Abnormal DNA synthesis in polyamine deficient cells revealed by bromodeoxyuridine-flow cytometry technique

Acrylamide affects proliferation and differentiation of the neural progenitor cell line C17.2 and the neuroblastoma cell line SH-SY5Y

Acrylamide is a well-known neurotoxic compound and people get exposed to the compound by food consumption and environmental pollutants. Since acrylamide crosses the placenta barrier, the fetus is also being exposed resulting in a risk for developmental neurotoxicity. In this study, the neural progenitor cell line C17.2 and the neuroblastoma cell line SH-SY5Y were used to study proliferation and differentiation as alerting indicators for developmental neurotoxicity. For both cell lines, acrylamide reduced the number of viable cells by reducing proliferation and inducing cell death in undifferentiated cells. Acrylamide concentrations starting at 10fM attenuated the differentiation process in SH-SY5Y cells by sustaining cell proliferation and neurite outgrowth was reduced at concentrations from 10pM. Acrylamide significantly reduced the number of neurons starting at 1μM and altered the ratio between the different phenotypes in differentiating C17.2 cell cultures. Ten micromolar of acrylamide also reduced the expression of the neuronal and astrocyte biomarkers. Although the neurotoxic concentrations in the femtomolar range seem to be specific for the SH-SY5Y cell line, the fact that micromolar concentrations of acrylamide seem to attenuate the differentiation process in both cell lines raises the interest to further investigations on the possible developmental neurotoxicity of acrylamide.

Norspermidine and novel Pd(II) and Pt(II) polynuclear complexes of norspermidine as potential antineoplastic agents against breast cancer

Background

New strategies are needed for breast cancer treatment and one initial step is to test new chemotherapeutic drugs in breast cancer cell lines, to choose candidates for further studies towards clinical use.

Methodology and Findings

The cytotoxic effects of a biogenic polyamine analogue – norspermidine – and its trinuclear Pd(II) and Pt(II) complexes – Pd₃NSpd₂ and Pt₃NSpd₂, respectively – were investigated in one immortalized normal-like and three breast cancer cell lines. The normal-like MCF-10A cells were least sensitive to the compounds, while growth inhibition and cell death was observed in the cancer cell lines. Norspermidine and its Pd(II) complex were generally shown to have stronger antiproliferative effects than the corresponding Pt(II) complex. Moreover, both norspermidine and the Pd(II) complex reduced the cellular activity of the growth-related enzyme, ornithine decarboxylase (ODC) to a lower level than the Pt(II) complex in most of the cell lines examined. Treatment with norspermidine or the Pd(II) complex reduced the number of colonies formed in a soft agar assay performed with the breast cancer cell lines, indicating that these compounds reduced the malignancy of the breast cancer cells. The effect of norspermidine or the Pd(II) complex on colony formation was much stronger than that observed for the Pt(II) complex. The results from a new mammalian genotoxicity screen together with those of a single cell gel electrophoresis assay indicated that none of the drugs were genotoxic at a 25 µM concentration.

Main Conclusions

Overall, norspermidine and its Pd(II) complex were shown to have strong antiproliferative effects. In comparison, the effects obtained with the Pd(II) complex were much stronger than that of the Pt(II) complex. The results obtained in the present study demonstrate that the trinuclear Pd(II) complex of norspermidine (Pd₃NSpd₂) may be regarded as a potential new metal-based drug against breast cancer, coupling a significant efficiency to a low toxicity.

Importance of polyamines in cell cycle kinetics as studied in a transgenic system

Polyamines are organic cations, which are considered essential for normal cell cycle progression. This view is based on results from numerous studies using a variety of enzyme inhibitors or polyamine analogues interfering with either the metabolism or the physiological functions of the polyamines. However, the presence of non-specific effects may be hard to rule out in such studies. In the present study, we have for the first time used a transgenic cell system to analyze the importance of polyamines in cell growth. We have earlier shown that expression of trypanosomal ODC in an ODC-deficient variant of CHO cells (C55.7) supported growth of these otherwise polyamine auxotrophic cells. However, one of the transgenic cell lines grew much slower than the others. As shown in the present study, the level of ODC activity was much lower in these cells, and that was reflected in a reduction of cellular polyamine levels. Analysis of cell cycle kinetics revealed that reduction of growth was correlated to prolongation of the G1, S, and G2+M phases in the cells. Providing exogenous putrescine to the cells resulted in a normalization of polyamine levels as well as cell cycle kinetics indicating a causal relationship.

