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Biomedical subjects

L Roizin-Towle

Publications and source records attributed to L Roizin-Towle.

At least 19 recordsLinked to original sources
PubMed1991

The response of human and rodent cells to hyperthermia.

Inherent cellular radiosensitivity in vitro has been shown to be a good predictor of human tumor response in vivo. In contrast, the importance of the intrinsic thermosensitivity of normal and neoplastic human cells as a factor in the responsiveness of human tumors to adjuvant hyperthermia has never been analyzed systematically. A comparison of thermal sensitivity and thermo-radiosensitization in four rodent and eight human-derived cell lines was made in vitro. Arrhenius plots indicated that the rodent cells were more sensitive to heat killing than the human, and the break-point was 0.5 degrees C higher for the human than rodent cells. The relationship between thermal sensitivity and the interaction of heat with X rays at low doses was documented by thermal enhancement ratios (TER's). Cells received either a 1 hr exposure to 43 degrees C or a 20 minute treatment at 45 degrees C before exposure to 300 kVp X rays. Thermal enhancement ratios ranged from 1.0 to 2.7 for human cells heated at 43 degrees C and from 2.1 to 5.3 for heat exposures at 45 degrees C. Thermal enhancement ratios for rodent cells were generally 2 to 3 times higher than for human cells, because of the fact that the greater thermosensitivity of rodent cells results in a greater enhancement of radiation damage. Intrinsic thermosensitivity of human cells has relevance to the concept of thermal dose; intrinsic thermo-radiosensitization of a range of different tumor cells is useful in documenting the interactive effects of radiation combined with heat.

Animals↗
PubMed1990

Studies with bifunctional bioreductive drugs. II. Cytotoxicity assayed with A-549 lung carcinoma cells of human origin.

A lung carcinoma cell line of human origin (A-549) cultured in vitro was used to investigate the cytotoxic effect of a range of bifunctional bioreductive drugs. The drugs tested consisted of nitroimidazoles or nitrofurans with terminal aziridine rings on the side chain and are designated RSU-1069, RSU-1164, RB-7040, RB-88716, and RB-88712. Measurements of the cytotoxicity in air demonstrated that methyl and alkyl addition to the aziridine ring reduced cell killing with progressive substitution of the alkylating moiety. A comparison was made of cytotoxicity in air and hypoxia with cells exposed to drugs for a 4-h period. A direct comparison of the aerobic and hypoxic cytotoxicity of RSU-1069 in human (A-549) and rodent cells (V-79-379A) yielded similar results. The cytotoxicity factors, defined to be the ratio of drug concentrations under aerobic and hypoxic conditions which result in 10% cell survival, were found to be 40, 25, 18, and 8, respectively, for the four agents RSU-1069, RSU-1164, RB-88712, and RB-88716 tested in A-549 cells. It has been suggested that under aerobic conditions the aziridine ring is primarily responsible for aerobic toxicity, whereas under hypoxic conditions, the aziridine moiety combined with a reduced 2-nitro moiety produces a bifunctional agent (I. J. Stratford et al., Br. J. Cancer 53, 339-344, 1986).

Antineoplastic Agents↗
PubMed1990

Hyperthermia studies in polyamine-altered human lung carcinoma cells.

