Biomedical subjects

G E Adams

Publications and source records attributed to G E Adams.

At least 37 records · Page 2Linked to original sources

PubMed1994

Combination of photodynamic therapy (PDT) and melphalan in experimental tumors.

PURPOSE: To investigate whether application of "early" photodynamic therapy (PDT) using a disulphonated aluminium phthallocyanine photosensitizer can potentiate the action of melphalan in experimental RIF-1 tumors in vivo. METHODS AND MATERIALS: Tumors were irradiated with laser light of wavelength 675 nm 60 min after treatment with the photosensitizer and 15 min after melphalan. Melphalan pharmacokinetics were measured using high performance liquid chromatography with optical detection. RESULTS: Melphalan and PDT when given alone, caused a significant delay in tumor growth. This was increased for the combined treatment. Pharmacokinetic analyses showed that levels of free, unreacted melphalan in freely circulating blood are unaffected by combined treatment. However, significant differences in tumor levels were observed between treatment with melphalan alone or in combination. Whereas in the former, melphalan is still present in tumors after 2 h, it was not detectable even at the earliest time of 15-23 min for the combined treatment. CONCLUSION: The antitumor effects were additive with no evidence of significant potentiation.

Animals↗

PubMed1994

Bioreductive drugs for cancer therapy: the search for tumor specificity.

The activity of three different classes of bioreductive drug, i.e., heterocyclic nitro compounds, N-oxides and quinones are compared. The major characteristics of RB-6145, tirapazamine and E09 are summarized and future directions for development of new bioreductive drugs are outlined. The concept of potentiating bioreductive drug activity by increasing tumor hypoxia is described and illustrated in particular by the use of photodynamic therapy (PDT) in combination with RSU-1069. Examples of how the therapeutic effectiveness of this approach can be studied by the use of 31P magnetic resonance spectroscopy is described. The effects of manipulation of nitric oxide (NO) levels in tumors by the use of modifiers of NO-synthase activity is illustrated by studies with the inhibitor nitro-L-arginine in experimental tumors. Associated changes in tumor physiology indicate promise for potential applications in therapy. Finally, changes in expression of reductase enzyme levels are considered in the context of the heterogenous nature of the tumor microenvironment.

Animals↗

PubMed1994

31P MRS to monitor the induction of tumor hypoxia by the modification of the oxygen affinity of hemoglobin using BW 589C.

PURPOSE: BW 589C induces severe tumor hypoxia by modifying the affinity of oxyhemoglobin, causing a left shift of the oxygen-hemoglobin dissociation curve. 31P magnetic resonance spectra (MRS) was used to monitor the effects of BW 589C on tumor energy metabolism in three experimental tumor models. METHODS AND MATERIALS: HT-29 colon xenograft, murine transplantable RIF-1 fibrosarcoma and KHT sarcoma were studied in unanesthetised mice. 31P MR spectra were acquired on a 4.7 Tesla magnet before administering oral BW 589C (250 mg/kg) and after 3, 6, and 24 h. Samples of tail vein blood were then taken for 2,3 DPG levels for RIF-1 and HT-29 tumors. RESULTS: Doubling of inorganic phosphorus (Pi) to total phosphorus was observed 5-6 h after BW 589C for all three tumor types. Although the left shift due to BW 589C persists at 24 h, the level of Pi to total phosphorus returned to baseline with no significant difference from control values for the RIF-1 and HT-29 tumors. These results suggest that there was cellular metabolic adaptation to the reduction of oxygen delivery by BW 589C. This does not appear to involve 2,3 DPG as there was no significant alteration in tumor levels. The death of hypoxic cells may, also, have contributed to the recovery of Pi to total phosphorus. CONCLUSION: The efficacy of bioreductive drugs can be enhanced by increasing the severity of tumor hypoxia. 31P MRS in conjunction with other techniques for assessing the intratumor environment could play an important role in planning cancer therapy.

Animals↗

PubMed1994

Comparing the anti-tumor effect of several bioreductive drugs when used in combination with photodynamic therapy (PDT).

