Structure-function correlations of polyamine analog-induced increases in spermidine/spermine acetyltransferase activity

The cytosolic enzyme, spermidine/spermine acetyltransferase (SSAT), is distinguished by its role in polyamine interconversion and by its high inducibility in response to a variety of physiological and pharmacological stimuli. Among a series of fifteen polyamines and polyamine analogs, the most potent inducers of SSAT activity in cultured L1210 cells were found to be N1,N8-bis(ethyl)spermidine (BES) and N1,N12-bis(ethyl)spermine (BESm). Over a 24-hr exposure at 10 microM, enzyme activity rose 13- and 16-fold with BES and BESm, respectively, compared to 2- to 3-fold with the anticancer agent, methylglyoxal bis(guanylhydrazone). The increase in enzyme activity by BESm began rapidly and continued steadily with time so that by 48 hr it increased to about twenty times control. By inhibitor studies, the increase was found to be due to elevated protein synthesis predominantly at the level of translation and to an apparent prolongation of enzyme half-life related to enzyme stabilization. Among the analogs, the structural requirements for maximum enzyme induction were found to be critically dependent on aminopropyl moieties and on the presence, size and location of the alkyl groups. By structure-function comparisons, it was deduced that the known abilities of BES and BESm to regulate ornithine and S-adenosylmethionine decarboxylase activities or to inhibit cell growth occur independently of their effects on SSAT activity in L1210 cells.

Differential response to treatment with the bis(ethyl)polyamine analogues between human small cell lung carcinoma and undifferentiated large cell lung carcinoma in culture

We have compared the effects of treatment with each of three bis(ethyl)polyamine analogues on a human small cell lung carcinoma (SCLC) line, NCI H82, and a non-small cell line, NCI H157, an undifferentiated large cell lung carcinoma. The bis(ethyl)polyamines have been shown to interfere with polyamine metabolism, presumably by regulation of the polyamine biosynthetic pathway in a manner similar to the natural polyamines, in contrast to direct inhibition of specific enzymes, such as ornithine decarboxylase. Each of these compounds was found to be relatively inactive in reducing growth rate, polyamine levels, or polyamine biosynthetic enzyme activity in the SCLC cells, a line which we have previously shown to be particularly sensitive to inhibition of polyamine biosynthesis by the direct ornithine decarboxylase inhibitor difluoromethylornithine. By contrast, each of the bis(ethyl)polyamines tested was found to be markedly cytotoxic (at concentrations of only 10 microM) to the non-SCLC line, NCI H157. Interestingly, the non-SCLC line has previously been demonstrated to be resistant to polyamine depletion by difluoromethylornithine. For each bis(ethyl)polyamine, cytotoxicity was accompanied by nearly complete depletion of all intracellular polyamines and a decrease in ornithine decarboxylase activity to undetectable levels. The current study emphasizes the phenotypic variability which can exist in response to inhibitors of polyamine biosynthesis and suggests a class of agents which may have clinical utility against the treatment-resistant non-SCLC lung cancers.

Modulation of polyamine biosynthesis and transport by oncogene transfection

The effects of oncogene expression on phenomena related to polyamine metabolism were examined in Rat-1 cells stably transfected with EJ2-ras or N-myc oncogenes. In ras-transfected cells, ornithine decarboxylase activity was about 12-times higher than in either the parent or N-myc-transfected cell lines. By contrast, polyamine uptake was markedly increased in N-myc-transfected cells, as indicated by their enhanced sensitivity to the antiproliferative and enzyme regulatory effects of the polyamine analog, N1, N12-bis(ethyl)spermine (BESm), their intracellular accumulation of BESm and by their increased sensitivity to the growth inhibitory effects of methylglyoxalbis(guanylhydrazone)--another analog which utilizes the polyamine transport mechanism. These associations between N-myc and ras expression and critical aspects of polyamine metabolism suggest a possible role for the latter in facilitating the growth promoting properties of these oncogenes.

