Use of 3′-deoxy-3′-[18F]fluorothymidine PET to monitor early responses to radiation therapy in murine SCCVII tumors

Nanomedicine and Early Cancer Diagnosis: Molecular Imaging using Fluorescence Nanoparticles

Incorporating nanotechnology into fluorescent imaging and magnetic resonance imaging (MRI) has shown promising potential for accurate diagnosis of cancer at an earlier stage than the conventional imaging modalities. Molecular imaging (MI) aims to quantitatively characterize, visualize, and measure the biological processes or living cells at molecular and genetic levels. MI modalities have been exploited in different applications including noninvasive determination and visualization of diseased tissues, cell trafficking visualization, early detection, treatment response monitoring, and in vivo visualization of living cells. High-affinity molecular probe and imaging modality to detect the probe are the two main requirements of MI. Recent advances in nanotechnology and allied modalities have facilitated the use of nanoparticles (NPs) as MI probes. Within the extensive group of NPs, fluorescent NPs play a prominent role in optical molecular imaging. The fluorescent NPs used in molecular and cellular imaging can be categorized into three main groups including quantum dots (QDs), upconversion, and dyedoped NPs. Fluorescent NPs have great potential in targeted theranostics including cancer imaging, immunoassay- based cells, proteins and bacteria detections, imaging-guided surgery, and therapy. Fluorescent NPs have shown promising potentials for drug and gene delivery, detection of the chromosomal abnormalities, labeling of DNA, and visualizing DNA replication dynamics. Multifunctional NPs have been successfully used in a single theranostic modality integrating diagnosis and therapy. The unique characteristics of multifunctional NPs make them potential theranostic agents that can be utilized concurrently for diagnosis and therapy. This review provides the state of the art of the applications of nanotechnologies in early cancer diagnosis focusing on fluorescent NPs, their synthesis methods, and perspectives in clinical theranostics.

18F-FLT PET imaging of cellular proliferation in pancreatic cancer

Pancreatic ductal adenocarcinoma is known for its poor prognosis. Since the development of computerized tomography, magnetic resonance and endoscopic ultrasound, novel imaging techniques have struggled to get established in the management of patients diagnosed with pancreatic adenocarcinoma for several reasons. Thus, imaging assessment of pancreatic cancer remains a field with scope for further improvement. In contrast to cross-sectional anatomical imaging methods, molecular imaging modalities such as positron emission tomography (PET) can provide information on tumour function. Particularly, tumour proliferation may be assessed by measurement of intracellular thymidine kinase 1 (TK1) activity level using thymidine analogues radiolabelled with a positron emitter for use with PET. This approach, has been widely explored with [(18)F]-fluoro-3'-deoxy-3'-L-fluorothymidine ((18)F-FLT) PET. This manuscript reviews the rationale and physiology behind (18)F-FLT PET imaging, with special focus on pancreatic cancer and other gastrointestinal malignancies. Potential benefit and challenges of this imaging technique for diagnosis, staging and assessment of treatment response in abdominal malignancies are discussed.

Detection of metastatic tumors after γ-irradiation using longitudinal molecular imaging and gene expression profiling of metastatic tumor nodules

A few recent reports have indicated that metastatic growth of several human cancer cells could be promoted by radiotherapy. C6-L cells expressing the firefly luciferase (fLuc) gene were implanted subcutaneously into the right thigh of BALB/c nu/nu mice. C6-L xenograft mice were treated locally with 50-Gy γ-irradiation (γ-IR) in five 10-Gy fractions. Metastatic tumors were evaluated after γ-IR by imaging techniques. Total RNA from non-irradiated primary tumor (NRPT), γ-irradiated primary tumor (RPT), and three metastatic lung nodule was isolated and analyzed by microarray. Metastatic lung nodules were detected by BLI and PET/CT after 6–9 weeks of γ-IR in 6 (17.1%) of the 35 mice. The images clearly demonstrated high [¹⁸F]FLT and [¹⁸F]FDG uptake into metastatic lung nodules. Whole mRNA expression patterns were analyzed by microarray to elucidate the changes among NRPT, RPT and metastatic lung nodules after γ-IR. In particular, expression changes in the cancer stem cell markers were highly significant in RPT. We observed the metastatic tumors after γ-IR in a tumor-bearing animal model using molecular imaging methods and analyzed the gene expression profile to elucidate genetic changes after γ-IR.

Molecular Imaging to Plan Radiotherapy and Evaluate Its Efficacy

Molecular imaging plays a central role in the management of radiation oncology patients. Specific uses of imaging, particularly to plan radiotherapy and assess its efficacy, require an additional level of reproducibility and image quality beyond what is required for diagnostic imaging. Specific requirements include proper patient preparation, adequate technologist training, careful imaging protocol design, reliable scanner technology, reproducible software algorithms, and reliable data analysis methods. As uncertainty in target definition is arguably the greatest challenge facing radiation oncology, the greatest impact that molecular imaging can have may be in the reduction of interobserver variability in target volume delineation and in providing greater conformity between target volume boundaries and true tumor boundaries. Several automatic and semiautomatic contouring methods based on molecular imaging are available but still need sufficient validation to be widely adopted. Biologically conformal radiotherapy (dose painting) based on molecular imaging-assessed tumor heterogeneity is being investigated, but many challenges remain to fully exploring its potential. Molecular imaging also plays increasingly important roles in both early (during treatment) and late (after treatment) response assessment as both a predictive and a prognostic tool. Because of potentially confounding effects of radiation-induced inflammation, treatment response assessment requires careful interpretation. Although molecular imaging is already strongly embedded in radiotherapy, the path to widespread and all-inclusive use is still long. The lack of solid clinical evidence is the main impediment to broader use. Recommendations for practicing physicians are still rather scarce. (18)F-FDG PET/CT remains the main molecular imaging modality in radiation oncology applications. Although other molecular imaging options (e.g., proliferation imaging) are becoming more common, their widespread use is limited by lack of tracer availability and inadequate reimbursement models. With the increasing presence of molecular imaging in radiation oncology, special emphasis should be placed on adequate training of radiation oncology personnel to understand the potential, and particularly the limitations, of quantitative molecular imaging applications. Similarly, radiologists and nuclear medicine specialists should be sensitized to the special need of the radiation oncologist in terms of quantification and reproducibility. Furthermore, strong collaboration between radiation oncology, nuclear medicine/radiology, and medical physics teams is necessary, as optimal and safe use of molecular imaging can be ensured only within appropriate interdisciplinary teams.

