Polyamine-DNA Interactions: Possible Site of New Cancer Chemotherapeutic Intervention

The effects of polyamines on the structure of nucleic acids in cell-free systems and in cell culture systems are reviewed. Evidence suggests that polyamine depletion inhibits cell growth and may cause conformational changes in DNA. These effects may be exploited to cause changes in the action of drugs and may be used to advantage in combination treatment protocols. A discussion of theoretical models of the interactions, physicochemical evidence for conformational changes, and the effects of anticancer drugs in cells depleted of polyamines is presented.

Antizyme and antizyme inhibitor activities influence cellular responses to polyamine analogs

Close structural analogs of spermidine and spermine, polyamine mimetics, are potential chemotheraputic agents as they depress cellular polyamines required for tumor growth. Specific mimetic analogs stimulate synthesis of the regulatory protein antizyme (AZ), which not only inactivates the initial enzyme in polyamine biosynthesis but also inhibits cellular uptake of polyamines. The role of AZ induction in influencing cellular uptake of representative analogs was investigated using three analogs produced by Cellgate Inc., CGC-11047, CGC-11102, and CGC-11144, which exhibit markedly distinct AZ-inducing potential. An inverse correlation was noted between the AZ-inducing activity of a compound and the steady-state levels accumulated in cells. As some tumor cells over express AZI as a means of enhancing the polyamines required for aggressive growth, analog sensitivity was examined in transgenic CHO cells expressing exogenous antizyme inhibitor protein (AZI). Although AZI over expression increased cell sensitivity to analogs, the degree of this affect varied with the analog used.

Molecular Basis of Inward Rectification: Structural Features of the Blocker Defined by Extended Polyamine Analogs

Polyamines cause inward rectification of Kir K(+) channels by blocking deep within the channel pore. We investigated structural constraints of polyamine block of strongly rectifying mutant K(ATP) channels (Kir6.2[L164C,N160D,C166S] + SUR1). We studied three groups of polyamine analogs: 1) conformationally restricted linear tetra-amines with a cycloalkyl or alkene group between the second and third amines (CGC-11047, CGC-11093, CGC-11099, and CGC-11098), 2) conformationally restricted linear deca-amines with a cycloalkyl or alkene group between the fifth and sixth amines (CGC-11150, CGC-11179, and CGC-11241), and 3) cyclic tetra-amines (CGC-11174, CGC-11197, CGC-11199, and CGC-11254). All linear analogs cause a voltage-dependent block similar to that of spermine, but slightly weaker (at 1 microM, V(1/2) for spermine block = -10 +/- 1 mV, Z = 2.9 +/- 0.1, n = 19; V(1/2) for analogs varies from polyamine -7 to +10 mV, Z = 2.6-3.9). These data indicate tolerance for conformational restriction and an upper limit to the voltage dependence of the blocking process. There was no voltage-dependent block by the cyclic compounds; instead, they induce irreversible rundown of the current. Structural models of Kir channels suggest that a narrow entry at the top of the cytoplasmic pore may exclude cyclic analogs from the inner cavity, thereby explaining the structure-activity relationship that we observe.

cis-Unsaturated analogues of 3,8,13,18,23-pentaazapentacosane (BE-4-4-4-4): synthesis and growth inhibitory effects on human prostate cancer cell lines

From the results of our previous physicochemical studies of polyamine-nucleic acid interactions, we concluded that polyamine analogues in cisoidal conformation are capable of wrapping around the major groove of the double helix, of displacing natural polyamines from their nucleic acid binding sites, and of inhibiting cell division. On the basis of this hypothesis, nine unsaturated pentamines, formally derived from the cytotoxic pentamine 3,8,13,18,23-pentaazapentacosane (BE-4-4-4-4), were prepared in an attempt to increase antineoplastic activity. Cis-double bonds were introduced in all possible sites in the saturated pentaazapentacosane structure of BE-4-4-4-4 to yield two pentacosenes, four pentacosadienes, two pentacosatrienes, and one pentacosatetraene. Cis-double bonds should also provide good targets for mixed-function oxidases that might eliminate the accumulation of unsaturated pentamines in serum, thereby reducing systemic toxicity in animals. We determined the ability of these new pentamines to inhibit growth in four cultured human prostate cancer cell lines (LnCap, DU145, PC-3, and DuPro) using a MTT assay. LnCap and DU145 cells were very sensitive, PC-3 cells were relatively resistant, and DuPro cells were intermediate in sensitivity to most of these synthetic pentamines. In all cell lines, pentamines that had unsaturation(s) at the end of the chain showed the highest cell growth inhibitory effects. The cellular uptake, effects on cellular polyamine levels, and cytotoxicity of these pentamines on one representative prostate cancer cell line (DuPro) were further examined with a colony-forming efficiency (CFE) assay. The pentamines with unsaturation(s) at the end of the chain were once again the most cytotoxic among both the saturated (BE-4-4-4-4) and unsaturated analogues. Appreciable amounts of all pentamines entered DuPro cells and depleted cellular polyamine pools by day 6 of treatment. For most pentamines, however, cell growth inhibitory and cytotoxic effects could not be directly correlated either with their cellular uptake or with their ability to deplete cellular polyamine pools. The position of the double bonds in the aliphatic backbone seems to be the most important determinant of cytotoxicity. For some pentamines, however, depletion of cellular polyamines may add to their efficacy.

Conformationally restricted analogues of 1N,14N-bisethylhomospermine (BE-4-4-4): synthesis and growth inhibitory effects on human prostate cancer cells

Twelve analogues of 1N,14N-bisethylhomospermine (BE-4-4-4) with restricted conformations were synthesized in the search for cancer chemotherapeutic agents with higher cytotoxic activities and lower systemic toxicities than BE-4-4-4. The central butane segment of BE-4-4-4 was replaced with a 1,2-substituted cyclopropane ring, a 1,2-substituted cyclobutane ring, and a 2-butene residue. In each case, the cis/trans-isomeric pair was synthesized. Cis-monounsaturation(s) was also introduced at the outer butane segment(s) of BE-4-4-4. The two possible cis-dienes and a cis-triene formally derived from the tetraazaeicosane skeleton of BE-4-4-4 were also prepared. Four cultured human prostate cancer cell lines (LnCap, DU145, DuPro, and PC-3) were treated with the new tetramines to examine their effects on cell growth with a MTT assay. One representative cell line (DuPro) was selected to further study the cellular uptake of the novel tetramines, their effects on intracellular polyamine pools, and their cytotoxicity. All tetramines entered the cells, reduced cellular putrescine and spermidine pools while exerting only a small effect on the spermine pool, inhibited cell growth, and killed 2-3 logs of cells after 6 days of treatment at 10 microM. Four new tetramines, the two cyclopropyl isomers, the trans-cyclobutyl isomer, and the (5Z)-tetraazaeicosene, were more cytotoxic than their saturated counterpart (BE-4-4-4). Their cytotoxicity, however, could not be correlated either with their cellular uptake or with their ability to deplete intracellular polyamine pools. We attribute their cytotoxicity to their specific molecular structures. The cytotoxicity was markedly reduced when the central butane segment was deprived of its rotational freedom by replacing it with a double bond. Introduction of a triple bond or a benzene-1,2-dimethyl residue at the central segment of the polyamine chain, led to complete loss of biological activity. The conformationally restricted alicyclic derivatives were not only more cytotoxic than was the freely rotating BE-4-4-4 by several orders of magnitude but also had much lower systemic toxicities than the latter. Thus, we obtained new tetramines with a wider therapeutic window than BE-4-4-4.

