Anti-cancer effectiveness of a novel ceramide analog on chemo-sensitive and chemo-resistant breast cancers.

INTRODUCTION: Ceramides are known to show anti-cancer activity. A novel ceramide analog, (S,E)-3-hydroxy-2-(2-hydroxybenzylidene)amino-N-tetradecylpropanamide (analog 315) was developed as part of a larger study focused on finding more effective breast cancer treatments. OBJECTIVE: To assess whether analog 315 shows any or a combination of the following effects in breast cancer cells in vitro: inhibiting proliferation, inducing apoptosis, and altering protein expression. Also, to determine whether it inhibits chemo-resistant breast cancer tumor growth in vivo mouse model. METHODS: In vitro cell proliferation and apoptosis after treatment with analog 315 were assessed in three breast cancer cell lines (MCF-7, MCF-7TN-R, and MDA-MB-231) and reported. Protein expression was assessed by microarray assay. For the in vivo studies, chemo-resistant breast cancer cells were used for tumor development in two groups of mice (treated and control). Analog 315 (25 mg/kg/day) or control (dimethyl sulfoxide) was administered intraperitoneally for 7 days. Effects of analog 315 on inhibiting the growth of chemo-resistant breast cancer tumors after treatment are reported. RESULTS: Analog 315 reduced MCF-7TN-R chemo-resistant tumor burden (volume and weight) in mice. Liver metastasis was observed in control mice, but not in the treated animals. Ki-67, a proliferation marker for breast cancer cells, increased significantly ( P  < 0.05) in control tumor tissue. In vitro studies showed that analog 315 inhibited cell proliferation, altered protein expression and induced apoptosis in all three breast cancer cell lines studied, of which the effects on MCF-7TN-R cells were the most significant. CONCLUSION: Analog 315 reduced tumor growth in chemo-resistant breast cancer, inhibited cell proliferation, altered protein expression, and induced apoptosis in all three cell lines studied.

Design, Synthesis, and Biological Studies of Flavone-Based Esters and Acids as Potential P450 2A6 Inhibitors.

As a potential means for smoking cessation and consequently prevention of smoking-related diseases and mortality, in this study, our goal was to investigate the inhibition of nicotine metabolism by P450 2A6. Smoking is the main cause of many diseases and disabilities and harms nearly every organ of the body. As reported by the Centers for Disease Control and Prevention (CDC), more than 16 million Americans are living with diseases caused by smoking. On average, the life expectancy of a smoker is about 10 years less than a nonsmoker. Smoking cessation can substantially reduce the incidence of smoking-related diseases, including cancer. At least, 70 of the more than 7000 cigarette smoke components, including polycyclic aromatic hydrocarbons, N-nitrosamines, and aromatic amines, are known carcinogens. Nicotine is the compound responsible for the addictive and psychopharmacological effects of tobacco. Cytochrome P450 enzymes are responsible for the phase I metabolism of many tobacco components, including nicotine. Nicotine is mainly metabolized by cytochrome P450s 2A6 and 2A13 to cotinine. This metabolism decreases the amount of available nicotine in the bloodstream, leading to increased smoking behavior and thus exposure to tobacco toxicants and carcinogens. Here, we report the syntheses and P450 2A6 inhibitory activities of a number of new flavone-based esters and acids. Three of the flavone derivatives studied were found to be potent competitive inhibitors of the enzyme. Docking studies were used to determine the possible mechanisms of the activity of these inhibitors.

Developing new ceramide analogs and identifying novel sphingolipid-controlled genes against a virus-associated lymphoma.

Primary effusion lymphoma (PEL) is an aggressive malignancy with poor prognosis even under chemotherapy. Kaposi sarcoma-associated herpesvirus (KSHV), one of the human oncogenic viruses, is the principal causative agent. Currently, there is no specific treatment for PEL; therefore, developing new therapies is of great importance. Sphingolipid metabolism plays an important role in determining the fate of tumor cells. Our previous studies have demonstrated that there is a correlation between sphingolipid metabolism and KSHV+ tumor cell survival. To further develop sphingolipid metabolism-targeted therapy, after screening a series of newly synthesized ceramide analogs, here, we have identified compounds with effective anti-PEL activity. These compounds induce significant PEL apoptosis, cell-cycle arrest, and intracellular ceramide production through regulation of ceramide synthesizing or ceramide metabolizing enzymes and dramatically suppress tumor progression without visible toxicity in vivo. These new compounds also increase viral lytic gene expression in PEL cells. Our comparative transcriptomic analysis revealed their mechanisms of action for inducing PEL cell death and identified a subset of novel cellular genes, including AURKA and CDCA3, controlled by sphingolipid metabolism, and required for PEL survival with functional validation. These data provide the framework for the development of promising sphingolipid-based therapies against this virus-associated malignancy.