Selective regulation of S-adenosylmethionine decarboxylase activity by the spermine analogue 6-spermyne

Polyamine-biosynthesis activity is known to be negatively regulated by intracellular polyamine pools. Accordingly, treatment of cultured L1210 cells with 10 microM-spermine rapidly and significantly lowered ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (AdoMetDC) activities in a sequential manner. By contrast, treatment for 48 h with 10 microM of the unsaturated spermine analogue 6-spermyne lowered AdoMetDC activity, but not ODC activity. An initial decrease in ODC activity at 2 h was attributed to a transient increase in free intracellular spermidine and spermine brought about through their displacement by the analogue. Thereafter, ODC activity recovered steadily to control values as 6-spermyne pools increased and spermidine and spermine pools decreased owing to analogue suppression of AdoMetDC activity. The apparent ability of 6-spermyne to regulate AdoMetDC, but not ODC, activity suggests an interesting structure-function correlation and demonstrates that the typical co-regulation of these enzyme activities can be dissociated. This, in turn, may reflect the existence of independent regulatory binding sites for the two enzymes.

Control of ornithine decarboxylase activity in alpha-difluoromethylornithine-resistant L1210 cells by polyamines and synthetic analogues

The regulation of ornithine decarboxylase (ODC) activity by the polyamine derivatives N1,N8-bis(ethyl)-spermidine and N1,N12-bis(ethyl)spermine was studied using a line of L1210 cells resistant to alpha-difluoromethylornithine (D-R cells), which contain very high levels of ODC, and a synthetic mRNA prepared from a plasmid containing an insert corresponding to ODC mRNA adjacent to an SP6 RNA polymerase promoter. Studies in which ODC protein was labeled in the D-R cells by exposure to [35S]methionine indicated that the polyamine derivatives and their physiological counterparts led to an increased rate of degradation of ODC and to a rapid reduction in ODC synthesis without affecting the content of ODC mRNA. Direct evidence that the polyamine derivatives act by inhibiting the translation of the ODC mRNA was obtained by studying their effects on the translation of ODC mRNA in reticulocyte lysates. This translation was strongly inhibited by the addition of N1,N8-bis(ethyl)spermidine, spermidine, N1,N12-bis(ethyl)spermine, or spermine but was not affected much by putrescine. The inhibition of the translation of ODC mRNA by either of the bis(ethyl) polyamine derivatives occurred at concentrations which stimulated total protein synthesis showing the selectivity of the reduction in ODC. The effects of polyamine derivatives and polyamines on translation of the plasmid-derived ODC mRNA were identical with those found with the D-R L1210 cell mRNA. This synthetic ODC mRNA lacks 261 bases of the 5'-leader sequences and 200 bases plus the poly(A) section from the 3'-nontranslated sequence. Therefore, these regions appear not to influence sensitivity of the ODC mRNA to inhibition of translation by polyamine derivatives.

Demonstration of ferric L-parabactin-binding activity in the outer membrane of Paracoccus denitrificans

Under low-iron conditions, Paracoccus denitrificans excretes a catecholamine siderophore, L-parabactin, to sequester and utilize iron. In this report, we demonstrate the presence of stereospecific high-affinity ferric L-parabactin-binding activity associated with P. denitrificans membranes grown in low-iron medium. Isolated outer membrane components were shown to be three to four times higher in specific activity for ferric L-parabactin. The same amount of binding activity existed whether or not the radiolabel was present in the metal (55Fe) or the ligand (3H) portion of ferric parabactin chelate, suggesting that binding was to the intact complex. Ion-exchange chromatography of a Triton X-100-solubilized outer membrane mixture on DEAE-cellulose resulted in a 10-fold increase in binding activity relative to that present in whole membranes. Polypeptide profiles by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the products of each stage of the purification showed that binding activity copurified with one or more of the low-iron-induced outer membrane proteins in the 80-kilodalton (kDa) region. Membrane proteins and [55Fe]ferric L-parabactin electrophoresed in nondenaturing gels demonstrated the presence of membrane component(s) which stereo-specifically bound ferric L-parabactin, thus providing independent confirmation of the binding assay results. Moreover, when the band labeled by [55Fe]ferric L-parabactin was excised and profiled by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, 80-kDa polypeptides were the major components present. These results demonstrate the presence of a high-affinity ferric L-parabactin receptor in P. denitrificans membranes and suggest that one or more of the 80-kDa low-iron-induced polypeptides are components of the ferric L-parabactin receptor.

