A Novel Platinum Compound Inhibits Constitutive Stat3 Signaling and Induces Cell Cycle Arrest and Apoptosis of Malignant Cells

James Turkson,Shumin Zhang,Linda B Mora,Audrey Burns,Said Sebti,Richard Jove

doi:10.1074/jbc.m502694200

James Turkson, Shumin Zhang + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m502694200

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Abstract

Previous studies have established constitutive activation of Stat3 protein as one of the molecular changes required for tumorigenesis. To develop novel therapeutics for tumors harboring constitutively active Stat3, compounds from the NCI 2000 diversity set were evaluated for inhibition of Stat3 DNA-binding activity in vitro. Of these, a novel platinum (IV) compound, IS3 295, interacted with Stat3 and inhibited its binding to specific DNA-response elements. Further analysis suggested noncompetitive-type kinetics for the inhibition of Stat3 binding to DNA. In human and mouse tumor cell lines with constitutively active Stat3, IS3 295 selectively attenuated Stat3 signaling, thereby inducing cell growth arrest at G0/G1 phase and apoptosis. Moreover, in transformed cells, IS3 295 repressed expression of cyclin D1 and bcl-xL, two of the known Stat3-regulated genes that are overexpressed in malignant cells, suggesting that IS3 295 mediates anti-tumor cell activity in part by blocking Stat3-mediated sub-version of cell growth and apoptotic signals. Together, our findings provide evidence for the inhibition of Stat3 activity and biological functions by IS3 295 through interaction with Stat3 protein. This study represents a significant advance in small molecule-based approaches to target Stat3 and suggests potential new applications for platinum (IV) complexes as modulators of the Stat3 pathway for cancer therapy.

Highlights

In contrast to the tightly regulated normal signal transducer and activator of transcription (STAT) signaling, constitutive activation of STAT proteins is frequently observed in human tumors [11, 12] and has been linked to tumor progression
electrophoretic mobility shift assay (EMSA) analysis showed that the simultaneous addition of IS3 295 and the high affinity sis-inducible element (hSIE) oligonucleotide probe to nuclear extracts containing activated Stat3 protein resulted in inhibition of Stat3 DNA-binding activity, as observed in Fig. 1A, suggesting that Stat3 has a higher preference for IS3 295 over hSIE
We reported on novel platinum (IV) complexes that inhibit the Stat3 transcription factor and induce anti-tumor cell activity [38]

Summary

Introduction

In contrast to the tightly regulated normal STAT signaling, constitutive activation of STAT proteins is frequently observed in human tumors [11, 12] and has been linked to tumor progression. Analysis by EMSA showed that preincubation with IS3 295 of cell lysates containing E2F1 prior to incubation with a 32P-labeled dihydrofolate reductase promoter sequence as probe had no significant effect on the DNA-binding activity (Fig. 1B, panel i).

Results

Conclusion