Biomedical subjects

E W Gerner

Publications and source records attributed to E W Gerner.

At least 73 records · Page 4Linked to original sources

PubMed1987

Spermidine mediates degradation of ornithine decarboxylase by a non-lysosomal, ubiquitin-independent mechanism.

The mechanism of spermidine-induced ornithine decarboxylase (ODC, E.C. 4.1.1.17) inactivation was investigated using Chinese hamster ovary (CHO) cells, maintained in serum-free medium, which display a stabilization of ODC owing to the lack of accumulation of putrescine and spermidine (Glass and Gerner: Biochem. J., 236:351-357, 1986; Sertich et al.: J. Cell Physiol., 127:114-120, 1986). Treatment of cells with 10 microM exogenous spermidine leads to rapid decay of ODC activity accompanied by a parallel decrease in enzyme protein. Analysis of the decay of [35S]methionine-labeled ODC and separation by two-dimensional electrophoresis revealed no detectable modification in ODC structure during enhanced degradation. Spermidine-mediated inactivation of ODC occurred in a temperature-dependent manner exhibiting pseudo-first-order kinetics over a temperature range of 22-37 degrees C. In cultures treated continuously, an initial lag was observed after treatment with spermidine, followed by a rapid decline in activity as an apparent critical concentration of intracellular spermidine was achieved. Treating cells at 22 degrees C for 3 hours with 10 microM spermidine, followed by removal of exogenous polyamine, and then shifting to varying temperatures, resulted in rates of ODC inactivation identical with that determined with a continuous treatment. Arrhenius analysis showed that polyamine mediated inactivation of ODC occurred with an activation energy of approximately 16 kcal/mol. Treatment of cells with lysosomotrophic agents (NH4Cl, chloroquine, antipain, leupeptin, chymostatin) had no effect on ODC degradation. ODC turnover was not dependent on ubiquitin-dependent proteolysis. Shift of ts85 cells, a temperature-sensitive mutant for ubiquitin conjugation, to 39 degrees C (nonpermissive for ubiquitin-dependent proteolysis) followed by addition of spermidine led to a rapid decline in ODC activity, with a rate similar to that seen at 32 degrees C (the permissive temperature). In contrast, spermidine-mediated ODC degradation was substantially decreased by inhibitors of protein synthesis (cycloheximide, emetine, and puromycin). These data support the hypothesis that spermidine regulates ODC degradation via a mechanism requiring new protein synthesis, and that this occurs via a non-lysosomal, ubiquitin-independent pathway.

Animals↗

PubMed1987

Accumulation of heat shock protein 70 RNA and its relationship to protein synthesis after heat shock in mammalian cells.

Heat stress induces a set of heat shock proteins (hsps) in a wide variety of species. In response to either a mild (5 min X 45 degrees C) or severe (30 min X 45 degrees C) heat shock, the timing of expression of the hsps and the recovery of general protein synthesis in rat embryonic fibroblasts was dependent on the duration of the hyperthermic exposure. Synthesis of mRNA coding for an hsp of Mr approximately equal to 70,000 (hsp 70) followed immediately after the mild heat shock but was delayed after the severe heat shock. Appearance of the hsps paralleled the synthesis and decay of RNA and was indicative that new RNA synthesis was required for hsp 70 expression. Inhibition of protein synthesis by cycloheximide after the mild heat shock increased the maximal accumulation of hsp 70 encoding mRNA but did not prevent the subsequent decrease in this mRNA species. These results suggest that mammalian cells control the expression of hsp 70 primarily at the level of transcription, and that the normal pattern of hsp 70 mRNA turnover after an inducing heat stress is not dependent on new protein synthesis.

Animals↗

PubMed1987

Phosphorylation of a high molecular weight DNA polymerase alpha.