Coumarins and P450s, Studies Reported to-Date.

Cytochrome P450 enzymes (CYPs) are important phase I enzymes involved in the metabolism of endogenous and xenobiotic compounds mainly through mono-oxygenation reactions into more polar and easier to excrete species. In addition to their role in detoxification, they play important roles in the biosynthesis of endogenous compounds and the bioactivation of xenobiotics. Coumarins, phytochemicals abundant in food and commonly used in fragrances and cosmetics, have been shown to interact with P450 enzymes as substrates and/or inhibitors. In this review, these interactions and their significance in pharmacology and toxicology are discussed in detail.

The sphingosine kinase 2 inhibitor ABC294640 displays anti-non-small cell lung cancer activities in vitro and in vivo.

Non-small cell lung cancer (NSCLC) accounts for about 85-90% of lung cancer cases, and is the number one killer among cancers in the United States. The majorities of lung cancer patients do not respond well to conventional chemo- and/or radio-therapeutic regimens, and have a dismal 5-year survival rate of ∼15%. The recent introduction of targeted therapy and immunotherapy gives new hopes to NSCLC patients, but even with these agents, not all patients respond, and responses are rarely complete. Thus, there is still an urgent need to identify new therapeutic targets in NSCLC and develop novel anti-cancer agents. Sphingosine kinase 2 (SphK2) is one of the key enzymes in sphingolipid metabolism. SphK2 expression predicts poor survival in NSCLC patients, and is associated with Gefitinib-resistance. In this study, the anti-NSCLC activities of ABC294640, the only first-in-class orally available inhibitor of SphK2, were explored. The results obtained indicate that ABC294640 treatment causes significant NSCLC cell apoptosis, cell cycle arrest and suppression of tumor growth in vitro and in vivo. Moreover, lipidomics analyses revealed the complete signature of ceramide and dihydro(dh)-ceramide species in the NSCLC cell-lines with or without ABC294640 treatment. These findings indicate that sphingolipid metabolism targeted therapy may be developed as a promising strategy against NSCLC.

Inhibition of breast tumor growth in mice after treatment with ceramide analog 315.

The aim of this study was to evaluate the anticancer and antitumor activities of ceramide analog 315 in nude mice. Nude mice (n=10) were injected bilaterally with 5×10 MDA-MB-231 cells on each side. Tumors were allowed to form for 2 weeks. The mice were then divided into two groups (n=5 in each group). The control group mice were injected with 25 µl of dimethyl sulfoxide and the treatment group mice were injected with 10 mg/kg of analog 315 (in dimethyl sulfoxide, 25 µl volume) every day for a period of 3 weeks. Animal weights and tumors were measured every week for 3 weeks. At the end of the experimental period, control animals had retained excess fluid, and showed larger tumor sizes compared with the treated group (2.95 vs. 1.67 g). A 45% reduction in tumor size and 80% decrease in tumor volume were observed in the treatment group. There was a significant increase in the weights of liver (10%) and spleen (19%) between the control and treated animals. Hematoxylin and Eosin staining of MDA-MB-231 tumor sections revealed more acellular necrotic regions in tumors from the treatment groups compared with the ones from the control group. Ki67, a proliferation marker was higher in number in control tumor section (71.8±12.8) compared to the treatment tumor section (37.4±10.4) (P<0.001). Photomicrographs showed metastatic tumor burden in kidney, lungs, and spleen collected from the control group mice bearing MDA-MB-231 tumors. Treatment group mice showed normal microscopic tissue architecture. Overall, our study showed tumor growth inhibition and antimetastatic effects for the novel ceramide analog 315.

