Exploring novel capping framework: high substituent pyridine-hydroxamic acid derivatives as potential antiproliferative agents.

PURPOSE: Histone deacetylases (HDACs) play a vital role in the epigenetic regulation of gene expression due to their overexpression in several cancer forms. Therefore, these enzymes are considered as a potential anticancer drug target. Different synthetic and natural structures have been studied as HDACs inhibitors; based on available structural design information, the capping group is important for the biological activity due to the different interactions in the active site entrance. The present study aimed to analyze high substituted pyridine as a capping group, which included carrying out the synthesis, antiproliferative activity analysis, and docking studies of these novel compounds. METHODS: To achieve the synthesis of these derivatives, four reaction steps were performed, generating desired products 15a-k. Their effects on cell proliferation and gene expression of p21, cyclin D1, and p53 were determined using the sulphorhodamine B (SRB) method and quantitative real-time polymerase chain reaction. The HDAC1, HDAC6, and HDAC8 isoforms were used for performing docking experiments with our 15a-k products. RESULT: The products 15a-k were obtained in overall yields of 40-71%. Compounds 15j and 15k showed the highest antiproliferative activity in the breast (BT-474 and MDA-MB-231) and prostate (PC3) cancer cell lines at a concentration of 10 µM. These compounds increased p21 mRNA levels and decreased cyclin D1 and p53 gene expression. The docking study showed an increment in the strength, and in the number of interactions performed by the capping moiety of the tested molecules compared with SAHA; interactions displayed are mainly van der Waals, π-stacking, and hydrogen bond. CONCLUSION: The synthesized compounds 2-thiophene (15j) and 2-furan (15k) pyridine displayed cell growth inhibition, regulation of genes related to cell cycle progression in highly metastatic cancer cell lines. The molecular coupling analysis performed with HDAC1, HDAC6 and HDAC8 showed an increment in the number of interactions performed by the capping moiety and consequently in the strength of the capping group interaction.

STAT1 potentiates oxidative stress revealing a targetable vulnerability that increases phenformin efficacy in breast cancer.

Bioenergetic perturbations driving neoplastic growth increase the production of reactive oxygen species (ROS), requiring a compensatory increase in ROS scavengers to limit oxidative stress. Intervention strategies that simultaneously induce energetic and oxidative stress therefore have therapeutic potential. Phenformin is a mitochondrial complex I inhibitor that induces bioenergetic stress. We now demonstrate that inflammatory mediators, including IFNγ and polyIC, potentiate the cytotoxicity of phenformin by inducing a parallel increase in oxidative stress through STAT1-dependent mechanisms. Indeed, STAT1 signaling downregulates NQO1, a key ROS scavenger, in many breast cancer models. Moreover, genetic ablation or pharmacological inhibition of NQO1 using ß-lapachone (an NQO1 bioactivatable drug) increases oxidative stress to selectively sensitize breast cancer models, including patient derived xenografts of HER2+ and triple negative disease, to the tumoricidal effects of phenformin. We provide evidence that therapies targeting ROS scavengers increase the anti-neoplastic efficacy of mitochondrial complex I inhibitors in breast cancer.

Calcitriol induces estrogen receptor α expression through direct transcriptional regulation and epigenetic modifications in estrogen receptor-negative breast cancer cells.

Patients with estrogen receptor (ER) α-negative breast tumors have a poor prognosis and are not suitable for hormone therapy. Previously, we demonstrated that calcitriol, the active metabolite of vitamin D, induces ERα expression and re-establishes the response to antiestrogens in ER-negative breast cancer cells. However, the mechanisms involved in this process have not been elucidated. Therefore, the present study was undertaken to investigate the mechanisms implicated in the calcitriol-induced ERα expression in ER-negative breast cancer cells. Using EMSA and ChIP assays, we found that the calcitriol/vitamin D receptor (VDR)/retinoic X receptor (RXR) complex binds to putative vitamin D response elements (VDREs) in the ERα gene promoter region. In addition, we established by a fluorometric assay that calcitriol decreased DNA-methyltransferase and histone deacetylase activities. Flow cytometry and qPCR analyses showed that co-treatment of calcitriol with inhibitors of the histone deacetylase and DNA methyltransferase, and genistein significantly increased ERα expression, compared to that observed with the compounds alone. In conclusion, the calcitriol-dependent ERα induction in ER-negative breast cancer cells results from binding of the VDR-RXR complex to VDREs in the ERα gene promoter region, including the downregulation of enzymes with chromatin-remodeling activities. These results may bring forth novel mechanistic knowledge into the actions of calcitriol in ERα-negative breast cancer.