Synthetic polyamine analogues as antineoplastics

In this paper, we report on the synthesis and biological activity of a number of N-alkylated spermine compounds. The dialkylspermines N1,N12-dimethylspermine (DMSPM-2), N1,N12-diethylspermine (DESPM-3), and N1,N12-dipropylspermine (DPSPM-4) are all shown to inhibit the growth of L1210 cells in culture with IC50 values of less than 1 microM at 96 h. Furthermore, DESPM-3 is shown to be similarly active against Daudi and HL-60 cells in culture. A structure-activity relationship is shown to exist between the position at which spermine is alkylated and its antiproliferative properties. The activity of 10 microM DESPM-3 against L1210 cells was shown to be cytostatic, with greater than 90% cell viability by trypan blue exclusion, even after a 144-h exposure. When L1210 cells were treated with 10 microM DESPM-3 over a 144-h period, their size and mitochondrial DNA content were gradually but substantially diminished. However, flow cytometric measurements of the nuclear DNA content of these treated cells at 96 h indicated only slightly reduced S and G2 populations and significant changes only after 144 h. A cloning assay performed on the cells after 96 h of exposure to this drug (10 microM) indicated that the cells were not growing. Finally, when male DBA/2 mice, inoculated with L1210 leukemia cells, were treated with DESPM-3, their life span was increased in excess of 200% relative to untreated controls. Moreover, many long-term survivors were apparently tumor free at the end of the experiment (60 days).

Enzyme regulation as an approach to interference with polyamine biosynthesis--an alternative to enzyme inhibition

The progress reviewed here would seem to validate the regulatory approach to interference with polyamine biosynthesis as an antiproliferative strategy. To our knowledge, this is the first example, among anticancer drugs, of pharmacological intervention of a biochemical pathway based strictly on regulatory control. Several features of polyamine biology naturally favor this approach and may account for its relative success. These include (a) the nature of the regulatory mechanisms themselves, (b) the exquisite sensitivity of the pathway to regulatory control, (c) the rapid turnover of ODC and AdoMetDC, (d) the different structural specificity of ODC and AdoMetDC regulation versus growth-dependent functions, and (e) the direct dependence of growth on sustained polyamine biosynthesis. As such, the regulatory approach to interference with polyamine biosynthesis offers several advantages over the use of specific enzyme inhibitors (Table 10). Of these, perhaps, the more significant are the facts that more than one enzyme can be simultaneously and specifically suppressed and that compensatory mechanisms, which otherwise counter the effects of enzyme inhibitors (11), are not invoked. We are encouraged by the concurrence of in vitro mechanistic findings with the predictions of the hypothesis for the regulatory approach and by the in vitro and in vivo growth inhibitory effects of the analogs against murine leukemia. One disadvantage of the regulatory analogs, such as BESm, has been that, as with specific polyamine inhibitors such as DFMO, analog-induced polyamine depletion results in cytostatic growth inhibition. While this response may help to minimize host toxicities, it clearly compromises antitumor activity. An intriguing exception to this generality has recently been found among human lung carcinoma cell lines. Previously, Luk et al. (93, 94) and others (95) reported that, among a spectrum of human lung carcinoma lines, small cell carcinoma was exquisitely sensitive to the ODC inhibitor, DFMO. Not only did these cells display a cessation of growth but also an inability to survive during DFMO-induced polyamine depletion. Studies extending these findings to long term maintenance therapy in human small cell lung carcinoma implants in athymic mice revealed sustained growth inhibition of the tumor for longer than one year (96). Casero et al. (97) now find that human large cell carcinoma, which is otherwise refractory to chemotherapeutic intervention, displays a cytotoxic response in vitro to polyamine depletion induced by BES or BESm but not by DFMO.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of polyamine biosynthetic activity by spermidine and spermine analogs--a novel antiproliferative strategy

Interference with polyamine biosynthesis by analog-mediated regulatory mechanisms represents a viable alternative to the use of specific enzyme inhibitors as an antiproliferative strategy. The approach is unique among antimetabolite approaches and is made possible by unusual characteristics inherent to the polyamines and their biosynthetic pathway. Current antitumor data obtained with these analogs provides indication of their potential usefulness as antitumor agents but, at the same time, demonstrates the need for improvement. This latter might be attained by the rational design of analogs which (a) bind more tightly at enzyme regulatory sites, (b) which are less able to substitute for natural polyamines in growth related functions and (c) which are eliminated less rapidly from tumor-bearing animals. At the same time, the continued preclinical development of available analogs might proceed most productively by targeting large cell lung carcinoma and melanoma and by examining the generality of the relationship between oncogene expression and the accompanying sensitivity to regulatory analogs.

