In vitro analysis of transport and metabolism of 4'-thiothymidine in human tumor cells

Predictive value of local control by 4'-[methyl-11C]-thiotymidine PET volume parameters in p16-negative oropharyngeal, hypopharyngeal, and supraglottic squamous cell carcinoma

PURPOSE

We investigated the potential of baseline 4'-[methyl- 11 C]-thiothymidine ([ 11 C]4DST) PET for predicting loco-regional control of head and neck squamous cell carcinoma (HNSCC).

METHODS

A retrospective analysis was performed using volumetric parameters, such as SUVmax, proliferative tumor volume (PTV), and total lesion proliferation (TLP), of pretreatment [ 11 C]4DST PET for 91 patients with HNSCC with primary lesions in the oral cavity, hypopharynx, supraglottis, and oropharynx, which included p16-negative patients. PTV and TLP were calculated for primary lesions and metastatic lymph nodes combined. We examined the association among the parameters and relapse-free survival and whether case selection focused on biological characteristics improved the accuracy of prognosis prediction.

RESULTS

The area under the curves (AUCs) using PTV and TLP were high for the oropharyngeal/hypopharyngeal/supraglottis groups (0.91 and 0.87, respectively), whereas that of SUVmax was 0.66 ( P  < 0.01). On the other hand, the oral group had lower AUCs for PTV and TLP (0.72 and 0.77, respectively). When all cases were examined, the AUCs using PTV and TLP were 0.84 and 0.83, respectively.

CONCLUSION

Baseline [ 11 C]4DST PET/CT volume-based parameters can provide important prognostic information with p16-negative oropharyngeal, hypopharyngeal, and supraglottic cancer patients.

Correlation of 4'-[methyl-11C]-thiothymidine PET with Ki-67 immunohistochemistry separately in patients with newly diagnosed and recurrent gliomas

OBJECTIVE

4'-[methyl-11C]-thiothymidine (4DST) uptake on PET was correlated with proliferative activity separately in patients with newly diagnosed and recurrent gliomas.

METHODS

A total of 29 patients, 18 with newly diagnosed gliomas and 11 with recurrent gliomas who underwent 4DST PET/computed tomography (CT) were available for a retrospective analysis of prospectively collected data. The maximum standardized uptake value (SUVmax) of tumor (T) and the mean SUV of normal contralateral hemisphere (N) were calculated, and the tumor-to-normal (T/N) ratio was determined. Proliferative tumor volume (PTV) and total lesion proliferation (TLP) were also calculated. Proliferative activity as indicated by the Ki-67 index was estimated in tissue specimens. Immunohistochemical findings were correlated with 4DST PET parameters.

RESULTS

All gliomas but three newly diagnosed gliomas had 4DST uptake on PET. No significant differences in SUVmax, T/N ratio, PTV, or TLP were observed between the newly diagnosed and recurrent gliomas. In the former, correlations between SUVmax (r = 0.57, P = 0.02), T/N ratio (r = 0.51, P = 0.03), PTV (r = 0.74, P < 0.001), and TLP (r = 0.76, P < 0.001) and the Ki-67 index were found. In the latter, the results did not seem to suggest any correlations between any of the PET parameters and Ki-67 index.

CONCLUSION

Although preliminary, these results suggest that 4DST PET may be useful for the noninvasive evaluation of proliferation in patients with newly diagnosed gliomas. These data in a small recurrent patient population do not support a clear-cut correlation between 4DST uptake and proliferation.

Correlation of 4'-[methyl-11C]-thiothymidine PET with Gd-enhanced and FLAIR MRI in patients with newly diagnosed glioma

PURPOSE

To elucidate the biological association between tumor proliferation, tumor infiltration and neovascularization, we analyzed the association between volumetric information of 4'-[methyl-¹¹C]thiothymidine (4DST) positron emission tomography (PET) and fluid-attenuated inversion recovery (FLAIR) and T1-weighted gadopentetate dimeglumine (Gd)-enhanced magnetic resonance imaging (MRI), in patients with newly diagnosed glioma.

METHODS

A total of 23 patients with newly diagnosed glioma who underwent both 4DST PET/CT and Gd-enhanced MRI before therapy were available for a retrospective analysis of prospectively collected data. The maximum standardized uptake value (SUVmax) for tumor (T) and the mean SUV for normal contralateral hemisphere (N) were calculated, and the tumor-to-normal (T/N) ratio was determined. Proliferative tumor volume (PTV) from 4DST PET and the volume of Gd enhancement (GdV) and hyperintense region on FLAIR (FLAIRV) from MRI were calculated.

