title: Solenopsin A and analogs exhibit ceramide-like biological activity.
abstract: BACKGROUND
  (-)-Solenopsin A is a piperidine alkaloid that is a component of the venom of the fire ant Solenopsis invicta. Previously, we have demonstrated that solenopsin exhibit anti-angiogenic activity and downregulate phosphoinositol-3 kinase (PI3K) in the p53 deficient renal cell carcinoma cell line 786-O. Solenopsin has structural similarities to ceramide, a major endogenous regulator of cell signaling and cancer therapy induced apoptosis.
  
  
  METHODS
  Different analogs of solenopsin were synthesized in order to explore structure-activity relationships. The anti-proliferative effect of solenopsin and analogs was tested on six different cell lines, including three tumor cell lines, two normal cutaneous cell lines, and one immortalized hyperproliferative cell line. FRET-based reporters were used to study the affect of solenopsin and analogs on Akt activity and PDK1 activation and sucrose density gradient fractionation was performed to examine recruitment of PTEN to membrane rafts. Western-blotting was used to evaluate the affect of solenopsin and analogs on the Akt and the MAPK 44/42 pathways in three different tumor cell lines. Measurement of cellular oxygen consumption rate together with autophagy staining was performed to study mitochondrial function. Finally, the affect of solenopsin and analogs on ROS production was investigated.
  
  
  RESULTS
  In this paper we demonstrate that solenopsin analogs with potent anti-proliferative effects can be synthesized from inexpensive dimethylpyridines. To determine whether solenopsin and analogs act as ceramide analogs, we examined the effect of solenopsin and analogs on two stereotypic sites of ceramide activity, namely at lipid rafts and mitochondria. We found that native solenopsin, (-)-solenopsin A, inhibits functional Akt activity and PDK1 activation in lipid rafts in a similar fashion as ceramide. Both cis and trans analogs of solenopsin reduce mitochondrial oxygen consumption, increase reactive oxygen, and kill tumor cells with elevated levels of Akt phosphorylation. However, only solenopsin induces mitophagy, like ceramide.
  
  
  CONCLUSIONS
  The requirements for ceramide induced mitophagy and inhibition of Akt activity and PDK1 activation in lipid rafts are under strict stereochemical control. The naturally occurring (-)-solenopsin A mimic some of the functions of ceramide and may be therapeutically useful in the treatment of hyperproliferative and malignant disorders of the skin, even in the presence of elevated levels of Akt.
authors.affiliation: Department of Dermatology, Emory University School of Medicine, Atlanta, GA USA.
authors.forename: Isabella
authors.initials: I
authors.lastname: Karlsson
authors.affiliation: Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD USA.
authors.forename: Xin
authors.initials: X
authors.lastname: Zhou
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC USA.
authors.forename: Raquela
authors.initials: R
authors.lastname: Thomas
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, Union University, Jackson, TN USA.
authors.forename: Allorie T
authors.initials: AT
authors.lastname: Smith
authors.affiliation: Department of Dermatology, Emory University School of Medicine, Atlanta, GA USA.
authors.forename: Michael Y
authors.initials: MY
authors.lastname: Bonner
authors.affiliation: Center for Drug Design, Department of Pharmaceutical Sciences, College of Pharmacy, Mercer University, Atlanta, GA USA.
authors.forename: Pooja
authors.initials: P
authors.lastname: Bakshi
authors.affiliation: Center for Drug Design, Department of Pharmaceutical Sciences, College of Pharmacy, Mercer University, Atlanta, GA USA.
authors.forename: Ajay K
authors.initials: AK
authors.lastname: Banga
authors.affiliation: Center for Drug Design, Department of Pharmaceutical Sciences, College of Pharmacy, Mercer University, Atlanta, GA USA.
authors.forename: J Phillip
authors.initials: JP
authors.lastname: Bowen
authors.affiliation: Department of Chemistry & Biochemistry, University of North Carolina Greensboro, Greensboro, NC USA.
authors.forename: Ghassan
authors.initials: G
authors.lastname: Qabaja
authors.affiliation: Department of Chemistry & Biochemistry, University of North Carolina Greensboro, Greensboro, NC USA.
authors.forename: Shavon L
authors.initials: SL
authors.lastname: Ford
authors.affiliation: Department of Chemistry & Biochemistry, University of North Carolina Greensboro, Greensboro, NC USA.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Ballard
authors.affiliation: Department of Chemistry & Biochemistry, University of North Carolina Greensboro, Greensboro, NC USA.
authors.forename: Kimberly S
authors.initials: KS
authors.lastname: Petersen
authors.affiliation: Department of Physiology and Renal Division, Emory University School of Medicine, Atlanta, GA USA.
authors.forename: Xuechen
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Physiology and Renal Division, Emory University School of Medicine, Atlanta, GA USA.
authors.forename: Guangping
authors.initials: G
authors.lastname: Chen
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC USA.
authors.forename: Besim
authors.initials: B
authors.lastname: Ogretmen
authors.affiliation: Department of Pharmacology and Molecular Sciences, The Johns Hopkins University School of Medicine, Baltimore, MD USA.
authors.forename: Jin
authors.initials: J
authors.lastname: Zhang
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, Union University, Jackson, TN USA.
authors.forename: E Blake
authors.initials: EB
authors.lastname: Watkins
authors.affiliation: Department of Urology, Emory University School of Medicine, Atlanta, GA USA.
authors.forename: Rebecca S
authors.initials: RS
authors.lastname: Arnold
authors.affiliation: Department of Dermatology, Emory University School of Medicine, Atlanta, GA USA ; Atlanta Veterans Administration Hospital, and Winship Cancer Institute, Emory University, Atlanta, GA USA.
authors.forename: Jack L
authors.initials: JL
authors.lastname: Arbiser
keywords: Akt; Ceramide; Mitophagy; Reactive oxygen; Solenopsin A