New bis-thiazolium analogues as potential antimalarial agents: design, synthesis, and biological evaluation.

Bis-thiazolium salts are able to inhibit phosphatidylcholine biosynthesis in Plasmodium and to block parasite proliferation in the low nanomolar range. However, due to their physicochemical properties (i.e., permanent cationic charges, the flexibility, and lipophilic character of the alkyl chain), the oral bioavailability of these compounds is low. New series of bis-thiazolium-based drugs have been designed to overcome this drawback. They feature linker rigidification via the introduction of aromatic rings and/or a decrease in the overall lipophilicity through the introduction of heteroatoms. On the basis of the structure-activity relationships, a few of the promising compounds (9, 10, and 11) were found to exhibit potent antimalarial in vitro and in vivo activities (EC(50) < 10 nM and ED(50) ip < 0.7 mg/kg).

Disulfide prodrugs of albitiazolium (T3/SAR97276): synthesis and biological activities.

We report herein the design, synthesis, and biological screening of a series of 15 disulfide prodrugs as precursors of albitiazolium bromide (T3/SAR97276, compound 1), a choline analogue which is currently being evaluated in clinical trials (phase II) for severe malaria. The corresponding prodrugs are expected to revert back to the active bis-thiazolium salt through an enzymatic reduction of the disulfide bond. To enhance aqueous solubility of these prodrugs, an amino acid residue (valine or lysine) or a phosphate group was introduced on the thiazolium side chain. Most of the novel derivatives exhibited potent in vitro antimalarial activity against P. falciparum. After oral administration, the cyclic disulfide prodrug 8 showed the best improvement of oral efficacy in comparison to the parent drug.

Exploration of potential prodrug approach of the bis-thiazolium salts T3 and T4 for orally delivered antimalarials.

We report here the synthesis and biological evaluation of a series of 37 compounds as precursors of potent antimalarial bis-thiazolium salts (T3 and T4). These prodrugs were either thioester, thiocarbonate or thiocarbamate type and were synthesized in one step by reaction of an alkaline solution of the parent drug with the appropriate activated acyl group. Structural variations affecting physicochemical properties were made in order to improve oral activity. Twenty-five of them exhibited potent antimalarial activity with IC(50) lower than 7nM against Plasmodium falciparum in vitro. Notably, 3 and 22 showed IC(50)=2.2 and 1.8nM, respectively. After oral administration 22 was the most potent compound clearing the parasitemia in Plasmodium vinckei infected mice with a dose of 1.3mg/kg.

Synthesis and evaluation of bis-thiazolium salts as potential antimalarial drugs.

An innovative therapeutic approach based on the use of dicationic derivatives was previously designed to inhibit the biosynthesis of phosphatidylcholine in Plasmodium spp. Among these, bis-thiazolium salts were shown to block proliferation of the malaria parasite at concentrations in the low nanomolar range. However, due to unsuitable molecular properties such as the presence of the two polar heads and flexibility in the linker, these compounds have low oral bioavailability. To characterize the structural requirements of the linker that lead to more rigid analogues with fewer rotatable bonds but which retain antimalarial activity, a new series of compounds incorporating an aryl moiety and eventually oxygen atoms were prepared, and their biological activity was evaluated. Structure-activity relationships suggest that the optimal linker construct is an aromatic group with two n-butyl chains branched at the para position; two new leads (compounds 39 and 40) were selected for further development.

Short peptide nucleic acids (PNA) inhibit hepatitis C virus internal ribosome entry site (IRES) dependent translation in vitro.

The internal ribosome entry site (IRES) of hepatitis C virus (HCV) which governs the initiation of protein synthesis from viral RNA represents an ideal target for antisense approaches. Using an original bicistronic plasmid, we first established that sequence and translational activity of HCV IRESs cloned from six patients, whether responders or not to combination therapy, were conserved. We then tested the hypothesis that antisense molecules, i.e. short peptide nucleic acids (PNA), could inhibit HCV translation by binding to the highly conserved IIId or IV loop regions of the IRES. Five 6-10mer PNAs were designed. They strongly inhibit HCV IRES-driven translation in a rabbit reticulocyte lysate assay. This inhibition was highly specific since corresponding PNAs with only one mismatch were inactive. Short phosphorothioate oligonucleotides of same sequence were unable to inhibit HCV translation. PNA molecule was shown to have anti-HCV activity in Huh-7.5 cells when electroporated with a full-length HCV genome construct. Using oligonucleotide as carrier, PNA was also transfected in HCV replicon-harboring cells and in JFH1 infected Huh-7.5 cells.

A cyclic PNA-based compound targeting domain IV of HCV IRES RNA inhibits in vitro IRES-dependent translation.

A cyclic molecule 1 constituted by a hepta-peptide nucleic acid sequence complementary to the apical loop of domain IV of hepatitis C virus (HCV) internal ribosome entry site (IRES) RNA has been prepared via a 'mixed' liquid-phase strategy, which relies on easily available protected PNA and poly(2-aminoethylglycinamide) building blocks. This compound 1 has been elaborated to mimic 'loop-loop' interactions. For comparison, its linear analog has also been investigated. Although preliminary biological assays have revealed the ability of 1 to inhibit in vitro the HCV IRES-dependent translation in a dose-dependent manner, the linear analog has shown a slightly higher activity.