RESULTS

All gliomas but 3 diffuse astrocytomas and one anaplastic astrocytoma had 4DST uptake and Gd enhancement on MRI. There was no significant difference between PTV and GdV although the exact edges of the tumor differed in each modality. The FLAIRV was significantly larger than PTV (P < 0.001). Significant correlations between PTV and GdV (ρ = 0.941, P < 0.001) and FLAIRV (ρ = 0.682, P < 0.001) were found.

CONCLUSION

These preliminary results indicate that tumor proliferation assessed by 4DST PET is closely associated with tumor-induced neovascularization determined by Gd-enhanced MRI in patients with newly diagnosed glioma.

Efficacy of cell proliferation imaging with 4DST PET/CT for predicting the prognosis of patients with esophageal cancer: a comparison study with FDG PET/CT

PURPOSE

4'-[Methyl-11C] thiothymidine (4DST) incorporates into DNA directly and is a PET tracer used for cell proliferation imaging. The aim of this study was to evaluate the prediction of prognosis with pretreatment 4DST PET/CT compared to fluorodeoxyglucose (FDG) PET/CT in patients with esophageal cancer.

METHODS

In this prospective study, we analyzed 46 patients (68.2 ± 10.0 years old) with pathologically proven esophageal squamous cell cancer who underwent pretreatment 4DST and FDG PET/CT. The maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), total lesion glycolysis (TLG), and total lesion proliferation (TLP) were measured for FDG and 4DST PET. The study endpoints were progression-free survival (PFS) and overall survival (OS). Patients' clinical backgrounds, including age, histological type, clinical stage, and surgical treatment, were adjusted using the Cox proportional-hazards model.

RESULTS

In the follow-up period (median 18.8 (interquartile range: 10.1-29.0) months), 26 and 19 patients showed disease progression and cancer-related death, respectively. After adjusting for clinical variables, only the 4DST parameters (SUVmax (p = 0.001) and TLP (p = 0.022)) were statistically significant for predicting PFS. FDG MTV (p = 0.031), 4DST SUVmax (p = 0.022), and TLP (p = 0.023) were statistically significant for predicting OS. Of the PET parameters, 4DST SUVmax yielded the highest adjusted hazard ratio for both PFS (4.88, 95% confidence intervals (CI): 1.83-12.97) and OS (4.19, 95% CI: 1.23-14.20).

CONCLUSION

Higher accumulation of 4DST in the primary tumor may lead to shorter OS and PFS. 4DST PET/CT is useful for predicting prognosis and may outperform FDG PET/CT.

4'-[methyl-11C]-thiothymidine as a proliferation imaging tracer for detection of colorectal cancer: comparison with 18F-FDG

OBJECTIVE

The novel radiotracer, 4'-[methyl-¹¹C]-thiothymidine (¹¹C-4DST), was developed based on the DNA incorporation method as a cell proliferation marker. This study investigated the feasibility of ¹¹C-4DST positron emission tomography/computed tomography (PET/CT) for detection of colorectal cancer, as compared with 2-deoxy-2-¹⁸F-fluoro-D-glucose (¹⁸F-FDG) PET/CT, and to correlate the two radiotracers with proliferative activity.

METHODS

A total of 18 patients with newly diagnosed colorectal cancer underwent both ¹¹C-4DST and ¹⁸F-FDG PET/CT. Tumor lesions were identified as areas of focally increased uptake, exceeding that of adjacent normal tissue. For semiquantitative analysis, the maximal standardized uptake value (SUV_max) was calculated. Proliferative activity as quantified by the Ki-67 index was estimated in tumor specimens.

RESULTS

In all 18 patients, colorectal cancers were detected by both ¹¹C-4DST and ¹⁸F-FDG PET/CT. The median (± SD) SUV_max for ¹¹C-4DST (6.02 ± 2.55) was significantly lower than that for ¹⁸F-FDG (13.91 ± 7.62) (P < 0.001). ¹¹C-4DST SUV_max and ¹⁸F-FDG SUV_max showed a significant correlation (r = 0.69, P = 0.002). ¹¹C-4DST SUV_max and Ki-67 index were weakly correlated (r = 0.50, P = 0.04). ¹⁸F-FDG SUV_max and Ki-67 index were not significantly correlated (r = 0.44, P = 0.06).

CONCLUSIONS

Despite a significantly lower uptake of ¹¹C-4DST than that of ¹⁸F-FDG, detection of colorectal cancer was also feasible with ¹¹C-4DST PET/CT. ¹¹C-4DST PET/CT might have a role in the noninvasive assessment of proliferation in colorectal cancer.

