Antiproliferative and apoptotic effects of iron chelators on human cervical carcinoma cells

Persistent ferroptosis promotes cervical squamous intraepithelial lesion development and oncogenesis by regulating KRAS expression in patients with high risk-HPV infection

Cervical squamous cell carcinoma (CSCC) is a type of female cancer that affects millions of families worldwide. Human papillomavirus (HPV) infection is the main reason for CSCC formation, and squamous intraepithelial lesions (SILs) induced by high-risk HPV (HR-HPV) infection are considered precancerous lesions. A previous study reported that HPV-infected cancer cells were able to counteract lipid peroxidation for survival. Recent research has reported that ferroptosis acts in an iron-dependent lipid peroxidation manner to kill cancer cells, and it is proposed as a new approach for female cancer therapy. Here, we investigated the role of ferroptosis throughout SIL development into CSCC. We found that ferroptosis occurred in SIL, but anti-ferroptosis emerged in CSCC. Our data further indicated that an antiferroptotic effect was formed in response to persistent ferroptosis and then promoted oncogenesis. Altogether, we provide novel insight into ferroptosis in cervical SIL development and suggest a potential therapeutic target for the treatment of CSCC.

Toxicity of the iron siderophore mycobactin J in mouse macrophages: Evidence for a hypoxia response

Mycobacterium tuberculosis, the causative agent of tuberculosis, is an obligate intracellular pathogen that lives within the phagosome of macrophages. Here we demonstrate that the siderophore mycobactin J, produced by the closely related intracellular pathogen Mycobacterium paratuberculosis, is toxic to murine macrophage cells. Its median lethal dose, 10 μM, is lower than that of the iron chelators desferrioxamine B and TrenCAM, an enterobactin analog. To determine the source of this toxicity, we conducted microarray, ELISA, and metabolite profiling experiments. The primary response is hypoxia-like, which implies iron starvation as the underlying cause of the toxicity. This observation is consistent with our recent finding that mycobactin J is a stronger iron chelator than had been inferred from previous studies. Mycobactin J is known to partition into cell membranes and hydrophobic organelles indicating that enhanced membrane penetration is also a likely factor. Thus, mycobactin J is shown to be toxic, eliciting a hypoxia-like response under physiological conditions.

Iron-Sulfur Cluster Biogenesis as a Critical Target in Cancer

Cancer cells preferentially accumulate iron (Fe) relative to non-malignant cells; however, the underlying rationale remains elusive. Iron-sulfur (Fe-S) clusters are critical cofactors that aid in a wide variety of cellular functions (e.g., DNA metabolism and electron transport). In this article, we theorize that a differential need for Fe-S biogenesis in tumor versus non-malignant cells underlies the Fe-dependent cell growth demand of cancer cells to promote cell division and survival by promoting genomic stability via Fe-S containing DNA metabolic enzymes. In this review, we outline the complex Fe-S biogenesis process and its potential upregulation in cancer. We also discuss three therapeutic strategies to target Fe-S biogenesis: (i) redox manipulation, (ii) Fe chelation, and (iii) Fe mimicry.

Hydroxypyridinone-Based Iron Chelators with Broad-Ranging Biological Activities

Iron plays an essential role in all living cells because of its unique chemical properties. It is also the most abundant trace element in mammals. However, when iron is present in excess or inappropriately located, it becomes toxic. Excess iron can become involved in free radical formation, resulting in oxidative stress and cellular damage. Iron chelators are used to treat serious pathological disorders associated with systemic iron overload. Hydroxypyridinones stand out for their outstanding chelation properties, including high selectivity for Fe³⁺ in the biological environment, ease of derivatization, and good biocompatibility. Herein, we overview the potential for multifunctional hydroxypyridinone-based chelators to be used as therapeutic agents against a wide range of diseases associated either with systemic or local elevated iron levels.

Iron chelators in cancer therapy

Iron chelators have long been a target of interest as anticancer agents. Iron is an important cellular resource involved in cell replication, metabolism and growth. Iron metabolism is modulated in cancer cells reflecting their increased replicative demands. Originally, iron chelators were first developed for use in iron overload disorders, however, their potential as anticancer agents has been gaining increasing interest. This is due, in part, to the downstream effects of iron depletion such as the inhibition of proliferation through ribonucleotide reductase activity. Additionally, some chelators form redox active metal complexes with iron resulting in the production of reactive oxygen species and oxidative stress. Newer synthetic iron chelators such as Deferasirox, Triapine and di-2-pyridylketone-4,4,-dimethyl-3-thiosemicrbazone (Dp44mt) have improved pharmacokinetic properties over the older chelator Deferoxamine. This review examines and discusses the various iron chelators that have been trialled for cancer therapy including both preclinical and clinical studies. The successes and shortcomings of each of the chelators and their use in combination therapies are highlighted and future potential in the cancer therapy world is considered.

Five new complexes with deferiprone and N,N-donor ligands: evaluation of cytotoxicity against breast cancer MCF-7 cell line and HSA-binding determination

In this study, five new complexes containing deferiprone (dfp) and N,N-donor ligands [bipyridine (bpy), 1,10-phenanthroline (phen) and ethylenediamine (en)] were synthesized: [Fe(dfp)₂(bpy)](PF₆) (1), [Fe(dfp)₂(phen)](PF₆) (2), [Cu₂(dfp)₂(bpy)₂](PF₆)₂ (3), [Ga(dfp)₂(bpy)](PF₆) (4), and [Fe(dfp)₂(en)](PF₆) (5). Characterization of these complexes was carried out through elemental analysis and FT-IR, and single-crystal X-ray crystallography was used to determine their structures. Whilst the polyhedron has a distorted octahedral geometry in 1, 2, 4, and 5, it adopts a distorted square-pyramidal geometry in 3. Interaction of these compounds with human serum albumin (HSA) has been investigated through electronic absorption and fluorescence titration techniques. Emission quenching was performed separately for each complex at three different temperatures and thermodynamic parameters were calculated using binding constants to better understand the power of different binding forces with the HSA. Results demonstrated that compounds interact strongly with the HSA with a static quenching mechanism. Our evaluation of the cytotoxicity of complexes against the breast cancer MCF-7 cell line showed that complex 2 presents a better cytotoxicity than the standard cis-Pt. Finally, using the AutoDock 4.2 program, simulations to analyze the mechanism of complex-HSA interactions and their binding mode were carried out. Results showed that the best binding mode is located in subdomain IB for 1, 2, and 4, in I/II for 3, and in IA/IIA for 5. Communicated by Ramaswamy H. Sarma.