PURPOSE: To compare the effect on the RIF-1 murine sarcoma of nine bioreductive agents from five different classes when used in combination with either photodynamic therapy or clamping. METHODS AND MATERIALS: RIF-1 tumors implanted intradermally in C3H mice were treated with either 50J photodynamic therapy or with 120 min clamping in combination with either misonidazole, pimonidazole, metronidazole, nimorazole, RB6145, RSU1069, SR4233, mitomycin-C, or RB90740. The tumors were measured 3 times-per-week until reaching 4 x their initial treatment volume. RESULTS: RSU1069 produced the greatest anti-tumor activity in combination with both photodynamic therapy and clamping. RB6145 also substantially enhanced the effect of photodynamic therapy and clamping whereas misonidazole induced a smaller, but significant increase. Mitomycin-C had no effect under clamped conditions, but greatly increased the tumorcidal effect of photodynamic therapy. Mitomycin-C also induced an effect when given with light alone. None of the other agents showed any augmentation of the tumor cell killing induced by photodynamic therapy. CONCLUSION: Of the bioreductive agents studied RSU1069, RB6145 and mitomycin-C showed the greatest anti-tumor response in combination with photodynamic therapy.

Animals↗

PubMed1994

Radiolytic and photochemical reduction of the hypoxic cytotoxin 1,2-dihydro-8-(4-methylpiperazinyl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine 5-oxide (RB90740) and a potential mechanism for hypoxia-selective toxicity.

PURPOSE: To study the reduction of RB90740 (1), a fused pyrazine mono-N-oxide that has an oxic:hypoxic cytotoxicity ratio of > 10 in a range of murine and human tumor cells in vitro. METHODS AND MATERIALS: Reduction of 1 has been initiated radiolytically and photochemically in aqueous solution and the products isolated and characterized by high performance liquid chromatography (HPLC). RESULTS: Radiolytic reduction of 1 leads to the formation of the 2-electron reduced product, 2. The stoichiometry of the reduction is pH dependent, increasing from 1 to 2 with increasing pH, but independent of the presence of formate or 2-methyl 2-propanol in the reduction mixture. A dimerization product, 3, is also found, which is produced in greater yields at lower pH (< 6). Photochemical reduction of 1 to 2 was also found to be facile. Photolysis of 1 also leads to a deoxyribonucleic acid cleavage reaction. CONCLUSION: Since 2 is not cytotoxic towards hypoxic cells at concentrations at which 1 is toxic, a probable candidate as the cytotoxic species under hypoxic conditions is the 1-electron reduced intermediate species.

Animals↗

PubMed1994

Pharmacokinetics, metabolism and distribution of 1,2-dihydro-8-(4-methylpiperazinyl)-4-phenylimidazo [1,2-A] pyrido [3,2-E] pyrazine-5-oxide in C3H mice.

PURPOSE: 1,2-Dihydro-8-(4-methylpiperazinyl)-4-phenylimidazo [1,2-a] pyrido [3,2-e] pyrazine-5-oxide (RB90740) is a bioreductive drug with an oxic to hypoxic toxicity ratio of 16 in cultured V79 cells in vitro. The aim of this study was to examine the pharmacokinetics, metabolism and distribution of the drug in tumor bearing C3H mice. METHODS AND MATERIALS: A high pressure liquid chromatography assay for the quantitative determination of concentrations of the drug and its metabolites has been developed and used to examine their distribution in blood, RIF-1 and KHT tumors, brain, muscle, and liver tissue. Urine and feces collected for 24 h after drug administration have been examined for the drug and its metabolism products. RESULTS: Three metabolites, two of which have been identified, have been observed in mouse tissue. 1,2-Dihydro-8-(4-methylpiperazinyl)-4-phenylimidazo [1,2-a]pyrido[3,2-e]pyrazine (RB92815) is the two-electron reduced species, which is observed in liver, urine and occassionally in tumor samples. 1,2-dihydro-8-(4-piperazinyl)-4-phenylimidazo [1,2-a]pyrido[3,2-e]pyrazine-5-oxide (RB1739), the N-demethylated compound, is observed in urine and liver. Elimination of the drug after an intraperitoneal dose of 50 mg/kg is biphasic with t(1)2 alpha = 3 min and t(1)2 beta = 219 min. The area under the curve for blood concentration vs. time is 1.4 mg ml min-1. The drug is preferentially taken up into tumor tissue as is apparent from the area under the curve values for RIF-1 (28.3 mg ml min-1) and KHT (18.4 mg ml min-1) tumors. CONCLUSION: From these values of the area under the curve it is suggested that the drug is present in tumor tissue at concentrations sufficient to eliminate the hypoxic fraction provided reduction to a toxic species occurs. Bioreduction by the addition of two electrons to form RB92815 occurs in some tumors, but it is not known if this is due to an obligate two-electron detoxifying step or if reduction occurs by single electron additions via a toxic free radical species.

