Photo-controlled delivery of a potent analogue of doxorubicin.

Highly cytotoxic agents have found an important niche in targeted anticancer therapy. Here we develop a new light release strategy for the targeting of one of these agents, 2-pyrrolinodoxorubicin, showing dramatic enhancements in toxicity with light and single digit nM potency.

Ethynylflavones, highly potent, and selective inhibitors of cytochrome P450 1A1.

The flavone backbone is a well-known pharmacophore present in a number of substrates and inhibitors of various P450 enzymes. In order to find highly potent and novel P450 family I enzyme inhibitors, an acetylene group was incorporated into six different positions of flavone. The introduction of an acetylene group at certain locations of the flavone backbone lead to time-dependent inhibitors of P450 1A1. 3'-Ethynylflavone, 4'-ethynylflavone, 6-ethynylflavone, and 7-ethynylflavone (KI values of 0.035-0.056 µM) show strong time-dependent inhibition of P450 1A1, while 5-ethynylflavone (KI value of 0.51 µM) is a moderate time-dependent inhibitor of this enzyme. Meanwhile, 4'-ethynylflavone and 6-ethynylflavone are highly selective inhibitors toward this enzyme. Especially, 6-ethynylflavone possesses a Ki value of 0.035 µM for P450 1A1 177- and 15-fold lower than those for P450s 1A2 and 1B1, respectively. The docking postures observed in the computational simulations show that the orientation of the acetylene group determines its capability to react with P450s 1A1 and 1A2. Meanwhile, conformational analysis indicates that the shape of an inhibitor determines its inhibitory selectivity toward these enzymes.

3-Ketone-4,6-diene ceramide analogs exclusively induce apoptosis in chemo-resistant cancer cells.

Multidrug-resistance is a major cause of cancer chemotherapy failure in clinical treatment. Evidence shows that multidrug-resistant cancer cells are as sensitive as corresponding regular cancer cells under the exposure to anticancer ceramide analogs. In this work we designed five new ceramide analogs with different backbones, in order to test the hypothesis that extending the conjugated system in ceramide analogs would lead to an increase of their anticancer activity and selectivity towards resistant cancer cells. The analogs with the 3-ketone-4,6-diene backbone show the highest apoptosis-inducing efficacy. The most potent compound, analog 406, possesses higher pro-apoptotic activity in chemo-resistant cell lines MCF-7TN-R and NCI/ADR-RES than the corresponding chemo-sensitive cell lines MCF-7 and OVCAR-8, respectively. However, this compound shows the same potency in inhibiting the growth of another pair of chemo-sensitive and chemo-resistant cancer cells, MCF-7 and MCF-7/Dox. Mechanism investigations indicate that analog 406 can induce apoptosis in chemo-resistant cancer cells through the mitochondrial pathway. Cellular glucosylceramide synthase assay shows that analog 406 does not interrupt glucosylceramide synthase in chemo-resistant cancer cell NCI/ADR-RES. These findings suggest that due to certain intrinsic properties, ceramide analogs' pro-apoptotic activity is not disrupted by the normal drug-resistance mechanisms, leading to their potential use for overcoming cancer multidrug-resistance.

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 ß-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.

Thermochemical studies of epoxides and related compounds.

Gas-phase heats of formation for the four butene oxide isomers are reported. They were obtained by measuring the condensed-phase heat of reduction to the corresponding alcohol using reaction calorimetry. Heats of vaporization were determined and allow gas-phase heats of formation to be obtained. The experimental measurements are compared to calculations obtained using a variety of computational methods. Overall, the G3 and CBS-APNO methods agree quite well with the experimental data. The influence of alkyl substituents on epoxide stability is discussed. Comparisons to alkenes, cyclopropanes, aziridines, thiiranes, and phosphiranes are also made. Isodesmic-type reactions were used to determine strain energies of the epoxides and related compounds with various substituents.

7-Ethynylcoumarins: selective inhibitors of human cytochrome P450s 1A1 and 1A2.

To discover new selective mechanism-based P450 inhibitors, eight 7-ethynylcoumarin derivatives were prepared through a facile two-step synthetic route. Cytochrome P450 activity assays indicated that introduction of functional groups in the backbone of coumarin could enhance the inhibition activities toward P450s 1A1 and 1A2, providing good selectivity against P450s 2A6 and 2B1. The most potent product 7-ethynyl-3,4,8-trimethylcoumarin (7ETMC) showed IC(50) values of 0.46 µM and 0.50 µM for P450s 1A1 and 1A2 in the first six minutes, respectively, and did not show any inhibition activity for P450s 2A6 and 2B1 even at the dose of 50 µM. All of the inhibitors except 7-ethynyl-3-methyl-4-phenylcoumarin (7E3M4PC) showed mechanism-based inhibition of P450s 1A1 and 1A2. In order to explain this mechanistic difference in inhibitory activities, X-ray crystallography data were used to study the difference in conformation between 7E3M4PC and the other compounds studied. Docking simulations indicated that the binding orientations and affinities resulted in different behaviors of the inhibitors on P450 1A2. Specifically, 7E3M4PC with its two-plane structure fits into the P450 1A2's active site cavity with an orientation leading to no reactive binding, causing it to act as a competitive inhibitor.

Development of flavone propargyl ethers as potent and selective inhibitors of cytochrome P450 enzymes 1A1 and 1A2.

Naturally occurring flavonoids are known to be metabolized by several cytochrome P450 enzymes including P450s 1A1, 1A2, 1B1, 2C9, 3A4, and 3A5. In general flavonoids can act as substrates, inducers, and/or inhibitors of P450 enzymes. The position of the substituents on the flavone backbone has been shown to impact the biological activity against P450 enzymes. To explore the effect of a propargyl ether substitution on flavones and flavanones, 2´-flavone propargyl ether (2´-PF), 3´-flavone propargyl ether (3´-PF), 4´-flavone propargyl ether (4´-PF), 5-flavone propargyl ether (5-PF), 6-flavone propargyl ether (6-PF), 7-flavone propargyl ether (7-PF), 6-flavanone propargyl ether (6-PFN), and 7- flavanone propargyl ether (7-PFN) were synthesized. All of the newly synthesized compounds and the parent hydroxy flavones were tested for both direct inhibition and mechanism-based inhibition of cytochrome P450 enzymes 1A1, 1A2, 2A6, and 2B1. The flavone propargyl ether derivatives were found to be more potent inhibitors of P450s 1A1 and 1A2. None of the flavones and flavanones in our study showed any inhibition of P450 2A6. Only 2´-PF and 6-PFN inhibited P450 2B1. 3´-PF showed direct inhibition of P450 1A1 with the highest observed potency of 0.02 µM, in addition to its ability to cause mechanism-based inhibition with KI and kinactivation values of 0.24 µM and 0.09 min-1 for this enzyme. 7- Hydroxy flavone also exhibited mechanism-based inhibition of P450 1A1 with KI and kinactivation values of 2.43 µM and 0.115 min-1. Docking studies and QSAR studies on P450 enzymes 1A1 and 1A2 were performed which revealed important insights into the nature of binding of these molecules and provided us with good QSAR models that can be used to design new flavone derivatives.