Linking Cancer Metabolic Dysfunction and Genetic Instability through the Lens of Iron Metabolism

Iron (Fe) is an essential element that plays a fundamental role in a wide range of cellular functions, including cellular proliferation, DNA synthesis, as well as DNA damage and repair. Because of these connections, iron has been strongly implicated in cancer development. Cancer cells frequently have changes in the expression of iron regulatory proteins. For example, cancer cells frequently upregulate transferrin (increasing uptake of iron) and down regulate ferroportin (decreasing efflux of intracellular iron). These changes increase the steady-state level of intracellular redox active iron, known as the labile iron pool (LIP). The LIP typically contains approximately 2% intracellular iron, which primarily exists as ferrous iron (Fe²⁺). The LIP can readily contribute to oxidative distress within the cell through Fe²⁺-dioxygen and Fenton chemistries, generating the highly reactive hydroxyl radical (HO^•). Due to the reactive nature of the LIP, it can contribute to increased DNA damage. Mitochondrial dysfunction in cancer cells results in increased steady-state levels of hydrogen peroxide and superoxide along with other downstream reactive oxygen species. The increased presence of H₂O₂ and O₂^•- can increase the LIP, contributing to increased mitochondrial uptake of iron as well as genetic instability. Thus, iron metabolism and labile iron pools may play a central role connecting the genetic mutational theories of cancer to the metabolic theories of cancer.

Role of iron in cancer development by viruses

Increased levels of iron in body are attributed to higher cancer risk. Given the fact that 16% of all human cancers are caused by viral infections, iron is suggested to play an important role in carcinogenesis particularly those induced by viral infections. The present study provides an updated summary of the literature and the plausible mechanisms of iron involvement in cancer development by viruses. Our understanding about the interplay between viral infections and iron in different settings particularly cancer development is yet to be improved as it may shed a new light in development of new therapeutic strategies.

Ironing out the role of the cyclin-dependent kinase inhibitor, p21 in cancer: Novel iron chelating agents to target p21 expression and activity

Iron (Fe) has become an important target for the development of anti-cancer therapeutics with a number of Fe chelators entering human clinical trials for advanced and resistant cancer. An important aspect of the activity of these compounds is their multiple molecular targets, including those that play roles in arresting the cell cycle, such as the cyclin-dependent kinase inhibitor, p21. At present, the exact mechanism by which Fe chelators regulate p21 expression remains unclear. However, recent studies indicate the ability of chelators to up-regulate p21 at the mRNA level was dependent on the chelator and cell-type investigated. Analysis of the p21 promoter identified that the Sp1-3-binding site played a significant role in the activation of p21 transcription by Fe chelators. Furthermore, there was increased Sp1/ER-α and Sp1/c-Jun complex formation in melanoma cells, suggesting these complexes were involved in p21 promoter activation. Elucidating the mechanisms involved in the regulation of p21 expression in response to Fe chelator treatment in neoplastic cells will further clarify how these agents achieve their anti-tumor activity. It will also enhance our understanding of the complex roles p21 may play in neoplastic cells and lead to the development of more effective and specific anti-cancer therapies.

Dysregulated lncRNA-UCA1 contributes to the progression of gastric cancer through regulation of the PI3K-Akt-mTOR signaling pathway

The long non-coding RNA (lncRNA) urothelial carcinoma-associated 1 (UCA1) has been recently shown to be dysregulated during disease occurrence and to play an important role in the progression of several cancers. However, the biological role and potential regulation mechanism of UCA1 in the carcinogenesis of gastric cancer remain unclear. In the present study, we found that UCA1 was aberrantly upregulated in gastric cancer tissues and gastric cancer cell lines, and was associated with TNM stage and metastasis. UCA1 silencing significantly inhibited gastric cancer BGC-823 cell proliferation and increased its apoptosis. We also found that UCA1 played an important role in the migration and invasion of gastric cancer cells in vitro and in vivo. The molecular mechanism of UCA1 suggested that UCA1 regulates the PI3K-Akt-mTOR signaling proteins and their downstream mediators, to alter gastric cancer progression in vitro and in vivo. Collectively, the results showed a pivotal role of UCA1 in the tumorigenesis of gastric cancer. In addition, the study characterized a novel lncRNA-mRNA regulatory network, which may lead to a better understanding of the pathogenesis of gastric cancer and assist in lncRNA-directed diagnosis and therapy for this malignancy.

Iron-responsive element-binding protein 2 plays an essential role in regulating prostate cancer cell growth

Iron-responsive element-binding proteins (IRPs) are master regulators of cellular iron homeostasis. Our previous work demonstrated that iron homeostasis is altered in prostate cancer and contributes to prostate cancer progression. Here we report that prostate cancer cells overexpress IRP2 and that overexpression of IRP2 drives the altered iron phenotype of prostate cancer cells. IRP2 knockdown in prostate cancer cell lines reduces intracellular iron and causes cell cycle inhibition and apoptosis. Cell cycle analysis demonstrates that IRP2-depleted prostate cancer cells accumulate in G0/G1 due to induction of p15, p21, and p27. Activation of these pathways is sufficient to significantly reduce the growth of PC3 prostate tumors in vivo. In contrast, IRP1 knockdown does not affect iron homeostasis and only modestly affects cell growth, likely through an iron-independent mechanism. These results demonstrate that upregulation of IRP2 in prostate cancer cells co-opts normal iron regulatory mechanisms to facilitate iron retention and drive enhanced tumor growth.