Design of Fluorescent Coumarin-Hydroxamic Acid Derivatives as Inhibitors of HDACs: Synthesis, Anti-Proliferative Evaluation and Docking Studies.

Coumarin-hydroxamic acid derivatives 7a-k were herein designed with a dual purpose: as antiproliferative agents and fluorescent probes. The compounds were synthesized in moderate yields (30-87%) through a simple methodology, biological evaluation was carried out on prostate (PC3) and breast cancer (BT-474 and MDA-MB-231) cell lines to determine the effects on cell proliferation and gene expression. For compounds 7c, 7e, 7f, 7i and 7j the inhibition of cancer cell proliferation was similar to that found with the reference compound at a comparable concentration (10 µM), in addition, their molecular docking studies performed on histone deacetylases 1, 6 and 8 showed strong binding to the respective active sites. In most cases, antiproliferative activity was accompanied by greater levels of cyclin-dependent kinase inhibitor p21, downregulation of the p53 tumor suppressor gene, and regulation of cyclin D1 gene expression. We conclude that compounds 7c, 7e, 7f, 7i and 7j may be considered as potential anticancer agents, considering their antiproliferative properties, their effect on the regulation of the genes, as well as their capacity to dock to the active sites. The fluorescent properties of compound 7j and 7k suggest that they can provide further insight into the mechanism of action.

Chronic moderate ethanol intake differentially regulates vitamin D hydroxylases gene expression in kidneys and xenografted breast cancer cells in female mice.

Factors affecting vitamin D metabolism may preclude anti-carcinogenic effects of its active metabolite calcitriol. Chronic ethanol consumption is an etiological factor for breast cancer that affects vitamin D metabolism; however, the mechanisms underlying this causal association have not been fully clarified. Using a murine model, we examined the effects of chronic moderate ethanol intake on tumoral and renal CYP27B1 and CYP24A1 gene expression, the enzymes involved in calcitriol synthesis and inactivation, respectively. Ethanol (5% w/v) was administered to 25-hydroxyvitamin D3-treated or control mice during one month. Afterwards, human breast cancer cells were xenografted and treatments continued another month. Ethanol intake decreased renal Cyp27b1 while increased tumoral CYP24A1 gene expression.Treatment with 25-hydroxyvitamin D3 significantly stimulated CYP27B1 in tumors of non-alcohol-drinking mice, while increased both renal and tumoral CYP24A1. Coadministration of ethanol and 25-hydroxyvitamin D3 reduced in 60% renal 25-hydroxyvitamin D3-dependent Cyp24a1 upregulation (P<0.05). We found 5 folds higher basal Cyp27b1 than Cyp24a1 gene expression in kidneys, whereas this relation was inverted in tumors, showing 5 folds more CYP24A1 than CYP27B1. Tumor expression of the calcitriol target cathelicidin increased only in 25-hydroxyvitamin D3-treated non-ethanol drinking animals (P<0.05). Mean final body weight was higher in 25-hydroxyvitamin D3 treated groups (P<0.001). Overall, these results suggest that moderate ethanol intake decreases renal and tumoral 25-hydroxyvitamin D3 bioconversion into calcitriol, while favors degradation of both vitamin D metabolites in breast cancer cells. The latter may partially explain why alcohol consumption is associated with vitamin D deficiency and increased breast cancer risk and progression.

Calcitriol stimulates gene expression of cathelicidin antimicrobial peptide in breast cancer cells with different phenotype.

