Targeting Ribonucleotide Reductase M2 and NF-κB Activation with Didox to Circumvent Tamoxifen Resistance in Breast Cancer

Abstract

Tamoxifen is widely used as an adjuvant therapy for patients with estrogen receptor (ERa)-positive tumors. However, the clinical benefit is often limited because of the emergence of drug resistance. In this study, overexpression of ribonucleotide reductase M2 (RRM2) in MCF-7 breast cancer cells resulted in a reduction in the effectiveness of tamoxifen, through downregulation of ERa66 and upregulation of the 36-kDa variant of ER (ERa36). We identified that NF-kB, HIF1a, and MAPK/JNK are the major pathways that are affected by RRM2 overexpression and result in increased NF-kB activity and increased protein levels of EGFR, HER2, IKKs, Bcl-2, RelB, and p50. RRM2-overexpressing cells also exhibited higher migratory and invasive properties. Through time-lapse microscopy and protein profiling studies of tamoxifen-treated MCF-7 and T-47D cells, we have identified that RRM2, along with other key proteins, is altered during the emergence of acquired tamoxifen resistance. Inhibition of RRM2 using siRRM2 or the ribonucleotide reductase (RR) inhibitor didox not only eradicated and effectively prevented the emergence of tamoxifen-resistant populations but also led to the reversal of many of the proteins altered during the process of acquired tamoxifen resistance. Because didox also appears to be a potent inhibitor of NF-kB activation, combining didox with tamoxifen treatment cooperatively reverses ER-a alterations and inhibits NF-kB activation. Finally, inhibition of RRM2 by didox reversed tamoxifenresistant in vivo tumor growth and decreased in vitro migratory and invasive properties, revealing a beneficial effect of combination therapy that includes RRM2 inhibition to delay or abrogate tamoxifen resistance.

Didox (3,4-dihydroxybenzohydroxamic acid) suppresses IL-33-induced cytokine production in primary mouse mast cells

“…Didox also suppressed NFκB and AP-1 transcriptional activities. This finding supports previous studies in which Didox inhibited LPS-induced p65 expression in macrophages and reduced RelB, p65, and p50 phosphorylation and NF B transcriptional activity in breast cancer cells [24, 31]. Since NFκB and AP-1 regulate cytokine expression, and NFκB is critical for IL-33 effects on mast cells [39], our results suggest that NFκB and AP-1 suppression is functionally important in this model.…”

“…Originally developed to treat cancer, Didox has been studied as a potential therapeutic for cytomegalovirus, HIV infection, sickle cell anemia, acute myeloid leukemia, and breast cancer [22, 27, 31–34]. Phase I and II clinical trials have shown Didox administration to have low toxicity and minimal side effects in patients [19–21].…”

ROCK2/rasHa co-operation induces malignant conversion via p53 loss, elevated NF-κB and tenascin C-associated rigidity, but p21 inhibits ROCK2/NF-κB-mediated progression

“…This latter result not only shows the requirement for ROCK er -mediated NF-κβ expression to facilitate progression, but also demonstrated that p21 responses eliminated NF-κβ expression independent of ROCK2 signalling. 44,47 Furthermore, down-regulation of NF-κβ paralleled increasing basal layer p53 expression 26 which restored the p21/p53-mediated resistance to malignant conversion. 20,23 Indeed, this direct p21-mediated antagonism to NF-κβ signalling was recently demonstrated in liver carcinogenesis where p21 knockout was shown to be pivotal to progression following loss of NEMO, a major NF-kβ pathway regulator.…”

“…25,43 Constitutive NF-κβ overexpression is relatively common, particularly in breast carcinogenesis, making NF-κβ inhibitors another therapeutic avenue. 44 4HT-treated K14.ROCK er /HK1.ras 1205 papillomas and K14.ROCK er hyperplasia exhibited elevated basallayer NF-κβ expression, absent in HK1.ras or control histotypes; suggesting early, ROCK erspecific roles for NF-κβ deregulation. This 4HT-ROCK er -mediated NF-κβ expression is consistent with activation of NF-κβ by Rho-induced, nuclear translocation of p65/RelA; independent of Ras GTPases.…”

Tamoxifen inhibits cell proliferation by impaired glucose metabolism in gallbladder cancer

“…Therefore, identification of new roles (indication) of old drugs (clinical drugs) is thought to be of great importance for rapid drug development and would provide promising potential for clinical use. 12,13 It is generally believed that TAM plays a major role in the competitive binding and inhibition of ER, 14,15 while some other studies claimed different mechanism, such as inhibiting protein kinase C (PKC). An estimated 2-3 times higher incidence was found in females than males.…”