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D J Chaplin

Publications and source records attributed to D J Chaplin.

At least 73 records · Page 4Linked to original sources
PubMed1995

The effect of blood flow modification on intra- and extracellular pH measured by 31P magnetic resonance spectroscopy in murine tumours.

Intra- and extracellular pH (pHi and pHe) were measured simultaneously by 31P magnetic resonance spectroscopy (MRS) in CaNT tumours before and after blood flow modification. Before modification, pHi was 7.1 +/- 0.09 (n = 11) and pHe [measured with an MRS-visible extracellular marker, 3-aminopropyl phosphonate (3-APP)] was 6.7 +/- 0.05 (n = 8). Chemical shift imaging and localised MRS experiments showed that the 3-APP signal was only from the tumour, not surrounding tissue. After modification by vascular occlusion, independent of whether tumours were maintained at room temperature (22-24 degrees C) or kept warm (33-35 degrees C), there was a decrease in pHi and pHe with pHi decreasing to a greater extent. Qualitatively similar results were found using flavone acetic acid (FAA) as a blood flow modifier; only four out of nine tumours responded to FAA. Concomitant with the reduction of the pH gradient after modification was a decrease in the phosphorylation state of the adenine nucleotides measured either as ATP/Pi by MRS or [ATP]/[ADP][P(i)] in tumour extracts. These results indicate that the intracellular uptake of chemotherapeutic drugs which are dependent on the transmembrane pH gradient will not be enhanced in cells made ischaemic as a result of vascular shutdown.

Adenosine Triphosphate↗
PubMed1995

Cytotoxic effect of RB 6145 in human tumour cell lines: dependence on hypoxia, extra- and intracellular pH and drug uptake.

Low pH and hypoxia are a common feature of many solid tumours. This study examined the effect of these two conditions on the cytotoxic properties of the bifunctional agent RB 6145, the prodrug of RSU 1069. The effect of acidic pH on RB 6145 toxicity was examined in six human tumour cell lines under hypoxic conditions and was found to have little effect in HT 29, A549, U373 and HT 144 cells. Treatment was for 1 h at 37 degrees C, pH 6.4 or 7.4. Significant potentiation of RB 6145 toxicity was observed in SiHa cells (enhancement ratio; ERpH approximately 1.6) and in U1 cells (ERpH approximately 1.4). In these two cell lines the potentiation of RB 6145 toxicity arising from hypoxia was large, with ERHyp approximately 11 and 15 in SiHa and U1 cells respectively. SiHa cells, which show a pH effect and HT 29 cells, which do not, were chosen for further comparative studies of drug uptake )nd regulation of intracellular pH. High-performance liquid chromatography (HPLC) determinations of the uptake of RB 6145 and its dervatives showed that in SiHa cells, intracellular to extracellular drug concentration ratio (Ci/Ce) at 1 h was approximately 40% higher at pH 6.4 than at pH 7.4, whereas in HT 29 cells Ci/Ce was approximately 25% lower. Under conditions of acidic extracellular pH, regulation of pH was somewhat less effective in SiHa cells, where pHi dropped to within 0.2 pH units of the extracellular pH over a 2.5 h treatment at pH 6.4. It seems likely that increased drug uptake was at least part of the basis for the observed potentiation of RB 6145 toxicity in SiHa cells. A model which would better explain the results for both cell lines might also include the possibility that low pH per se potentiates cytotoxic damage to a modest extent and that it is offset or augmented by altered uptake in HT 29 and SiHa cells respectively.

Cell Hypoxia↗
PubMed1995

Biological effectiveness of fractionated dose of pions in microscopic SCCVII tumors: comparison between tumor control dose and tumor growth time assays.