Monitoring the early biologic response of esophageal carcinoma after irradiation with 18F-FLT: an in-vitro and in-vivo study

OBJECTIVE

The aim of our study was to explore the value of 3'-deoxy-3'-[F]fluorothymidine (F-FLT) and F-FLT PET in monitoring the early biologic response of esophageal carcinoma after irradiation in vitro and in vivo.

METHODS

After 2, 4, and 8 h of irradiation at different doses (0, 5, 10, and 15 Gy) of esophageal carcinoma cells in vitro, the uptake ratio of F-FLT, the relative cell survival rate, and ATP levels were measured. The tumor uptake ratio of F-FLT [tumor-to-nontumor (T/NT)] was measured through PET scans before and on the first, seventh, and 15th day after irradiation. The expression of proliferating cell nuclear antigen and Ki-67 was determined in both untreated and treated tumors.

RESULTS

Compared with the control group, the uptake ratio changes of F-FLT after 2 h of irradiation with 5 Gy showed no statistical significance (3.65±0.17 vs. 4.00±0.17%, P>0.05), whereas the uptake ratios of the other groups decreased notably (F=33.93, P<0.01). The differences in the relative survival rates were not statistically significant (F=4.02, P>0.05). Linear regression analysis indicated a significant correlation between F-FLT and ATP levels (r=0.89, P<0.01). On F-FLT PET scan images of the xenografts, the baseline uptake ratio (T/NT) was 2.24±0.06. It decreased to 1.99±0.09, 1.85±0.04, and 1.15±0.10 at 1, 7, and 15 days after irradiation with 10 Gy. Tumor uptake of F-FLT was closely correlated with proliferating cell nuclear antigen and Ki-67 expressions (r=0.83, P<0.001, and r=0.88, P<0.001).

CONCLUSION

The uptake changes of F-FLT in esophageal carcinoma cells and tumor xenografts may reflect the early biological response of esophageal carcinoma after irradiation. Thus, F-FLT PET may be potentially used to monitor the early response of esophageal carcinoma after radiotherapy.

Effectiveness of PET/CT with (18)F-fluorothymidine in the staging of patients with squamous cell head and neck carcinomas before radiotherapy

AIM

The aim of our study was to compare the staging of the disease declared before anticancer treatment was begun with the staging that was found after the planning PET/CT scanning with (18)F-FLT was performed.

BACKGROUND

PET/CT in radiotherapy planning of head and neck cancers can facilitate the contouring of the primary tumour and the definition of metastatic lymph nodes.

MATERIALS AND METHODS

Between November 2010 and November 2013, 26 patients suffering from head and neck carcinomas underwent planning PET/CT examination with (18)F-FLT. We compared the staging of the disease and the treatment strategy declared before and after (18)F-FLT-PET/CT was performed.

RESULTS

The findings from (18)FLT-PET/CT led in 22 patients to a change of staging: in 19 patients it led to upstaging of the disease and in 3 patients it led to downstaging of the disease. In one patient, a secondary malignancy was found.

CONCLUSIONS

We have confirmed in this study that the use of (18)F-FLT-PET/CT scanning in radiotherapy planning of squamous cell head and neck carcinomas has a great potential in the precise evaluation of disease staging and consequently in the precise determination of target volumes.

Predictive Value of Early-Stage Uptake of 3'-Deoxy-3'-18F-Fluorothymidine in Cancer Cells Treated with Charged Particle Irradiation

The aim of this study was to investigate whether 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) can monitor the early response of tumor cell proliferation to charged particle irradiation in vitro and in vivo.

METHODS

In vitro, after 0.1, 0.5, 1, 5, and 10 Gy of proton or carbon ion irradiation, (18)F-FLT cell uptake was examined at 24 h and cell proliferation ability was measured from days 1 to 4. In vivo, after 0.5, 1, and 5 Gy of proton or carbon ion irradiation, (18)F-FLT PET imaging was performed on tumor-bearing BALB/c nu/nu mice at 24 h and tumor growth was measured from days 1 to 7. Tumor-to-background ratios of standardized uptake values were calculated to assess the (18)F-FLT accumulation in tumors. Both cells and mice also received x-irradiation as a control.

RESULTS

In vitro, (18)F-FLT cell uptake was significantly lower after 1 Gy of proton irradiation (P < 0.05) and carbon ion irradiation (P < 0.05) and after 5 Gy of x-irradiation (P < 0.01), but cell proliferation ability at these doses did not show significant differences until day 3. In vivo, (18)F-FLT tumor uptake was significantly lower after 1 Gy of proton (P < 0.001) and carbon ion irradiation (P < 0.01) and after 5 Gy of x-irradiation (P < 0.001), but tumor growth did not significantly differ at these doses until day 4 after proton irradiation, day 3 after carbon ion irradiation, and day 5 after x-irradiation.

CONCLUSION

The reduction in (18)F-FLT uptake after charged particle irradiation was more rapid than the change in tumor growth in vivo or the change in cell proliferation ability in vitro. Therefore, (18)F-FLT is a promising tracer for monitoring the early response of cancer to charged particle irradiation.

Dye-Doped Fluorescent Nanoparticles in Molecular Imaging: A Review of Recent Advances and Future Opportunities

Molecular imaging (MI) is an in vivo assessment of characterization and quantitatively measurement of biological processes at the molecular level. Determination of pathologies of malfunctioned tissues without invasive biopsies or surgical procedures, early detection, monitoring of treatment process and visualization of cell trafficking are advantages of this approach. One example of basic requirement of MI is high affinity molecular probe that acts as the source of image contrast. Recent advances in nanotechnology have developed the use of nanoparticles as MI probe. Optical molecular imaging is one of the main categories of molecular imaging with great potentials for in vivo cell trafficking. Fluorescent nanoparticles are a major group of nanoparticles in optical molecular imaging. Dye-doped, quantum dots and up conversion particles are three classes of fluorescent nanoparticles. This paper reviews the basic principles of molecular imaging based on nanoparticles focusing on the optical molecular imaging. The characteristics of dye-doped nanoparticles, their as well as of that are reviewed in this paper.