BACKGROUND: In normal and neoplastic cells, growth-promoting, proangiogenic, cytotoxic and pro-apoptotic effects have all been attributed to cathelicidin antimicrobial peptide (CAMP). Nevertheless, little is known about the factors regulating this peptide expression in breast cancer. Herein we asked if the well-known antineoplastic hormone calcitriol could differentially modulate CAMP gene expression in human breast cancer cells depending on the cell phenotype in terms of efficacy and potency. METHODS: The established breast cancer cell lines MCF7, BT-474, HCC1806, HCC1937, SUM-229PE and a primary cell culture generated from invasive ductal breast carcinoma were used in this study. Calcitriol regulation of cathelicidin gene expression in vitro and in human breast cancer xenografts was studied by real time PCR. Tumorigenicity was evaluated for each cell line in athymic mice. RESULTS: Estrogen receptor (ER)α + breast cancer cells showed the highest basal CAMP gene expression. When incubated with calcitriol, CAMP gene expression was stimulated in a dose-dependent and cell phenotype-independent manner. Efficacy of calcitriol was lower in ERα + cells when compared to ERα- cells (<10 vs. >70 folds over control, respectively). Conversely, calcitriol lowest potency upon CAMP gene expression was observed in the ERα-/EGFR+ SUM-229PE cell line (EC50 = 70.8 nM), while the highest was in the basal-type/triple-negative cells HCC1806 (EC50 = 2.13 nM) followed by ERα + cells MCF7 and BT-474 (EC50 = 4.42 nM and 14.6 nM, respectively). In vivo, lower basal CAMP gene expression was related to increased tumorigenicity and lack of ERα expression. Xenografted triple-negative breast tumors of calcitriol-treated mice showed increased CAMP gene expression compared to vehicle-treated animals. CONCLUSIONS: Independently of the cell phenotype, calcitriol provoked a concentration-dependent stimulation on CAMP gene expression, showing greater potency in the triple negative HCC1806 cell line. Efficacy of calcitriol was lower in ERα + cells when compared to ERα- cells in terms of stimulating CAMP gene expression. Lower basal CAMP and lack of ERα gene expression was related to increased tumorigenicity. Our results suggest that calcitriol anti-cancer therapy is more likely to induce higher levels of CAMP in ERα- breast cancer cells, when compared to ERα + breast cancer cells.

In vivo dual targeting of the oncogenic Ether-à-go-go-1 potassium channel by calcitriol and astemizole results in enhanced antineoplastic effects in breast tumors.

BACKGROUND: The oncogenic ether-à-go-go-1 potassium channel (EAG1) activity and expression are necessary for cell cycle progression and tumorigenesis. The active vitamin D metabolite, calcitriol, and astemizole, a promising antineoplastic drug, target EAG1 by inhibiting its expression and blocking ion currents, respectively. We have previously shown a synergistic antiproliferative effect of calcitriol and astemizole in breast cancer cells in vitro, but the effect of this dual therapy in vivo has not been studied. METHODS: In the present study, we explored the combined antineoplastic effect of both drugs in vivo using mice xenografted with the human breast cancer cell line T-47D and a primary breast cancer-derived cell culture (MBCDF). Tumor-bearing athymic female mice were treated with oral astemizole (50 mg/kg/day) and/or intraperitoneal injections of calcitriol (0.03 µg/g body weight twice a week) during 3 weeks. Tumor sizes were measured thrice weekly. For mechanistic insights, we studied EAG1 expression by qPCR and Western blot. The expression of Ki-67 and the relative tumor volume were used as indicators of therapeutic efficacy. RESULTS: Compared to untreated controls, astemizole and calcitriol significantly reduced, while the coadministration of both drugs further suppressed, tumor growth (P < 0.05). In addition, the combined therapy significantly downregulated tumoral EAG1 and Ki-67 expression. CONCLUSIONS: The concomitant administration of calcitriol and astemizole inhibited tumor growth more efficiently than each drug alone, which may be explained by the blocking of EAG1. These results provide the bases for further studies aimed at testing EAG1-dual targeting in breast cancer tumors expressing both EAG1 and the vitamin D receptor.

