Anticancer activity of the iron facilitator LS081

FGFR1 governs iron homeostasis via regulating intracellular protein degradation pathways of IRP2 in prostate cancer cells

The acquisition of ectopic fibroblast growth factor receptor 1 (FGFR1) expression is well documented in prostate cancer (PCa) progression, notably in conferring tumor growth advantage and facilitating metastasis. However, how FGFR1 contributes to PCa progression is not fully revealed. Here we report that ectopic FGFR1 in PCa cells promotes transferrin receptor 1 (TFR1) expression and expands the labile iron pool (LIP), and vice versa. We further demonstrate that FGFR1 stabilizes iron regulatory proteins 2 (IRP2) and therefore, upregulates TFR1 via promoting IRP2 binding to the IRE of TFR1. Deletion of FGFR1 in DU145 cells decreases the LIP, which potentiates the anticancer efficacy of iron chelator. Intriguingly, forced expression of IRP2 in FGFR1 depleted cells reinstates TFR1 expression and LIP, subsequently restoring the tumorigenicity of the cells. Together, our results here unravel a new mechanism by which FGFR1 drives PCa progression and suggest a potential novel target for PCa therapy.

Iron Metabolism in Prostate Cancer; From Basic Science to New Therapeutic Strategies

An increasing amount of research has recently strengthened the case for the existence of iron dysmetabolism in prostate cancer. It is characterized with a wide array of differential expression of iron-related proteins compared to normal cells. These proteins control iron entry, cellular iron distribution but also iron exit from prostate cells. Iron dysmetabolism is not an exclusive feature of prostate cancer cells, but it is observed in other cells of the tumor microenvironment. Disrupting the machinery that secures iron for prostate cancer cells can retard tumor growth and its invasive potential. This review unveils the current understanding of the ways that prostate cancer cells secure iron in the tumor milieu and how can we exploit this knowledge for therapeutic purposes.

High preoperative serum ferritin predicted poor prognosis in non-metastatic colorectal cancer

Objectives:

To validate the prognostic significance of preoperative serum iron metabolism parameters in non-metastatic colorectal cancer patients treated with curative resection.

Methods:

We conducted a prospective cohort study in the Department of Surgical Oncology, WuXi 4th People’s Hospital, WuxiChina, between March 2010 and September 2013. The relationships of serum iron metabolism parameters with other variables were examined. The prognostic significance was evaluated using the Kaplan Meier curve and Cox proportional hazards regression model.

Results:

Five hundred and fourteen patients were eligible for analysis. The levels of the 3 iron metabolism parameters were interdependent. Hemoglobin level was positively correlated with serum iron and transferrin, and was negatively correlated with ferritin. Compared with peri-neural invasion (PNI)-negative patients, PNI-positive patients had higher serum iron (p=0.03) and ferritin levels (p=0.01). Compared with patients with the lowest quartile level of ferritin, patients with the highest quartile level of ferritin had a 2.21 (95% CI: 1.18-4.14) fold increased mortality risk in the univariate and 2.56 (95% CI: 1.10-5.96) in the multivariate Cox proportional hazards models. When stratified by TNM stages, it was only in stage III patients that serum ferritin remained statistically prognostically significant.

Conclusions:

Preoperative serum ferritin appeared as an independent adverse risk factor in non-metastatic colorectal cancer.

Novel thiosemicarbazones regulate the signal transducer and activator of transcription 3 (STAT3) pathway: inhibition of constitutive and interleukin 6-induced activation by iron depletion