Dual tracer evaluation of dynamic changes in intratumoral hypoxic and proliferative states after radiotherapy of human head and neck cancer xenografts using radiolabeled FMISO and FLT

BACKGROUND

Radiotherapy is an important treatment strategy for head and neck cancers. Tumor hypoxia and repopulation adversely affect the radiotherapy outcome. Accordingly, fractionated radiotherapy with dose escalation or altered fractionation schedule is used to prevent hypoxia and repopulation. 18F-fluoromisonidazole (FMISO) and 18F-fluorothymidine (FLT) are noninvasive markers for assessing tumor hypoxia and proliferation, respectively. Thus, we evaluated the dynamic changes in intratumoral hypoxic and proliferative states following radiotherapy using the dual tracers of 18F-FMISO and 3H-FLT, and further verified the results by immunohistochemical staining of pimonidazole (a hypoxia marker) and Ki-67 (a proliferation marker) in human head and neck cancer xenografts (FaDu).

METHODS

FaDu xenografts were established in nude mice and assigned to the non-radiation-treated control and two radiation-treated groups (10- and 20-Gy). Tumor volume was measured daily. Mice were sacrificed 6, 24, and 48 hrs and 7 days after radiotherapy. 18F-FMISO, and 3H-FLT and pimonidazole were injected intravenously 4 and 2 hrs before sacrifice, respectively. Intratumoral 18F-FMISO and 3H-FLT levels were assessed by autoradiography. Pimonidazole and Ki-67 immunohistochemistries were performed.

RESULTS

In radiation-treated mice, tumor growth was significantly suppressed compared with the control group, but the tumor volume in these mice gradually increased with time. Visual inspection showed that intratumoral 18F-FMISO and 3H-FLT distribution patterns were markedly different. Intratumoral 18F-FMISO level did not show significant changes after radiotherapy among the non-radiation-treated control and radiation-treated groups, whereas 3H-FLT level markedly decreased to 59 and 45% of the non-radiation-treated control at 6 hrs (p<0.0001) and then gradually increased with time in the 10- and 20-Gy-radiation-treated groups. The pimonidazole-positive hypoxic areas were visually similar in both the non-radiation-treated control and radiation-treated groups. No significant differences were observed in the percentage of pimonidazole-positive cells and Ki-67 index.

CONCLUSION

Intratumoral 18F-FMISO level did not change until 7 days, whereas 3H-FLT level markedly decreased at 6 hrs and then gradually increased with time after a single dose of radiotherapy. The concomitant monitoring of dynamic changes in tumor hypoxia and proliferation may provide important information for a better understanding of tumor biology after radiotherapy and for radiotherapy planning, including dose escalation and altered fractionation schedules.

18FDG, [18F]FLT, [18F]FAZA, and 11C-methionine are suitable tracers for the diagnosis and in vivo follow-up of the efficacy of chemotherapy by miniPET in both multidrug resistant and sensitive human gynecologic tumor xenografts

Expression of multidrug pumps including P-glycoprotein (MDR1, ABCB1) in the plasma membrane of tumor cells often results in decreased intracellular accumulation of anticancer drugs causing serious impediment to successful chemotherapy. It has been shown earlier that combined treatment with UIC2 anti-Pgp monoclonal antibody (mAb) and cyclosporine A (CSA) is an effective way of blocking Pgp function. In the present work we investigated the suitability of four PET tumor diagnostic radiotracers including 2-[(18)F]fluoro-2-deoxy-D-glucose ((18)FDG), (11)C-methionine, 3'-deoxy-3'-[(18)F]fluorothymidine ((18)F-FLT), and [(18)F]fluoroazomycin-arabinofuranoside ((18)FAZA) for in vivo follow-up of the efficacy of chemotherapy in both Pgp positive (Pgp(+)) and negative (Pgp(-)) human tumor xenograft pairs raised in CB-17 SCID mice. Pgp(+) and Pgp(-) A2780AD/A2780 human ovarian carcinoma and KB-V1/KB-3-1 human epidermoid adenocarcinoma tumor xenografts were used to study the effect of the treatment with an anticancer drug doxorubicin combined with UIC2 and CSA. The combined treatment resulted in a significant decrease of both the tumor size and the accumulation of the tumor diagnostic tracers in the Pgp(+) tumors. Our results demonstrate that (18)FDG, (18)F-FLT, (18)FAZA, and (11)C-methionine are suitable PET tracers for the diagnosis and in vivo follow-up of the efficacy of tumor chemotherapy in both Pgp(+) and Pgp(-) human tumor xenografts by miniPET.

PET probes beyond (18)F-FDG

During the past several decades, positron emission tomography (PET) has been one of the rapidly growing areas of medical imaging; particularly, its applications in routine oncological practice have been widely recognized. At present, (18)F-fluorodeoxyglucose ((18)F-FDG) is the most broadly used PET probe. However, (18)F-FDG also suffers many limitations. Thus, scientists and clinicians are greatly interested in exploring and developing new PET imaging probes with high affinity and specificity. In this review, we briefly summarize the representative PET probes beyond (18)F-FDG that are available for patients imaging in three major clinical areas (oncology, neurology and cardiology), and we also discuss the feasibility and trends in developing new PET probes for personalized medicine.

Early reduction in tumour [18F]fluorothymidine (FLT) uptake in patients with non-small cell lung cancer (NSCLC) treated with radiotherapy alone

PURPOSE

Changes in tumour 3'-deoxy-3'-[(18)F]fluorothymidine (FLT) uptake during concurrent chemo-radiotherapy in patients with non-small cell lung cancer (NSCLC) have been reported, at variable time points, in two pilot positron emission tomography (PET) studies. The aim of this study was to assess whether FLT changes occur early in response to radiotherapy (RT) without concurrent chemotherapy and whether such changes exceed test-retest variability.

