Triglyceride modulation by acifran analogs: activity towards the niacin high and low affinity G protein-coupled receptors HM74A and HM74

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Abstract

Niacin is known to exert profound beneficial effects on cholesterol levels in humans, although its use is somewhat hampered by the gram quantities necessary to exert effects and the prevalence of compliance-limiting skin flushing side effects that occur. Recently, two G protein-coupled receptors (GPCRs) for niacin were identified and characterized as high (HM74A; GPR109A) and low (HM74; GPR109B) affinity receptors based on the binding affinities of niacin. These receptors also bind acifran (AY-25,712), which is known to modulate lipid levels like niacin, with similar affinities. Twelve analogs of acifran were chemically synthesized. One analogue demonstrated a dose-dependent decrease in serum triglycerides in rats within 3 h of oral administration. Next, the acifran analogs were assessed for their activity towards the high and low affinity niacin receptors expressed in CHO-K1 cells. Constructs expressing HM74A or HM74 were stably transfected into CHO-K1 cells and shown to elicit phosphorylation of p42 and p44 mitogen-activated protein kinase (ERK1/ERK2) phosphorylation upon addition of niacin or acifran. The presence of functionally coupled GPCRs was further confirmed using Pertussis toxin, which completely inhibited the ability of either niacin or acifran to elicit phospho-ERK1/ERK2. The EC50 of p-ERK1/ERK2 for niacin for the high and low affinity receptors was 47 nM and indeterminate (i.e., >100 μM), respectively, while the EC50 for acifran was 160 and 316 nM, respectively. Two chemical analogs of acifran demonstrated robust phosphorylation of ERK1/ERK2. Collectively, these data suggest that the synthesis of acifran analogs may be a suitable path for developing improved HM74A agonists.

Section snippets

Materials and methods

Synthesis of acifran analogs. Acifran analogs were synthesized using standard chemistry techniques, as outlined by the Ayerst Laboratory patents 4,169,202 and 4,244,958. The key step in the synthesis is the base-promoted cyclo-condensation reaction of functionalized α-hydroxyketones with diethyloxalate, to give the furancarboxylic acids. All analogs were purified by recrystallization or flash chromatography and analyzed for purity and integrity using standard analytical techniques (HPLC, LC-MS,

In vivo efficacy of acifran analogs

Selected acifran analogs (compounds 15 and 79) were examined in the fructose-fed rat model for their ability to lower serum TGs in comparison to acifran that served as a positive control. Table 2 summarizes the results. As expected, acifran exhibited a dose-dependent decrease in serum TGs. Activity is likely due to the S-enantiomer (compound 8), as the R-enantiomer (compound 7) was found to be inactive. Of the other compounds tested only compound 5, which contains a fluorine on the phenyl

Discussion

The synthesis of acifran (AY-25,712; see Table 1 for structure), a known hypolipidemic agent, was first reported by scientists at Ayerst Laboratories in the now expired US Patents 4,169,202 and 4,244,958, and in the literature [22], [23]. It has been suggested that acifran acts to lower serum lipids by a mechanism similar to that of niacin by lowering serum TGs, elevating HDL-C, and possibly lowering LDL-C cholesterol [17]. A compound with such a profile would be of particular value to patients

Acknowledgments

This work was supported, in part, by Small Business Innovation Research grants from the NIDDK to Stuart A. Ross (DK71401) and from NHLBI to Allan R. Moorman (1R43 HL63590-01 and 1R43 HL62831-01). We thank Anne Carrington for development of the fructose-fed rat model and Heather Smiarowski and Kathy Ellwood for animal husbandry.

References (24)

  • W.J. Mack et al.

    One-year reduction and longitudinal analysis of carotid intima-media thickness associated with colestipol/niacin therapy

    Stroke

    (1993)
  • E.A. Nikkila et al.

    Prevention of progression of coronary atherosclerosis by treatment of hyperlipidemia: a seven year prospective angiographic study

    Br. Med. J.

    (1984)
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    1

    These two authors contributed equally to this work.

    2

    Present address: Novartis Institute for Biomedical Research, 250 Massachusetts Avenue, Cambridge, MA 02139, USA.

    3

    Present address: King Pharmaceuticals Research and Development Inc., 4000 CentreGreen Way, Suite 300, Cary, NC 27513, USA.

    4

    Present address: Adipogenix, 801 Albany Street, Boston, MA 02118, USA.

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