Canada R G, Paltoo D N
Laboratory of Biophysical Cytochemistry, Department of Physiology and Biophysics, Howard University College of Medicine, Washington, DC 20059, USA.
Biochim Biophys Acta. 1998 Nov 19;1448(1):85-98. doi: 10.1016/s0167-4889(98)00127-x.
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.
铽（Tb3+）已被证明可增加顺铂在耐顺铂的人乳腺癌和卵巢癌细胞中的细胞蓄积及细胞毒性。采用时间分辨Tb3+发光来描述顺铂与耐顺铂的C13细胞的结合。在C13细胞的质膜中鉴定出一个高亲和力的Tb3+结合位点（n = 105±2 fmol/细胞，Kd = 36.3±5.2 μM）。提示Tb3+的结合是通过与质膜中色氨酸残基的阳离子-π相互作用发生的，从而导致Tb3+的强度和寿命增强。Stern-Volmer猝灭分析表明，Tb3+结合位点不易被水环境接近。顺铂对Tb3+-C13强度的猝灭是通过静态猝灭过程发生的，涉及直接电子交换相互作用以及间接偶极-偶极共振能量转移机制。Tb3+-C13-顺铂复合物的形成并不干扰Tb3+的高亲和力结合；顺铂和Tb3+彼此在5至10埃范围内结合。提示一种特异性的铽/顺铂结合蛋白在顺铂的细胞蓄积和细胞毒性中起作用。因此，顺铂跨质膜的转运也必定涉及易化扩散过程。我们的结果表明，Tb3+与质膜的结合可能在逆转顺铂耐药性方面具有潜在用途。
