Discovery of RC-752, a Novel Sigma-1 Receptor Antagonist with Antinociceptive Activity: A Promising Tool for Fighting Neuropathic Pain

Neuropathic pain (NP) is a chronic condition resulting from damaged pain-signaling pathways. It is a debilitating disorder that affects up to 10% of the world's population. Although opioid analgesics are effective in reducing pain, they present severe risks; so, there is a pressing need for non-opioid pain-relieving drugs. One potential alternative is represented by sigma-1 receptor (S1R) antagonists due to their promising analgesic effects. Here, we report the synthesis and biological evaluation of a series of S1R antagonists based on a 2-aryl-4-aminobutanol scaffold. After assessing affinity toward the S1R and selectivity over the sigma-2 receptor (S2R), we evaluated the agonist/antagonist profile of the compounds by investigating their effects on nerve growth factor-induced neurite outgrowth and aquaporin-mediated water permeability in the presence and absence of oxidative stress. (R/S)-RC-752 emerged as the most interesting compound for S1R affinity (K_i S1R = 6.2 ± 0.9) and functional antagonist activity. Furthermore, it showed no cytotoxic effect in two normal human cell lines or in an in vivo zebrafish model and was stable after incubation in mouse plasma. (R/S)-RC-752 was then evaluated in two animal models of NP: the formalin test and the spinal nerve ligation model. The results clearly demonstrated that compound (R/S)-RC-752 effectively alleviated pain in both animal models, thus providing the proof of concept of its efficacy as an antinociceptive agent.

From Nature to Synthetic Compounds: Novel 1(N),2,3 Trisubstituted-5-oxopyrrolidines Targeting Multiple Myeloma Cells

The insurgence of drug resistance in treating Multiple Myeloma (MM) still represents a major hamper in finding effective treatments, although over the past decades new classes of drugs, such as proteasome inhibitors and immunomodulatory drugs, have been discovered. Recently, our research team, within a Nature-Aided Drug Discovery project, isolated from Hibiscus Sabdariffa L. calyces the secondary metabolite called Hib-ester which possesses antiproliferative properties against human multiple myeloma RPMI 8226 cells, reduces migration and cell invasion and inhibits proteasome without neurotoxic effects. In the present study, we explored the chemical spaces of the hit compound Hib-ester. We explored the structure-activity relationships (SAR), and we optimized the scaffold through sequentially modifying Hib-ester subunits. Compound screening was performed based on cytotoxicity against the RPMI 8226 cells to assess the potential efficacy toward human MM. The ability of the most effective molecules to inhibit the proteasome was evaluated and the binding mode of the most promising compounds in the proteasome chymotrypsin binding pocket was deciphered through molecular modeling simulations. Compounds 13 and 14 are more potent than Hib-ester, demonstrating that our strategy was suitable for the identification of a novel chemotype for developing possible drug candidates and hopefully widening the drug armamentarium against MM.

Exploring the RC-106 Chemical Space: Design and Synthesis of Novel (E)-1-(3-Arylbut-2-en-1-yl)-4-(Substituted) Piperazine Derivatives as Potential Anticancer Agents

Despite the fact that significant advances in treatment of common cancers have been achieved over the years, orphan tumors still represent an important unmet medical need. Due to their complex multifactorial origin and limited number of cases, such pathologies often have very limited treatment options and poor prognosis. In the search for new anticancer agents, our group recently identified RC-106, a Sigma receptor modulator endowed with proteasome inhibition activity. This compound showed antiproliferative activity toward different cancer cell lines, among them glioblastoma (GB) and multiple myeloma (MM), two currently unmet medical conditions. In this work, we directed our efforts toward the exploration of chemical space around RC-106 to identify new active compounds potentially useful in cancer treatment. Thanks to a combinatorial approach, we prepared 41 derivatives of the compound and evaluated their cytotoxic potential against MM and GB. Three novel potential anticancer agents have been identified.