Animals↗

PubMed1994

The role of DT-diaphorase in determining the sensitivity of human tumor cells to tirapazamine (SR 4233).

PURPOSE: To determine the dependency of the aerobic and hypoxic toxicity of tirapazamine on the intracellular activity of DT-diaphorase. METHODS AND MATERIALS: A panel of 18 human cell lines comprising predominantly small cell and nonsmall cell lung cancer and breast cancer lines were used. The activity of DT-diaphorase was determined in cytosolic preparations from cell lysates. The toxicity of tirapazamine was determined using the MTT assay after either 96 or 3 h aerobic exposure or 3 h treatment in hypoxia. RESULTS: The cell lines exhibited a 5000-fold range in DT-diaphorase activity. In toxicity experiments, values of IC50 range from 10.2-120 microM and from 155-1230 for 96 and 3 h aerobic exposures, respectively. In N2, IC50s ranged from 8-55 microM. None of the toxicity values correlate with activity of DT-diaphorase, neither did the ratio of aerobic:hypoxic toxicity (differential toxicity). CONCLUSION: The expression of DT-diaphorase in human tumor cells does not affect the toxicity of tirapazamine.

Antineoplastic Agents↗

PubMed1994

The accuracy and reproducibility of measuring blood flow in murine tumours by the D2O uptake and clearance techniques.

The use of D2O as an NMR visible tracer to monitor murine tumour blood flow (TBF) by both the wash-in and wash-out methods has been investigated. The factors that influence the models used to fit the data and the error on the measurement of the clearance and uptake rates have been assessed. The study concentrates on the uptake method which allows TBF to be measured without the need to use anaesthetic. Also, administering the D2O remotely to the mouse means it can remain undisturbed, in the magnet bore, between control and post-treatment readings. The uptake method in KHT and RIF-1 transplanted murine tumours has been investigated in a series of control experiments and after modifying TBF by hydralazine (5 mg/kg) and photodynamic therapy. These studies showed that four uptake measurements could be made on the same mouse at 20 min intervals without affecting TBF, control values were the same for anaesthetized and unanaesthetized mice and the values obtained for RIF-1 tumours were marginally higher than those obtained for the KHT tumours. The decrease in TBF seen after modification was in good agreement with published data where TBF results were obtained by using D2O clearance, radioactive tracers or laser Doppler flowmetry.

Animals↗

PubMed1994

Factors affecting sensitivity to EO9 in rodent and human tumour cells in vitro: DT-diaphorase activity and hypoxia.

Twenty-three human tumour cell lines (lung, breast, and colon) and eight rodent cell lines were evaluated for their sensitivity to the quinone-based anticancer drug EO9 [3-hydroxymethyl-5-aziridinyl-1-methyl-2-(1H indole-4,7-dione)prop-beta-en-alpha-o1]. Sensitivity was compared with the intracellular levels of DT-diaphorase, and cell lines showing highest enzyme activity tended to be the most sensitive to EO9. The role of DT-diaphorase in determining drug sensitivity was confirmed by using the enzyme inhibitor dicoumarol, which protects cells containing high levels of DT-diaphorase from the cytotoxic action of EO9. Hypoxia increased the cytotoxicity of cells containing low but not high levels of DT-diaphorase, implying that both 1- and 2-electron reductive activation processes can be important for expression of EO9 toxicity. It is concluded that EO9 is a potentially useful agent in the enzyme directed approach to the use of bioreductive drugs in cancer therapy.

Animals↗

PubMed1994

Phosphorus metabolism during growth of lymphoma in mouse liver: a comparison of 31P magnetic resonance spectroscopy in vivo and in vitro.

Large phosphomonoester (PME) signals are detected in the phosphorus magnetic resonance spectra (31P MRS) of many neoplastic and rapidly dividing tissues. In addition, alterations in phosphodiester (PDE) signals are sometimes seen. The present study of a murine lymphoma growing in liver showed a positive correlation between the hepatic PME/PDE ratio measured in vivo by 31P MRS at 4.7 T and the degree of lymphomatous infiltration in the liver, quantified by histology. High-resolution 31P MRS of liver extracts at 9.7 T showed that the PME peak consists largely of phosphoethanolamine (PE) and to a lesser extent of phosphocholine (PC). The concentration of both PE and PC increased positively with lymphomatous infiltration of the liver. In vivo, the PDE peak contains signals from phospholipids (mostly phosphatidylethanolamine and phosphatidylcholine) and the phospholipid breakdown products glycerophosphoethanolamine (GPE) and glycerophosphocholine (GPC). Low levels of GPE and GPC were detected in the aqueous extracts of the control and infiltrated livers; their concentrations remained unchanged as the infiltration increased. The total concentration of phospholipids measured by 31P MRS of organic extracts decreased about 3-fold as the infiltration increased to 70%. Thus, our data showed that the increased PME/PDE ratio in vivo is due to both an increase in the PME metabolites and a decrease in the PDE metabolites. We propose that this ratio can be used as a non-invasive measure of the degree of lymphomatous infiltration in vivo.