[(1)N,(12)N]Bis(Ethyl)-cis-6,7-dehydrospermine: a new drug for treatment and prevention of Cryptosporidium parvum infection of mice deficient in T-cell receptor alpha

Cryptosporidium parvum infection of T-cell receptor alpha (TCR-alpha)-deficient mice results in a persistent infection. In this study, treatment with a polyamine analogue (SL-11047) prevented C. parvum infection in suckling TCR-alpha-deficient mice and cleared an existing infection in older mice. Treatment with putrescine, while capable of preventing infection, did not clear C. parvum from previously infected mice. These findings provide further evidence that polyamine metabolic pathways are targets for new anticryptosporidial chemotherapeutic agents.

Polyamines decrease Ca(2+) sensitivity of tension and increase rates of activation in skinned cardiac myocytes

Owing in part to their interactions with membrane proteins, polyamines (e.g., spermine, spermidine, and putrescine) have been identified as potential modulators of membrane excitability and Ca(2+) homeostasis in cardiac myocytes. To investigate whether polyamines also affect cardiac myofilament proteins, we assessed the effects of polyamines on contractility using rat myocytes and trabeculae that had been permeabilized with Triton X-100. Spermine, spermidine, and putrescine reversibly increased the [Ca(2+)] required for half-maximal tension (i.e., right-shifted tension pCa curves), with the following order of efficacy: spermine (+4) > spermidine (+3) > putrescine (+2). However, synthetic analogs that differed from spermine in charge distribution were not as effective as spermine in altering isometric tension. None of the polyamines had a significant effect on maximal tension, except at high concentrations. After flash photolysis of DM-Nitrophen (a caged Ca(2+) chelator), spermine accelerated the rate of tension development at low and intermediate but not high [Ca(2+)]. These results indicate that polyamines, especially spermine, interact with myofilament proteins to reduce apparent Ca(2+) binding affinity and speed cross-bridge cycling kinetics at submaximal [Ca(2+)].

Conformationally restricted analogues of 1N,12N-bisethylspermine: synthesis and growth inhibitory effects on human tumor cell lines

Eight analogues of 1N,12N-bisethylspermine (BES) with restricted conformations were synthesized in the search for new spermine mimetics with cytotoxic activities. By replacing the central butane segment of BES with a 1,2-disubstituted cyclopropane ring, a pair of cis/trans-isomers was obtained that introduced a spatial constraint in the otherwise freely mobile butane chain. An analogous pair of isomers was obtained when the butane segment was replaced with a 1, 2-disubstituted cyclobutane ring or with a 2-butene residue. The six new BES analogues thus obtained (three pairs of cis/trans-isomers) were growth inhibitory at low-micromolar concentrations against four human tumor cell lines (A549, HT-29, U251MG, and DU145) but were less growth inhibitory against two other human tumor cell lines (PC-3 and MCF7). 1N,12N-Bisethylspermyne, where the central butane segment of BES was replaced by the rigid 2-butyne segment, was devoid of growth inhibitory activity against five of the six human cell lines studied (DU145 being the only exception), a clear indication of the importance of conformational mobility at the 4N, 9N-butane segment of BES for its biological activity. When the butane segment was replaced by a benzene-1,2-dimethyl residue, the resulting BES analogue was devoid of growth inhibitory activity despite its cisoid conformation. The cytotoxicity of the analogues does not seem to be directly related to their uptake by the cells or to their effects on cellular polyamine levels. BES analogues with restricted conformations but which contained the equivalent of a two-carbon unit, rather than the natural four-carbon unit, at the central segment, such as 1,2-diaminocyclopropyl or 1, 2-diaminocyclobutyl derivatives, were devoid of growth inhibitory effects at the concentrations studied. The development of conformationally restricted polyamine analogues appears to show promise in the further quest for polyamine-related therapeutic agents with specificity of action.

Effects of 1,2-naphthoquinones on human tumor cell growth and lack of cross-resistance with other anticancer agents

The sensitivity of human tumor and rat prostate tumor cells to a series of naphthoquinones, including tricyclic compounds of the beta-lapachone and dunnione families as well as 4-alkoxy-1,2-naphthoquinones, was evaluated. To better understand the mechanism of cytotoxicity of 1,2-naphthoquinones, the roles of various resistance mechanisms including P-glycoprotein, multidrug resistant associated protein, glutathione (GSH) and related enzymes, altered topoisomerase activity, and overexpression of genes that control apoptosis (bcl-2 and bc-xL) were studied. MCF7 cells were most sensitive to the naphthoquinones with IC50 values ranging from 1.1 to 10.8 microM, as compared to 2.5 to >32 microM for HT29 human colon, A549 human lung, CEM leukemia and AT3.1 rat prostate cancer cells. MCF7 ADR cells, selected for resistance to adriamycin (ADR), displayed cross-resistance to the tricyclic 1,2-naphthoquinones. Drug efflux via a P-glycoprotein mechanism was ruled out as a mechanism of resistance to 1,2-naphthoquinones, since KB-V1 cells expressing high levels of P-glycoprotein and the KB-3.1 parent line were equally sensitive to these compounds. Any resistance of the tricyclic naphthoquinones noted in ADR-resistant cells appeared to relate to the GSH redox cycle and could be circumvented by exposure to buthionine sulfoximine or by changing the structure from a tricyclic derivative to a 4-alkoxy-1,2-naphthoquinone. The 1,2-naphthoquinones were found to be cytotoxic against CEM/VM-1 and CEM/M70-B1 cells that were selected for resistance to teniposide or merbarone, respectively. In addition, cells overexpressing bcl-2 or bcl-xL proteins were as sensitive to 1,2-naphthoquinones as were control cells. Because of their effectiveness in drug-resistant cells, these agents appear to hold promise as effective chemotherapeutic agents.

Reaction of beta-lapachone and related naphthoquinones with 2-mercaptoethanol: a biomimetic model of topoisomerase II poisoning by quinones

1,2-Naphthoquinones, such as beta-lapachone, 4-alkoxy-1,2-naphthoquinones, and tetrahydrofuran-1,2-naphthoquinones, react rapidly with 2-mercaptoethanol in benzene to give 1,4-, 1,2-, 1,3- and 1,6-Michael-type adducts that are formed by the addition of the thiol group to the quinone ring. Menadione (2-methyl-1,4-naphthoquinone) reacts with the thiol reagent very slowly under the same reaction conditions. Although the formation of the adducts can be followed by 1H-NMR, attempts to isolate the adducts failed due to their retroconversion to the starting products. On addition of a Lewis acid, however, the adducts undergo cyclization reactions that give stable derivatives that can be isolated and characterized. Determination of the structures of the derivatives allowed for the identification of the adducts from which they originated. Thus, beta-lapachone and 2,3-dinordunnione underwent 1,4- and 1,2-Michael type additions to the quinone ring, while 4-pentyloxy-1,2-naphthoquinone underwent two simultaneous Michael additions to the quinone ring of the naphthoquinone. Menadione underwent a single 1,3-addition. The alkylation rates of the thiol group of 2-mercaptoethanol by the naphthoquinones parallel the naphthoquinones efficiencies in inducing DNA cleavage through DNA-bound topoisomerase II. These results support our hypothesis that the cytotoxic effect of the naphthoquinones derive, at least in part, from their alkylation of exposed thiol residues on the topoisomerase II-DNA complex.

Effects of polyamine analogues on prostatic adenocarcinoma cells in vitro and in vivo

PURPOSE

The overall purpose of this study was to determine the potential usefulness of 1,19-di-(ethylamino)-5,10,15-triazononadecane (BE-4-4-4-4) in the treatment of prostate cancer using in vitro and in vivo models. More specifically the objectives were: (1) to determine the in vitro and in vivo sensitivity of human and rat prostate cancer cells to two polyamine analogues N1,N11-di(ethyl)norspermine (DENSPM) and BE-4-4-4-4; (2) to determine whether the mechanism of cell kill occurred through an apoptotic pathway; and (3) to determine the toxicity associated with therapeutic doses of BE-4-4-4-4 using an animal model.