Microbial iron chelator-induced cell cycle synchronization in L1210 cells: potential in combination chemotherapy

Parabactin, a microbial iron chelator (a siderophore), is shown to be a more potent cell synchronization agent than either desferrioxamine or hydroxyurea. When the L1210 cell cycle is blocked with parabactin, cells are held at the G1-S border. If the ligand is later washed away, the block is reversed, and the cells cascade into S phase. The cells are synchronized through three cell cycles. The siderophore-induced block is exploited in the inhibition of growth of L1210 cells by combination with the antineoplastics, doxorubicin (Adriamycin), cytarabine, and bischloroethyl nitrosourea. The growth-inhibitory effects of Adriamycin, cytarabine, and bischloroethyl nitrosourea in combination with parabactin are shown to be dependent on the time frame in which the combination of drugs is presented to the cells. The results are in keeping with changes in L1210 cell cycle kinetics induced by the catecholamide chelator, parabactin.

Relative abilities of bis(ethyl) derivatives of putrescine, spermidine, and spermine to regulate polyamine biosynthesis and inhibit L1210 leukemia cell growth

It has been shown previously (Porter et al., Cancer Res., 45: 2050-2057, 1985) that the N1,N8-bis(ethyl) derivative of spermidine has significant antiproliferative activity which appears to derive from its regulatory effects on the polyamine biosynthetic pathway, particularly on ornithine decarboxylase activity. In the present study, N1,N4-bis(ethyl)putrescine (BEP) and N1,N12-bis(ethyl)spermine (BESm) were compared with N1,N8-bis(ethyl)spermidine (BES) in their ability to inhibit cell growth and regulate polyamine biosynthesis. With cultured L1210 murine leukemia cells, the IC50 values at 48 h were approximately 2 mM for BEP, 30 microM for BES, and 1 microM for BESm making the latter the most effective polyamine inhibitor or analogue thus far identified. At concentrations which approximated IC50 values and yielded similar intracellular concentrations at 48 h (1500-2000 pmol/10(6) cells), the effects of the analogues on polyamine biosynthesis generally correlated with their antiproliferative activity. BEP, at 1 mM, exerted relatively minor effects on polyamine biosynthesis. By contrast, 100 microM BES totally eliminated ornithine decarboxylase activity, depleted putrescine and spermidine pools, and decreased spermine pools by 40%. AdoMet decarboxylase activity was lowered slightly. The most impressive effects were obtained with 10 microM BESm which decreased ornithine and AdoMet decarboxylase activities by 99 and 84%, respectively; depleted putrescine and spermidine pools; and decreased spermine pools by 73%. None of the analogues, at 1 or 3 mM, had significant direct inhibitory effects on the decarboxylase activities from untreated cells with the exception of BESm which inhibited ornithine but not AdoMet decarboxylase activity. Thus, the effects of the analogues on these enzymes in treated cells are presumed to be mainly mediated by regulatory mechanisms. In this regard, BESm was superior to BES since both ornithine and AdoMet decarboxylase activities were suppressed. Given its unique activities, BESm would seem to have potential as both an antiproliferative agent and also as an experimental probe for studying regulation of the polyamine pathway, particularly AdoMet decarboxylase.

Regulation of ornithine decarboxylase activity by spermidine and the spermidine analogue N1N8-bis(ethyl)spermidine