Calcitriol restores antiestrogen responsiveness in estrogen receptor negative breast cancer cells: a potential new therapeutic approach.

BACKGROUND: Approximately 30% of breast tumors do not express the estrogen receptor (ER) α, which is necessary for endocrine therapy approaches. Studies are ongoing in order to restore ERα expression in ERα-negative breast cancer. The aim of the present study was to determine if calcitriol induces ERα expression in ER-negative breast cancer cells, thus restoring antiestrogen responses. METHODS: Cultured cells derived from ERα-negative breast tumors and an ERα-negative breast cancer cell line (SUM-229PE) were treated with calcitriol and ERα expression was assessed by real time PCR and western blots. The ERα functionality was evaluated by prolactin gene expression analysis. In addition, the effects of antiestrogens were assessed by growth assay using the XTT method. Gene expression of cyclin D1 (CCND1), and Ether-à-go-go 1 (EAG1) was also evaluated in cells treated with calcitriol alone or in combination with estradiol or ICI-182,780. Statistical analyses were determined by one-way ANOVA. RESULTS: Calcitriol was able to induce the expression of a functional ERα in ER-negative breast cancer cells. This effect was mediated through the vitamin D receptor (VDR), since it was abrogated by a VDR antagonist. Interestingly, the calcitriol-induced ERα restored the response to antiestrogens by inhibiting cell proliferation. In addition, calcitriol-treated cells in the presence of ICI-182,780 resulted in a significant reduction of two important cell proliferation regulators CCND1 and EAG1. CONCLUSIONS: Calcitriol induced the expression of ERα and restored the response to antiestrogens in ERα-negative breast cancer cells. The combined treatment with calcitriol and antiestrogens could represent a new therapeutic strategy in ERα-negative breast cancer patients.

Calcitriol reduces thrombospondin-1 and increases vascular endothelial growth factor in breast cancer cells: implications for tumor angiogenesis.

Calcitriol, a potent antineoplastic vitamin D metabolite, inhibits proliferation, induces apoptosis and slows the growth of tumors. Calcitriol also may exert either antiangiogenic or proangiogenic effects depending on the tissue. Vascular endothelial growth factor (VEGF) and thrombospondin-1 (Tsp-1) are key factors involved in promoting and inhibiting angiogenesis, respectively. The effects of calcitriol on Tsp-1 have not been studied in the mammary gland, while VEGF regulation is not clear, since opposite outcomes have been demonstrated. Therefore, the present study was undertaken to investigate the effects of calcitriol on VEGF and Tsp-1 expression in primary breast tumor-derived cells and a panel of established breast cancer cell lines. In vivo studies in athymic mice were also performed in order to gain further insight into the biological effects of calcitriol on angiogenesis. Real time-PCR and ELISA analyses showed that calcitriol stimulated VEGF mRNA expression and protein secretion while elicited the opposite effect on Tsp-1 in 7 out of 8 cell lines studied, independently of the cell phenotype (P<0.05 in n=5). In vivo, calcitriol significantly inhibited the relative tumoral volume after 4 weeks of treatment; however, serum VEGF was higher in calcitriol-treated animals compared to controls (P<0.05). The integrated fluorescence intensity analysis of CD31, a vessel marker, showed that xenografted breast cancer cells developed tumors with similar vascular density regardless of the treatment. Nevertheless, larger necrotic areas were observed in the tumors of calcitriol-treated mice compared to controls. Since the antineoplastic activity of calcitriol has been consistently demonstrated in several studies including this one, our results suggest that the antitumoral effect of calcitriol in vivo involve different mechanisms not necessarily related to the inhibition of tumor vascularization. Overall, our findings indicate that calcitriol can impact the angiogenic process in breast cancer by regulating VEGF and Tsp-1 expression. This article is part of a Special Issue entitled '16th Vitamin D Workshop'.