Different cell cycle kinetic effects of N 1,N 11-diethylnorspermine-induced polyamine depletion in four human breast cancer cell lines

Anti-cancer stem cell activity of a sesquiterpene lactone isolated from Ambrosia arborescens and of a synthetic derivative

New regimens are constantly being pursued in cancer treatment, especially in the context of treatment-resistant cancer stem cells (CSCs) that are assumed to be involved in cancer recurrence. Here, we investigated the anti-cancer activity of sesquiterpene lactones (SLs) isolated from Ambrosia arborescens and of synthetic derivatives in breast cancer cell lines, with a specific focus on activity against CSCs. The breast cancer cell lines MCF-7, JIMT-1, and HCC1937 and the normal-like breast epithelial cell line MCF-10A were treated with the SLs damsin and coronopilin, isolated from A. arborescens, and with ambrosin and dindol-01, synthesized using damsin. Inhibitory concentration 50 (IC₅₀) values were obtained from dose-response curves. Based on IC₅₀ values, doses in the μM range were used for investigating effects on cell proliferation, cell cycle phase distribution, cell death, micronuclei formation, and cell migration. Western blot analysis was used to investigate proteins involved in cell cycle regulation as well as in the NF-κB pathway since SLs have been shown to inhibit this transcription factor. Specific CSC effects were investigated using three CSC assays. All compounds inhibited cell proliferation; however, damsin and ambrosin were toxic at single-digit micromolar ranges, while higher concentrations were required for coronopilin and dindol-01. Of the four cell lines, the compounds had the least effect on the normal-like MCF-10A cells. The inhibition of cell proliferation can partly be explained by downregulation of cyclin-dependent kinase 2. All compounds inhibited tumour necrosis factor-α-induced translocation of NF-κB from the cytoplasm to the nucleus. Damsin and ambrosin treatment increased the number of micronuclei; moreover, another sign of DNA damage was the increased level of p53. Treatment with damsin and ambrosin decreased the CSC subpopulation and inhibited cell migration. Our results suggest that these compounds should be further investigated to find efficient CSC-inhibiting compounds.

Spiro-bicyclo[2.2.2]octane derivatives as paclitaxel mimetics. Synthesis and toxicity evaluation in breast cancer cell lines

Paclitaxel is one of the most important anti-cancer agents introduced during the last 20 years. However, the use of paclitaxel is limited by undesirable side effects as well as the development of drug resistance. Here, we report a synthetic strategy towards spiro-bicyclo[2.2.2]octane derivatives, which includes double Michael addition and ring-closing metathesis as key synthetic steps. This strategy was used to synthesize a series of spiro-bicyclic compounds designed to be paclitaxel mimetics, which were evaluated in human breast-derived cell lines. One of these paclitaxel mimetics showed toxicity, although at higher concentrations than paclitaxel itself. In addition, two other spiro-bicyclic compounds, lacking the paclitaxel side chain, showed toxicity.

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.

Polyamine pathway inhibition as a novel therapeutic approach to treating neuroblastoma

Polyamines are highly regulated essential cations that are elevated in rapidly proliferating tissues, including diverse cancers. Expression analyses in neuroblastomas suggest that up-regulation of polyamine pro-synthetic enzymes and down-regulation of catabolic enzymes is associated with poor prognosis. Polyamine sufficiency may be required for MYCN oncogenicity in MYCN amplified neuroblastoma, and targeting polyamine homeostasis may therefore provide an attractive therapeutic approach. ODC1, an oncogenic MYCN target, is rate-limiting for polyamine synthesis, and is overexpressed in many cancers including neuroblastoma. Inhibition of ODC1 by difluoromethylornithine (DFMO) decreased tumor penetrance in TH-MYCN mice treated pre-emptively, and extended survival and synergized with chemotherapy in treating established tumors in both TH-MYCN and xenograft models. Efforts to augment DFMO activity, or otherwise maximally reduce polyamine levels, are focused on antagonizing polyamine uptake or augmenting polyamine export or catabolism. Since polyamine inhibition appears to be clinically well tolerated, these approaches, particularly when combined with chemotherapy, have great potential for improving neuroblastoma outcome in both MYCN amplified and non-MYCN amplified neuroblastomas.

