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D J Chaplin

Publications and source records attributed to D J Chaplin.

At least 127 records · Page 7Linked to original sources
PubMed1989

Mechanism for the reduction of tumour hypoxia by nicotinamide and the clinical relevance for radiotherapy.

Nicotinamide (1000 mg/kg; i.p.) enhanced the radiation response of the SCCVII tumour, producing an ER of almost 1.5 in a growth delay assay. Separating tumour cells as a function of fluorescent labelling with Hoechst 33342, suggested that this enhancement may be primarily a result of the elimination of acutely hypoxic cells in tumours. Nicotinamide also decreased mean arterial blood pressure in mice. These results are discussed with respect to their clinical applicability.

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PubMed1989

Evidence for intermittent radiobiological hypoxia in experimental tumour systems.

This paper describes flow and static fluorescence cytometry techniques to visualize and quantitate acute radiobiological hypoxia resulting from transient fluctuation in tumour blood flow in experimental tumour systems. The application of these techniques in two murine tumour systems provides evidence that such hypoxia exists and reduces the effectiveness of single doses of radiation. Possible mechanisms for and implications of these findings are discussed.

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PubMed1989

Reduction of tumour blood flow by vasoactive drugs: a role in cancer therapy.

The potential use of tumour blood flow reductions, induced by the vasodilator hydralazine, in cancer therapy are described. Data obtained in experimental tumour systems indicate that with appropriate scheduling and drug combinations, hydralazine can increase the therapeutic effectiveness of certain chemotherapeutic agents whether used alone or in combination with other modalities such as radiation or hyperthermia.

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PubMed1988

The effect of artificially induced hyperglycemia on the radiation response of the Lewis lung and EMT6 tumor models.

The effect of hyperglycemia, induced by administration of glucose, on the radiation response of the Lewis lung and EMT6 tumor models has been evaluated. Neither acute (single i.p. injection of 8 mg/glucose) nor chronic (multiple i.p. injections of 6 mg/g glucose plus glucose in the water bottles) administrations of glucose increased the radiation response of either tumor. A combination of a single i.p. injection of glucose and a reduction of the O2 content of the inspired gas to 10 per cent did by itself reduce cell survival by 55-75 per cent in the EMT6 and 80-90 per cent in the Lewis lung carcinoma. However, this treatment had little effect on the shape of the radiation dose-response curve, and simply gave rise to a parallel shift of the survival curve, indicating that this treatment had little or no specificity for hypoxic cells.

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PubMed1988

Postirradiation modification of tumor blood flow: a method to increase the effectiveness of chemical radiosensitizers.

The effect of postirradiation hypoxia induced by administration of the vasodilator hydralazine on the efficacy of misonidazole and RSU-1069 used in combination with radiation has been evaluated. Studies with the Lewis lung carcinoma indicate that hydralazine at a dose of 5 mg/kg reduces tumor blood flow and consequently increases the amount of hypoxia in the tumor tissue. Administration of hydralazine immediately after radiation treatment increased the amount of cell kill. However, the increase in cell kill was more pronounced when hydralazine was used in treatment regimes in which misonidazole (0.2 mg/g) or RSU-1069 (0.02 mg/g) was administered pre- or postirradiation. The finding that similar effects are observed if the nitroimidazoles were administered either before or after radiation in the regimes involving hydralazine suggests that the enhanced cell killing observed is due to hypoxic cell cytotoxicity. In contrast to the effects of hydralazine on the response of tumors to radiation plus misonidazole or RSU-1069, it has no effect on the response of mouse intestine to such treatment regimes. Thus therapeutic gain may accrue from the use of hydralazine in radiation treatments which incorporate the nitroimidazole radiosensitizers misonidazole and RSU-1069.

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PubMed1987

Intermittent blood flow in a murine tumor: radiobiological effects.

Little is known about how and why hypoxia arises in tumors, i.e., whether hypoxia is a chronic process resulting from diffusion limitations or occurs more acutely due to transient changes in blood perfusion. We have investigated the nature of hypoxia in the murine squamous carcinoma SCC VII using a new fluorescence-activated cell-sorting technique which facilitates isolation of viable tumor cells as a function of their distance from the blood supply. The technique utilizes the DNA binding/diffusion properties of the bisbenzamide fluorochrome Hoechst 33342. This compound has a very short distribution half-life from the blood after i.v. injection but remains bound within tumor cells even after disaggregation, redistributing with a half-life greater than 2 h. Cells can thus be sorted on the basis of their staining intensity (proximity to the blood supply), and varying the Hoechst 33342 administration protocol provides the basis for elucidating transient changes in blood flow that result in acute radiobiological hypoxia. Using this technique, we have demonstrated that acute hypoxia results from transient changes in blood perfusion in 500-mg SCC VII tumors. Independent confirmation of the intermittent blood flow has been obtained using histological techniques.

