3'-Deoxy-3'-[(18)F]fluorothymidine (FLT) uptake in breast cancer cells as a measure of proliferation after doxorubicin and docetaxel treatment.

INTRODUCTION: The nucleoside analogue [(18)F]fluorothymidine (FLT) has been designed as a marker of cell proliferation that can be imaged in vivo by positron emission tomography. Clinical pilot studies have demonstrated decreasing FLT uptake following antiproliferative chemotherapy of breast cancer. However, the significance of posttreatment FLT uptake has not been evaluated at the cell level. The aim of this study was to investigate whether FLT uptake detects proliferation inhibition induced by docetaxel or doxorubicin treatment in an in vitro breast cancer model. METHODS: Breast cancer cells (MCF-7) were treated with docetaxel or doxorubicin for 24 h at drug doses inducing 25-99% inhibition of clonogenic survival (IC(25) to IC(99)). Cellular FLT uptake was estimated at 4 h and at 1, 3 and 5 days interval from chemotherapy. [(3)H]Thymidine incorporation and S-phase fraction were measured for comparison. Analysis of variance and the Bland-Altman difference plot were employed for statistical analysis. RESULTS: After treatment, FLT uptake was declined in dependence of the proliferation inhibition mediated by both chemotherapeutic agents (all P<.0001). The decrease of FLT was greater after doxorubicin treatment than after the corresponding docetaxel dose. With doxorubicin (IC(99)), FLT accumulation was reduced by 70% as early as 4 h after treatment. FLT uptake was closely correlated to [(3)H]thymidine incorporation and S-phase fraction (r=.84 to .93). CONCLUSIONS: Right after docetaxel or doxorubicin treatment, FLT uptake corresponds to the reduction of tumor cell proliferation induced. [(18)F]FLT appears promising for monitoring chemosensitivity in breast cancer.

[18F]FLT PET for diagnosis and staging of thoracic tumours.

The nucleoside analogue 3'-deoxy-3'-[18F]fluorothymidine (FLT) has been introduced for imaging of tumour cell proliferation by positron emission tomography (PET). This study evaluated the use of FLT in patients with thoracic tumours prior to treatment. Whole-body FLT PET was performed in 16 patients with 18 tumours [17 thoracic tumours (nine non-small cell lung cancers, five oesophageal carcinomas, two sarcomas, one Hodgkin's lymphoma) and one renal carcinoma] before treatment. Fluorine-18 fluorodeoxyglucose (FDG) PET was performed for comparison except in those patients with oesophageal carcinoma. For semi-quantitative analysis, the average and maximum standardised uptake values (avgSUV and maxSUV, respectively) (FLT, 114+/-20 min p.i.; FDG, 87+/-8 min p.i.; 50% isocontour region of interest) was calculated. All 17 thoracic tumours and 19/20 metastases revealed significant FLT accumulation, resulting in easy delineation from surrounding tissue. The additional small grade 1 renal carcinoma was not detected with either FLT or FDG. In most lung tumours (avgSUV 1.5-8.2) and metastases, FLT showed intense uptake. However, one of two spinal bone metastases was missed owing to the high physiological FLT uptake in the surrounding bone marrow. Oesophageal carcinoma primaries (avgSUV 2.7-10.0) and occasional metastases showed particularly favourable tumour/non-tumour contrast. Compared with FDG, tumour uptake of FLT was lower (avgSUV, P=0.0006; maxSUV, P=0.0001), with a significant linear correlation (avgSUV, r2=0.45; maxSUV, r2=0.49) between FLT and FDG. It is concluded that FLT PET accurately visualises thoracic tumour lesions. In the liver and the bone marrow, high physiological FLT uptake hampers detection of metastases. On the other hand, FLT may be favourable for imaging of brain metastases owing to the low physiological uptake.

Early changes in [18F]FLT uptake after chemotherapy: an experimental study.

This study evaluated the use of 3'-deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) for monitoring of the early effects of anticancer chemotherapy on tumour cell proliferation. Cells derived from human oesophageal squamous cell carcinoma (OSC-1) were grown for 2 days and incubated with cisplatin (CDDP), 5-fluorouracil (5-FU), methotrexate (MTX) or gemcitabine (GEM) for 4 h. Cultures were incubated with drug doses (CDDP: 0.67, 6.7, 67 micro M; 5-FU 15.4, 154, 1,540 micro M; MTX: 4.4, 44, 440 micro M; GEM: 0.0067, 0.067, 0.67 micro M) corresponding to approximately 10%-95% proliferation inhibition (MTX: 10%-75%). Treatment was stopped and cells were allowed to recover for 4, 24 or 72 h. [(18)F]FLT was added for 10-180 min. Control cultures were incubated with [(18)F]fluorodeoxyglucose (FDG). Cell counts, viability, clonogenic activity and cell cycle distribution estimated by flow cytometry were used to evaluate the cytotoxic effects of chemotherapy. Strikingly, FLT uptake per 10(5) viable cells was increased seven- to tenfold 24 h after treatment with 5-FU or MTX irrespective of dose. Thus, total FLT uptake per tissue culture exceeded that of controls despite a considerable decrease in overall cell counts due to cytostasis up to 72 h after treatment. 5-FU-treated cells showed accumulation in early S phase (overall S phase: 88% vs 42%). GEM treatment resulted in a more moderate increase in total FLT accumulation, to a maximum of fivefold at the dose close to the IC(50). In contrast, FLT accumulation was significantly reduced at cytostatic concentrations of CDDP and was still decreasing in a dose-related manner at 72 h despite considerable S phase arrest. With 5-FU or CDDP, the uptake of FDG did not differ significantly from control values 24 h after treatment. These findings demonstrate that tumour cell uptake of FLT - in contrast to that of FDG - reveals specific changes depending on the cytostatic drug used for treatment. The antimetabolites 5-FU and MTX massively increase FLT accumulation per cell independent of dose, i.e. cytotoxicity. Early after treatment, this increase is not predictive of proliferation inhibition but reflects activated salvage pathway of DNA synthesis. By contrast, CDDP results in an early decline in FLT but not in FDG uptake. This drug-specific modulation of FLT uptake has to be taken into account in positron emission tomography studies using FLT for treatment monitoring.