A chemical inhibitor of PPM1D that selectively kills cells overexpressing PPM1D

Abstract

The PPM1D gene is aberrantly amplified in a range of common cancers and encodes a protein phosphatase that is a potential therapeutic target. However, the issue of whether inhibition of PPM1D in human tumour cells that overexpress this protein compromises their viability has not yet been fully addressed. We show here, using an RNA interference (RNAi) approach, that inhibition of PPM1D can indeed reduce the viability of human tumour cells and that this effect is selective; tumour cell lines that overexpress PPM1D are sensitive to PPM1D inhibition whereas cell lines with normal levels are not. Loss of viability associated with PPM1D RNAi in human tumour cells occurs via the activation of the kinase P38. To identify chemical inhibitors of PPM1D, a high-throughput screening of a library of small molecules was performed. This strategy successfully identified a compound that selectively reduces viability of human tumour cell lines that overexpress PPM1D. As expected of a specific inhibitor, the toxicity to PPM1D overexpressing cell lines after inhibitor treatment is P38 dependent. These results further validate PPM1D as a therapeutic target and identify a proof-of-principle small molecule inhibitor.

An integrative genomic and transcriptomic analysis reveals molecular pathways and networks regulated by copy number aberrations in basal-like, HER2 and luminal cancers

“…Novel strategies for targeting PAK4 and its family members in cancer are under investigation [45]. Ingenuity Pathway Analysis of HER2 cancers substantiates previous findings for the use of PPM1D-targeted therapies in this subgroup [1,35] and revealed that PI3K and ERK/MAPK canonical pathways are significantly enriched for genes that are amplified and overexpressed in luminal tumours (e.g. PAK1, PPP2R5A and PRKAR1A).…”

Wip1 confers G2 checkpoint recovery competence by counteracting p53-dependent transcriptional repression

“…Chk1, Chk2, p38, and Mdm2, all direct regulators of p53 (Takekawa et al, 2000;Lu et al, 2004Lu et al, , 2005Lu et al, , 2007Fujimoto et al, 2006;Shreeram et al, 2006a;Oliva-Trastoy et al, 2007). Moreover, Wip1 inhibition or RNAi decreases the proliferation of p53-positive, but not p53-negative cancer cell lines (Parssinen et al, 2008;Rayter et al, 2008), and Wip1 is required for APC(Min)-induced colon tumour formation and intestinal stem cell maintenance through counteracting p53 (Demidov et al, 2007b). As expected, depletion of p53 by shRNA did not interfere with the ability of cells to arrest in G2 in response to doxorubicin (Bunz et al, 1998) ( Figure 3A).…”

Checkpoint control and cancer

“…However, as this compound affected the phosphorylation status of all mitogenactivated protein kinases, concerns remain about its specificity toward Wip1 and further modification may be necessary to generate a more selective inhibitor of Wip1 (Belova et al, 2005). Another cell-permeable, smallmolecule inhibitor of Wip1 (CCT007093, IC 50 ¼ 8.4 mM) has recently been reported to decrease the viability of the MCF7, KPL1 and MCF3B tumor cell lines (Rayter et al, 2008). Interestingly, this cytotoxic effect of Wip1 inhibition seems to be specific for tumors that overexpress Wip1, whereas cells with normal Wip1 levels tolerate the loss of Wip1 activity (Rayter et al, 2008).…”

“…Another potential pharmacological target in p53-positive tumors is Wip1, which acts in silencing of the G 2 checkpoint primarily through blocking the activity of p53 (Lindqvist et al, 2009a). Depletion of Wip1 by antisense oligonucleotides or by RNA interference decreased viability in cell lines derived from neuroblastoma, glioma, breast adenocarcinoma and ovarian clear cell carcinoma, indicating that a subset of cancer patients suffering from p53-positive tumors could benefit from blocking the activity of Wip1 (Saito-Ohara et al, 2003;Rayter et al, 2008;Tan et al, 2009;Wang et al, 2011). Indeed, PPM1D-knockout mice are viable and are protected from tumor development, indicating that loss of Wip1 activity is well-tolerated and may block tumor growth (Bulavin et al, 2004;Harrison et al, 2004).…”

“…Another cell-permeable, smallmolecule inhibitor of Wip1 (CCT007093, IC 50 ¼ 8.4 mM) has recently been reported to decrease the viability of the MCF7, KPL1 and MCF3B tumor cell lines (Rayter et al, 2008). Interestingly, this cytotoxic effect of Wip1 inhibition seems to be specific for tumors that overexpress Wip1, whereas cells with normal Wip1 levels tolerate the loss of Wip1 activity (Rayter et al, 2008). The cell death induced by CCT007093 was dependent on p38, which is a well-described substrate of Wip1, and mimicked the effect of Wip1 RNA interference, indicating that the observed phenotype indeed results from specific inhibition of Wip1.…”