Animals↗

PubMed1994

Magnetic resonance spectroscopic studies on 'real-time' changes in RIF-1 tumour metabolism and blood flow during and after photodynamic therapy.

Magnetic resonance spectroscopy (MRS) in situ was used to study changes in 31P metabolism occurring during and after treatment of murine RIF-1 tumours with photodynamic therapy (PDT). Tumours were irradiated using a fibreoptic light delivery system while the mice were in position within the magnet. Changes in 31P-MRS were observable during and immediately after treatments of several minutes' duration. Both the extent and duration of the increase in the Pi/total ratio were light dose dependent. The effect on the metabolism was also affected by the time interval (TL) between administering the photosensitiser disulphonated phthalocyanine, (A1S2Pc) and the light. With a dose of 50 J the increase in Pi/total was much faster when TL was 1 h than when TL was 24 h. This difference in rate probably reflects differences in the distribution of A1S2Pc within the tumour. Significant decreases in pH were only seen after a light dose of 50 J when TL was 1 h. Blood flow measurements using deuterium uptake were also carried out using MRS. These experiments showed that for a dose of 50 J the level of blood flow was reduced by approximately 90% of the control value within 10 min from the end of the 8 min light treatment. This occurred irrespective of the value of TL. The data indicate that it is possible to observe very early changes in 31P metabolism that can be attributed to direct cellular damage as opposed to the later changes indicative of overall tumour hypoxia caused by vascular damage.

Aluminum↗

PubMed1994

Manipulation and exploitation of the tumour environment for therapeutic benefit.

We describe aspects of the tumour microenvironment that are available as targets for manipulation. In particular, the question asked is whether hypoxia in tumours is a problem to be overcome, or a physiological abnormality to be exploited? Bioreductive drugs require metabolic reduction to generate cytotoxic metabolites. This process is facilitated by appropriate reductases and the lower oxygen conditions present in solid tumours compared with normal tissues. Because of their specificity, bioreductive drugs are used to help answer this question. Other aspects of tumour physiology and biochemistry that may be exploited include tissue dependent reductase expression, pH and angiogenesis.

Antineoplastic Agents↗

PubMed1994

One-electron oxidation of C(2) and C(3) methyl substituted 5,6-dihydroxyindoles: model pathways of melanogenesis.

One-electron oxidation of a series of C(2)- and C(3)-methyl substituted analogues of 5,6-dihydroxyindole (DHI), in the pH range 5-9, was studied using the technique of pulse radiolysis with spectrophotometric detection. This investigation was undertaken to further our understanding of the involvement of free radical species in the polymerization processes leading to melanin formation. The optical absorption spectra of the protonated indole semiquinone radicals resulting from the one-electron oxidation of C(2)- and C(3)-methyl substituted indoles were similar to those of their corresponding hydroxylated indoles. From this similarity, it is inferred that methylation at C(2) and C(3) of DHI has little or no effect upon the initial radicals. The semiquinone radicals of these analogues subsequently decay to yield the corresponding quinone methide/imine. However, methyl substitution at C(2) and C(3) of the quinone methide derived from these analogues results in their stabilization. This stabilization contracts with the reactivity of the corresponding quinone methide from DHI. Further, these stabilized quinone methides do not interact with the azide ion (N3-), in contrast to the reaction of N3- with the quinone methide of DHI. It is concluded that methylation at C(2) and C(3) of DHI will modify the pathways so that the polymerization processes are less effective than those with DHI.

Catechol O-Methyltransferase Inhibitors↗

PubMed1994

Radiation-induced luminescence in DNA: evidence for long-range electron migration.

