Determination of metabolic profiles of new chemical entities is a key step in the process of drug discovery, since it influences pharmacokinetic characteristics of therapeutic compounds. One of the main challenges of medicinal chemistry is not only to design compounds demonstrating beneficial activity, but also molecules exhibiting favourable pharmacokinetic parameters. Chemical compounds can be divided into those which are metabolized relatively fast and those which undergo slow biotransformation. Rapid biotransformation reduces exposure to the maternal compound and may lead to the generation of active, non-active or toxic metabolites. In contrast, high metabolic stability may promote interactions between drugs and lead to parent compound toxicity. In the present paper, issues of compound metabolic stability will be discussed, with special emphasis on its significance, in vitro metabolic stability testing, dilemmas regarding in vitro-in vivo extrapolation of the results and some aspects relating to different preclinical species used in in vitro metabolic stability assessment of compounds.

RNA interference (RNAi) is an efficient process of posttranscriptional gene silencing. In recent years it has been developed into a new technology in biopharmaceutical fields of science. RNAi products include short interference RNA (siRNA) but also short hairpin RNA (shRNA), bifunctional short hairpin RNA (bi-shRNA) and microRNA (miRNA). They combine with homologous fragments of the mRNA and cause its degradation. It results in inhibition of protein synthesis, or in mutation in the gene encoding it. RNAi has been used in analysis of genomes and creation of new animal models to test drugs. From the pharmaceutical point of view, what is the most important is its therapeutic application. So far the basic and clinical research has been focused on the following targets: macular degeneration, cancer and antiviral therapy. But there are also reports on clinical trials in asthma, hypercholesterolemia and genetic diseases such as inherited skin disorders and amyloidosis. Among over 20 therapeutics that reached clinical trials, only few are still investigated. Another few are clinical candidates. The review focuses on RNAi products under clinical evaluation and their most promising new applications.

The serotonergic system is involved in pathomechanisms of both epilepsy and neuropathic pain. So far, participation in the epileptogenesis and maintenance of epilepsy was proved for 5-HT_1A, 5-HT_2C, 5-HT₃, 5-HT₄ and 5-HT7 receptors as well as 5-HTT serotonin transporter. Depending on the receptor type or its localization, its stimulation may increase or decrease neuronal excitability. According to the available data, neuropathic pain mechanisms involve 5-HT_1A/1B/1D, 5-HT_2A/2B/2C, 5-HT₃, 5-HT₄, 5-HT₆, 5-HT₇ receptors and 5-HTT serotonin transporter. Changes in their expression modulate pain mainly by affecting the transmission through serotonergic descending pathways. Several compounds, whose mechanisms of action base on influence on the serotonergic system, are already in use. These are 5-HT₃ agonists (triptans) in case of migraine, tricyclic antidepressants or monoamine reuptake inhibitors in neuropathic pain treatment. In addition, selective and non-selective ligands are tested for their anticonvulsant or analgesic properties. Some ED₅₀ values have been already obtained in such animal models as maximal electroshock (MES)-induced seizures (epilepsy), spinal nerve ligation (SNL), chronic constriction injury (CCI) or formalin (neuropathic pain). This review shows that in case of drug discovery within the serotonergic system one must take into account special significance of factors such as: the species, the type of model, the route of administration, and the dose range.

Beta-blockers are a very important group of drugs widely used for the treatment of cardiovascular diseases. All aryloxyaminopropanols are chiral and show different stereoselectivity in their pharmacodynamic and pharmacokinetic properties for each enantiomer. The more potent beta-adrenoceptor blocking activity is generally associated with (S)-enantiomers. Most beta-blocking agents are sold as racemates although (R)- enantiomers not only show in some cases lack of activity but might be responsible for undesirable effects. Among reports on the direct enzymatic resolution of the most representative beta-blocker propranolol, the most interesting is N-acetylation method with commercially available lipases to yield (S)-Nacetylpropranolol. Another type of the one-step (S)-isomer biocatalytic preparation from racemic mixture of propranolol is the biodegradation with the fungus. Biocatalytic methods of obtaining homochiral beta-blockers that are focused on production of versatile precursors are widely described in literature. The strategies based on the use of glycidol and derivatives as C-3 synthones have been shown to be extremely useful for the introduction of the 2-propanol chain on the aromatic system. Halohydrins are the established intermediates in the preparation of optically active beta-blockers. Its resolution by esterhydrolases has been used as a standard alternative in preparation of the homochiral propranolol. Additionally, the enzymatic resolution of the following intermediates was reported: 1-azido-3- aryloxy-2-propanols, 4-(1-aryloxy)-3-hydroxybutyric acid esters, glycerol and cyanohydrin derivatives. However, even the highly enantioselective lipase-catalyzed process can only provide 50% of the starting racemate in an optically active form. An alternative method such as a reduction of a prochiral ketone by various strains of yeast might quantitatively provide an enantiomeric product with a yield greater than 50%. The reported substrates for microbial reductions were: 1-halo-aryloxypropan-2-ones and 1-acetoxyaryloxypropan- 2-ones.