Anti-human DNA polymerase alpha murine IgG SJK-287-38 [Tanaka, S., Hu, S.-Z., Wang, T. S.-F. & Korn, D. (1982) J. Biol. Chem. 257, 8386-8390] neutralized DNA polymerase alpha activity from rat embryonic fibroblasts infected with a temperature-sensitive transformation mutant of Rous sarcoma virus (tsLA24). After centrifugation of a crude cytosol fraction from log-phase cells in a 5-20% linear sucrose gradient, polypeptides of Mr approximately equal to 185,000 and 220,000 were immunoprecipitated only from gradient fractions containing DNA polymerase alpha activity. When similar cultures were incubated in medium containing [32P]orthophosphate, it was found that the Mr 220,000 protein was phosphorylated but that the other peptides specific for polymerase alpha activity did not contain detectable amounts of phosphate. Phospho amino acid analysis of the high molecular weight immunoprecipitable proteins indicated that the labeled amino acid was phosphoserine. Incubation of 2.5 units of crude DNA polymerase alpha with 4 units of agarose-immobilized alkaline phosphatase resulted in a nearly complete inhibition of DNA polymerase alpha activity. Subsequent incubation of this preparation with 5 or 50 microM ATP, but not the nonhydrolyzable analog adenosine 5'-[gamma-thio]triphosphate, restored the in vitro DNA polymerizing activity. These results demonstrate that a high molecular weight DNA polymerase alpha (Mr approximately equal to 220,000) is phosphorylated in cultured cells and that this protein is a substrate for a serine kinase rather than the tyrosine-specific protein kinase of Rous sarcoma virus. The results suggest that phosphorylation/dephosphorylation reactions modulate the activity of this polymerase.

Alkaline Phosphatase↗

PubMed1986

Post-translational modification of the protein-synthesis initiation factor eIF-4D by spermidine in rat hepatoma cells.

The rates of synthesis and turnover of the rare amino acid hypusine [N6-(4-amino-2-hydroxybutyl)-2,6-diaminohexanoic acid] in protein were studied in relationship to polyamine metabolism and growth rates in rat hepatoma tissue-culture (HTC) cells. Hypusine is selectively formed in the eukaryotic translation initiation factor eIF-4D, by a post-translational mechanism involving spermidine [Cooper, Park, Folk, Safer & Braverman (1983) Proc. Natl. Acad. Sci. U.S.A. 80, 1854-1857]. The half-life of the hypusine-containing protein was longer than 24 h. In cells whose intracellular spermidine pools had been initially depleted, by using DL-alpha-difluoromethylornithine (DFMO), maximum synthesis rates of hypusine in protein were 5-10 times higher, on restoration of endogenous spermidine contents by exogenous addition, than those observed in untreated exponential-phase cultures. In cells pretreated with DFMO, the rate of hypusine synthesis was constant for up to 1 h after the addition of 5 microM-spermidine, whereas endogenous spermidine contents varied from less than 1 to more than 10 nmol/mg of protein. However, the overall amount of hypusine formed, during the first 1 h after the addition of various concentrations of spermidine (0.05-10 microM) to the culture medium, was markedly dependent on the final endogenous spermidine content achieved at the end of the 1 h measurement interval. Early in exponential-phase growth, protein-bound hypusine was synthesized at a rate of 1-2 pmol/h per mg of protein. This rate decreased to less than 0.5 pmol/h per mg of protein when cell growth rates decreased as cultures reached high cell densities. Analysis of the polyamine substrate specificity for hypusine formation showed that N1-acetylspermidine did not compete with spermidine in the reaction, nor did N1-(buta-2,3-dienyl)-N2-methylbutane-1,4-diamine, and irreversible inhibitor of polyamine oxidase, block the reaction. On the basis of comparative radiolabelling experiments, spermine was either a poor substrate, or not a substrate, for hypusine formation. These results confirm that spermidine is the likely precursor of the aminohydroxybutyl moiety of hypusine, and show that overall hypusine formation, but not necessarily the synthesis rate, is dependent on the endogenous spermidine concentration, especially under conditions where spermidine concentrations are initially low, as is the case after DFMO treatment, and then increase.

