Curcumin Inhibits the PPARδ-p-Akt-GLUT1 Pathway and Ameliorates the Antiproliferative Effects of Doxorubicin in MDA-MB-231 Cells.

OBJECTIVE: The aim of the present study was to examine whether GLUT1 was involved in the antiproliferative activity of curcumin and doxorubicin by understanding mechanistically how curcumin regulated GLUT1. METHODS: Expression level of GLUT1 in MCF-7 and MDA-MB-231 cells were quantitated using quantitative real-time PCR and western blot. GLUT1 activity was inhibited in MDA-MB-231 cells with the pharmacological inhibitor WZB117 to assess the anti-proliferative effects of doxorubicin using MTT 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide).  To examine cell proliferation, trypan blue assay was used in cells transfected with GLUT1 siRNA or plasmid overexpressing GLUT1 with doxorubicin and/or commercially available curcumin. The role of PPARδ and Akt on the regulation of GLUT1 by curcumin was examined by overexpressing these proteins and western blot was employed to examine their protein expression. RESULTS: The data revealed that there was a 1.5 fold increase in GLUT1 mRNA and protein levels in MDA-MB-231 compared to MCF-7.  By inhibiting GLUT1 in triple negative breast cancer cell line, MDA-MB-231 with either the pharmacological inhibitor WZB117 or with GLUT1 siRNA, we observed the enhanced antiproliferative effects of doxorubicin. Additional observations indicated these effects can be reversed by the overexpression of GLUT1. Treatment of MDA-MB-231 with curcumin also revealed downregulation of GLUT1, with further growth suppressive effects when combined with doxorubicin.  Overexpression of GLUT1 blocked the growth suppressive role of curcumin and doxorubicin (p< 0.05). Mechanistically, we also observed that the regulation of GLUT1 by curcumin was mediated by the Peroxisome proliferator-activated receptor (PPAR) δ/Akt pathway. CONCLUSION: Our study demonstrates that regulation of GLUT1 by curcumin via the PPARδ/Akt signaling improves the efficacy of doxorubicin by promoting its growth inhibitory effects in MDA-MB-231 cells.

Impact of COVID-19 Pandemic on Ovarian Cancer Management: Adjusting to the New Normal.

COVID-19, also known as the coronavirus disease 2019, is caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) declared pandemic by the World Health Organization (WHO). As the world faces the coronavirus disease 2019 crisis, the oncology community is being impacted by unprecedented challenges. During this trying time, patients with ovarian cancer (OC) have been affected by a delay in diagnosis, surgery, chemotherapy and radiation treatments, and oncology follow-ups being conducted via telemedicine instead of in-person visits. OC patients and their oncologists are balancing the fears of COVID-19 and cancer treatment with the consequences of delaying cancer care. The delay in treatment care that women with OC are experiencing has resulted in higher levels of cancer worry, anxiety, and depression. In this article, we succinctly review the impact of the COVID-19 pandemic on the diagnosis and treatment and ongoing clinical trials of OC. We also discuss the psychological effects of COVID-19 on women with OC and alternative therapeutic strategies to limit in-person hospital visits to reduce the spread of the disease, and the impact of COVID-19 on OC patients.

Neuraminidase 1 regulates proliferation, apoptosis and the expression of Cadherins in mammary carcinoma cells.

The link between Neuraminidase 1 (Neu1) and cancer development has been highlighted in numerous studies. In an effort to understand the role of Neu1 in mammary carcinoma cells, we evaluated the effect of Neu1 on controlling cell proliferation and apoptosis, as well as regulating the expression of cadherins. By blocking the activity of Neu1 with oseltamivir phosphate or using siRNA to silence the Neu1 protein, we observed suppression of cell growth in MCF-7 and MDA-MB-231 cells. Enhanced cleaved caspase 3 expression was demonstrated in breast cancer cells treated with oseltamivir phosphate or in Neu1 knockdown mammary carcinoma cells. We also provided evidence of Neu1 reversing the epithelial-mesenchymal properties with associated changes to the respective cadherin family. Additional observations indicated that the phytochemical, honokiol downregulates the expression of Neu1. As a consequence of blocking Neu1, honokiol reduced the levels of sialic acid in the two subtypes of breast cancer. These findings provide evidence that Neu1 regulates cell growth and death, and facilitates cancer progression by modulating the expression levels of cadherins.

Activation of the CRABPII/RAR pathway by curcumin induces retinoic acid mediated apoptosis in retinoic acid resistant breast cancer cells.