Review of Ligand Specificity Factors for CYP1A Subfamily Enzymes from Molecular Modeling Studies Reported to-Date.

The cytochrome P450 (CYP) family 1A enzymes, CYP1A1 and CYP1A2, are two of the most important enzymes implicated in the metabolism of endogenous and exogenous compounds through oxidation. These enzymes are also known to metabolize environmental procarcinogens into carcinogenic species, leading to the advent of several types of cancer. The development of selective inhibitors for these P450 enzymes, mitigating procarcinogenic oxidative effects, has been the focus of many studies in recent years. CYP1A1 is mainly found in extrahepatic tissues while CYP1A2 is the major CYP enzyme in human liver. Many molecules have been found to be metabolized by both of these enzymes, with varying rates and/or positions of oxidation. A complete understanding of the factors that govern the specificity and potency for the two CYP 1A enzymes is critical to the development of effective inhibitors. Computational molecular modeling tools have been used by several research groups to decipher the specificity and potency factors of the CYP1A1 and CYP1A2 substrates. In this review, we perform a thorough analysis of the computational studies that are ligand-based and protein-ligand complex-based to catalog the various factors that govern the specificity/potency toward these two enzymes.

Structure-Function Studies of Naphthalene, Phenanthrene, Biphenyl, and Their Derivatives in Interaction with and Oxidation by Cytochromes P450 2A13 and 2A6.

Naphthalene, phenanthrene, biphenyl, and their derivatives having different ethynyl, propynyl, butynyl, and propargyl ether substitutions were examined for their interaction with and oxidation by cytochromes P450 (P450) 2A13 and 2A6. Spectral interaction studies suggested that most of these chemicals interacted with P450 2A13 to induce Type I binding spectra more readily than with P450 2A6. Among the various substituted derivatives examined, 2-ethynylnaphthalene, 2-naphthalene propargyl ether, 3-ethynylphenanthrene, and 4-biphenyl propargyl ether had larger ΔAmax/Ks values in inducing Type I binding spectra with P450 2A13 than their parent compounds. P450 2A13 was found to oxidize naphthalene, phenanthrene, and biphenyl to 1-naphthol, 9-hydroxyphenanthrene, and 2- and/or 4-hydroxybiphenyl, respectively, at much higher rates than P450 2A6. Other human P450 enzymes including P450s 1A1, 1A2, 1B1, 2C9, and 3A4 had lower rates of oxidation of naphthalene, phenanthrene, and biphenyl than P450s 2A13 and 2A6. Those alkynylated derivatives that strongly induced Type I binding spectra with P450s 2A13 and 2A6 were extensively oxidized by these enzymes upon analysis with HPLC. Molecular docking studies supported the hypothesis that ligand-interaction energies (U values) obtained with reported crystal structures of P450 2A13 and 2A6 bound to 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone, indole, pilocarpine, nicotine, and coumarin are of use in understanding the basis of possible molecular interactions of these xenobiotic chemicals with the active sites of P450 2A13 and 2A6 enzymes. In fact, the ligand-interaction energies with P450 2A13 4EJG bound to these chemicals were found to relate to their induction of Type I binding spectra.

Oxidation of pyrene, 1-hydroxypyrene, 1-nitropyrene and 1-acetylpyrene by human cytochrome P450 2A13.

1. The polycyclic hydrocarbons (PAHs), pyrene, 1-hydroxypyrene, 1-nitropyrene and 1-acetylpyrene, were found to induce Type I binding spectra with human cytochrome P450 (P450) 2A13 and were converted to various mono- and di-oxygenated products by this enzyme. 2. Pyrene was first oxidized by P450 2A13 to 1-hydroxypyrene which was further oxidized to di-oxygenated products, i.e. 1,8- and 1,6-dihydroxypyrene. Of five other human P450s examined, P450 1B1 catalyzed pyrene oxidation to 1-hydroxypyrene at a similar rate to P450 2A13 but was less efficient in forming dihydroxypyrenes. P450 2A6, a related human P450 enzyme, which did not show any spectral changes with these four PAHs, showed lower activities in oxidation of these compounds than P450 2A13. 3. 1-Nitropyrene and 1-acetylpyrene were also found to be efficiently oxidized by P450 2A13 to several oxygenated products, based on mass spectrometry analysis. 4. Molecular docking analysis supported preferred orientations of pyrene and its derivatives in the active site of P450 2A13, with lower interaction energies (U values) than observed for P450 2A6 and that several amino acid residues (including Ala-301, Asn-297 and Ala-117) play important roles in directing the orientation of these PAHs in the P450 2A13 active site. In addition, Phe-231 and Gly-329 were found to interact with pyrene to orient this compound in the active site of P450 1B1. 5. These results suggest that P450 2A13 is one of the important enzymes that oxidizes these PAH compounds and may determine how these chemicals are detoxicated and bioactivated in humans.

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.

Developing new ceramide analogs against non-small cell lung cancer (NSCLC).

Non-small cell lung cancer (NSCLC) constitutes the predominant form of lung cancer and stands as the leading cause of cancer-related mortality in the United States. Conventional chemotherapy and radiotherapy yield suboptimal responses in a significant portion of lung cancer patients, resulting in a discouraging 5-year survival rate of approximately 15%. Despite advancements in targeted therapy and immunotherapy, many NSCLC patients exhibit either negligible or partial responses, emphasizing the pressing necessity for the discovery of innovative anti-cancer agents. Our previous study demonstrated that ABC294640, an inhibitor of one of the key enzymes in sphingolipid metabolism, sphingosine kinase 2 (SphK2), displayed anti-NSCLC activities in vitro and in vivo. In the current study, through the screening of a series of newly synthesized ceramide analogs, we have identified new compounds, particularly analogs 403 and 953, that exhibit potent anti-NSCLC activities. These compounds induce significant NSCLC apoptosis by elevating intracellular pre-apoptotic ceramide and dihydro(dh)-ceramide production. Lipidomics analyses further elucidate the alterations in ceramide and dh-ceramide species signature/proportion across different NSCLC cell-lines induced by these novel ceramide analogs. Treatments with ceramide analogs 403 and 953 remarkably inhibit NSCLC progression in vivo without observable toxicity. Collectively, these findings establish a foundation for the development of promising sphingolipid-based therapies aimed at enhancing the prognosis of NSCLC.

Ethyl 2-[(2-oxo-2H-chromen-6-yl)-oxy]acetate.

Ethyl 2-[(2-oxo-2H-chromen-6-yl)-oxy]acetate, C13H12O5, a member of the pharmacologically important class of coumarins, crystallizes in the monoclinic C2/c space group in the form of sheets, within which mol-ecules are related by inversion centers and 21 axes. Multiple C-H⋯O weak hydrogen-bonding inter-actions reinforce this pattern. The planes of these sheets are oriented in the approximate direction of the ac face diagonal. Inter-sheet inter-actions are a combination of coumarin system π-π stacking and additional C-H⋯O weak hydrogen bonds between ethyl acet-oxy groups.

Potent mechanism-based inactivation of cytochrome P450 2B4 by 9-ethynylphenanthrene: implications for allosteric modulation of cytochrome P450 catalysis.

The mechanism-based inactivation of cytochrome P450 2B4 (CYP2B4) by 9-ethynylphenanthrene (9EP) has been investigated. The partition ratio and k(inact) are 0.2 and 0.25 min(-1), respectively. Intriguingly, the inactivation exhibits sigmoidal kinetics with a Hill coefficient of 2.5 and an S(50) of 4.5 µM indicative of homotropic cooperativity. Enzyme inactivation led to an increase in mass of the apo-CYP2B4 by 218 Da as determined by electrospray ionization liquid chromatography and mass spectrometry, consistent with covalent protein modification. The modified CYP2B4 was purified to homogeneity and its structure determined by X-ray crystallography. The structure showed that 9EP is covalently attached to Oγ of Thr 302 via an ester bond, which is consistent with the increased mass of the protein. The presence of the bulky phenanthrenyl ring resulted in inward rotations of Phe 297 and Phe 206, leading to a compact active site. Thus, binding of another molecule of 9EP in the active site is prohibited. However, results from the quenching of 9EP fluorescence by unmodified or 9EP-modified CYP2B4 revealed at least two binding sites with distinct affinities, with the low-affinity site being the catalytic site and the high-affinity site on the protein periphery. Computer-aided docking and molecular dynamics simulations with one or two ligands bound revealed that the high-affinity site is situated at the entrance of a substrate access channel surrounded by the F' helix, ß1-ß2 loop, and ß4 loop and functions as an allosteric site to enhance the efficiency of activation of the acetylenic group of 9EP and subsequent covalent modification of Thr 302.

Binding of diverse environmental chemicals with human cytochromes P450 2A13, 2A6, and 1B1 and enzyme inhibition.

A total of 68 chemicals including derivatives of naphthalene, phenanthrene, fluoranthene, pyrene, biphenyl, and flavone were examined for their abilities to interact with human P450s 2A13 and 2A6. Fifty-one of these 68 chemicals induced stronger Type I binding spectra (iron low- to high-spin state shift) with P450 2A13 than those seen with P450 2A6, i.e., the spectral binding intensities (ΔAmax/Ks ratio) determined with these chemicals were always higher for P450 2A13. In addition, benzo[c]phenanthrene, fluoranthene, 2,3-dihydroxy-2,3-dihydrofluoranthene, pyrene, 1-hydroxypyrene, 1-nitropyrene, 1-acetylpyrene, 2-acetylpyrene, 2,5,2',5'-tetrachlorobiphenyl, 7-hydroxyflavone, chrysin, and galangin were found to induce a Type I spectral change only with P450 2A13. Coumarin 7-hydroxylation, catalyzed by P450 2A13, was strongly inhibited by 2'-methoxy-5,7-dihydroxyflavone, 2-ethynylnaphthalene, 2'-methoxyflavone, 2-naphththalene propargyl ether, acenaphthene, acenaphthylene, naphthalene, 1-acetylpyrene, flavanone, chrysin, 3-ethynylphenanthrene, flavone, and 7-hydroxyflavone; these chemicals induced Type I spectral changes with low Ks values. On the basis of the intensities of the spectral changes and inhibition of P450 2A13, we classified the 68 chemicals into eight groups based on the order of affinities for these chemicals and inhibition of P450 2A13. The metabolism of chemicals by P450 2A13 during the assays explained why some of the chemicals that bound well were poor inhibitors of P450 2A13. Finally, we compared the 68 chemicals for their abilities to induce Type I spectral changes of P450 2A13 with the Reverse Type I binding spectra observed with P450 1B1: 45 chemicals interacted with both P450s 2A13 and 1B1, indicating that the two enzymes have some similarty of structural features regarding these chemicals. Molecular docking analyses suggest similarities at the active sites of these P450 enzymes. These results indicate that P450 2A13, as well as Family 1 P450 enzymes, is able to catalyze many detoxication and activation reactions with chemicals of environmental interest.

Cytochrome P450 family 1 inhibitors and structure-activity relationships.

With the widespread use of O-alkoxyresorufin dealkylation assays since the 1990s, thousands of inhibitors of cytochrome P450 family 1 enzymes (P450s 1A1, 1A2, and 1B1) have been identified and studied. Generally, planar polycyclic molecules such as polycyclic aromatic hydrocarbons, stilbenoids, and flavonoids are considered to potentially be effective inhibitors of these enzymes, however, the details of the structure-activity relationships and selectivity of these inhibitors are still ambiguous. In this review, we thoroughly discuss the selectivity of many representative P450 family 1 inhibitors reported in the past 20 years through a meta-analysis.

Study of Ceramide-Flavone Analogs Showing Self-Fluorescence and Anti-Proliferation Activities.

