Targeting Poly (ADP-Ribose) Polymerase Partially Contributes to Bufalin-Induced Cell Death in Multiple Myeloma Cells

Wei Liu,Wei Wei,He Huang,Yang Cao,Yu-Bao Chen,Ying-Li Wu,Hua Yan,Shao-Yong Lu,Yan Wang,Ferenc Gallyas

doi:10.1371/journal.pone.0066130

Abstract

Despite recent pharmaceutical advancements in therapeutic drugs, multiple myeloma (MM) remains an incurable disease. Recently, ploy(ADP-ribose) polymerase 1 (PARP1) has been shown as a potentially promising target for MM therapy. A previous report suggested bufalin, a component of traditional Chinese medicine (“Chan Su”), might target PARP1. However, this hypothesis has not been verified. We here showed that bufalin could inhibit PARP1 activity in vitro and reduce DNA–damage-induced poly(ADP-ribosyl)ation in MM cells. Molecular docking analysis revealed that the active site of bufalin interaction is within the catalytic domain of PAPR1. Thus, PARP1 is a putative target of bufalin. Furthermore, we showed, for the first time that the proliferation of MM cell lines (NCI-H929, U266, RPMI8226 and MM.1S) and primary CD138+ MM cells could be inhibited by bufalin, mainly via apoptosis and G2-M phase cell cycle arrest. MM cell apoptosis was confirmed by apoptotic cell morphology, Annexin-V positive cells, and the caspase3 activation. We further evaluated the role of PARP1 in bufalin-induced apoptosis, discovering that PARP1 overexpression partially suppressed bufalin-induced cell death. Moreover, bufalin can act as chemosensitizer to enhance the cell growth-inhibitory effects of topotecan, camptothecin, etoposide and vorinostat in MM cells. Collectively, our data suggest that bufalin is a novel PARP1 inhibitor and a potentially promising therapeutic agent against MM alone or in combination with other drugs.

Highlights

Poly(ADP-ribose) polymerase 1 (PARP1), a highly conserved DNA binding protein, is key in maintaining the genomic stability, repairing the DNA damage, and regulating transcriptional processes [1,2] by binding to cleaved DNA strands and catalyzing the NAD+-dependent addition of poly(ADP-ribose) (PAR) to target proteins
We demonstrate that bufalin can directly bind to and inhibit PARP1 activity, and that PARP1 inhibition contributes partially to bufalin-induced apoptosis in MM cells
Because PARP1 represents an attractive target for MM therapy and Ma et al predicted that PARP1 was a potential target of bufalin via the molecular docking method [25], we investigated whether bufalin can target PARP1 and exert its anti-myeloma activity

Summary

Introduction

Poly(ADP-ribose) polymerase 1 (PARP1), a highly conserved DNA binding protein, is key in maintaining the genomic stability, repairing the DNA damage, and regulating transcriptional processes [1,2] by binding to cleaved DNA strands and catalyzing the NAD+-dependent addition of poly(ADP-ribose) (PAR) to target proteins. PARP1 inhibitor-mediated synthetic lethality was suggested to be important in breast and ovarian tumors with BRCA1 or BRCA2 gene mutations [4]. Arising from this research, PARP1-targeting therapy is gaining acceptance as an important strategy to treat tumor cells with BRCA1 or BRCA2 deficiencies. Several PARP1 inhibitors are presently in clinical trials, and PARP1 inhibitors are being recognized as useful chemosensitizers in patients with BRCA–deficiency tumors, and for patients in which tumors have general homologous recombination defects [5]. Neri et al recently reported that elevated PARP1 expression was correlated with poor survival in MM and bortezomib-induced ‘‘BRCAness’’ (tumor cells with the homologous recombination deficiency) showed synergistic anti-tumor effects when paired with PARP1 inhibitors for killing MM cells [7]. PARP1 is a potentially promising target for MM therapy

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Results

Conclusion