The relative biological effectiveness (RBE) of fractionated pions for tumor growth time (TGT) assay changes with the endpoints, so it is essential to determine the RBE for tumor control dose (TCD) assay. For this purpose, the TCD50 of fractionated pions was compared with that of photons, and the RBEs for TGT and TCD assays were concurrently compared as a function of the effect level. A "convenient" RBE (cRBE) was substituted for the RBE when the comparison was made between similar fractionation schedules with different dose per fraction. SCCVII tumors (2 x 10(4) or 2 x 10(5) cells) were implanted into the feet of C3H mice and irradiated starting from 2 days after implantation at a total dose range of either 9.6-38.4 Gy pions (2.4-6.4 Gy per fraction) or 14.4-50.4 Gy photons (3.6-7.2 Gy per fraction) in 2-10 fractions over 5-6 days. The cRBE and the RBE at the iso-effective level of 30 days TGT were 1.53-1.60 for 2.4-4.8 Gy pions and 1.50 for 4-fractionated pions, respectively: there were only small differences within these schedules used. However, the cRBE values decreased from 1.60 to 1.15 with increasing TGT from 30 to 75 days. In contrast, the cRBE values for TCD50 increased from 1.08 to 1.40 (95% confidence limits [CL]; 1.18-1.63) with increasing evaluation time from 60 to 100 days: pions significantly inhibited late tumor appearance. The TCD50 at 100 days was 28.7 Gy (CL; 25.0-32.5 Gy) for pions and 40.3 Gy (CL; 36.3-44.2 Gy) for photons. In conclusion, the RBE for TCD50 was not predictable from the RBE for TGT assay. The cRBE value of 1.4 for microscopic tumor control was in close agreement with the reported values for skin reaction.

Animals↗
PubMed1995

The effect of nicotinamide on microregional blood flow within tumours assessed using laser Doppler probes.

Laser Doppler probes have been used to provide real-time spatial flow mapping of microregional erythrocyte flux within the murine Sarcoma F (SaF). The results demonstrate that fluctuations in microregional red blood cell flux are a common feature of SaF tumours, with approximately 50% of regions demonstrating a change of at least a factor of 2 over a one-hour sampling period and 16% of regions showing a greater than 5-fold change. Administration of 250 mg/kg nicotinamide induced a small reduction in the number of microregions showing fluctuations, 9% of regions demonstrated large fluctuations (i.e., > or = 5) relative to 16% in control tumours. At a dose of 500 mg/kg, the number of changes in microregional erythrocyte flux was increased. However, unlike either untreated or nicotinamide 250 mg/kg pretreated animals, these changes were mostly increases in microregional flow. Indeed, 12 of the 13 changes by a factor of 5 or greater, observed following nicotinamide at 500 mg/kg, were increases. This effect on microregional flow translated into only a 25% increase in macroregional flow determined by averaging all the regions sampled.

Animals↗
PubMed1995

Cytotoxic effect of tumour necrosis factor -alpha on sarcoma F cells at tumour relevant oxygen tensions.

We have investigated the response of a murine tumour cell line, the sarcoma F (SaF), to tumour necrosis factor-alpha (TNF) at oxygen tensions known to occur in vivo. Using the Eppendorf pO2 histograph, the oxygen status of SaF tumours grown in situ was assessed. The median pO2 of the SaF is less than 1% oxygen with over 90% of values at or below 15 mmHg (< 2% O2). SaF cells primed in vitro for 24 h at tumour relevant oxygen tensions required at least four times more TNF to reduce cell number to 50% of controls following a 24 h incubation period in 21% oxygen. Chronic exposure of SaF cells to hypoxia during several passages increased resistance to TNF more than 60-fold. The oxygen sensitizing effect is transient as the resistance of hypoxic cells to TNF was reversed after 24 h incubation in air. These data clearly show that oxygen tension is a key modulator of the cytotoxic action of this important cytokine.

Animals↗
PubMed1995

The ability of nicotinamide to inhibit the growth of a C3H mouse mammary carcinoma.

Experimental studies have suggested that nicotinamide and its analogs may inhibit the growth of murine tumours. We have now investigated this using a C3H mouse mammary carcinoma implanted into the right rear foot of female CDF1 mice. From days 1 to 30 after implantation mice were intraperitoneally (i.p.) injected with either 100, 200, 500 or 1,000 mg/kg nicotinamide. The tumour volume (+/- 1 S.E.) after 30 days in saline-treated mice had reached 1540 mm3 (+/- 260). No change in tumour growth was seen at that time with daily doses of up to 500 mg/kg nicotinamide, but at 1,000 mg/kg tumour volume was reduced to 904 mm3 (+/- 233). However, this large dose of nicotinamide was also toxic to the mice with some 16% of animals dying during the 30-day treatment period. A similar growth inhibition was seen with daily i.p. injections of 5 mg/kg fumagillin (tumour volume at 30 days = 821 +/- 191 mm3), a known inhibitor of angiogenesis, but whether this mechanism also explains the nicotinamide effect is not clear.

