Citation: Haustrate, A.; Shapovalov, G.; Spriet, C.; Cordier, C.; Kondratskyi, A.; Noyer, L.; Foulquier, F.; Prevarskaya, N.; Lehen’kyi, V. TRPV6 Calcium Channel Targeting by Antibodies Raised against Extracellular Epitopes Induces Prostate Cancer Cell Apoptosis. Cancers 2023, 15, 1825. https:// doi.org/10.3390/cancers15061825 Academic Editors: Luis A. Pardo and Árpád Szállási Received: 7 December 2022 Revised: 20 February 2023 Accepted: 10 March 2023 Published: 17 March 2023 Copyright: © 2023 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/). cancers Article TRPV6 Calcium Channel Targeting by Antibodies Raised against Extracellular Epitopes Induces Prostate Cancer Cell Apoptosis Aurélien Haustrate 1,2 , George Shapovalov 1 , Corentin Spriet 3 , Clément Cordier 1 , Artem Kondratskyi 1 , Lucile Noyer 1 , François Foulquier 3 , Natalia Prevarskaya 1 and V’yacheslav Lehen’kyi 1,2, * 1 Laboratory of Cell Physiology, INSERM U1003, Laboratory of Excellence Ion Channels Science and Therapeutics, Department of Biology, Faculty of Science and Technologies, University of Lille, 59650 Villeneuve d’Ascq, France; natacha.prevarskaya@univ-lille.fr (N.P.) 2 FONDATION ARC, 9 rue Guy Môquet, 94830 Villejuif, France 3 Unité de Glycobiologie Structurale et Fonctionnelle (UGSF), CNRS, UMR 8576, Université de Lille, 59000 Lille, France * Correspondence: vyacheslav.lehenkyi@univ-lille.fr; Tel.: +33-3-2033-7078 Simple Summary: The TRPV6 channel is upregulated in many cancers and is associated with bad prognosis. Despite this fact, no reliable tool to target TRPV6 is known so far. Two prospective antibodies have been generated capable of binding to TRPV6 and thereby transiently activating calcium currents. This transient activation of TRPV6 and increase in intracellular calcium led to the apoptosis induction of prostate cancer cells. Only cells showing no TRPV6 membrane expression avoided cell death. Thus, the activation of the TRPV6 channel per se is extremely efficient and is likely to be more prospective than its inhibition. Abstract: The TRPV6 calcium channel is known to be up-regulated in various tumors. The efforts to target the TRPV6 channel in vivo are still ongoing to propose an effective therapy against cancer. Here, we report the generation of two antibodies raised against extracellular epitopes corresponding to the extracellular loop between S1 and S2 (rb79) and the pore region (rb82). These antibodies generated a complex biphasic response with the transient activation of the TRPV6 channel. Store-operated calcium entry was consequently potentiated in the prostate cancer cell line LNCaP upon the treatment. Both rb79 and rb82 antibodies significantly decreased cell survival rate in a dose-dependent manner as compared to the control antibodies of the same isotype. This decrease was due to the enhanced cell death via apoptosis revealed using a sub-G1 peak in a cell cycle assay, TUNEL assay, and a Hoechst staining, having no effects in the PC3M trpv6−/− cell line. Moreover, all TUNEL-positive cells had TRPV6 membrane staining as compared to the control antibody treatment where TRPV6-positive cells were all TUNEL negative. These data clearly demonstrate that TRPV6 channel targeting using rb79 and rb82 antibodies is fatal and may be successfully used in the anticancer therapies. Keywords: therapeutic antibody; TRPV6 channel; tumor targeting; apoptosis 1. Introduction According to the French National Institute of Cancer (INCa), 384,442 new cancer cases were reported in France in 2015 with the death rate reaching 149,456 of the same year (http://lesdonnees.e-cancer.fr/, accessed on 19 May 2018). Literally, 411 persons die every day from cancer. Of them, the most mortality is from lung, colon-rectum, breast, and prostate (25.3%, 15.0%, 10.1, and 7.5% of the total number, respectively) cancers (http://lesdonnees.e-cancer.fr/, accessed on 19 May 2018). Moreover, the treatment is very expensive and has important consequences on patient health [1]. In Germany, for instance, Cancers 2023, 15, 1825. https://doi.org/10.3390/cancers15061825 https://www.mdpi.com/journal/cancers