT's examined (5-90 min). Indeed at all PIBT's the cell survival obtained for the carbogen nicotinamide and radiation combination was indistinguishable from that expected for a fully aerobic response. For PIBT's of 15 and 60 min we examined the influence of nicotinamide doses between 50 and 1,000 mg kg-1. Significant radiosensitizing effects were observed for all nicotinamide doses tested above 50 mg kg-1. Moreover for doses of 250 mg kg-1 and above the cell survival data was consistent with that expected for a fully aerobic response. No additional benefit accrued from raising the nicotinamide dose above 250 mg kg-1. These results indicate that significant radiosensitization may be expected even with clinically achievable nicotinamide doses when it is combined with carbogen breathing. Furthermore, the use of nicotinamide may reduce the critical importance of PIBT on the radiosensitization observed with carbogen.

Administration, Inhalation↗
PubMed1993

The effect of pH on the aerobic and hypoxic cytotoxicity of SR4233 in HT-29 cells.

We have observed that low pH can substantially potentiate the cytotoxic effect of the bioreductive drug SR4233 in aerobic HT-29 human tumour cells. No such potentiation was observed under hypoxic conditions. This pH effect might be relevant both to the therapeutic effectiveness and to the normal tissue toxicity of this new agent.

Antineoplastic Agents↗
PubMed1992

The response of murine B-16 melanoma to fractionated doses of pions.

The relative biological effectiveness (RBE) of pions has been studied in mouse B-16 melanoma transplanted into C57BL/6 mice. To determine the RBE at both high and low doses per fraction, a range of fractionation schedules was used, with 1, 4 and 10 fractions. The reference 250 kV X ray dose rate was 1.5 Gy/min which was much higher than the dose rate of pions (0.25 Gy/min). The RBE varied depending on the number of fractions and, within the same fractionation schedule, also on the dose per fraction. The RBE ranged from 1.15 for single fractions at 12.5 days of growth delay, to 1.80 for 10 fractions at 5 days of growth delay, which was determined by the time taken for the tumors to reach 5 times the average of their original volume. RBEs at the iso-effect level of 10 days growth delay were 1.20, 1.29 and 1.62 for single, 4 fractions and 10 fractions, respectively. RBE values were influenced by both the number of fractions and the dose per fraction, that is, the larger the number of fractions and the smaller the dose per fraction, the larger the value of RBE. In comparison with RBE of normal mouse skin, it was suggested that pion therapy may provide advantage over conventional photontherapy for radioresistant tumors such as this melanoma with the maximum therapeutic gain factor of 1.2. alpha/beta ratios for B-16 melanoma were also obtained from the 10 day growth delay iso-effect curve, and were 10.5 Gy and 32.6 Gy for X ray and pions, respectively.

Animals↗
PubMed1992

The effect of hypoxia and low pH on the cytotoxicity of chlorambucil.

Studies with mouse tumors have shown that the effectiveness of certain chemotherapeutic agents can be enhanced if they are used in appropriate combination with an anti-hypertensive drug such as hydralazine. This results in reduced tumor blood flow with, among other things, a consequent decrease in oxygenation and increase in acidity in the tumor tissue. The purpose of the present work was to determine to what extent hypoxia and low pH are involved in the mechanism of this effect for chlorambucil. V79-WNRE cells were exposed to various drug concentrations under aerobic or hypoxic conditions, pH 6.4 or 7.4. Measurements of cell survival following 1 hr exposure at 37 degrees C showed that pH 6.4 produced a large potentiation of cell killing by chlorambucil (ER = 4 approx.); hypoxia, on the other hand, had little effect. The potentiation was shown to be greatest for pH values below 7.0. HPLC measurements of drug uptake were made since it was anticipated that chlorambucil, a weak acid, might tend to accumulate in cells under conditions of low extracellular pH. It was found that at an extracellular pH of 6.4 the ratio of the intracellular (Ci) and extracellular (Ce) drug concentrations was increased 4.5 and 3.6 fold for aerobic and hypoxic conditions, respectively. This probably explains most, if not all, of the cell killing potentiation observed at low pH.

