Pyranoflavones: A Group of Small-Molecule Probes for Exploring the Active Site Cavities of Cytochrome P450 Enzymes 1A1, 1A2, and 1B1

Selective inhibition of P450 enzymes is the key to block the conversion of environmental procarcinogens to their carcinogenic metabolites in both animals and humans. To discover highly potent and selective inhibitors of P450s 1A1, 1A2, and 1B1, as well as to investigate active site cavities of these enzymes, 14 novel flavone derivatives were prepared as chemical probes. Fluorimetric enzyme inhibition assays were used to determine the inhibitory activities of these probes toward P450s 1A1, 1A2, 1B1, 2A6, and 2B1. A highly selective P450 1B1 inhibitor 5-hydroxy-4′-propargyloxyflavone (5H4′FPE) was discovered. Some tested compounds also showed selectivity between P450s 1A1 and 1A2. α-Naphthoflavone-like and 5-hydroxyflavone derivatives preferentially inhibited P450 1A2, while β-naphthoflavone-like flavone derivatives showed selective inhibition of P450 1A1. On the basis of structural analysis, the active site cavity models of P450 enzymes 1A1 and 1A2 were generated, demonstrating a planar long strip cavity and a planar triangular cavity, respectively

Rational Design of a Boron-Modified Triphenylethylene (GLL398) as an Oral Selective Estrogen Receptor Downregulator

Development of orally bioavailable nonsteroidal selective estrogen receptor downregulators (SERDs) provides clinical opportunities for the long-term treatment and adjuvant therapy of breast cancer at all stages. We describe the design, synthesis, and identification of a boron-modified GW7604 derivative (GLL398, <b>9</b>), a SERD candidate, in which a boronic acid functional group replaces the phenolic hydroxyl group of GW7604. Compound <b>9</b> strongly binds to ERα in a fluorescence resonance energy transfer binding assay (IC₅₀ = 1.14 nM) and potently degrades ERα in MCF-7 breast cancer cells (IC₅₀ = 0.21 μM). Most importantly, the introduction of the boronic acid group confers superior oral bioavailability of <b>9</b> (AUC = 36.9 μg·h/mL) in rats as compared to GW7604 (AUC = 3.35 μg·h/mL). The strikingly favorable pharmacokinetic property of <b>9</b> makes it a promising oral SERD suitable for clinical evaluation

Fulvestrant‑3 Boronic Acid (ZB716): An Orally Bioavailable Selective Estrogen Receptor Downregulator (SERD)

Orally bioavailable SERDs may offer greater systemic drug exposure, improved clinical efficacy, and more durable treatment outcome for patients with ER-positive endocrine-resistant breast cancer. We report the design and synthesis of a boronic acid modified fulvestrant (<b>5</b>, ZB716), which binds to ERα competitively (IC₅₀ = 4.1 nM) and effectively downregulates ERα in both tamoxifen-sensitive and tamoxifen-resistant breast cancer cells. Furthermore, It has superior oral bioavailability (AUC = 2547.1 ng·h/mL) in mice, indicating its promising clinical utility as an oral SERD

A Ligand-Based Drug Design. Discovery of 4‑Trifluoromethyl-7,8-pyranocoumarin as a Selective Inhibitor of Human Cytochrome P450 1A2

In humans, cytochrome P450 1A2 is the major enzyme metabolizing environmental arylamines or heterocyclic amines into carcinogens. Since evidence shows that planar triangle-shaped molecules are capable of selectively inhibiting P450 1A2, 16 triangular flavone, and coumarin derivatives were designed and synthesized for these studies. Among these compounds, 7,8-furanoflavone time-dependently inhibits P450 1A2 with a <i>K</i>_I value of 0.44 μM. With a 5 min preincubation in the presence of NADPH, 0.01 μM 7,8-furanoflavone completely inactivates P450 1A2 but does not influence the activities of P450s 1A1 and 1B1. Another target compound, 7,8-pyrano-4-trifluoromethylcoumarin, is found to be a competitive inhibitor, showing high selectivity for the inhibition of P450 1A2 with a <i>K</i>_i of 0.39 μM, 155- and 52-fold lower than its <i>K</i>_i values against P450s 1A1 and 1B1, respectively. In yeast AhR activation assays, 7,8-pyrano-4-trifluoromethyl­coumarin does not activate aryl hydrocarbon receptor when the concentration is lower than 1 μM, suggesting that this compound would not up-regulate AhR-caused P450 enzyme expression. In-cell P450 1A2 inhibition assays show that 7,8-pyrano-4-trifluoromethyl­coumarin decreases the MROD activity in HepG2 cells at concentrations higher than 1 μM. Thus, using 7,8-pyrano-4-trifluoromethyl­coumarin, a selective and specific P450 1A2 action suppression could be achieved, indicating the potential for the development of P450 1A2-targeting cancer preventive agents

A Ligand-Based Drug Design. Discovery of 4‑Trifluoromethyl-7,8-pyranocoumarin as a Selective Inhibitor of Human Cytochrome P450 1A2

In humans, cytochrome P450 1A2 is the major enzyme metabolizing environmental arylamines or heterocyclic amines into carcinogens. Since evidence shows that planar triangle-shaped molecules are capable of selectively inhibiting P450 1A2, 16 triangular flavone, and coumarin derivatives were designed and synthesized for these studies. Among these compounds, 7,8-furanoflavone time-dependently inhibits P450 1A2 with a <i>K</i>_I value of 0.44 μM. With a 5 min preincubation in the presence of NADPH, 0.01 μM 7,8-furanoflavone completely inactivates P450 1A2 but does not influence the activities of P450s 1A1 and 1B1. Another target compound, 7,8-pyrano-4-trifluoromethylcoumarin, is found to be a competitive inhibitor, showing high selectivity for the inhibition of P450 1A2 with a <i>K</i>_i of 0.39 μM, 155- and 52-fold lower than its <i>K</i>_i values against P450s 1A1 and 1B1, respectively. In yeast AhR activation assays, 7,8-pyrano-4-trifluoromethyl­coumarin does not activate aryl hydrocarbon receptor when the concentration is lower than 1 μM, suggesting that this compound would not up-regulate AhR-caused P450 enzyme expression. In-cell P450 1A2 inhibition assays show that 7,8-pyrano-4-trifluoromethyl­coumarin decreases the MROD activity in HepG2 cells at concentrations higher than 1 μM. Thus, using 7,8-pyrano-4-trifluoromethyl­coumarin, a selective and specific P450 1A2 action suppression could be achieved, indicating the potential for the development of P450 1A2-targeting cancer preventive agents