Iron mobilization, cytoprotection, and inhibition of cell proliferation in normal and transformed rat hepatocyte cultures by the hydroxypyridinone CP411, compared to CP20: a biological and physicochemical study

Potent in vivo efficacy of oral gallium maltolate in treatment-resistant glioblastoma

Background

Treatment-resistant glioblastoma (trGBM) is an aggressive brain tumor with a dismal prognosis, underscoring the need for better treatment options. Emerging data indicate that trGBM iron metabolism is an attractive therapeutic target. The novel iron mimetic, gallium maltolate (GaM), inhibits mitochondrial function via iron-dependent and -independent pathways.

Methods

In vitro irradiated adult GBM U-87 MG cells were tested for cell viability and allowed to reach confluence prior to stereotactic implantation into the right striatum of male and female athymic rats. Advanced MRI at 9.4T was carried out weekly starting two weeks after implantation. Daily oral GaM (50mg/kg) or vehicle were provided on tumor confirmation. Longitudinal MRI parameters were processed for enhancing tumor ROIs in OsiriX 8.5.1 (lite) with Imaging Biometrics Software (Imaging Biometrics LLC). Statistical analyses included Cox proportional hazards regression models, Kaplan-Meier survival plots, linear mixed model comparisons, and t-statistic for slopes comparison as indicator of tumor growth rate.

Results

In this study we demonstrate non-invasively, using longitudinal MRI surveillance, the potent antineoplastic effects of GaM in a novel rat xenograft model of trGBM, as evidenced by extended suppression of tumor growth (23.56 mm3/week untreated, 5.76 mm3/week treated, P < 0.001), a blunting of tumor perfusion, and a significant survival benefit (median overall survival: 30 days untreated, 56 days treated; P < 0.001). The therapeutic effect was confirmed histologically by the presence of abundant cytotoxic cellular swelling, a significant reduction in proliferation markers (P < 0.01), and vessel normalization characterized by prominent vessel pruning, loss of branching, and uniformity of vessel lumina. Xenograft tumors in the treatment group were further characterized by an absence of an invasive edge and a significant reduction in both, MIB-1% and mitotic index (P < 0.01 each). Transferrin receptor and ferroportin expression in GaM-treated tumors illustrated cellular iron deprivation. Additionally, treatment with GaM decreased the expression of pro-angiogenic markers (von Willebrand Factor and VEGF) and increased the expression of anti-angiogenic markers, such as Angiopoietin-2.

Conclusion

Monotherapy with the iron-mimetic GaM profoundly inhibits trGBM growth and significantly extends disease-specific survival in vivo.

Identifying a Deferiprone-Resveratrol Hybrid as an Effective Lipophilic Anti-Plasmodial Agent

Malaria i a serious health problem caused by Plasmodium spp. that can be treated by an anti-folate pyrimethamine (PYR) drug. Deferiprone (DFP) is an oral iron chelator used for the treatment of iron overload and has been recognized for its potential anti-malarial activity. Deferiprone-resveratrol hybrids (DFP-RVT) have been synthesized to present therapeutic efficacy at a level which is superior to DFP. We have focused on determining the lipophilicity, toxicity and inhibitory effects on P. falciparum growth and the iron-chelating activity of labile iron pools (LIPs) by DFP-RVT. According to our findings, DFP-RVT was more lipophilic than DFP (p < 0.05) and nontoxic to blood mononuclear cells. Potency for the inhibition of P. falciparum was PYR > DFP-RVT > DFP in the 3D7 strain (IC₅₀ = 0.05, 16.82 and 47.67 µM, respectively) and DFP-RVT > DFP > PYR in the K1 strain (IC₅₀ = 13.38, 42.02 and 105.61 µM, respectively). The combined treatment of DFP-RVT with PYR additionally enhanced the PYR activity in both strains. DFP-RVT dose-dependently lowered LIP levels in PRBCs and was observed to be more effective than DFP at equal concentrations. Thus, the DFP-RVT hybrid should be considered a candidate as an adjuvant anti-malarial drug through the deprivation of cellular iron.