Animals↗

PubMed1986

Polyamine-mediated turnover of ornithine decarboxylase in Chinese-hamster ovary cells.

We have used Chinese-hamster ovary (CHO) cells maintained in a chemically defined medium to study the regulation of ornithine decarboxylase (ODC) by polyamines. Cells maintained in the defined medium had no detectable putrescine, and approx. 1-3 units of ODC activity/10(6) cells, where 1 unit corresponds to 1 nmol of substrate decarboxylated in 30 min. The defined medium is ornithine-deficient, thus limiting the exogenous substrate for ODC, and subsequently decreasing intracellular polyamine accumulation. Restoration of intracellular putrescine and increased formation of spermidine by addition of exogenous ornithine or putrescine led to a marked decrease in ODC activity, which was paralleled by a decrease in a alpha-DL-difluoromethyl[3,4-3H]ornithine (DFMO)-binding protein of Mr approx. 53,000, which is precipitable with anti-ODC antibody. Calculation of DFMO binding per unit of activity showed no change in the specific activity of the enzyme. We identified [35S]methionine-labelled peptides corresponding to ODC by immunoprecipitation of radiolabeled whole cell proteins. Only one protein was precipitated, of Mr approx. 53 000, which co-migrated with the DFMO-binding protein. Immunoprecipitation of radiolabelled proteins from cells incubated in the presence of exogenous ornithine indicated that the observed activity decrease was not due to an inhibition of ODC protein synthesis. Analysis of immunoprecipitable ODC protein from cells that had been pulse-labelled with [35S]methionine, and then treated for 5 h with 100 microM-ornithine, -putrescine or -spermidine, revealed a distinct disappearance of labelled ODC protein after restoration of intracellular polyamine pools. No detectable turnover of ODC was observed in the absence of exogenous polyamine treatment. These data support the hypothesis that ODC protein, and subsequent activity, is regulated by intracellular polyamine content through mechanisms that influence turnover of the enzyme.

Animals↗

PubMed1986

Restoration of the polyamine contents in rat hepatoma tissue-culture cells after inhibition of polyamine biosynthesis. Relationship with cell proliferation.

The restoration of the polyamine content in polyamine-deficient rat hepatoma tissue-culture (HTC) cells, after short duration of incubation in the presence of DL-alpha-difluoromethylornithine (F2MeOrn) or of (2R,5R)-6-heptyne-2,5-diamine [(2R,5R)MAP], two potent irreversible inhibitors of L-ornithine decarboxylase, has been studied in relation to cell proliferation. Both L-ornithine decarboxylase inhibitors deplete the cells of their putrescine and spermidine contents within one day after their addition to the culture medium. Thereafter, intracellular putrescine and spermidine concentrations are restored to near control values within one day when (2R,5R)MAP is removed from the medium, but remain at low levels at least for one day or longer after removal of F2MeOrn. In both conditions, spermine concentration stays at normal or above normal values and cell growth rates are unaffected. Thus, the total intracellular spermine content per culture parallels, in fact, the increase in cell number. The continuous presence of the drugs maintains the depletion of putrescine and spermidine and decreases the total intracellular spermine content of the culture to the same order of magnitude as it reduces the increase in cell numbers. These findings suggest that the antiproliferative effects of these L-ornithine decarboxylase inhibitors in HTC cells is primarily associated with the limitation of spermine biosynthesis rather than to the almost complete reduction of the putrescine and spermidine pools.

Alkynes↗

PubMed1986

Altered polyamine metabolism in Chinese hamster cells growing in a defined medium.

