title: 5,6-Dihydro-5'-azacytidine (DHAC) affects estrogen sensitivity in estrogen-refractory human breast carcinoma cell lines.
abstract: BACKGROUND
  There is little effective therapy for patients with hormone-refractory breast cancer. Hormone resistance is frequently due to the transcriptional inactivation of the estrogen receptor (ER) gene. We determined the effect of DHAC, a cytosine DNA methyltransferase (CMT) inhibitor, on the estrogen sensitivity in three human breast carcinoma cell lines with intermediate to low levels of estrogen receptor (ER) expression: MCF7 (adriamycin-sensitive), MCF7M/Adr (adriamycin-resistant), and MDA-435, and one ER+ cell line, ZR75-1.
  
  
  METHODS
  Cells maintained in culture were exposed to DHAC or vehicle continuously for 14 days, then exposed to estradiol or tamoxifen and counted on day 21.
  
  
  RESULTS
  Exposure to DHAC did not affect estrogen sensitivity in ZR-75-1 and MCF7M/Adr cells. DHAC treatment of MCF7 and MDA-435 cells resulted in significant (p < 0.05) growth stimulation in response to estrogen at 10(-6) M, and to growth modulation by tamoxifen at 10(-5) to 10(-7) M.
  
  
  CONCLUSIONS
  These data suggest that DHAC can restore the estrogen sensitivity in ER-breast cancer. Thus, DHAC and other novel CMT inhibitors may have a clinical application in treating estrogen-refractory breast cancer patients by restoring the estrogen sensitivity and allowing these patients to respond again to conventional therapy with estrogen antagonists.
authors.affiliation: Institute for Drug Development, Cancer Therapy and Research Center, Nordan Colon Cancer Laboratory, San Antonio, Texas 78229, USA. eizbicka@saci.org
authors.forename: E
authors.initials: E
authors.lastname: Izbicka
authors.forename: K K
authors.initials: KK
authors.lastname: Davidson
authors.forename: R A
authors.initials: RA
authors.lastname: Lawrence
authors.forename: J R
authors.initials: JR
authors.lastname: MacDonald
authors.forename: D D
authors.initials: DD
authors.lastname: Von Hoff
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D001374:Azacitidine / Q000031:analogs & derivatives* / Q000494:pharmacology; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology; D015257:DNA-Cytosine Methylases / Q000037:antagonists & inhibitors*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D004967:Estrogens / Q000494:pharmacology*; D005260:Female; D006801:Humans; D011960:Receptors, Estrogen / Q000032:analysis; D013629:Tamoxifen / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D004791:Enzyme Inhibitors; D004967:Estrogens; D011960:Receptors, Estrogen; C013938:5,6-dihydro-5-azacytidine; D013629:Tamoxifen; D015257:DNA-Cytosine Methylases; D001374:Azacitidine