Background: Methicillin-resistant Staphylococcus aureus (MRSA) PK has been recently identified as a potential novel antimicrobial drug target. Results: Screening of a marine extract library led to the identification of several bis-indole alkaloids as novel potent and selective MRSA PK inhibitors. Conclusion:These results help to understand the mechanism of the antibacterial activities of marine bis-indole alkaloids. Significance: This study provides the basis for development of potential novel antimicrobials.

Sildenafil, tadalafil, and vardenafil each competitively inhibit cGMP hydrolysis by phosphodiesterase-5 (PDE5), thereby fostering cGMP accumulation and relaxation of vascular smooth muscle. Biochemical potencies (affinities) of these compounds for PDE5 determined by IC 50 , K D (isotherm), K D (dissociation rate), and K D ( 1 ⁄2 EC 50 ), respectively, were the following: sildenafil (3.7 Ϯ 1.4, 4.8 Ϯ 0.80, 3.7 Ϯ 0.29, and 11.7 Ϯ 0.70 nM), tadalafil (1.8 Ϯ 0.40, 2.4 Ϯ 0.60, 1.9 Ϯ 0.37, and 2.7 Ϯ 0.25 nM); and vardenafil (0.091 Ϯ 0.031, 0.38 Ϯ 0.07, 0.27 Ϯ 0.01, and 0.42 Ϯ 0.10 nM). Thus, absolute potency values were similar for each inhibitor, and relative potencies were vardenafil Ͼ Ͼ tadalafil Ͼ sildenafil. Binding of each 3 H inhibitor to PDE5 was specific as determined by effects of unlabeled compounds.

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The cGMP-binding cGMP-specific phosphodiesterase (PDE5) contains a catalytic domain that hydrolyzes cGMP and a regulatory (R) domain that contains two GAFs (a and b; GAF is derived from the proteins mammalian cGMP-binding PDEs, Anabaena adenylyl cyclases, and Escherichia coli (FhlA)). The R domain binds cGMP allosterically, provides for dimerization, and is phosphorylated at a site regulated by allosteric cGMP binding. Quaternary structures and cGMP-binding properties of 10 human PDE5A1 constructs containing one or both GAFs were characterized. Results reveal that: 1) high affinity homo-dimerization occurs between GAF a modules (K D <

Chemotherapy of human sleeping sickness, a fatal disease caused by the protozoan parasite Trypanosoma brucei, is in a dismal state, and the identification and characterization of new drug targets is an urgent prerequisite for an improvement of the dramatic situation in the field. Over the last several years, inhibitors of cyclic nucleotidespecific phosphodiesterases have proven to be highly successful drug candidates for an assortment of clinical conditions. Their potential as antiparasitic drugs has not been explored so far. This study reports the characterization of a cAMP-specific phosphodiesterase from T. brucei, TbPDE2C. This enzyme is a class I phosphodiesterase, and it is a member of a small enzyme family in T. brucei, TbPDE2. Inhibitors of this enzyme block the proliferation of bloodstream form trypanosomes in culture. RNA interference experiments demonstrated that the TbPDE2 family, and in particular TbPDE2C, are essential for maintaining intracellular cAMP concentrations within a physiological range. Bloodstream form trypanosomes are exquisitely sensitive to elevated concentrations of intracellular cAMP, and a disruption of TbPDE2C function quickly leads to the disruption of nuclear and cellular cell division, and to cell death. TbPDE2C might represent a novel drug target for the development of new and effective trypanocidal drugs.