Pharmacologic manipulation of metal pools in tumor cells is a promising strategy for cancer treatment. Here, we reveal how the iron-binding ligands desferrioxamine (DFO), di-2-pyridylketone-4,4-dimethyl-3-thiosemicarbazone (Dp44mT), and di-2-pyridylketone 4-cyclohexyl-4-methyl-3-thiosemicarbazone (DpC) inhibit constitutive and interleukin 6-induced activation of signal transducer and activator of transcription 3 (STAT3) signaling, which promotes proliferation, survival, and metastasis of cancer cells. We demonstrate that DFO, Dp44mT, and DpC significantly decrease constitutive phosphorylation of the STAT3 transcription factor at Tyr705 in the pancreatic cancer cell lines PANC-1 and MIAPaCa-2 as well as the prostate cancer cell line DU145. These compounds also significantly decrease the dimerized STAT3 levels, the binding of nuclear STAT3 to its target DNA, and the expression of downstream targets of STAT3, including cyclin D1, c-myc, and Bcl-2. Examination of upstream mediators of STAT3 in response to these ligands has revealed that Dp44mT and DpC could significantly decrease activation of the nonreceptor tyrosine kinase Src and activation of cAbl in DU145 and MIAPaCa-2 cells. In contrast to the effects of Dp44mT, DpC, or DFO on inhibiting STAT3 activation, the negative control compound di-2-pyridylketone 2-methyl-3-thiosemicarbazone, or the DFO:Fe complex, which cannot bind cellular iron, had no effect. This demonstrates the role of iron-binding in the activity observed. Immunohistochemical staining of PANC-1 tumor xenografts showed a marked decrease in STAT3 in the tumors of mice treated with Dp44mT or DpC compared with the vehicle. Collectively, these studies demonstrate suppression of STAT3 activity by iron depletion in vitro and in vivo, and reveal insights into regulation of the critical oncogenic STAT3 pathway.

The prognostic value of Smad4 mRNA in patients with prostate cancer

The tumor suppressor gene Smad4 has been localized to chromosome 18q21.1 and is a member of the Smad family that mediates the transforming growth factor β signaling pathway suppressing epithelial cell growth. However, variable expression of Smad4 messenger RNA (mRNA) has been reported, with a loss in some cancers and increased expression in others. The aim of the present study was to investigate the Smad4 mRNA expression in prostate cancer tissues and adjacent noncancerous tissues and its potential relevance to clinicopathological variables and prognosis. The expression change of Smad4 mRNA was detected by using real-time quantitative reverse transcriptase-polymerase chain reaction analysis. The data showed that the Smad4 mRNA expression level in prostate cancer tissues was significantly lower than those in noncancerous tissues. The results indicated that the low expression of Smad4 mRNA in prostate cancer was associated with lymph node metastasis, preoperative prostate-specific antigen (PSA), and Gleason score. Kaplan-Meier survival analysis showed that patients with high Smad4 mRNA expression have longer biochemical recurrence-free survival time compared to patients with low Smad4 mRNA expression. Multivariate analysis revealed that Smad4 mRNA expression was an independent predictor of biochemical recurrence-free survival. Our results emphasize that Smad4 mRNA can be used as a predictive biomarker.

Prognostication of prostate cancer based on NUCB2 protein assessment: NUCB2 in prostate cancer

BACKGROUND

Nucleobindin 2 (NUCB2) protein, a novel oncoprotein, is overexpressed in breast cancer. To date, there have been no published data regarding the role of NUCB2 protein expression in prostate cancer (PCa). Therefore, this study was performed to investigate the correlations between NUCB2 protein expression and prognosis in patients with PCa.

METHODS

Through immunohistochemistry, NUCB2 protein expression was evaluated in 60 benign prostatic hyperplasia (BPH) specimens and 180 PCa specimens. The correlation of NUCB2 protein expression with clinicopathological parameters was assessed using χ2 analysis. Kaplan-Meier analysis and Cox proportional hazards regression models were used to investigate the correlation between NUCB2 protein expression and prognosis of PCa patients.

RESULTS

The immunohistochemistry results showed that the expression level of NUCB2 in PCa cases was significantly higher than that in BPH tissues (P < 0.001). Moreover, statistical analysis also showed that high NUCB2 protein expression was positively related to seminal vesicle invasion, lymph node metastasis, angiolymphatic invasion, higher Gleason score, biochemical recurrence (BCR), and higher preoperative prostate-specific antigen (PSA). Furthermore, it was also shown that patients with high NUCB2 protein expression had significantly poorer overall survival and BCR- free survival compared with patients with low expression of NUCB2 protein. Multivariate Cox regression analysis revealed that high NUCB2 protein expression level was an independent prognostic factor for overall survival and BCR-free survival of patients with PCa.

CONCLUSIONS

NUCB2 protein expression showed a strong association with the potencies of BCR and progression of PCa, and that may be applied as a novel biomarker for the prediction of BCR, and helpful for improving the diagnosis, prognosis and treatment of PCa.

