A sesquiterpenelactone from Inula britannica induces anti-tumor effects dependent on Bcl-2 phosphorylation.
BACKGROUND
The over-expression of the anti-apoptotic protein Bcl-2 in cancer is associated with resistance to chemotherapeutic drugs. The phosphorylation of Bcl-2 is one mechanism by which anti-microtubule agents, such as paclitaxel or docetaxel, may inactivate Bcl-2. Although initially active in clinical studies, current anti-microtubule agents are only temporarily effective and the discovery of new agents is warranted.


METHODS
We isolated and identified two known sesquiterpenelactones, O, O-diacetylbritannilactone (OODABL) and O-acetylbritaanilactone (OABL) from the flowers of the medicinal plant Inula britannica and studied their mechanism of anti-tumor effects. To determine the biological significance of Bcl-2 phosphorylation, we used a baby rat kidney (BRK-p53) cell line that was transformed with EIA and a temperature-sensitive mutant p53. The BRK-p53 cell line was transfected with either a vector with wild type Bcl-2 or a vector in which Bcl-2 had mutations in the paclitaxel phosphorylation sites (pcDNA3.1 V5/His Bcl-2 S70, 87A).


RESULTS
OODABL and OABL induced phosphorylation of Bcl-2 in breast, ovary and prostate cancer cell lines and induced G2/M cell cycle arrest. Using the BRK cells with mutant Bcl-2 (BRK-Bcl-2-mt) and control (BRK-Bcl-2-wt), we found that OODABL induced phosphorylation of Bcl-2 at sites similar to paclitaxel. Phosphorylation of Bcl-2 was important for OODABL-induced cytotoxicity, since the abrogation of phosphorylation in BRK-Bcl-2-mt cells decreased OODABL-induced cytotoxicity.


CONCLUSIONS
We concluded that OODABL is cytotoxic in multiple tumor cell lines, and the cytotoxicity is dependent, at least in part, on the phosphorylation of Bcl-2.
Rafi
Mohamed M
MM
Department of Food Science, New Jersey Agricultural Experimentation Station, Cook College, Rutgers University, New Brunswick, New Jersey 08901-8520, USA. rafi@aesop.rutgers.edu
Bai
Nai-Sheng
NS
Chi-Tang-Ho
Rosen
Robert T
RT
White
Eileen
E
Perez
Denise
D
Dipaola
Robert S
RS
D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D004354:Drug Screening Assays, Antitumor; D035264:Flowers / Q000737:chemistry; D006801:Humans; D038143:Inula / Q000737:chemistry*; D007783:Lactones / Q000302:isolation & purification / Q000494:pharmacology*; D016297:Mutagenesis, Site-Directed; D010766:Phosphorylation / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism*; D051381:Rats; D012717:Sesquiterpenes / Q000302:isolation & purification / Q000494:pharmacology*
D007783:Lactones; C500400:O, O-diacetylbritannilactone; C500401:O-acetylbritaanilactone; D019253:Proto-Oncogene Proteins c-bcl-2; D012717:Sesquiterpenes