Role of Iron in the Molecular Pathogenesis of Diseases and Therapeutic Opportunities

Iron is an essential mineral that serves as a prosthetic group for a variety of proteins involved in vital cellular processes. The iron economy within humans is highly conserved in that there is no proper iron excretion pathway. Therefore, iron homeostasis is highly evolved to coordinate iron acquisition, storage, transport, and recycling efficiently. A disturbance in this state can result in excess iron burden in which an ensuing iron-mediated generation of reactive oxygen species imparts widespread oxidative damage to proteins, lipids, and DNA. On the contrary, problems in iron deficiency either due to genetic or nutritional causes can lead to a number of iron deficiency disorders. Iron chelation strategies have been in the works since the early 1900s, and they still remain the most viable therapeutic approach to mitigate the toxic side effects of excess iron. Intense investigations on improving the efficacy of chelation strategies while being well tolerated and accepted by patients have been a particular focus for many researchers over the past 30 years. Moreover, recent advances in our understanding on the role of iron in the pathogenesis of different diseases (both in iron overload and iron deficiency conditions) motivate the need to develop new therapeutics. We summarized recent investigations into the role of iron in health and disease conditions, iron chelation, and iron delivery strategies. Information regarding small molecule as well as macromolecular approaches and how they are employed within different disease pathogenesis such as primary and secondary iron overload diseases, cancer, diabetes, neurodegenerative diseases, infections, and in iron deficiency is provided.

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.

In vitro antiproliferative study of novel adamantyl pyridin-4-ones

The preparation of several N-aryl-substituted (phenyl, p-methylphenyl, p-methoxyphenyl, p-nitrophenyl, p-aminophenyl, p-hydroxyphenyl) 3-hydroxy-2-methylpyridin-4-ones as well as their adamantyl derivatives is described, and their in vitro antitumor properties were investigated. The compounds were synthesized in good yields using efficient synthetic routes and methods. Prepared derivatives were evaluated in an antiproliferative in vitro study on 4 cancer cell lines, namely HCT 116 (colon carcinoma), H 460 (lung carcinoma), MCF-7 (breast carcinoma) and K562 (chronic myelogenous leukemia). All tested compounds showed antiproliferative activity ranging from moderate to strong on all inspected cell lines with 4 adamantane containing derivatives being active and selective at low micromolar IC[Formula: see text] concentrations on HCT 116, H 460 and MCF-7. LDH cytotoxicity assay revealed that cytotoxic effects occur after 48 h of exposure. It was shown that there was no change in caspase activity in the treated cells, but there were changes in the cell cycle. All treated samples showed reduced number of cells in the S phase with increased G0/G1 (4b, 5a, 5b) and G2/M (4a) phase.

Involvement of polyamines in iron(III) transport in human intestinal Caco-2 cell lines

Natural polyamines such as putrescine (Put), spermidine (Spd), and spermine (Spm), which are present in the human diet in large amounts, associated with their active transporter, are assumed to play a role in non-heme iron uptake and iron bioavailability from nutrients. Enterocytes and hepatocytes play pivotal roles in the regulation of body iron homeostasis. In this study, we report the effects of natural polyamines on iron transport in the Caco-2 cell line. In enterocyte-like Caco-2 cells, polyamines did not significantly modulate the transepithelial iron flux across the cell monolayer cultured on permeable membranes. In contrast, Spd, Spm, and to a lesser extent, Put were shown to activate Caco-2 cell iron uptake and to induce an increase in the ferritin level. This iron co-transport in enterocytes, which involved an interaction between iron and polyamine then cell uptake of the polyamine-iron complexes by the polyamine transport system, was more pronounced in proliferating than in differentiated Caco-2 cells. Moreover, it was observed at physiological concentrations of both polyamines and iron. It could thus play a role in the rapid renewal of enterocytes. These data suggest the involvement of polyamines as components of the pool of transferrin-independent iron-chelating vectors. Further investigations are needed to demonstrate their biological relevance in physiological situations.

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.

Effects of deferasirox and deferiprone on cellular iron load in the human hepatoma cell line HepaRG

Two oral chelators, CP20 (deferiprone) and ICL670 (deferasirox), have been synthesized for the purpose of treating iron overload diseases, especially thalassemias. Given their antiproliferative effects resulting from the essential role played by iron in cell processes, such compounds might also be useful as anticancer agents. In the present study, we tested the impact of these two iron chelators on iron metabolism, in the HepaRG cell line which allowed us to study proliferating and differentiated hepatocytes. ICL670 uptake was greater than the CP20 uptake. The iron depletion induced by ICL670 in differentiated cells increased soluble transferrin receptor expression, decreased intracellular ferritin expression, inhibited (55)Fe (III) uptake, and reduced the hepatocyte concentration of the labile iron pool. In contrast, CP20 induced an unexpected slight increase in intracellular ferritin, which was amplified by iron-treated chelator exposure. CP20 also promoted Fe(III) uptake in differentiated HepaRG cells, thus leading to an increase of both the labile pool and storage forms of iron evaluated by calcein fluorescence and Perls staining, respectively. In acellular conditions, compared to CP20, iron removing ability from the calcein-Fe(III) complex was 40 times higher for ICL670. On the whole, biological responses of HepaRG cells to ICL670 treatment were characteristic of expected iron depletion. In contrast, the effects of CP20 suggest the potential involvement of this compound in the iron uptake from the external medium into the hepatocytes from the HepaRG cell line, therefore acting like a siderophore in this cell model.

