TiIV Uptake and Release by Human Serum Transferrin and Recognition of TiIV-Transferrin by Cancer Cells: Understanding the Mechanism of Action of the Anticancer Drug Titanocene Di
详细信息 查看全文
- 作者：Maolin Guo ; Hongzhe Sun ; Harry J. McArdle ; Lorraine Gambling ; and Peter J. Sadler
- 刊名：Biochemistry
- 出版年：2000
- 出版时间：August 22, 2000
- 年：2000
- 卷：39
- 期：33
- 页码：10023 - 10033
- 全文大小：150K
- 年卷期：v.39,no.33(August 22, 2000)
- ISSN：1520-4995
文摘
The organometallic anticancer agent titanocene dichloride, Cp2TiCl2, is now in phase II clinicaltrials as an anticancer drug, but its mechanism of action is poorly understood. We show here that theinteractions of Cp2TiCl2 with human serum transferrin (hTF) and that of Ti2-hTF with adenosine triphosphate(ATP) have characteristics that could allow transferrin to act as a mediator for titanium delivery to tumorcells. Such reactions may therefore be important to the anticancer activity of this new class of drugs.Cp2TiCl2 reacts rapidly with human apo-transferrin under physiological conditions (100 mM NaCl, 25mM bicarbonate, and 4 mM phosphate, pH 7.4) with carbonate as a synergistic anion. The Cp ligands arereleased from the drug. Two-dimensional [1H, 13C] NMR studies of 
-[13C]Met-hTF show that TiIV loadsthe C-lobe first followed by the N-lobe and binds in the specific FeIII sites. The protein conformationalchanges induced by TiIV appear to be similar to those induced by FeIII. Carbonate can act as a synergisticanion in Ti2-hTF but does not appear to be essential. A specific TiIV-hTF adduct is formed even in theabsence of bicarbonate. When the pH of Ti2-hTF solutions is lowered, no TiIV is released at the endosomalpH of ca. 5.0-5.5, but one TiIV dissociates between pH 4.5-2.0. In contrast, in the presence of 1 mMATP, all TiIV is readily released from both lobes when the pH is lowered from 7.0 to 4.5. Moreover, FeIIIdisplaces TiIV rapidly from the C-lobe of Ti2-hTF (<5 min) but only slowly (days) from the N-lobe.Thus, the species FeCTiN-hTF might also provide a route for TiIV entry into tumor cells via the transferrinreceptor. Ti2-hTF effectively blocked cell uptake of radiolabeled 59Fe-hTF into BeWo cells, a humanplacental choriocarcinoma cell line in culture. These results imply that titanium transferrin might berecognized by the transferrin receptor and be taken up into cancer cells.
-[13C]Met-hTF show that TiIV loadsthe C-lobe first followed by the N-lobe and binds in the specific FeIII sites. The protein conformationalchanges induced by TiIV appear to be similar to those induced by FeIII. Carbonate can act as a synergisticanion in Ti2-hTF but does not appear to be essential. A specific TiIV-hTF adduct is formed even in theabsence of bicarbonate. When the pH of Ti2-hTF solutions is lowered, no TiIV is released at the endosomalpH of ca. 5.0-5.5, but one TiIV dissociates between pH 4.5-2.0. In contrast, in the presence of 1 mMATP, all TiIV is readily released from both lobes when the pH is lowered from 7.0 to 4.5. Moreover, FeIIIdisplaces TiIV rapidly from the C-lobe of Ti2-hTF (<5 min) but only slowly (days) from the N-lobe.Thus, the species FeCTiN-hTF might also provide a route for TiIV entry into tumor cells via the transferrinreceptor. Ti2-hTF effectively blocked cell uptake of radiolabeled 59Fe-hTF into BeWo cells, a humanplacental choriocarcinoma cell line in culture. These results imply that titanium transferrin might berecognized by the transferrin receptor and be taken up into cancer cells.