Development of Robust 17(R),18(S)-Epoxyeicosatetraenoic Acid (17,18-EEQ) Analogues as Potential Clinical Antiarrhythmic Agents

17(R),18(S)-Epoxyeicosatetraenoic acid (EEQ) is a cytochrome P450 metabolite of eicosapentaenoic acid (EPA) and a powerful negative chronotrope with low nanomolar activity in a neonatal rat cardiomyocyte (NRCM) arrhythmia model. Prior studies identified oxamide 2b as a soluble epoxide hydrolase (sEH) stable replacement but unsuitable for in vivo applications due to limited oral bioavailability and metabolic stability. These ADME limitations have been addressed in an improved generation of negative chronotropes, e.g., 4 and 16, which were evaluated as potential clinical candidates.

Vascular hepoxilin and trioxilins mediate vasorelaxation through TP receptor inhibition in mouse arteries

AIM

12/15-lipoxygenase (12/15-LO) metabolizes arachidonic acid (AA) into several vasoactive eicosanoids. In mouse arteries, we previously characterized the enzyme's 15-LO metabolites 12(S)-hydroxyeicosatetraenoic acid (HETE), 15-HETE, hydroxyepoxyeicosatrienoic acids (HEETAs) and 11,12,15-trihydroxyeicosatrienoic acids (11,12,15-THETAs) as endothelium-derived relaxing factors. However, the observed 12-LO metabolites remained uncharacterized. The purpose of this study was to determine the structure and biological functions of eicosanoids generated by the enzyme's 12-LO activity.

METHODS

Metabolites extracted from aortas of C57BL/6 male mice were separated using a series of reverse and normal phase chromatographic steps and identified as hepoxilin A₃ , trioxilin A₃ and trioxilin C₃ by mass spectrometry. Activities of these natural compounds were tested on isometric tension and intracellular calcium release. The role of thromboxane (TP) receptor was determined in HEK293 cells overexpressing TPα receptor (TPα -HEK).

RESULTS

All identified vascular 12-LO metabolites were biologically active. In mouse mesenteric arteries, trioxilin A₃ , C₃ and hepoxilin A₃ (3 μm) relaxed arteries constricted with the thromboxane mimetic, U46619-constricted arteries (maximum relaxations of 78.9 ± 3.2, 29.7 ± 4.6, 82.2 ± 5.0 and 88.0 ± 2.4% respectively), but not phenylephrine-constricted arteries. In TPα-HEK cells, trioxilin A₃ , C₃ and hepoxilin A₃ (10 μm) inhibited U46619 (10 nM)-induced increases in intracellular calcium by 53.0 ± 7.2%, 32.8 ± 5.0% and 37.9 ± 13.5% respectively. In contrast, trioxilin B₃ and hepoxilin B₃ were not synthesized in arteries and exhibited little biological activity.

CONCLUSION

Trioxilin A₃ and C₃ and hepoxilin A₃ are endogenous vascular relaxing factors. They are not endothelium-derived hyperpolarizing factors but mediate vascular relaxation by inhibiting TP agonist-induced increases in intracellular calcium. Thus, they regulate vascular homeostasis by acting as endogenous TP antagonists.

Regio- and stereoselective monoepoxidation of dienes using methyltrioxorhenium: synthesis of allylic epoxides

Methyltrioxorhenium (MTO) complexed with pyridine was shown to be a highly effective catalyst for the regioselective monoepoxidation of conjugated di- and trienes using 30% H₂O₂ at or below room temperature. The resultant allylic epoxides, and the triols derived from them, are versatile synthetic intermediates as well as substructures present in many bioactive natural products. The site of epoxidation was dependent upon olefin substitution, olefin geometry (Z vs E), and the presence of electron-withdrawing substituents on adjacent carbons. For 1-acyl(silyl)oxypenta-2,4-dienes, epoxidation of the distal olefin was generally favored in contrast to the adjacent regioselectivity characteristic of Sharpless, peracid, and other directed epoxidations of hydroxylated dienes.

17(R),18(S)-epoxyeicosatetraenoic acid, a potent eicosapentaenoic acid (EPA) derived regulator of cardiomyocyte contraction: structure-activity relationships and stable analogues

17(R),18(S)-epoxyeicosatetraenoic acid [17(R),18(S)-EETeTr], a cytochrome P450 epoxygenase metabolite of eicosapentaenoic acid (EPA), exerts negative chronotropic effects and protects neonatal rat cardiomyocytes against Ca(2+)-overload with EC(50) ≈ 1-2 nM. Structure-activity studies revealed that a cis-Δ(11,12)- or Δ(14,15)-olefin and a 17(R),18(S)-epoxide are minimal structural elements for antiarrhythmic activity whereas antagonist activity was often associated with the combination of a Δ(14,15)-olefin and a 17(S),18(R)-epoxide. Compared with natural material, the agonist and antagonist analogues are chemically and metabolically more robust and several show promise as templates for future development of clinical candidates.

