Letter www.acsami.org
Thermo-Controlled in Situ Phase Transition of Polymer−Peptides on Cell Surfaces for High-Performance Proliferative Inhibition Sheng-Lin Qiao,†,‡ Yi Wang,†,‡ Yao-Xin Lin,†,‡ Hong-Wei An,†,‡ Yang Ma,†,‡ Li-Li Li,† Lei Wang,*,† and Hao Wang*,† †
CAS Center for Excellence in Nanoscience, CAS Key Laboratory for Biological Effects of Nanomaterials and Nanosafety, National Center for Nanoscience and Technology (NCNST), Beijing, 100190, P. R. China ‡ University of Chinese Academy of Science (UCAS), No. 19A Yuquan Road, Beijing, 100049, P. R. China S Supporting Information *
ABSTRACT: We herein report a thermocontrolled strategy for realizing in situ conformational transition of polymer−peptide conjugates at cell surfaces to manipulate and monitor HER2 receptor clustering, which finally result in effective breast cancer cell proliferation inhibition. Functional paring motifs (HBP) are covalently linked to a synthetic thermoresponsive polymer PNIPAAm to incorporate temperature control properties to HER2 targeting peptide. At 40 °C, the PNIPAAm polymers collapse and act as a “shield” to block the aggregation of HBP. Upon cooling to 35 °C, polymers are in their extended state and HBP are expose in aqueous and aggregate subsequently with enhanced fluorescence, allowing for promoting and in situ monitoring of receptor clustering. Ultimately, HER2 receptor clustering leads to cytoplasmic domain phosphorylation, which further results in effective cancer cell proliferation inhibition. We envision that this useful approach has the potential to be applied for molecule-targeted tumor therapy. KEYWORDS: self-assembly, polymer, peptide, temperature-responsive, cancer
Receptor tyrosine kinases (RTKs) are a family of cell surface receptors that play a critical role in regulating cellular activities, such as apoptosis,3 differentiation,4 and proliferation23 in biological systems. The regulation of RTKs clustering on cell membranes can precisely control cellular fates.24 Human epidermal growth factor receptor-2 (HER2), overexpressed in ∼30% of breast cancers, is one of the most important RTKs and whose presence is identified as a poor prognostic factor in HER2-positive tumors. Based on HER2, a humanized therapeutic monoclonal antibody, Herceptin, was clinically utilized for exceptional treatment of HER2 overexpressing breast cancers via binding to the extracellular domain of HER2 and interfering receptor dimerization, etc.25 Albeit the traditional biomolecules were used as indispensable ligands and capable of specifically activating receptor clustering, exercising control manner accordingly influencing cellular activities in such systems are important yet proved difficult. Herein, we demonstrated a thermocontrolled strategy for realizing in situ conformational transition of polymer−peptide conjugates on cellular membranes to manipulate and monitor HER2 receptor clustering, which finally resulted in effective
Stimuli-induced self-assembly under physiological/pathological conditions holds a myriad of attractive biological applications, including intracellular temperature mapping,1 enzymatic activity measurement,2 cell signaling regulation,3,4 diagnosis,5 drug delivery,6,7 and targeted therapy.8−12 However, the in situ construction of self-assemblies with specific stimuli responses for accurately regulating cellular activities remains a challenge. Aim to this purpose, numerous biomaterials have been designed with desirable biomedical functions upon selfassembly under physical or biological stimuli.13 Among them, peptide-based self-assemblies have been paid wide attention because of their good biocompatibility and bioactivity.14−16 Conjugation with synthetic stimuli-responsive polymers has been a versatile way to add new values, advanced features and unique properties to peptides.17 Thermoresponsive polymers that feature a lower critical solution temperature (LCST),18 have been studied extensively and designed to act as promising smart “on−off” switches for drug delivery,19 gene transfection,20 etc. Nanostructured thermoresponsive polymers that respond to miniscule changes in temperature result in drastic discontinuous changes in their physical properties.21 Upon cooling below LCST, the polymers underwent a conformational transition from a dehydrated collapsed globule to a hydrated coil in water, realizing controlled unleashing of hydrophobic cargoes.22 © XXXX American Chemical Society
Received: April 17, 2016 Accepted: June 27, 2016
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DOI: 10.1021/acsami.6b04580 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX
Letter
ACS Applied Materials & Interfaces
Scheme 1. Schematic Representation of Thermocontrol over HBP Aggregate on Cell Surfaces for Manipulating and Monitoring HER2 Receptor Clustering
Scheme 2. Synthesis of Thermoresponsive Polymer−Peptides (PBPn): (i) AIBN, DMP, DMF, N2, 70 °C, 24 h; (ii) DCC/ DMAP, CH2Cl2, rt, 12 h; (iii) TEA, DMSO, 37 °C, 12 h
breast cancer cell proliferation inhibition (Scheme 1). In this study, the biocompatible and modifiable temperature-sensitive polymer poly(N-isopropylacrylamide), PNIPAAm, was chosen and modified to act as the thermoresponsive backbone. In addition, a functional paring motif (HBP) was obtained by tethering a HER2 targeting peptide (CGKGGMSRTMSG) to a hydrophobic bis(pyrenes) molecule (BP) that can aggregate in polar environment and exhibited aggregation-induced fluorescence (AIE) feature.26 HBP were covalently linked to the thermoresponsive polymers to give PBPn (n = 1, 2, or 3). By tuning the HBP ratio, PBP1 was screened to have a LCST close
to physiological temperature. The targeting peptides endowed PBPn targetability to HER2 receptors on HER2 overexpressed cancer cell surfaces. At 40 °C (>LCST), the PNIPAAm polymers collapsed and acted as a “shield” to block the aggregation of HBP. Upon cooling down to 35 °C (
