Binding of terbium and cisplatin to C13* human ovarian cancer cells using time-resolved terbium luminescence

Biochim Biophys Acta. 1998 Nov 19;1448(1):85-98. doi: 10.1016/s0167-4889(98)00127-x.

Abstract

Terbium (Tb3+) has been shown to increase the cellular accumulation and cytotoxicity of cisplatin in cisplatin-resistant human breast and ovarian cancer cells. Time-resolved Tb3+ luminescence was used to describe the binding of cisplatin to cisplatin-resistant C13* cells. A high-affinity Tb3+ binding site was identified in the plasma membrane of the C13* cells (n=105+/-2 fmol/cell and Kd=36. 3+/-5.2 microM). The binding of Tb3+ is suggested to occur through a cation-pi interaction with tryptophan residues in the plasma membrane, resulting in an enhancement of the intensity and lifetime of Tb3+. Stern-Volmer quenching analysis revealed that the Tb3+ binding site is not readily accessible to the aqueous environment. The quenching of the Tb3+-C13* intensity by cisplatin occurred by static quenching processes, involving both a direct electron-exchange interaction as well as an indirect dipole-dipole resonant energy transfer mechanism. Formation of the Tb3+-C13*-cisplatin complex does not interfere with the high-affinity binding of Tb3+; cisplatin and Tb3+ bind within 5 to 10 A of each other. A specific terbium/cisplatin binding protein is suggested to play a role in the cellular accumulation and cytotoxicity of cisplatin. Therefore, the transport of cisplatin across the plasma membrane must also involve a facilitated diffusion process. Our results indicate that the binding of Tb3+ to the plasma membrane may be potentially useful in the reversal of cisplatin resistance.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Antineoplastic Agents / metabolism*
  • Binding Sites
  • Biological Transport
  • Cisplatin / metabolism*
  • Drug Interactions
  • Drug Resistance
  • Female
  • Humans
  • Luminescent Measurements
  • Models, Theoretical
  • Ovarian Neoplasms / metabolism*
  • Spectrometry, Fluorescence
  • Terbium / chemistry
  • Terbium / metabolism*

Substances

  • Antineoplastic Agents
  • Terbium
  • Cisplatin