METHODS

In order to determine the ability of these drugs to cause in vitro cytotoxicity, colony-forming assays were performed utilizing the well-characterized Dunning rat prostate cancer cell lines AT3.1, AT6.1 and AT6.3, and the androgen-insensitive human prostate cancer cell lines DU145, DuPro-1 and TSU-Pr1. Apoptotic cell death was determined using DNA laddering and DAPI staining of nuclei. The antitumor activity of BE-4-4-4-4 was evaluated by treatment of DuPro- and PC-3 xenograft tumors in nude mice.

RESULTS

BE-4-4-4-4 was shown to be approximately 4 to 86 times more cytotoxic in clonogenic assays than DENSPM in both rat and human prostate carcinoma cell lines. Cells treated with cytotoxic doses of DENSPM or BE-4-4-4-4 showed no signs of apoptosis using either DNA laddering or DAPI staining of nuclei. There was a significant inhibition of DuPro-1 tumors for animals treated with BE-4-4-4-4 compared with control animals. Equitoxic doses of BE-4-4-4-4 resulted in greater tumor inhibition than DENSPM, although the difference was not significant. After treatment with therapeutic doses of BE-4-4-4-4, histopathologic evaluation indicated minimal to mild necrosis and inflammation in the kidneys on days 15 and 22 following treatment. On day 35, there was no necrosis or regeneration present in the kidney, indicating that the toxicity was transient and that regeneration of epithelial cells was complete with apparent return to normalcy.

CONCLUSIONS

These initial studies demonstrate that BE-4-4-4-4 is cytotoxic against rat and human prostate cancer cells in culture and effective against DuPro-1 xenografts in nude mice. Polyamine analogues, such as DENSPM or BE-4-4-4-4, should be considered for clinical use in the treatment of prostate adenocarcinomas.

Somatic mutational mechanisms involved in intestinal tumor formation in Min mice

We have demonstrated previously that intestinal tumor formation in B6 Min/+ mice is always accompanied by loss of the wild-type adenomatous polyoposis coli (Apc) allele and that intestinal tumor multiplicity in B6 Min/+ mice can be significantly increased by treatment with a single dose of N-ethyl-N-nitrosourea (ENU). Here, we show that some tumors from ENU-treated Min/+ mice can form without complete elimination of Apc+. At least 25% of these tumors acquired somatic Apc truncation mutations. Interestingly, some ENU-induced tumors demonstrated loss of the Apc+ allelic marker examined by the quantitative PCR assay used here. Using two methods of mutation detection, we identified no Apc mutations in at least 12% of the tumors from ENU-treated B6 Min/+ mice. Finally, no H- or K-ras-activating mutations were detected in intestinal tumors from either untreated or ENU-treated Min/+ mice. The majority of somatic human APC mutations in intestinal tumors lead to APC truncation. Our results demonstrate that somatic Apc truncation mutations also frequently occur in ENU-induced intestinal tumors in Min mice.

Induction of DNA topoisomerase II-mediated DNA cleavage by beta-lapachone and related naphthoquinones

Recent studies have suggested that 3,4-dihydro-2,2-dimethyl-2H-naphtho[1,2-b]pyran-5,6-dione (beta-lapachone) inhibits DNA topoisomerase I by a mechanism distinct from that of camptothecin. To study the mechanism of action of beta-lapachone, a series of beta-lapachone and related naphthoquinones were synthesized, and their activity against drug-sensitive and -resistant cell lines and purified human DNA topoisomerases as evaluated. Consistent with the previous report, beta-lapachone does not induce topoisomerase I-mediated DNA breaks. However, beta-lapachone and related naphthoquinones, like menadione, induce protein-linked DNA breaks in the presence of purified human DNA topoisomerase IIalpha. Poisoning of topoisomerase IIalpha by beta-lapachone and related naphthoquinones is independent of ATP and involves the formation of reversible cleavable complexes. The structural similarity between menadione, a para-quinone, and beta-lapachone, an ortho-quinone, together with their similar activity in poisoning topoisomerase IIalpha, suggests a common mechanism of action involving chemical reactivity of these quinones. Indeed, both quinones form adducts with mercaptoethanol, and beta-lapachone is 10-fold more reactive. There is an apparent correlation between the rates of the adduct formation with thiols and of the topoisomerase II-poisoning activity of the aforementioned quinones. In preliminary studies, beta-lapachone and related naphthoquinones are found to be cytotoxic against a panel of drug-sensitive and drug-resistant tumor cell lines, including MDR1-overexpressing cell lines, camptothecin-resistant cell lines, and the atypical multidrug-resistant CEM/V-1 cell line.

Capturing the promise of science in medical schools

To gain a better understanding of the effects on medical schools of transformations in medical practice, science, and public expectations, the Association of American Medical Colleges (AAMC) constituted the Advisory Panel on the Mission and Organization of Medical Schools (APMOMS) in 1994. APMOMS created six working groups to address the issues deemed by panel members to be of highest priority. This article is a report of the findings of the Working Group on Capturing the Promise of Medical Research, which addressed questions concerning the direction of research and the integration of scientific developments in medical education and practice. The working group explored a broad panorama of issues, including those related to sustaining the accomplishments, momentum, and progress of medical research. A dominant theme emerged: the central importance of an environment of discovery to the core missions of medical schools. The present article consists of the group's comments and recommendations on the main topic-the promise of biomedical research in relation to medical education-and their comments and recommendations on five other topics that have important relationships to the main topic and to the group's central charge. These are ethics; academia-industry relations; the administrative structure of medical schools; university-medical school relations; and research funding.

Preserving medical schools' academic mission in a competitive marketplace

To gain a better understanding of the effects on medical schools of transformations in medical practice, science, and public expectations, the AAMC in 1994 formed the Advisory Panel on the Mission and Organization of Medical Schools and appointed six working groups to address relevant issues. This article is a report of the findings of the Working Group on Preserving Medical Schools' Academic Mission in a Competitive Marketplace, which was charged with exploring how medical schools could acquire and/or preserve an adequate patient base for teaching, research, and income generation in a competitive marketplace. The other groups' reports will appear in future issues of Academic Medicine. To understand the diversity of approaches that schools have taken to achieve this goal and to preserve their missions, the group interviewed representatives of nine medical schools, selected to represent a cross section of U.S. medical schools. The interviews took place on four occasions between June 1995 and March 1996. The information and comments shared by participants helped the working group gain insight into the fundamental issues it had been charged to address, including those of new delivery structures, what value schools offer to delivery structures, how education and research can be incorporated and supported financially, possible new pressures on relationships between medical schools and teaching hospitals, changes in faculty physicians' employment relationships and terms, and the role of the medical school in graduate medical education. In collecting and analyzing the data, the working group focused on the distinction between protecting an institution's existing enterprise and preserving an institution's core mission. This article gives a detailed overview of the information and comments each school presented, organized under the appropriate question. The working group's conclusions and commentaries on the findings follow. An appendix presents more detailed summaries of the schools' presentations, organised as case studies. The picture that emerges is complex. The working group concluded that medical schools will take a variety of approaches to define and preserve their missions. Most, but not all, medical schools will be able to secure the patient bases necessary to fulfill their missions even in a competitive marketplace. However, the nature of many of the schools is likely to change, and it is not clear whether the core missions of education and research will continue at their present levels at all schools.