The effect of polyamine depletion on the survival response of human lung carcinoma cells (A-549) to acute heating at 45 degrees C and its effect on the induction and decay of thermotolerance were investigated in exponential and plateau-phase cells. A 48-h exposure to 1 mM alpha-difluoromethylornithine (DFMO), an irreversible inhibitor of ornithine decarboxylase, was used to deplete intracellular levels of putrescine and spermidine. Inhibition of polyamine synthesis had no effect on the survival of exponential cells to heating at 45 degrees C, but slightly enhanced the killing of slowly proliferating plateau-phase cells. While DFMO treatment did not inhibit the development of thermotolerance, it caused a reduction in the thermotolerance ratio of exponential cells from 2.6 to 1.80, and from 1.66 to 1.59 in plateau-phase cells. DFMO caused thermotolerance to decay more rapidly in polyamine-depleted cells as well. Flow cytometry demonstrated that DFMO did not alter the cell cycle distribution of plateau-phase cells (i.e., greater than 73% in G1/G0), but caused a block and time-dependent accumulation of exponential cells in G1/G0. The cytostatic properties of DFMO in exponential cells which favor its use with phase-specific agents, and its ability to alter the magnitude and decay of thermotolerance in human carcinoma cells suggest a potential role for this nontoxic agent in clinically oriented hyperthermia studies.

Acclimatization↗
PubMed1986

A comparison of the heat and radiation sensitivity of rodent and human derived cells cultured in vitro.

A human lung and breast carcinoma cell line of epithelial origin (A-549 and MCF-7) were compared with a rodent fibroblast line (V-79) for their sensitivity to killing by X rays and heat, in addition, a correlation was sought between loss of endogenous thiols and thermosensitivity. Endogenous cellular thiols play a major role in many protective, enzymatic and synthetic processes in mammalian cells. Glutathione, a key non-protein thiol, not only protects against radiation and peroxide-induced damage, but is also a primary intracellular reductant. Thiol depletion was achieved using two agents that work by totally different mechanisms--one a substrate for glutathione-S-transferase (Diethylmaleate) and the other an inhibitor of a key enzyme in the gamma-glutamyl cycle (Buthionine-SR-Sulfoximine). The results of this study demonstrated that thiol depletion by DEM to 50% of the control values had no effect on the response of hamster cells to acute (45 degrees C) or chronic (42.5 degrees C) hyperthermia. Substantial potentiation of heat damage, however, was seen at thiol levels below 10% at 42.5 degrees C. Thiol depletion by BSO to levels of 25% of the control values had no sensitizing effect on the heat sensitivity of hamster or human lung carcinoma cells at 45 degrees C. For any given heat exposure, the human cells were markedly more resistant to killing than the hamster cells, however, they were more radiosensitive than the V79, line when exposed to 300 kVp X rays (D0's of 1.65 vs. 2.52 Gy). The results of this study indicate that thiols do not play a critical role in mammalian cell thermosensitivity at 45 degrees C and indicate that the use of human carcinoma cell lines may better predict heat inactivation in human cells in vivo.

Animals↗
PubMed1986

Oxygen dependence for chemosensitization by misonidazole.

Misonidazole (MISO) potentiates the cell killing effect of certain chemotherapy agents, but only under hypoxic conditions. The purpose of the present study was to define the range of oxygen concentrations over which chemosensitization by MISO takes place using mammalian cells cultured in vitro, and to compare this with the oxygen levels required for radiosensitization. V-79 hamster cells, attached to permanox dishes, were gassed with known concentrations of oxygen (less than 10 to 200,000 ppm) and treated with 1 and 5 mM MISO for 4 h previous to exposure to the chemotherapy agent, melphalan. In a parallel series of experiments, under the same gassing conditions, cells were irradiated with graded doses of X-rays at various oxygen concentrations. The K factor i.e. the oxygen concentration which defined half the maximum effect was found to be approximately 4776 ppm for radiosensitization and approximately 400 ppm for chemosensitization by MISO. It is evident that a significantly more stringent level of hypoxia is required for chemosensitization by MISO to take place than for radiosensitization.

Animals↗
PubMed1985

Selective enhancement of hypoxic cell killing by melphalan via thiol depletion: in vitro studies with hypoxic cell sensitizers and buthionine sulfoximine.

