Proteomic analysis of the effect of hemin in breast cancer.

Heme, an iron-containing prosthetic group found in many proteins, carries out diverse biological functions such as electron transfer, oxygen storage and enzymatic reactions. Hemin, the oxidised form of heme, is used to treat porphyria and also to activate heme-oxygenase (HO) which catalyses the rate-limiting step in heme degradation. Our group has previously demonstrated that hemin displays antitumor activity in breast cancer (BC). The aim of this work has been to study the effect of hemin on protein expression modifications in a BC cell line to gain insight into the molecular mechanisms of hemin antitumor activity. For this purpose, we carried out proteome analysis by Mass Spectrometry (MS) which showed that 1309 proteins were significantly increased in hemin-treated cells, including HO-1 and the proteases that regulate HO-1 function, and 921 proteins were significantly decreased. Furthermore, the MS-data analysis showed that hemin regulates the expression of heme- and iron-related proteins, adhesion and cytoskeletal proteins, cancer signal transduction proteins and enzymes involved in lipid metabolism. By biochemical and cellular studies, we further corroborated the most relevant in-silico results. Altogether, these results show the multiple physiological effects that hemin treatment displays in BC and demonstrate its potential as anticancer agent.

Iron cycle disruption by heme oxygenase-1 activation leads to a reduced breast cancer cell survival.

Heme oxygenase-1 (HO-1), which catalyzes heme degradation releasing iron, regulates several processes related to breast cancer. Iron metabolism deregulation is also connected with several tumor processes. However the regulatory relationship between HO-1 and iron proteins in breast cancer remains unclear. Using human breast cancer biopsies, we found that high HO-1 levels significantly correlated with low DMT1 levels. Contrariwise, high HO-1 levels significantly correlated with high ZIP14 and prohepcidin expression, as well as hemosiderin storage. At mRNA level, we found that high HO-1 expression significantly correlated with low DMT1 expression but high ZIP14, L-ferritin and hepcidin expression. In in vivo experiments in mice with genetic overexpression or pharmacological activation of HO-1, we detected the same expression pattern observed in human biopsies. In in vitro experiments, HO-1 activation induced changes in iron proteins expression leading to an increase of hemosiderin, ROS levels, lipid peroxidation and a decrease of the growth rate. Such low growth rate induced by HO-1 activation was reversed when iron levels or ROS levels were reduced. Our findings demonstrate an important role of HO-1 on iron homeostasis in breast cancer. The changes in iron proteins expression when HO-1 is modulated led to the iron accumulation deregulating the iron cell cycle, and consequently, generating oxidative stress and low viability, all contributing to impair breast cancer progression.

Identification of an AP1-ZFP36 Regulatory Network Associated with Breast Cancer Prognosis.

It has been established that ZFP36 (also known as Tristetraprolin or TTP) promotes mRNA degradation of proteins involved in inflammation, proliferation and tumor invasiveness. In mammary epithelial cells ZFP36 expression is induced by STAT5 activation during lactogenesis, while in breast cancer ZFP36 expression is associated with lower grade and better prognosis. Here, we show that the AP-1 transcription factor components, i.e. JUN, JUNB, FOS, FOSB, in addition to DUSP1, EGR1, NR4A1, IER2 and BTG2, behave as a conserved co-regulated group of genes whose expression is associated to ZFP36 in cancer cells. In fact, a significant down-modulation of this gene network is observed in breast, liver, lung, kidney, and thyroid carcinomas compared to their normal counterparts. In breast cancer, the normal-like and Luminal A, show the highest expression of the ZFP36 gene network among the other intrinsic subtypes and patients with low expression of these genes display poor prognosis. It is also proposed that AP-1 regulates ZFP36 expression through responsive elements detected in the promoter region of this gene. Culture assays show that AP-1 activity induces ZFP36 expression in mammary cells in response to prolactin (PRL) treatment thorough ERK1/2 activation. These results suggest that JUN, JUNB, FOS and FOSB are not only co-expressed, but would also play a relevant role in regulating ZFP36 expression in mammary epithelial cells.

Phosphonate analogues of 1α, 25 dihydroxyvitamin D3 are promising candidates for antitumoural therapies.

The active metabolite of vitamin D, 1α, 25 dihydroxyvitamin D3 (calcitriol) is classically known to regulate calcium and phosphate homeostasis and bone mineralization. In addition, calcitriol has also been documented to act as a potent anticancer agent in multiple cell culture and animal models of cancer. However, major side effects, such as hypercalcemia, hinder broad-spectrum therapeutic uses of calcitriol in cancer chemotherapy. Synthesis of calcitriol analogues with the same or increased antiproliferative and pro-differentiating activities, and with reduced undesired effects on calcium and bone metabolism, is getting significant attention towards rational therapeutics to treat cancer. In this regard, phosphonate analogues have been shown to display a certain degree of dissociation between the vitamin D activity in vitro and undesired hypercalcemia in vivo. However, few phosphonates have been described in the literature and fewer of them tested for antitumoral effects. Our group has synthesized a novel vitamin D analogue (EM1) bearing an alkynylphosphonate moiety that combines the low calcemic properties of phosphonates with the decreased metabolic inactivation due to the presence of a triple bond between C-23 and C-24. Biological assays demonstrated that this analogue has potent antiproliferative effects in a wide panel of tumour cell lines, even in those resistant to calcitriol treatment. Importantly, EM1 does not show toxic effects in animals, even administered at high doses and for extended periods of time. In the current review we discuss the effects and the potential application in cancer of vitamin D and its derivatives, with an emphasis on phosphonate analogues.