Chinese hamster cells (line CHO) maintained in McCoy's 5A medium (modified) supplemented with insulin (10 micrograms/ml), transferrin (5 micrograms/ml), and ferrous sulfate (1.1 microgram/ml) proliferate at rates similar to cultures growing in the McCoy's medium supplemented with 10% fetal bovine serum. Colony-forming ability is similar in cultures supplemented with either serum or the combination of growth factors. By 6 hours after replacement of serum with growth factors, ornithine decarboxylase (ODCase) activity increases, reaching a maximum value by 24 hours after serum replacement. This maximum is cell density dependent and can exceed a 30-fold increase over enzyme activity in cultures supplemented with serum. The increased enzyme activity is due to a decrease in the turnover rate of the enzyme, based on protein synthesis inhibition studies, and an accumulation of active enzyme molecules rather than an activation of existing molecules, since the catalytic activity of ODCase, determined using the radiolabeled form of alpha-difluoromethylornithine (an enzyme-activated, irreversible inhibitor of ODCase) in concert with supplements. Intracellular putrescine and spermidine levels are substantially decreased when cultures are maintained in medium supplemented with insulin, transferrin, and ferrous sulfate, rather than serum, which is the sole source of exogenous ornithine. Titration of cultures growing in the defined medium with ornithine leads to a decrease in ODCase activity and an increase in intracellular putrescine and spermidine levels. Putrescine- and spermidine-dependent S-adenosyl-L-methionine decarboxylase activities are similar in cultures maintained in either medium. These data demonstrate that some, but not all, aspects of polyamine biosynthesis are affected by the availability of ornithine, the first substrate in the pathway.

Adenosylmethionine Decarboxylase↗

PubMed1986

Analysis of the length of S-phase required to show sister chromatid differential staining.

In vitro studies of BrdU-dependent sister chromatid differential staining typically employ two cycles of BrdU incorporation. Experiments are described which determined the actual fraction of both S-phases that the rat embryonic fibroblasts (Rat-1) cells had to traverse in order to show distinctive differential staining. Following synchronization of cells by a combination of serum deprivation and hydroxyurea blockage, sister chromatid differential staining, labelling index, mitotic index, and per cent DNA replication are determined. Results indicate that only approximately 50% of the first S-phase is necessary in order to show distinctive differential staining. The importance of this finding to studies of cellular proliferation using BrdU incorporation is discussed.

Animals↗

PubMed1986

Effects of cycloheximide on thermotolerance expression, heat shock protein synthesis, and heat shock protein mRNA accumulation in rat fibroblasts.

A single hyperthermic exposure can render cells transiently resistant to subsequent high temperature stresses. Treatment of rat embryonic fibroblasts with cycloheximide for 6 h after a 20-min interval at 45 degrees C inhibits protein synthesis, including heat shock protein (hsp) synthesis, and results in an accumulation of hsp 70 mRNA, but has no effect on subsequent survival responses to 45 degrees C hyperthermia. hsp 70 mRNA levels decreased within 1 h after removal of cycloheximide but then appeared to stabilize during the next 2 h (3 h after drug removal and 9 h after heat shock). hsp 70 mRNA accumulation could be further increased by a second heat shock at 45 degrees C for 20 min 6 h after the first hyperthermic exposure in cycloheximide-treated cells. Both normal protein and hsp synthesis appeared increased during the 6-h interval after hyperthermia in cultures which received two exposures to 45 degrees C for 20 min compared with those which received only one treatment. No increased hsp synthesis was observed in cultures treated with cycloheximide, even though hsp 70 mRNA levels appeared elevated. These data indicate that, although heat shock induces the accumulation of hsp 70 mRNA in both normal and thermotolerant cells, neither general protein synthesis nor hsp synthesis is required during the interval between two hyperthermic stresses for Rat-1 cells to express either thermotolerance (survival resistance) or resistance to heat shock-induced inhibition of protein synthesis.

Animals↗

PubMed1986

Modulation of etoposide cytotoxicity and DNA strand scission in L1210 and 8226 cells by polyamines.