Animals↗
PubMed1992

Biochemical and physiological changes induced by nicotinamide in a C3H mouse mammary carcinoma and CDF1 mice.

We have continued our investigation into the mechanism by which nicotinamide can enhance radiation damage in tumors, using a C3H mouse mammary carcinoma grown in CDF1 mice. Biochemical analysis of tumor extracts showed that nicotinamide (1000 mg/kg; i.p.) increased the ATP/Pi and ATP/ADP + AMP ratios. This change in metabolic activity was consistent with nicotinamide increasing tumor oxygenation. Moreover, the greatest effect occurred 0.5-2.5 hr after drug injection, a time at which radiosensitization by nicotinamide in this tumor had previously been shown to be maximal. These changes were observed without any apparent modification in tumor blood perfusion, measured using the 86-RbCl uptake procedure, and occurred despite nicotinamide producing a 50% decrease in mean arterial blood pressure, estimated directly by a carotid cannulation technique.

Adenosine Diphosphate↗
PubMed1992

Tumor blood flow changes induced by chemical modifiers of radiation response.

This study was designed to investigate blood flow changes induced by chemical agents that are commonly used in combination with radiation therapy. The hypoxic cell cytotoxin RSU 1069 at a dose of 100 mg/kg was shown to reduce blood flow by 80% in both SCCVII and C3H mammary tumors. Blood flow reductions of 30-40% were also observed in both tumors following administration of the radiation sensitiser pimonidazole (Ro-03-8799) at a dose of 500 mg/kg. Moreover studies in the C3H mammary tumor indicated that this effect was tumor size-dependent, being more profound and of longer duration in 500 mg than in 100 mg tumors. Blood flow decreases were also observed in the SCCVII tumor after administration of adriamycin at a dose of 15 mg/kg. Blood flow decreased by over 80% immediately after drug administration but recovered to remain 20% below control values 1 hr after drug administration. In contrast to the other agents studied, cis platinum at a dose of 2 mg/kg produced a small 20-30% increase in blood flow which persisted over the 1 hr observation period. The potential implications of these findings are discussed.

Animals↗
PubMed1992

Blood flow modification in the SCCVII tumor: effects of 5-hydroxytryptamine, hydralazine, and propranolol.

The effects of hydralazine, 5-hydroxytryptamine (5-HT), and propranolol on blood flow in the SCCVII tumor were assessed using laser Doppler flowmetry. Both hydralazine and 5-HT, at doses of 1 and 5 mg/kg, reduced blood flow, as did propranolol at 10 mg/kg. Hydralazine and 5-HT at doses of 0.25 mg/kg slightly increased tumor blood flow, and a 10-20% increase in blood flow was also observed after 1 mg/kg of propranolol. However, propranolol at 1 mg/kg enhanced the blood flow reduction observed with 1 mg/kg of hydralazine. The concomitant administration of hydralazine and propranolol at these doses also translated into increased potentiation of the tumor cytotoxicity of the hypoxic cell cytotoxin RSU-1069.

Animals↗
PubMed1991

Photofrin uptake by murine macrophages.

The uptake of Photofrin by murine peritoneal macrophages in vivo and in vitro was examined. Cellular Photofrin content was measured either by performing a fluorometric assay or by using 14C-labeled drug. For comparison, the uptake of Photofrin by murine SCCVII tumor cells (squamous cell carcinoma) was also examined under the same conditions. The data demonstrate that macrophages have a much greater capacity for Photofrin uptake than SCCVII tumor cells. Photofrin contents at 24 h after drug administration (25 mg/kg) measured 420 +/- 90 (SD), 74 +/- 15, and 15 +/- 2 ng/micrograms of cell protein for peritoneal macrophages, tumor-associated macrophages, and SCCVII tumor cells, respectively. Factors that modify macrophage activity also influence the uptake of the drug by macrophages. The results support the assumption that Photofrin uptake by macrophages is dominated by phagocytosis of highly aggregated components of the drug. In vivo accumulated Photofrin material in peritoneal macrophages, tumor-associated macrophages, and tumor cells has shown very similar in vitro clearance from all three cell types. Only 20-30% of Photofrin was lost from the cells during the initial 24 h, mainly between 1 and 4 h of clearance incubation.