Animals↗
PubMed1995

Effect of endothelin-1 and sarafotoxin S6c on blood flow in a rat tumor.

The modification of tumor blood flow resulting from administration of endothelin-1 (ET-1) and sarafotoxin S6c (SX6c) was examined in female CBH rats. Blood flow in subcutaneous HSN tumors and normal tissues was measured by tissue uptake of 125I-labeled iodoantipyrine ([125I])IAP). A 75% increase in tumor blood flow was observed after 1 nM/kg ET-1, contrasting with flow in normal tissue, which was unaffected or reduced. The exception to this was the brain, in which blood flow was increased by 30%, resulting from a rise in mean arterial blood pressure (MABP) and the absence of vasoconstriction. Paradoxically, a significant drop in the tumor vascular resistance was observed after 1 nM/kg ET-1, whereas in all other tissues the vascular resistance was significantly increased. Vascular responses to SX6c differed from those observed with ET-1. At 1 nM/kg SX6c, blood flow in the tumor was increased to 175% of the control as a result of the increase in MABP, which was similar to ET-1. However, unlike ET-1, there was no associated vasodilatation. Vascular resistance was increased in all normal tissues with 1 nM/kg SX6c, corresponding to decreases in blood flow in the contralateral skin, skeletal muscle, and small intestine. This study therefore demonstrates that the vascular responses to ET-1 and SX6c are unique in the HSN tumor compared to normal tissues. This atypical response of the tumor vasculature may therefore be exploitable to improve the delivery of blood-borne anti-cancer agents in therapy.

Animals↗
PubMed1994

Relationship between radiobiological hypoxia in tumors and electrode measurements of tumor oxygenation.

PURPOSE: To determine whether electrode measurements of tumor oxygenation, made in a variety of murine tumor models, correlate with estimates of radiobiological hypoxia in the same tumor systems. METHODS AND MATERIALS: The tumor models used were a C3H mammary carcinoma grown in the feet of CDF1 mice; the SCCVII, KHT and RIF-1 tumors grown in the feet or flanks of C3H/Km mice; and the CaNT and SaF tumors grown on the backs of CBA mice. All treatments were performed when tumors were about 200 mm3 in size. Radiobiological hypoxic fractions were determined using either a paired survival curve assay, with survival measured 0-24 h after irradiation, or using a clamped tumor control assay, with percent local tumor control estimated 90 days after treatment. Measurements of tumor oxygen partial pressure (pO2) distributions were performed using Eppendorf oxygen electrodes. RESULTS: The hypoxic fractions determined from the radiation response data were about 1% in RIF-1 and SCCVII, 12% in C3H and KHT, 28% in CaNT and up to 38% in SaF tumors. When this data was compared with the tumor oxygenation measurements it was found that as hypoxic fraction increased the mean, median, and the percentage of pO2 values < or = 5 mmHg showed a trend towards poorer oxygenation status. However, none of these pO2 changes were significantly correlated with hypoxia. Moreover, the pO2 values < or = 2.5 mmHg indicated an improvement in oxygen status with increasing hypoxic fraction. CONCLUSION: Electrode measurements of tumor oxygenation alone may, therefore, not be a good indicator of tumor hypoxia across different tumor cell lines.

Animals↗
PubMed1994

The influence of microenvironment on the cytotoxicity of TNF [symbol: see text] vitro.

