title: Highly lipophilic 3-epi-betulinic acid derivatives as potent and selective TGR5 agonists with improved cellular efficacy.
abstract: OBJECTIVE
  TGR5 is a G protein-coupled receptor that is expressed in intestinal L-cells and stimulates glucagon-like peptide 1 (GLP-1) secretion. TGR5 may represent a novel target for the treatment of metabolic disorder. Here, we sought to design and synthesize a series of TGR5 agonists derived from the natural product betulinic acid.
  
  
  METHODS
  A series of betulinic acid derivatives were designed and synthesized. A cAMP assay was established using a HEK293 cell line expressing human TGR5. Luciferase reporter assay was established using HEK293 cells transfected with plasmids encoding human FXR and luciferase reporter. A human intestinal L-cell line NCI-H716 was used to evaluate the effects of the betulinic acid derivatives on GLP-1 secretion in vitro.
  
  
  RESULTS
  Biological data revealed that the 3-α-OH triterpenoids consistently show increased potency for TGR5 compared to their 3-β-OH epimers. 3-OH esterification increased the lipophilicity and TGR5 activity of 3-α betulinic derivatives and enhanced the activity differences between 3-α and 3-β derivatives. The 3-α-acyloxy betulinic acids also exhibited a significant dose-dependent GLP-1 secretion effect.
  
  
  CONCLUSIONS
  This study demonstrates that highly lipophilic 3-epi-betulinic acid derivatives can be potent and selective TGR5 agonists with improved cellular efficacy, and our research here provides a new strategy for the design and development of potent TGR5 agonists.
authors.affiliation: State Key Laboratory of Drug Research, CAS Key Laboratory of Receptor Research, the National Center for Drug Screening, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China.
authors.forename: Xiao-yin
authors.initials: XY
authors.lastname: Wang
authors.affiliation: State Key Laboratory of Drug Research, CAS Key Laboratory of Receptor Research, the National Center for Drug Screening, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China.
authors.forename: Shu-yong
authors.initials: SY
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Drug Research, CAS Key Laboratory of Receptor Research, the National Center for Drug Screening, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China.
authors.forename: Jing
authors.initials: J
authors.lastname: Li
authors.affiliation: State Key Laboratory of Drug Research, CAS Key Laboratory of Receptor Research, the National Center for Drug Screening, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China.
authors.forename: Hua-nan
authors.initials: HN
authors.lastname: Liu
authors.affiliation: State Key Laboratory of Drug Research, CAS Key Laboratory of Receptor Research, the National Center for Drug Screening, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China.
authors.forename: Xin
authors.initials: X
authors.lastname: Xie
authors.affiliation: State Key Laboratory of Drug Research, CAS Key Laboratory of Receptor Research, the National Center for Drug Screening, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, Shanghai 201203, China.
authors.forename: Fa-jun
authors.initials: FJ
authors.lastname: Nan
mesh_terms: D000284:Administration, Oral; D000818:Animals; D000242:Cyclic AMP / Q000378:metabolism; D017930:Genes, Reporter; D052216:Glucagon-Like Peptide 1 / Q000378:metabolism; D057809:HEK293 Cells; D056945:Hep G2 Cells; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000187:drug effects; D015394:Molecular Structure; D053978:Pentacyclic Triterpenes; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D043562:Receptors, G-Protein-Coupled / Q000819:agonists* / Q000235:genetics; D013329:Structure-Activity Relationship; D014162:Transfection; D014315:Triterpenes / Q000008:administration & dosage / Q000138:chemical synthesis / Q000493:pharmacokinetics / Q000494:pharmacology*; D000094062:Betulinic Acid; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D000242:Cyclic AMP; D052216:Glucagon-Like Peptide 1; D053978:Pentacyclic Triterpenes; D018160:Receptors, Cytoplasmic and Nuclear; D043562:Receptors, G-Protein-Coupled; D014315:Triterpenes; D000094062:Betulinic Acid; D000099150:Receptor, Farnesoid X-Activated; C473772:GPBAR1 protein, human