Aminoflavone Inhibits α6-integrin and Growth of Tamoxifen Resistant Breast Cancer

Approximately 40% of estrogen receptor positive (ER+) breast cancer patients develop resistance to standard of care agent tamoxifen, while ER negative (ER-) breast cancer patients are intrinsically resistant to tamoxifen. Resistance often promotes metastasis, recurrence and death. Tumor-initiating cells (TICs) represent key contributors to resistance and adhesion protein α6-integrin is a putative TIC biomarker. Investigational agent Aminoflavone (AF) demonstrates efficacy against breast cancer cells irrespective of ER status. Interestingly, we found tamoxifen resistant (TamR) cells and tumors exhibited elevated α6-integrin expression in comparison to their tamoxifen sensitive counterparts. AF effectively disrupted mammospheres enriched for TICs and reduced α6-integrin levels in tamoxifen sensitive and TamR cells. AF further inhibited α6-integrin’s pro-cancer signaling in TamR cells. Additionally, AF altered the miRNA expression profile of tamoxifen sensitive and TamR mammosphere-derived cells. Our data suggest that AF inhibits α6-integrin signaling and alters the expression of specific miRNAs to reduce TIC capacity and counteract tamoxifen resistance

Cancer stem cells: Culprits in endocrine resistance and racial disparities in breast cancer outcomes

Breast cancer stem cells (BCSCs) promote endocrine therapy (ET) resistance, also known as endocrine resistance in hormone receptor (HR) positive breast cancer. Endocrine resistance occurs via mechanisms that are not yet fully understood. In vitro, in vivo and clinical data suggest that signaling cascades such as Notch, hypoxia inducible factor (HIF), and integrin/Akt promote BCSC-mediated endocrine resistance. Once HR positive breast cancer patients relapse on ET, targeted therapy agents such as cyclin dependent kinase inhibitors are frequently implemented, though secondary resistance remains a threat. Here, we discuss Notch, HIF, and integrin/Akt pathway regulation of BCSC activity and potential strategies to target these pathways to counteract endocrine resistance. We also discuss a plausible link between elevated BCSC-regulatory gene levels and reduced survival observed among African American women with basal-like breast cancer which lacks HR expression. Should future studies reveal a similar link for patients with luminal breast cancer, then the use of agents that impede BCSC activity could prove highly effective in improving clinical outcomes among African American breast cancer patients.Fil: Mavingire, Nicole. Loma Linda University Health School of Medicine; Estados UnidosFil: Campbell, Petreena. Loma Linda University Health School of Medicine; Estados UnidosFil: Wooten, Jonathan. Loma Linda University Health School of Medicine; Estados UnidosFil: Aja, Joyce. University of the Philippines Diliman; FilipinasFil: Davis, Melissa B. New York Presbyterian Hospital; Estados UnidosFil: Loaiza Perez, Andrea Irene. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncología "Ángel H. Roffo"; ArgentinaFil: Brantley, Eileen. Loma Linda University Health School of Medicine; Estados Unido

Aryl Hydrocarbon Receptor Ligand 5F 203 Induces Oxidative Stress That Triggers DNA Damage in Human Breast Cancer Cells

Breast tumors often show profound sensitivity to exogenous oxidative stress. Investigational agent 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F 203) induces aryl hydrocarbon receptor (AhR)-mediated DNA damage in certain breast cancer cells. Since AhR agonists often elevate intracellular oxidative stress, we hypothesize that 5F 203 increases reactive oxygen species (ROS) to induce DNA damage, which thwarts breast cancer cell growth. We found that 5F 203 induced single-strand break formation. 5F 203 enhanced oxidative DNA damage that was specific to breast cancer cells sensitive to its cytotoxic actions, as it did not increase oxidative DNA damage or ROS formation in nontumorigenic MCF-10A breast epithelial cells. In contrast, AhR agonist and procarcinogen benzo[a]pyrene and its metabolite, 1,6-benzo[a]pyrene quinone, induced oxidative DNA damage and ROS formation, respectively, in MCF-10A cells. In sensitive breast cancer cells, 5F 203 activated ROS-responsive kinases: c-Jun-N-terminal kinase (JNK) and p38 mitogen activated protein kinase (p38). AhR antagonists (alpha-naphthoflavone, CH223191) or antioxidants (N-acetyl-l-cysteine, EUK-134) attenuated 5F 203-mediated JNK and p38 activation, depending on the cell type. Pharmacological inhibition of AhR, JNK, or p38 attenuated 5F 203-mediated increases in intracellular ROS, apoptosis, and single-strand break formation. 5F 203 induced the expression of cytoglobin, an oxidative stress-responsive gene and a putative tumor suppressor, which was diminished with AhR, JNK, or p38 inhibition. Additionally, 5F 203-mediated increases in ROS production and cytoglobin were suppressed in AHR100 cells (AhR ligand-unresponsive MCF-7 breast cancer cells). Our data demonstrate 5F 203 induces ROS-mediated DNA damage at least in part via AhR, JNK, or p38 activation and modulates the expression of oxidative stress-responsive genes such as cytoglobin to confer its anticancer action