PURPOSE: Investigations were undertaken to study the influence of oxygen levels on tumor necrosis factor [symbol: see text] (TNF [symbol: see text] toxicity in vitro. METHODS AND MATERIALS: The cell line used to assess the cytotoxicity of TNF [symbol: see text] the mouse fibroblast line L929. The cell line was incubated under conditions of 21%, 10%, 5% and 2% oxygen either before or during exposure to TNF [symbol: see text]. All incubations with TNF were for 24 h in the presence of 1 microgram/ml actinomycin D. Cell number was assessed immediately following treatment by a colormetric method. RESULTS: By preincubating L929 cells under various oxygen conditions for 24 h prior to incubating with TNF [symbol: see text], we show that pretreatment does influence TNF [symbol: see text] cytotoxicity since up to 50 times more TNF [symbol: see text] is required to elicit the same survival level when L929 cells have been preincubated for 24 h at oxygen levels relevant to those in solid tumors, that is 2% rather than at 21%. A 24 h preincubation under an environment of 5% oxygen is not as effective at inducing resistance to TNF [symbol: see text] as incubation under 2% oxygen. However, this resistance could be significantly enhanced by lengthening the preincubation time. Indeed cells cultured for five passages under 5% oxygen levels are approximately 50 times more resistant to TNF [symbol: see text] than cells cultured under 21% oxygen. The resistance induced by conditions of reduced oxygen tension could be reversed over a 24 h period if cells were returned to an environment containing of reduced oxygen tension could be reversed over a 24 h period if cells were returned to an environment containing 21% oxygen. CONCLUSION: The oxygen content of the cellular microenvironment has a profound influence on the cytotoxic action of TNF.

Animals↗
PubMed1994

Ischaemia induced cell death in tumors: importance of temperature and pH.

PURPOSE: Increasing attention has focussed on the therapeutic potential of agents which can reduce tumor blood flow and induce ischaemia for long enough to result in tumor cell death. A confounding factor in this approach is the fact that the core temperature of superficial tumors reduces when the supplying blood flow is occluded and therefore protects the tumor cells from "metabolic" death. Consequently, we have tested the importance of tumor temperature on the relationship between vascular occlusion and cell death. METHODS AND MATERIALS: The murine tumor CaNT used in this study was implanted subcutaneously in the dorsum. Total vascular occlusion was achieved by physically occluding the blood supply to the tumors for periods between 1 and 20 h. The mouse temperature was controlled by placing the whole body in a thermostatically controlled incubator maintained at 35 degrees C. Tumor cell survival was assessed using an excision assay and by measuring the delay in growth of treated tumors. Measurement of tumor pH was achieved using microelectrodes. RESULTS: The core temperature of unclamped tumors was approximately 33 degrees C, but fell by about 5 degrees C during vascular occlusion at room temperature. Tumor cell survival was decreased with increasing periods of vascular occlusion at room temperature, but a greater reduction in cell survival and correspondingly increased regrowth delay was observed when the tumor temperature was prevented from cooling below preocclusion values. The extracellular pH (pHe) fell during vascular occlusion and this reduction was greater when the tumor temperature was maintained at preocclusion values. This extracellular acidosis is expected to partly explain the observation of greater tumor cell death in those tumors whose temperature does not reduce during occlusion. CONCLUSION: The temperature of superficial tumors reduces in response to vascular occlusion. This may result in an underestimation of the cytotoxicity of agents which reduce tumor blood flow as the tumor cooling protects the cells from the acidosis that accumulates within the occluded tumor.

Animals↗
PubMed1994

The effect of low pH and hypoxia on the cytotoxic effects of SR4233 and mitomycin C in vitro.

PURPOSE: We examined the effect of acidic pH and hypoxia on the cytotoxicity of SR4233 and mitomycin C in vitro. METHODS AND MATERIALS: The importance of tumor microenvironment to the response of solid tumors to cytotoxic treatment is well established. The bioreductive drug SR4233 has a very substantial selective toxicity for hypoxic cells. We have used both Chinese hamster and human tumor cells to investigate the influence of low pH and hypoxia on the response of cultured cells to treatment with SR4233 or mitomycin C. RESULTS: We found that low pH (6.6) had little effect on the hypoxic toxicity of SR4233; under aerobic conditions, however, low pH substantially increased the cytotoxic effects of 1 h exposure to SR4233, with drug dose enhancement ratios (ER) of 3.9 and 2.5 in V79 and HT-29 cells, respectively. In similar studies with mitomycin C, hypoxia had little effect on the cytotoxicity of mitomycin C in V79 cells, though a low pH of 6.6 enhanced the cytotoxicity under both aerobic and hypoxic conditions (ER approximately 2). In HT-29 cells, neither low pH nor hypoxia had any significant effect on mitomycin C toxicity. CONCLUSION: Low pH, like hypoxia, is a common feature of solid tumors and can be an important determinant of the cytotoxic effect of bioreductive drugs such as SR4233 and mitomycin C.

