Rrm2 And Mutant P53 As Therapeutic Targets In Tnbc.

Abstract Triple negative breast cancer (TNBC) is a highly aggressive type of cancer associated with poor prognosis and characterized by the absence of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor type 2 (HER2). TNBC accounts for 10 - 15% of all new cases of breast cancer. TNBC is heterogenous in nature (70% basal-like) and currently doesn't have effective targeted therapy. As such, dose-dense chemotherapeutic agents used in combination, such as doxorubicin (DOXO) with cyclophosphamide, is the regimen of choice for TNBC. However, DOXO has limited efficacy as a therapeutic agent owing to acquired drug resistance and its cardiotoxic effects. Ribonucleotide reductase (RR) is the rate limiting enzyme required for the conversion of ribonucleotide to deoxyribonucleotide in DNA synthesis during cell proliferation. Didox (3,4 dihydroxybenzohydroxamic acid) is a unique RR inhibitor with iron chelating and free radical scavenging properties. We have previously identified that ribonucleotide reductase M2 (RRM2) is upregulated in TNBC cells and is a key contributor to acquired drug resistance. We found that Didox not only inhibits RRM2, but it also reduces mutant p53 protein levels and inhibits the activation of the NF-κB pathway. Through this inhibition, we found that Didox works synergistically with DOXO to inhibit TNBC tumor growth while also minimizing DOXO-induced cardiac damage in mice. In our present study, we have observed that RRM2 expression is upregulated in TNBC patients from three independent data sets and that high RRM2 levels are associated with lower recurrence free survival (RFS) and overall survival (OS). Interestingly, high levels of RRM2 were only predictive of lower RFS and OS in patients with wild-type p53 but not mutant p53. Additionally, we have found that Didox downregulates mutant p53 protein levels in TNBC cell lines but does not alter total p53 in cells with functioning p53. Our data confirms that Didox induced downregulation of mutant p53 is not a transcriptional effect. Finally, we have identified that RRM2 protein levels increase in TNBC with progression of stage as measured in patient tissue microarray analysis. Our data presents a novel and promising approach for the treatment of TNBC that involves inhibition of RRM2, NF-kB activation, and mutant p53 that merits further clinical investigation in human models. Citation Format: Nahid Sultana, Elizabeth A. Wilson, Howard L. Elford, Jesika S. Faridi. RRM2 and mutant p53 as therapeutic targets in TNBC [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1240.