Calcium and P-glycoprotein independent synergism between schweinfurthins and verapamil

Ryan M. Sheehy, Craig H. Kuder, Zoe Bachman, Raymond J. Hohl

Research output: Contribution to journalArticlepeer-review

9 Scopus citations


Schweinfurthins are intriguing natural products with anti-cancer activities and as yet incompletely understood mechanisms of action. We investigated whether inhibitors of P-glycoprotein (Pgp), in a manner analogous to other natural products, might enhance schweinfurthins’ growth inhibitory actions by increasing intracellular schweinfurthin levels. Both the schweinfurthin-sensitive glioblastoma multiforme cell line SF-295 and relatively insensitive lung carcinoma cell line A549 were treated with 2 schweinfurthin analogs: 3-deoxyschweinfurthin B-pnitro bis-stilbene (3dSB-PNBS) and 50-methylschweinfurthin G (methyl-G). There was a synergistic enhancement of growth inhibition with the combination of the Pgp inhibitor verapamil and both analogs in SF-295 cells. Methyl-G, verapamil, and the combination did not result in alterations to intracellular calcium concentration. Verapamil increased the intracellular concentration of 3dSB-PNBS in both SF-295 and A549 cells in a Pgp-independent manner. Methyl-G, verapamil, and the combination do not result in increased ER stress. Methyl-G increased the intracellular concentration of a known Pgp substrate, Rhodamine 123 in SF-295 cells. Reduction of cellular cholesterol leads to the accumulation of Pgp substrates, as Pgp requires cholesterol for proper function. Since 3dSB enhances lovastatin-induced upregulation of the cholesterol efflux pump ABCA1, it is intriguing that cotreatment with cholesterol rescued the methyl-G-induced increase in Rhodamine 123 intracellular concentration. These studies support the hypothesis that verapamil potentiates the schweinfurthin growth inhibitory effect by increasing its intracellular concentration.

Original languageEnglish (US)
Pages (from-to)1259-1268
Number of pages10
JournalCancer Biology and Therapy
Issue number8
StatePublished - 2015

All Science Journal Classification (ASJC) codes

  • Molecular Medicine
  • Oncology
  • Pharmacology
  • Cancer Research


Dive into the research topics of 'Calcium and P-glycoprotein independent synergism between schweinfurthins and verapamil'. Together they form a unique fingerprint.

Cite this