Polyamine biosynthesis in intact cells can be exquisitely controlled with exogenous polyamines through the regulation of rate-limiting biosynthetic enzymes, particularly ornithine decarboxylase (ODC). In an attempt to exploit this phenomenon as an antiproliferative strategy, certain polyamine analogues have been identified [Porter, Cavanaugh, Stolowich, Ganis, Kelly & Bergeron (1985) Cancer Res. 45, 2050-2057] which lower ODC activity in intact cells, have no direct inhibitory effects on ODC, are incapable of substituting for spermidine (SPD) in supporting cell growth, and are growth-inhibitory at micromolar concentrations. In the present study, the most effective of these analogues, N1N8-bis(ethyl)SPD (BES), is compared with SPD in its ability to regulate ODC activity in intact L1210 cells and in the mechanism(s) by which this is accomplished. With respect to time and dose-dependence of ODC suppression, both polyamines closely paralleled one another in their response curves, although BES was slightly less effective than SPD. Conditions of minimal treatment leading to near-maximal ODC suppression (70-80%) were determined and found to be 3 microM for 2 h with either SPD or BES. After such treatment, ODC activity was fully recovered within 2-4 h when cells were re-seeded in drug-free media. By assessing BES or [3H]SPD concentrations in treated and recovered cells, it was possible to deduce that an intracellular accumulation of BES or SPD equivalent to less than 6.5% of the combined cellular polyamine pool was sufficient to invoke ODC regulatory mechanisms. Decreases in ODC activity after BES or SPD treatment were closely paralleled by concomitant decreases in ODC protein. Since cellular ODC mRNA was not similarly decreased by either BES or SPD, it was concluded that translational and/or post-translational mechanisms, such as increased degradation of ODC protein or decreased translation of ODC mRNA, were probably responsible for regulation of enzyme activity. Experimental evidence indicated that neither of these mechanisms seemed to be mediated by cyclic AMP or ODC-antizyme induction. On the basis of the consistent similarities between BES and SPD in all parameters studied, it is concluded that the analogue most probably acts by the same mechanisms as SPD in regulating polyamine biosynthesis.

Comparison and characterization of growth inhibition in L1210 cells by alpha-difluoromethylornithine, an inhibitor of ornithine decarboxylase, and N1,N8-bis(ethyl)spermidine, an apparent regulator of the enzyme

The cellular effects of alpha-difluoromethylornithine (DFMO), an inhibitor of ornithine decarboxylase (ODC), and N1,N8-bis(ethyl)spermidine (BES), an apparent regulator of the enzyme were compared in cultured L1210 cells. Unlike DFMO, BES has no direct inhibitory effect on ODC activity. Rather the polyamine analogue is believed, from previous studies, to behave similarly to exogenous spermidine in its ability to suppress intracellular ODC activity but not in its ability to perform functions required for cell growth. The kinetics and extent of growth inhibition by 30 microM or 100 microM BES and 1 mM DFMO were nearly identical as were their effects on macromolecular precursor incorporation with leucine being the first and most significantly affected. By flow cytometry, neither BES nor DFMO induced obvious perturbations in the cell cycle. Both compounds effectively eliminated ODC activity in treated cells and depleted putrescine and spermidine pools with very similar kinetics of decline. These close similarities in drug effects between BES and DFMO, an established polyamine inhibitor, support previous indications that BES induces growth inhibition by depletion of cellular polyamines. BES differed distinctly from the ODC inhibitor by decreasing spermine pools, and by not increasing S-adenosyl-methionine decarboxylase activity, S-adenosylmethionine pools, or stimulating cellular uptake of polyamines. The data suggest that enzyme regulation by polyamine analogues such as BES represents a viable alternative to enzyme inhibition as an antiproliferative strategy directed at polyamine biosynthesis.

Effects of the Vibrio cholerae siderophore vibriobactin on the growth characteristics of L1210 cells

The microbial iron chelator vibriobactin, N-[3-(2,3-dihydroxybenzamido)propyl]-1,3-bis[2-(2, 3-dihydroxyphenyl)-trans-5-methyl-2-oxazoline-4-carboxamido]-propane, is shown to inhibit the growth of L1210 cells in culture, with an IC50 value of 2 microM. Its biological activity is assigned to the ligand's ability to chelate iron as indicated by the disappearance of its antimitotic properties on iron chelate preformation or on O-methylation. The ligand is shown to have pronounced effects on cell cycle kinetics introducing a G1/S phase block. When treated cells are washed free of the ligand with fresh media they cascade into a high S phase in 5 hrs. Furthermore, after exposure of L1210 cells to vibriobactin (10 microM) for 5 hrs followed by removal of the drug, cells display different doubling times relative to untreated controls, with lower bromodeoxyuridine (BrdUrd) incorporation and no apparent cell death as shown by a 51Cr release assay. The effects on cell kinetics are consistent with inhibition of ribonucleotide reductase. Finally, vibriobactin is also shown to be active with a human Burkitt lymphoma cell line (Daudi).