METHODS

Sixteen patients with NSCLC, scheduled to have radical RT, underwent FLT PET once/twice at baseline to assess reproducibility and/or after 5-11 RT fractions to evaluate response. Primary and nodal malignant lesions were manually delineated on CT and volume, mean and maximum standardized uptake values (SUV(mean) and SUV(max)) estimated. Analysis included descriptive statistics and parameter fitting to a mixed-effects model accounting for patients having different numbers of evaluable lesions.

RESULTS

In all, 35 FLT PET scans from 7 patients with a total of 18 lesions and 12 patients with a total of 30 lesions were evaluated for reproducibility and response, respectively. SUV(mean) reproducibility in primary tumours (SD 8.9%) was better than SUV(max) reproducibility (SD 12.6%). In nodes, SUV(mean) and SUV(max) reproducibilities (SD 18.0 and 17.2%) were comparable but worse than for primary tumours. After 5-11 RT fractions, primary tumour SUV(mean) decreased significantly by 25% (p = 0.0001) in the absence of significant volumetric change, whereas metastatic nodes decreased in volume by 31% (p = 0.020) with a larger SUV(mean) decrease of 40% (p < 0.0001). Similar changes were found for SUV(max).

CONCLUSION

Across this group of NSCLC patients, RT induced an early, significant decrease in lesion FLT uptake exceeding test-retest variability. This effect is variable between patients, appears distinct between primary and metastatic nodal lesions, and in primary tumours is lower than previously reported for concurrent chemo-RT at a similar time point. These results confirm the potential for FLT PET to report early on radiation response and to enhance the clinical development of novel drug-radiation combinations by providing an interpretable, early pharmacodynamic end point.

[18F]FDG and [18F]FLT positron emission tomography imaging following treatment with belinostat in human ovary cancer xenografts in mice

BACKGROUND

Belinostat is a histone deacetylase inhibitor with anti-tumor effect in several pre-clinical tumor models and clinical trials. The aim of the study was to evaluate changes in cell proliferation and glucose uptake by use of 3'-deoxy-3'-[(18)F]fluorothymidine ([18F]FLT) and 2-deoxy-2-[(18)F]fluoro-D-glucose ([18F]FDG) positron emission tomography (PET) following treatment with belinostat in ovarian cancer in vivo models.

METHODS

In vivo uptake of [18F]FLT and [18F]FDG in human ovary cancer xenografts in mice (A2780) were studied after treatment with belinostat. Mice were divided in 2 groups receiving either belinostat (40 mg/kg ip twice daily Day 0-4 and 6-10) or vehicle. Baseline [18F]FLT or [18F]FDG scans were made before treatment (Day 0) and repeated at Day 3, 6 and 10. Tracer uptake was quantified using small animal PET/CT.

RESULTS

Tumors in the belinostat group had volumes that were 462 ± 62% (640 mm(3)) at Day 10 relative to baseline which was significantly different (P = 0.011) from the control group 769 ± 74% (926 mm(3)). [18F]FLT SUVmax increased from baseline to Day 10 (+30 ± 9%; P = 0.048) in the control group. No increase was observed in the treatment group. [18F]FDG SUVmean was significantly different in the treatment group compared to the control group (P = 0.0023) at Day 10. Within treatment groups [18F]FDG uptake and to a lesser extent [18F]FLT uptake at Day 3 were significantly correlated with tumor growth at Day 10.

CONCLUSIONS

[18F]FDG uptake early following treatment initiation predicted tumor sizes at Day 10, suggesting that [18F]FDG may be a valuable biomarker for non-invasive assessment of anti-tumor activity of belinostat.

Monitoring tumor proliferative response to radiotherapy using (18)F-fluorothymidine in human head and neck cancer xenograft in comparison with Ki-67

OBJECTIVE

Although radiotherapy is an important treatment strategy for head and neck cancers, it induces tumor repopulation which adversely affects therapeutic outcome. In this regard, fractionated radiotherapy is widely applied to prevent tumor repopulation. Evaluation of tumor proliferative activity using (18)F-fluorothymidine (FLT), a noninvasive marker of tumor proliferation, may be useful for determining the optimal timing of and dose in the repetitive irradiation. Thus, to assess the potentials of FLT, we evaluated the sequential changes in intratumoral proliferative activity in head and neck cancer xenografts (FaDu) using FLT.

METHODS

FaDu tumor xenografts were established in nude mice and assigned to control and two radiation-treated groups (10 and 20 Gy). Tumor volume was measured daily. (3)H-FLT was injected intravenously 2 h before killing. Mice were killed 6, 24, 48 h, and 7 days after the radiation treatment. Intratumoral (3)H-FLT level was visually and quantitatively assessed by autoradiography. Ki-67 immunohistochemistry (IHC) was performed.

RESULTS

In radiation-treated mice, the tumor growth was significantly suppressed compared with the control group, but the tumor volume in these mice gradually increased with time. In the visual assessment, intratumoral (3)H-FLT level diffusely decreased 6 h after the radiation treatment and then gradually increased with time, whereas no apparent changes were observed in Ki-67 IHC. Six hours after the radiation treatment at 10 and 20 Gy, the intratumoral (3)H-FLT level markedly decreased to 45 and 40 % of the control, respectively (P < 0.0001 vs control), and then gradually increased with time. In each radiation-treated group, the (3)H-FLT levels at 48 h and on day 7 were significantly higher than that at 6 h. The intratumoral (3)H-FLT levels in both treated groups were 68 and 60 % at 24 h (P < 0.001), 71 and 77 % at 48 h (P < 0.001), and 83 and 81 % on day 7 (P = NS) compared with the control group.

CONCLUSION

Intratumoral FLT uptake level markedly decreased at 6 h and then gradually increased with time. Sequential evaluation of intratumoral proliferative activity using FLT can be beneficial for determining the optimal timing of and dose in repetitive irradiation of head and neck cancer.

18F-FLT PET during radiotherapy or chemoradiotherapy in head and neck squamous cell carcinoma is an early predictor of outcome

This prospective study used sequential PET with the proliferation tracer 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) to monitor the early response to treatment of head and neck cancer and evaluated the association between PET parameters and clinical outcome.

