PubMed Health⌕ Search

Biomedical subjects

D J Chaplin

Publications and source records attributed to D J Chaplin.

At least 109 records · Page 6Linked to original sources
PubMed1990

Combination of nicotinamide and hyperthermia to eliminate radioresistant chronically and acutely hypoxic tumor cells.

The interaction among nicotinamide, radiation, and heat was studied in vivo using a C3H mouse mammary carcinoma grown in the feet of CDF1 mice. Response following local tumor treatment was assessed by tumor control and regrowth delay. Nicotinamide (1000 mg/kg i.p.) produced maximal radiosensitization when injected 30 min to 2 h before irradiation [enhancement ratios (ERs), 1.2-1.5]. Radiation damage was also increased by heating tumors (43.5 degrees C for 60 min) 4 h after irradiation (ERs = 1.6-2.6). This combined radiation and heat treatment was enhanced by nicotinamide but the effect depended on the assay procedure, such that although a significant increase was observed with the tumor control assay, only a slight increase was seen using regrowth delay as the end point. The development of moist desquamation in normal feet was used to estimate skin damage after irradiation. Nicotinamide and heat both resulted in a small yet significant increase in skin damage (ERs less than 1.2 and 1.1, respectively). A combined treatment resulted in a greater ER of 1.7, but when compared to the tumor response it still gave a therapeutic gain. A histological fluorescent staining technique was used to assess functional tumor vasculature at two periods in time separated by 20 min. Under normal conditions 7.7% of the vessels in this tumor were functional at one time but not the other. This value was reduced to 2.8% after nicotinamide administration. Since these fluctuations in blood flow can result in acute hypoxia we conclude that while heat eliminates chronically hypoxic tumor cells, nicotinamide probably removes the presence of acute hypoxia.

Animals↗
PubMed1990

Effect of nicotinamide on the microregional heterogeneity of oxygen delivery within a murine tumor.

Nicotinamide, an agent previously reported to reduce hypoxia and increase the irradiation response of experimental tumors, has been evaluated for its effect on the occurrence of acute hypoxia in the murine squamous cell tumor SCCVII. Treatment of C3H mice bearing 500-750-mg subcutaneous tumors with nicotinamide (1.0 mg/g intraperitoneally) 1 hour prior to irradiation resulted in an enhancement ratio of 1.3 (+/- 0.1). We assessed the effect of nicotinamide on the response of acutely hypoxic cells in vivo using a recently developed fluorescence-activated-cell sorting technique. This technique employs the in vivo pharmacokinetic and DNA binding properties of the bisbenzamide stain Hoechst 33342. The results clearly show that nicotinamide, at the doses used, reduces the amount of acute hypoxia in these SCCVII tumors. We confirmed these findings using a histological technique that facilitates the assessment of functional tumor vasculature at two instances in time. This method shows that nicotinamide reduces the number of vessels opening and closing over a 20-minute period from 10.3% to 2.0%. The identification of a compound that can modify the dynamic fluctuations in microregional oxygen delivery in tumors could have important implications for radiation therapy.

Animals↗
PubMed1990

The potentiation of radiation damage by nicotinamide in the SCCVII tumour in vivo.

We have continued our assessment of the ability of nicotinamide to sensitize tumours to radiation. Using the SCCVII carcinoma and estimating tumour response by either a regrowth delay or an in vivo/in vitro survival assay, it was found that a large single dose of nicotinamide (1000 mg/kg) increased radiation-induced tumour damage. This effect was observed regardless of whether the tumour was grown intramuscularly, subcutaneously or intradermally, or whether the nicotinamide was administered intraperitoneally, intravenously or orally. The enhancement was maximal when the drug was given between 30 min and 2 h prior to irradiation and resulted in enhancement ratios ranging from 1.1 to 1.7. Although the radiation response of tumours was dependent on tumour size, the radiation enhancement produced by nicotinamide was not. Utilizing the technique of labelling tumour cells with the fluorescent stain Hoechst 33342, we were able to identify the presence of both chronic and acutely hypoxic cells in this tumour model and obtained results suggesting that apart from reducing chronic hypoxia, nicotinamide may also have the ability to decrease the level of radioresistant acute hypoxia.

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

Combination therapy of pions and SPG (Sonifilan, Schizophyllan), a biological response modifier for mouse tumor systems.

