Novel Hydrophilic Riminophenazines as Potent Antiprotozoal Agents

Aminopyridines in the development of drug candidates against protozoan neglected tropical diseases

Neglected tropical diseases (NTDs) pose a major threat in tropical zones for impoverished populations. Difficulty of access, adverse effects or low efficacy limit the use of current therapeutic options. Therefore, development of new drugs against NTDs is a necessity. Compounds containing an aminopyridine (AP) moiety are of great interest for the design of new anti-NTD drugs due to their intrinsic properties compared with their closest chemical structures. Currently, over 40 compounds with an AP moiety are on the market, but none is used against NTDs despite active research on APs. The aim of this review is to present the medicinal chemistry work carried out with these scaffolds, against protozoan NTDs: Trypanosoma cruzi, Trypanosoma brucei or Leishmania spp.

Studies on the Oxidation of Aromatic Amines Catalyzed by Trametes versicolor Laccase

The bio-oxidation of a series of aromatic amines catalyzed by T. versicolor laccase has been investigated exploiting either commercially available nitrogenous substrates [(E)-4-vinyl aniline and diphenyl amine] or ad hoc synthetized ones [(E)-4-styrylaniline, (E)-4-(prop-1-en-1-yl)aniline and (E)-4-(((4-methoxyphenyl)imino)methyl)phenol]. At variance to their phenolic equivalents, the investigated aromatic amines were not converted into the expected cyclic dimeric structures under T. versicolor catalysis. The formation of complex oligomeric/polymeric or decomposition by-products was mainly observed, with the exception of the isolation of two interesting but unexpected chemical skeletons. Specifically, the biooxidation of diphenylamine resulted in an oxygenated quinone-like product, while, to our surprise, in the presence of T. versicolor laccase (E)-4-vinyl aniline was converted into a 1,2-substited cyclobutane ring. To the best of our knowledge, this is the first example of an enzymatically triggered [2 + 2] olefin cycloaddition. Possible reaction mechanisms to explain the formation of these products are also reported.

From DC18 to MR07: A Metabolically Stable 4,4'-Oxybisbenzoyl Amide as a Low-Nanomolar Growth Inhibitor of P. falciparum

To improve the metabolic stability of a 4,4'-oxybisbenzoyl-based novel and potent (nanomolar-range IC₅₀ ) antiplasmodial agent previously described by us, in silico-guided structure-activity relationship (SAR) campaigns have been conducted to substitute its peptide decorations with more metabolically stable residues. The effects of the various structural modifications were then correlated with the antiplasmodial activity in vitro in phenotypic assays. Among the several derivatives synthetized and compared with the 3D-pharmacophoric map of the original lead, a novel compound, characterized by a western tert-butyl glycine residue and an eastern 1S,2S-aminoacyclohexanol, showed low-nanomolar-range antiplasmodial activity, no signs of cross-resistance and, most importantly, 47-fold improved Phase I metabolic stability when incubated with human liver microsomes. These results highlight the efficacy of in silico-guided SAR campaigns which will allow us to further optimize the structure of the new lead aiming at testing its efficacy in vivo using different routes of administration.

Models for cytotoxicity screening of antileishmanial drugs: what has been done so far?

A growing number of studies have demonstrated the in vitro potential of an impressive number of antileishmanial candidates in the past years. However, the lack of uniformity regarding the choice of cell types for cytotoxicity assays may lead to uncomparable and inconclusive data. In vitro assays relying solely on non-phagocytic cell models may not represent a realistic result as the effect of an antileishmanial agent should ideally be presented based on its cytotoxicity profile against reticuloendothelial system cells. In the present review, we have assembled studies published in the scientific literature from 2015 to 2021 that explored leishmanicidal candidates, emphasising the main host cell models used for cytotoxicity assays. The pros and cons of different host cell types as well as primary cells and cell lines are discussed in order to draw attention to the need to establish standardised protocols for preclinical testing when assessing new antileishmanial candidates.

Clofazimine derivatives as potent broad-spectrum antiviral agents with dual-target mechanism

Thirty-two clofazimine derivatives, of which twenty-two were new, were synthesized and evaluated for their antiviral effects against both rabies virus and pseudo-typed SARS-CoV-2, taking clofazimine (1) as the lead. Among them, compound 15f bearing 4-methoxy-2-pyridyl at the N5-position showed superior or comparable antiviral activities to lead 1, with the EC₅₀ values of 1.45 μM and 14.6 μM and the SI values of 223 and 6.1, respectively. Compound 15f inhibited rabies and SARS-CoV-2 by targeting G or S protein to block membrane fusion, as well as binding to L protein or nsp13 to inhibit intracellular biosynthesis respectively, and thus synergistically exerted a broad-spectrum antiviral effect. The results provided useful scientific data for the development of clofazimine derivatives into a new class of broad-spectrum antiviral candidates.

Optimization of the clofazimine structure leads to a highly water-soluble C3-aminopyridinyl riminophenazine endowed with improved anti-Wnt and anti-cancer activity in vitro and in vivo

Triple-negative breast cancer (TNBC) is a cancer subtype critically dependent upon excessive activation of Wnt pathway. The anti-mycobacterial drug clofazimine is an efficient inhibitor of canonical Wnt signaling in TNBC, reducing tumor cell proliferation in vitro and in animal models. These properties make clofazimine a candidate to become first targeted therapy against TNBC. In this work, we optimized the clofazimine structure to enhance its water solubility and potency as a Wnt inhibitor. After extensive structure-activity relationships investigations, the riminophenazine 5-(4-(chlorophenyl)-3-((2-(piperazin-1-yl)ethyl)imino)-N-(pyridin-3-yl)-3,5-dihydrophenazin-2-amine (MU17) was identified as the new lead compound for the riminophenazine-based targeted therapy against TNBC and Wnt-dependent cancers. Compared to clofazimine, the water-soluble MU17 displayed a 7-fold improved potency against Wnt signaling in TNBC cells resulting in on-target suppression of tumor growth in a patient-derived mouse model of TNBC. Moreover, allowing the administration of reduced yet effective dosages, MU17 displayed no adverse effects, most notably no clofazimine-related skin coloration.

Design, Synthesis and In Vitro Investigation of Novel Basic Celastrol Carboxamides as Bio-Inspired Leishmanicidal Agents Endowed with Inhibitory Activity against Leishmania Hsp90

The natural triterpene celastrol (CE) is here used as lead compound for the design and synthesis of a panel of eleven CE carboxamides that were tested in vitro for their growth inhibitory activity against Leishmania infantum and L.tropica parasites. Among them, in vitro screening identified four basic CE carboxamides endowed with nanomolar leishmanicidal activity, against both the promastigotes and the intramacrophage Leishmania amastigotes forms. These compounds also showed low toxicity toward two human (HMEC-1 and THP-1) and one murine (BMDM) cell lines. Interestingly, the most selective CE analogue (compound 3) was also endowed with the ability to inhibit the ATPase activity of the Leishmania protein chaperone Hsp90 as demonstrated by the in vitro assay conducted on a purified, full-length recombinant protein. Preliminary investigations by comparing it with the naturally occurring Hsp90 active site inhibitor Geldanamycin (GA) in two different in vitro experiments were performed. These promising results set the basis for a future biochemical investigation of the mode of interaction of celastrol and CE-inspired compounds with Leishmania Hsp90.