The anticancer agent etoposide (VP-16) produces DNA strand scission in intact tumor cells or isolated nuclei. This activity may be mediated by topoisomerase II, an enzyme capable of producing double strand breaks in mammalian cells. Two established tumor cell lines were examined to see whether polyamines, which alter DNA conformation and topoisomerase II activities, affected the cytotoxicity, strand scission, and antitumor efficacy of VP-16. L1210 murine leukemia and 8226 human myeloma cells were treated with alpha-difluoromethylornithine (DFMO) to reduce intracellular polyamine levels via inhibition of ornithine decarboxylase. The polyamines putrescine and spermidine were markedly reduced by a 48-h incubation with 50 microM DFMO. This DFMO concentration did not inhibit colony formation in either cell line, but did reduce the growth rate of both cultures. In contrast, VP-16 produced a dose-dependent inhibition of colony formation. This was especially marked in the 8226 cell line. This correlated with DNA single strand breaks (SSBs) detected by the alkaline elution technique. When cells previously treated with DFMO were exposed to VP-16, a synergistic inhibition of colony formation (determined by isobologram analysis) was observed. However, VP-16-induced SSBs were only marginally increased by the DFMO pretreatment. When putrescine was combined concurrently with VP-16, both the in vitro cytotoxic effects and the number of DNA SSBs in L1210 cells were significantly reduced. These results demonstrate that putrescine inhibits VP-16-induced SSBs and commensurate cytotoxic effects, while DFMO, which depletes intracellular putrescine and partially reduces intracellular spermidine, acts to produce synergistic cytotoxic effects when combined with VP-16.

Animals↗

PubMed1985

Activation of ornithine decarboxylase in monolayer cells treated with trypsin.

When monolayer Chinese hamster cells are treated with trypsin for short periods of time, ornithine decarboxylase (ODCase) activity increases two- to fourfold. This increase can be blocked by aprotinin, a protease inhibitor, and is not observed when cultures are dislodged from substrate mechanically prior to contact with exogenous trypsin. The trypsin-induced increase in ornithine decarboxylase activity is not due to degradation of enzyme or inhibitor molecules or to new enzyme synthesis. Immunoprecipitable protein, radiolabeled with [3H]alpha-difluoromethylornithine in vitro, is the same molecular weight in cells harvested with or without trypsin. Protein-bound levels of this specific enzyme-activated irreversible inhibitor of ornithine decarboxylase are unchanged by trypsin treatments that increase enzyme activity. Trypsin treatment of rat embryonic fibroblasts, transformed by a temperature-sensitive mutant of Rous sarcoma virus, increases ODCase activity in cells growing at the nonpermissive, but not at the permissive, temperature for the transformed phenotype. These results suggest that ornithine decarboxylase can be activated by exogenous trypsin treatment in a manner that is dependent on cell adhesion properties, which are modified in transformed cells.

Animals↗

PubMed1984

Floppy eyelid with hyperglycinemia.

A 31-year-old man with spastic paraparesis (diagnosed when he was 10 years old) and hyperglycinemia (diagnosed when he was 19 years old) had an intermittently swollen right eye and blurred vision. His right upper eyelid was S-shaped and edematous, the lateral canthal tendon was flaccid, and the eyelid everted easily. After the floppy eyelid syndrome was diagnosed, the patient underwent a tarsal strip procedure to shorten and tighten the lax upper eyelid. This relieved his symptoms, which have not recurred in the year since surgery.

Adult↗

PubMed1984

Dissociation of 68,000 Mr heat shock protein synthesis from thermotolerance expression in rat fibroblasts.

