Jimmy R. Theriault

Discovery of small-molecule enhancers of reactive oxygen species that are nontoxic or cause genotype-selective cell death.

Elevation of reactive oxygen species (ROS) levels has been observed in many cancer cells relative to nontransformed cells, and recent reports have suggested that small-molecule enhancers of ROS may selectively kill cancer cells in various in vitro and in vivo models. We used a high-throughput screening approach to identify several hundred small-molecule enhancers of ROS in a human osteosarcoma cell line. A minority of these compounds diminished the viability of cancer cell lines, indicating that ROS elevation by small molecules is insufficient to induce death of cancer cell lines. Three chemical probes (BRD5459, BRD56491, BRD9092) are highlighted that most strongly elevate markers of oxidative stress without causing cell death and may be of use in a variety of cellular settings. For example, combining nontoxic ROS-enhancing probes with nontoxic doses of l-buthionine sulfoximine, an inhibitor of glutathione synthesis previously studied in cancer patients, led to potent cell death in more than 20 cases, suggesting that even nontoxic ROS-enhancing treatments may warrant exploration in combination strategies. Additionally, a few ROS-enhancing compounds that contain sites of electrophilicity, including piperlongumine, show selective toxicity for transformed cells over nontransformed cells in an engineered cell-line model of tumorigenesis. These studies suggest that cancer cell lines are more resilient to chemically induced increases in ROS levels than previously thought and highlight electrophilicity as a property that may be more closely associated with cancer-selective cell death than ROS elevation.

Identification of Inhibitors of PvdQ, an Enzyme Involved in the Synthesis of the Siderophore Pyoverdine.

Pseudomonas aeruginosa produces the peptide siderophore pyoverdine, which is used to acquire essential Fe3+ ions from the environment. PvdQ, an Ntn hydrolase, is required for the biosynthesis of pyoverdine. PvdQ knockout strains are not infectious in model systems, suggesting that disruption of siderophore production via PvdQ inhibition could be exploited as a target for novel antibacterial agents, by preventing cells from acquiring iron in the low iron environments of most biological settings. We have previously described a high-throughput screen to identify inhibitors of PvdQ that identified inhibitors with IC50 values of ∼100 μM. Here, we describe the discovery of ML318, a biaryl nitrile inhibitor of PvdQ acylase. ML318 inhibits PvdQ in vitro (IC50 = 20 nM) by binding in the acyl-binding site, as confirmed by the X-ray crystal structure of PvdQ bound to ML318. Additionally, the PvdQ inhibitor is active in a whole cell assay, preventing pyoverdine production and limiting the growth of P. aeruginosa under iron-limiting conditions.

Discovery of a New Molecular Probe ML228: An Activator of the Hypoxia Inducible Factor (HIF) Pathway

Hypoxia and ischemia are linked to several serious public health problems that affect most major organ systems. Specific examples include diseases of the cardiovascular, pulmonary, renal, neurologic, and musculoskeletal systems. The most significant pathway for cellular response to hypoxia is the hypoxia inducible factor (HIF) pathway. HIFs are transcription factors responsible for the activation of genes which encode proteins that mediate adaptive responses to reduced oxygen availability. A high-throughput cell-based HIF-mediated gene reporter screen was carried out using the NIHs Molecular Libraries Small Molecule Repository to identify activators of the HIF pathway. This communication describes the subsequent medicinal chemistry optimization of a triazine scaffold that led to the identification of the new molecular probe ML228. A discussion of HIF activation SAR within this chemotype as well as detailed in vitro characterization of the probe molecule is presented here.