Animals↗
PubMed1991

The use of blood flow modifiers to improve the treatment response of solid tumors.

There is now considerable interest in the possible use of agents which can change blood flow in solid tumors and thereby alter the response of tumors to different treatments. In the current presentation we briefly review the types of agents which have the potential to modify tumor blood flow, using nicotinamide. hydralazine, and pyrazinamide as examples and illustrate how they can be used to improve the response of murine tumors to radiation, hyperthermia and cyclophosphamide.

Animals↗
PubMed1991

Drug induced perturbations in tumor blood flow: therapeutic potential and possible limitations.

Chemical modulation of tumor blood flow has until recently received relatively little attention as a therapeutic tool. Developments in the last few years, both in technology and in drug development, have changed this perspective. Fluorescence activated cell sorting techniques have provided evidence for the existence of acutely hypoxic cells resulting from transient fluctuations in microregional tumor blood flow in experimental tumor systems. We have used such techniques to assess the effects of three systemically administered agents, nicotinamide, flunarazine and Flusol-DA, on the amount of acute hypoxia in the SCCVII tumor. The most effective agent identified in this study is the benzamide analog nicotinamide. We suggest that compounds which modulate such hypoxia could well have a role in radiation therapy, particularly when combined with techniques which increase the oxygen carrying capacity of the blood. The potential of tumor blood flow reduction to improve the effectiveness of bioreductive agents administered alone or in combination with radiation and/or hyperthermia, is well established in experimental systems. Further data are presented, which show that combining hydralazine and the beta-blocker propranolol can provide greater reduction in tumor blood flow than observed with hydralazine alone. Potential limitations of drug induced reduction in tumor blood flow are discussed including the possibility of inducing hypoxia in normal tissues.

Animals↗
PubMed1991

Effect of angiotensin II on intermittent tumour blood flow and acute hypoxia in the murine SCCVII carcinoma.

Effects of the vasoconstrictor angiotensin II on tumour microvascular perfusion and oxygenation were examined in the murine SCCVII carcinoma grown subcutaneously in C3H/He mice. Angiotensin II infusion (2 micrograms/kg/min) caused an increase in mouse arterial blood pressure from 85 (2) mm Hg (mean, S.D.) to 112 (7) mm Hg. During drug infusion, tumour red blood cell (RBC) flow (measured by laser doppler flowmetry) increased 206 (50%) (P less than 0.001) in unanaesthetised animals and 305 (90%) (P less than 0.001) in mice immobilised with ketamine and diazepam. As assessed using a fluorescent double-staining technique, angiotensin II reduced staining mismatch (indicative of intermittent blood flow) in SCCVII microvasculature from 8.1 (2.5%) of total vessels to 2.0 (1.3%) (P less than 0.001). However, a large proportion of this reduction could be attributed to volume loading. Angiotensin II reduced but did not completely eliminate the radiobiological acute hypoxia which results from intermittent tumour vessel non-perfusion. We propose that angiotensin II improves tumour microcirculatory flow distribution via its systemic actions, by elevating perfusion pressure, thereby preventing collapse and/or temporary flow stasis in tumour microvessels.

Angiotensin II↗
PubMed1991

Nicotinamide, Fluosol DA and Carbogen: a strategy to reoxygenate acutely and chronically hypoxic cells in vivo.