Characterization of L1210 cell growth inhibition by the bacterial iron chelators parabactin and compound II

Microbial siderophores represent a class of iron chelators characterized by their high affinity (i.e., formation constants, greater than 10(40) M) for ferric iron. Previously, we demonstrated that the bacterial siderophores, N-[3-(2,3-dihydroxybenzamido)propyl]-N-[4-(2, 3-dihydroxybenzamino)butryl]-2-(2-hydroxyphenyl) trans-5-methyloxazoline-4-carboxamide (Parabactin) and N1,N8-bis(2,3-dihydroxybenzoyl)spermidine (Compound II), inhibit the growth of L1210 cells and the replication of DNA (but not RNA) viruses at low micromolar concentrations (Biochem. Biophys. Res. Commun., 121: 848-854, 1984). The basis for this antiproliferative effect on L1210 cells has now been investigated further. Onset of growth inhibition induced by 5 microM Parabactin occurs much earlier than with an equimolar concentration of Compound II but, once established by either chelator, inhibition appears to be irreversible. Growth inhibition was fully preventable with exogenous FeCl3 when given at the same time as the chelators. Flow cytometric analysis revealed a G1-S cycle block following treatment for 4 h with either 5 microM Parabactin or 30 microM Compound II. The block was readily reversed with exogenous FeCl3, allowing cells to progress to mid-S phase by 3 h and to G1 again by 9 h. Thereafter, cells accumulated at a second block located at S phase. The treatment conditions required for the initial cell cycle block (at 4 h) were adapted for subsequent studies. Clonogenicity of L1210 cells in soft agar following a 4-h exposure was reduced to 22% of control by 5 microM Parabactin and to 16% by 30 microM Compound II. Neither growth inhibition in suspension culture nor decreased clonogenicity in soft agar could be reversed with exogenous iron, following treatment with the chelators. Both chelators caused an early and significant decrease in [14C]thymidine incorporation over the 4-h period (50% inhibitory concentration at 4 h, 0.4 microM for Parabactin and 6.0 microM for Compound II). [3H]Uridine incorporation was inhibited later than [14C]thymidine and to a much lesser extent, while [3H]leucine incorporation was not significantly affected. Treatment of cells with 5 microM Parabactin or Compound II for 4 h decreased deoxy-adenosine triphosphate pools by 38 and 70%, respectively, and increased deoxythymidine triphosphate pools by 67 and 36%, respectively, suggesting interference with ribonucleotide reductase. Indeed, extracts of cells treated for 4 h with either 5 microM Parabactin or 30 microM Compound II exhibit a 97 to 98% decrease in cytidine-5'-diphosphate reductase activity compared to control, whereas DNA polymerase was elevated slightly.(ABSTRACT TRUNCATED AT 400 WORDS)

Mechanism and stereospecificity of the parabactin-mediated iron-transport system in Paracoccus denitrificans

The mechanism by which Paracoccus denitrificans utilizes parabactin in its iron-transport apparatus is examined. The cellular uptake of 55Fe-parabactin, its enantiomer, as well as a large number of its homologues and analogues are measured. Furthermore, the ability of these catecholamide ligands to stimulate microbial growth is also determined. The results of these studies point out several structural boundary conditions which the microorganism sets when utilizing iron chelates.

Biological properties of N4- and N1,N8-spermidine derivatives in cultured L1210 leukemia cells

