Effects of diethyl spermine analogues in human bladder cancer cell lines in culture

Inhibition of autophagy enhances DENSpm-induced apoptosis in human colon cancer cells in a p53 independent manner

PURPOSE

One of the recently developed polyamine (PA) analogues, N ¹ ,N¹¹-diethylnorspermine (DENSpm), has been found to act as an apoptotic inducer in melanoma, breast, prostate and colon cancer cells. Also, its potential to induce autophagy has been established. Unfolded protein responses and starvation of amino acids are known to trigger autophagy. As yet, however, the molecular mechanism underlying PA deficiency-induced autophagy is not fully clarified. Here, we aimed to determine the apoptotic effect of DENSpm after autophagy inhibition by 3-methyladenine (3-MA) or siRNA-mediated Beclin-1 silencing in colon cancer cells.

METHODS

The apoptotic effects of DENSpm after 3-MA treatment or Beclin-1 silencing were determined by PI and AnnexinV/PI staining in conjunction with flow cytometry. Intracellular PA levels were measured by HPLC, whereas autophagy and the expression profiles of PA key players were determined in HCT116, SW480 and HT29 colon cancer cells by Western blotting.

RESULTS

We found that DENSpm-induced autophagy was inhibited by 3-MA treatment and Beclin-1 silencing, and that apoptotic cell death was increased by PA depletion and spermidine/spermine N¹-acetyltransferase (SSAT) upregulation. We also found that autophagy inhibition led to DENSpm-induced apoptosis through Atg5 down-regulation, p62 degradation and LC3 lipidation in both HCT116 and SW480 cells. p53 deficiency did not alter the response of the colon cancer cells to DENSpm-induced apoptotic cell death under autophagy suppression conditions.

CONCLUSIONS

From our results we conclude that DENSpm-induced apoptotic cell death is increased when autophagy is inhibited by 3-MA or Beclin-1 siRNA through PA depletion and PA catabolic activation in colon cancer cells, regardless p53 mutation status.

Lack of functional p53 renders DENSpm-induced autophagy and apoptosis in time dependent manner in colon cancer cells

Polyamines (PAs), such as putrescine, spermidine and spermine, are alkyl-amines that are essential for cell growth, proliferation, differentiation and cancer progression in eukaryotic cells. A designed PA analogue; DENSpm, induces cell cycle arrest, inhibits proliferation and induces apoptosis in melanoma, breast, prostate, lung and colon cancer cells. Although the mechanism by which DENSpm induces apoptosis has been examined, the effect of DENSpm on autophagy has not been investigated yet. Therefore, in this study, our objective was to determine the role of p53 in the DENSpm-induced autophagy/apoptotic regulation in a time-dependent manner in colon cancer cells. Exposure of HCT 116 colon cancer cells to DENSpm decreased cell viability in a dose- and time-dependent manner. However, the p53 mutant, SW480, and deficient HCT 116 p53(-/-) cells were more resistant to DENSpm treatment compared to HCT 116 p53(+/+) cells. The resistant profile caused by p53 defect also caused a cell type-specific response to PA pool depletion and SSAT overexpression. In addition to PA depletion, DENSpm induced apoptosis by activating the mitochondria-mediated pathway in a caspase-dependent manner regardless of p53 expression in colon cancer cells. Concomitantly, we determined that DENSpm also affected autophagy in HCT 116 p53(+/+), SW480 and HCT 116 p53(-/-) colon cancer cells for different periods of exposure to DENSpm. Therefore, this study revealed that effect of DENSpm on cell death differs due to p53 protein expression profile. In addition, DENSpm-induced autophagy may be critical in drug resistance in colon cancer cells.

Increased toxicity of a trinuclear Pt-compound in a human squamous carcinoma cell line by polyamine depletion

BACKGROUND

Mononuclear platinum anticancer agents hold a pivotal place in the treatment of many forms of cancers, however, there is a potential to improve response to evade resistance development and toxic side effects. BBR3464 is a promising trinuclear platinum anticancer agent, which is a polyamine mimic. The aim was to investigate the influence of polyamine pool reduction on the cytotoxic effects of the trinuclear platinum complex BBR3464 and cisplatin. Polyamine pool reduction was achieved by treating cells with either the polyamine biosynthesis inhibitor α-difluoromethylornithine (DFMO) or the polyamine analogue N1,N11-diethylnorspermine (DENSPM).