Silencing of the polyamine catabolic key enzyme SSAT prevents CDK inhibitor-induced apoptosis in Caco-2 colon cancer cells

Roscovitine and purvalanol are purine derivative cyclin-dependent kinase (CDK) inhibitors that induce apoptosis in various types of cancer cells. However, their impact on the apoptotic cell death mechanism requires further elucidation. Natural polyamines putrescine, spermidine and spermine play essential roles in the regulation of cell growth and proliferation. Increased levels of polyamines in cells are considered to be involved in cancer progression. Intracellular polyamine levels are under the control of several catabolic enzymes, such as spermidine/spermine-N-acetyl transferase (SSAT), acetylpolyamine oxidase (APAO) and spermine oxidase (SMO), which could be altered by several therapeutic drugs. However, the possible role of polyamines in drug-induced apoptosis has yet to be clarified. In the present study, our aim was to determine the modulation of the polyamine catabolic pathway related to CDK inhibitor-induced apoptosis in Caco-2 cells. We found that roscovitine and purvalanol (each 20 μM) induced apoptosis by activating caspase-9 and -3, and inhibiting the mitochondrial membrane potential in Caco-2 cells. CDK inhibitors decreased the intracellular putrescine and spermine levels without affecting spermidine levels. Although both roscovitine and purvalanol induced SSAT expression, they did not exert a significant effect on the APAO expression profile. SSAT transient silencing prevented roscovitine-induced apoptosis compared to parental cells. Thus, we concluded that roscovitine and purvalanol significantly induce apoptosis in Caco-2 cells by modulating the polyamine catabolism, and that SSAT could be an important target in evaluating the potential role of polyamines in apoptotic cell death.

Novel anti-apoptotic effect of the retinoblastoma protein: implications for polyamine analogue toxicity

The retinoblastoma protein (pRb) pathway is frequently altered in breast cancer cells. pRb is involved in the regulation of cell proliferation and cell death. The breast cancer cell line L56Br-C1 does not express pRb and is extremely sensitive to treatment with the polyamine analogue N(1),N(11)-diethylnorspermine (DENSPM) which causes apoptosis. Polyamines are essential for the regulation of cell proliferation, cell differentiation and cell death. DENSPM depletes cells of polyamines, e.g., by inducing the activity of the polyamine catabolic enzyme spermidine/spermine N(1)-acetyltransferase (SSAT). In this study, L56Br-C1 cells were transfected with human pRb-cDNA. Overexpression of pRb inhibited DENSPM-induced cell death and DENSPM-induced SSAT activity. This suggests that the pRb protein level is a promising marker for polyamine depletion sensitivity and that there is a connection between pRb and the regulation of SSAT activity. We also show that SSAT protein levels and SSAT activity do not always correlate, suggesting that there is an unknown regulation of SSAT.

A systems analysis of the chemosensitivity of breast cancer cells to the polyamine analogue PG-11047

BACKGROUND

Polyamines regulate important cellular functions and polyamine dysregulation frequently occurs in cancer. The objective of this study was to use a systems approach to study the relative effects of PG-11047, a polyamine analogue, across breast cancer cells derived from different patients and to identify genetic markers associated with differential cytotoxicity.

METHODS

A panel of 48 breast cell lines that mirror many transcriptional and genomic features present in primary human breast tumours were used to study the antiproliferative activity of PG-11047. Sensitive cell lines were further examined for cell cycle distribution and apoptotic response. Cell line responses, quantified by the GI50 (dose required for 50% relative growth inhibition) were correlated with the omic profiles of the cell lines to identify markers that predict response and cellular functions associated with drug sensitivity.

