Tracers to monitor the response to chemotherapy: in vitro screening of four radiopharmaceuticals

Abstract

Objectives: It has been postulated that radiopharmaceuticals can be used to predict the therapeutic response to (chemo)therapy, which could lead to individualized treatment regimens. In this study, 18F-deoxyglucose, 99mTc-tetrofosmin, 125I-deoxyuridineribose, and 125I-methyltyrosine were tested for this purpose.

Methods: The uterine sarcoma cell line MES-SA (MDR-) and its multidrug resistant variant, MES-SA/Dx5 (MDR+), were used. The MDR+ cells express high levels of P-glycoprotein, which makes them relatively resistant to various chemotherapeutic agents. Cells were cultured in the presence of escalating concentrations of doxorubicin, and the cellular uptake of the radiopharmaceuticals was determined.

Results: Decreasing 18F-deoxyglucose uptake at escalating doxorubicin concentrations reflected the chemosensitivity of the cells: 18F-deoxyglucose uptake in the MDR- cells was reduced to 40% of the baseline level in the presence of 1 microM of doxorubicin, compared to 74% in the MDR+ cells. The 125I-deoxyuridineribose uptake in MDR- cells was reduced to 2% of the baseline level when cultured at a concentration of 1 microM of doxorubicin, while this was 79% in the MDR+ cells. The same trend was observed with 125I-methyltyrosine. The enhanced doxorubicin chemosensitivity of MDR+ cells in the presence of verapamil, a modulator of P-glycoprotein, was reflected by the reduced uptake of 18F-deoxyglucose, 125I-deoxyuridineribose, and 125I-methyltyrosine. Furthermore, baseline 99mTc-tetrofosmin uptake in MDR+ cells was more than six-fold lower than in MDR- cells.

Conclusion: In the presence of doxorubicin, the uptake of 18F-deoxyglucose, 125I-deoxyuridineribose and, to a lesser extent, 125I-methyltyrosine is more pronouncedly reduced in MDR- cells than in MDR+ cells. The reversal of doxorubicin-resistance of MDR+ cells by verapamil was also reflected by the uptake of 18F-deoxyglucose, 125I-deoxyuridineribose, and 125I-methyltyrosine. 99mTc-tetrofosmin uptake reflected P-glycoprotein expression without exposure to doxorubicin.