Background: Many current anti-cancer drugs used to treat breast cancer mediate tumor cell death through the induction of apoptosis. Cancer cells, however, often acquire multidrug-resistance following prolonged exposure to chemotherapeutics. Consequently, molecular pathways involved in tumor cell proliferation have become potential targets for pharmacological intervention. Ceramides are tumor suppressor lipids naturally found in the cell membrane, and are central molecules in the sphingolipid signalling pathway. Methods: Our lab has targeted the ceramide signaling pathway for potential pharmacological intervention in the treatment of breast cancer. Previously, we have shown that certain ceramide analogs have therapeutic potential in the treatment of chemo-sensitive and multidrug-resistant breast cancers. Using the most active analog from our previous studies as the lead compound, new analogs containing a flavone moiety were designed and synthesized. In general, flavone derivatives often show interesting pharmacological properties, and compounds based on these molecules have been found useful in many different therapeutic areas including anti-tumor, anti-coagulants, and anti-HIV therapy. Results: Synthesis and biological evaluation of five new flavonoid ceramide analogs are reported here. These compounds were also shown to be self-fluorescent, which can be useful when investigating their distribution and action in cancer cells. Conclusion: Four out of the five flavone ceramide analogs in this study showed significant anti-proliferation activities in the three cell lines studied, MDA-MB-232, MCF-7, and MCF-7TN-R; some showing varying degrees of selectivity. The mechanisms involved in cell proliferation inhibition are complicated and further studies are needed.

Inhibition of cytochrome p450 enzymes by quinones and anthraquinones.

In silico docking studies and quantitative structure-activity relationship analysis of a number of in-house cytochrome P450 inhibitors have revealed important structural characteristics that are required for a molecule to function as a good inhibitor of P450 enzymes 1A1, 1A2, 2B1, and/or 2A6. These insights were incorporated into the design of pharmacophores used for a 2D search of the Chinese medicine database. Emodin, a natural anthraquinone isolated from Rheum emodi and known to be metabolized by cytochrome P450 enzymes, was one of the hits and was used as the lead compound. Emodin was found to inhibit P450s 1A1, 1A2, and 2B1 with IC(50) values of 12.25, 3.73, and 14.89 µM, respectively. On the basis of the emodin molecular structure, further similarity searches of the PubChem and ZINC chemical databases were conducted resulting in the identification of 12 emodin analogues for testing against P450s 1A1-, 1A2-, 2B1-, and 2A6-dependent activities. 1-Amino-4-chloro-2-methylanthracene-9,10-dione (compound 1) showed the best inhibition potency for P450 1A1 with an IC(50) value of 0.40 µM. 1-Amino-4-chloro-2-methylanthracene-9,10-dione (compound 1) and 1-amino-4-hydroxyanthracene-9,10-dione (compound 2) both inhibited P450 1A2 with the same IC(50) value of 0.53 µM. In addition, compound 1 acted as a mechanism-based inhibitor of cytochrome P450s 1A1 and 1A2 with K(I) and K(inactivation) values of 5.38 µM and 1.57 min(-1) for P450 1A1 and 0.50 µM and 0.08 min(-1) for P450 1A2. 2,6-Di-tert-butyl-5-hydroxynaphthalene-1,4-dione (compound 8) directly inhibited P450 2B1 with good selectivity and inhibition potency (IC(50) = 5.66 µM). Docking studies using the 3D structures of the enzymes were carried out on all of the compounds. The binding modes of these compounds revealed the structural characteristics responsible for their potency and selectivity. Compound 1, which is structurally similar to compound 2 with the presence of an amino group at position 1, showed a difference in the mechanism of inhibition toward P450s 1A1 and 1A2. The mechanism-based inhibition seen for compound 1 may be attributed to the presence of the methyl group at the 2-position, in close proximity to the amino group. Compound 2, which is otherwise similar, lacks that methyl moiety and did not show mechanism-based inhibition.

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.

Insights on cytochrome p450 enzymes and inhibitors obtained through QSAR studies.

The cytochrome P450 (CYP) superfamily of heme enzymes play an important role in the metabolism of a large number of endogenous and exogenous compounds, including most of the drugs currently on the market. Inhibitors of CYP enzymes have important roles in the treatment of several disease conditions such as numerous cancers and fungal infections in addition to their critical role in drug-drug interactions. Structure activity relationships (SAR), and three-dimensional quantitative structure activity relationships (3D-QSAR) represent important tools in understanding the interactions of the inhibitors with the active sites of the CYP enzymes. A comprehensive account of the QSAR studies on the major human CYPs 1A1, 1A2, 1B1, 2A6, 2B6, 2C9, 2C19, 2D6, 2E1, 3A4 and a few other CYPs are detailed in this review which will provide us with an insight into the individual/common characteristics of the active sites of these enzymes and the enzyme-inhibitor interactions.