METHODS

Forty-eight patients with head and neck cancer underwent (18)F-FLT PET/CT before and during the second and fourth weeks of radiotherapy or chemoradiotherapy. Mean maximum standardized uptake values for the hottest voxel in the tumor and its 8 surrounding voxels in 1 transversal slice (SUVmax(9)) of the PET scans were calculated, as well as PET-segmented gross tumor volumes using visual delineation (GTVVIS) and operator-independent methods based on signal-to-background ratio (GTVSBR) and 50% isocontour of the maximum signal intensity (GTV50%). PET parameters were evaluated for correlations with outcome.

RESULTS

(18)F-FLT uptake decreased significantly between consecutive scans. An SUVmax(9) decline ≥ 45% and a GTVVIS decrease ≥ median during the first 2 treatment weeks were associated with better 3-y disease-free survival (88% vs. 63%, P = 0.035, and 91% vs. 65%, P = 0.037, respectively). A GTVVIS decrease ≥ median in the fourth treatment week was also associated with better 3-y locoregional control (100% vs. 68%, P = 0.021). These correlations were most prominent in the subset of patients treated with chemoradiotherapy. Because of low (18)F-FLT uptake levels during treatment, GTVSBR and GTV50% were unsuccessful in segmenting primary tumor volume.

CONCLUSION

In head and neck cancer, a change in (18)F-FLT uptake early during radiotherapy or chemoradiotherapy is a strong indicator for long-term outcome. (18)F-FLT PET may thus aid in personalized patient management by steering treatment modifications during an early phase of therapy.

[18F]FLT and [18F]FDG PET for non-invasive treatment monitoring of the nicotinamide phosphoribosyltransferase inhibitor APO866 in human xenografts

INTRODUCTION

APO866 is a new anti-tumor compound inhibiting nicotinamide phosphoribosyltransferase (NAMPT). APO866 has an anti-tumor effect in several pre-clinical tumor models and is currently in several clinical phase II studies. 3'-deoxy-3'-[18F]fluorothymidine ([18F]FLT) is a tracer used to assess cell proliferation in vivo. The aim of this study was non-invasively to study effect of APO866 treatment on [18F]FLT and 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) uptake.

METHODS

In vivo uptake of [18F]FLT and [18F]FDG in human ovary cancer xenografts in mice (A2780) was studied at various time points after APO866 treatment. Baseline [18F]FLT or [18F]FDG scans were made before treatment and repeated after 24 hours, 48 hours and 7 days. Tumor volume was followed with computed tomography (CT). Tracer uptake was quantified using small animal PET/CT. One hour after iv injection of tracer, static PET scans were performed. Imaging results were compared with Ki67 immunohistochemistry.

RESULTS

Tumors treated with APO866 had volumes that were 114% (24 h), 128% (48 h) and 130% (Day 7) relative to baseline volumes at Day 0. In the control group tumor volumes were 118% (24 h), 145% (48 h) and 339% (Day 7) relative to baseline volumes Day 0. Tumor volume between the treatment and control group was significantly different at Day 7 (P = 0.001). Compared to baseline, [18F]FLT SUVmax was significantly different at 24 h (P<0.001), 48 h (P<0.001) and Day 7 (P<0.001) in the APO866 group. Compared to baseline, [18F]FDG SUVmax was significantly different at Day 7 (P = 0.005) in the APO866 group.

CONCLUSIONS

APO866 treatment caused a significant decrease in [18F]FLT uptake 24 and 48 hours after treatment initiation. The early reductions in tumor cell proliferation preceded decrease in tumor volume. The results show the possibility to use [18F]FLT and [18F]FDG to image treatment effect early following treatment with APO866 in future clinical studies.

[18F]FLT PET for non-invasive assessment of tumor sensitivity to chemotherapy: studies with experimental chemotherapy TP202377 in human cancer xenografts in mice

Aim

3′-deoxy-3′-[¹⁸F]fluorothymidine ([18F]FLT) is a tracer used to assess cell proliferation in vivo. The aim of the study was to use [18F]FLT positron emission tomography (PET) to study non-invasively early anti-proliferative effects of the experimental chemotherapeutic agent TP202377 in both sensitive and resistant tumors.

Methods

Xenografts in mice from 3 human cancer cell lines were used: the TP202377 sensitive A2780 ovary cancer cell line (n = 8–16 tumors/group), the induced resistant A2780/Top216 cell line (n = 8–12 tumors/group) and the natural resistant SW620 colon cancer cell line (n = 10 tumors/group). In vivo uptake of [18F]FLT was studied at baseline and repeated 6 hours, Day 1, and Day 6 after TP202377 treatment (40 mg/kg i.v.) was initiated. Tracer uptake was quantified using small animal PET/CT.

Results

TP202377 (40 mg/kg at 0 hours) caused growth inhibition at Day 6 in the sensitive A2780 tumor model compared to the control group (P<0.001). In the A2780 tumor model TP202377 treatment caused significant decrease in uptake of [18F]FLT at 6 hours (-46%; P<0.001) and Day 1 (-44%; P<0.001) after treatment start compared to baseline uptake. At Day 6 uptake was comparable to baseline. Treatment with TP202377 did not influence tumor growth or [18F]FLT uptake in the resistant A2780/Top216 and SW620 tumor models. In all control groups uptake of [18F]FLT did not change. Ki67 gene expression paralleled [18F]FLT uptake.

Conclusion

Treatment of A2780 xenografts in mice with TP202377 (single dose i.v.) caused a significant decrease in cell proliferation assessed by [18F]FLT PET after 6 hours. Inhibition persisted at Day 1; however, cell proliferation had returned to baseline at Day 6. In the resistant A2780/Top216 and SW620 tumor models uptake of [18F]FLT did not change after treatment. With [18F]FLT PET it was possible to distinguish non-invasively between sensitive and resistant tumors already 6 hours after treatment initiation.

Usefulness of 3'-deoxy-3'-18F-fluorothymidine PET for predicting early response to chemoradiotherapy in head and neck cancer

This study compared the utility of 3'-deoxy-3'-(18)F-fluorothymidine PET ((18)F-FLT PET) with that of (18)F-FDG PET for assessment of the early locoregional clinical outcomes of chemoradiotherapy for head and neck squamous cell carcinomas.