Deferiprone Enhances Temozolomide Cytotoxicity in Glioma Cells

Glioblastoma is the most malignant primary brain tumor with a median survival of 15 months. Temozolomide (TMZ) is the standard of care for these patients. Iron chelators have been shown to have anti-tumor activity; however, deferiprone (DFP), an orally administered iron chelator, has not been previously evaluated in gliomas. In the present study, we found that combination treatment in glioma cells with TMZ and DFP significantly reduced cell viability, produced cell cycle arrest at G2/M phase, and enhanced apoptosis. TMZ and DFP might be a potent new combination treatment for glioblastoma.

Iron chelator-induced apoptosis via the ER stress pathway in gastric cancer cells

Many reports have shown the anticancer effects of iron deficient on cancer cells, but the effects of iron-chelators on gastric cancer have not been clearly elucidated. Recently, we reported that iron chelators induced an antiproliferative effect in human malignant lymphoma and myeloid leukemia cells. In the present study, we investigated the antitumor activity of these two iron-chelating agents, deferoxamine (DFO) and deferasirox (DFX), with gastric cancer cell lines, and their apoptosis-inducing effects as the potential mechanism. We found that iron chelators displayed significant antiproliferative activity in human gastric cancer cell lines, which may be attributed to their induction of G1 phase arrest and apoptosis. We also found that iron chelators induced reactive oxygen species (ROS) production, resulting in the activation of both c-Jun N-terminal kinase (JNK) and endoplasmic reticulum (ER) stress apoptotic pathways in gastric cancer cells. Taken together, our data suggest that iron chelators induced apoptosis in gastric cancer, involving ROS formation ER stress and JNK activation.

Dietary administration of the probiotic SpPdp11: Effects on the intestinal microbiota and immune-related gene expression of farmed Solea senegalensis treated with oxytetracycline

Few antimicrobials are currently authorised in the aquaculture industry to treat infectious diseases. Among them, oxytetracycline (OTC) is one of the first-choice drugs for nearly all bacterial diseases. The objective of this study was to evaluate the effect of the dietary administration of OTC both alone and jointly with the probiotic Shewanella putrefaciens Pdp11 (SpPdp11) on the intestinal microbiota and hepatic expression of genes related to immunity in Senegalese sole (Solea senegalensis) juveniles. The results demonstrated that the richness and diversity of the intestinal microbiota of fish treated with OTC decreased compared with those of the control group but that these effects were lessened by the simultaneous administration of SpPdp11. In addition, specimens that received OTC and SpPdp11 jointly showed a decreased intensity of the Denaturing Gradient Gel Electrophoresis (DGGE) bands related to Vibrio genus and the presence of DGGE bands related to Lactobacillus and Shewanella genera. The relationship among the intestinal microbiota of fish fed with control and OTC diets and the expression of the NADPH oxidase and CASPASE-6 genes was demonstrated by a Principal Components Analysis (PCA) carried out in this study. In contrast, a close relationship between the transcription of genes, such as NKEF, IGF-β, HSP70 and GP96, and the DGGE bands of fish treated jointly with OTC and SpPdp11 was observed in the PCA study. In summary, the results obtained in this study demonstrate that the administration of OTC results in the up-regulation of genes related to apoptosis but that the joint administration of OTC and S. putrefaciens Pdp11 increases the transcription of genes related to antiapoptotic effects and oxidative stress regulation. Further, a clear relationship between these changes and those detected in the intestinal microbiota is established.

Inhibitory effect of iron withdrawal by chelation on the growth of human and murine mammary carcinoma and fibrosarcoma cells

Since iron uptake is essential for cell growth, rapidly dividing cancer cells are sensitive to iron depletion. To explore the effect of iron withdrawal on cancer cell growth, mouse and human mammary carcinoma cells (4T1 and MDA-MB-468, respectively) and mouse and human fibrosarcoma cells (L929 and HT1080, respectively) were cultured in the absence or presence of DIBI, a novel iron-chelating polymer containing hydroxypyridinone iron-ligand functionality. Cell growth was measured by a colorimetric assay for cell metabolic activity. DIBI-treated 4T1, MDA-MB-468, L929 and HT1080 cells, as well as their normal counterparts, showed a dose- and time-dependent reduction in growth that was selective for human cancer cells and mouse fibrosarcoma cells. The inhibitory effect of DIBI on fibrosarcoma and mammary carcinoma cell growth was reversed by addition of exogenous iron in the form of iron (III) citrate, confirming the iron selectivity of DIBI and that its inhibitory activity was iron-related. Fibrosarcoma and mammary carcinoma cell growth inhibition by DIBI was associated with S-phase cell cycle arrest and low to moderate levels of cell death by apoptosis. Consistent with apoptosis induction following DIBI-mediated iron withdrawal, fibrosarcoma and mammary carcinoma cells exhibited mitochondrial membrane permeabilization. A comparison of DIBI to other iron chelators showed that DIBI was superior to deferiprone and similar to or better than deferoxamine for inhibition of fibrosarcoma and mammary carcinoma cell growth. These findings suggest that iron withdrawal from the tumor microenvironment with a selective and potent iron chelator such as DIBI may prevent or inhibit tumor progression.

microRNAs' differential regulations mediate the progress of Human Papillomavirus (HPV)-induced Cervical Intraepithelial Neoplasia (CIN)

Background

microRNA (miRNA)’s direct regulation on target mRNA is affected by complex factors beyond miRNA. Therefore, at different stages during the course of carcinogenesis, miRNA may regulate different targets, which we termed ‘miRNA’s differential regulation’. HPV-induced cervical intraepithelial neoplasia (CIN) is an important pre-cancerous course ahead of cervical cancer formation. Currently, the molecular mechanisms of CIN progress remain poorly understood, and it is interesting to unravel this from the perspective of miRNA differential regulation.

Results

In this study, we performed transcriptome analysis of miRNAs and mRNAs for the totally 24 cervical samples in three stages (normal, CIN I, and CIN III) along CIN progress, and proposed the SIG++ algorithm to detect the miRNA — mRNA pairs with significant regulation change, and further proposed the definitions of Efficient Pair, Efficient Target, and Related Effector Biological Process, as the elemental steps to construct miRNA differential regulatory network. Finally, for the course of disease progressing from normal stage to CIN I stage, and for the course of disease progressing from CIN I stage to CIN III stage, miRNA differential regulatory networks were constructed, respectively, based on two distinct strategies: one is founded on the knowledge of human GO biological processes to detect Efficient Targets and Related Effector Biological Processes, the other is solely founded on literature review to detect the targets closely related to cervical carcinogenesis and instructive in revealing mechanisms that promote CIN development.

