The combination of racemic praziquantel, (RS)-PZQ, with aliphatic dicarboxylic acids of the homologous series HOOC−(CH 2 ) n −COOH (with n = 0−8) and the unsaturated analogues of succinic acid as cocrystal formers via liquid-assisted grinding provided a total of nine 1:1 and 2:1 cocrystals with oxalic acid, malonic acid, succinic acid (two polymorphic phases), maleic acid, fumaric acid, glutaric acid, adipic acid, and pimelic acid. The cocrystalline phases were identified first by XRPD analysis and then structurally characterized by IR spectroscopy and, as far as possible, by single-crystal X-ray diffraction analysis. Crystals suitable for XRD analysis were obtained for seven cocrystals and, additionally, for (RS)-PZQ. The analysis of the supramolecular interactions in the crystal structures has shown that the dominant hydrogen bonding patterns within the cocrystals are heterodimeric motifs formed through O−H•••O hydrogen bonds between PZQ and the dicarboxylic acids, which mostly contain additionally at least one secondary C−H•••O contact. In all crystal structures, the PZQ molecules are connected with each other through cyclic homodimeric hydrogen bonding interactions formed mainly through C−H•••O, but also through C−H•••π contacts, giving overall 1D, 2D or 3D hydrogen bonded networks. The crystallographic study also allowed us to establish that there are two main rotational conformers for PZQ, which differ in the configuration of the CO groups in the piperazinone−cyclohexylcarbonyl segment. In the crystal structure of (RS)-PZQ, all four independent molecules in the asymmetric unit have the syn-conformation, which in the hemihydrates, viz. (R)-PZQ•0.5H 2 O and (S)-PZQ•0.5H 2 O, and all cocrystals except for one are switched to the anti-antagonist.

In part I of this review we assessed nanoscience-related definitions as applied to pharmaceuticals and we discussed all 43 currently approved drug formulations, which are widely publicized as nanopharmaceuticals or nanomedicines. In continuation, here we review the currently ongoing clinical trials within the broad field of nanomedicine. Confining the definition of nanopharmaceuticals to therapeutic formulations, in which the unique physicochemical properties expressed in the nanosize range, when man-made, play the pivotal therapeutic role, we found an apparently low number of trials, which reflects neither the massive investments made in the field of nanomedicine nor the general hype associated with the term “nano.” Moreover, after an extensive search for information through clinical trials, we found only two clinical trials with materials that show unique nano-based properties, ie, properties that are displayed neither on the atomic nor on the bulk material level.

Despite being a conceptually appealing alternative to conventional antibiotics, a major challenge toward the successful implementation of antisense treatments for bacterial infections is the development of efficient oligonucleotide delivery systems. Cationic vesicles (bolasomes) composed of dequalinium chloride (“DQAsomes”) have been used to deliver plasmid DNA across the cardiolipin-rich inner membrane of mitochondria. As cardiolipin is also a component of many bacterial membranes, we investigated the application of cationic bolasomes to bacteria as an oligonucleotide delivery system. Antisense sequences designed in silico to target the expression of essential genes of the bacterial pathogen, Clostridium difficile , were synthesized as 2′- O -methyl phosphorothioate gapmer antisense oligonucleotides (ASO). These antisense gapmers were quantitatively assessed for their ability to block mRNA translation using luciferase reporter and C. difficile protein expression plasmid constructs in a coupled transcription–translation system. Cationic bolaamphiphile compounds (dequalinium derivatives) of varying alkyl chain length were synthesized and bolasomes were prepared via probe sonication of an aqueous suspension. Bolasomes were characterized by particle size distribution, zeta potential, and binding capacities for anionic oligonucleotide. Bolasomes and antisense gapmers were combined to form antisense nanocomplexes. Anaerobic C. difficile log phase cultures were treated with serial doses of gapmer nanocomplexes or equivalent amounts of empty bolasomes for 24 hours. Antisense gapmers for four gene targets achieved nanomolar minimum inhibitory concentrations for C. difficile , with the lowest values observed for oligonucleotides targeting polymerase genes rpoB and dnaE . No inhibition of bacterial growth was observed from treatments at matched dosages of scrambled gapmer nanocomplexes or plain, oligonucleotide-free bolasomes compared to untreated control cultures. We describe the novel application of cationic bolasomes to deliver ASOs into bacteria. We also report the first successful in vitro antisense treatment to inhibit the growth of C. difficile .

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