AhR ligand aminoflavone suppresses α6-integrin–Src–Akt signaling to attenuate tamoxifen resistance in breast cancer cells

More than 40% of patients with luminal breast cancer treated with endocrine therapy agent tamoxifen demonstrate resistance. Emerging evidence suggests tumor initiating cells (TICs) and aberrant activation of Src and Akt signaling drive tamoxifen resistance and relapse. We previously demonstrated that aryl hydrocarbon receptor ligand aminoflavone (AF) inhibits the expression of TIC gene α6-integrin and disrupts mammospheres derived from tamoxifen-sensitive breast cancer cells. In the current study, we hypothesize that tamoxifen-resistant (TamR) cells exhibit higher levels of α6-integrin than tamoxifen-sensitive cells and that AF inhibits the growth of TamR cells by suppressing α6-integrin–Src–Akt signaling. In support of our hypothesis, TamR cells and associated mammospheres were found to exhibit elevated α6-integrin expression compared with their tamoxifen-sensitive counterparts. Furthermore, tumor sections from patients who relapsed on tamoxifen showed enhanced α6-integrin expression. Gene expression profiling from the TCGA database further revealed that basal-like breast cancer samples, known to be largely unresponsive to tamoxifen, demonstrated higher α6-integrin levels than luminal breast cancer samples. Importantly, AF reduced TamR cell viability and disrupted TamR mammospheres while concomitantly reducing α6-integrin messenger RNA and protein levels. In addition, AF and small interfering RNA against α6-integrin blocked tamoxifen-stimulated proliferation of TamR MCF-7 cells and further sensitized these cells to tamoxifen. Moreover, AF reduced Src and Akt signaling activation in TamR MCF-7 cells. Our findings suggest elevated α6-integrin expression is associated with tamoxifen resistance and AF suppresses α6-integrin–Src–Akt signaling activation to confer activity against TamR breast cancer.Fil: Campbell, Petreena S.. Loma Linda University School of Medicine; Estados UnidosFil: Mavingire, Nicole. Loma Linda University School of Medicine; Estados UnidosFil: Khan, Salma. Loma Linda University School of Medicine; Estados UnidosFil: Rowland, Leah K.. Loma Linda University School of Medicine; Estados UnidosFil: Wooten, Jonathan V.. Loma Linda University School of Medicine; Estados UnidosFil: Opoku Agyeman, Anna. Loma Linda University School of Medicine; Estados UnidosFil: Guevara, Ashley. Loma Linda University School of Medicine; Estados UnidosFil: Soto, Ubaldo. Loma Linda University School of Medicine; Estados UnidosFil: Cavalli, Fiorella. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncología "Ángel H. Roffo"; ArgentinaFil: Loaiza Perez, Andrea Irene. Universidad de Buenos Aires. Facultad de Medicina. Instituto de Oncología "Ángel H. Roffo"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Nagaraj, Gayathri. Loma Linda University School of Medicine; Estados UnidosFil: Denham, Laura J.. Loma Linda University School of Medicine; Estados UnidosFil: Adeoye, Olayemi. Loma Linda University School of Medicine; Estados UnidosFil: Jenkins, Brittany D.. Henry Ford Cancer Institute; Estados UnidosFil: Davis, Melissa B.. Henry Ford Cancer Institute; Estados UnidosFil: Schiff, Rachel. Baylor College of Medicine; Estados UnidosFil: Brantley, Eileen J.. Loma Linda University School of Medicine; Estados Unido