Conclusions

This study provided the conception of miRNA’s differential regulation, the algorithm for how to identify them during disease development, and the strategy for how to construct miRNA differential regulatory network with instructive biological meanings. The finally constructed networks provide clues for understanding CIN progress.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-015-0145-3) contains supplementary material, which is available to authorized users.

Restoring the secretory function of irradiation-damaged salivary gland by administrating deferoxamine in mice

OBJECTIVES

One of the major side effects of radiotherapy for treatments of the head and neck cancer is the radiation-induced dysfunction of salivary glands. The aim of the present study is to investigate the efficacy of deferoxamine (DFO) to restore the secretory function of radiation-damaged salivary glands in mice.

METHODS

DFO (50 mg/kg/d) was administered intraperitoneally in C57BL/6 mice for 3 days before and/or after point-fixed irradiation (18 Gy) of submandibular glands. The total 55 mice were randomly divided into: (1) Normal group: mice received no treatment (n = 5); (2) Irradiation group (IR): mice only received irradiation (n = 5); (3) Pre-DFO group (D+IR) (n = 10); (4) Pre+Post DFO group (D+IR+D) (n = 10); (5) Post-DFO group (IR+D) (n = 10); (6) For each DFO-treated group, the mice were intraperitoneally injected with 0.1 ml sterilized water alone (by which DFO was dissolved) for 3 days before and/or after irradiation, and served as control. Sham1: Pre-sterilized water group (n = 5); sham2: Pre+Post sterilized water group (n = 5); sham3: Post-sterilized water group (n = 5). The salivary flow rate (SFR) was assessed at 30th, 60th and 90th day after irradiation, respectively. After 90 days, all mice were sacrificed and their submandibular glands were removed for further examinations.

RESULTS

The salivary glands showed remarkable dysfunction and tissue damage after irradiation. DFO restored SFR in the irradiated glands to a level comparable to that in normal glands and angiogenesis in damaged tissue was greatly increased. DFO also increased the expression levels of HIF-1α and VEGF while reduced apoptotic cells. Furthermore, Sca-1+cells were preserved in the salivary glands treated with DFO before IR.

CONCLUSIONS

Our results indicate DFO could prevent the radiation-induced dysfunction of salivary glands in mice. The mechanism of this protective effect may involve increased angiogenesis, reduced apoptosis of acinar cells and more preserved stem cells.

Blocking eIF5A modification in cervical cancer cells alters the expression of cancer-related genes and suppresses cell proliferation

Cancer etiology is influenced by alterations in protein synthesis that are not fully understood. In this study, we took a novel approach to investigate the role of the eukaryotic translation initiation factor eIF5A in human cervical cancers, where it is widely overexpressed. eIF5A contains the distinctive amino acid hypusine, which is formed by a posttranslational modification event requiring deoxyhypusine hydroxylase (DOHH), an enzyme that can be inhibited by the drugs ciclopirox and deferiprone. We found that proliferation of cervical cancer cells can be blocked by DOHH inhibition with either of these pharmacologic agents, as well as by RNA interference-mediated silencing of eIF5A, DOHH, or another enzyme in the hypusine pathway. Proteomic and RNA analyses in HeLa cervical cancer cells identified two groups of proteins in addition to eIF5A that were coordinately affected by ciclopirox and deferiprone. Group 1 proteins (Hsp27, NM23, and DJ-1) were downregulated at the translational level, whereas group 2 proteins (TrpRS and PRDX2) were upregulated at the mRNA level. Further investigations confirmed that eIF5A and DOHH are required for Hsp27 expression in cervical cancer cells and for regulation of its key target IκB and hence NF-κB. Our results argue that mature eIF5A controls a translational network of cancer-driving genes, termed the eIF5A regulon, at the levels of mRNA abundance and translation. In coordinating cell proliferation, the eIF5A regulon can be modulated by drugs such as ciclopirox or deferiprone, which might be repositioned to control cancer cell growth.

Iron chelation in the treatment of cancer: a new role for deferasirox?

Iron plays a crucial role in a number of metabolic pathways including oxygen transport, DNA synthesis, and ATP generation. Although insufficient systemic iron can result in physical impairment, excess iron has also been implicated in a number of diseases including ischemic heart disease, diabetes, and cancer. Iron chelators are agents which bind iron and facilitate its excretion. Experimental iron chelators have demonstrated potent anti-neoplastic properties in a number of cancers in vitro. These agents have yet to be translated into clinical practice, however, largely due to the significant side effects encountered in pre-clinical models. A number of licensed chelators, however, are currently in clinical use for the treatment of iron overload associated with certain non-neoplastic diseases. Deferasirox is one such agent and the drug has shown significant anti-tumor effects in a number of in vitro and in vivo studies. Deferasirox is orally administered and has demonstrated a good side effect profile in clinical practice to date. It represents an attractive agent to take forward into clinical trials of iron chelators as anti-cancer agents.

Novel chelators for cancer treatment: where are we now?

SIGNIFICANCE

Under normal circumstances, cellular iron levels are tightly regulated due to the potential toxic effects of this metal ion. There is evidence that tumors possess altered iron homeostasis, which is mediated by the perturbed expression of iron-related proteins, for example, transferrin receptor 1, ferritin and ferroportin 1. The de-regulation of iron homeostasis in cancer cells reveals a particular vulnerability to iron-depletion using iron chelators. In this review, we examine the absorption of iron from the gut; its transport, metabolism, and homeostasis in mammals; and the molecular pathways involved. Additionally, evidence for alterations in iron processing in cancer are described along with the perturbations in other biologically important transition metal ions, for example, copper(II) and zinc(II). These changes can be therapeutically manipulated by the use of novel chelators that have recently been shown to be highly effective in terms of inhibiting tumor growth.

