New Adamantane Phenylalkylamines with σ‑Receptor Binding Affinity and Anticancer Activity, Associated with Putative Antagonism of Neuropathic Pain Stefanos Riganas, †,∥ Ioannis Papanastasiou, † George B. Foscolos,* ,† Andrew Tsotinis, † Guillaume Serin, ‡ Jean-Franc ̧ ois Mirjolet, ‡ Kostas Dimas, § Vassilios N. Kourafalos, ∥ Andreas Eleutheriades, ∥ Vassilios I. Moutsos, ∥ Humaira Khan, ∥ Stavroula Georgakopoulou, ∥ Angeliki Zaniou, ∥ Margarita Prassa, ∥ Maria Theodoropoulou, ∥ Athanasios Mantelas, ∥ Stavroula Pondiki, ∥ and Alexandre Vamvakides ∥ † Department of Pharmaceutical Chemistry, Faculty of Pharmacy, National and Kapodistrian University of Athens, Panepistimioupoli-Zografou, 15771 Athens, Greece ‡ Oncodesign S.A., 20 Rue Mazen, F-21076 Dijon, France § Division of Pharmacology, Foundation for Biomedical Research of the Academy of Athens (FBRAA), 11527 Athens, Greece ∥ Anavex Life Sciences, 27 Marathonos Avenue, 15351 Pallini, Athens, Greece * S Supporting Information ABSTRACT: The synthesis of the adamantane phenylalkylamines 2a−d, 3a−c, and 4a−e is described. These compounds exhibited significant antiproliferative activity, in vitro, against eight cancer cell lines tested. The σ 1 , σ 2 , and sodium channel binding affinities of compounds 2a, 3a, 4a, and 4c−e were investigated. The most interesting analogue, 4a, exhibited significant in vivo anticancer profile on pancreas, prostate, leukemia, and ovarian cancer cell line xenografts together with apoptosis and caspase-3 activation. Inhibition of the cancer cells cycle at the sub-G1 level was also obtained with 4a. Finally, encouraging results were observed with 4a in vivo on mice, suggesting putative antimetastatic and analgesic activities of this compound. ■ INTRODUCTION Cancer and neurogenerative diseases, two of the most important areas for medical research, both implicate σ- receptors. σ-Ligands can therefore be expected to be putative anticancer drugs. 1−5 Indeed, σ-receptors are expressed to a greater degree in tumors than they are in the surrounding normal tissue. 6−13 σ-Receptors have been classified as a distinct pharmacological entity, and their function was shown to be unrelated to the function of opioid receptors. 2,5,14 On the basis of the ligand selectivity in the binding assays, two subtypes, σ 1 and σ 2 receptors, were identified. 2,5,15 Further, σ 1 -receptors have been shown to be involved in programmed cell death (apoptosis), with σ 1 -agonists being antiapoptotic and neuro- protective, with putative antineurodegenerative activity. 2,16−20 σ 1 -Antagonists or σ 2 -agonists are proapoptotic and can, because of the high expression of σ 1 and σ 2 receptors in the rapidly proliferating cancer cells, 6−13 act as putative anticancer drugs by inducing cell death via apoptosis. 21−32 There is considerable evidence of antiproliferative and cytotoxic activity for σ 1 - antagonists, 21,23,24,26,29,31 σ 2 -putative agonists, 22,23,25,28,30 mixed σ 1 /σ 2 -ligands, 21,23,26 and even one σ 1 -agonist. 27 More specifi- cally, it has been shown that σ 1 -ligands (putative antagonists) induce caspase-dependent apoptosis, 24,31 which is in accord with recent observations that σ 1 -agonists prevent caspase-3 activation. 2,17,19 On the other hand, σ 2 -ligands (putative agonists) have been shown to activate a caspase-independent apoptotic pathway and were proposed as putative anticancer drugs, 22,25 but caspase-3 activation was also described for σ 2 anticancer ligands. 28,30,31 Recent data have also suggested the importance of the σ 1 -receptor modulated ion channels (Na + , K + , Cl − , Ca 2+ ) 2,32−35 and σ 1 -receptor binding of cholesterol in lipid rafts concerning the proliferation of cancer cells. 36,37 The Na + channels, in particular, are modulated by σ 1 -receptors and are implicated in the adhesion, migration, and apoptosis of cancer cells. 34,35,38−40 Important advances were recently made on the mechanism of action of σ-ligands and their putative role as therapeutic anticancer agents. In particular, the σ 1 -receptor was cloned 2,41 allowing more accurate pharmacological evaluation 42 of its specific role in the endoplasmic reticulum (ER), in the apoptosis of cancer cells, 1,2,4,16 and in its connection with the impairing action on the G 0 /G 1 cell cycle phases. 31,32 Classical SAR studies indicated that the presence of a cycloalkyl or aryl group attached to the cationic amine center via a linker of a three- to five-membered chain (including a heteroatom) was essential for affinity at the σ-receptors. 43,44 In previous work, we reported 1-[p-[α-(1-adamantyl)benzyl]- phenyl]piperazines 1 as antiproliferative agents. Piperazine 1a (R = CH 3 ) presented appreciable anticancer activity, which was related to its affinity for σ-receptors and binding to site 2 of the Received: September 10, 2012 Article pubs.acs.org/jmc © XXXX American Chemical Society A dx.doi.org/10.1021/jm3013008 | J. Med. Chem. XXXX, XXX, XXX−XXX