Efficacy of 4'-[methyl-11C] thiothymidine PET/CT before and after neoadjuvant therapy for predicting therapeutic responses in patients with esophageal cancer: a pilot study

Background

4′-[Methyl-11C] thiothymidine (4DST) has been introduced as a new cell proliferation imaging PET tracer that incorporates into DNA directly. The aim of this prospective study was to evaluate the efficacy of 4DST PET/CT for predicting responses to neoadjuvant therapy in patients with esophageal cancer comparing with FDG PET/CT.

Methods

Twenty-six patients who had pre- and post-therapeutic 4DST and FDG PET/CT and underwent esophagectomy following neoadjuvant therapy were used for the analysis. Based on pathological findings, patients were divided into two groups: non-responders and responders. The maximum standardized uptake value (SUVmax), metabolic tumor volume, total lesion glycolysis, and total lesion proliferation of the primary lesion were measured for FDG and 4DST PET.

Results

The pathological diagnosis revealed 16 responders and 10 non-responders. Non-responders showed significantly higher 4DST post-therapeutic SUVmax (_postSUVmax) than responders, whereas FDG _postSUVmax showed no statistically significant difference (non-responders vs. responders: 4DST, 6.7 vs. 3.3, p = 0.001; FDG, 6.1 vs. 4.5, p = 0.11). Responders showed a greater reduction in percentage changes of 4DST and FDG SUVmax (ΔSUVmax) from baseline to post-therapeutic PET (non-responders vs. responders: 4DST, − 2.9% vs. − 56.7%, p < 0.001; FDG, − 36.3% vs. − 72.6%, p < 0.001). In ROC analysis, ΔSUVmax and _postSUVmax with 4DST provided great diagnostic performance for predicting responses (area under the curve: 4DST ΔSUVmax = 0.92, 4DST _postSUVmax = 0.88).

Conclusions

4DST PET/CT has a great potential for predicting pathologic response to neoadjuvant therapy in patients with esophageal cancer; it may be slightly superior to that with FDG PET/CT.

Correlation of 4'-[methyl-11C]-thiothymidine uptake with human equilibrative nucleoside transporter-1 and thymidine kinase-1 expressions in patients with newly diagnosed gliomas

OBJECTIVE

We examined expressions of human equilibrative nucleoside transporter-1 (hENT1) and thymidine kinase-1 (TK1), the key enzyme in 4'-[methyl-¹¹C]-thiothymidine (4DST) phosphorylation, to elucidate the mechanism of 4DST uptake in patients with newly diagnosed gliomas.

METHODS

A total of 19 patients with newly diagnosed gliomas were examined with 4DST PET. Tumor lesions were identified as areas of focally increased uptake, exceeding that of normal brain background. For semi-quantitative analysis, tumor-to-contralateral normal brain tissue (T/N) ratio was determined by dividing the maximal standardized uptake value (SUV) for tumor by that of the mean SUV for reference tissue. The expressions of hENT1, TK1 and Ki-67 in tumor specimens were examined by immunohistochemistry and compared with 4DST T/N ratio.

RESULTS

All but two gliomas showed focally increased 4DST uptake. All gliomas showed hENT1 staining, except one grade II glioma, which was also not visualized on 4DST PET. A significant correlation was observed between T/N ratio and hENT1 score (ρ = 0.90, p < 0.001). All gliomas showed TK1 staining, except two gliomas which were also not visualized on 4DST PET. There was a significant correlation between T/N ratio and TK1 score (ρ = 0.92, p < 0.001). There was a significant correlation between T/N ratio and Ki-67 index (ρ = 0.50, p < 0.03).

CONCLUSION

Results of this preliminary study indicate that expressions of hENT1 and TK1 appear to be important determinants of 4DST uptake in newly diagnosed gliomas.

Evaluation of DNA synthesis with carbon-11-labeled 4′-thiothymidine

In the cancer research field, the preferred method for evaluating the proliferative activity of cancer cells in vivo is to measure DNA synthesis rates. The cellular proliferation rate is one of the most important cancer characteristics, and represents the gold standard of pathological diagnosis. Positron emission tomography (PET) has been used to evaluate in vivo DNA synthetic activity through visualization of enhanced nucleoside metabolism. However, methods for the quantitative measurement of DNA synthesis rates have not been fully clarified. Several groups have been engaged in research on 4′-[methyl-¹¹C]-thiothymidine (¹¹C-4DST) in an effort to develop a PET tracer that allows quantitative measurement of in vivo DNA synthesis rates. This mini-review summarizes the results of recent studies of the in vivo measurement of cancer DNA synthesis rates using ¹¹C-4DST.