RECENT ADVANCES

Such chelators include those of the thiosemicarbazone class that were originally thought to target only ribonucleotide reductase, but are now known to have multiple effects, including the generation of cytotoxic radicals.

CRITICAL ISSUES

Several chelators have shown marked anti-tumor activity in vivo against a variety of solid tumors. An important aspect is the toxicology and the efficacy of these agents in clinical trials.

FUTURE DIRECTIONS

As part of the process of the clinical assessment of the new chelators, an extensive toxicological assessment in multiple animal models is essential for designing appropriate dosing protocols in humans.

Mechanism of the antitumoral activity of deferasirox, an iron chelation agent, on mantle cell lymphoma

Mantle cell lymphoma (MCL) characterized by the t(11;14)(q13;q32) translocation, resulting in cyclin D1 overexpression, is one of the most challenging lymphomas to treat. Iron chelators, such as deferasirox, have previously been shown to exhibit anti-proliferative properties; however, their effect on MCL cells has never been investigated. We showed that deferasirox exhibited antitumoral activity against the MCL cell lines HBL-2, Granta-519 and Jeko-1, with 50% inhibitory concentration (IC(50)) values of 7.99 ± 2.46 μM, 8.93 ± 2.25 μM and 31.86 ± 7.26 μM, respectively. Deferasirox induced apoptosis mediated through caspase-3 activation and decreased cyclin D1 protein levels resulting from increased proteasomal degradation. We also demonstrated down-regulation of phosphor-RB (Ser780) expression, which resulted in increasing levels of the E2F/RB complex and G(1)/S arrest. Finally, we showed that deferasirox activity was dependent on its iron chelating ability. The present data indicate that deferasirox, by down-regulating cyclin D1 and inhibiting its related signals, may constitute a promising adjuvant therapeutic molecule in the strategy for MCL treatment.

Circulating biomarkers of iron storage and clearance of incident human papillomavirus infection

BACKGROUND

Iron is an essential mineral for both cellular and pathogen survival and is essential for viral replication. In turn, iron metabolism has been shown to be altered by several viral infections. However, little is known about the association between iron status and human papillomavirus (HPV) natural history. We hypothesize iron to be an HPV cofactor that is associated with longer duration of infection.

METHODS

Ferritin and soluble transferrin receptor (sTfR) were measured in baseline serum samples from 327 women enrolled in the Ludwig-McGill cohort. Incident HPV clearance rates (any-type, oncogenic HPV, nononcogenic HPV, and HPV-16) over a 3 year time period were estimated from Cox proportional hazard models accounting for correlations between multiple infections.

RESULTS

Women with ferritin levels above the median were less likely to clear incident oncogenic HPV [adjusted hazard ratio (AHR), 0.73; 95% confidence interval (CI), 0.55-0.96] and HPV-16 infections (AHR, 0.29; 95% CI, 0.11-0.73). Using physiologic cutoff points, women with enriched iron stores (>120 μg/L) were less likely to clear incident oncogenic HPV infections than those with low levels of iron (<20 μg/L; AHR, 0.34; 95% CI, 0.15-0.81).

CONCLUSION

This study observed that women with the highest ferritin levels were less likely to clear incident oncogenic and HPV-16 infections than women with low ferritin. Rising iron stores may decrease probability of clearing new HPV infection, possibly by promoting viral activity and contributing to oxidative DNA damage.

IMPACT

This novel study suggests that elevated iron stores may put women at risk for persistent HPV infection, an early event in cervical carcinogenesis. Further examination of the association between iron status and HPV natural history is warranted.

HPV16E6-dependent c-fos expression contributes to AP-1 complex formation in SiHa cells

To date, the major role of HPV16E6 in cancer has been considered to be its ability to inhibit the p53 tumor-suppressor protein, thereby thwarting p53-mediated cytotoxic responses to cellular stress signals. Here, we show that HPV16E6-dependent c-fos oncogenic protein expression contributes to AP-1 complex formation under oxidative stress in SiHa cells (HPV16-positive squamous cell carcinoma of the cervix). In addition, we examined the role of HPV16E6 in TGF-α-induced c-fos expression and found that the c-fos protein expression induced by TGF-α is HPV16E6 dependent. Thus, our results provide the first evidence that HPV16E6 contributes to AP-1 complex formation after both ligand-dependent and independent EGFR activation, suggesting a new therapeutic approach to the treatment of HPV-associated tumors.

Stimulation of proliferation in the colorectal mucosa by gastrin precursors is blocked by desferrioxamine

Precursors of the peptide hormone gastrin stimulate proliferation in the colorectal mucosa and promote the development of colorectal carcinoma. Gastrins bind two ferric ions selectively and with high affinity, and the biological activity of glycine-extended gastrin (Ggly) in vitro is dependent on the presence of ferric ions. The aim of the present study was to determine whether or not iron is required for biological activity of progastrin and Ggly in vivo. Rats that had undergone a colostomy were infused with Ggly, and proliferation was measured in the defunctioned rectal mucosa. Proliferation was also measured in the colonic mucosa of hGAS and MTI-Ggly mice, which, by definition, overexpress progastrin and Ggly, respectively. The requirement for iron was assessed by thrice-weekly injection of the chelating agent desferrioxamine (DFO). The proliferation index in the defunctioned rectal mucosa was significantly increased in the Ggly-infused rats, and the increase was significantly reduced after treatment with DFO. Treatment with DFO significantly reduced the crypt height and proliferation index in the colonic mucosa of hGAS and MTI-Ggly mice but had no effect on the same variables in wild-type mice. These observations are consistent with the hypothesis that the biological activity of progastrin and Ggly in vivo is dependent on the presence of ferric ions and further suggest that chelating agents may block the stimulatory effects of gastrin precursors in the development of colorectal carcinoma.

Differential regulation of iron chelator-induced IL-8 synthesis via MAP kinase and NF-kappaB in immortalized and malignant oral keratinocytes

Background

Interleukin-8 (IL-8) is a cytokine that plays an important role in tumor progression in a variety of cancer types; however, its regulation is not well understood in oral cancer cells. In the present study, we examined the expression and mechanism of IL-8 in which it is involved by treating immortalized (IHOK) and malignant human oral keratinocytes (HN12) cells with deferoxamine (DFO).