The relationship between thiol depletion and its enhancement of melphalan (L-PAM) cytotoxicity was studied with the use of V-79-379A Chinese hamster cells in vitro. Selective killing of hypoxic cells by use of a specific and nonspecific reducer of endogenous cellular thiols was the approach used in combining drugs with disparate mechanisms of action. Noncytotoxic concentrations of agents were employed in those experiments designed to mimic a practical scheme for their implementation in vivo. Cells made hypoxic by gassing in suspension with 95% nitrogen and 5% CO2 were treated with buthionine S-R-sulfoximine (BSO), a specific inhibitor of glutathione synthesis and a hypoxic cell sensitizer (i.e., either misonidazole or SR-2508) before their exposure to the alkylating agent. Cellular loss of nonprotein thiols by treatment with BSO correlated with enhanced L-PAM toxicity; however, a far greater effect was achieved when this enzymatic inhibitor was used in combination with a hypoxic cell sensitizer. This chemopotentiation of hypoxic cell killing by L-PAM, along with little potentiation of toxic cell killing, indicated the practical and potential benefit of this sort of drug therapy in vivo.

Animals↗
PubMed1984

Depletion of intracellular GSH and NPSH by buthionine sulfoximine and diethyl maleate: factors that influence enhancement of aerobic radiation response.

Many investigators have observed aerobic sensitization of V79, CHO and A549 (human lung carcinoma) cells upon depletion of GSH using buthionine sulfoximine (BSO). Recently we discovered that this aerobic sensitization can be reversed if WR-2721 or N-acetylcysteine is added to the cells just prior to irradiation. Reversal requires that the exogenous thiols be present during the time of irradiation. One possible explanation was that these thiols entered the cells and either increased the pool of cellular nonprotein thiols or reversed the thiol-depleted state by stimulation of GSH synthesis. Cells treated with BSO do not readily regenerate intracellular GSH because this agent irreversibly inhibits gamma-glutamyl synthetase. For A549 monolayer cultures, there is approximately 50% regeneration 6 hr after removal of 0.01 mM BSO, 20% 6 hr after 0.1 mM BSO, and only 5% 6 hr after 0.5 mM BSO. We found that addition of WR-2721 or N-acetylcysteine to BSO-treated cells did not affect the rate of regeneration of intracellular GSH. Thus, reversal of the aerobic sensitization of A549 cells by BSO cannot be explained on the basis of intracellular thiol levels alone, or by rapid reversal of BSO inhibition. In addition, diethylmaleate (DEM)-treated cells are considerably different from BSO-treated cells with respect to the ability to regenerate GSH. After removal of DEM, A549 cells immediately begin GSH resynthesis, and return to control levels occurs within 2 hr. Exogenous 5 mM GSH increases the rate of resynthesis of GSH in DEM-treated cells, but not in BSO-treated cells.

Aerobiosis↗
PubMed1984

Chemosensitization: do thiols matter?

It is well known that endogenous sulfhydryls are radioprotective in mammalian cells. Their comparable role in chemotherapeutic drug toxicity has been known for almost as long but less well defined. Thiol depletion as a mechanism responsible for enhanced cytotoxicity of melphalan was assayed by pretreatment of cells in vitro with misonidazole and buthionine sulfoximine (BSO). Hypoxic cell sensitizers, such as MISO, deplete endogenous thiols by metabolic activation under hypoxic conditions to thiol reactive intermediates, whereas BSO specifically inhibits a key enzyme in the synthesis of glutathione. For a given level of thiol reduction, sensitization to melphalan was far greater by preincubation with MISO than it was for BSO. This indicated that thiol reduction itself was not the sole factor involved in chemosensitization by MISO. As evidence that the method of thiol depletion predisposes to the expression of biological damage, it was shown that cells preincubated with MISO were appreciably more vulnerable to oxidative stress than those exposed to BSO. BSO was shown to totally inhibit the repair of damage from a preincubation treatment with MISO, demonstrating that recovery is dependent upon thiol regeneration. Thiol depletion "per se" is a good qualitative but not necessarily a quantitative indicator of chemosensitization--the biological and biochemical function of the thiol depleting agents used influences further drug interactions. The results of the study with these two agents suggest that thiols may play a potentially more critical role in the repair rather than the initiation of drug-induced damage.

