The plant alkaloid cryptolepine induces p21WAF1/CIP1 and cell cycle arrest in a human osteosarcoma cell line

Int J Oncol. 2007 Oct;31(4):915-22.


We previously established a bioassay method to screen for compounds that activate the promoter activity of p21(WAF1/CIP1), a potent inhibitor of cyclin-dependent kinases, in a p53-independent manner. As an activator of p21(WAF1/CIP1) promoter activity, we isolated cryptolepine (CLP: 5-methyl indolo (2,3b)-quiniine), an indoloquinoline alkaloid, from the traditional Ayurvedic medicinal plant Sida cordifolia. We show here that CLP induces the expression of p21(WAF1/CIP1) with growth arrest in p53-mutated human osteosarcoma MG63 cells. Four micromolar of CLP completely inhibited the growth of MG63 cells and caused G2/M-phase arrest. CLP up-regulated the expression of p21(WAF1/CIP1) at both mRNA and protein levels in a dose-dependent manner. Using several mutant p21(WAF1/CIP1) promoter constructs, we found that the CLP-responsive element is an Sp1 site at -82 relative to the transcription start site of the p21(WAF1/CIP1) promoter. These findings suggest that CLP arrests the growth of MG63 cells by activating the p21(WAF1/CIP1) promoter through the specific Sp1 site in a p53-independent manner. In addition, CLP-mediated cell cycle arrest was reduced by the knockout of the p21(WAF1/CIP1) gene in human colon cancer HCT116 cells, suggesting that the cell cycle arrest by CLP was at least partially mediated through the induction of p21(WAF1/CIP1) expression. Although we need further study of chemotherapeutic effect in vivo, these results raise the possibility that CLP might be a suitable chemotherapeutic agent for treatment of osteosarcoma.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenocarcinoma / drug therapy
  • Adenocarcinoma / metabolism
  • Adenocarcinoma / pathology
  • Antineoplastic Agents, Phytogenic / pharmacology*
  • Blotting, Western
  • Bone Neoplasms / drug therapy*
  • Bone Neoplasms / metabolism
  • Bone Neoplasms / pathology
  • Cell Division / drug effects*
  • Cell Proliferation / drug effects
  • Colonic Neoplasms / drug therapy
  • Colonic Neoplasms / metabolism
  • Colonic Neoplasms / pathology
  • Cyclin-Dependent Kinase Inhibitor p21 / genetics
  • Cyclin-Dependent Kinase Inhibitor p21 / metabolism*
  • Electrophoretic Mobility Shift Assay
  • G2 Phase / drug effects*
  • Humans
  • Indole Alkaloids / pharmacology*
  • Luciferases
  • Osteosarcoma / drug therapy*
  • Osteosarcoma / metabolism
  • Osteosarcoma / pathology
  • Promoter Regions, Genetic / genetics
  • Quinolines / pharmacology*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Response Elements
  • Sp1 Transcription Factor / metabolism
  • Topoisomerase II Inhibitors
  • Transcription, Genetic
  • Tumor Cells, Cultured / drug effects
  • Tumor Suppressor Protein p53 / metabolism


  • Antineoplastic Agents, Phytogenic
  • Cyclin-Dependent Kinase Inhibitor p21
  • Indole Alkaloids
  • Quinolines
  • RNA, Messenger
  • Sp1 Transcription Factor
  • Topoisomerase II Inhibitors
  • Tumor Suppressor Protein p53
  • cryptolepine
  • Luciferases