Rapid caspase-dependent cell death in cultured human breast cancer cells induced by the polyamine analogue N(1),N(11)-diethylnorspermine

The spermine analogue N(1),N(11)-diethylnorspermine (DENSPM) efficiently depletes the cellular pools of putrescine, spermidine and spermine by down-regulating the activity of the polyamine biosynthetic enzymes and up-regulating the activity of the catabolic enzyme spermidine/ spermine N(1)-acetyltransferase (SSAT). In the breast cancer cell line L56Br-C1, treatment with 10 microm DENSPM induced SSAT activity 60 and 240-fold at 24 and 48 h after seeding, respectively, which resulted in polyamine depletion. Cell proliferation appeared to be totally inhibited and within 48 h of treatment, there was an extensive apoptotic response. Fifty percent of the cells were found in the sub-G(1) region, as determined by flow cytometry, and the presence of apoptotic nuclei was morphologically assessed by fluorescence microscopy. Caspase-3 and caspase-9 activities were significantly elevated 24 h after seeding. At 48 h after seeding, caspase-3 and caspase-9 activities were further elevated and at this time point a significant activation of caspase-8 was also found. The DENSPM-induced cell death was dependent on the activation of the caspases as it was inhibited by the general caspase inhibitor Z-Val-Ala-Asp fluoromethyl ketone. The results are discussed in the light of the L56Br-C1 cells containing mutated BRCA1 and p53, two genes involved in DNA repair.

Different roles of spermine in glucocorticoid- and Fas-induced apoptosis

Two experimental systems representative of the mitochondrial and death receptor apoptotic pathways are the dexamethasone-induced programmed cell death in mouse thymocytes and the antibody-mediated cross-ligation of the Fas receptor in the human leukemic T-cell line Jurkat, respectively. In both cell systems, caspase-9, -8, and -3 were activated upon induction of apoptosis and a sub-G(1) peak appeared as a sign of ongoing DNA fragmentation. Addition of 1 mM spermine together with dexamethasone inhibited caspase activation and the appearance of the sub-G(1) peak in mouse thymocytes. In contrast, Fas-induced cell death was totally unaffected by spermine addition. Spermine addition significantly elevated the spermine concentration in both thymocytes and Jurkat cells. Thus, spermine per se did not inhibit the caspases but rather their activation. The fact that spermine inhibited caspase activation only in the thymocytes implies that spermine inhibited dexamethasone-induced apoptosis upstream of caspase-9 activation.

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.

Treatment of cells with the polyamine analog N, N11-diethylnorspermine retards S phase progression within one cell cycle

When Chinese hamster ovary cells were seeded in the presence of the spermine analog N1,N11-diethylnorspermine (DENSPM), cell proliferation ceased; this was clearly apparent by cell counting 2 days after seeding the cells. However, 1 day after seeding there was a slight difference in cell number between control and DENSPM-treated cultures. To investigate the reason for this easily surpassed slight difference, we used a sensitive bromodeoxyuridine/flow cytometry method. Cell cycle kinetics were studied during the first cell cycle after seeding cells in the absence or presence of DENSPM. Our results show that DENSPM treatment did not affect the progression of the cells through G1 or the first G1/S transition that took place after seeding the cells. The first cell cycle effect was a delay in S phase as shown by an increase in the DNA synthesis time. The following G2/M transition was not affected by DENSPM treatment. DENSPM treatment inhibited the transient increases in putrescine, spermidine, and spermine pools that took place within 24 h after seeding. Thus, in conclusion, the first cell cycle phase affected by the inhibition of polyamine biosynthesis caused by DENSPM was the S phase. Prolongation of the other cell cycle phases occurred at later time points, and the G1 phase was affected before the G2/M phase.