BOPC1 Enantiomers Preparation and HuR Interaction Study. From Molecular Modeling to a Curious DEEP-STD NMR Application

The Hu family of RNA-binding proteins plays a crucial role in post-transcriptional processes; indeed, Hu-RNA complexes are involved in various dysfunctions (i.e., inflammation, neurodegeneration, and cancer) and have been recently proposed as promising therapeutic targets. Intrigued by this concept, our research efforts aim at identifying small molecules able to modulate HuR-RNA interactions, with a focus on subtype HuR, upregulated and dysregulated in several cancers. By applying structure-based design, we had already identified racemic trans-BOPC1 as promising HuR binder. In this Letter, we accomplished the enantio-resolution, the assignment of the absolute configuration, and the recognition study with HuR of enantiomerically pure trans-BOPC1. For the first time, we apply DEEP (differential epitope mapping)-STD NMR to study the interaction of BOPC1 with HuR and compare its enantiomers, gaining information on ligand orientation and amino acids involved in the interaction, and thus increasing focus on the in silico binding site model.

Novel Compounds Targeting the RNA-Binding Protein HuR. Structure-Based Design, Synthesis, and Interaction Studies

The key role of RNA-binding proteins (RBPs) in regulating post-transcriptional processes and their involvement in several pathologies (i.e., cancer and neurodegeneration) have highlighted their potential as therapeutic targets. In this scenario, Embryonic Lethal Abnormal Vision (ELAV) or Hu proteins and their complexes with target mRNAs have been gaining growing attention. Compounds able to modulate the complex stability could constitute an innovative pharmacological strategy for the treatment of numerous diseases. Nevertheless, medicinal-chemistry efforts aimed at developing such compounds are still at an early stage. As part of our ongoing research in this field, we hereby present the rational design and synthesis of structurally novel HuR ligands, potentially acting as HuR-RNA interferers. The following assessment of the structural features of their interaction with HuR, combining saturation-transfer difference NMR and in silico studies, provides a guide for further research on the development of new effective interfering compounds of the HuR-RNA complex.

PEG 400/Cerium Ammonium Nitrate Combined with Microwave-Assisted Synthesis for Rapid Access to Beta-Amino Ketones. An Easy-to-Use Protocol for Discovering New Hit Compounds

Compound libraries are important requirement in target-based drug discovery. In the present work, a small focused compound library based on β-aminoketone scaffold has been prepared combining microwave-assisted organic synthesis (MAOS) with polymer-assisted solution phase synthesis (PASPS) and replacing reaction workup standard purification procedures with solid phase extraction (SPE). Specifically, the effects of solvent, such as dioxane, dimethylformamide (DMF), polyethylene glycol 400 (PEG 400), temperature, irradiation time, stoichiometric ratio of reagents, and catalysts (HCl, acetic acid, cerium ammonium nitrate (CAN)) were investigated to maximize both conversion and yield. The optimized protocol generally afforded the desired products in satisfying yields and purities. The designed library is a part of our current research on sigma 1 receptor modulators, a valuable tool for the identification of novel potential hit compounds.

Gaining in pan-affinity towards sigma 1 and sigma 2 receptors. SAR studies on arylalkylamines

Sigma Receptor (SR) modulators are involved in different signal transduction pathways, representing important pharmacological/therapeutic tools in several pathological conditions, such as neurodegenerative diseases and cancers. To this purpose, numerous compounds have been developed in order to target selectively one of the two subtypes (S1R and S2R) as chemotherapeutic agent. However, experiments have also shown that ligands which are able to bind both SR subtypes can be useful for the diagnosis and/or the treatment of cancers. Therefore, the discovery of compounds with good affinity towards both S1R and S2R ('pan-modulators') is also of great interest and still represents a challenge up to now. For this reason, we synthesized novel arylalkylamines with the aim to obtain compounds with S1R and S2R affinity in the nM range and, by modeling quantitative structure-activity relationships (QSARs), we identified the essential structural features to obtain promising pan-compounds.

Bradykinin antagonists modified with dipeptide mimetic β-turn inducers

Bradykinin (BK) is involved in a wide variety of pathophysiological processes. Potent BK peptide antagonists can be developed introducing constrained unnatural amino acids, necessary to force the secondary structure of the molecule. In this paper, we report a structure-activity relationship study of two peptide analogues of the potent B2 antagonist HOE 140 by replacing the D-Tic-Oic dipeptide with conformationally constrained dipeptide mimetic beta-turn inducers.