Methods

IL-8 production was measured by an enzyme-linked immunoabsorbent assay and reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. Electrophoretic mobility shift assays was used to determine NF-κB binding activity. Phosphorylation and degradation of the I-κB were analyized by Western blot.

Results

IHOK cells incubated with DFO showed increased expression of IL-8 mRNA, as well as higher release of the IL-8 protein. The up-regulation of DFO-induced IL-8 expression was higher in IHOK cells than in HN12 cells and was concentration-dependent. DFO acted additively with IL-1β to strongly up-regulate IL-8 in IHOK cells but not in HN12 cells. Accordingly, selective p38 and ERK1/2 inhibitors for both kinases abolished DFO-induced IL-8 expression in both IHOK and HN12 cells. Furthermore, DFO induced the degradation and phosphorylation of IκB, and activation of NF-κB. The IL-8 inducing effects of DFO were mediated by a nitric oxide donor (S-nitrosoglutathione), and by pyrrolidine dithiocarbamate, an inhibitor of NF-κB, as well as by wortmannin, which inhibits the phosphatidylinositol 3-kinase-dependent activation of NAD(P)H oxidase.

Conclusion

This results demonstrate that DFO-induced IL-8 acts via multiple signaling pathways in immortalized and malignant oral keratinocytes, and that the control of IL-8 may be an important target for immunotheraphy against human oral premalignant lesions.

Sensitivity of cells to apoptosis induced by iron deprivation can be reversibly changed by iron availability

We tested the effect of iron deprivation on cell death induction in human Raji cells pre-adapted to differing availability of extracellular iron. Iron deprivation was achieved by incubation in a defined iron-free medium. Original Raji cells have previously been adapted to long-term culture in a defined medium with 5 microg/ml of iron-saturated human transferrin as a source of iron. Raji/lowFe cells were derived from original Raji cells by subsequent adaptation to culture in the medium with 50 microm ferric citrate as a source of iron. Raji/lowFe-re cells were derived from Raji/lowFe cells by re-adaptation to the transferrin-containing (5 microg/ml) medium. Iron deprivation induced cell death in both Raji cells and Raji/lowFe-re cells; that is, cells pre-adapted to a near optimum source of extracellular iron (5 microg/ml of transferrin). However, Raji/lowFe cells preadapted to a limited source of extracellular iron (50 microm ferric citrate) became resistant to the induction of cell death by iron deprivation. We demonstrated that cell death induction by iron deprivation in Raji cells correlates with the activation of executioner caspase-3 and the cleavage of caspase-3 substrate, poly-ADP ribose polymerase. Two other executioner caspases, caspase-7 and caspase-6, were not activated. Taken together, we suggest that in human Raji cells, iron deprivation induces apoptotic cell death related to caspase-3 activation. However, the sensitivity of the cells to death induction by iron deprivation can be reversibly changed by extracellular iron availability. The cells pre-adapted to a limited source of extracellular iron became resistant.

p38 and ERK MAP kinase mediates iron chelator-induced apoptosis and -suppressed differentiation of immortalized and malignant human oral keratinocytes

Iron is essential for neoplastic cell growth, and iron chelators have been tested for potential anti-proliferative and anti-cancer effects, but the effects of iron chelators on oral cancer have not been clearly elucidated. To determine the mechanism of cell death induced by iron chelators, we explored the pathways of the three structurally related mitogen-activated protein (MAP) kinase subfamilies during iron chelator-induced apoptosis and differentiation of immortalized human oral keratinocytes (IHOK) and oral cancer cells (HN4). The iron chelator deferoxamine (DFO) exerted potent time- and dose-dependent inhibitory effects on the growth and apoptosis of IHOK and HN4 cells. DFO strongly activates p38 MAP kinase and extracellular signal-regulated kinase (ERK), but does not activate c-Jun N-terminal kinase/stress-activated protein kinase. Of the three MAP kinase blockers used, the selective p38 MAP kinase inhibitor SB203580 and ERK inhibitor PD98059 protected IHOK and HN4 cells against iron chelator-induced cell death, which indicates that the p38 and ERK MAP kinase is a major mediator of apoptosis induced by this iron chelator. Interestingly, treatment of IHOK and HN4 cells with SB203580 and PD98059 abolished cytochrome c release, as well as the activation of caspase-3 and caspase-8. DFO suppressed the expression of epithelial differentiation markers such as involucrin, CK6, and CK19, and this suppression was blocked by p38 and ERK MAP kinase inhibitors. Collectively, these data suggested that p38 and ERK MAP kinase plays an important role in iron chelator-mediated cell death and in the suppression of differentiation of oral immortalized and malignant keratinocytes, by activating a downstream apoptotic cascade that executes the cell death pathway.

Iron overload enhances epithelial cell proliferation in endometriotic lesions induced in a murine model

BACKGROUND

Iron deposits are characteristic of endometriotic lesions, and pelvic iron concentrations are higher in endometriosis patients than in women without endometriosis. In this study, the effect of iron overload and iron chelation on the development of endometriosis in a murine model was investigated.

METHODS

Human menstrual endometrium was injected i.p. into nude mice, either alone (controls) or supplemented with erythrocytes or desferrioxamine (DFO), an iron chelator. After 5 days, the iron load of endometriosis-like lesions and peritoneal macrophages and fluid was evaluated. Lesions were quantified by immunohistochemical morphometry, and their proliferative activity was assessed.

RESULTS

Injection of erythrocytes into the pelvic cavity caused iron overload in lesions (P < 0.025) and peritoneal macrophages (P < 0.01) and fluid (P < 0.05), whereas DFO effectively reduced iron status in lesions (P < 0.05) and macrophages (P < 0.01) compared with controls. No difference was observed in the number or surface area of lesions between the three groups. Erythrocytes increased (P < 0.05) and DFO significantly decreased (P < 0.01) the proliferative activity of lesions.

