Comparison of the kinetics of active efflux of ^99mTc‐MIBI in cells with P‐glycoprotein‐mediated and multidrug‐resistance protein‐associated multidrug‐resistance phenotypes

Abstract

The overexpression of two membrane glycoproteins, P-glycoprotein and multidrug-resistance protein (MRP 1 ) is a major cause of resistance to chemotherapeutic agents in the treatment of human cancers. Both proteins confer a similar multidrug-resistant (MDR) phenotype. Tc-MIBI, a myocardial imaging agent, which is also useful for the detection of a variety of tumours, has been shown to be a substrate for P-glycoprotein and MRP 1 . It thus may provide additional information about the P-glycoprotein and MRP 1 status of tumour cells.In order to obtain information on the substrate specificity of these proteins, we have studied the transport kinetics of Tc-MIBI in two cell lines, K562/ADR and GLC 4 /ADR, which overexpress P-glycoprotein and MRP 1, respectively. The mean active efflux coefficient ka, which is proportional to the ratio of maximal efflux rate V M to the apparent Michaelis-Menten constant K m , used to characterise the efficiency of the active efflux, was very similar being 1.9 Ϯ0.6ϫ10 Ϫ11 s Ϫ1 · cells · ml and 1.3Ϯ 0.5ϫ10 Ϫ11 s Ϫ1 · cells · ml for drug-resistant K562 and GLC4, respectively. These values are 50Ϫ100-times lower than for daunorubicin and other anthracycline derivatives, strongly suggesting that the efficiency of both transporters to pump Tc-MIBI is by far less than that to efflux anthracyclines. Our data show that (a) P-glycoprotein and MRP transporter efficiencies to wash out Tc-MIBI are similar, in spite of a different suspected mechanism of its transport and (b) that both transporters are less efficient to pump Tc-MIBI than to pump anthracyclines (the k a parameter is about 100-times lower for TC-MIBI than for anthracycline).Keywords : multidrug-resistance; P-glycoprotein; multidrug-resistance protein; technetium hexakis(methoxyisobutylisonitrile).Cancer cells lines treated in vitro with one of a group of (Hughes, 1994), which have ATP-binding sites (Cornwell et al., amphipathic cytotoxic drugs frequently assumes a multidrug-re-1987; McGrath et al., 1989). In the case of P-glycoprotein, there sistant (MDR) phenotype (Bradley and Ling, 1988), the cells is considerable experimental evidence that the protein causes becoming resistant to a range of structurally and functionally resistance by transporting neutral or positively charged drugs out unrelated drugs. The classical form of drug resistance is caused of the cell (Gottesman and Pastan, 1993). The mechanism by by enhanced expression of the mdr 1 gene, which encodes the P-which MRP 1 mediates reduced drug accumulation in resistant glycoprotein. P-glycoprotein is an ATP-dependent drug exporter cells is less well understood. However, it has been clearly establocated in the plasma membrane of various cell types (Gottes-lished that it has the properties of an organic anion transporter man and Pastan, 1993). Recently, a second ATP-dependent (GS-X pump) (Loe et al., 1996; Leier et al., 1994 ; Müller et transporter of anti-tumour drugs has been identified in mamma-al., 1994). Despite considerable overlap in substrate specificity lian cells, the...

Usefulness of 99mTc-Sestamibi Scintigraphy in Suggesting the Therapeutic Effect of Chemotherapy against Gastric Cancer

“…It has been suggested that MRP also affects the accumulation of 99m Tc-MIBI in some types of cancer (25)(26)(27), but our study could not demonstrate any correlation between MRP expression and ER or DR in 99m Tc-MIBI imaging in gastric cancer. Similar to our finding, previous studies reported that an increased expression of P-gp, but not of MRP, correlates with low accumulation of 99m Tc-MIBI in some types of malignancy, such as lung cancer (28) and hepatocellular carcinoma (29).…”

New insights into the P‐glycoprotein‐mediated effluxes of rhodamines

“…Valinomycin and FCCP were dissolved in ethanol. Synthesis of the radio labelled compound [hexakis(methoxyisobutylisonitrile) technetium (I)] ( 99m Tc-MIBI) was performed with a one-step kit formulation as described previously [9].…”

“…To be sure that in K + -buffer plasma and mitochondrial potentials were dissipated, we used a totally different method to check it. We measured the Tc-MIBI accumulation in sensitive cells as described in [9]. Due to its lipophilic cationic nature, Tc-MIBI may distribute across biological membranes in response to the transmembrane potential in a manner similar to cationic rhodamines.…”

“…P-gp can transport neutral and positively charged molecules but not negatively charged ones. Despite the advances of recent years, we still have an unclear view of the molecular mechanism by which P-gp transports such a wide diversity of compounds across the membrane [5][6][7][8][9].Recently, we have performed several studies using K562 intact cells to describe the kinetics of anthracycline transport in MDR cells in order to predict how modifications in the anthracycline molecule affect its transport characteristics [10][11][12][13]. In the present paper we have used the same cell line to characterize the transport of several rhodamines.…”

“…P-gp can transport neutral and positively charged molecules but not negatively charged ones. Despite the advances of recent years, we still have an unclear view of the molecular mechanism by which P-gp transports such a wide diversity of compounds across the membrane [5][6][7][8][9].…”