CARP-1 Functional Mimetics: A Novel Class of Small Molecule Inhibitors of Medulloblastoma Cell Growth

Abdelkader E Ashour,Lisa A Polin,Adel R Abd-Allah,Shazia Jamal,Arun K Rishi,Ahmed M Alafeefy,Khairy M A Zoheir,Adi L Tarca,Edi Levi,Vino T Cheryan,Magesh Muthu,Rajvir Dahiya

doi:10.1371/journal.pone.0066733

Abstract

Medulloblastomas (MBs) constitute an aggressive class of intracranial pediatric tumors. Current multimodality treatments for MBs include surgery, ionizing radiation, and chemotherapy. Toxic side effects of therapies coupled with high incidence of recurrence and the metastatic spread warrant development of more effective, less toxic therapies for this disease. CARP-1/CCAR1 is a peri-nuclear phospho-protein that is a co-activator of the cell cycle regulatory anaphase promoting complex/cyclosome (APC/C) E3 ligase. CARP-1 functional mimetics (CFMs) are a novel class of small molecule compounds that interfere with CARP-1 binding with APC/C subunit APC-2, and suppress growth of a variety of cancer cells in part by promoting apoptosis. Here we investigated MB growth inhibitory potential of the CFMs and found that CFM-4 inhibits growth of MB cells in part by inducing CARP-1 expression, promoting PARP cleavage, activating pro-apoptotic stress-activated protein kinases (SAPK) p38 and JNK, and apoptosis. Gene-array-based analysis of the CFM-4-treated Daoy MB cells indicated down-regulation of a number of key cell growth and metastasis-promoting genes including cell motility regulating small GTP binding protein p21Rac1, and extracellular matrix metallopeptidase (MMP)-10. Moreover, CFM-4 treatment stimulated expression of a number of molecules such as neurotrophin (NTF)3, and NF-κB signaling inhibitors ABIN1 and 2 proteins. Overexpression of NTF3 resulted in reduced MB cell viability while knock-down of NTF3 interfered with CFM-4-dependent loss of viability. CFMs also attenuated biological properties of the MB cells by blocking their abilities to migrate, form colonies in suspension, and invade through the matrix-coated membranes. Together our data support anti-MB properties of CFM-4, and provide a proof-of-concept basis for further development of CFMs as potential anti-cancer agents for MBs.

Highlights

Medulloblastoma is a common childhood brain cancer
In light of our earlier studies indicating requirement of various caspase activities in transduction of CFM4-dependent growth inhibitory signaling in human breast cancer cells [16], and the fact that CARP-1 functional mimetics (CFMs) promoted poly(ADP-ribose) polymerase (PARP) cleavage in MB cells (Figure 2C), we determined whether caspases were activated following exposure of the MB cells to CFMs
Consistent with the ability of CFMs to inhibit growth of the breast and other cancer cells [16], we found that CFMs stimulate apoptosis signaling while suppressing molecules/pathways regulating MB cell cycle and cell growth

Summary

Introduction

Medulloblastoma is a common childhood brain cancer. It is a highly malignant tumor type with poor overall prognosis [1]. Differential expression of some antigens and receptors such as neurotrophin receptor p75NTR/TrkC is often noted in common variants of MB and serves as a marker of favorable outcome [5,6]. Recent gene expression profiling studies have defined four MB subgroups that include sonic hedgehog subgroup, the WNT subgroup, and subgroups 3 and 4 [7]. Whole genome sequencing of a number of primary medulloblastoma tumors representing all the four subgroups further revealed that mutations in different epigenetic modifiers may distinguish MB subgroups 3 and 4, presenting potential for targeting of subgroup-specific alterations for therapeutic benefit [8]

Methods

Results

Conclusion