METHODS

A human squamous cell carcinoma cell line, LU-HNSCC-4, established from a primary head and neck tumour was used to evaluate cellular effects of each drug alone or combinations thereof. High-performance liquid-chromatography was used to quantify intracellular polyamine contents. Inductively coupled mass spectroscopy was used to quantify intracellular platinum uptake. Cells were exposed to DFMO or DENSPM during 48 h at concentrations ranging from 0 to 5 mM or 0 to 10 μM, respectively. Thereafter, non-treated and treated cells were exposed to cisplatin or BBR3464 during 1 h at concentrations ranging from 0 to 100 μM. A 96-well assay was used to determine cytotoxicity after five days after treatment.

RESULTS

The cytotoxic effect of BBR3464 on LU-HNSCC-4 cells was increased after cells were pre-treated with DENSPM or DFMO, and the interaction was found to be synergistic. In contrast, the interaction between cisplatin and DFMO or DENSPM was near-additive to antagonistic. The intracellular levels of the polyamines putrescine and spermidine were decreased after treatment with DFMO, and treatment with DENSPM resulted in an increase in putrescine level and concomitant decrease in spermidine and spermine levels. The uptake of BBR3464 was significantly increased after pre-treatment of the cells with DFMO, and varied dependent on the concentration of DENSPM. The uptake of cisplatin was unchanged.

CONCLUSIONS

Taken together, these results demonstrate that combinations of polyamine synthesis inhibitors with BBR3464 appear to be a promising approach to enhance the anticancer activity against HSCC.

Nuclear localization of human spermine oxidase isoforms - possible implications in drug response and disease etiology

The recent discovery of the direct oxidation of spermine via spermine oxidase (SMO) as a mechanism through which specific antitumor polyamine analogues exert their cytotoxic effects has fueled interest in the study of the polyamine catabolic pathway. A major byproduct of spermine oxidation is H2O2, a source of toxic reactive oxygen species. Recent targeted small interfering RNA studies have confirmed that SMO-produced reactive oxygen species are directly responsible for oxidative stress capable of inducing apoptosis and potentially mutagenic DNA damage. In the present study, we describe a second catalytically active splice variant protein of the human spermine oxidase gene, designated SMO5, which exhibits substrate specificities and affinities comparable to those of the originally identified human spermine oxidase-1, SMO/PAOh1, and, as such, is an additional source of H2O2. Importantly, overexpression of either of these SMO isoforms in NCI-H157 human non-small cell lung carcinoma cells resulted in significant localization of SMO protein in the nucleus, as determined by confocal microscopy. Furthermore, cell lines overexpressing either SMO/PAOh1 or SMO5 demonstrated increased spermine oxidation in the nucleus, with accompanying alterations in individual nuclear polyamine concentrations. This increased oxidation of spermine in the nucleus therefore increases the production of highly reactive H2O2 in close proximity to DNA, as well as decreases nuclear spermine levels, thus altering the protective roles of spermine in free radical scavenging and DNA shielding, and resulting in an overall increased potential for oxidative DNA damage in these cells. The results of these studies therefore have considerable significance both with respect to targeting polyamine oxidation as an antineoplastic strategy, and in regard to the potential role of spermine oxidase in inflammation-induced carcinogenesis.

Targeting polyamine metabolism and function in cancer and other hyperproliferative diseases

The polyamines spermidine and spermine and their diamine precursor putrescine are naturally occurring, polycationic alkylamines that are essential for eukaryotic cell growth. The requirement for and the metabolism of polyamines are frequently dysregulated in cancer and other hyperproliferative diseases, thus making polyamine function and metabolism attractive targets for therapeutic intervention. Recent advances in our understanding of polyamine function, metabolic regulation, and differences between normal cells and tumour cells with respect to polyamine biology, have reinforced the interest in this target-rich pathway for drug development.

Inhibition of cell proliferation and induction of apoptosis by N1,N11-diethylnorspermine-induced polyamine pool reduction

Reduction of cellular polyamine pools results in inhibition of cell proliferation and sometimes in induction of cell death. Reduction of cellular polyamine pools can be achieved by several strategies involving all the mechanisms of polyamine homoeostasis, i.e. biosynthesis, catabolism and transport across the cell membrane. In the present paper, we concentrate on results achieved using the polyamine analogue DENSPM (N1,N11-diethylnorspermine) on different cell lines. We discuss polyamine levels in DENSPM-treated cells in relation to effects on cell cycle kinetics and induction of apoptosis. To really understand the role of polyamines in cell cycle regulation and apoptosis, we believe it is now time to go through the vast polyamine literature in a meta-analysis-based manner. This short review does not claim to be such a study, but it is our hope to stimulate such studies in the polyamine field. Such work is especially important from the viewpoint of introducing drugs that affect polyamine homoeostasis in the treatment of various diseases such as cancer.

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.

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.