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PubMed1987

The effect of hydralazine on the tumor cytotoxicity of the hypoxic cell cytotoxin RSU-1069: evidence for therapeutic gain.

The effect of the vasodilator hydralazine on both the tumor and systemic toxicity of RSU-1069 has been evaluated in C57B1 mice bearing Lewis lung tumors. The results obtained indicate that both hydralazine and RSU-1069 are cytotoxic to the Lewis lung tumor on their own. However, administration of hydralazine (5 mg/kg PO) at times up to either 3 hr before or 3 hr after RSU-1069 (0.1 mg/g IP) results in a level of cell killing greater than expected from additive effects. This potentiation by hydralazine was observed with doses of RSU-1069 from 0.01 to 0.1 mg/g. The results obtained using excision assays were confirmed using in situ growth delay as the endpoint. Growth delay (+/- s.e.m.) values for tumors to double in volume of 1.5 (+/- 1.2), 2.0 (+/- 1.3) and 6.0 (+/- 0.9) were obtained for hydralazine (5 mg/kg PO) alone, RSU-1069 (0.1 mg/g IP) alone and for hydralazine administered at the same time as RSU-1069 respectively. In contrast to the potentiating effect of hydralazine on the tumor cytotoxicity of RSU-1069, it had no significant effect on the systemic toxicity of RSU-1069 as measured by LD50/30d. No detailed studies to examine the mechanism responsible for the potentiation of tumor cytotoxicity have been performed in the present study. However, the results obtained would be consistent with previous reports that vasodilators such as hydralazine can selectively reduce tumor blood flow and thus oxygenation. Such reduced tumor oxygenation would increase the cytotoxic effects of RSU-1069 which is known to be more toxic to cells at reduced oxygen levels.

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PubMed1987

The response of mouse epidermis to fractionated doses of pi mesons.

An extensive series of preclinical experiments are described in which the relative biological effectiveness (RBE) of pions from TRIUMF has been determined for mouse skin. To measure the RBE at both high and low doses per fraction, a range of fractionation schedules was used, with 1, 2, 4, 10, and 20 fractions. Because the pion dose rate is much lower than the dose rate of X or gamma-rays used in radiotherapy, two sets of reference X ray data were obtained: one at the same dose rate as the pions (15 cGy min-1), and another at the more conventional 150 cGy min-1. This allowed a "biophysical" RBE for equivalent dose rates and a "practical" RBE for preclinical evaluation to be calculated. The pion RBE was significantly higher for 20 small fractions than for fewer large doses. The absolute value of RBE depends upon the dose rate of the reference X ray treatments. The "practical" RBE increased from 1.05 at high doses to 1.45 at the smallest dose per fraction tested. The "biophysical" RBE for equivalent dose rates ranged from 1.20 at high doses to 1.5 for 20 fractions.

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PubMed1987

Cytotoxicity of RSU 1069 in spheroids and murine tumors.

Hypoxia following treatment with the alkylating nitroimidazole, RSU 1069, greatly enhanced cell killing in the Lewis lung tumor and Chinese hamster V79 spheroids. When mice were injected with RSU-1069 and tumors were excised after 3 hr to measure colony formation in soft agar, significant cell killing was observed. However, if tumors were excised 18 hr after drug injection, viability was increased, and cell killing was confined to cells distant from the blood supply. In subsequent experiments, viability observed at 3 hr could be greatly increased if the tumors were cooled to 4 degrees C immediately after excision, and were then rapidly disaggregated. This suggested that the hypoxia which occurred after animal sacrifice and during the tumor disaggregation procedure was sufficient to account for the additional cell killing at early times after drug injection. Results using V79 spheroids similarly suggest that tumor excision soon after injection of RSU 1069 can give false information on RSU 1069 toxicity if efforts are not made to prevent tumor hypoxia during processing. In spheroids, hypoxia-induced toxicity after aerobic exposure decreased as the time between RSU 1069 exposure and hypoxic incubation increased; spheroid cells exposed to RSU 1069 under air lost sensitivity to subsequent hypoxic incubation with a half-time of about 10 hr, representing the time for cell turnover and/or repair from damage produced under aerobic conditions.

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PubMed1987

Chemosensitization by misonidazole in CCNU-treated spheroids and tumours.