Influence of volumetric 4'-[methyl-11C]-thiothymidine PET/CT parameters for prediction of the clinical outcome of head and neck cancer patients

OBJECTIVE

This prospective study compared the value of pretreatment 4'-[methyl-¹¹C]-thiothymidine (¹¹C-4DST) volumetric parameters and those of 2-deoxy-2-[18F] fluoro-D-glucose (¹⁸F-FDG) in predicting the clinical outcome in patients with head and neck squamous cell carcinoma (HNSCC).

METHODS

Fifty patients with HNSCC underwent ¹¹C-4DST PET/CT and ¹⁸F-FDG PET/CT prior to anticancer therapy. ¹⁸F-FDG metabolic tumor volume (¹⁸F-FDG MTV) and total lesion glycolysis (TLG) were calculated from ¹⁸F-FDG PET, and ¹¹C-4DST MTV and total lesion proliferation (TLP) were calculated from ¹¹C-4DST PET. All parameters were measured for the primary lesion and metastatic lymph nodes. Associations between clinical factors and PET/CT parameters and prognostic value were analyzed.

RESULTS

Receiver-operating characteristic analysis revealed that MTV, TLG, and TLP acquired from the primary lesion and metastatic lymph nodes were good parameters for predicting disease relapse and death. The area under the curves (AUCs) ranged from 0.63 to 0.71 for ¹⁸F-FDG PET/CT parameters. The AUCs of ¹¹C-4DST PET/CT parameters were larger than those of ¹⁸F-FDG (range 0.72-0.81). Univariate analysis revealed that individuals with tumors showing a high value for any PET/CT parameter were at a significantly increased risk of relapse. Upon multivariate analysis, ¹⁸F-FDG MTV, ¹¹C-4DST MTV and ¹¹C-4DST TLP were significant independent factors for relapse-free survival (P = 0.04, P = 0.0001 and P = 0.0005, respectively).

CONCLUSION

Pretreatment ¹¹C-4DST PET/CT volume-based parameters can provide important prognostic information about patients with HNSCC.

Comparison of 4'-[methyl-(11)C]thiothymidine ((11)C-4DST) and 3'-deoxy-3'-[(18)F]fluorothymidine ((18)F-FLT) PET/CT in human brain glioma imaging

Background

3′-deoxy-3′-[¹⁸F]fluorothymidine (¹⁸F-FLT) has been used to evaluate tumor malignancy and cell proliferation in human brain gliomas. However, ¹⁸F-FLT has several limitations in clinical use. Recently, ¹¹C-labeled thymidine analogue, 4′-[methyl-¹¹C]thiothymidine (¹¹C-4DST), became available as an in vivo cell proliferation positron emission tomography (PET) tracer. The present study was conducted to evaluate the usefulness of ¹¹C-4DST PET in the diagnosis of human brain gliomas by comparing with the images of ¹⁸F-FLT PET.

Methods

Twenty patients with primary and recurrent brain gliomas underwent ¹⁸F-FLT and ¹¹C-4DST PET scans. The uptake values in the tumors were evaluated using the maximum standardized uptake value (SUVmax), the tumor-to-normal tissue uptake (T/N) ratio, and the tumor-to-blood uptake (T/B) ratio. These values were compared among different glioma grades. Correlation between the Ki-67 labeling index and the uptake values of ¹¹C-4DST and ¹⁸F-FLT in the tumor was evaluated using linear regression analysis. The relationship between the individual ¹⁸F-FLT and ¹¹C-4DST uptake values in the tumors was also examined.

Results

¹¹C-4DST uptake was significantly higher than that of ¹⁸F-FLT in the normal brain. The uptake values of ¹¹C-4DST in the tumor were similar to those of ¹⁸F-FLT resulting in better visualization with ¹⁸F-FLT. No significant differences in the uptake values of ¹⁸F-FLT and ¹¹C-4DST were noted among different glioma grades. Linear regression analysis showed a significant correlation between the Ki-67 labeling index and the T/N ratio of ¹¹C-4DST (r = 0.50, P < 0.05) and ¹⁸F-FLT (r = 0.50, P < 0.05). Significant correlations were also found between the Ki-67 labeling index and the T/B ratio of ¹¹C-4DST (r = 0.52, P < 0.05) and ¹⁸F-FLT (r = 0.55, P < 0.05). A highly significant correlation was observed between the individual T/N ratio of ¹¹C-4DST and ¹⁸F-FLT in the tumor (r = 0.79, P = 0.0001).

Conclusions

The present study demonstrates that ¹¹C-4DST is useful for the imaging of human brain gliomas with PET. A relatively higher background uptake of ¹¹C-4DST in the normal brain compared to ¹⁸F-FLT limits the detection of low-tracer-uptake tumors. Moreover, no superiority was found in ¹¹C-4DST over ¹⁸F-FLT in the evaluation of cell proliferation.