CONCLUSIONS

Iron overload does not appear to affect lesion establishment but may contribute to the further growth of endometriosis by promoting cell proliferation of lesions. Iron chelator treatment could therefore be beneficial in endometriosis to prevent iron overload in the pelvic cavity and decrease cellular proliferation of lesions.

Heme oxygenase-1/carbon monoxide: from basic science to therapeutic applications

The heme oxygenases, which consist of constitutive and inducible isozymes (HO-1, HO-2), catalyze the rate-limiting step in the metabolic conversion of heme to the bile pigments (i.e., biliverdin and bilirubin) and thus constitute a major intracellular source of iron and carbon monoxide (CO). In recent years, endogenously produced CO has been shown to possess intriguing signaling properties affecting numerous critical cellular functions including but not limited to inflammation, cellular proliferation, and apoptotic cell death. The era of gaseous molecules in biomedical research and human diseases initiated with the discovery that the endothelial cell-derived relaxing factor was identical to the gaseous molecule nitric oxide (NO). The discovery that endogenously produced gaseous molecules such as NO and now CO can impart potent physiological and biological effector functions truly represented a paradigm shift and unraveled new avenues of intense investigations. This review covers the molecular and biochemical characterization of HOs, with a discussion on the mechanisms of signal transduction and gene regulation that mediate the induction of HO-1 by environmental stress. Furthermore, the current understanding of the functional significance of HO shall be discussed from the perspective of each of the metabolic by-products, with a special emphasis on CO. Finally, this presentation aspires to lay a foundation for potential future clinical applications of these systems.

Iron chelator-induced growth arrest and cytochrome c-dependent apoptosis in immortalized and malignant oral keratinocytes

BACKGROUND

Many studies have shown the anti-proliferative effects of iron deprivation on cancer cells, but the effects of iron-chelators on oral cancer have not been clearly elucidated.

METHODS

To investigate the effects of an iron chelator, desferrioxamine (DFO), on the growth of immortalized human oral keratinocytes (IHOK), primary oral cancer cells (HN4), metastatic oral cancer cells (HN12) and human skin keratinocytes (HaCaT) in the MTT assay, three-dimensional (3D) raft cultures, Western blotting, cell cycle analysis, nuclear staining and cytochrome c expression for apoptosis signaling pathway were used.

RESULTS

Desferrioxamine inhibited the growth of immortalized IHOK and HaCaT and malignant HN4 and HN12 keratinocytes in a time- and dose-dependent manner according to the MTT assay. The 3D organotypic culture also revealed that DFO-treated cells showed less epithelial maturation, less surface keratinization and decreased epithelial thickness. The major mechanism of growth inhibition with the micromolar DFO treatment was by the induction of apoptosis, which was supported by nuclear DAPI staining, DNA fragmentation analysis and flow cytometric analysis for sub-G(1) phase arrest and Annexin V-FITC (fluorescein isothiocyanate) staining. Furthermore, Bax expression increased together with p53 and p21(WAF1/CIP1), while the Bcl-2 expression decreased in the immortalized and malignant keratinocytes treated with DFO. Time-dependent cytochrome c from mitochondria was observed in DFO-treated IHOK and oral cancer cells and was accompanied by the activation of caspase-3 in IHOK cells.

CONCLUSION

These results demonstrate that DFO has growth inhibitory effects on immortalized and malignant oral keratinocytes through the induction of apoptosis and suggest that further evaluation of DFO as a potential therapeutic agent for human oral precancerous lesions is warranted.

Dihydroartemisinin Is Cytotoxic to Papillomavirus-Expressing Epithelial Cells In vitro and In vivo

Nearly all cervical cancers are etiologically attributable to human papillomavirus (HPV) infection and pharmaceutical treatments targeting HPV-infected cells would be of great medical benefit. Because many neoplastic cells (including cervical cancer cells) overexpress the transferrin receptor to increase their iron uptake, we hypothesized that iron-dependent, antimalarial drugs such as artemisinin might prove useful in treating HPV-infected or transformed cells. We tested three different artemisinin compounds and found that dihydroartemisinin (DHA) and artesunate displayed strong cytotoxic effects on HPV-immortalized and transformed cervical cells in vitro with little effect on normal cervical epithelial cells. DHA-induced cell death involved activation of the mitochondrial caspase pathway with resultant apoptosis. Apoptosis was p53 independent and was not the consequence of drug-induced reductions in viral oncogene expression. Due to its selective cytotoxicity, hydrophobicity, and known ability to penetrate epithelial surfaces, we postulated that DHA might be useful for the topical treatment of mucosal papillomavirus lesions. To test this hypothesis, we applied DHA to the oral mucosa of dogs that had been challenged with the canine oral papillomavirus. Although applied only intermittently, DHA strongly inhibited viral-induced tumor formation. Interestingly, the DHA-treated, tumor-negative dogs developed antibodies against the viral L1 capsid protein, suggesting that DHA had inhibited tumor growth but not early rounds of papillomavirus replication. These findings indicate that DHA and other artemisinin derivatives may be useful for the topical treatment of epithelial papillomavirus lesions, including those that have progressed to the neoplastic state.

Iron deprivation induces apoptosis via mitochondrial changes related to Bax translocation

In order to elucidate the mechanisms involved in apoptosis induction by iron deprivation, we compared cells sensitive (38C13) and resistant (EL4) to apoptosis induced by iron deprivation. Iron deprivation was achieved by incubation in a defined iron-free medium. We detected the activation of caspase-3 as well as the activation of caspase-9 in sensitive cells but not in resistant cells under iron deprivation. Iron deprivation led to the release of cytochrome c from mitochondria into the cytosol only in sensitive cells but it did not affect the cytosolic localization of Apaf-1 in both sensitive and resistant cells. The mitochondrial membrane potential (Deltapsi(m)) was dissipated within 24 h in sensitive cells due to iron deprivation. The antiapoptotic Bcl-2 protein was found to be associated with mitochondria in both sensitive and resistant cells and the association did not change under iron deprivation. On the other hand, under iron deprivation we detected translocation of the proapoptotic Bax protein from the cytosol to mitochondria in sensitive cells but not in resistant cells. Taken together, we suggest that iron deprivation induces apoptosis via mitochondrial changes concerning proapoptotic Bax translocation to mitochondria, collapse of the mitochondrial membrane potential, release of cytochrome c from mitochondria, and activation of caspase-9 and caspase-3.