Misonidazole has been demonstrated to enhance the cytotoxicity of several common antineoplastic drugs in vitro and in vivo, and its mechanism of action as a chemosensitizer, though still unknown, is thought to be dependent upon hypoxia. We have used fluorescence-activated cell sorting to evaluate chemopotentiation by misonidazole as a function of cell position in V79 spheroids and KHT tumours. CCNU toxicity was enhanced in all cell subpopulations of both tumours and spheroids, with greater consistency than might be predicted on the basis of the known variations in oxygen tension. Further, both misonidazole and CCNU as single agents were preferentially toxic in the less well oxygenated regions of each system, arguing that differential toxicity cannot be implicated in the chemopotentiation observed. In fact, increased treatment toxicity did not necessarily lead to increased chemopotentiation, nor was potentiation directly related to the metabolism/binding of the misonidazole. Chemopotentiation in multicell systems thus appears to be a complex, multi-factorial process.

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PubMed1987

Radiosensitization by nicotinamide in vivo: a greater enhancement of tumor damage compared to that of normal tissues.

In this report we describe various aspects of tumor and normal tissue radiosensitization by nicotinamide. The LD50 for a single injection of nicotinamide in C3H mice was found to be 2050 mg/kg. When a large nonlethal dose (1000 mg/kg) was injected into tumor-bearing mice, peak plasma and tumor levels were reached 30-60 min after injection and decayed with a half-life of about 3 h. This dose of nicotinamide enhanced radiation-induced cell killing in three different tumor models (EMT6, Lewis Lung, and RIF-1) when injected at least 1 h before irradiation and produced enhancement ratios (ERs) of between 1.2 and 1.7. The ER in the EMT6 tumor was dependent on the dose of nicotinamide injected, but even at doses as low as 25% of the LD50 value an ER greater than 1.5 could still be observed. In two normal tissue assays (jejunum crypt cell survival and mean skin reaction) ERs of less than 1.2 were obtained. These results, and the fact that high levels can be tolerated in humans, suggest that nicotinamide, or a structurally related compound, could be a likely candidate for development in clinical trials.

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PubMed1986

Pions and pig skin: preclinical evaluation of RBE for early and late damage.

The skin of 50 pigs has been irradiated with negative pi mesons and with X rays in order to determine the RBE for early epidermal and later dermal damage. Late fibrosis was not studied. Four, 7, 9 and 10 fractions were used. An estimate of the RBE was made from the reactions on each pig for both early and late damage so that interanimal variability would be avoided. The data were also averaged to obtain mean dose response curves. There was no tendency for higher RBE's for late than for early skin damage. These pig studies have demonstrated an RBE of about 1.5 for early epidermal reactions and a slightly lower RBE (approximately 1.4) for later dermal damage in the same animals. This indicates that at doses of about 2.0 to 3.5 Gy pions, the medium wave skin damage is unlikely to be more severe than would be predicted from the early skin reactions and the accumulated clinical experience with X rays. However, if the trend to a steeper slope for the RBE versus dose per fraction for late injury is correct, as indicated by other published studies a relative increase in the late injury might be expected if much lower doses per fraction are used. The present clinical studies at Vancouver using 15 X 2.1 Gy pions indicate that an RBE of 1.5 is appropriate for epithelia, brain and colorectum.

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PubMed1986

Acute hypoxia in tumors: implications for modifiers of radiation effects.

Radioresistant hypoxic cells have been shown to occur in nearly all the animal tumors studied to date. Furthermore, there is a large amount of evidence, albeit indirect, that hypoxic cells exist and impair the effectiveness of radiation therapy in some human cancers. Surprisingly little is known, however, about the natural history of such hypoxic cells. Recently in our laboratories, we have developed methods which enable us to select and analyse cells from tumors as a function of their distance from the tumor blood supply. Utilizing this technique, we have been able to demonstrate using SCCVII tumors greater than or equal to 500 mg that even cells close to the blood supply may become hypoxic at any particular time. This information provides direct evidence that, at least for that tumor, hypoxia can result from transient fluctuations in blood perfusion. The existence of acutely, as well as, chronically hypoxic cells within tumors has several implications for treatment strategies. Treatments designed to increase oxygen content in the blood may not be particularly effective in sensitizing acutely hypoxic cells. However small, freely diffusable radiosensitizers would distribute throughout the tumor, and should be equally effective in sensitizing both acutely and chronically hypoxic cells to radiation. Acute hypoxia may thus be the best possible indicator for the use of chemical radiosensitizers in radiation therapy.

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PubMed1986

The radiosensitizing and toxic effects of RSU-1069 on hypoxic cells in a murine tumor.

