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Biomedical subjects

S Rockwell

Publications and source records attributed to S Rockwell.

At least 127 records · Page 7Linked to original sources
PubMed1985

Radiosensitization of EMT6 cells by four platinum complexes.

The greatest research effort in producing radiation sensitizers has been directed toward organic compounds. However, platinum complexes also have radiosensitizing capabilities, perhaps because they bind to DNA. The compound described here are dichloro complexes of bivalent platinum with one or two potentially radiosensitizing ligands. The radiosensitization of oxygenated and hypoxic exponentially growing EMT6 cells in vitro was measured. The dose modifying factors obtained with 200 microM and 400 microM trans-bis(2-nitroimidazole)dichloroplatinum II (NIPt) in hypoxic cells were 1.5 and 2.1, respectively. For trans-bis(2-amino-5-nitrothiazole)dichloroplatinum II (Plant) under the same conditions, the dose modifying factor was 1.5 at 200 microM and 1.8 at 400 microM. Neither compound sensitized oxygenated cells when tested similar protocols. Unlike the trans complexes, (1,2-diamino-4-nitrobenzene)dichloroplatinum II (Plato) was cytotoxic toward the hypoxic cells in the absence of X rays. The time course of cytotoxicity for 100 microM Plato in exponentially growing cells showed rapid killing of hypoxic cells, and much less toxicity toward oxygenated cells. In radiosensitization studies, dose modifying factors of 1.6 and 2.0 were found with 200 microM and 400 microM Plato in hypoxic cells. The compound did not sensitize aerobic cells. The well-known platinum complex cis-dipyridinedichloroplatinum II (PyPt) represents a cis-platinum heterocyclic aromatic complex that does not have a nitro-functionality. The dose modifying factor obtained with 400 microM PyPt in hypoxic cells was 1.7. On a molar basis, the nitro-functional platinum complexes appear to be more effective as hypoxic cell radiosensitizers than the corresponding free ligands.

Animals↗
PubMed1985

Use of a perfluorochemical emulsion to improve oxygenation in a solid tumor.

The ability of the perfluorochemical emulsion, Fluosol-DA, to oxygenate the naturally-occurring hypoxic cells of solid tumors was examined. BALB/c mice bearing EMT6 mouse mammary tumors were given in a single i.v. injection of 0.015 ml/g of Fluosol, and were then treated with 95% O2/5% CO2 for 30 min before irradiation with graded doses of X rays. The pretreatment increased the cytotoxic effect of the radiation, as assayed by colony formation in vitro. The dose-response curve for the combination regimen was parallel to that for radiation alone, but was offset towards lower survivals. This change is consistent with the change which would be expected if the pretreatment decreased the proportion of hypoxic cells in the tumors. Studies with unoxygenated perfluorochemical emulsions in vivo and in vitro and studies with O2/CO2 alone in vivo suggested that the survival curve changes did not reflect either direct cytotoxic effects of the perfluorochemical emulsion or the O2/CO2-breathing, or radiosensitizing or physiologic effects of either agent alone. The data reported here suggest that oxygenated perfluorochemical emulsions may decrease the proportion of hypoxic cells in solid animal tumors and encourage further preclinical evaluation of these agents as potential adjuvants to radiotherapy.

Animals↗
PubMed1985

Enhancement of mitomycin C cytotoxicity to hypoxic tumor cells by dicoumarol in vivo and in vitro.

Previous work by our laboratories demonstrated that dicoumarol can increase the enzymatic activation of mitomycin C (MC) to alkylating species by tumor cell sonicates under hypoxic conditions. To determine whether this increased generation of reactive metabolites would result in increased cytotoxicity, we examined the effect of this combination on the viability of EMT6 cells treated in vitro under hypoxic and oxygenated conditions. Dicoumarol increased the cytotoxicity of MC to these neoplastic cells under hypoxic conditions and decreased the toxicity of the antibiotic to aerobic cells. These findings suggested that dicoumarol might enhance the toxicity of MC to the hypoxic cells of solid tumors, without increasing the toxic side effects of the antibiotic to the host. Treatment of EMT6 tumor-bearing animals with both dicoumarol and MC significantly decreased the survival of the radioresistant hypoxic tumor cells from that obtained with MC alone. In contrast, the leukopenia produced by the antibiotic was not exacerbated by the addition of dicoumarol. These results suggest that a treatment regimen combining dicoumarol and MC might be a useful adjunct to radiation therapy for the eradication of the radioresistant hypoxic cells in solid tumors.

