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Protein expression profiling identifies differential modulation of homologous recombination by platinum-based antitumor agents



Oxaliplatin and satraplatin demonstrate activity against cisplatin-resistant tumor cells. Although the two platinum analogs are structurally-related, oxaliplatin is more active. Therefore, studies focusing on protein expression profiling were undertaken to identify the molecular mechanism for the difference in antitumor activity.


We included cisplatin as reference and DAP as a Pt(IV)-prodrug of oxaliplatin to offset Pt(IV) status of satraplatin, and utilized A2780, cisplatin-resistant 2780CP/Cl-16, U2OS, and HCT-116 tumor cells in the investigation. Protein expressions following drug exposures were examined by reverse-phase protein array and ingenuity pathway analysis. Cell cycle was assessed by flow cytometry, cytotoxicity by growth inhibition assay, and homologous recombination (HR) by a GFP reporter assay.


Clustering analysis paired oxaliplatin with DAP and, surprisingly, satraplatin with cisplatin. This correlated with differential upregulation of p53/p21 pathway, with S and G2/M arrests by cisplatin and satraplatin in contrast to G1 arrest by oxaliplatin and DAP. Moreover, Rad51 and BRCA1 were severely downregulated by oxaliplatin and DAP, but not cisplatin and satraplatin. As a result, HR was inhibited only by oxaliplatin and DAP and this also contributed to their greater drug activity over cisplatin and satraplatin.


Oxaliplatin and DAP robustly activate p53 and p21, which downregulate HR proteins to enhance drug activity. More significantly, since oxaliplatin induces a BRCAness state, it may have potential against BRCA-proficient cancers. Satraplatin, on the other hand, resembled cisplatin in its protein expression profile, which indicates that small changes in chemical structure can substantially alter signal transduction pathways to modulate drug activity.

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The authors would like to thank Dr. Haifeng Zhu at MD Anderson Cancer Center for his invaluable advice in hierarchical clustering analysis. Thanks also to Gerald Thai for his excellent technical assistance. The research support from the U.S. Public Health Service Grants CA211975 to ZHS and CA16672 to MD Anderson Cancer Center awarded by the National Cancer Institute, and in part from the Megan McBride Franz Endowed Research Fund, is gratefully acknowledged.

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GH, XX and ZHS: designed and/or conducted the experiments, and analyzed and interpreted the data; GH and ZHS: wrote the initial draft of the manuscript, and XX: contributed to revision for the final version.

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Correspondence to Zahid H. Siddik.

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He, G., Xie, X. & Siddik, Z.H. Protein expression profiling identifies differential modulation of homologous recombination by platinum-based antitumor agents. Cancer Chemother Pharmacol 85, 1129–1140 (2020).

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  • Platinum complexes
  • Protein expression
  • Cell cycle
  • BRCA1
  • Rad51
  • Homologous recombination