Female C3H mice aged 8-10 weeks with transplanted KHT sarcoma or SCCVII tumor were used to investigate the antitumor effect of SPG (Sonifilan, Schizophyllan) alone and in combination with local irradiation of pions with 4 fractions of 400 cGy (total 1600 cGy). Daily doses of 10 mg/kg of SPG were given intramuscularly to the mice bearing KHT sarcoma for 14 consecutive days from day 7, and to mice bearing SCCVII tumor for 20 consecutive days from day 7 and thereafter three times a week for another 2 weeks. The antitumor effect was evaluated by the changes in tumor volume, survival curves, and the number of pulmonary metastatic nodules on the surface of the lungs. SPG failed to exert any antitumor effect and any life-prolonging effect for the KHT sarcoma. As for SCCVII tumor, in the group treated with pions and SPG, tumor growth decreased significantly (p less than 0.01) compared with the group treated with pion only, and life prolonging effect and metastasis-suppressing effect were also observed (p less than 0.04). In conditions of minimal residual disease brought about by pion irradiation, the adjuvant effect of a Biological Response Modifier (BRM) SPG may prove to be a promising method of cancer therapy for some tumors.

Animals↗
PubMed1990

Intermittent blood flow in the KHT sarcoma--flow cytometry studies using Hoechst 33342.

The administration of the fluorescent DNA stain, Hoechst 33342, to mice bearing the KHT sarcoma, combined with flow cytometry, can be used to select cells according to their proximity to functional vasculature. Different protocols of administration of Hoechst 33342 were used in order to differentiate between the presence of temporary and chronically hypoxic cells. The results show a large difference in radiosensitivity between cells close to, and distant from, functional vasculature. However, this pattern of radiosensitivity is observed only when the staining period with Hoechst 33342 is short and coincides with the period of irradiation. When the radiation treatment is temporally divorced from the staining period then the radiosensitivity and staining intensity are not related. This result can be interpreted as indicating that hypoxic cells exist within this tumour as a result of fluctuations in tumour blood flow.

Animals↗
PubMed1990

Modification of tumour radiation response in vivo by the benzamide analogue pyrazinamide.

Pyrazinamide, the pyrazine analogue of nicotinamide, has been evaluated for its ability to modify the radiation response of hypoxic cells both in vivo and in vitro. Results obtained with three different murine tumour systems EMT6, LLC and SCCVII showed that pyrazinamide at a dose of 0.5 mg g-1 i.p. resulted in enhanced radiation response. Dose modification factors of between 1.3 and 1.6 were observed using in vivo/in vitro clonogenic assays. This enhancement was greater than that obtained in mouse intestine using crypt cell survival as an endpoint (DMF 1.1). In contrast to the tumour data in vivo, the in vitro results indicate that pyrazinamide displays little radiosensitising or toxic properties towards hypoxic CHO cells in culture. These results suggest that pyrazinamide exerts its effects in vivo either by directly perturbing tumour physiology or by being converted to an active metabolite. Blood flow studies performed using laser Doppler flowmetry indicate that pyrazinamide produces a small (32%) increase in overall tumour blood flow in the SCCVII tumour. Based on this finding, additional studies on tumour perfusion at the microregional level were performed in the SCCVII tumour using a histological technique involving injection of fluorescent stains which demarcate functional vasculature. The data show that when compared to saline injected controls, pyrazinamide reduced the number of vessels opening and closing over a 20 min period from 10.2% to 3.8%. This finding suggests that pyrazinamide may exert its effects at least in part by reducing the occurrence of acute hypoxia resulting from dynamic changes in microregional perfusion.

Animals↗
PubMed1990

Effect of vascular marker Hoechst 33342 on tumour perfusion and cardiovascular function in the mouse.

The fluorescent stain Hoechst 33342 (H33342) has been employed extensively as an in vivo marker of functional tumour vasculature. We have found that H33342 causes a transient, dose-dependent decrease in tumour red blood cell (RBC) flow in SCCVII tumours as measured using laser Doppler flowmetry. After intravenous bolus injection of 15 mg kg-1 to anaesthetised mice, blood flow in subcutaneous back tumours declined to 19 +/- 11% of pretreatment values, returning to normal in less than 7 min. The effect was less pronounced in mice bearing foot tumours in which flow decreased to 52 +/- 14% of pretreatment values in unanaesthetised mice and to 50 +/- 15% in anaesthetised animals. RBC flow in foot tumours remained significantly depressed for only 2-3 min. A dose of 5 mg kg-1 was not significantly vasoactive in back tumours. H33342 also caused a transient 20 +/- 6 mmHg decline in mouse arterial blood pressure. Blood pH and haematocrit, and tumour cell oxygen consumption were unchanged by H33342. H33342-induced flow changes did not affect results obtained using an in vivo double staining protocol provided that the interval between stain injections was greater than 5 min. Due to its transient effects on tumour perfusion, the stain caused radiobiological tumour hypoxia if injected immediately prior to X-irradiation. Injection 20 min before irradiation had no influence on tumour radiation response. We conclude that the transient nature of H33342-induced perturbations in mouse cardiovascular physiology and tumour blood flow must always be considered but do not preclude the use of the stain as a vascular marker to detect spontaneous tumour blood flow fluctuations or acute hypoxia.

