Abstract 209: Zinc is essential for the efficacy of p53 reactivating drugs

Abstract

Abstract According to the International Zinc Nutrition Consultative Group, 20% of the world's population lack sufficient Zinc in their diet. Zinc is required by >200 different proteins including the most extensively studied Zinc-finger protein p53 that is considered guardian of genome. Its crucial role in p53 core domain folding has been proven, as disruption of this interaction greatly reduces or abrogates p53 DNA binding and transactivation of target genes. Therefore, alterations in Zinc homeostasis may impair p53 activity and also reduce the efficacy of wt-p53 re-activating drugs. Recently, we have shown that Zinc is necessary for proper wt-p53 re-activation and cancer cell apoptosis by small molecule inhibitors of HDM2 such as MI-219 (Oncogene 2010). As a logical extension to our these results, in this clinically translatable study we show that Zinc is crucial for the activity of mutant p53 reactivated by PRIMA and provide evidence for using combination therapies with PRIMA that include supplemental Zinc for the treatment of mut-p53 tumors. ZnCl2 (64 µM) enhanced PRIMA (0-100 µM) anti-tumor activity (induced growth inhibition and apoptosis and suppressed colony formation) in multiple pancreatic, colon and breast cancer cell lines. Chelation of Zinc by chelex 100 resin not only blocked the activity of PRIMA, but also suppressed reactivation of the mut-p53 and its downstream effector molecules 14-33σ, Bax and p21 as detected by western blot analysis. N,N,N'N′-tetrakis(−)[2-pyridylmethyl]-ethylenediamine (TPEN), a specific Zinc chelator, but not 1,2-bis-(o-aminophenoxy)-ethane-N,N,N′,N′-tetraacetic acid (Bapta-AM), a calcium chelator or desferroxamine, a iron chelator blocked PRIMA-induced apoptosis. Zinc chelation by TPEN suppressed p53 nuclear localization that is important for its transcriptional activity. Zinc did not affect PRIMA activity in p53 null cells, suggesting that this was indeed a p53 dependent phenomenon. Addition of Zinc suppressed the known p53 feedback MDM2 activation, which could be restored by TPEN. Before wt- or mut-p53 re-activating drugs such as MI-219 and PRIMA make their way into the clinic for cancer patients who usually have mild to moderate Zinc deficiency, we believe that the results of our findings will help in the design of novel combination strategies with Zinc for better survival outcome. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 209. doi:10.1158/1538-7445.AM2011-209