Anaerobiosis↗
PubMed1985

Porfiromycin as a bioreductive alkylating agent with selective toxicity to hypoxic EMT6 tumor cells in vivo and in vitro.

Hypoxic cells may limit the curability of solid tumors by conventional chemotherapeutic agents and radiotherapy. Agents which are preferentially toxic to cells with low oxygen contents could therefore be useful as adjuncts to the regimens now used to treat these cancers. To date, the best agent of this type that we have tested is porfiromycin. Porfiromycin is similar to mitomycin C in its toxicity to hypoxic EMT6 cells in vitro but has much less toxicity than mitomycin C to well-oxygenated EMT6 cells. EMT6 cell sonicates reduce mitomycin C and porfiromycin to reactive electrophiles at similar rates under hypoxic conditions, a finding that correlates with cytotoxicity, whereas the rate of production of reactive species from both drugs is very slow under aerobic conditions. We also show that porfiromycin is capable of killing hypoxic radiation-resistant cells in solid EMT6 tumors. Appropriate regimens combining porfiromycin (which preferentially kills hypoxic cells) and radiation (which preferentially kills aerated cells) may therefore be especially efficacious for the treatment of solid tumors.

Alkylating Agents↗
PubMed1985

Effects of clumps and clusters on survival measurements with clonogenic assays.

The growth of colonies in semisolid medium is receiving widespread attention as a possible test for predicting the clinical response of individual human tumors to specific drugs. One problem encountered in these studies is the difficulty of preparing single-cell suspensions from solid tumors. Often, microscopic examination of the cultures just after plating reveals many clusters or clumps of cells; these are often large enough and numerous enough that some plates are counted or fixed immediately so that this "background" can be subtracted from the "colony" count used to assess cell viability. However, this correction addresses only one of the problems created by the presence of clumps and clusters. It does not eliminate errors and artifacts introduced by multiplicity (multiple clonogenic cells contributing to a colony), abortive clones, and cell volume changes, or by inhomogeneities in the microenvironment, cell metabolism, and drug distribution within clumps. Because of such factors, survival curves determined using suspensions contaminated with clumps and clusters may provide inaccurate assessments of the true drug sensitivity of the individual tumor cells.

Animals↗
PubMed1984

Hypoxic fractions of solid tumors: experimental techniques, methods of analysis, and a survey of existing data.

Hypoxic fractions are measured by indirect techniques, which compare the response of tumors to large single doses of radiation given under normal aeration and artificial hypoxia. This paper reviews hypoxic fraction measurements and measurement techniques, giving particular attention to the biological, technical, and statistical aspects of the assays; the implicit assumptions underlying the analyses; and the dependence of the determinations on the assay conditions and the tumor and host characteristics. The three major hypoxic fraction assay techniques (paired survival curve, clamped tumor control, and clamped growth delay) share common biological assumptions. They require that the survival curves of naturally and artificially hypoxic cells have the same slope and intercept. They assume that the majority of the cells are either fully oxic or fully hypoxic. They assume that the methods used to induce artificial hypoxia leave no oxygenated regions and that tumor cells rendered artificially hypoxic are no less viable than cells in normally-aerated tumors. The universal validity of these assumptions is questionable. Each technique uses additional special assumptions and each may measure a different population of hypoxic cells. This paper reviews 92 hypoxic fraction determinations in 42 tumor systems. Radiobiologically hypoxic cells appear to be present in the majority of macroscopic solid rodent tumors. The hypoxic fraction was found to increase as the tumor size increased from microscopic to macroscopic; the dependence of hypoxic fraction on tumor size at macroscopic sizes was less clear. The site of tumor implantation, the use of anesthesia, and certain host characteristics may influence the hypoxic fraction. The hypoxic fraction generally did not depend on the tumor growth rate, transplantation history, or histology. These findings indicate that hypoxic cells are a common feature of solid tumors in rodents and provide no evidence that hypoxic cells should not be present in human tumors.

