title: Long-term androgen-ablation causes increased resistance to PI3K/Akt pathway inhibition in prostate cancer cells.
abstract: BACKGROUND
  In advanced stages of prostate cancer, the phosphatidylinositol-3' kinase (PI3K)/Akt signaling cascade, one of the major survival pathways in the cell, is frequently constitutively activated due to mutation or loss of the tumor suppressor protein phosphatase and tensin homolog deleted on chromosome 10 (PTEN). Using cell culture models representing different tumor stages, we explored the effect of inhibition of this survival pathway on the induction of apoptosis.
  
  
  METHODS
  Inhibition of the survival kinase Akt and induction of apoptosis was analyzed in androgen-insensitive DU145 and PC-3 cells, in androgen-responsive LNCaP, and in androgen-independent long-term androgen-ablated LNCaP-abl cells representing therapy-resistant prostate cancer cells. Activated Akt was determined by immunoblotting using a phospho-Akt specific antibody. Induction of apoptosis was analyzed employing annexing V and propidium iodide staining and flow cytometry and measurement of cleavage of the caspases substrate poly-ADP-ribose polymerase (PARP).
  
  
  RESULTS
  IGF-1, EGF, and heregulin but not PDGF or activators of protein kinase A induced phosphorylation of Akt in DU145 cells and activation was completely blocked by the PI3K inhibitor LY294002. In the hormone-responsive prostate cancer cell line LNCaP that has a constitutively switched-on Akt kinase, LY294002 caused a dose- and time-dependent Akt inhibition, which was absent in long-term androgen-ablated LNCaP sublines. In agreement with the resistance to inhibition of the PI3K/Akt pathway, long-term androgen-ablated LNCaP sublines remained relatively resistant to induction of cell death by LY294002 or the cytotoxic drug etoposide. Inhibition of the PI3K/Akt pathway restored the sensitivity of long-term androgen-ablated cells to induction of apoptosis by a cytotoxic drug almost completely.
  
  
  CONCLUSIONS
  These results suggest that long-term androgen ablation therapy for prostate cancer reinforces the PI3K/Akt pathway and impedes its inhibition thus contributing to increased resistance of tumor cells to induction of apoptosis. With regard to treatment of therapy-refractory prostate cancer, these findings suggest effectiveness of a combination of cytotoxic treatment and inhibition of the PI3K-Akt survival pathway in tumor cells after failure of androgen-ablation therapy.
authors.affiliation: Department of Urology, University of Innsbruck, Austria.
authors.forename: Karina
authors.initials: K
authors.lastname: Pfeil
authors.forename: Iris E
authors.initials: IE
authors.lastname: Eder
authors.forename: Thomas
authors.initials: T
authors.lastname: Putz
authors.forename: Reinhold
authors.initials: R
authors.lastname: Ramoner
authors.forename: Zoran
authors.initials: Z
authors.lastname: Culig
authors.forename: Florian
authors.initials: F
authors.lastname: Ueberall
authors.forename: Georg
authors.initials: G
authors.lastname: Bartsch
authors.forename: Helmut
authors.initials: H
authors.lastname: Klocker
mesh_terms: D000726:Androgen Antagonists / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor; D002867:Chromones / Q000494:pharmacology*; D004351:Drug Resistance; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004815:Epidermal Growth Factor / Q000378:metabolism; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D008297:Male; D009025:Morpholines / Q000494:pharmacology*; D020890:Neuregulin-1 / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011471:Prostatic Neoplasms / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors*; D051057:Proto-Oncogene Proteins c-akt; D013997:Time Factors
chemical_list: D000726:Androgen Antagonists; D002867:Chromones; D004791:Enzyme Inhibitors; D009025:Morpholines; D020890:Neuregulin-1; D000081082:Phosphoinositide-3 Kinase Inhibitors; D011518:Proto-Oncogene Proteins; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D004815:Epidermal Growth Factor; D007334:Insulin-Like Growth Factor I; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt