Abstract 2739: Specific interaction of human MGMT with ER-{alpha} in breast cancer cells: Co-degradation of MGMT and ER- {alpha} proteins by either fulvestrant or O6-benzylguanine and its therapeutic significance

This study investigated whether i) MGMT is modulated by endocrine therapies, ii) MGMT interacts with ER-signaling components and iii) if such findings are exploitable for improved breast cancer treatment. The ER-α positive cell lines MCF-7, T47D and ER- α negative MDAMB 468 cells, all MGMT-proficient, were treated with Fulvestrant (Faslodex, ICI 182, 780) or O6-benzylguanine (BG) in various experiments. Fulvestrant is a pure antiestrogen that binds to ER without eliciting any transcriptional effects, but leads to the receptor degradation through the ubiquitin-proteasome (ub-P) pathway. BG is a specific pseudosubstrate for MGMT currently in clinical trials that inactivate the repair protein resulting in its degradation, again by the ub-P pathway. Fulvestrant (0.1-1 µM) induced a dose- and time-dependent inhibition of MGMT's DNA repair activity with a 75% inhibition after 1 µM treatment at 72 h. Interestingly, western blot analyses showed a progressive loss of both ER-α and MGMT proteins in Fulvestrant -treated cells. The MGMT in ER- α negative MDMAB cells was not affected by the drug. Similarly, BG (20-50 µM) induced a time-dependent significant destruction of the ER- α and MGMT proteins in cells. Immunoprecipitation using antibodies to either MGMT or ER- α followed by western blot analyses showed that the two proteins exist physically associated in breast cancer cells. siRNA and shRNAs specific for MGMT downregulated both the ER- α and MGMT proteins in MCF-7 cells c...
Source: Cancer Research - Category: Cancer & Oncology Authors: Tags: Experimental and Molecular Therapeutics Source Type: research