The ability of polyamine analogues to induce Z-DNA structure in synthetic polynucleotides in vitro inversely correlates with their effects on cytotoxicity of cis-diaminedichloroplatinum (II) (CDDP) in human brain tumor cell lines

We studied the effects of 72 h pretreatment with five polyamine analogues on the cytotoxicity of cis-diaminedichloroplatinum (II) (CDDP) in U-251 MG and SF-188 human brain tumor cells. A colony forming efficiency assay showed that the pretreatment with clinically important analogues 1,11-bis(ethylamino)-4, 8-diazaundecane (BE-3-3-3), 1,14-bis(ethylamino)-5,10-diazatetradecane (BE-4-4-4), and 1,l9-bis(ethylamino)-5,10,15-triazanonadecane (BE-4-4-4-4) increased the cytotoxicity of CDDP by 1.3 to 2.3-fold; 1,19-diamino-5,10, 15-triazanonadecane (4-4-4-4) did not affect CDDP cytotoxicity, and 1,11-diamino-4,8-diazaundecane (3-3-3) protected cells from the cytotoxic effects of CDDP. An alkaline elution assay detected a small increase in DNA interstrand crosslinks accompanying the enhancement of CDDP cytotoxicity only in cells pretreated with BE-3-3-3. This study is the first to show that the Z-DNA inducing abilities of the polyamine analogues in synthetic polynucleotides in vitro correlates inversely with their effects on CDDP cytotoxicity in human tumor cells in culture.

A new model for disruption of the ornithine decarboxylase gene, SPE1, in Saccharomyces cerevisiae exhibits growth arrest and genetic instability at the MAT locus

Ornithine decarboxylase (ODC) is a rate-determining enzyme of the polyamine-biosynthetic pathway. We sought to produce cells with impaired ODC function in order to study the biological functions of polyamines. Saccharomyces cerevisiae strains were obtained by one-step gene replacement of a 900 bp fragment of the yeast ODC gene (SPE1) with the yeast URA3 gene. Spores derived from SPE1/spe1 cells germinated at reduced efficiency relative to SPE1/SPE1. Sustained growth of spe1 haploid mutants in polyamine-free medium led to intracellular polyamine depletion, reduction in budding index, G1 arrest and cessation of growth, and cells that were large and misshapen. All of these effects were completely reversed by adding polyamines to the medium, even after 5 days of polyamine starvation. A diploid yeast strain bearing two copies of disrupted spe1 lost heterozygosity at the mating-type locus more often when grown in the absence of polyamines than when grown in their presence, indicating that polyamine deficiency leads to either chromosome loss or to mitotic recombination.

The structure of polyamine analogues determines haemoglobin production and cytotoxicity in murine erythroleukaemia cells

The naturally occurring polyamine spermine induces haemoglobin synthesis in murine erythroleukaemia (MEL) cells. We have studied the ability of various polyamine analogues to inhibit cell growth and induce haemoglobin production. Polyamine analogues with free terminal amino groups were good inducers of haemoglobin production in MEL cells. Haemoglobin levels correlated with the number of positive charges: pentamines (five positive charges) were stronger inducers than tetramines (four positive charges). Compounds ethylated at their terminal amines were poor inducers of haemoglobin production but good inhibitors of MEL cell growth. These results provide evidence that polyamine analogues support specific biological functions of polyamines in MEL cells and suggest relationships between polyamine structure and function.

Spermine induces haemoglobin synthesis in murine erythroleukaemia cells

The naturally occurring polyamine spermine induces haemoglobin synthesis in murine erythroleukaemia (MEL) cells. Haemoglobin production was accompanied by accumulation of cytoplasmic beta-globin mRNA and growth inhibition, but not by cell-cycle block or changes in cell volume. Hexamethylene-bisacetamide (HMBA), a well known differentiating agent, also induces haemoglobin production, but causes a G1 block and decreases cell volume. These findings indicate that HMBA and spermine affect MEL cells differently, even though both induce haemoglobin production.

Slowing proliferation in head and neck tumors: in vitro growth inhibitory effects of the polyamine analog BE-4-4-4-4 in human squamous cell carcinomas

PURPOSE

These preclinical studies were carried out to examine the potential of the antiproliferative polyamine analog 1,19-bis-(ethylamino)-5,10,15-triazanonadecane (BE-4-4-4-4) to serve as a therapy adjuvant to radiation for patients with rapidly dividing tumors of the head and neck (H&N).

METHODS AND MATERIALS

Cytostatic and cytotoxic effects of this polyamine analog were investigated in three squamous cell carcinoma (SCC) cell lines derived from human H&N tumors.

RESULTS

Growth inhibition was achieved in all cell lines within 3-4 days of continuous 10 microM drug exposure, and inhibition of cell cycle proliferation kinetics was confirmed via flow cytometry. Cytotoxicity was pronounced (3-4 log cell kill) in the SCC-38 and SCC-4Y cell lines with continuous 10 microM analog exposure over 5 days, and was minimal in the SCC-13Y cell line. No demonstrable effect of BE-4-4-4-4 on single dose radiation survival was identified in any SCC cell line. Ornithine decarboxylase (ODC) activity was rapidly inhibited (1-2 h) following 10 microM BE-4-4-4-4 exposure in all SCC cell lines (approximately 90%), whereas identical exposure to 10 microM difluoromethylornithine (DFMO) induced animal ODC inhibition (approximately 10%). Dose-dependent depletion of endogenous polyamines (putrescine, spermidine, spermine) was achieved in all SCC cell lines following 1 microM and 10 microM BE-4-4-4-4 exposures. Difluoromethylornithine was significantly less potent than BE-4-4-4-4 in its capacity to deplete endogenous polyamines, with no measureable depletion of spermine pools even with 5 mM x 48 h DFMO exposures.

CONCLUSIONS

These data evaluate cytostatic and cytotoxic properties of the polyamine analog BE-4-4-4-4 in human SCCs, and suggest a role for investigation of such agents as an adjuvant to radiation in the therapeutic approach to rapidly dividing human tumors such as those that occur in the H&N.

Polyamines as targets for therapeutic intervention

Polyamines are ubiquitous cell components essential for normal growth. Compounds interfering with polyamine biosynthesis or function have considerable potential for use as therapeutic agents. Inhibitors of ornithine decarboxylase have been shown to be valuable for the treatment of diseases caused by parasitic protozoa, most notably African sleeping sickness. They may also be useful chemopreventive and antineoplastic agents. Inhibitors of S-adenosylmethionine decarboxylase also have potential as treatments of these diseases. Protocols minimizing uptake of exogenous polyamines via the polyamine-transport system will probably be needed for the full potential of the inhibitors to be realized. Polyamine analogues, notably those with ethyl or benzyl groups on the terminal nitrogen atoms, have potent antiproliferative activity and are promising agents for the treatment of cancer. These analogues are transported by the polyamine-transport system, and their therapeutic effects are less likely to be blocked by the availability of the exogenous polyamines.

Two polyamine analogs (BE-4-4-4 and BE-4-4-4-4) directly affect growth, survival, and cell cycle progression in two human brain tumor cell lines

1,14-Bis-(ethyl)-amino-5,10-diazatetradecane N1,N11-bis(ethyl)norspermine (BE-4-4-4) and 1,19-bis-(ethylamino)-5,10,15 triazanonadecane (BE-4-4-4-4) are two relatively new polyamine analogs synthesized for use as antineoplastic agents. In human brain tumor cell lines U-251 MG and SF-767, both agents inhibited cell growth, were cytotoxic, induced a variable G1/S block, and depleted intracellular polyamines. Since intracellular polyamine depletion did not always correlate with growth inhibition, cell survival, or cell cycle progression, it cannot completely explain the effects of these agents on growth, survival, and cell cycle progression in U-251 MG and SF-767 cells.

