  Citation: Rocchi, P.; Brichart-Vernos, D.; Lux, F.; Morfin, I.; David, L.; Rodriguez-Lafrasse, C.; Tillement, O. A New Generation of Ultrasmall Nanoparticles Inducing Sensitization to Irradiation and Copper Depletion to Overcome Radioresistant and Invasive Cancers. Pharmaceutics 2022, 14, 814. https://doi.org/10.3390/ pharmaceutics14040814 Academic Editor: Leonard I. Wiebe Received: 24 February 2022 Accepted: 29 March 2022 Published: 7 April 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). pharmaceutics Article A New Generation of Ultrasmall Nanoparticles Inducing Sensitization to Irradiation and Copper Depletion to Overcome Radioresistant and Invasive Cancers Paul Rocchi 1,2,† , Delphine Brichart-Vernos 1,3,† , François Lux 1,4, *, Isabelle Morfin 5 , Laurent David 6 , Claire Rodriguez-Lafrasse 3,7,† and Olivier Tillement 1,† 1 Institut Lumière Matière, Université Claude Bernard Lyon 1CNRS UMR 5306, 69622 Villeurbanne, France; rocchi@nhtheraguix.com (P.R.); delphine.brichart@univ-lyon1.fr (D.B.-V.); olivier.tillement@univ-lyon1.fr (O.T.) 2 NH TherAguix SA, 38240 Meylan, France 3 Cellular and Molecular Radiobiology Laboratory, Lyon-Sud Medical School, UMR CNRS 5822/IP2I, Univ. Lyon, Lyon 1 University, 69921 Oullins, France; claire.lafrasse-rodriguez@univ-lyon1.fr 4 Institut Universitaire de France (IUF), 75000 Paris, France 5 LiPhy, Université Grenoble Alpes, CNRS, UMR UMR5588, 38401 Grenoble, France; isabelle.morfin@univ-grenoble-alpes.fr 6 Ingénierie des Matériaux Polymères, Université de Lyon, Université Claude Bernard Lyon 1, Université Jean Monet, Institut National des Sciences Appliquées de Lyon, CNRS, UMR 5223, 15, bd A. Latarjet, 69622 Villeurbanne, France; laurent.david@univ-lyon1.fr 7 Department of Biochemistry and Molecular Biology, Lyon-Sud Hospital, Hospices Civils of Lyon, 69310 Pierre-Bénite, France * Correspondence: francois.lux@univ-lyon1.fr; Tel.: +33-4-72-43-12-00 † These authors contribute equally to the work. Abstract: An emerging target to overcome cancer resistance to treatments is copper, which is upregu- lated in a wide variety of tumors and may be associated with cancer progression and metastases. The aim of this study was to develop a multimodal ultrasmall nanoparticle, CuPRiX, based on the clinical AGuIX nanoparticle made of the polysiloxane matrix on which gadolinium chelates are grafted. Such hybrid nanoparticles allow: (i) a localized depletion of copper in tumors to prevent tumor cell dissemination and metastasis formation and (ii) an increased sensitivity of the tumor to radiotherapy (RT) due to the presence of high Z gadolinium (Gd) atoms. CuPRiX nanoparticles are obtained by controlled acidification of AGuIX nanoparticles. They were evaluated in vitro on two cancer cell lines (lung and head and neck) using the scratch-wound assay and clonogenic cell survival assay. They were able to reduce cell migration and invasion and displayed radiosensitizing properties. Keywords: copper depletion; ultrasmall nanoparticle; radiosensitization 1. Introduction Copper is a trace metal playing a key role in a wide variety of metabolic processes. An analysis of the human proteome allowed the identification of 54 copper-binding proteins in- volved in endogenous processes such as mitochondrial respiration, antioxidant defense and extracellular matrix cross-linking [1]. Copper levels must be finely regulated to maintain homeostasis for proper cell function. Any disruption of this balance can lead to sicknesses such as Wilson’s disease (copper overload) and Menkes disease (copper deficiency) or, as described in different preclinical and clinical works, to cancer progression [2–4]. Copper may play a role in tumor growth, epithelial-to-mesenchymal transition (EMT), stabilization of the tumor microenvironment [5] and pre-metastasis niche formation [6]. It can also induce a pro-angiogenic response, which is of great importance since tumor size is limited to 1–2 mm in the absence of new blood vessel formation. Copper is also an essential cofactor of various metalloproteins known to be closely correlated with tumor Pharmaceutics 2022, 14, 814. https://doi.org/10.3390/pharmaceutics14040814 https://www.mdpi.com/journal/pharmaceutics