Pathogenesis of haemophilic synovitis: experimental studies on blood-induced joint damage

Hemarthrosis is a common manifestation of haemophilia, and joint arthropathy remains a frequent complication. Even though the exact mechanisms related to blood-induced joint disease have not yet been fully elucidated, it is likely that iron deposition in the synovium induces an inflammatory response that causes not only immune system activation but also stimulates angiogenesis. This process ultimately results in cartilage and bone destruction. Investigating the processes that occur in the early stages of blood-induced joint disease in humans has been very limited. Therefore, the use of haemophilic animal models is critical to augment the understanding of this phenomenon. This article discusses three cellular regulators (p53, p21 and TRAIL) induced in synovial tissue that are important for iron metabolism. A cartilage remodelling programme induced by the release of cytokines and growth factors that result in articular damage is also discussed. Full elucidation of the pathogenesis of haemophilic joint disease is required to identify new avenues for prevention and therapy.

Antiproliferative and apoptotic effects in rat and human hepatoma cell cultures of the orally active iron chelator ICL670 compared to CP20: a possible relationship with polyamine metabolism

OBJECTIVE

Iron loading has been observed to have a hyperproliferative effect on hepatocytes in vitro and on tumour cells in vivo; removal of this iron being required to induce antitumour activity.

MATERIAL AND METHODS

Antiproliferative effects of orally active tridentate iron chelator ICL670 (deferasirox) and bidentate iron chelator CP20 (deferiprone), mediated through the chelation of intracellular iron, were compared in rat hepatoma cell line FAO and human hepatoma cell line HUH7.

RESULTS

In FAO cell cultures, we have shown that ICL670 decreased cell viability and DNA replication and induced apoptosis more efficiently than an iron-binding equivalent concentration of CP20. Moreover, ICL670 decreased significantly the number of the cells in G(2)-M phase. In the HUH7 cell cultures, ICL670 and a four-time higher iron-binding equivalent concentration of CP20, decreased cell viability and DNA replication in the same range. CP20 increased the number of the cells in G(2)-M phase. However, ICL670 inhibited polyamine biosynthesis by decreasing ornithine decarboxylase mRNA level; in contrast, CP20 increased polyamine biosynthesis, particularly putrescine level, by stimulating spermidine-spermine N(1)-acetyl transferase activity that could activate the polyamine retro-conversion pathway. By mass spectrometry, we observed that ICL670 cellular uptake was six times higher than CP20.

CONCLUSIONS

These results suggest that ICL670 has a powerful antitumoural effect and blocks cell proliferation in neoplastic cells by a pathway different from that of CP20 and may constitute a potential adjuvant drug for anticancer therapy.

Modulation of cell proliferation and polyamine metabolism in rat liver cell cultures by the iron chelator O-trensox

The antiproliferative effects of the iron chelator O-trensox and the ornithine-decarboxylase (ODC) inhibitor alpha-difluoromethylornithine (DFMO) were characterized in the rat hepatoma cell line FAO, the rat liver epithelial cell line (RLEC) and the primary rat hepatocyte cultures stimulated by EGF. We observed that O-trensox and DFMO decreased cell viabilty and DNA replication in the three culture models. The cytostatic effect of O-trensox was correlated to a cytotoxicity, higher than for DFMO, and to a cell cycle arrest in G0/G1 or S phases. Moreover, O-trensox and DFMO decreased the intracellular concentration of spermidine in the three models without changing significantly the spermine level. We concluded that iron, but also polyamine depletion, decrease cell growth. However, the drop in cell proliferation obtained with O-trensox was stronger compared to DFMO effect. Altogether, our data provide insights that, in the three rat liver cell culture models, the cytostatic effect of the iron chelator O-trensox may be the addition of two mechanisms: iron and polyamine depletion.