Eleven novel spermidine (SPD) derivatives were synthesized as potential anticancer agents and evaluated for their ability to compete with [3H]SPD for cellular uptake, to inhibit cell growth, to affect polyamine biosynthesis, to suppress enzyme activity, and to substitute for SPD in supporting growth of cultured L1210 leukemia cells. The compounds included a series of N4-SPD derivatives (N4-methyl-SPD, N4-ethyl-SPD, N4-acetyl-SPD, N4-hexyl-SPD, N4-hexanoyl-SPD, N4-benzyl-SPD, and N4-benzoyl-SPD) and a series of N1,N8-SPD derivatives [N1,N8-bis(ethyl)-SPD, N1,N8-bis(acetyl)-SPD, N1,N8-bis(propyl)-SPD, and N1,N8-bis(propionyl)-SPD]. Uptake studies revealed N4-alkyl derivatives to be the most effective competitive inhibitors of [3H]SPD uptake (Ki, 26 to 43 microM) followed by N1,N8-alkyl derivatives (Ki, 71 to 115 microM), then N4-acyl derivatives (Ki, 115 to greater than 500 microM), and N1,N8-acyl derivatives (Ki, greater than 500 microM). The data indicate the relative importance of the terminal amines and of charge as determinants of cellular uptake. Of the 11 derivatives, only N4-hexyl-SPD, N1,N8-bis(ethyl)-SPD, and N1,N8-bis(propyl)-SPD demonstrated antiproliferative activity at 0.1 mM with 50%-inhibitory concentration values at 48 h of 30, 40, and 50 microM, respectively. In the case of the N1,N8-SPD derivatives, recovery from growth inhibition was enhanced considerably by exogenous SPD, suggesting involvement of polyamine depletion. At 10 to 30 microM, both N1,N8-bis(ethyl)-SPD and N1,N8-bis(propyl)-SPD (but not N4-hexyl-SPD) inhibited polyamine biosynthesis as indicated by significant reductions in polyamine pools and in biosynthetic enzyme activities. The more effective of the two, N1,N8-bis(ethyl)-SPD, depleted intracellular putrescine and SPD and reduced spermine by approximately 50% at 96 h and decreased ornithine and S-adenosylmethionine decarboxylase activities by 98 and 62%, respectively. Since neither derivative (at 5 mM) directly inhibited these enzymes from untreated cell extracts by significantly more than SPD itself, it is suspected that they act by regulating enzyme levels. As a measure of regulatory potential of the derivatives, ornithine decarboxylase was assayed in cells treated for 24 h and compared to the effects of 10 microM SPD which reduced the enzyme activity by 80%. None of the N4-SPD derivatives affected ornithine decarboxylase activity, while N1,N8-bis(ethyl)- and (propyl)-SPD were nearly as effective as SPD. Apparently, the central amine of the molecule is critical for regulatory function.(ABSTRACT TRUNCATED AT 400 WORDS)

Influence of iron on in vivo proliferation and lethality of L1210 cells

The ability of iron to stimulate the growth of L1210 cells both in DBA-2 mice and in cell culture is evaluated. Although in vitro stimulation is absent, in vivo studies clearly indicate higher numbers of tumor cells in the presence of supplemental iron. When mice were given iron i.p., at levels comparable to clinical doses for humans (24 mg/kg body weight), the tumor load recovered from their peritoneum was substantially greater than from controls without iron supplements. Furthermore, at higher levels of supplemental iron (250 mg Fe/kg body weight), the pretreated animals inoculated with L1210 cells died in 9.7 d whereas controls died in 12.2 d (i.e., 25% faster). As expected, the lower iron dose (24 mg/kg) also resulted in shorter life spans, although the effects were less striking. It is the belief of these authors that these data support the opinion that "anemia of chronic disease" associated with leukemia and possibly other malignancies may represent a host defense mechanism as has been postulated by others (1, 8).

Treatment with alpha-difluoromethylornithine plus a spermidine analog leads to spermine depletion and growth inhibition in cultured L1210 leukemia cells

Of the three biological polyamines, putrescine (Put), spermidine (Spd), and spermine (Spm), the relevance of Spm to cell proliferation has yet to be defined because of our general inability to deplete it selectively in intact cells. In the present study, Spm depletion was accomplished by treating cultured L1210 cells for 96 hr with alpha-difluoromethylornithine (DFMO) and an analog of Spd such as aminopropylcadaverine, N4-methylSpd, N4-ethylSpd, or homoSpd. DFMO, a specific inhibitor of ornithine decarboxylase, halts continued polyamine biosynthesis and the Spd analog serves as a functional substitute for Spd. Thus, while the Spd analog fulfills the role(s) of Spd in cell proliferation, Spm becomes steadily depleted. In cells treated with DFMO plus the analog, aminopropylcadaverine, Spm pools decline steadily and growth inhibition occus after 48 hr (when Spm pools decline to 60% of control). By 96 hr, Spm is approximately 15% of control and growth is less than 30%. Prevention studies with exogenous polyamines confirm a causal relationship between Spm depletion and growth inhibition. The critical levels of polyamines for cell proliferation to take place were found to be 30% of control for Spd and 60% for Spm. The use of DFMO plus a Spd analog is proposed as a system for studying the cellular consequences of Spm depletion. Spd depletion can be achieved for comparison purposes by treating cells with DFMO alone.