The radiation-induced "in-pulse" luminescence emission from solid DNA containing either metronidazole or a highly electron-affinic 5-nitrofuran in the range 3-2000 (w:w) base pairs per additive molecule has been investigated in vacuo at 293 K using electron pulses of energy below 260 keV. The luminescence intensity at 450 nm from DNA decreases with increasing content of the additive in the sample and approaches a limiting level at high concentrations of the additives. At these higher concentrations the limiting value represents about 50% of that observed from DNA alone. It is shown that the efficiency of the additives in reducing the luminescence intensity is dependent upon their redox potential E1(7); this dependence is consistent with these additives acting as electron acceptors. It is concluded that the ability of the electron acceptors to reduce the luminescence is related to the electron affinity of E1(7) of the acceptors and electron migration distances of at least 300 base pairs are proposed.

DNA↗

PubMed1993

The effect of hypoxia on acquired drug resistance and response to epidermal growth factor in Chinese hamster lung fibroblasts and human breast-cancer cells in vitro.

Prolonged hypoxia induced transient drug resistance in Chinese hamster lung fibroblasts. Previously hypoxic cells were resistant to adriamycin and resistant to etoposide. Complete recovery of etoposide sensitivity was observed following reaeration for 24 hr. A change in P-glycoprotein expression was unlikely to contribute to the resistance caused by hypoxia, since adriamycin resistance was not reversed by verapamil. However, alteration in the plasma membrane structure may be involved, since previously hypoxic cells were resistant to extracellular superoxide radical generated by the addition of xanthine/xanthine oxidase. In contrast, adriamycin sensitivity was not altered by hypoxia in 3 human breast-cancer cell lines. MDA-468 and MCF-7/Adr differed in their response to EGF, independent of the presence of hypoxia. These results suggest that hypoxic-stress-induced drug resistance is not generalized.

Animals↗

PubMed1993

Modification of energy metabolism and radiation response of a murine tumour by changes in nitric oxide availability.

The nitric oxide donor, SIN-1 and nitric oxide synthase inhibitor, nitro-L-arginine were examined for their effects on energy metabolism using 31P magnetic resonance spectroscopy, and on radiation sensitivity in the transplantable murine tumour, SCCVII/Ha. SIN-1 at 2 mg/kg i.v. reduced Pi/total by 40-50% within 10 min and increased X-ray sensitivity 3 fold, consistent with increased tumour oxygenation. Nitro-L-arginine at 10 mg/kg i.v. increased Pi/total by 250% at 45 min and was maintained for at least 2 hr. Nitro-L-arginine also increased radiation resistance 3-5 fold, consistent with the induction of tumour hypoxia. The results indicate that tumour energy metabolism may be altered through drug induced modification of nitric oxide availability, and that these changes are sufficient to modify tumour sensitivity to X-rays.

Animals↗

PubMed1993

Phosphomonoester is associated with proliferation in human breast cancer: a 31P MRS study.

Phospholipid metabolism of human breast cancer was studied by 31P magnetic resonance spectroscopy (MRS). In vivo localised 31P MR spectra were obtained from the tumour alone using phase modulated rotating frame imaging. For 31 tumours, median (range) phosphomonoester (PME) to ATP ratio was 1.48 (0.57-3.78) and phosphodiester (PDE) to ATP ratio was 1.65 (0.44-3.89). DNA index and S phase fraction (SPF) were measured by flow cytometry of paraffin embedded tissue. Twelve (39%) tumours were diploid and 19 aneuploid. Median (range) SPF for 29 assessable tumours was 5.3% (0.6-28%), with significantly greater median SPF for aneuploid tumours (9.3%) than diploid (3.8%, P = 0.007). There was a significant association between PME/ATP and SPF (P = 0.03) due to a significant correlation for aneuploid tumours (P = 0.01). High resolution 31P MRS of extracts from 18 tumours (including seven studied in vivo) demonstrated that the PME peak consists predominantly of phosphoethanolamine (PE) with a smaller contribution from phosphocholine (PC) (median (range) PE/PC: 3.02 (1.13-5.09)). Changes in PME/ATP were observed for two tumours where tamoxifen stablized disease and may be consistent with the cytostatic effects of this drug.

Adenosine Triphosphate↗

PubMed1993

Synthesis of the enantiomers of the bioreductively-activated cytotoxin RSU-1069 and its prodrug RB6145 and lack of stereoselectivity in their cytotoxicity and radiosensitization in vitro.

The R(+)- and S(-)-enantiomers of the radiosensitizer and bioreductively-activated cytotoxin RSU-1069 and their prodrugs have been synthesised. The parent drugs were evaluated as radiosensitizers and bioreductively-activated cytotoxins in vitro. No stereoselectivity in the activities in vitro of the two enantiomers was evident and both compounds were potent hypoxia-selective agents.

Antineoplastic Agents↗