The organization of replicon clusters is not affected by polyamine depletion

Earlier investigations have shown that polyamine depletion affects DNA replication negatively. DNA is synthesized in replicons which are gathered in replicon clusters. DNA replication is initiated simultaneously in every replicon of a replicon cluster. By pulse labeling cells with the thymidine analog bromodeoxyuridine and then detecting bromodeoxyuridine in situ with immunofluorescence, replicon clusters can be studied. We have used this method to investigate the effects of 2-difluoromethylornithine (DFMO)- and 4-amidinoindan-1-one 2'-amidinohydrazone (CGP 48664)-mediated polyamine depletion on the organization of replicon clusters. The cells were studied by fluorescence microscopy and confocal laser scanning microscopy. Our studies give at hand that neither the number nor the distribution of replicon clusters were affected even after 4 days of treatment with 5 mM DFMO or 20 microM CGP 48664, indicating that polyamine depletion did not affect the organization of replicon clusters. However, the fluorescence intensity of the replicon clusters was much lower in inhibitor-treated cells. The results indicate that the impaired DNA replication observed in polyamine-depleted cells is not due to an effect on the initiation step of DNA replication, but rather on the elongation process. To confirm that it is possible to observe changes in the organization of replicon clusters using bromodeoxyuridine, we treated the cells with various drugs that affect DNA replication. Aphidicolin, which inhibits DNA elongation, gave results similar to those of DFMO and CGP 48664.

Ordered cell cycle phase perturbations in Chinese hamster ovary cells treated with an S-adenosylmethionine decarboxylase inhibitor

The polyamines putrescine, spermidine, and spermine are needed for normal cell cycle progression and polyamine-depleted cells cease to proliferate. We have investigated cell cycle perturbations in Chinese hamster ovary cells seeded in the presence of 4-amidinoindan-1-one 2'-amidinohydrazone (CGP 48664), a potent inhibitor of S-adenosylmethionine decarboxylase, an enzyme which is essential for the synthesis of spermidine and spermine. At 9 h and at 1, 2, and 3 days after seeding, cells were labelled with the thymidine analog bromodeoxyuridine (BrdUrd) for 30 min, after which the BrdUrd-containing medium was removed and the cells were allowed to progress through the cell cycle in BrdUrd-free medium before sampling (post-labelling time). Using flow cytometry, coupled with an indirect immunofluorenscence technique, utilizing monoclonal anti-BrdUrd and secondary fluorescein-isothiocyanate-conjugated antibodies, and the DNA stain propidium iodide, cellular BrdUrd and DNA contents were quantified. By investigating the movement of BrdUrd-nonlabelled G1 cells into S phase during the post-labelling time, a measure of the G1/S transition was obtained. The time of appearence in G1 of BrdUrd-labelled cells which had divided was used to monitor the length of the G2+M phase. A measure of the S phase length (DNA synthesis time) was obtained by monitoring the progression of BrdUrd-labelled cells through S phase. CGP 48664-induced spermine depletion significantly increased the length of the S phase already 9 h after seeding cells in the presence of the inhibitor. No effects on the G1/S transition or on the length of the G2+M phase were observed until 2 days after seeding.

Normal G1/S transition and prolonged S phase within one cell cycle after seeding cells in the presence of an ornithine decarboxylase inhibitor

We have previously found that DNA replication was affected within one cell cycle after seeding Chinese hamster ovary (CHO) cells in the presence of the polyamine biosynthesis inhibitor 2-difluoromethylornithine (DFMO). We could, however, not rule out if this was due to an effect on the G1/S transition and/or on DNA synthesis elongation. In the present paper, we use a bromodeoxyuridine- flow cytometric method to more specifically study the G1/S transition, the S phase length, and the progression of cells from S phase through G2+M and into G1, after seeding plateau phase CHO cells at low density in the absence or presence of 5 mM DFMO. We report here that DFMO-induced polyamine depletion increased the length of the S phase within one cell cycle after seeding of CHO cells in the presence of the inhibitor. No effect on the G1/S transition was observed until 2 days after seeding, suggesting that a DFMO-induced lengthening of the G1 phase occurred later than the effect on S phase progression. These results imply that the G2+M phase was not prolonged until 2 days after seeding CHO cells in the presence of DFMO.