Rat embryonic fibroblasts growing exponentially at either 35, 37, or 39 degrees C were exposed to 42 degrees C for times up to 6 hr. Cell survival was unaffected by this heat shock in cultures growing at 39 degrees C but survival was decreased in a temperature dependent manner in cells growing at 37 or 35 degrees C. Exposure to 42 degrees C of cells previously adapted to 35 or 37 degrees C resulted in the induction of heat shock proteins (hsps) with apparent molecular weights of 68,000 (hsp 68), 70,000 (hsp 70), and 89,000 (hsp 89); cells previously adapted to 39 degrees C expressed all hsps except hsp 68. Inasmuch as the synthesis of certain hsps may function to protect cells from thermal damage, these data indicate that hsp 68 may not be required for this adaptation-related thermotolerant survival response. Hsp 68 may only be expressed in cells destined to die.

Acclimatization↗

PubMed1983

Dose-rate dependence of heat radiosensitization.

The dose rate dependence of heat radiosensitization was studied using rat astrocytoma cells in culture and a clinically relevant protocol of heat dose and heat radiation sequence. Cells were treated with a minimally toxic heat dose of 43 degrees C for 30 minutes, after which they were irradiated with varying doses of radiation at dose rates ranging from 0.567 to 300 cGy/min. This heat dose substantially reduced the extrapolation number (n), but had little effect on Do of the radiation survival curve at dose rates of 50 cGy/min or greater. At dose rates less than 10 cGy/min, 43 degrees C for 30 min had little effect on n and only for the lowest dose rate studied (0.567 cGy/min) was there a significant reduction in Do (60%). The thermal enhancement ratio did not vary inversely with radiation dose rate over the dose rate range studied but, instead, was maximal at the two dose rate extremes (0.567 and 300 cGy/min). These data demonstrate that a clinically relevant heat dose enhances very low dose rate, as well as high dose rate, ionizing radiation, but suggest that little benefit is to be gained from using dose rates intermediate between conventional radiotherapeutic high dose rates or dose rates representative of interstitial implants.

Animals↗

PubMed1983

Sensitization to heat by the polyamines and their analogs.

The polyamines putrescine, spermidine, and spermine have been shown to sensitize Chinese hamster ovary (CHO) cells to the cytotoxic effects of elevated temperatures. This sensitization occurs in the order spermine greater than spermidine greater than putrescine. A series of homologs of the diamine putrescine demonstrated little variance in the degree of potentiation until a chain length equivalent to that of spermidine was employed (1,8-diaminooctane). Two compounds bearing structural similarities to spermidine gave rather different results when combined with heat. Methylglyoxal bis(guanylhydrazone) (MGBG), an antiproliferative drug, sensitized cells to heat, while S-2-(3-aminopropylamino)-ethyl phosphoric acid (WR-2721), a radioprotector, had no measureable effect on 43 degrees C-induced cytotoxicity. Together, these results point out the primary importance of two terminal amino groups separated by either carbon, or carbon and nitrogen, atoms in an aliphatic chain in the observed sensitization of heat-induced cytotoxicity by polyamines. These data suggest specific dimensional characteristics of the presumed negatively charged structure(s) with which the polyamines are interacting to elicit this effect.

Amifostine↗

PubMed1983

Polyamines and polyamine biosynthesis in cells exposed to hyperthermia.

The issue of how polyamines act to sensitize cultured cells to the lethal effects of hyperthermia was investigated using Chinese hamster cells which were induced to express thermotolerance. Intracellular levels of these naturally occurring polycations were manipulated in certain situations by treating whole cells with methylglyoxal bis-(guanylhydrazone), an inhibitor of the S-adenosyl-L-methionine decarboxylases. Exogenous spermine as low as 100 microM in the culture media dramatically sensitized cells expressing thermotolerance to the lethal effects of subsequent 42 degrees C exposures. When thermotolerance was differentially induced in cultures exposed to 42.4 degrees C by varying the rate of heating from 37 to 42.4 degrees C, the most resistant cells had the highest levels of intracellular spermidine and spermine. This finding was explainable in part by the observation that the putrescine-dependent S-adenosyl-L-methionine decarboxylase activity was minimally affected in cells expressing the greatest degree of thermotolerance. When this enzyme activity was inhibited by drug, lowered intracellular polyamine levels did not correspond with subsequent survival responses to heat. Interestingly, cultures treated with methylglyoxal bis-(guanylhydrazone) 24 hr previous to heat exposure showed a reduced capacity to express rate of heating-induced thermotolerance. Together, these results demonstrate that the polyamines, especially spermidine and spermine, enhance hyperthermia-induced cell killing by some mechanism involving the plasma membrane. Further, our data suggest that methylglyoxal bis-(guanylhydrazone) can act to affect thermal responses by a mechanism(s) other than modification of intracellular polyamine levels.