Anesthesia↗
PubMed1984

Enhancement of artificial lung metastases by misonidazole.

The effect of treatment with the hypoxic cell radiosensitizer misonidazole on the formation of artificial lung metastases was examined. Both single treatments with large doses of misonidazole and fractionated treatments with smaller doses of misonidazole were found to increase the number of lung tumors developing after intravenous injection of EMT6 mouse mammary carcinoma cells. The immunologic and physiologic effects of the nitroimidazole were postulated to be responsible for the enhancement of lung tumor formation.

Animals↗
PubMed1984

Combination therapy with misonidazole and mitomycin C: lack of chemosensitization of EMT6 tumor cells in vivo or in vitro.

The effect of the nitroimidazole misonidazole on the cytotoxicity of mitomycin C was examined using EMT6 Rw tumors in mice and EMT6 cells in culture. In contrast to reports by others using a different tumor system, we were unable to detect any significant increase of mitomycin cytotoxicity by misonidazole in vivo using tumor cell survival or host toxicity endpoints. Studies with cells in vitro provided no evidence for marked chemosensitization of either hypoxic or aerobic cells.

Animals↗
PubMed1984

Tumor-to-tumor variability in the hypoxic fractions of experimental rodent tumors.

Paired determinations of the radiation responses of normally-aerated and artificially hypoxic rodent tumors, performed to measure the hypoxic fractions of the tumors, were obtained from our own laboratories and from the literature. The data were reanalyzed to assess whether the variabilities in the radiation responses of the normally-aerated and artificially hypoxic tumors were similar. If there were large differences in the hypoxic fractions of individual tumors within the experiments, the variability in the data from aerobic tumors would be expected to be greater than the variability in the data from artificially hypoxic tumors (which should all be brought to uniform hypoxia and therefore uniform radioresistance). The analyses revealed the variability to be as great or greater for hypoxic tumors as for normally-aerated tumors. This finding suggests that factors other than tumor-to-tumor differences in oxygenation produce most of the variability in the radiation responses of individual tumors from an experimental tumor line.

Animals↗
PubMed1984

Role of NADPH:cytochrome c reductase and DT-diaphorase in the biotransformation of mitomycin C1.

Hypoxic cells of solid tumors are difficult to eradicate by X-irradiation or chemotherapy; as an approach to this problem, our laboratories are investigating the effects of the bioreductive alkylating agent mitomycin C (MC) on hypoxic cells. This antibiotic was preferentially toxic to EMT6 mouse mammary tumor cells and V79 Chinese hamster lung fibroblasts under hypoxic conditions, but it was equitoxic to Chinese hamster ovary cells in the presence and absence of oxygen. All cell lines catalyzed the formation of reactive metabolites under hypoxic conditions and contained NADPH:cytochrome c reductase and DT-diaphorase, two enzymes which may be responsible for the cellular activation of MC. Although a correlation existed between enzymatic activities and the formation of reactive metabolites from MC, there was no correspondence between these parameters and the degree of cytotoxicity expressed by MC under hypoxic conditions. Purified NADPH:cytochrome c reductase reduced MC in the absence of oxygen, with addition of cytochrome P-450 enhancing, but not participating directly in, the reduction reaction. Addition of NADP+ to cell sonicates substantially reduced NADPH:cytochrome c reductase activity, while the formation of reactive metabolites was affected only slightly; converse results were observed using mersalyl. Exposure of cell sonicates to dicumarol inhibited DT-diaphorase activity, while the rate of formation of reactive metabolites of MC was enhanced. The findings suggest that NADPH:cytochrome c reductase and some as yet to be identified enzyme(s) are important for the reductive activation of MC. DT-diaphorase and cytochrome P-450 are not directly involved in the activation of MC, but they appear to modulate the degree of activation to reactive species, which are presumably responsible for the observed cytotoxicity.

Animals↗
PubMed1984

Failure of 5-thio-D-glucose to alter cell survival in irradiated or unirradiated EMT6 tumors.