Design and testing of novel cytotoxic polyamine analogues

We designed three polyamine analogues, 1,14-diamino-N5-methyl-5,10- diazatetradecane (5me-4-4-4), 1,14-diamino-N5,N5-dimethyl-5,10-diazatetradecane (Q-Amm-4-4-4), and 1,14-bis-(ethylamino)-N5,N5-dimethyl-5,10-diazatetradecane (BE-Q-Amm-4-4-4), on the basis of computer modeling and physical-chemical studies of polyamine-DNA interactions. These analogues differ from natural polyamines and from one another in the charge distribution on their aliphatic backbone. We found that 10 microM 5me-4-4-4 did not inhibit growth and was not cytotoxic to the human brain tumor cell lines SF-767 and SF-126. The same concentrations of Q-Amm-4-4-4 and BE-Q-Amm-4-4-4 inhibited cell growth and killed more than 90% of each cell type on day 7 of the experiment. BE-Q-Amm-4-4-4 was slightly more toxic than Q-Amm-4-4-4 in both cell lines. All three agents either decreased or completely depleted intracellular putrescine and spermidine. Q-Amm-4-4-4 and BE-Q-Amm-4-4-4 each also lowered spermine. The fact that 5me-4-4-4 was nontoxic but that Q-Amm-4-4-4 was cytotoxic and inhibited growth suggests that the charge distribution along the surface of the aliphatic backbone of polyamines is important in determining growth inhibition and cytotoxicity.

Pretreatment with the polyamine analog 1,19-bis-(ethylamino)-5,10,15-triazanonadecane (BE-4-4-4-4) inhibits etoposide cytotoxicity in U-251 MG (NCI) human brain tumor cells

We studied whether pretreatment of U-251 MG human brain tumor cells with the polyamine analog 1,19-bis-(ethylamino)-5,10,15-triazanonadecane (BE-4-4-4-4) affected the cytotoxicity of the topoisomerase II inhibitor etoposide. We found that BE-4-4-4-4 protected cells from the cytotoxic effects of etoposide. Possible mechanisms for this protection may be related to enhanced DNA-nuclear matrix association in analog-treated cells.

Effect of 1,19-bis(ethylamino)-5,10,15-triazanonadecane on human tumor xenografts

The polyamine analogue 1,19-bis(ethylamino)-5,10,15-triazanonadecane (BE-4-4-4-4), 5 mg/kg i.p., was given twice daily on days 0-3 and 7-10 (cycle 1) to nude mice with human malignant gliomas (SF-767 and U-87 MG), lung adenocarcinoma (A549), and colon carcinomas (HCT116 and HT29). A second cycle of drug was given to mice with SF-767 and A549 tumors on days 42-45 and 49-52. The maximum animal weight loss varied between 4 and 12%, which was observed 10-15 days following the initiation of treatment, but no overt toxic reactions were noted. The SF-767 brain tumors were extremely responsive to BE-4-4-4-4 alone (3 of 8 complete regressions after 2 cycles); however, the growth of the U-87 MG brain tumor was only slightly inhibited by BE-4-4-4-4 treatment. There was significant inhibition of tumor growth after treatment with one cycle of BE-4-4-4-4 in animals carrying the A549, HCT116, and HT29 tumors. At day 73, the growth of the A549 tumor was inhibited by 78 and 89% following one or two cycles of BE-4-4-4-4, respectively. The mitotic index of A549 tumors was 18 times greater in control mice than in those treated with BE-4-4-4-4 for one or two cycles 99 days after initiation of treatment. 1,3-Bis(2-chloroethyl)-1-nitrosourea (BCNU) was given to mice carrying the U-87 MG or A549 tumors on day 4 (cycle 1) and day 46 (cycle 2) in the maximal tolerated dose of 50 mg/kg for BCNU alone and 40 mg/kg for BCNU plus BE-4-4-4-4. BCNU alone significantly inhibited the growth of U-87 MG tumors but not the growth of A549 tumors. Treatment with the combination of BCNU and BE-4-4-4-4 was significantly better than BCNU alone for A549 tumors and better than BE-4-4-4-4 alone for U87 tumors. However, in both animal groups treated with the combination, there was a significant weight loss, which was not observed for animals treated with either agent alone. These data suggest a role for BE-4-4-4-4 in the treatment of brain, lung, and colon tumors.

Radiopotentiation of human brain tumor cells by the spermine analog N1,N14-bis(ethyl)homospermine

PURPOSE

To determine whether the cytotoxicity produced by radiation can be increased by the spermine analog N1,N14-bis(ethyl)homospermine (BE-4-4-4).

METHODS AND MATERIALS

Two human tumor cell lines, SF-126 and U-251 MG, were either treated with 0.1 or 0.4 microM BE-4-4-4 for 3 or 4 days, or with 0.2 microM BE-4-4-4 for 4 days. At the end of BE-4-4-4 treatment, cells were irradiated and assayed immediately. Polyamine levels, cell survival, and cell number were determined.

RESULTS

In SF-126 cells, treatment with 0.2 microM BE-4-4-4 for 4 days killed about 50% of the cells and also increased the cytotoxicity of radiation. The dose enhancement ratio was approximately 1.3:1.5, which is similar to that reported for alpha-difluoromethylornithine. Polyamine levels were partially depleted, and growth was inhibited to about 60% of control levels. Pretreatment of cells with either 0.1 or 0.4 microM BE-4-4-4 for 3 or 4 days produced less of an increase in radiation-induced cytotoxicity, even though these exposures killed 30-40% or 60-90% of the cells, respectively. Similar treatment with 0.1-0.4 microM BE-4-4-4 in U-251 MG cells had minimal effects on cytotoxicity and growth inhibition, while treatment with 1.0 microM and 2.0 microM BE-4-4-4 for 4 days produced more than a 50% depletion in polyamine levels and partial inhibition in growth, but failed to demonstrate radiopotentiation.

CONCLUSION

The cytotoxic polyamine analog BE-4-4-4 can increase the cytotoxicity caused by radiation in at least one cell line. The amount of potentiation depends on the concentration of the analog, with the most occurring at the intermediate concentration. Because we did not observe potentiation in both cell lines, and because of the dose dependence seen in SF-126 cells, the clinical efficacy produced by combined BE-4-4-4 and radiation protocols may be limited.

Radiation brain injury is reduced by the polyamine inhibitor alpha-difluoromethylornithine

Alpha-difluoromethylornithine (DFMO) was used to reduce 125I-induced brain injury in normal beagle dogs. Different DFMO doses and administration schedules were used to determine if the reduction in brain injury was dependent on dose and/or dependent upon when the drug was administered relative to the radiation treatment. Doses of DFMO of 75 mg/kg/day and 37.5 mg/kg/day given 2 days before, during and for 14 days after irradiation reduced levels of putrescine (PU) in the cerebrospinal fluid relative to controls. Volume of edema was significantly reduced by 75 mg/kg/day of DFMO before, during and after irradiation and by the same dose when the drug was started immediately after irradiation. A reduction in edema volume after 37.5 mg/kg/day before, during and after irradiation was very near significance. Ultrafast CT studies performed on dogs that received a DFMO dose of 75 mg/kg/day before, during and after irradiation suggested that the reduced edema volume was associated with reduced vascular permeability. Volume of necrosis and volume of contrast enhancement (breakdown of the blood-brain barrier) were significantly lower than controls only after a DFMO dose of 75 mg/kg/day before, during and after irradiation. These latter data, coupled with the findings relative to edema, suggest that different mechanisms may be involved with respect to the effects of DFMO on brain injury, or that the extents of edema, necrosis and breakdown of the blood-brain barrier may depend upon different levels of polyamine depletion. The precise mechanisms by which DFMO exerts the effects observed here need to be determined.

