Inhibition of cyclooxygenase (COX)-2 expression by Tet-inducible COX-2 antisense cDNA in hormone-refractory prostate cancer significantly slows tumor growth and improves efficacy of chemotherapeutic drugs.
OBJECTIVE
Overexpression of the proinflammatory enzyme cyclooxygenase (COX)-2 is associated with the progression of various malignancies; the role of COX-2 in prostate cancer is less clear. The significance of COX-2 in prostate cancer growth and response to chemotherapy was investigated in an androgen-refractory prostate cancer cell line using a Tet-inducible antisense COX-2 expression system.


METHODS
An antisense COX-2 cDNA construct under the control of a doxycycline-inducible promoter was transfected into a prostate cancer cell line, PC-3ML. Modulations of cell growth, apoptosis, and chemosensitivity in the presence or absence of doxycycline were analyzed. Tumor incidence, growth rate, and response to two cytotoxic drugs, COL-3 [chemically modified tetracycline-3-(6-demethyl-6-deoxy-4-dedimethylamino-tetracycline)] and Taxotere (docetaxel), were investigated in tumor xenografts. Apoptotic incidences and tumor microvessel density in tumors were determined by immunohistochemistry.


RESULTS
Conditional suppression of COX-2 in PC-3ML caused reduced cell proliferation, decreased levels of phosphorylated AKT, G(0)-G(1) arrest, and increased apoptosis and caspase-3 activity. Suppression of COX-2 increased Bax protein and decreased Bcl-x(L) protein in vitro. COX-2 antisense-expressing PC-3ML tumors showed a 57% growth delay compared with nontransfected or vector controls. Oral administration of COL-3 (40 mg/kg, oral gavage) or Taxotere (2.3 mg/kg, intraperitoneally; 3x per week) in tumor-bearing mice further slowed tumor growth (65% and approximately 94%, respectively). Compared with the control group, the occurrence of apoptosis in antisense COX-2 tumors was eight times higher, and the tumor microvessel density was three times lower.


CONCLUSIONS
These results provide direct evidence that constitutive expression of COX-2 in prostate cancer has both angiogenic and cytoprotective functions. Suppression of tumor cell COX-2 is sufficient to enhance chemotherapy response in prostate cancer.
Dandekar
Devendra S
DS
Department of Urology and Sylvester Comprehensive Cancer Center, University of Miami School of Medicine, Miami, Florida 33101, USA.
Lokeshwar
Bal L
BL
D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D051546:Cyclooxygenase 2; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors / Q000494:pharmacology*; D018076:DNA, Complementary / Q000235:genetics / Q000378:metabolism; D000077143:Docetaxel; D004359:Drug Therapy, Combination; D015971:Gene Expression Regulation, Enzymologic; D008297:Male; D051379:Mice; D008833:Microcirculation; D009376:Neoplasms, Hormone-Dependent / Q000201:enzymology* / Q000235:genetics / Q000517:prevention & control; D016376:Oligonucleotides, Antisense / Q000494:pharmacology*; D011451:Prostaglandin-Endoperoxide Synthases / Q000378:metabolism*; D011471:Prostatic Neoplasms / Q000201:enzymology* / Q000235:genetics / Q000517:prevention & control; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D043823:Taxoids / Q000494:pharmacology; D013752:Tetracycline / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
C494827:Bax protein, mouse; C494812:Bcl2l1 protein, mouse; D052246:Cyclooxygenase 2 Inhibitors; D016861:Cyclooxygenase Inhibitors; D018076:DNA, Complementary; D016376:Oligonucleotides, Antisense; D019253:Proto-Oncogene Proteins c-bcl-2; D043823:Taxoids; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D000077143:Docetaxel; D051546:Cyclooxygenase 2; D011451:Prostaglandin-Endoperoxide Synthases; D013752:Tetracycline