Animals↗
PubMed1984

Factors associated with the preincubation effect of hypoxic cell sensitizers in vitro and their possible implications in chemosensitization.

The enhancement of melphalan toxicity was observed by preincubation of V-79- 379A cells in spinner culture with multiple doses of misonidazole (miso) or SR-2508 under hypoxic conditions. Chemosensitization was shown to be a function of sensitizer concentration and duration of exposure to the alkylating agent. A preincubation exposure of cells with 5 mM miso reduced endogenous cell thiols to less than 5% of controls and enhanced melphalan toxicity by a factor of 4.7. Cells preincubated with miso not only had lower levels of nonprotein thiols, but also were shown to have altered levels of intracellular calcium and a lower threshold to oxidative stress as measured by toxicity to cysteamine or H2O2. Preincubated cells, hypoxic cells, and cells receiving moderate hyperthermia (42.5 degrees C for 3 hr) all showed increased sensitivity to either cysteamine or H2O2. The increased killing of preincubated cells by cysteamine was shown to be similar to that of H2O2, and the dramatic reduction of cysteamine toxicity by catalase indicated H2O2 was the major reaction associated with this effect. These results indicate that preincubated cells exhibit a variety of biological effects that may significantly influence their response to further treatment with drugs or radiation, especially where peroxidative and free radical mechanisms are involved. The depletion of endogenous thiols, calcium disturbance, and vulnerability to oxidative stress are factors to be considered when interpreting mechanisms of combined drug action and effects that may potentially be exploited in terms of therapeutic gains.

Animals↗
PubMed1984

Biological effects of heat.

The biological effects of heat appear to be favorable for its use to treat cancer. Heat kills cells in a predictable and repeatable way. The age response function complements X-rays in that S-phase cells are most sensitive, and at the same time cells that are at low pH or are nutritionally deprived are also more sensitive. This offers the possibility that cycling tumor cells and quiescent cells that have respired to hypoxia may be more sensitive to heat than are the slowly turning over cells of the normal tissues responsible for late effects. Thermotolerance, in general, represents a problem and a complication in clinical practice but may be exploited to advantage. The interaction of heat with ionizing radiation has been studied extensively and is complex; in general, heat inhibits the repair of both sublethal and potentially lethal X-ray damage, but it is not obvious how to exploit this to advantage. By contrast, the potentiation by heat of the action of chemotherapy agents has been relatively neglected. This is a promising area, since local hyperthermia can "target" drug action in a way not otherwise possible. Heat is a weak mutagen and has not been shown to be a carcinogen; this is a most desirable property at a time of increasing concern for the oncogenic potential of agents used to treat cancer.

Animals↗
PubMed1981

Studies with cis-diamminedichloro-platinum II and exogenous polyamines using mammalian cells in culture.

Polyamines, such as putrescine and spermine, are naturally occurring substances intimately associated with normal and neoplastic growth. High levels are found in cancer patients and are associated with tumour growth. Experiments with V79 hamster cells cultured in vitro have demonstrated that the presence of putrescine and spermine can significantly reduce the cytotoxicity of the commonly used chemotherapy agent cis-DDP. These data may have clinical implications.

Animals↗
PubMed1978

Studies with bleomycin and misonidazole on aerated and hypoxic cells.

Bleomycin is a chemotherapuetic drug used primarily in the treatment of squamous-cell carcinoma, while misonidazole is an effective radiosensitizer and potent cytotoxic agent selectively affecting hypoxic cells. V79 Chinese hamster cells were used to investigate the cytotoxicity of bleomycin (BLM) under aerated and hypoxic conditions as a function of drug concentration. At a lowered temperature of 17.5 degrees C, or at an elevated temperature of 42.5 degrees C, hypoxic cells are more sensitive to killing by BLM than aerated cells. At either of these temperatures, progression through the cell cycle is inhibited. However, at 37.5 degrees C, mimicking a clinical situation, the sensitivies are reversed, and hypoxic cells are appreciably more resistant. Although many factors are involved, the major reason for this is that aerated cells are cycling while hypoxic cells are not. Aerated cells can progress into phases of the cell cycle where they are more sensitive to killing by BLM. Misoinidazole (=Ro-07-0582) was used in combination with BLM, since its mode of action has been shown to be psecific for killing hypoxic cells. It concomitant use with BLM could be of potential use in chemotherapy when confronted with the hypoxic cell component of solid tumours.

Bleomycin↗
PubMed1975

Hypoxic sensitizers: radiobiological studies at the cellular level.

The nitroimidazoles have been found to selectively sensitize hypoxic cells to the effects of irradiation. The latest in this family of drugs is RO-07-0582, which is able to mimic 80% of the oxygen effect at a concentration of 5 mM by modifying the sensitivity of hypoxic cells to single doses of gamma rays; however, it is not a substitution for oxygen in promoting the repair of sublethal radiation damage between split doses. Studies show that it is a powerful cytotoxic agent as well and selectively operates against hypoxic cells.

Animals↗
PubMedDate not supplied

Enhanced cytotoxicity of melphalan by prolonged exposure to nitroimidazoles: the role of endogenous thiols.

It was first demonstrated that prolonged exposure of hypoxic V-79 cells to misonidazole prior to irradiation produced an increased radiosensitization in 1977; it was postulated that the reduction of misonidazole resulted in intermediates capable of depleting cells of endogenous thiols, substances known to play a role in the hydrogen repair of target radicals produced by ionizing radiation. The present study shows that a prolonged exposure of V-79 cells to a variety of nitroimidazoles (misonidazole, Ro-05-9963, SR-2508, and MTR1-80) results in an enhanced cytotoxicity when these cells are subsequently exposed to melphalan. This process of enhanced melphalan toxicity occurred only when cells were pretreated with misonidazole under hypoxic conditions, suggesting that nitroreduction is necessary for chemosensitization as it is for increased radiosensitization. Different nitroimidazoles tested vary in the extent to which they sensitize cells to the subsequent action of melphalan. Repair from a misonidazole pretreatment is essentially complete by six hours. This study demonstrated that cysteamine could reduce the cytotoxicity of misonidazole and the enhancement of melphalan toxicity. This was an effect reversible with time and one implying similar mechanisms for the preincubation effect observed in vitro for radiation and chemotherapy agents.

Animals↗
PubMedDate not supplied

Thermotolerance in human cells of normal and neoplastic origin.

Thermotolerance was assayed under controlled conditions in normal and neoplastic human cells with the aim of identifying intrinsic differences in the acquisition of heat resistance. Carcinoma cells from colon (WIDR) and lung (A-549) were compared to fibroblasts (AG-1522) and primary explants of umbilical vein endothelial cells (HUVEC) in terms of their response to a 20 min heat shock at 45 degrees C. Single cell survival, heat shock protein (HSP) synthesis, and glutathione were studied as common endpoints. Production of HSPs was immediate in normal derived cells, and was evident in neoplastic cells 2 h following heat shock. Maximum translation of 70 and 90 kDa HSPs was observed at 6 h in all cell types and ceased by 24 h. Maximum cell survival peaked 4-24 h after the second heat dose showing a close association with HSP synthesis. Thermotolerance developed rapidly and decayed slowly over the next 5 days in normal and transformed cells. There was no correlation between the development of thermotolerance and endogenous glutathione content in all cells. There is little to distinguish thermotolerance in normal and neoplastic cells when compared on an equal basis as demonstrated here, indicating that therapeutic gain in vivo may be largely dependent on tumour physiology.

Cell Survival↗