Interaction of a polyamine analogue, 1,19-bis-(ethylamino)-5,10,15- triazanonadecane (BE-4-4-4-4), with DNA and effect on growth, survival, and polyamine levels in seven human brain tumor cell lines

Computer graphics modeling and physicochemical studies of spermine-DNA interactions, as well as experiments in cell culture, indicate that a polyamine analogue with strong affinity for nucleic acids but poor ability to condense and aggregate DNA in vitro should act as an antiproliferative agent if it can enter cells. On the basis of our studies of polyamine-DNA interactions, we designed a pentamine, 1,19-bis(ethylamino)-5,10,15- triazanonadecane (BE-4-4-4-4), that had these characteristics. Measurement of melting temperature and ultraviolet light scattering studies show that the affinity of this analogue for calf-thymus DNA is about 4 times higher than that of spermine, whereas its ability to aggregate DNA is slightly poorer than that of spermine. Studies in U-87 MG, U-251 MG, SF-126, SF-188, SF-763, SF-767, and DAOY human brain tumor cells in tissue culture showed that treatment for more than 96 h with concentrations of 5 microM BE-4-4-4-4 or greater inhibited growth; decreased levels of putrescine, spermidine, and spermine; and decreased colony-forming ability in all cell lines. The cytotoxicity of the analogue varied among cell lines; DAOY and SF-767 were the most sensitive and the most resistant lines, respectively. In SF-763 cells, growth inhibition by BE-4-4-4-4 could be partially reversed by the addition of putrescine, spermidine, or spermine 1 day after BE-4-4-4-4 addition, but in U-251 MG cells, growth inhibition was reversed only by spermine and not by other polyamines. When any of the naturally occurring polyamines was added simultaneously with BE-4-4-4-4, growth inhibition was completely blocked. The data suggest that a threshold intracellular concentration of BE-4-4-4-4 is needed to manifest the growth-inhibitory and cytotoxic effects. In most cell lines, once that threshold level is reached, the growth-inhibitory and cytotoxic properties of the analogue are manifest irrespective of cellular polyamine levels. Further increases in the BE-4-4-4-4 concentration or incubation time reduce the intracellular polyamine levels but do not significantly increase growth inhibition. In U-87 MG and DAOY cells, however, prolonged incubation with higher concentrations of BE-4-4-4-4 causes additional growth inhibition along with depletion of intracellular polyamines.(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of the polyamine analogs BE-3-7-3, 3-8-3, and BE-3-8-3 on human brain tumor cell growth and survival

Based on computer modeling, physicochemical studies of spermine-DNA interactions, and cell culture experiments, we hypothesized that polyamine analogs with hydrocarbon chain lengths differing from natural polyamines and a stronger affinity for nucleic acids than spermine should have a cellular antiproliferative effect. We tested three spermine analogs with long hydrocarbon chains, 1,16-diamino-4,12-diazahexadecane (3-8-3), 1,16-bis(ethyl)amino-4,12-diazahexadecane (BE-3-8-3), and 1,15-bis(ethyl)amino-4,11-diazapentadecane (BE-3-7-3) in human brain tumor cell lines U-251 MG, SF-126, and SF-188. Analog concentrations < or = 5 microM inhibited growth and colony-forming efficiency in each cell line by treatment day 5, with significant decreases in putrescine and spermidine, but not spermine, levels. These findings suggest that potentially cytotoxic polyamine analogs can be specified on the basis of their hydrocarbon chain length and DNA affinity.

Treatment with a polyamine analog alters DNA-matrix association in HeLa cell nuclei: a nucleoid halo assay

The polyamine analog 1,14-bis(ethylamino)-5,10-diazatetradecane (BE-4-4-4) depletes polyamines and inhibits the growth of tumor cells in tissue culture. We treated HeLa cells in culture with BE-4-4-4 for different time periods to produce different degrees of polyamine depletion. The cells were lysed and dehistonized to obtain nucleoids containing DNA attached to the nuclear matrix. Titration of the nucleoids with propidium iodide caused an uncoiling of negatively supercoiled DNA, resulting in the formation of a halo surrounding the nucleoid periphery. The halo diameters in both the BE-4-4-4-treated cells and the untreated control cells were measured using a fluorescence image analysis system. As compared to the control cells, the BE-4-4-4-treated cells showed a 20-25% decrease in halo diameter, indicating that there was less relaxation of the negative supercoils in the nuclear DNA of the BE-4-4-4-treated cells than in the controls.

Differential effects of spermine and its analogues on the structures of polynucleotides complexed with ethidium bromide

The interactions of spermine and polyamine analogues with synthetic polynucleotides of various base sequences complexed with ethidium bromide (EB) were investigated using measurements of fluorescence intensity and steady-state fluorescence polarization. Spermine and polyamine analogues displaced some but not all of the EB bound to poly(dA-dT).poly(dA-dT) or poly(dG-dC).poly(dG-dC), suggesting that polyamines may stabilize these polynucleotides in a conformation with reduced affinity for EB. Modifications of the aliphatic backbone of spermine have pronounced effects on its ability to displace EB from poly(dA-dT).poly(dA-dT) but not from poly-(dG-dC).poly(dG-dC). Spermine and some but not all of the polyamine analogues caused fluorescence depolarization when they interacted with the complex of EB and poly(dA-dT).poly-(dA-dT). Neither spermine nor any of the analogues, however, induced fluorescence depolarization in the complex of EB with poly(dG-dC).poly(dG-dC) or poly(dA).poly(dT). This suggests that spermine and some spermine analogues induce structural changes specific to alternating A-T sequences.

Effects of fractionated radiation therapy on human brain tumor multicellular spheroids

We investigated the cytotoxic effects of fractionated radiation therapy on multicellular spheroids of human malignant glioma cell lines U-87 MG, U-251 MG, and U-373 MG. Graded doses of x-rays were administered in 1, 3, 8, 15, and 30 fractions over 15 days. The isoeffect dose for a 1 log cell kill ranged from 4-4.5 Gy for a single fraction to 7-8 Gy for an 8-fraction protocol; no additional dose-sparing was achieved with more fractions. Therefore, the effects of individual doses (1.56 Gy) of the 8-fraction protocol were studied in U-251 MG spheroids. A cell survival assay showed that the first dose of radiation killed 30-50% of the cells; subsequent doses usually killed fewer cells. The cell kill after all 8 doses was about 1.0 log. No consistent relationship between the intracellular glutathione level and fraction number was observed. The 24-hour labeling index of the spheroids did not decrease until after the second fraction. Thus, the higher cell kill of the first dose does not seem to be related to cell cycle synchrony. Multinuclear and mononuclear giant cells were limited almost entirely to the periphery of the spheroids and increased with the number of radiation fractions. We conclude that multicellular spheroids can be used to study the biological effects of fractionated radiation therapy on human brain tumor cells. Although this model cannot be used to evaluate the effect of radiation on normal tissue, it may be useful in developing more effective radiation therapy protocols for human brain tumors.

The effects of O6-benzylguanine and hypoxia on the cytotoxicity of 1,3-bis(2-chloroethyl)-1-nitrosourea in nitrosourea-resistant SF-763 cells

O6-Alkylguanine-DNA alkyltransferase (AGT) activity is associated with resistance of brain tumor cell lines to the cytotoxic effects of 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). SF-763 cells exhibit high AGT activity and are resistant to BCNU. In this study, we compared the effects of the AGT inhibitor O6-benzylguanine (BG) on the cytotoxicity of BCNU in oxic and hypoxic SF-763 cells; we also measured AGT activity, ornithine decarboxylase (ODC) activity, and polyamine levels to determine if there was any correlation with cell survival as determined by colony-forming efficiency assay. Exponentially growing monolayer cells were pretreated with 10 microM BG for 2 h under oxic or hypoxic (95% nitrogen/5% CO2) conditions and then exposed to graded concentrations of BCNU for 1 h. BG significantly lowered AGT activity but had no cytotoxic effect in oxic or hypoxic cells; hypoxia alone was not cytotoxic. The cytotoxicity of BCNU was 4 times higher in BG-treated hypoxic cells than in oxic cells treated with BCNU alone; the BCNU doses required for a 1-log cell kill were 75 and 300 microM, respectively. ODC activity was lowered by hypoxia alone but was not significantly affected by BG in either hypoxic or oxic cells. Polyamine levels were not significantly affected by hypoxia or BG. These results indicate that pretreatment with BG dramatically lowers AGT activity and increases the cytotoxicity of BCNU in both oxic and hypoxic SF-763 cells. The mechanism of this enhanced cytotoxicity is apparently unrelated to ODC activity or polyamine levels.