Iron-mediated stability of PAI-1 mRNA in adenocarcinoma cells—involvement of a mRNA-binding nuclear protein

This study reports the stability of mRNA of type-1 plasminogen activator inhibitor (PAI-1), the major physiologic inhibitor of plasminogen activation, by deferoxamine-aided iron deprivation, in PC3 adenocarcinoma cells. ELISA and Northern analyses studies revealed dose-dependent increase in PAI-1 expression by deferoxamine-treated cells. Co-treatment with ferric citrate quenched the effect of deferoxamine, confirming the role of iron in PAI-1 regulation. DRB-based RNA chase experiments suggested that post-transcriptional mechanism was involved in PAI-1 regulation. De-novo protein synthesis was necessary for this regulation. Electrophoretic mobility shift assay revealed the presence of a nuclear protein, binding to the 3'-UTR of PAI-1 mRNA in an iron-mediated manner. This is the first report of iron-mediated mRNA-protein interaction in PAI-1, involved in mRNA stability.

Benefits and risks of deferiprone in iron overload in Thalassaemia and other conditions: comparison of epidemiological and therapeutic aspects with deferoxamine

Deferiprone is the only orally active iron-chelating drug to be used therapeutically in conditions of transfusional iron overload. It is an orphan drug designed and developed primarily by academic initiatives for the treatment of iron overload in thalassaemia, which is endemic in the Mediterranean, Middle East and South East Asia and is considered an orphan disease in the European Union and North America. Deferiprone has been used in several other iron or other metal imbalance conditions and has prospects of wider clinical applications. Deferiprone has high affinity for iron and interacts with almost all the iron pools at the molecular, cellular, tissue and organ levels. Doses of 50-120 mg/kg/day appear to be effective in bringing patients to negative iron balance. It increases urinary iron excretion, which mainly depends on the iron load of patients and the dose of the drug. It decreases serum ferritin levels and reduces the liver and heart iron content in the majority of chronically transfused iron loaded patients at doses >80 mg/kg/day. It is metabolised to a glucuronide conjugate and cleared through the urine in the metabolised and a non-metabolised form, usually of a 3 deferiprone: 1 iron complex, which gives the characteristic red colour urine. Peak serum levels of deferiprone are observed within 1 hour of its oral administration and clearance from blood is within 6 hours. There is variation among patients in iron excretion, the metabolism and pharmacokinetics of deferiprone. Deferiprone has been used in more than 7500 patients aged from 2-85 years in >50 countries, in some cases daily for >14 years. All the adverse effects of deferiprone are considered reversible, controllable and manageable. These include agranulocytosis with frequency of about 0.6%, neutropenia 6%, musculoskeletal and joint pains 15%, gastrointestinal complains 6% and zinc deficiency 1%. Discontinuation of the drug is recommended for patients developing agranulocytosis. Deferiprone is of similar therapeutic index to subcutaneous deferoxamine but is more effective in iron removal from the heart, which is the target organ of iron toxicity and mortality in iron-loaded thalassaemia patients. Deferiprone is much less expensive to produce than deferoxamine. Combination therapy of deferoxamine and deferiprone has been used in patients not complying with subcutaneous deferoxamine or experiencing toxicity or not excreting sufficient amounts of iron with use of either drug alone. New oral iron-chelating drugs are being developed, but even if successful these are likely to be more expensive than deferiprone and are not likely to become available in the next 5-8 years. About 25% of treated thalassaemia patients in Europe and more than 50% in India are using deferiprone. For most thalassaemia patients worldwide who are not at present receiving any form of chelation therapy the choice is between deferiprone and fatal iron toxicity.

Iron withdrawal strategies fail to prevent the growth of SiHa-induced tumors in mice

OBJECTIVE

Cervical carcinoma is a human papillomavirus (HPV)-associated cancer for which treatment options still mainly rely on surgical procedures, with or without adjuvant radiotherapy and chemotherapy. We have previously shown that the chemically unrelated iron chelators desferrioxamine and deferiprone inhibit the growth and induce the apoptosis of HPV-positive cervical carcinoma cell lines, suggesting that iron chelators may represent a potential therapeutic approach for the treatment of cervical carcinoma. The present study was designed to investigate the effect of iron deprivation on the growth of human cervical carcinoma xenografts in athymic nude mice.

METHODS

Nude mice (nu/nu) of BALB/c background were treated with iron chelators [desferrioxamine (DFO), deferiprone (L1), or starch-DFO conjugate] or were fed with an iron-poor diet 6 weeks prior to subcutaneous injection of Si-Ha cells. These treatments were continued for 5 weeks after injection of the tumor cells. Treatment with the maximum tolerated doses of DFO, L1, or starch-DFO conjugate induced no significant iron deprivation in non-iron-overloaded mice, while an iron-poor diet led to a dramatic decrease in serum iron, transferrin iron saturation, and ferritin levels. However, neither iron chelators nor an iron-poor diet could significantly inhibit tumor growth.

CONCLUSION

Despite a potent antitumor effect in vitro, iron chelators fail to prevent the growth of cervical carcinoma xenografts in mice. On the basis of these results, clinical trials with iron chelators in patients with cervical carcinoma appear inappropriate.

Role of iron and ferritin in TNFalpha-induced apoptosis in HeLa cells

We found that tumor necrosis factor alpha (TNFalpha)-induced apoptosis in HeLa cells was accompanied by a approximately 2-fold increase in H- and L-ferritin and a decrease in transferrin receptor, two indices of increased iron availability. Iron supplementation and overexpression of H-ferritin or its mutant with an inactivated ferroxidase center reduced by about approximately 50% the number of apoptotic cells after TNFalpha-treatment, while overexpression of L-ferritin was ineffective. The data indicate that H-ferritin has an anti-apoptotic activity unrelated to its ferroxidase activity and to its capacity to modify cellular iron metabolism.