Adenosylmethionine Decarboxylase↗

PubMed1982

Clinical hyperthermia: results of a phase I trial employing hyperthermia alone or in combination with external beam or interstitial radiotherapy.

Forty-three patients with advanced, locally accessible neoplasms were treated in a Phase I clinical trial employing hyperthermia alone or hyperthermia combined with either high-dose-rate external beam or low-dose-rate interstitial radiotherapy (interstitial thermoradiography). All patients had failed previous conventional therapeutic attempts, including various combinations of surgery, chemotherapy and radiation therapy. Many had received tolerance or near tolerance levels of prior radiation that restricted dose prescriptions in this trial to subcurative values. A number of tumors with different histologies were treated, including squamous cell carcinoma (14), adenocarcinoma (14), melanoma (8), malignant fibrous histiocytoma (2), and sarcoma (5). The response evaluation criteria used included no response (NR--less than 50% decrease in tumor volume), partial response (PR--50% less than or equal to tumor volume reduction less than 100%) and complete response (CR--complete tumor disappearance). For all tumor types, hyperthermia therapy alone resulted in a total response rate of 45% (27% PR, 18% CR). Hyperthermia combined with high-dose-rate external beam radiotherapy yielded a total response rate of 80% (53% PR, 27% CR). Seventeen patients treated with interstitial thermoradiography displayed a 100% total response rate (29% PR, 71% CR). By tumor histologies for all treatment groups, total response rates have ranged from 50% to 79% for all types except melanoma, which has shown a 100% (8/8) response rate to date. Response durations have varied from one to 24 months. Twelve of the 43 patients remain alive; three have no evidence of disease (NED) while nine have either stable local disease or are NED in the treated volumes but have metastatic disease. Complications have been minimal and have included one third-degree burn and three second-degree burns from fringing RF fields, one vaginal-rectal fistula, a superficial focal soft tissue necrosis, and some minor blistering. The results of this Phase I trial demonstrate that hyperthermia alone or combined with radiation can be safely applied in the treatment of malignant disease. Most importantly, the data suggest that hyperthermia, especially when combined with interstitial thermoradiography, can yield remarkable results in the eradication of local cancers.

Adenocarcinoma↗

PubMed1982

Delayed sensitization to heat by inhibitors of polyamine-biosynthetic enzymes.

Exposure of Chinese hamster ovary cells to the enzyme inhibitors methylglyoxal bis(guanylhydrazone and alpha-difluoromethylornithine (DFMO) results in increased sensitivity to hyperthermia. While methylglyoxal bis(guanylhydrazone) demonstrates pronounced cytotoxicity at moderate extracellular concentrations, DFMO is tolerated well by this cell line at concentrations of up to 10 mM, as assayed by clonogenic survival after treatments at 37 degrees. An 8-hr preincubation at 37 degrees with either drug elicits increasing sensitivity to 43 degrees hyperthermia treatments with time after removal of the drug. In contrast to results obtained by heating in the presence of the drugs during the 8-hr exposure, DFMO acts as the more effective sensitizing agent for this delayed effect on progeny of DFMO-treated populations. This phenomenon seems to result from depletion of intracellular putrescine, because the effect can be at least partially recovered by providing the cells with an exogenous source of this diamine. The potential for in vivo heat sensitization by the non-toxic agent DFMO has yet to be investigated but may have intriguing clinical possibilities.

Animals↗