alpha-Difluoromethylornithine alters calcium signaling in platelet-derived growth factor-stimulated A172 brain tumor cells in culture

alpha-Difluoromethylornithine (DFMO), an irreversible inhibitor of the polyamine biosynthetic enzyme ornithine decarboxylase, inhibits the growth of brain tumor cell lines and is undergoing clinical trials as a treatment for brain tumors. Platelet-derived growth factor (PDGF) is thought to regulate the growth and development of precursors of both normal and neoplastic astrocytic cells; calcium signaling is thought to play a role in the transduction of PDGF signals. Using laser fluorescence image cytometry, flow cytometry, and spectrofluorometry, we studied the effect of DFMO on the calcium signals induced by PDGF in A172 human glioblastoma cells. Four days of treatment with 5 mM DFMO substantially shortened PDGF-induced calcium signals. The effect was reversed more than 10 h but less than 24 h after putrescine treatment, even though polyamines were repleted 4 h after putrescine and spermidine were added. DFMO did not substantially affect intracellular calcium release or the timing of the opening and closing of plasma membrane calcium channels. These findings support the notion that calcium signaling may be a target for inhibitors of polyamine metabolism.

Production of stable phenotypes from 9L rat brain tumor multicellular spheroids treated with 1,3-bis(2-chloroethyl)-1-nitrosourea

During chemotherapy and regrowth of brain tumors, tumor-cell heterogeneity, and possibly tumor progression, may change as a result of both the selective forces and mutagenic effects of treatment. We have isolated and characterized drug-response variants of multicellular rat 9L brain-tumor spheroids exposed to 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU). Ten colonies were isolated from spheroids disaggregated immediately after treatment, and 10 colonies were isolated from treated spheroids disaggregated after 1 week in suspension culture. The sensitivity to BCNU was determined by assays of sister chromatid exchange and colony-forming efficiency in monolayer cultures of each subline after a 1-hr exposure to graded doses of BCNU. Three classes of response were found: BCNU sensitivity increased, decreased, or was comparable to that of uncloned, parent 9L cells. Resistant phenotypes were predominant (8/10) in sublines from spheroids disaggregated immediately after treatment, whereas hypersensitive phenotypes (4/8) were isolated only from spheroids disaggregated after 1 week of regrowth. Since subpopulations isolated immediately after treatment do not have the same biological characteristics as those isolated after a period of regrowth, these data suggest that tumor-cell heterogeneity may be generated by distinct processes at various times during therapy. The predominance of hypersensitive sublines obtained by the regrowth protocol may have resulted from the recovery of cells that would have died if isolated but were instead able to repair the drug-induced damage when left in contact with neighboring, possibly resistant cells. Two resistant and two hypersensitive sublines were studied further.

Role of ornithine decarboxylase suppression and polyamine depletion in the antiproliferative activity of polyamine analogs

Two transfected cell lines, one carrying a mammalian ornithine decarboxylase (ODC) that is suppressed by polyamines and one carrying a trypanosomal ODC that is not, were used to ask whether ODC suppression is necessary for the antiproliferative activities of two polyamine analogs, N1,N8-bis(ethyl)spermidine (BES) and N1,N14-bis(ethyl)homospermine (BE444). Both analogs accumulated within cells and suppressed S-adenosylmethionine decarboxylase, as well as polyamine-sensitive mouse ODC activity. Neither drug was able to suppress the activity of the polyamine-refractory trypanosome ODC. But, whereas BE444 was able to inhibit growth of both cell lines, BES could inhibit only growth of cells carrying the polyamine-sensitive ODC, under conditions that cause prolonged depletion of endogenous polyamines. We conclude from these studies that the antiproliferative activity of BES, a less potent drug, requires the suppression of ODC. The efficacy of BE444 is enhanced by its ability to suppress ODC. However, it can function without ODC suppression, whereas BES cannot.

Effect of spermine on sperm capacitation of guinea pig in vitro

Spermine (Sp) 10(-5) mM had vigorous activity of guinea pig spermatozoa, while it completely abolished sperm forward motility (SFM) at a concentration of 10(-3) mM. There appeared to be a dose relationship to inhibition to motility. 2-Difluoromethylornithine 10 mM antagonized the Sp-induced inhibition of SFM after 3 h of incubation. Capacitation of a guinea pig sperm was inhibited by Sp in a concentration-dependent manner. The majority of acrosome-reacted sperm did not display hyperactivated motility. Precapacitated sperm were able to undergo the acrosome reaction (AR) in the presence of Sp. Moreover, Sp-mediated inhibition of capacitation was a reversible process. Once sperm capacitation was completed, Sp no longer inhibited AR. Before capacitation, the content of Sp in spermatozoa was 4.5 +/- 0.5 micrograms/5 x 10(7) cells, whereas in case of capacitated spermatozoa it was significantly decreased (2.1 +/- 0.4 micrograms/5 x 10(7) cells). The penetration of spermatozoa into the zona-free hamster eggs in the presence of Sp was markedly decreased, but it did not affect the fertilizability of ova as compared to the control. These results suggest that Sp may be an inhibitory agent of sperm capacitation in guinea pig in vitro, and it may also be involved in the modulation of capacitation.

Effect of polyamine depletion on chromatin structure in U-87 MG human brain tumour cells

The chromatin structure of polyamine-depleted U-87 MG human brain tumour cells was studied by following the kinetics of digestion of cell nuclei by micrococcal nuclease and bovine pancreatic DNAase I. Cells growing in monolayers were treated with either alpha-difluoromethylornithine (DFMO), to deplete putrescine and spermidine, or N1,N14-bis(ethyl)homospermine (BE-4-4-4), to deplete putrescine, spermidine and spermine. BE-4-4-4 increased the initial rates of digestion and the magnitudes of limit digest by both enzymes; DFMO increased the limit digests without affecting initial digestion rates. Addition of 1 mM-putrescine 1 day after addition of DFMO reversed the effect of DFMO on limit digests. (Because polyamine uptake is low in cells treated with BE-4-4-4, and because putrescine does not reverse the growth-inhibitory effects of BE-4-4-4, reversal of the effects of BE-4-4-4 with putrescine was not attempted.) The increases in initial rates and limit digests did not result from changes in the lengths of nucleosomal or linker DNA, from blocks in cell-cycle progression, or from growth inhibition caused by DFMO or BE-4-4-4. Thus, because the limit digest is highest in cells with the lowest polyamine levels, it seems clear that the enhanced enzymic digestion of nuclei is caused by polyamine depletion and its possible effect on chromatin structure.

Modification of radiation-induced brain injury by alpha-difluoromethylornithine

The effect of alpha-difluoromethylornithine (DFMO) on 125I-induced brain injury was investigated in a dog model. Cerebrospinal putrescine levels were reduced from baseline levels 1-2 weeks after irradiation in animals treated with 125I and DFMO, while putrescine levels were elevated in 125I and saline-treated animals. In addition, the time course of changes in the volumes of edema, necrosis, and tissue showing evidence of blood-brain barrier breakdown was altered significantly by DFMO treatment. The most significant alterations occurred 2-4 weeks after irradiation, at which times the average volumes of damage in DFMO-treated animals were reduced compared to saline-treated animals. The time course of alterations in blood-to-brain transfer, brain-to-blood transfer, and vascularity following irradiation was also altered by DFMO treatment. Analysis of variance demonstrated a strong relationship of blood-to-brain transfer and vascularity to volume of edema, suggesting that the effect of DFMO on edema may be partially mediated by its effects on blood-brain barrier breakdown.

