Downregulation of mdr-1 expression by 8-Cl-cAMP in multidrug resistant MCF-7 human breast cancer cells

S. Scala, A. Budillon, Z. Zhan, Y. S. Cho-Chung, J. Jefferson, M. Tsokos, S. E. Bates

Research output: Contribution to journalArticlepeer-review


8-Cl-cAMP, a site-selective analogue of cAMP, decreased mdr-1 expression in multidrug-resistant human breast cancer cells. A sixfold reduction of mdr- 1 mRNA expression by 8-Cl-cAMP began within 8 h of treatment and was associated with a decrease in the synthesis of P-glycoprotein and with an increase in vinblastine accumulation. A reduction in mdr-1 expression after 8-Cl-cAMP treatment was also observed in multidrug-resistant human ovarian cancer cell lines. 8-Cl-cAMP is known to change the ratio between the two regulatory subunits, RI and RII, of protein kinase A (PKA). We observed that RIα decreased within 24 h of 8-Cl-cAMP treatment, that RIIβ increased after as few as 3 h of treatment, and that PKA catalytic activity remained unchanged during 48 h of 8-Cl-cAMP treatment. The results are consistent with the hypothesis that mdr-1 expression is regulated in part by changes in PKA isoenzyme levels. Although 8-Cl-cAMP has been used to differentiate cells in other model systems, the only differentiating effect that could be detected after 8-Cl-cAMP treatment in the MCF-7TH cells was an increase in cytokeratin expression. Evidence that the reduction of mdr-1 mRNA occurred at the level of gene transcription was obtained by measuring chloramphenicol acetyltransferase (CAT) mRNA in MCF-7TH cells transfected with an mdr-1 promoter-CAT construct prior to 8-Cl-cAMP treatment. Thus, 8-Cl-cAMP is able to downregulate mdr-1 expression and suggests a new approach to reversal of drug resistance in human breast cancer.

Original languageEnglish
Pages (from-to)1026-1034
Number of pages9
JournalJournal of Clinical Investigation
Issue number2
Publication statusPublished - 1995


  • cAMP
  • MDR
  • P-glycoprotein
  • protein kinase A
  • reversal

ASJC Scopus subject areas

  • Medicine(all)


Dive into the research topics of 'Downregulation of mdr-1 expression by 8-Cl-cAMP in multidrug resistant MCF-7 human breast cancer cells'. Together they form a unique fingerprint.

Cite this