Prolonged Extracellular Signal-Regulated Kinase 1/2 Activation during Fibroblast Growth Factor 1- or Heregulin β1-Induced Antiestrogen-Resistant Growth of Breast Cancer Cells Is Resistant to Mitogen-Activated Protein/Extracellular Regulated Kinase Kinase Inhibitors

Abstract

Increased growth factor receptor signaling is implicated in antiestrogen-resistant breast tumors suggesting that abrogation of such signaling could restore or prolong sensitivity to antihormonal agents. Activation of the mitogen-activated protein/extracellular regulated kinase kinase (MEK)-extracellular regulated kinase (ERK)1/2 cascade is a common component of such pathways. We investigated the ability of the MEK activation inhibitor U0126 to block the increased growth of estrogen receptor-positive MCF-7 breast cancer cells caused by fibroblast growth factor 1 (FGF-1), heregulin ␤1 (HRG␤1), and epidermal growth factor (EGF) in the presence of the pure antiestrogen ICI 182780 (Faslodex; fulvestrant). We found that either FGF-1 or HRG␤1 but not EGF substantially reduced the inhibitory effects of U0126 on growth and ERK1/2 activation, including the combined inhibitory effects of U0126 and ICI 182780. FGF-1 and HRG␤1 also reduced the inhibition of ERK1/2 phosphorylation by the MEK inhibitors PD98059 and PD184161. Interestingly, a transiently transfected dominant-negative MEK1 completely abrogated activation of a coexpressed green fluorescent protein-ERK2 reporter by all three of the factors. Despite a short-lived activation of Ras and Raf-1 by all three of the growth factors, both FGF-1 and HRG␤1, unlike EGF, induced a prolonged activation of MEK and ERK1/2 in these cells. Thus, activation of FGF-1-and HRG␤1-specific signaling causes MEK-dependent prolonged activation of ERK1/2, which is incompletely susceptible to known MEK inhibitors. We also demonstrate that the cytosolic phospholipase A2 inhibitor arachidonyl trifluoro methyl ketone and the pan PKC inhibitor bisindolymaleimide abrogated U0126-resistant phosphorylation of ERK1/2 induced by HRG␤1 but not by FGF-1. Phosphorylation of ERK5 by all three of the factors was also resistant to U0126 suggesting that its activation is not sufficient to overturn growth inhibition due to diminished ERK1/2 activation. Therefore, therapy combining antiestrogens and MEK inhibitors may be ineffective in some antiestrogen-resistant estrogen receptor-positive breast cancers.

In vitro study of the interaction of heregulin-functionalized magnetic–optical nanorods with MCF7 and MDA-MB-231 cells

“…38 Due to these superior qualities, Fe-Au NRs also have the potential to replace SPIONs in targeted molecular imaging and/or hyperthermia, where high particle concentrations are needed. 38,39 Thus, this study confirms that the physical and chemical properties of the nanorods can be tuned to selectively bind to cells 25 expressing high level of receptors, and suggests that targeting metastasized cells in circulation for diagnostic applications could be highly selective.…”

“…Sequential images in Figure 2B show how the scattered light intensity depends on the orientation of the rod where q is the angle between the polarization axis and the rod's longitudinal axis. The optical signature of the gold nanorod was characterized by the polarization dependent change in the scattering intensity of the two 25 bright stripes, which is a result of optical effects associated with the cylindrical geometry of the nanorod, the plasmonic modes excited on the Au section of the nanorod, the ultra-high collection angle of the 1.49 NA objective lens, and the illumination geometry. The dark stripe along the middle of the rod's longitudinal axis resulted from the shadow produced by the cylindrical rod when imaged in transmission direction.…”

“…Other potential 25 candidates are the soft composite materials with programmable shape changes: Stripes that twist or bend, 22 and tubes that collapse upon exposure to weak magnetic fields 23 can be further exploited for their use as magnetic tweezers probes. Figure 3A illustrates that streptavidin (STR) was successfully localized to the Au tips of the nanorods using fluorescently-labeled biotin.…”

“…For example, gold nanoparticles can be readily functionalized with antibodies and polynucleotides, and act as contrast agents for X-ray based computer tomography and near infrared imaging when excited at their plasmon resonance frequencies. Even 25 more interestingly, coating Au nanoparticles on dielectric spheres has been found to enhance their optical properties. 4 Superparamagnetic iron oxide nanoparticles (SPIONs) have also been used for targeting and imaging of specific cancers in vivo 3 and the fact that these nanomaterials also adsorb magnetic radiation has led to their use as agents for hypothermia therapy.…”

“…Particle binding rates were not affected by the presence of free HRG up to 100 nM, a concentration that is two orders of magnitude higher than that needed to induce prolonged activation of mitogen-activated protein kinase/extracellular signalregulated kinase 1/2 (MAPK/ERK) pathway in these cells. 25 The local apparent concentration of HRG on the gold tips of rods was calculated by dividing the estimated number of HRG molecules to the contact volume, which is the contact area 15 multiplied by the estimated diameter of the molecule. The number of molecules was estimated by adjusting the previouslymeasured surface coverage of a similarly sized heterobifunctional PEG coated on spherical particles.…”