Effect on N1,N14-bis-(ethyl)-homospermine (BE-4-4-4) on the growth of U-251 MG and SF-188 human brain tumor cells

We studied the effects of the spermine analogue N1,N14-bis-(ethyl)-homospermine (BE-4-4-4) on growth, survival and polyamine levels in cultured U-251 MG and SF-188 human brain tumor cells. After 48 hr of treatment at concentrations of 1 microM or higher, BE-4-4-4 accumulated in cells with a concomitant decrease in intracellular putrescine, spermidine and spermine concentrations. Growth inhibition by 10 microM BE-4-4-4 began at 6 hr and peaked between 16 and 24 hr. The analogue was also increasingly cytotoxic with doses between 1 and 10 microM and with treatment times between 16 and 48 hr. Polyamines added 1 day after BE-4-4-4 lowered the intracellular concentrations of the analogue but did not reverse its growth-inhibitory activity. When added simultaneously with the analogue, however, polyamines caused a decrease in analogue concentration that was accompanied by a block to the growth inhibition. BE-4-4-4 has a higher affinity for DNA than spermine has, but is less able to aggregate DNA. Its growth-inhibitory and cytotoxic effects support our hypothesis that polyamine analogues that enter cells and replace natural polyamines at DNA binding sites, without fulfilling their biologic functions, should act as antiproliferative agents.

Calcium channels in PDGF-stimulated A172 cells open after intracellular calcium release and are not voltage-dependent

Using laser image cytometry and Indo-1 fluorescence, we investigated the intracellular free Ca2+ concentration ([Ca2+]i) of confluent A172 human glioblastoma cells stimulated by the BB homodimer of platelet-derived growth factor (PDGF-BB). The shape of the calcium transients and the delay time between stimulation and the beginning of the transient varied considerably. The percentage of responsive cells, the peak [Ca2+]i and the duration of the response were directly related to PDGF-BB dose, while the delay time was inversely related; the maximal response occurred at a PDGF-BB concentration of 20 ng/ml. Studies with EGTA and inorganic calcium-channel blockers (Ni2+, La3+) showed that the increase of [Ca2+]i resulted from initial release of intracellular stores and subsequent calcium influx across the plasma membrane. Opening of calcium channels in the plasma membrane, monitored directly by studying Mn2+ quenching of Indo-1 fluorescence, was stimulated by PDGF-BB and blocked by La3+; the opening occurred 55 +/- 10 s after the initial increase in [Ca2+]i. Therefore, in these tumor cells, intracellular release always occurs before channel opening in the plasma membrane. Depolarization of cells with high extracellular [K+] did not generally induce calcium transients but did decrease calcium influx. L-type calcium-channel blockers (verapamil, nifedipine, and diltiazem) had little or no effect on the calcium influx induced by PDGF-BB. These results indicate that PDGF-BB induces calcium influx by a mechanism independent of voltage-sensitive calcium channels in A172 human glioblastoma cells.

Implications and concepts of polyamine-nucleic acid interactions

Modeling, x-ray diffraction, and solution studies have contributed to the understanding of interactions between polyamines and nucleic acids. Polyamines stabilize a variety of unusual DNA structures and conformations in vitro, including both the left-handed Z and the right-handed A DNA. In addition, polyamines condense DNA and may be important in bending specific sequences. Investigations into the mechanisms of these effects provide support for both specific and nonspecific interactions between polyamines and DNA. Although exact relationships between the binding of polyamines and conformational changes in nucleic acids are still being clarified, polyamines remain important candidates for regulators of DNA conformation in vivo.

Attachment of A172 human glioblastoma cells affects calcium signalling: a comparison of image cytometry, flow cytometry, and spectrofluorometry

The intracellular free calcium concentration ([Ca2+]i) of indo-1 loaded A172 human glioblastoma cells stimulated by platelet-derived growth factor (PDGF) was studied in cell suspensions by flow cytometry and spectrofluorometry and in confluent monolayers by laser image cytometry and spectrofluorometry. With all three techniques, the percentage of responsive cells, peak [Ca2+]i, and the duration of response were directly related, and the delay time was inversely related to PDGF dose. The maximum response occurred at a PDGF concentration of about 20 ng/ml. Basal and peak [Ca2+]i did not differ significantly from method to method even though different calibration procedures were used. Cells in suspension monitored by both spectrofluorometry and flow cytometry displayed significantly shorter calcium responses than attached cells. This did not appear to be a direct effect of trypsinization. Spectral analysis of indo-1 in cytoplasm, 40% glycerol, and aqueous solutions showed significant differences in the isosbestic point and quantum efficiency. Calibration of [Ca2+]i with spectrofluorometry is more accurate using the ratio of fluorescence intensities than the fluorescence intensities measured at either 405 or 485 nm.

Effects of variation in the structure of spermine on the association with DNA and the induction of DNA conformational changes

The effects of spermine and spermine analogues on the B-Z transition of poly(dG-me5dC) and on the aggregation and 'melting' temperature of calf thymus DNA were studied by spectroscopic methods. The association constants of these polyamines with double- and single-stranded calf thymus DNA were calculated from their effects on the melting temperature. The effect of these compounds on the release of ethidium bromide (EB) from an EB-DNA complex were measured by a spectrofluorimetric method. This efficiency of the polyamine-induced B-Z transition strongly depended on the length of the central carbon chains of the compounds and on the functional groups attached to the carbon chains. Both the terminal primary amino groups and the length of the central carbon chain affected the aggregation of DNA. The affinity of the analogues for DNA increased as the number of n-butyl groups increased, but decreased with either an increase or a decrease in the length of the central carbon chain. The effect of spermine and spermine analogues on the release of EB from an EB-DNA complex did not always correlate with the affinities of analogues for calf thymus DNA. In particular, tetra-amines with more than one n-butyl group bound better to DNA than did spermine, but released bound EB and induced aggregation of DNA less well than did spermine. We postulate that either a bend and/or other localized conformational changes of DNA are responsible for the spermine-induced aggregation of DNA and the release of EB from the EB-DNA complex.

Differential drug sensitivity conferred by growth status detected in a mixed population of cycling and noncycling cells

The noncycling cell compartment of tumors is considered to be an important target for chemotherapeutic agents; yet, it has been difficult to accurately quantitate its contribution to tumor response because of a lack of methods that can readily discern the relative sensitivities of cycling and noncycling cells. We have used antibodies against bromodeoxyuridine-substituted DNA in a unique experimental protocol that provides a basis for distinguishing the cycling and noncycling cell compartments and detecting their respective levels of drug-induced chromosome damage. A mixed population of cycling and noncycling cells was obtained by culturing 9L rat brain tumor cells as multicellular spheroids. Cell cycle compartments and phase distributions were monitored with flow cytometry using bivariate analysis of DNA content and bromodeoxyuridine incorporation. Bromodeoxyuridine labeling was manipulated to differentially label metaphases from cycling and noncycling cells for sister chromatid exchange. This is based on the differential staining patterns of chromatids and metaphases that are obtained from cells that have replicated in the presence of bromodeoxyuridine. The chromosome damage in each cell cycle compartment following exposure to the chemotherapeutic agent 1,3-bis(2-chloroethyl)-1-nitrosourea was assessed by the number of sister chromatid exchanges induced by treatment. Noncycling cells were shown to be more sensitive to 1,3-bis(2-chloroethyl)-1-nitrosourea-induced damage than were cycling cells. However, when allowed to remain noncycling for 24 h after treatment, the number of exchanges decreased in noncycling cells, which may indicate their ability to recover from damage. These results illustrate an experimental protocol that permits simultaneous assessment of cell cycle compartment recruitment and sister chromatid exchange induction in cells derived from a cytokinetically complex population containing both cycling and noncycling cells.