Atovaquone-Statine “Double-Drugs” with High Antiplasmodial Activity

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.

Novel molecule combinations and corresponding hybrids targeting artemisinin-resistant Plasmodium falciparum parasites

Malaria is still considered as the major parasitic disease and the development of artemisinin resistance does not improve this alarming situation. Based on the recent identification of relevant malaria targets in the artemisinin resistance context, novel drug combinations were evaluated against artemisinin-sensitive and artemisinin-resistant Plasmodium falciparum parasites. Corresponding hybrid molecules were also synthesized and evaluated for comparison with combinations and individual pharmacophores (e.g. atovaquone, mefloquine or triclosan). Combinations and hybrids showed remarkable antimalarial activity (IC₅₀ = 0.6 to 1.1 nM for the best compounds), strong selectivity, and didn't present any cross-resistance with artemisinin. Moreover, the combination triclosan + atovaquone showed high activity against artemisinin-resistant parasites at the quiescent stage but the corresponding hybrid lost this pharmacological property. This result is essential since only few molecules active against quiescent artemisinin-resistant parasites are reported. Our promising results highlight the potential of these combinations and paves the way for pharmacomodulation work on the best hybrids.

Into the Fray! A Beginner's Guide to Medicinal Chemistry

Modern medicinal chemistry is a complex, multidimensional discipline that operates at the interface of the chemical and biological sciences. The medicinal chemistry contribution to drug discovery is typically described in the context of the well-recited linear progression of the drug discovery pipeline. However, compound optimization is idiosyncratic to each project, and clear definitions of hit and lead molecules and the subsequent progress along the pipeline becomes easily blurred. In addition, this description lacks insight into the entangled relationship between chemical and pharmacological properties, and thus provides limited guidance on how innovative medicinal chemistry strategies can be applied to solve optimization problems, regardless of the stage in the pipeline. Through discussion and illustrative examples, this article seeks to provide insights into the finesse of medicinal chemistry and the subtlety of balancing chemical properties pharmacology. In so doing, it aims to serve as an accessible and simple-to-digest guide for anyone who wishes to learn about the underlying principles of medicinal chemistry, in a context that has been decoupled from the pipeline description.

Plasmepsin Inhibitors in Antimalarial Drug Discovery: Medicinal Chemistry and Target Validation (2000 to Present)

Plasmepsins represent novel antimalarial drug targets. However, plasmepsin-based antimalarial drug discovery efforts in the past 2 decades have generally suffered some drawbacks including lack of translatability of target inhibition to potent parasite inhibition in vitro and in vivo as well as poor selectivity over the related human aspartic proteases. Most studies reported in this period have over-relied on the use of hemoglobinase plasmepsins I-IV (particularly I and II) as targets for the new inhibitors even though these are known to be nonessential at the asexual stage of parasite development. Therefore, future antimalarial drug discovery efforts seeking to identify plasmepsin inhibitors should focus on incorporating non-hemoglobinase plasmepsins such as V, IX, and X in their screening in order to maximize chances of success. Additionally, there is need to go beyond just target enzymatic activity profiling to establishing cellular activity, physicochemical as well as drug metabolism and pharmacokinetics properties and finally in vivo proof-of-concept while ensuring selectivity over related human host proteases.

Discovery and Pharmacophore Mapping of a Low-Nanomolar Inhibitor of P. falciparum Growth

The treatment of malaria, the most common parasitic disease worldwide and the third deadliest infection after HIV and tuberculosis, is currently compromised by the dramatic increase and diffusion of drug resistance among the various species of Plasmodium, especially P. falciparum (Pf). In this view, the development of new antiplasmodial agents that are able to act via innovative mechanisms of action, is crucial to ensure efficacious antimalarial treatments. In one of our previous communications, we described a novel class of compounds endowed with high antiplasmodial activity, characterized by a pharmacophore never described before as antiplasmodial and identified by their 4,4'-oxybisbenzoyl amide cores. Here, through a detailed structure-activity relationship (SAR) study, we thoroughly investigated the chemical features of the reported scaffolds and successfully built a novel antiplasmodial agent active on both chloroquine (CQ)-sensitive and CQ-resistant Pf strains in the low nanomolar range, without displaying cross-resistance. Moreover, we conducted an in silico pharmacophore mapping.

Are Antimalarial Hybrid Molecules a Close Reality or a Distant Dream?

Emergence of drug-resistant Plasmodium falciparum strains has led to a situation of haste in the scientific and pharmaceutical communities. Hence, all their efforts are redirected toward finding alternative chemotherapeutic agents that are capable of combating multidrug-resistant parasite strains. In light of this situation, scientists have come up with the concept of hybridization of two or more active pharmacophores into a single chemical entity, resulting in "antimalarial hybrids." The approach has been applied widely for generation of lead compounds against deadly diseases such as cancer and AIDS, with a proven potential for use as novel drugs, but is comparatively new in the sphere of antimalarial drug discovery. A sudden surge has been evidenced in the number of studies on the design and synthesis of hybrids for treating malaria and may be regarded as proof of their potential advantages over artemisinin-based combination therapy (ACT). However, it is evident from recent studies that most of the potential advantages of antimalarial hybrids, such as lower toxicity, better pharmacokinetics, and easier formulation, have yet to be realized. A number of questions left unaddressed at present need to be answered before this approach can progress to the late stages of clinical development and prove their worth in the clinic. To the best of our knowledge, this compilation is the first attempt to shed light on the shortcomings that are surfacing as more and more studies on molecular hybridization of the active pharmacophores of known antimalarials are being published.

Dicarboxylic esters: Useful tools for the biocatalyzed synthesis of hybrid compounds and polymers

Dicarboxylic acids and their derivatives (esters and anhydrides) have been used as acylating agents in lipase-catalyzed reactions in organic solvents. The synthetic outcomes have been dimeric or hybrid derivatives of bioactive natural compounds as well as functionalized polyesters.

Discovery of oxybisbenzoylamides as a new class of antimalarial agents

A new antimalarial pharmacophore has been obtained starting from previously described dual inhibitors of Plasmodium falciparum.

Exploiting enzymatic regioselectivity: a facile methodology for the synthesis of polyhydroxylated hybrid compounds

Polyhydroxylated hybrid molecules have been synthesized using a protocol based on the regioselective acylation of the target compounds with activated dicarboxylic acids catalyzed by Novozym-435. The procedure implies that the mixed ester derivatives prepared and isolated from the first esterification step act as acylating agents in the second esterification step.

A wortmannin-cetuximab as a double drug

Double drugs are obtained when two pharmacologically active entities are covalently joined to improve potency. We conjugated the viridin Wm with a self-activating linkage to cetuximab and demonstrated the retention of immunoreactivity by the conjugate. Though cetuximab lacked a growth inhibitory activity against A549 cells, the Wm-cetuximab conjugate had an antiproliferative IC(50) of 155 nM in vitro. The chemistry of attaching a self-releasing Wm to clinically approved antibodies is general and, in selected instances, may yield antibody-based double drugs with improved efficacy.