The antineoplastic effects of the glucose analog 5-thio-D-glucose (5TG) were tested using EMT6 mouse mammary tumors in vivo and EMT6 cells in cell culture. In vitro, 5TG selectively killed hypoxic EMT6 cells. However, administration of 5TG to mice bearing EMT6 tumors produced no significant toxicity to the cells of unirradiated tumors and did not alter the survival of cells in irradiated tumors. Fasting the mice to lower blood glucose concentrations before administration of 5TG increased the toxicity of the drug to the mice, but did not allow more efficacious treatment of the tumors. The data provided no evidence that 5-thio-D-glucose can be used effectively for the treatment of solid tumors, either as a cytotoxic agent or as a radiosensitizer.

Animals↗
PubMed1983

Development of an in vitro assay for the survival of cells suspended from BA1112 rat sarcomas.

A method has been developed for the in vitro assay of the survival of BA1112 rat sarcoma cells following treatment in vivo. The BA1112 tumor was not adapted for growth in culture and was maintained by serial transplantation in vivo. The assay used a feeder layer of heavily irradiated cells to eliminate any changes in plating efficiency caused by the large number of dying cells which must be plated when assaying cell survival after intensive treatments. The plating efficiency of the tumor cells was not affected significantly by the age of the feeder layer (between 1 and 4 days), the density at which the experimental cells were plated or the interval between preparation of the cell suspension and plating (up to 4 hr). Using the in vitro assay a survival curve was determined for cells from tumors irradiated in air-breathing animals. This curve was similar to that determined previously for BA1112 tumor cells using an in vivo assay to measure cell survival.

Animals↗
PubMed1983

Inhibition of delayed hypersensitivity by metronidazole and misonidazole.

The effect on cell-mediated immunity of two hypoxic cell radiosensitizers, metronidazole and misonidazole, was examined. Immunocompetence was assayed by measuring delayed hypersensitivity reactions in mice sensitized on the abdomen with 2,4-dinitro-1-fluorobenzene (DNFB) and subsequently challenged on the ears with DNFB. Single and fractionated treatments with misonidazole or metronidazole were found to suppress delayed hypersensitivity reactions to DNFB. This finding is in agreement with other data in the literature which show that many imidazoles, including nitroimidazoles, inhibit aspects of the cell-mediated immune response in animals and man. The potential immunosuppressive effects of nitroheterocyclic radiosensitizers should be considered when these agents are evaluated in the laboratory or used in the clinic.

Animals↗
PubMed1983

Effects of mitomycin C alone and in combination with X-rays on EMT6 mouse mammary tumors in vivo.

The effects of mitomycin C alone and in combination with radiation on the cells of EMT6 mouse mammary tumors in BALB/cKaRw mice were examined. At doses near the toxic level, approximately 98% of the tumor cells were killed by a single injection of mitomycin C. Both proliferating and quiescent cells and both hypoxic and aerobic cells were killed by the drug. Cytotoxicity with mitomycin C occurred rapidly and was apparently complete within 30 minutes after injection of the drug . No evidence was found for repair of potentially lethal mitomycin C damage or sublethal mitomycin C damage by the tumor cells. Mitomycin C and radiation in combination produced an additive cytotoxicity; neither agent was found to alter significantly the shape of the dose-response curve for the other agent. The cytotoxicity of mitomycin C and radiation in combination depended on the sequence and timing of the treatments; additive toxicities were obtained when mitomycin C was given just after, just before, or up to 24 hours before irradiation, but the combination was less effective when mitomycin C was given 2-12 hours after irradiation.

Animals↗
PubMed1982

Cytotoxicities of mitomycin C and x rays to aerobic and hypoxic cells in vitro.

Aerobic and hypoxic EMT6 mouse mammary tumor cels in exponential growth in vitro were used to study cell survival after treatment with radiation (250kV X rays) and mitomycin C in various combinations. The cytotoxicities of the two agents were found to be additive as judged by comparing dose-response curves for each agent alone with survival curves after combination therapy and by isobologram analysis. The cytotoxicities resulting from combination treatments were found to be independent of the sequence of the treatments or the interval between treatments.

Aerobiosis↗