The effect of Nicotinamide and/or treatment with Fluosol DA and Carbogen breathing on the radiation response of 500-750 mg SCCVII and KHT tumours has been evaluated. Pretreatment with Fluosol DA/Carbogen or Nicotinamide resulted in relatively modest enhancements of radiation damage with enhancement factors of 1.1 and 1.3 being observed using an in vivo/in vitro clonogenic end-point. A combination of Nicotinamide and Fluosol DA/Carbogen resulted in a larger enhancement factor of 1.6 over the radiation dose ranges studied. These modification factors reflect a value close to that expected for a fully aerobic response in this survival range. Growth delay studies in the SCCVII tumour provided similar results. Using a recently developed fluorescence activated cell sorting technique, which utilizes the in vivo pharmacokinetic and DNA binding properties of the bisbenzamide stain Hoechst 33342, the effect of Nicotinamide and/or Fluosol DA/Carbogen schedules on the occurrence of acute hypoxia was assessed. The results clearly show that Nicotinamide significantly reduces the amount of 'acute hypoxia', but has a lesser effect on 'chronic' hypoxic cells. However, combinations of Nicotinamide and Fluosol DA/Carbogen significantly increase the response of both 'acutely' and 'chronically hypoxic' cells. The results provide evidence that a combination of Nicotinamide and Fluosol DA/Carbogen can provide an effective way of reoxygenating both acutely and chronically hypoxic cells.

Animals↗
PubMed1991

Distribution of Photofrin between tumour cells and tumour associated macrophages.

Photofrin levels in cells derived from SCCVII tumours, excised from mice that previously received the drug, were measured using a fluorescence activated cell sorter (FACS). Concomitantly, in the same cells the FACS was used to measure fluorescein isothiocyanate (FITC) fluorescence that originated from FITC-conjugated antimouse IgG added to the cell suspension before sorting. This later measurement enabled discrimination between IgG negative tumour malignant cells and IgG positive host cells (primarily macrophages). In addition, cellular Photofrin content in 'tumour' and 'host' cells sorted by FACS was determined by chemical extraction. The measurements were performed for the time intervals 1-96 h post Photofrin administration. The data showed consistently higher Photofrin levels in the 'host cells', i.e., tumour associated macrophages (TAM), than in 'tumour' cells. On a per cell basis, at any time point studied there was a minimum of 1.7 times more Photofrin in 'host' than in 'tumour cells', while at 4-12 h postadministration, ratios of up to 3.0 times were observed. This corresponds to ratio values greater than 9, when based on Photofrin content per micrograms cell protein.

Animals↗
PubMed1991

Spatial characterization of glutathione depletion in the KHT sarcoma using flow cytometry.

Intravenous administration of the fluorescent DNA stain Hoechst 33342 to tumour-bearing mice was used to label cells proportionally to their proximity from the vasculature. Flow cytometry was used to sort cells from the tumour into populations based on their Hoechst 33342-derived fluorescence. The cell populations were then assayed for their glutathione (GSH) content and their radiosensitivity. Tumours from mice pretreated with buthionine sulphoximine (BSO) were compared with untreated animals. The major findings of this study suggest that the cellular GSH concentration within tumours decreases with distance from the vasculature, and that the GSH concentration within cells from all locations in the tumour can be depleted by enzymatically inhibiting its synthesis using BSO. This depletion of GSH resulted in a small degree of hypoxic radiosensitization of cells both distal and proximal to the vasculature.

Animals↗
PubMed1991

The response of mouse tumours to fractionated doses of pions: determination of therapeutic gain factor.

Using the same experimental system which had been used to determine the pion relative biological effectiveness (RBE) for skin of mouse foot by Chaplin et al., we have determined the pion RBE for KHT sarcoma and SCCVII tumour transplanted in the foot of C3H mice. The pion RBE obtained by the tumour growth delay time method in comparison with 250 kVp X-rays at a dose rate of 150 cGy per min was determined to be 1.20, 1.28 and 1.50 with single, 4 and 10 fractions, respectively, for KHT sarcoma. As for SCCVII tumour, it was determined to be 1.17, 1.45 and 2.05 with single, 4 and 10 fractions respectively. Therefore, it has been concluded that pions have various values of RBE depending on the tumour system involved. KHT sarcoma is a tumour which grows very rapidly, on the contrary, SCCVII tumour shows somewhat slower growth characteristics. These differences of RBE between these two tumour systems possibly stem from differences in the amount of hypoxic cells and/or their rates of reoxygenation. As for therapeutic gain factor, a maximum value of 1.45 was obtained with 10 fractions using the SCCVII tumour. Pions seem to be most effective (in multiple fractions) against tumours of relatively slow growth.

Animals↗