Mitoferrin-2-dependent mitochondrial iron uptake sensitizes human head and neck squamous carcinoma cells to photodynamic therapy

Photodynamic therapy (PDT) is a promising approach to treat head and neck cancer cells. Here, we investigated whether mitochondrial iron uptake through mitoferrin-2 (Mfrn2) enhanced PDT-induced cell killing. Three human head and neck squamous carcinoma cell lines (UMSCC1, UMSCC14A, and UMSCC22A) were exposed to light and Pc 4, a mitochondria-targeted photosensitizer. The three cell lines responded differently: UMSCC1 and UMSCC14A cells were more resistant, whereas UMSCC22A cells were more sensitive to Pc 4-PDT-induced cell death. In non-erythroid cells, Mfrn2 is an iron transporter in the mitochondrial inner membrane. PDT-sensitive cells expressed higher Mfrn2 mRNA and protein levels compared with PDT-resistant cells. High Mfrn2-expressing cells showed higher rates of mitochondrial Fe(2+) uptake compared with low Mfrn2-expressing cells. Bafilomycin, an inhibitor of the vacuolar proton pump of lysosomes and endosomes that causes lysosomal iron release to the cytosol, enhanced PDT-induced cell killing of both resistant and sensitive cells. Iron chelators and the inhibitor of the mitochondrial Ca(2+) (and Fe(2+)) uniporter, Ru360, protected against PDT plus bafilomycin toxicity. Knockdown of Mfrn2 in UMSCC22A cells decreased the rate of mitochondrial Fe(2+) uptake and delayed PDT plus bafilomycin-induced mitochondrial depolarization and cell killing. Taken together, the data suggest that lysosomal iron release and Mfrn2-dependent mitochondrial iron uptake act synergistically to induce PDT-mediated and iron-dependent mitochondrial dysfunction and subsequent cell killing. Furthermore, Mfrn2 represents a possible biomarker of sensitivity of head and neck cancers to cell killing after PDT.

Pharmacology of iron transport

Elucidating the molecular basis for the regulation of iron uptake, storage, and distribution is necessary to understand iron homeostasis. Pharmacological tools are emerging to identify and distinguish among different iron transport pathways. Stimulatory or inhibitory small molecules with effects on iron uptake can help characterize the mechanistic elements of iron transport and the roles of the transporters involved in these processes. In particular, iron chelators can serve as potential pharmacological tools to alleviate diseases of iron overload. This review focuses on the pharmacology of iron transport, introducing iron transport membrane proteins and known inhibitors.

Iron facilitator LS081 reduces hypoxia-inducible factor-1α protein and functions as anticancer agent in hepatocellular carcinoma

Hypoxia inducible factor-1α (HIF-1α) has a central role in cellular oxygen-sensing, and its overexpression in many types of cancer is considered important in tumor progression. Thus, targeting HIF-1α production and activity has been of great therapeutic interest. In normoxic conditions, HIF-1α is hydroxylated by oxygen-dependent prolyl-hydroxylases, which require ferrous iron for its activity. The tumor suppressor protein von Hippel Lindau binds to the hydroxylated HIF-1α, which is then ubiquitinated and degraded by proteasomes. We focused on the physiological degradation machinery of HIF-1α mediated by prolyl hydroxylases. Previously, we identified a small molecule, LS081, that is capable of stimulating iron uptake into cells. In the present study, we aimed to inhibit the expression of HIF-1α protein and growth of hepatocellular carcinoma by using the iron-facilitating activity of LS081. In the human hepatocellular carcinoma cell lines Hep3B and HepG2, a combination of LS081 and ferric ammonium citrate (LS081/FeAC) inhibited HIF-1α protein expression but did not inhibit HIF-1α mRNA expression. A mutated HIF-1α protein, which has proline residues that were replaced with alanine and transfected into HEK293 cells, was not affected by the combination of LS081 and FeAC. Furthermore, the iron-facilitating activity of LS081 resulted in Hep3B and HepG2 growth inhibition in vitro and in vivo. These results indicate that the iron-facilitating activity of LS081 inhibits HIF-1α expression through prolyl-hydroxylation of HIF-1α and might have a therapeutic effect in the treatment of hepatocellular carcinoma.