CYP3A4 mediates growth of estrogen receptor-positive breast cancer cells in part by inducing nuclear translocation of phospho-Stat3 through biosynthesis of (±)-14,15-epoxyeicosatrienoic acid (EET)

CYP3A4 expression in breast cancer correlates with decreased overall survival, but the mechanisms are unknown. Cytochrome P450 gene profiling by RNAi silencing demonstrates that CYP3A or 2C8 gene expression is specifically required for growth of the breast cancer lines MCF7, T47D, and MDA-MB-231. CYP3A4 silencing blocks the cell cycle at the G(2)/M checkpoint and induces apoptosis in the MCF7 line, thereby inhibiting anchorage-dependent growth and survival. CYP3A4 was profiled for NADPH-dependent arachidonic acid (AA) metabolism and synthesized AA epoxygenase products (±)-8,9-, (±)-11,12-, and (±)-14,15-epoxyeicosatrienoic acid (EET) (total turnover of ∼2 pmol/pmol CYP3A4/min) but not hydroxylase products (±)-15-, (±)-19-, or 20-hydroxyeicosatetraenoic acid. Furthermore, eicosanoid profiling revealed that MCF7 cells synthesize EETs in a CYP3A4-dependent manner. The (±)-14,15-EET regioisomer selectively rescues breast cancer cells from CYP3A4 silencing in a concentration-dependent fashion and promotes mitogenesis and anchorage-dependent cloning. Stat3 (Tyr-705) phosphorylation was inhibited by CYP3A4 silencing, providing a potential mechanism for CYP3A4 involvement in breast cancer cell growth. Silencing Stat3 blocks breast cancer cell growth and abrogates (±)-14,15-EET-induced proliferation, indicating a Stat3 requirement for (±)-14,15-EET-mediated cell growth. Although silencing of CYP3A4 reduces nuclear Tyr(P)-705-Stat3, (±)-14,15-EET restores this signaling process and promotes Tyr(P)-705-Stat3 translocation to the nucleus, suggesting that (±)-14,15-EET may be involved in an autocrine/paracrine pathway driving cell growth. These studies indicate that CYP3A4 is a highly active AA epoxygenase that promotes Stat3-mediated breast cancer cell growth in part through (±)-14,15-EET biosynthesis. Furthermore, these studies indicate an essential role for Stat3 as a mediator of epoxygenase activity in breast cancer.

14,15-Epoxyeicosa-5,8,11-trienoic acid (14,15-EET) surrogates containing epoxide bioisosteres: influence upon vascular relaxation and soluble epoxide hydrolase inhibition

All-cis-14,15-epoxyeicosa-5,8,11-trienoic acid (14,15-EET) is a labile, vasodilatory eicosanoid generated from arachidonic acid by cytochrome P450 epoxygenases. A series of robust, partially saturated analogues containing epoxide bioisosteres were synthesized and evaluated for relaxation of precontracted bovine coronary artery rings and for in vitro inhibition of soluble epoxide hydrolase (sEH). Depending upon the bioisostere and its position along the carbon chain, varying levels of vascular relaxation and/or sEH inhibition were observed. For example, oxamide 16 and N-iPr-amide 20 were comparable (ED(50) 1.7 microM) to 14,15-EET as vasorelaxants but were approximately 10-35 times less potent as sEH inhibitors (IC(50) 59 and 19 microM, respectively); unsubstituted urea 12 showed useful activity in both assays (ED(50) 3.5 microM, IC(50) 16 nM). These data reveal differential structural parameters for the two pharmacophores that could assist the development of potent and specific in vivo drug candidates.

Generation of Nucleophilic Chromium Acetylides from gem-Trichloroalkanes and Chromium Chloride: Synthesis of Propargyl Alcohols

Nucleophilic mixed chromium(II) and chromium(III) acetylides are generated from the smooth reduction of primary 1,1,1-trichloroalkanes with chromium(II) chloride in the presence of an excess amount of triethylamine at room temperature. These species arise from chromium(III) vinylidene carbenoids. It has been demonstrated that uncommon low-valent Cr(II) acetylides are formed by C-H insertion of Cr(II)Cl(2) into terminal alkynes, formed in situ through the Fritsch- Buttenberg-Wiechell (FBW) rearrangement, whereas Cr(III) acetylides are concomitantly generated by HCl elimination from the chromium(III) vinylidene carbenoid. Both divergent pathways result, overall, in the formation of nucleophilic acetylides. In situ trapping with electrophilic aldehydes afforded propargyl alcohols. Furthermore, deuteration experiments and the use of deuterium labeled 1,1,1-trichloroalkane substrates demonstrated the prevalence of low-valent Cr(II) acetylides, potentially useful, yet highly elusive synthetic intermediates.

Cascade synthesis of (E)-2-alkylidenecyclobutanols

A facile, one-pot reaction cascade condenses 1,1,1-trichloroalkanes with alpha,beta-unsaturated ketones to unexpectedly furnish moderate to good yields of (E)-2-alkylidenecyclobutanols.