Animals↗
PubMed1994

The influence of tumour temperature on ischemia-induced cell death: potential implications for the evaluation of vascular mediated therapies.

We have evaluated the influence of tumour temperature on the kinetics and extent of tumour cell death following induction of ischemia. Induction of ischemia in SCCVII tumours implanted subcutaneously in the back of syngeneic C3H mice results in a rapid cooling of the tumour from a resting value of 35.2 degrees C, towards ambient temperature. In the SCCVII tumour no significant cell kill is detected in the first hour of ischemia. At longer times cell kill was detected and a survival level of 2 x 10(-2) was attained after 6 h of ischemia. However, if the tumours were maintained at a temperature of 37 degrees C following induction of ischemia a more rapid and dramatic reduction in cell survival is observed with a survival level of approximately 10(-5) being attained after 4 h of ischemia. Qualitatively similar results are obtained using the Lewis lung tumour implanted in C57BL mice. Similar rapid cooling following occlusion of the blood supply is observed in the C3H/TIF tumour implanted in the foot. For the C3H/TIF induction of ischemia for up to 6 h resulted in no significant growth delay provided the tumours were kept at room temperature. However, if the tumours were maintained at a temperature of 37 degrees C during the ischemic insult significant growth delay was observed for all clamping times exceeding 1 h. These results show the importance of tumour temperature on the kinetics and extent of tumour cell kill during ischemia. This finding has particular relevance for studies in which agents known to reduce tumour blood flow are used in animals bearing superficially located tumours.

Animals↗
PubMed1994

The radiation response of KHT sarcomas following nicotinamide treatment and carbogen breathing.

Preclinical investigations have demonstrated that both diffusion- and perfusion-limited hypoxic cells may exist in tumors. One approach to target such hypoxic cell subpopulations is through the combined application of nicotinamide (NIC) administration and carbogen (5% CO2:95% O2) breathing. Because carbogen pre-irradiation breathing time (PIBT) can markedly influence the radiosensitizing effectiveness of this gas mixture, in the present experiments the effect of localized radiation on the transplantable KHT sarcoma was investigated in mice receiving NIC while breathing carbogen for various periods of time. When mice were given carbogen prior to radiation therapy, there was a minimum in tumor cell survival for PIBTs of 2-30 min. Longer PIBTs led to a loss of the radiosensitizing effect. NIC, administered as a 1000-mg/kg dose, effectively enhanced radiation cell killing in this tumor if given 45 min to 2 h prior to radiotherapy. In experiments in which either agent was combined on its own under optimum conditions (carbogen, 10 min PIBT; or NIC, 1000 mg/kg 2 h prior to irradiation), with a range of single doses of radiation, the results showed an enhancement ratio of approximately 1.9 as determined from the ratio of the slopes of the cell survival curves obtained in the absence or presence of the radiation sensitizer. This sensitizing effect could not be increased further when NIC and carbogen breathing were combined under optimum conditions.

Administration, Inhalation↗
PubMed1994

Enhancement of cyclophosphamide cytotoxicity in vivo by the benzamide analogue pyrazinamide.

The ability of pyrazinamide to enhance the in vivo cytotoxicity of cyclophosphamide in Lewis lung and RIF-1 tumours was investigated. Using an in vivo/in vitro excision assay a large single dose of pyrazinamide (500 mg kg-1 i.p.) was shown to enhance the tumour cell killing by cyclophosphamide. This enhancement was greatest when pyrazinamide was administered before the alkylating agent and had a dose-modifying effect on all cyclophosphamide doses tested, giving rise to a mean (+/- 1 s.e.) enhancement ratio (ER) of 1.54 (+/- 0.15) for the Lewis lung and 1.24 (+/- 0.08) for the RIF-1 tumour. Pyrazinamide also increased the cytotoxic action of cyclophosphamide in a normal tissue, namely white blood cell counts. However, the ER was only 1.14 (+/- 0.08), which although not significantly different from the value seen in RIF-1 was significantly less than the ER obtained with Lewis lung, suggesting the possibility of a therapeutic gain. This benzamide analogue did not appear to inhibit recovery from cyclophosphamide-induced potentially lethal damage in tumours, nor did it alter the bioactivation of cyclophosphamide or the subsequent clearance of the cytotoxic species from the plasma, so the mechanism for this chemosensitisation remains unclear.

Animals↗