Animals↗
PubMed1990

Toxicity of [PtCl2(NH3)L] in hypoxia; L = misonidazole or metronidazole.

There is increasing interest in compounds which show selective toxicity to the resistant hypoxic portions of tumors. Cisplatin does not generally show preferential toxicity in hypoxic cells, as do nitroimidazoles. It is proposed that attachment of a nitroimidazole could add a degree of hypoxic selectivity to Pt agents. Platinum complexes containing one nitroimidazole ligand bind to DNA and show higher toxicity in hypoxic than aerobic CHO cells. Cis and trans isomers of complexes with misonidazole (a 2-nitroimidazole) and metronidazole (a 5-nitroimidazole) are compared with respect to binding to DNA (approximately the same), reduction potential (trans miso greater than cis miso greater than cis metro greater than trans metro), and toxicity (trans greater than cis miso, cis greater than trans metro, with trans miso approximately cis metro in hypoxia, despite significantly different reduction potentials). The effect of platination on nitroimidazole toxicity is not entirely explained by DNA binding and increased reduction potential. These compounds do not exhibit cross resistance with cisplatin in L1210 resistant cells. This factor, their selectivity for hypoxia, and preliminary results in vivo indicating potentiation of anti-tumor activity by the vasoactive compound, hydralazine, which increases tumor hypoxia, suggest further development of these compounds for use in tumors with resistant hypoxic portions.

Aerobiosis↗
PubMed1989

Hydralazine-induced tumor hypoxia: a potential target for cancer chemotherapy.

Currently available cancer chemotherapeutic agents have been designed to exploit subtle differences in proliferation and biochemistry that are known to exist between host and malignant cells. However, chemotherapeutic agents may also be used to exploit physiological differences between cancer and normal tissue. The present study was conducted to determine whether the reduction in blood flow to the tumor (and thus oxygen delivery) induced by the vasodilator hydralazine would increase the cytotoxicity of drugs known to be more toxic in regions of reduced oxygenation. Results obtained with three murine tumor models clearly demonstrate that hydralazine potentiates the tumor cytotoxicity of such agents to a greater extent than it does their systemic toxicity. This study indicates a potential strategy for increasing the efficacy of certain cancer chemotherapeutic agents in solid tumors.

Animals↗
PubMed1989

Histological evidence for nonperfused vasculature in a murine tumor following hydralazine administration.

The effect of the vasodilator hydralazine on tumor vascular function has been evaluated in C3H/He mice bearing subcutaneously implanted SCCVII squamous cell carcinoma. Changes in microregional perfusion following hydralazine administration were observed using a double fluorescent staining technique. Hydralazine-induced alterations in tumor blood flow were measured using laser Doppler flowmetry. The results obtained indicate that hydralazine causes a dose-dependent reduction in functional tumor vasculature implying complete flow stasis and/or vascular collapse in some vessels. Fifteen minutes after a dose of 10 mg/kg intravenously, perfusion in 36 +/- 5% (SEM) of tumor vessels was completely abolished. In addition to cessation of perfusion in individual vessels, hydralazine eliminated flow in large patches of vasculature distributed non-uniformly throughout the tumor. Hydralazine (10 mg/kg i.v.) resulted in a 67 +/- 5% (SEM) reduction in tumor red blood cell (RBC) flow as measured by laser Doppler techniques. The mean number of moving red blood cells declined by 35 +/- 8%, suggesting a reduction in microvascular volume. These results support the hypothesis that following hydralazine administration, perfusion stops completely in some blood vessels probably as a result of vascular collapse or flow stasis.

Animals↗
PubMed1989

Potentiation of the tumor cytotoxicity of melphalan by vasodilating drugs.

Previous studies have shown that several vasoactive drugs can selectively reduce blood flow and increase hypoxia in experimental tumor systems. Our studies with one such agent, the vasodilator hydralazine, have clearly demonstrated that it can increase the tumor cytotoxicity of drugs which are known to be more toxic under hypoxic conditions. We have now extended our investigations to determine whether such selective reductions in tumor blood flow induced by hydralazine can increase the tumor cytotoxicity of other classes of cancer chemotherapeutic drugs. Our initial studies have involved the alkylating agent melphalan. Administration of hydralazine (5 mg/kg IP) at various times before or after melphalan results in increased tumor cytotoxicity in the Lewis lung carcinoma. An enhancement factor of between 2 and 3 was obtained in this tumor system. Similar results are observed if the vasodilator cadralazine is used. In contrast to the enhancement of the tumor cytotoxicity of melphalan by hydralazine, systemic toxicity is only increased by a factor of 1.2. Therefore, therapeutic gain may accrue from the use of vasodilating agents in combination with melphalan. Studies using spheroids to establish the mechanism responsible for the enhanced tumor cytotoxicity indicate that both hypoxia and pH can influence melphalan toxicity.