RESULTS

The concentrations of PG-11047 needed to inhibit growth of members of the panel of breast cell lines varied over a wide range, with basal-like cell lines being inhibited at lower concentrations than the luminal cell lines. Sensitive cell lines showed a significant decrease in S phase fraction at doses that produced little apoptosis. Correlation of the GI50 values with the omic profiles of the cell lines identified genomic, transcriptional and proteomic variables associated with response.

CONCLUSIONS

A 13-gene transcriptional marker set was developed as a predictor of response to PG-11047 that warrants clinical evaluation. Analyses of the pathways, networks and genes associated with response to PG-11047 suggest that response may be influenced by interferon signalling and differential inhibition of aspects of motility and epithelial to mesenchymal transition.

Cells and polyamines do it cyclically

Cell-cycle progression is a one-way journey where the cell grows in size to be able to divide into two equally sized daughter cells. The cell cycle is divided into distinct consecutive phases defined as G(1) (first gap), S (synthesis), G(2) (second gap) and M (mitosis). A non-proliferating cell, which has retained the ability to enter the cell cycle when it receives appropriate signals, is in G(0) phase, and cycling cells that do not receive proper signals leave the cell cycle from G(1) into G(0). One of the major events of the cell cycle is the duplication of DNA during S-phase. A group of molecules that are important for proper cell-cycle progression is the polyamines. Polyamine biosynthesis occurs cyclically during the cell cycle with peaks in activity in conjunction with the G(1)/S transition and at the end of S-phase and during G(2)-phase. The negative regulator of polyamine biosynthesis, antizyme, shows an inverse activity compared with the polyamine biosynthetic activity. The levels of the polyamines, putrescine, spermidine and spermine, double during the cell cycle and show a certain degree of cyclic variation in accordance with the biosynthetic activity. When cells in G(0)/G(1) -phase are seeded in the presence of compounds that prevent the cell-cycle-related increases in the polyamine pools, the S-phase of the first cell cycle is prolonged, whereas the other phases are initially unaffected. The results point to an important role for polyamines with regard to the ability of the cell to attain optimal rates of DNA replication.

Polyamine depletion with two different polyamine analogues causes DNA damage in human breast cancer cell lines

It is well known that the positively charged polyamines have a DNA-stabilizing function and that polyamine depletion alters chromatin function. We have previously shown that polyamine depletion causes an S phase prolongation, and others have shown that there is an accumulation of Okazaki-like fragments in polyamine-depleted cells. In the present study, we have used the comet assay to investigate polyamine depletion-induced DNA strand breaks. Three breast cancer cell lines and one normal-like breast cell line were treated with the polyamine analogue N(1),N(11)-diethylnorspermine or with the polyamine biosynthesis inhibitor 4-amidinoindan-1-one 2'-amidinohydrazone (CGP 48664). The comet assay showed that polyamine depletion resulted in DNA strand breaks. We also show that these DNA strand breaks occurred in cells where there was no expression of gamma-H2AX, which is a marker of DNA double-strand breaks. Thus, our conclusion is that polyamine depletion causes DNA single-strand breaks, which may be the cause for the observed delay in S phase progression.

Effect of polyamine deficiency on proteins involved in Okazaki fragment maturation

Polyamine depletion causes S phase prolongation, and earlier studies indicate that the elongation step of DNA replication is affected. This led us to investigate the effects of polyamine depletion on enzymes crucial for Okazaki fragment maturation in the two breast cancer cell lines MCF-7 and L56Br-C1. In MCF-7 cells, treatment with N(1),N(11)-diethylnorspermine (DENSPM) causes S phase prolongation. In L56Br-C1 cells the prolongation is followed by massive apoptosis. In the present study we show that L56Br-C1 cells have substantially lower basal expressions of two Okazaki fragment maturation key proteins, DNA ligase I and FEN1, than MCF-7 cells. Thus, these two proteins might be promising markers for prediction of polyamine depletion sensitivity, something that can be useful for cancer treatment with polyamine analogues. DENSPM treatment affects the cellular distribution of FEN1 in L56Br-C1 cells, but not in MCF-7 cells, implying that FEN1 is affected by or involved in DENSPM-induced apoptosis.