Due to the anti-proliferative and anti-apoptotic effects of retinoic acid (RA), this hormone has emerged as a target for several diseases, including cancer. However, development of retinoid resistance is a critical issue and efforts to understand the retinoid signaling pathway may identify useful biomarkers for future clinical trials. Apoptotic responses of RA are exhibited through the cellular RA-binding protein II (CRABPII)/retinoic acid receptor (RAR) signaling cascade. Delivery of RA to RAR by CRABPII enhances the transcriptional activity of genes involved in cell death and cell cycle arrest. The purpose of this study was to investigate the role of curcumin in sensitizing RA-resistant triple-negative breast cancer (TNBC) cells to RA-mediated apoptosis. We provide evidence that curcumin upregulates the expression of CRABPII, RARß and RARγ in two different TNBC cell lines. Co-treatment of the cells with curcumin and RA results in increased apoptosis as demonstrated by elevated cleavage of poly(ADP-ribose) polymerase and cleaved caspase-9. Additionally, silencing CRABPII reverses curcumin sensitization of TNBC cells to the apoptotic inducing effects of RA. These findings provide mechanistic insights into sensitizing TNBC cells to RA-mediated cell death by curcumin-induced upregulation of the CRABPII/RAR pathway.

Regulation of Mucin 1 and multidrug resistance protein 1 by honokiol enhances the efficacy of doxorubicin-mediated growth suppression in mammary carcinoma cells.

Understanding the link between chemoresistance and cancer progression may identify future targeted therapy for breast cancer. One of the mechanisms by which chemoresistance is attained in cancer cells is mediated through the expression of multidrug resistance proteins (MRPs). Acquiring drug resistance has been correlated to the emergence of metastasis, accounting for the progression of the disease. One of the diagnostic markers of metastatic progression is the overexpression of a transmembrane protein called Mucin 1 (MUC1) which has been implicated in reduced survival rate. The objective of this study was to understand the relationship between MUC1 and MRP1 using natural phenolic compound isolated from Magnolia grandiflora, honokiol, in mammary carcinoma cells. We provide evidence that honokiol suppresses the expression level of MUC1 and MRP1 in mammary carcinoma cells. In a time-dependent manner, honokiol-mediated reduction of MUC1 is followed by a reduction of MRP1 expression in the breast cancer cells. Additionally, silencing MUC1 suppresses the expression level of MRP1 and enhances the efficacy of doxorubicin, an MRP1 substrate. Taken together, these findings suggest MUC1 regulates the expression of MRP1 and provides a direct link between cancer progression and chemoresistance in mammary carcinoma cells.

Curcumin restores sensitivity to retinoic acid in triple negative breast cancer cells.

BACKGROUND: A major obstacle in the use of retinoid therapy in cancer is the resistance to this agent in tumors. Retinoic acid facilitates the growth of mammary carcinoma cells which express high levels of fatty acid-binding protein 5 (FABP5). This protein delivers retinoic acid to peroxisome proliferator-activated receptor ß/δ (PPARß/δ) that targets genes involved in cell proliferation and survival. One approach to overcome resistance of mammary carcinoma cells to retinoic acid is to target and suppress the FABP5/ PPARß/δ pathway. The objective of this research was to investigate the effect of curcumin, a polyphenol extract from the plant Curcuma longa, on the FABP5/ PPARß/δ pathway in retinoic acid resistant triple negative breast cancer cells. METHODS: Cell viability and proliferation of triple negative breast cancer cell lines (MDA-MB-231 and MD-MB-468) treated with curcumin and/or retinoic was analyzed using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and 5-bromo-2'-deoxyuridine (BrdU). Expression level of FABP5 and PPARß/δ in these cells treated with curcumin was examined by Western Blotting analysis and Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR). Effect of curcumin and retinoic acid on PPARß/δ target genes, PDK1and VEGF-A were also examined using qRT-PCR. Western Blotting was utilized to examine the protein expression level of the p65 subunit of NF-κB. RESULTS: Treatment of retinoic acid resistant triple negative breast cancer cells with curcumin sensitized these cells to retinoic acid mediated growth suppression, as well as suppressed incorporation of BrdU. Further studies demonstrated that curcumin showed a marked reduction in the expression level of FABP5 and PPARß/δ. We provide evidence that curcumin suppresses p65, a transcription factor known to regulate FABP5. The combination of curcumin with retinoic acid suppressed PPARß/δ target genes, VEGF-A and PDK1. CONCLUSIONS: Curcumin suppresses the expression level of FABP5 and PPARß/δ in triple negative mammary carcinoma cells. By targeting the FABP5/PPARß/δ pathway, curcumin prevents the delivery of retinoic acid to PPARß/δ and suppresses retinoic acid-induced PPARß/δ target gene, VEGF-A. Our data demonstrates that suppression of the FABP5/ PPARß/δ pathway by curcumin sensitizes retinoic acid resistant triple negative breast cancer cells to retinoic acid mediated growth suppression.

