¹⁸F-FET and ¹⁸F-FCH uptake in human glioblastoma T98G cell lines

Abstract

BackgroundDespite complex treatment of surgery, radiotherapy and chemotherapy, high grade gliomas often recur. Differentiation between post-treatment changes and recurrence is difficult. 18F-methyl-choline (18F-FCH) is frequently used in staging and detection of recurrent prostate cancer disease as well as some brain tumours; however accumulation in inflammatory tissue limits its specificity. The 18F-ethyl-tyrosine (18F-FET) shows a specific uptake in malignant cells, resulting from increased expression of amino acid transporters or diffusing through the disrupted blood-brain barrier. 18F-FET exhibits lower uptake in machrophages and other inflammatory cells. Aim of this study was to evaluate 18F-FCH and 18F-FET uptake by human glioblastoma T98G cells.Material and methodsHuman glioblastoma T98G or human dermal fibroblasts cells, seeded at a density to obtain 2 × 105 cells per flask when radioactive tracers were administered, grew adherent to the plastic surface at 37°C in 5% CO2 in complete medium. Equimolar amounts of radiopharmaceuticals were added to cells for different incubation times (20 to 120 minutes) for 18F-FCH and 18F-FET respectively. The cellular radiotracer uptake was determined with a gamma counter. All experiments were carried out in duplicate and repeated three times. The uptake measurements are expressed as the percentage of the administered dose of tracer per 2 × 105 cells. Data (expressed as mean values of % uptake of radiopharmaceuticals) were compared using parametric or non-parametric tests as appropriate. Differences were regarded as statistically significant when p<0.05.ResultsA significant uptake of 18F-FCH was seen in T98G cells at 60, 90 and 120 minutes. The percentage uptake of 18F-FET in comparison to 18F-FCH was lower by a factor of more than 3, with different kinetic curves.18F-FET showed a more rapid initial uptake up to 40 minutes and 18F-FCH showed a progressive rise reaching a maximum after 90 minutes.Conclusions18F-FCH and 18F-FET are candidates for neuro-oncological PET imaging. 18F-FET could be the most useful oncological PET marker in the presence of reparative changes after therapy, where the higher affinity of 18F-FCH to inflammatory cells makes it more difficult to discriminate between tumour persistence and non-neoplastic changes. Additional studies on the influence of inflammatory tissue and radionecrotic cellular components on radiopharmaceutical uptake are necessary.

Effects of Photons Irradiation on 18F-FET and 18F-DOPA Uptake by T98G Glioblastoma Cells

“…After irradiation, as with other radiopharmaceuticals we previously reported (Pasi et al, 2017), the net uptake normalized to 2 × 10 5 cells appears to be increased, but most noticeable is the striking change of the TAC pattern. We observed that the percentage of damaged cells 35 h after irradiation as shown by PI and annexin V fluorescent staining increases in an exponential pattern (4% at 2 Gy, 9% at 10 Gy and 21% at 20% vs. 3% of control), whereas the 18 F-DOPA uptake at peak value increases in a linear one (Figure 4).…”

“…The uptake measurements are expressed as the percentage of the administered dose of tracer per 2 × 10 5 cells after correction for negative control uptake (flasks containing no cells with complete medium and incubated with radiopharmaceutical). Damaged cells were evaluated with propidium iodide (PI) and annexin V fluorescent staining as previously described (Pasi et al, 2017).…”

“…18 F-choline ( 18 F-FCH), a fluorinated phosphatidylcholine precursor, is approved for diagnosis of prostate and hepatocellular carcinomas, and its use is currently extending to other cancers, including GBM. Our previous research demonstrated that 18 F-FCH is able to trace tumor behavior in terms of higher uptake for increased doses of radiation treatment (Pasi et al, 2017).…”

Uptake of 18F-FET and 18F-FCH in Human Glioblastoma T98G Cell Line after Irradiation with Photons or Carbon Ions

“…The FCH uptake after photons irradiation ( Figure 4 ) tends to increase as dose increases, and the uptake pattern is more linear with time, still increasing at the end of observation (2 hours) without the transient washout at 60 minutes we previously described [ 15 , 17 ] in nonirradiated cells. Such uptake pattern is about the same if we consider the 2 Gy curve of both photons and carbon ions (Figures 5 and 6 ); however, the uptake at the end of observation is about 1% higher with carbon ions.…”

“…Subsequently, we tested the FET affinity for neoplastic tissue, confirming its potential as a viable oncological PET marker [ 17 ].…”