RSU-1069 is one of a group of compounds of particular interest in radiobiology, since it combines the nitroimidazole ring with a side chain bearing a monofunctional alkylating agent. This compound has been shown to be a potent radiosensitizer both in vitro and in vivo. Furthermore, it has recently been shown to be an effective hypoxic cell cytotoxin in vitro. Our studies have been carried out using the SCCVII squamous carcinoma implanted subcutaneously in C3H mice, using a technique we recently developed which facilitates isolation of tumor cell subpopulations from known locations relative to the tumor blood supply. The response of the separated tumor subpopulations was assessed using a soft agar clonogenic assay. For radiosensitization studies, RSU-1069 was administered i.p. at 0.5 mumol/g 20 min before irradiation and the tumors excised 20 min after irradiation. For toxicity studies, tumors were excised 16-18 hr after RSU-1069 administration. The results obtained to date clearly demonstrate that RSU-1069 is an efficient hypoxic cell radiosensitizer and cytotoxin in this murine tumor and has little effect on well perfused (i.e., oxic) cells.

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PubMed1986

Oxygen and nitroreductase-dependent binding of AF-2 in spheroids and murine tumors.

Fluorescent nitroheterocycles such as AF-2 may be useful in identifying hypoxic cells in tumors. Since binding is dependent on rate of drug metabolism (nitroreduction) as well as cellular oxygen content, flow cytometric analysis of cells from tumors and spheroids was used to quantify AF-2 binding, and differential pulse polarography was used to measure reduction of AF-2 by several mammalian cell lines, spheroids and tumor cells. Hypoxic V79 spheroid cells and Lewis lung tumor cells bound 20 times more AF-2 than oxic cells, and binding proceeded with first order kinetics. Nitroreductase activity varied about tenfold among different tumor cells. As expected, the rate of binding of AF-2 correlated well with the rate of nitroreduction. Oral injection of AF-2 (5 mg) was the most successful method of administration to tumor-bearing mice. In mice injected with both AF-2 and Hoechst 33342 (which stains well-perfused cells), SCCVII tumor cells which contained the most Hoechst contained the least AF-2. Although minimal toxicity by AF-2 was observed in these tumors, binding of AF-2 was barely sufficient for detection using flow cytometry.

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PubMed1986

Potentiation of RSU-1069 tumour cytotoxicity by 5-hydroxytryptamine (5-HT).

It is known that many solid animal tumours have a lower oxygenation level than most normal tissues and, in addition, that this level of oxygenation can be further decreased by systemic administration of 5-hydroxytryptamine (5-HT). The present study has investigated if such selective decrease in tumour oxygenation can be exploited by using the hypoxic cell cytotoxin, RSU-1069. The results obtained show that 5-HT at a dose of 5 mg kg-1, although not cytotoxic alone, can potentiate the cytotoxic effects of RSU-1069 in the Lewis lung carcinoma over the dose range 0.01-0.15 mg g-1. Maximum potentiation occurs when 5-HT is administered after RSU-1069. Potentiation of RSU-1069 cytotoxicity was observed using both the soft agar excision assay as an endpoint as well as in situ growth delay. In addition, the study shows that potentiation of RSU-1069 (0.1 mg g-1) cytotoxicity can be seen with 5-HT doses as low as 0.5 mg kg-1. In contrast to the tumour cytotoxicity results, 5-HT at a dose of 5 mg kg-1 i.p. did not affect the systemic toxicity, as measured by LD50/7d of RSU-1069. Thus, these results indicate that 5-HT can increase the therapeutic efficiency of RSU-1069. Such a finding is consistent with the rationale that selective reduction in tumour blood flow and oxygenation induced by 5-HT can be exploited using the hypoxic cell cytotoxin RSU-1069.

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PubMed1985

Pharmacokinetics, binding and distribution of Hoechst 33342 in spheroids and murine tumours.

The fluorescent stain Hoechst 33342, when injected i.v. into mice, has an LD50 of 300 micrograms g-1. The stain exits rapidly from the blood, with a half-life of 110 sec following an injection of 10 micrograms g-1, but remains bound within target cells, redistributing with a half-life longer than 2 h. This results in a gradient of drug binding outward from capillaries which can be used to estimate regional perfusion via fluorescence microscopy of frozen tissue sections. For tumour tissues that can be dispersed into single cell suspensions, intracellular Hoeschst 33342 can be quantified by flow cytometry, and cell populations can be selected on the basis of their fluorescence (distance from the vasculature) using a fluorescence-activated cell sorter. Our results in tumours and in spheroids indicate that the rate of stain uptake by different cell subpopulations in situ is much more dependent on stain delivery than on selective uptake. Retention of the stain in spheroids is sufficiently stable to allow cell sorting several hours post-injection. Hoechst 33342 thus appears to have considerable potential as an agent for quantifying tissue perfusion, and for allowing selection of tumour cell subpopulations to assess response to radiation and drugs.

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