A cell-active inhibitor of mitogen-activated protein kinase phosphatases restores paclitaxel-induced apoptosis in dexamethasone-protected cancer cells

Abstract

Mitogen-activated protein kinase phosphatase (MKP)-1 is a dual-specificity phosphatase that negatively regulates the activity of mitogen-activated kinases and that is overexpressed in human tumors. Contemporary studies suggest that induction of MKP-1 during chemotherapy may limit the efficacy of clinically used antineoplastic agents. Thus, MKP-1 is a rational target to enhance anticancer drug activity, but suitable small-molecule inhibitors of MKP-1 are currently unavailable. Here, we have used a high-content, multiparameter fluorescence-based chemical complementation assay for MKP activity in intact mammalian cells to evaluate the cellular MKP-1 and MKP-3 inhibitory activities of four previously described, quinonebased, dual-specificity phosphatase inhibitors, that is, NSC 672121, NSC 95397, DA-3003-1 (NSC 663284), and JUN-1111. All compounds induced formation of reactive oxygen species in mammalian cells, but only one (NSC 95397) inhibited cellular MKP-1 and MKP-3 with an IC 50 of 13 Mmol/L. Chemical induction of MKP-1 by dexamethasone protected cells from paclitaxel-induced apoptosis but had no effect on NSC 95397. NSC 95397 phenocopied the effects of MKP-1 small inhibitory RNA by reversing the cytoprotective effects of dexamethasone in paclitaxeltreated cells. Isobologram analysis revealed synergism between paclitaxel and NSC 95397 only in the presence of dexamethasone. The data show the power of a welldefined cellular assay for identifying cell-active inhibitors of MKPs and support the hypothesis that small-molecule inhibitors of MKP-1 may be useful as antineoplastic agents under conditions of high MKP-1 expression. [Mol Cancer Ther 2008;7(2):330 -40]

Follicle-Stimulating Hormone (FSH)-dependent Regulation of Extracellular Regulated Kinase (ERK) Phosphorylation by the Mitogen-activated Protein (MAP) Kinase Phosphatase MKP3

“…GCs were pretreated without or with NSC 663284, a selective CDC25A, CDC25B, and CDC25C inhibitor that does inhibit MKP1(DUSP1) or MKP3(DUSP6) (43,44 A, GCs were pretreated without (DMSO) or with 5 M NSC 663284, a selective CDC25A, CDC25B, and CDC25C inhibitor (which does not inhibit MKP1(DUSP1) or MKP3(DUSP6)) for 30 min, followed by treatment without (veh) and with FSH for 30 min. Samples were collected as described in Fig.…”

TLR4 signaling in effector CD4+ T cells regulates TCR activation and experimental colitis in mice

“…To validate that the increased inflammation observed in the absence of TLR4 signaling in the Il10 -/-mice is related to the lack of induction of MKPs, we inhibited MKPs in vivo using a cell-permeable, quinone-based inhibitor of dual-specificity phosphatases, NSC 95397, which inhibits both MKP-1 and MKP-3 (25). Injection of a single dose of this compound into Il10 -/-mice resulted 3 days later in significant body weight loss and diarrhea as compared with vehicle-treated mice (Supplemental Figure 12, A and B).…”

Mitogen-Activated Protein Kinase Phosphatase-1 in Human Breast Cancer Independently Predicts Prognosis and Is Repressed by Doxorubicin

“…This mechanism is viewed as a feedback control to attenuate MAPK signaling (4,5,11,12). MKP-1 seems to play an important role in tumorigenesis (4,13,14) and counterbalances the cytotoxicity of various anticancer drugs (4,(14)(15)(16)(17)(18)(19)(20)(21). In this regard, anthracyclines, alkylating agents, taxanes, cisplatin, or proteasome inhibitors induce apoptosis in part by activation of the JNK pathway (15,16).…”

“…In this regard, anthracyclines, alkylating agents, taxanes, cisplatin, or proteasome inhibitors induce apoptosis in part by activation of the JNK pathway (15,16). Notably, high levels of MKP-1 may dephosphorylate JNK and therefore limit the cytotoxicity of these agents (14,16,17,(19)(20)(21)(22)(23)(24). Conversely, down-modulation of MKP-1 might be proapoptotic by facilitating a persistent JNK phosphorylation (4,17).…”

“…In breast cancer cells, MKP-1 was a significant mediator of chemoresistance to anthracyclines, alkylating agents, and taxanes (15,18,19). Proteasome inhibitors induce MKP-1 and this induction played an antiapoptotic role (16,(20)(21)(22)(23).…”