DNA topoisomerases (topos) are essential enzymes that regulate the topological state of DNA during cellular processes such as replication, transcription, recombination, and chromatin remodeling. Topoisomerase I (Topo I) is a ubiquitous nuclear enzyme which catalyzes the relaxation of superhelical DNA generating a transient single strand nick in the duplex, through cycles of cleavage and religation. Topoisomerase II (Topo II) mediates the ATP-dependent induction of coordinated nicks in both strands of the DNA duplex, followed by crossing of another double strand DNA through the transiently broken duplex. Although the biological functions of Topoisomerases are important for ensuing genomic integrity, the ability to interfere with enzymes or generate enzyme-mediated damage is an effective strategy for cancer therapy and, in this connection, DNA topos (I and II) proved to be the excellent targets of clinically significant classes of anticancer drugs. Actually, specific Topo I and Topo II inhibitors reversibly trap the enzyme-DNA complexes, thus converting topos into physiological poisons, able to produce permanent DNA damage, which triggers cell death. Given that both enzymes are good targets, it would be desirable to jointly inhibit them, but use-limiting toxicity of sequential or simultaneous combinations of Topo I and II poisons include severe to life-threatening neutropenia and anemia. Furthermore, the emergence of resistance phenomena to Topo I inhibitors is often accompanied by a concomitant rise in the level of Topo II expression and viceversa, leading to the failure of clinical therapies. In this regard, a single compound able to inhibit both Topo I and II may present the advantage of improving antitopoisomerase activity, with reduced toxic side effects, with respect to the combination of two inhibitors. Due to the high interest in such compounds, this review represents an update of previous works dealing with the development of dual Topo I and II inhibitors as novel anti-cancer agents. The newly collected derivatives have been described focusing attention on their chemical structures and their biological profiles.

Over the years, researchers in drug discovery have taken advantage of the use of privileged structures to design innovative hit/lead molecules. The α-ketoamide motif is found in many natural products, and it has been widely exploited by medicinal chemists to develop compounds tailored to a vast range of biological targets, thus presenting clinical potential for a plethora of pathological conditions. The purpose of this perspective is to provide insights into the versatility of this chemical moiety as a privileged structure in drug discovery. After a brief analysis of its physical–chemical features and synthetic procedures to obtain it, α-ketoamide-based classes of compounds are reported according to the application of this motif as either a nonreactive or reactive moiety. The goal is to highlight those aspects that may be useful to understanding the perspectives of employing the α-ketoamide moiety in the rational design of compounds able to interact with a specific target.

The imaging of translocator 18 kDa protein (TSPO) in living human brain with radioligands by positron emission tomography (PET) has become an important means for the study of neuroinflammatory conditions occurring in several neuropsychiatric disorders. The widely used prototypical PET radioligand [¹¹C](R)-PK 11195 ([¹¹C](R)-1; [N-methyl-¹¹C](R)-N-sec-butyl-1-(2-chlorophenyl)-N-methylisoquinoline-3-carboxamide) gives a low PET signal and is difficult to quantify, whereas later generation radioligands have binding sensitivity to a human single nucleotide polymorphism (SNP) rs6971, which imposes limitations on their utility for comparative quantitative PET studies of normal and diseased subjects. Recently, azaisosteres of 1 have been developed with improved drug-like properties, including enhanced TSPO affinity accompanied by moderated lipophilicity. Here we selected three of these new ligands (7–9) for labeling with carbon-11 and for evaluation in monkey as candidate PET radioligands for imaging brain TSPO. Each radioligand was readily prepared by ¹¹C-methylation of an N-desmethyl precursor and was found to give a high proportion of TSPO-specific binding in monkey brain. One of these radioligands, [¹¹C]7, the direct 4-azaisostere of 1, presents many radioligand properties that are superior to those reported for [¹¹C]1, including higher affinity, lower lipophilicity, and stable quantifiable PET signal. Importantly, 7 was also found to show very low sensitivity to the human SNP rs6971 in vitro. Therefore, [¹¹C]7 now warrants evaluation in human subjects with PET to assess its utility for imaging TSPO in human brain, irrespective of subject genotype.

A key role of the mitochondrial Translocator Protein 18 KDa (TSPO) in neuroinflammation has been recently proposed. However, little is known about TSPO-activated pathways underlying the modulation of reactive microglia. In the present work, the TSPO activation was explored in an in vitro human primary microglia model (immortalized C20 cells) under inflammatory stimulus. Two different approaches were used with the aim to (i) pharmacologically amplify or (ii) silence, by the lentiviral short hairpin RNA, the TSPO physiological function. In the TSPO pharmacological stimulation model, the synthetic steroidogenic selective ligand XBD-173 attenuated the activation of microglia. Indeed, it reduces and increases the release of pro-inflammatory and anti-inflammatory cytokines, respectively. Such ligand-induced effects were abolished when C20 cells were treated with the steroidogenesis inhibitor aminoglutethimide. This suggests a role for neurosteroids in modulating the interleukin production. The highly steroidogenic ligand XBD-173 attenuated the neuroinflammatory response more effectively than the poorly steroidogenic ones, which suggests that the observed modulation on the cytokine release may be influenced by the levels of produced neurosteroids. In the TSPO silencing model, the reduction of TSPO caused a more inflamed phenotype with respect to scrambled cells. Similarly, during the inflammatory response, the TSPO silencing increased and reduced the release of pro-inflammatory and anti-inflammatory cytokines, respectively. In conclusion, the obtained results are in favor of a homeostatic role for TSPO in the context of dynamic balance between anti-inflammatory and pro-inflammatory mediators in the human microglia-mediated inflammatory response. Interestingly, our preliminary results propose that the TSPO expression could be stimulated by NF-κB during activation of the inflammatory response.