Animals↗
PubMed1989

The use of fluorescent probes to identify regions of transient perfusion in murine tumors.

Sequential intravenous injection of two fluorescent stains, Hoechst 33342 and DiOC7(3), can be used to quantify transient perfusion in experimental tumors. Regions of unmatched staining, indicative of intermittent perfusion, occur when vessels open or close in the 20 minute interval between administration of the dyes. In the murine SCCVII carcinoma, 8.9 +/- 2.4% (SD) of vessels in 0.5 g subcutaneous tumors had labelling of adjacent cells with only one stain, suggesting complete vessel closure lasting at least 5 minutes. Regions of intermittent perfusion were not homogeneously distributed throughout the tumor and larger tumors exhibited more mismatch than smaller tumors. Transient perfusion was observed in both subcutaneous and intramuscular tumor implants and was not significantly affected by restraint of the animal or by ketamine/diazepam anesthesia.

Animals↗
PubMed1989

Use of a carbocyanine dye as a marker of functional vasculature in murine tumours.

An intravenously administered fluorescent carbocyanine dye, DiOC7(3), has been evaluated for use in conjunction with Hoechst 33342 as a marker of murine tumour vasculature. DiOC7(3) stains cells immediately adjacent to blood vessels and thus, like Hoechst 33342, outlines perfused tumour vasculature. The different fluorescence excitation and emission properties of DiOC7(3) and Hoechst 33342 permit discrimination of the stains in the same tissue section. Mice tolerate a DiOC7(3) dose of 1 mg kg-1 i.v. with no ill effects. The dye has a distribution half-life in blood of 180s and staining of perivascular tumour cells is sufficiently stable to allow visualisation of vasculature for up to 30 min after DiOC7(3) injection. However, DiOC7(3) causes a 75% reduction in tumour blood flow as measured by laser Doppler techniques. Consequently, the compound appears to be most suitable as a second vascular marker, administered at some time after Hoechst 33342, to detect temporal and spatial fluctuations in tumour perfusion.

Animals↗
PubMed1989

Effect of different stopping volumes of clinical pion beams at TRIUMF on the mouse small intestine.

The survival of mouse jejunal crypt cells was measured using a microcolony assay following irradiation with one of three different pion stopping volumes. All treatments were done using the beam spot scanning system developed for clinical therapy at TRIUMF. Treatment volumes were Small, 10 ml of volume using 4 beam spots with a narrow stopping peak; Moderate, 40 ml of volume using 4 beam spots with an extended peak; Large, 1.2 liters of volume using 37 spots with an extended peak. The dose rate fluctuated considerably during treatment because of the scanning procedure. The relative biological effectiveness (RBE) values of pions were 1.11, 1.04, and 1.16 for the small, moderate, and large volumes, respectively. As the width of the stopping peak increased, from the narrow 4-cm peak of the small volume to the 12-cm peak of the moderate volume, the effectiveness of the pion beam decreased. This presumably reflects the low linear energy transfer contribution of the large number of passing pions in the wider stopping peak. The results indicate, however, a greater biological effectiveness for the large volume than for the moderate volume. Even though these fields had stopping peaks of similar width, the field size and dose rate were different. Although the increase in RBE may be partly due to an increased neutron flux from the larger volume, our results suggest that much of this apparent increase could be explained by differences in dose rate as a function of time for pions versus X rays.

Animals↗
PubMed1989

Tumor radiosensitization by nicotinamide: a result of improved perfusion and oxygenation.

Nicotinamide has been shown to sensitize tumors to radiation in preference to normal tissues. We have extended our studies to examine the mechanism responsible for this radiosensitization, using the EMT6 tumor model. Our results confirm that nicotinamide (1000 mg/kg) significantly enhances the radiation damage in this tumor when given as a single intraperitoneal injection 90 min before irradiation. The data also show that nicotinamide does not directly sensitize hypoxic cells to radiation either in vitro or in vivo. Excising tumors immediately after irradiation and exposing them to nicotinamide (7 mM) for 24 h similarly failed to increase the radiation damage, implying that nicotinamide does not inhibit the repair of radiation-induced potentially lethal damage. Nicotinamide did, however, produce a decrease in the binding of [14C]-misonidazole in tumors, consistent with a reduction in the degree of tumor hypoxia. There was also an increase in mean tumor cell fluorescence of Hoechst 33342 in nicotinamide-treated mice compared to that of controls, suggesting that the increase in tumor oxygenation was probably a consequence of an increase in tumor blood perfusion.

Animals↗