Involvement of Fatty Acid Binding Protein 5 and PPARß/δ in Prostate Cancer Cell Growth.

Fatty acid binding protein 5 (FABP5) delivers ligands from the cytosol directly to the nuclear receptor PPARß/δ and thus facilitates the ligation and enhances the transcriptional activity of the receptor. We show here that expression levels of both FABP5 and PPARß/δ are correlated with the tumorigenic potential of prostate cancer cell lines. We show further that FABP5 comprises a direct target gene for PPARß/δ and thus the binding protein and its cognate receptor are engaged in a positive feedback loop. The observations demonstrate that, similarly to effects observed in mammary carcinomas, activation of the FABP5/PPARß/δ pathway induces PPARß/δ target genes involved in cell survival and growth and enhances cell proliferation and anchorage-independent growth in prostate cancer cells. Furthermore, the data show that downregulation of either FABP5 or PPARß/δ inhibits the growth of the highly malignant prostate cancer PC3M cells. These studies suggest that the FABP5/PPARß/δ pathway may play a general role in facilitating tumor progression and that inhibition of the pathway may comprise a novel strategy in treatment of cancer.

Fatty acid-binding protein 5 and PPARbeta/delta are critical mediators of epidermal growth factor receptor-induced carcinoma cell growth.

Epidermal growth factors and their receptors (EGFRs) promote breast cancer cell proliferation and can drive tumorigenesis. However, the molecular mechanisms that mediate these effects are incompletely understood. We previously showed that mammary tumor development in the mouse model of breast cancer MMTV-neu, a model characterized by amplification of the EGFR ErbB2 in mammary tissue, correlates with a marked up-regulation of fatty acid-binding protein 5 (FABP5). FABP5 functions to deliver ligands to and enhance the transcriptional activity of the nuclear receptor peroxisome proliferator-activated receptor beta/delta (PPARbeta/delta), a receptor whose target genes include genes involved in cell growth and survival. We show here that in MCF-7 mammary carcinoma cells, EGFR signaling directly up-regulates the expression of FABP5. The data demonstrate that treatment of these cells with the EGFR ligand heregulin-beta1 signals through the ERK and the phophatidylinositol-3-kinase cascades, resulting in activation of the transcription factor NF-kappaB. In turn, NF-kappaB induces the expression of FABP5 through two cognate response elements in the promoter of this gene. The observations further demonstrate that FABP5 and PPARbeta/delta are critical mediators of the ability of EGFR to enhance cell proliferation, indicating that this transcriptional pathway plays a key role in EGFR-induced tumorigenesis. Additional observations indicate that the expression of FABP5 is down-regulated by the Krüppel-like factor KLF2, suggesting a tumor suppressor activity for this factor.

Inhibition of mammary carcinoma cell growth by RXR is mediated by the receptor's oligomeric switch.

Ligands that activate the nuclear receptor retinoid X receptor (RXR) display potent anticarcinogenic activities, but the mechanisms by which these compounds inhibit carcinoma cell growth are poorly understood. While RXR can regulate gene expression due to its intrinsic ligand-activated transcription function, this receptor can also regulate transcription by functioning as a ligand-controlled DNA architectural factor. It was thus reported that apo-RXR self-associates into tetramers and that each dimer within these tetramers can separately bind to an RXR response element. Hence, DNA binding by RXR tetramers may bring distant genomic regions into close physical proximity. As ligand binding induces the dissociation of RXR tetramers into dimers, it can alter gene expression by modulating the DNA architecture. Here, we show that inhibition of mammary carcinoma cell growth by RXR ligands stems from the ability of these compounds to regulate the oligomeric state of RXR and is independent of the direct intrinsic transcriptional activity of the receptor. The data suggest that compounds that trigger dissociation of RXR tetramers may comprise a novel class of anticarcinogenic agents.