METHODS

From May 2006 to September 2010, 28 patients with head and neck squamous cell carcinomas underwent (18)F-FLT and (18)F-FDG PET before radiation therapy (RT), 4 wk after the initiation of RT, and 5 wk after completion of RT. PET images were evaluated qualitatively for regions of focally increased metabolism and were analyzed in relation to residual accumulation and local disease control.

RESULTS

During RT, (18)F-FLT uptake decreased more significantly than (18)F-FDG uptake. (18)F-FLT accumulations disappeared in 34 of 54 lesions (63%), and negative predictive value was 97%. (18)F-FDG PET during RT also had a high negative predictive value (100%), but only 9 lesions (16%) showed complete absence of accumulation. The specificity and overall accuracy of (18)F-FLT PET were significantly higher than those of (18)F-FDG PET both during and after RT. In particular, high significance was attributable to the results of the evaluations of primary lesions. There were significant differences in 3-y local control between the residual-accumulation and no-accumulation groups on both posttreatment (18)F-FLT PET (P < 0.0001) and posttreatment (18)F-FDG PET (P = 0.0081).

CONCLUSION

(18)F-FLT PET during RT and early follow-up facilitates the selection of optimal further therapy and the prediction of outcomes.

Development of radiotracers for oncology--the interface with pharmacology

There is an increasing role for positron emission tomography (PET) in oncology, particularly as a component of early phase clinical trials. As a non-invasive functional imaging modality, PET can be used to assess both pharmacokinetics and pharmacodynamics of novel therapeutics by utilizing radiolabelled compounds. These studies can provide crucial information early in the drug development process that may influence the further development of novel therapeutics. PET imaging probes can also be used as early biomarkers of clinical response and to predict clinical outcome prior to the administration of therapeutic agents. We discuss the role of PET imaging particularly as applied to phase 0 studies and discuss the regulations involved in the development and synthesis of novel radioligands. The review also discusses currently available tracers and their role in the assessment of pharmacokinetics and pharmacodynamics as applied to oncology.

Early detection of tumor response by FLT/microPET Imaging in a C26 murine colon carcinoma solid tumor animal model

Fluorine-18 fluorodeoxyglucose ((18)F-FDG) positron emission tomography (PET) imaging demonstrated the change of glucose consumption of tumor cells, but problems with specificity and difficulties in early detection of tumor response to chemotherapy have led to the development of new PET tracers. Fluorine-18-fluorothymidine ((18)F-FLT) images cellular proliferation by entering the salvage pathway of DNA synthesis. In this study, we evaluate the early response of colon carcinoma to the chemotherapeutic drug, lipo-Dox, in C26 murine colorectal carcinoma-bearing mice by (18)F-FDG and (18)F-FLT. The male BALB/c mice were bilaterally inoculated with 1 × 10(5) and 1 × 10(6) C26 tumor cells per flank. Mice were intravenously treated with 10 mg/kg lipo-Dox at day 8 after (18)F-FDG and (18)F-FLT imaging. The biodistribution of (18)F-FDG and (18)F-FLT were followed by the microPET imaging at day 9. For the quantitative measurement of microPET imaging at day 9, (18)F-FLT was superior to (18)F-FDG for early detection of tumor response to Lipo-DOX at various tumor sizes (P < 0.05). The data of biodistribution showed similar results with those from the quantification of SUV (standard uptake value) by microPET imaging. The study indicates that (18)F-FLT/microPET is a useful imaging modality for early detection of chemotherapy in the colorectal mouse model.

Applications of molecular imaging

Today molecular imaging technologies play a central role in clinical oncology. The use of imaging techniques in early cancer detection, treatment response, and new therapy development is steadily growing and has already significantly impacted on clinical management of cancer. In this chapter, we overview three different molecular imaging technologies used for the understanding of disease biomarkers, drug development, or monitoring therapeutic outcome. They are (1) optical imaging (bioluminescence and fluorescence imaging), (2) magnetic resonance imaging (MRI), and (3) nuclear imaging (e.g., single-photon emission computed tomography (SPECT) and positron emission tomography (PET)). We review the use of molecular reporters of biological processes (e.g., apoptosis and protein kinase activity) for high-throughput drug screening and new cancer therapies, diffusion MRI as a biomarker for early treatment response and PET and SPECT radioligands in oncology.

Comparison of FLT-PET and FDG-PET for visualization of head and neck squamous cell cancers

PURPOSE

We compared 3'[F-18]fluoro-3'-deoxythymidine (FLT) positron emission tomography (PET) and 2-deoxy-2-[F-18]fluoro-D-glucose (FDG) for PET visualization of head and neck squamous cell cancers (HNSCCs) and evaluated which might better reflect proliferative activity as indicated by the Ki-67 index.

PROCEDURES

A total of 43 patients with HNSCCs were examined with FLT-PET and FDG-PET. The PET images were evaluated qualitatively for regions of focally increased metabolism and for semiquantitative analysis the maximum standardized uptake value (SUV) was calculated.

RESULTS

For depiction of primary tumours, the sensitivity of both approaches was 100%. The mean (± SD) SUV for FLT (5.65 ± 2.96) was significantly lower than that for FDG (10.9 ± 4.91; p < 0.0001). No significant differences were found for the T category. However, the mean (± SD) FLT SUV was significantly higher in poorly than in well-differentiated tumours (6.49 ± 3.13 vs. 4.2 ± 2.08; p < 0.04). Similarly, FDG SUVs in poorly and moderately differentiated tumours (12.72 ± 4.8 and 11.46 ± 4.64) were significantly higher than in well-differentiated tumours (7.45 ± 3.51; p < 0.004 and p < 0.02). No significant correlation was observed with the Ki-67 index for either.

CONCLUSION

FLT-PET showed as high a sensitivity as FDG-PET for the detection of primary HNSCC lesions, although uptake of FLT was significantly lower than that of FDG.

