AG14361 is, to our knowledge, the first high-potency PARP-1 inhibitor with the specificity and in vivo activity to enhance chemotherapy and radiation therapy of human cancer.

Human rhinoviruses, the most important etiologic agents of the common cold, are messenger-active single-stranded monocistronic RNA viruses that have evolved a highly complex cascade of proteolytic processing events to control viral gene expression and replication. Most maturation cleavages within the precursor polyprotein are mediated by rhinovirus 3C protease (or its immediate precursor, 3CD), a cysteine protease with a trypsin-like polypeptide fold. Highresolution crystal structures of the enzyme from three viral serotypes have been used for the design and elaboration of 3C protease inhibitors representing different structural and chemical classes. Inhibitors having ␣,␤-unsaturated carbonyl groups combined with peptidyl-binding elements specific for 3C protease undergo a Michael reaction mediated by nucleophilic addition of the enzyme's catalytic Cys-147, resulting in covalent-bond formation and irreversible inactivation of the viral protease. Direct inhibition of 3C proteolytic activity in virally infected cells treated with these compounds can be inferred from dose-dependent accumulations of viral precursor polyproteins as determined by SDS͞PAGE analysis of radiolabeled proteins. Cocrystal-structure-assisted optimization of 3C-protease-directed Michael acceptors has yielded molecules having extremely rapid in vitro inactivation of the viral protease, potent antiviral activity against multiple rhinovirus serotypes and low cellular toxicity. Recently, one compound in this series, AG7088, has entered clinical trials.

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Nonionic methylated branched hydrocarbon surfactants, poly(ethylene glycol) 2,6,8-trimethyl-4-nonyl ethers, form water-in-carbon dioxide (W/C) microemulsions. A concentration of 1.0 wt % of the octa(ethylene glycol) 2,6,8-trimethyl-4-nonyl ether (5b-C 12 E 8 ) stabilized up to 1.1 wt % of water (corrected molar water/surfactant ratio, W o c ≈ 28) from 35 to 65 °C and above 240 bar. Methylation and branching of surfactant tails enhance the formation of stable W/C microemulsions as they (1) raise surfactant solubility in CO 2 by weakening interactions between tails and lower surfactant solubility in water by inhibiting micellization, (2) shift the curvature toward bending about water, and (3) reduce overlap between surfactant tails and weaken interdroplet interactions. The hydrodynamic radii of microemulsion droplets measured by dynamic light scattering (1.6-3.0 nm) increases with a decrease in temperature, at constant CO 2 density, due to stronger interactions between the headgroups and water. The W/C microemulsions solubilize lysozyme in CO 2 at a level of 0.28 mg/mL in CO 2 and 36 mg/mL in the water droplet.

Poly(ADP-ribose) polymerase (PARP)-1 (EC 2.4.2.30) is a nuclear enzyme that promotes the base excision repair of DNA breaks. Inhibition of PARP-1 enhances the efficacy of DNA alkylating agents, topoisomerase I poisons, and ionizing radiation. Our aim was to identify a PARP inhibitor for clinical trial from a panel of 42 potent PARP inhibitors (K i , 1.4 -15.1 nmol/L) based on the quinazolinone, benzimidazole, tricyclic benzimidazole, tricyclic indole, and tricyclic indole-1-one core structures. We evaluated chemosensitization of temozolomide and topotecan using LoVo and SW620 human colorectal cells; in vitro radiosensitization was measured using LoVo cells, and the enhancement of antitumor activity of temozolomide was evaluated in mice bearing SW620 xenografts. Excellent chemopotentiation and radiopotentiation were observed in vitro, with 17 of the compounds causing a greater temozolomide and topotecan sensitization than the benchmark inhibitor AG14361 and 10 compounds were more potent radiosensitizers than AG14361. In tumor-bearing mice, none of the compounds were toxic when given alone, and the antitumor activity of the PARP inhibitortemozolomide combinations was unrelated to toxicity. Compounds that were more potent chemosensitizers in vivo than AG14361 were also more potent in vitro, validating in vitro assays as a prescreen. These studies have identified a compound, AG14447, as a PARP inhibitor with outstanding in vivo chemosensitization potency at tolerable doses, which is at least 10 times more potent than the initial lead, AG14361. The phosphate salt of AG14447 (AG014699), which has improved aqueous solubility, has been selected for clinical trial. [Mol Cancer Ther 2007;6(3):945 -56]

Structural studies of antibiotics not only provide a short cut to medicine allowing for rational structure-based drug design, but may also capture snapshots of dynamic intermediates that become ‘frozen’ after inhibitor binding1,2. Myxopyronin inhibits bacterial RNA polymerase (RNAP) by an unknown mechanism3. Here we report the structure of dMyx—a desmethyl derivative of myxopyronin B4—complexed with a Thermus thermophilus RNAP holoenzyme. The antibiotic binds to a pocket deep inside the RNAP clamp head domain, which interacts with the DNA template in the transcription bubble5,6. Notably, binding of dMyx stabilizes refolding of the β’-subunit switch-2 segment, resulting in a configuration that might indirectly compromise binding to, or directly clash with, the melted template DNA strand. Consistently, footprinting data show that the antibiotic binding does not prevent nucleation of the promoter DNA melting but instead blocks its propagation towards the active site. Myxopyronins are thus, to our knowledge, a first structurally characterized class of antibiotics that target formation of the pre-catalytic transcription initiation complex—the decisive step in gene expression control. Notably, mutations designed in switch-2 mimic the dMyx effects on promoter complexes in the absence of antibiotic. Overall, our results indicate a plausible mechanism of the dMyx action and a stepwise pathway of open complex formation in which core enzyme mediates the final stage of DNA melting near the transcription start site, and that switch-2 might act as a molecular checkpoint for DNA loading in response to regulatory signals or antibiotics. The universally conserved switch-2 may have the same role in all multisubunit RNAPs.

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Diblock and graft copolymers for which the blocks are sufficiently different in their solvation properties often self-assemble into micelle structures. In this feature article we emphasize only diblock polymers. We discuss various aspects of this field including the synthesis of diblock polymers containing fluorescent probes placed at precise points in the polymer chain and the preparation and characterization of polymer micelles. These chromophores may undergo photoredox chemistry or be utilized as probes of the local micelle environment. We also discuss our studies of the rate of release of absorbed small molecules (e.g., phenanthrene, pyrene) using fluorescence techniques. Last we describe our approach to the modification of surfaces by either adsorption or chemical attachment of polymer micelles.