Antineoplastic and antiherpetic activity of spermidine catecholamide iron chelators

A series of iron chelating agents including the bacterial siderophores, parabactin and bis-N1,N8(2,3 dihydroxybenzoyl )spermidine, and four related compounds were synthesized and tested biologically. They were found: (a) to inhibit growth of cultured L1210 leukemia cells at IC50 values of 2-14 microM, (b) to inhibit replication of the DNA virus, herpes simplex type I, in monkey kidney cells at IC50 values of 0.4 microM ( parabactin ) to 55 microM, and (c) to be inactive against the RNA virus, vesicular stomatitis, at concentrations up to 1 mM. All effects were fully preventable by exogenous Fe (III). The activities correlated generally with the iron formation constants (10(36) to 10(48) moles/1) and more specifically with the lipophilicity of the compounds. The data suggest inhibition of DNA (but not RNA) synthesis by interference with the iron-containing enzyme, ribonucleotide reductase.

Aliphatic chain length specificity of the polyamine transport system in ascites L1210 leukemia cells

A series of diamine homologues of putrescine and triamine homologues of spermidine was used to determine the structural specificity of the polyamine transport system in ascites L1210 leukemia cells by measuring their ability to compete with [3H]-putrescine, [3H]spermidine, or [3H]spermine for uptake. Transport specificity among the diamines (as indicated by K1 constants) was greatest for those having chain lengths similar to that of spermidine and least for those similar to putrescine. Among the triamines, transport specificity was greatest for those having an overall chain length similar to those of spermidine and spermine. The homologue competition profiles were relatively the same for [3H]putrescine, [3H]spermidine, or [3H]spermine, suggesting that all three polyamines utilize the same transport system. This was further substantiated by uptake kinetic plots which showed that the three polyamines were competitive inhibitors of one another. In terms of receptor specificity, the ranking order among the polyamines was as follows: spermine (apparent Km, 1.6 microM) greater than spermidine (apparent Km, 2.2 microM) greater than putrescine (apparent Km, 8.5 microM). This information should prove useful in designing anticancer agents which are intended to utilize this transport system.

Bacteriostatic and fungostatic action of catecholamide iron chelators

Iron starvation as a means of controlling the proliferation of microorganisms was evaluated in vitro with spermidine catecholamide iron chelators. The growth of Escherichia coli and Pseudomonas aeruginosa was sensitive only to (D,L)-parabactin, whereas the growth of Candida albicans and Staphylococcus aureus was sensitive to a variety of catecholamide chelators. The disappearance of catecholamide activity upon methylation of the catechol hydroxyls, as well as iron reversal experiments, strongly suggests that the mechanism by which these compounds suppress growth is dependent upon their ability to sequester iron.

Spermidine requirement for cell proliferation in eukaryotic cells: structural specificity and quantitation

Six structural homologs of spermidine and five of its precursor, putrescine, were studied for their ability to prevent cytostasis of cultured L1210 leukemia cells induced by alpha-difluoromethylornithine (DFMO), a specific inhibitor of putrescine biosynthesis. High-performance liquid chromatography and competition studies with spermidine indicated that the homologs, which vary in the length of the carbon chain separating the amines, penetrated the cells. The structural specificity of the spermidine carrier was defined. Three of the six spermidine homologs supported cell growth during a 48-hour incubation in the presence of DFMO, indicating that a two-carbon extension of spermidine structure was tolerated for biological function. Two of the five putrescine homologs supported growth after being converted by the cells to their respective spermidine homologs. The central nitrogen of spermidine appears to be essential for function since diamines of chain length comparable to that of spermidine did not prevent DFMO cytostasis. No more than 15 percent of the spermidine normally present in L1210 cells was required for cell proliferation in the presence of DFMO.