Radiotracers for noninvasive molecular imaging of tumor cell death

The need to monitor cancer therapy-induced cellular and tissue changes using noninvasive imaging techniques continues to stimulate both basic and clinical research. Monitoring changes in cellular proliferative capacity that occur after treatment with radiation and/or chemotherapy has the potential to provide longitudinal information on the cellular dynamics of tumors before, during, and after therapeutic intervention. Cells can lose their reproductive potential through one of several mechanisms, including apoptosis and autophagy (which are forms of programmed cell death), premature senescence, or necrosis. When a tumor responds to therapy, current imaging methods do not provide information about the exact mechanism of cell death executed. We are now beginning to develop the molecular imaging tools that will enable us to noninvasively image cell death mechanisms both in experimental models and in the clinical cancer environment. Studies with these imaging tools will contribute to a better understanding of therapeutic responses and assist in the design and evaluation of more effective treatments. This review examines the state-of-the-art in the use of (radio)tracers for the purpose of imaging mechanisms of tumor cell inactivation (cell death) in animal models and in clinical trials.

The challenges of integrating molecular imaging into the optimization of cancer therapy

We review novel, in vivo and tissue-based imaging technologies that monitor and optimize cancer therapeutics. Recent advances in cancer treatment centre around the development of targeted therapies and personalisation of treatment regimes to individual tumour characteristics. However, clinical outcomes have not improved as expected. Further development of the use of molecular imaging to predict or assess treatment response must address spatial heterogeneity of cancer within the body. A combination of different imaging modalities should be used to relate the effect of the drug to dosing regimen or effective drug concentration at the local site of action. Molecular imaging provides a functional and dynamic read-out of cancer therapeutics, from nanometre to whole body scale. At the whole body scale, an increase in the sensitivity and specificity of the imaging probe is required to localise (micro)metastatic foci and/or residual disease that are currently below the limit of detection. The use of image-guided endoscopic biopsy can produce tumour cells or tissues for nanoscopic analysis in a relatively patient-compliant manner, thereby linking clinical imaging to a more precise assessment of molecular mechanisms. This multimodality imaging approach (in combination with genetics/genomic information) could be used to bridge the gap between our knowledge of mechanisms underlying the processes of metastasis, tumour dormancy and routine clinical practice. Treatment regimes could therefore be individually tailored both at diagnosis and throughout treatment, through monitoring of drug pharmacodynamics providing an early read-out of response or resistance.

Molecular imaging-based dose painting: a novel paradigm for radiation therapy prescription

Dose painting is the prescription of a nonuniform radiation dose distribution to the target volume based on functional or molecular images shown to indicate the local risk of relapse. Two prototypical strategies for implementing this novel paradigm in radiation oncology are reviewed: subvolume boosting and dose painting by numbers. Subvolume boosting involves the selection of a "target within the target," defined by image segmentation on the basis of the quantitative information in the image or morphologically, and this is related to image-based target volume selection and delineation. Dose painting by numbers is a voxel-level prescription of dose based on a mathematical transformation of the image intensity of individual pixels. The quantitative use of images to decide both where and how to delivery radiation therapy in an individual case is also called theragnostic imaging. Dose painting targets are imaging surrogates for cellular or microenvironmental phenotypes associated with poor radioresponsiveness. In this review, the focus is on the following positron emission tomography tracers: FDG and choline as surrogates for tumor burden, fluorothymidine as a surrogate for proliferation (or cellular growth fraction) and hypoxia-sensitive tracers, including [(18)F] fluoromisonidazole, EF3, EF5, and (64)Cu-labeled copper(II) diacetyl-di(N(4)-methylthiosemicarbazone) as surrogates of cellular hypoxia. Research advances supporting the clinicobiological rationale for dose painting are reviewed as are studies of the technical feasibility of optimizing and delivering realistic dose painted radiation therapy plans. Challenges and research priorities in this exciting research field are defined and a possible design for a randomized clinical trial of dose painting is presented.

Imaging in interventional oncology

Medical imaging in interventional oncology is used differently than in diagnostic radiology and prioritizes different imaging features. Whereas diagnostic imaging prioritizes the highest-quality imaging, interventional imaging prioritizes real-time imaging with lower radiation dose in addition to high-quality imaging. In general, medical imaging plays five key roles in image-guided therapy, and interventional oncology, in particular. These roles are (a) preprocedure planning, (b) intraprocedural targeting, (c) intraprocedural monitoring, (d) intraprocedural control, and (e) postprocedure assessment. Although many of these roles are still relatively basic in interventional oncology, as research and development in medical imaging focuses on interventional needs, it is likely that the role of medical imaging in intervention will become even more integral and more widely applied. In this review, the current status of medical imaging for intervention in oncology will be described and directions for future development will be examined.

Monitoring early responses to irradiation with dual-tracer micro-PET in dual-tumor bearing mice

AIM: To monitor the early responses to irradiation in primary and metastatic colorectal cancer (CRC) with ¹⁸F-fluorothymidine (¹⁸F-FLT) and ¹⁸F-fluorodeoxyglucose (¹⁸F-FDG) small-animal position emission tomography (micro-PET).

METHODS: The primary and metastatic CRC cell lines, SW480 and SW620, were irradiated with 5, 10 and 20 Gy. After 24 h, the cell cycle phases were analyzed. A dual-tumor-bearing mouse model of primary and metastatic cancer was established by injecting SW480 and SW620 cells into mice. micro-PET with ¹⁸F-FLT and ¹⁸F-FDG was performed before and 24 h after irradiation with 5, 10 and 20 Gy. The region of interest (ROI) was drawn over the tumor and background to calculate the ratio of tumor to non-tumor (T/NT) in tissues. Immunohistochemical assay and Western blotting were used to examine the levels of integrin β_3, Ki-67, vascular endothelial growth factor receptor 2 (VEGFR2) and heat shock protein 27 (HSP27).