Impairment of DNA replication within one cell cycle after seeding of cells in the presence of a polyamine-biosynthesis inhibitor

Chinese hamster ovary (CHO) cells in the plateau phase were seeded in the absence or presence of 5 mM 2-difluoromethylornithine (F2MeOrn), an enzyme-activated irreversible inhibitor of ornithine decarboxylase. The thymidine analogue bromodeoxyuridine (BrdUrd, 5 microM) was added to the culture medium 30 min before sampling of the cells, which occurred 1-17 h after seeding. Using flow cytometry, coupled with an indirect immunofluorescence technique, which utilized monoclonal BrdUrd and secondary fluorescein-isothiocyanate-conjugated antibodies, and the DNA stain propidium iodide, cellular BrdUrd and DNA contents were quantified. To determine if there was a perturbation in the progression of cells through the S phase, the distribution of BrdUrd-labelled cells in the S phase was evaluated in two ways: (a) by calculating the mean DNA content of BrdUrd-labelled cells in relation to the mean DNA contents of G1 and G2 cells (relative movementzero) and (b) by studying DNA histograms of BrdUrd-labelled cells. By using both evaluation methods, we show that DNA replication was impaired during the first cell cycle that was initiated after seeding CHO cells in the presence of F2MeOrn. The cells appeared to enter the S phase normally but were then delayed in their progression through this phase. The impairment of F2MeOrn treatment on DNA replication was apparent at 9 h after seeding, a time point at which the putrescine pool was depleted, the spermidine pool was approximately halved, and the spermine pool was unaffected, when compared to corresponding pools of control cells. When cells were seeded in the presence of F2MeOrn and putrescine, the effect on DNA replication was prevented. The rates of incorporation of [3H]uridine and [3H]leucine into RNA and protein, respectively, were the same in control and in F2MeOrn-treated cells for at least up to 11 h after seeding.

Effects of N1-guanyl-1,7-diaminoheptane, an inhibitor of deoxyhypusine synthase, on the growth of tumorigenic cell lines in culture

N1-guanyl-1,7-diaminoheptane (GC7) is a potent inhibitor of deoxyhypusine synthase (DHS), the enzyme that catalyzes the first step in the hypusination of eukaryotic translation initiation factor 5A (eIF-5A). Since eIF-5A is the only known cellular substrate for DHS and GC7 has been reported to block the proliferation of CHO cells, it has been suggested that DHS may be a novel target for anti-cancer therapy. In the present study we investigated the antiproliferative effect of GC7 on several tumorigenic cell lines under various growth conditions. We found that this compound inhibits the proliferation of H9 cells in suspension culture and the growth of HeLa cells and v-src-transformed NIH3T3 cells under both anchorage-dependent and anchorage-independent conditions. Moreover, studies with NIH3T3 cells and v-src-transformed NIH3T3 cells show that GC7 inhibits the growth of both cell lines in monolayer culture with similar potency and could not reverse the transformed phenotype. In addition, the v-src-transformed cells grown under both anchorage-dependent and anchorage-independent conditions showed similar sensitivity toward GC7. These data indicate that GC7 acts as a general antiproliferative agent and does not appear to preferentially target tumorigenic cell types. Cell cycle analysis show that GC7 reduces the CHO-K1 cell population in the G1-phase of the cell cycle by 42% and increases the number of cells in the S-phase by 44%. This cell cycle distribution profile strikingly resembles the distribution of cells treated with puromycin. This result supports the hypothesis that the synthesis of a subset of proteins important for the S-phase progression of CHO-K1 cells might be dependent upon hypusinated eIF-5A. Thus the antiproliferative effect of GC7 appears to be related to its interference with the progression of cell cycle, which also provides a possible explanation for the lack of selectivity of GC7 between nontransformed and transformed cell types tested in this study.