WIP1 Phosphatase as a Potential Therapeutic Target in Neuroblastoma

Abstract

The wild-type p53-induced phosphatase 1 (WIP1) is a serine/threonine phosphatase that negatively regulates multiple proteins involved in DNA damage response including p53, CHK2, Histone H2AX, and ATM, and it has been shown to be overexpressed or amplified in human cancers including breast and ovarian cancers. We examined WIP1 mRNA levels across multiple tumor types and found the highest levels in breast cancer, leukemia, medulloblastoma and neuroblastoma. Neuroblastoma is an exclusively TP53 wild type tumor at diagnosis and inhibition of p53 is required for tumorigenesis. Neuroblastomas in particular have previously been shown to have 17q amplification, harboring the WIP1 (PPM1D) gene and associated with poor clinical outcome. We therefore sought to determine whether inhibiting WIP1 with a selective antagonist, GSK2830371, can attenuate neuroblastoma cell growth through reactivation of p53 mediated tumor suppression. Neuroblastoma cell lines with wild-type TP53 alleles were highly sensitive to GSK2830371 treatment, while cell lines with mutant TP53 were resistant to GSK2830371. The majority of tested neuroblastoma cell lines with copy number gains of the PPM1D locus were also TP53 wild-type and sensitive to GSK2830371A; in contrast cell lines with no copy gain of PPM1D were mixed in their sensitivity to WIP1 inhibition, with the primary determinant being TP53 mutational status. Since WIP1 is involved in the cellular response to DNA damage and drugs used in neuroblastoma treatment induce apoptosis through DNA damage, we sought to determine whether GSK2830371 could act synergistically with standard of care chemotherapeutics. Treatment of wild-type TP53 neuroblastoma cell lines with both GSK2830371 and either doxorubicin or carboplatin resulted in enhanced cell death, mediated through caspase 3/7 induction, as compared to either agent alone. Our data suggests that WIP1 inhibition represents a novel therapeutic approach to neuroblastoma that could be integrated with current chemotherapeutic approaches.

Wip1 inhibitor GSK2830371 inhibits neuroblastoma growth by inducing Chk2/p53-mediated apoptosis

“…Moreover, amplification of the PPM1D gene locus on 17q23 has been frequently reported in various cancers, including primary NB tumors21. Previous studies have shown that high expression of PPM1D predicts poor outcome in NB patients, which suggests PPM1D may play a critical role in the tumorigenesis of NB22 and therefore may have value as a therapeutic target in NB. Yet, the in vivo efficacy of Wip1 inhibitors is still poorly understood.…”

Role of wild-type p53-induced phosphatase 1 in cancer

“…In addition, a previous report demonstrated that Wip1 was significantly overexpressed in 56% of cancer tissues, and promoted tumor progression to a higher stage, poor prognosis and chemotherapy resistance (Table I) (32). Therefore, these data suggest that the inhibition of Wip1 expression levels may be a potential therapeutic target.…”

“…Therefore, these data suggest that the inhibition of Wip1 expression levels may be a potential therapeutic target. GSK2830371 is a Wip1 selective antagonist able to significantly inhibit 96.5% of Wip1 activity in neuroblastoma cell lines, which promotes p53 function and apoptotic responses (32). Furthermore, GSK2830371 had a synergistic effect on the antiproliferative properties of the chemotherapeutic agents adriamycin and carboplatin (32).…”

“…In pediatric types of cancer, overexpression of Wip1 contributes to a number of malignant characteristics, including tumor progression, aggressive phenotype and poor prognosis (32,34,37). In addition, a Wip1 inhibitor may be a promising novel candidate for targeted therapeutic strategies for these severe tumors.…”

Wild-type p53-induced phosphatase 1 is a prognostic marker and therapeutic target in bladder transitional cell carcinoma

“…Wip1 is encoded by protein phosphatase magnesium-dependent 1 Δ, which is located on the 17q22/24 human chromosomal region, and is a member of the protein phosphatase type 2C (PP2C) family. Previous studies have demonstrated that Wip1 is overexpressed in various types of cancer and that Wip1 is associated with cancer development, suggesting that this protein may be a tumor biomarker and therapeutic target (6)(7)(8)(9). However, the expression and role of Wip1 in bladder cancer have not yet been investigated.…”