Abstract 838: Mdm2 and oncogenic mutant p53 as biomarkers for potential drug targets in estrogen receptor positive and triple negative breast cancer
Authors: Polotskaia Alla , Brekman Angelika , Bargonetti Jill 
Published: February 2011

Abstract
The study of Mdm2 and oncogenic p53 as biomarkers for potential drug targets in breast cancers has not been developed. Triple negative breast cancers often have gain-of-function oncogenic mutant p53 while estrogen receptor positive breast cancers retain wild-type p53 and over-express Mdm2. We are investigating how to inhibit the growth of various types of breast cancer cell lines when p53 function is compromised. Here we report two approaches. The first approach utilizes the nucleoside analogue 8-aminoadenosine (8-amino-Ado) and the second approach utilizes inducible RNA interference for oncogenic mdm2 or p53. 8-amino-Ado is under pre-clinical investigation for the treatment of hematological malignancies. We investigated if 8-amino-Ado could inhibit breast cancer cell growth and promote cell death in a manner that did not require functional p53 protein and compared this to gemcitabine (a nucleoside analogue used to treat breast cancer). We used the triple negative breast cancer cell lines MDA-MB-231 and MDA-MB-468 as well as the estrogen receptor positive breast cancer cell line MCF-7. 8-amino-Ado promoted death of the triple negative mutant p53 breast cancers as well, or better, than it did for the estrogen receptor positive wild-type p53 breast cancer and in all cases was superior to gemcitabine. For the second approach we constructed cell lines using an inducible shRNA vector that contained a naturally occurring miR sequence. We previously showed that mutant p53 is required for the survival of MDA-MB-231 cells in the absence of serum. Using an inducible p53 shRNA we see that the mutant p53 found in MDA-MB-231 and MDA-MB-468 gives these cells a survival advantage in the absence of serum and when p53 is knocked down the cells die without PARP cleavage, suggesting non-apoptotic cell death. Estrogen increases the expression of Mdm2 in MCF-7 cells and therefore we investigated if the growth activation feature of estrogen in MCF-7 cells required Mdm2 protein. Induction of mdm2 shRNA reduced the Mdm2 protein level and increased the p21 protein level without a detectable change in p53. Induction of mdm2 shRNA caused a corresponding decrease in estrogen-activated MCF-7 cell growth. Inducible expression of shRNA to p53 or the control construct had no effect on the growth of MCF-7 cells. Our data suggest that 8-amino-Ado induced death occurs via a p53-independent pathway and thus might be beneficial for the treatment of all breast cancers. Additionally Mdm2 and oncogenic mutant p53 are biomarkers that can be used to screen for interfering RNA based and 8-amino-Ado therapeutic approaches for estrogen receptor positive and triple negative breast cancers.
This work was supported by The Breast Cancer Research Foundation.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 838.