RESULTS: The proportion of SW480 and SW620 cells in the G₂-M phase was decreased with an increasing radiation dose. The proportion of SW480 cells in the G₀-G₁ phase was increased from 48.33% ± 4.55% to 87.09% ± 7.43% (P < 0.001) and that of SW620 cells in the S-phase was elevated from 43.57% ± 2.65% to 66.59% ± 7.37% (P = 0.021). In micro-PET study, with increasing dose of radiation, ¹⁸F-FLT uptake was significantly reduced from 3.65 ± 0.51 to 2.87 ± 0.47 (P = 0.008) in SW480 tumors and from 2.22 ± 0.42 to 1.76 ± 0.45 (P = 0.026) in SW620 tumors. ¹⁸F-FDG uptake in SW480 and SW620 tumors was reduced but not significantly (F = 0.582, P = 0.633 vs F = 0.273, P = 0.845). Dose of radiation was negatively correlated with ¹⁸F-FLT uptake in both SW480 and SW620 tumors (r = -0.727, P = 0.004; and r = -0.664, P = 0.009). No significant correlation was found between ¹⁸F-FDG uptake and radiation dose in SW480 or SW620 tumors. HSP27 and integrin β₃ expression was higher in SW480 than in SW620 tumors. The T/NT ratio for ¹⁸F-FLT uptake was positively correlated with HSP27 and integrin β₃ expression (r = 0.924, P = 0.004; and r = 0.813, P = 0.025).

CONCLUSION: ¹⁸F-FLT is more suitable than ¹⁸F-FDG in monitoring early responses to irradiation in both primary and metastatic lesions of colorectal cancer.

Early detection of response to experimental chemotherapeutic Top216 with [18F]FLT and [18F]FDG PET in human ovary cancer xenografts in mice

Background

3′-deoxy-3′-[¹⁸F]fluorothymidine (¹⁸F-FLT) is a tracer used to assess cell proliferation in vivo. The aim of the study was to use ¹⁸F-FLT positron emission tomography (PET) to study treatment responses to a new anti-cancer compound. To do so, we studied early anti-proliferative effects of the experimental chemotherapy Top216 non-invasively by PET.

Methodology/Principal Findings

In vivo uptake of ¹⁸F-FLT in human ovary cancer xenografts in mice (A2780) was studied at various time points after Top216 treatment (50 mg/kg i.v. at 0 and 48 hours) was initiated. Baseline ¹⁸F-FLT scans were made before either Top216 (n = 7–10) or vehicle (n = 5–7) was injected and repeated after 2 and 6 hours and 1 and 5 days of treatment. A parallel study was made with 2′-deoxy-2′-[¹⁸F]fluoro-D-glucose (¹⁸F-FDG) (n = 8). Tracer uptake was quantified using small animal PET/CT. Imaging results were validated by tumor volume changes and gene-expression of Ki67 and TK1. Top216 (50 mg/kg 0 and 48 hours) inhibited the growth of the A2780 tumor compared to the control group (P<0.001). ¹⁸F-FLT uptake decreased significantly at 2 hours (−52%; P<0.001), 6 hours (−49%; P = 0.002) and Day 1 (−47%; P<0.001) after Top216 treatment. At Day 5 ¹⁸F-FLT uptake was comparable to uptake in the control group. Uptake of ¹⁸F-FLT was unchanged in the control group during the experiment. In the treatment group, uptake of ¹⁸F-FDG was significantly decreased at 6 hours (−21%; P = 0.003), Day 1 (−29%; P<0.001) and Day 5 (−19%; P = 0.05) compared to baseline.

Conclusions/Significance

One injection with Top216 initiated a fast and significant decrease in cell-proliferation assessable by ¹⁸F-FLT after 2 hours. The early reductions in tumor cell proliferation preceded changes in tumor size. Our data indicate that ¹⁸F-FLT PET is promising for the early non-invasive assessment of chemotherapy effects in both drug development and for tailoring therapy in patients.

Molecular imaging in cancer treatment

The success of cancer therapy can be difficult to predict, as its efficacy is often predicated upon characteristics of the cancer, treatment, and individual that are not fully understood or are difficult to ascertain. Monitoring the response of disease to treatment is therefore essential and has traditionally been characterized by changes in tumor volume. However, in many instances, this singular measure is insufficient for predicting treatment effects on patient survival. Molecular imaging allows repeated in vivo measurement of many critical molecular features of neoplasm, such as metabolism, proliferation, angiogenesis, hypoxia, and apoptosis, which can be employed for monitoring therapeutic response. In this review, we examine the current methods for evaluating response to treatment and provide an overview of emerging PET molecular imaging methods that will help guide future cancer therapies.

Molecular PET and PET/CT imaging of tumour cell proliferation using F-18 fluoro-L-thymidine: a comprehensive evaluation

Positron emission tomography (PET) using F-18 fluoro-3'-deoxy-3-L-fluorothymidine (FLT) offers noninvasive assessment of cell proliferation in vivo. The most important application refers to the evaluation of tumour proliferative activity, representing a key feature of malignancy. Most data to date suggest that FLT is not a suitable biomarker for staging of cancers. This is because of the rather low fraction of tumour cells that undergo replication at a given time with subsequently relatively low tumour FLT uptake. In addition, generally, the high FLT uptake in liver and bone marrow limits the diagnostic use. We describe the current status on preclinical and clinical applications of FLT-PET including our own experience in brain tumours. The future of FLT-PET probably lies in the evaluation of tumour response to therapy and more importantly, in the prediction of early response in the course of treatment. The level of FLT accumulation in tumours depends on thymidine kinase 1 activity and on the therapy-induced activation of the salvage pathway and expression of nucleoside transporters. Therefore, cytostatic agents that cause arrest of the cell cycle in the S-phase may initially increase FLT uptake rather than reducing the tumour cell accumulation. In addition, agents that block the endogenous thymidine pathway may lead to overactivity of the salvage pathway and increase tumour FLT uptake. In contrast, many therapeutic agents inhibit both pathways and subsequently reduce tumour FLT uptake. Further studies comparing FLT with F-18 fluorodeoxyglucose-PET will be important to determine the complementary advantage of FLT-PET in early cancer therapy response assessment. Further research should be facilitated by simplified synthesis of FLT with improved yields and an increasing commercial availability.

Molecular imaging in clinical trials

Imaging of biological processes using specific molecular probes allows exploration of the mechanism of action and efficacy for new therapies. This molecular imaging has made use of modalities including single photon emission computed tomography (SPECT), positron emission tomography (PET), magnetic resonance imaging (MRI), and optical techniques. Molecular imaging can be used to explore many of the hallmarks of cancer biology, including angiogenesis, proliferation, tissue invasion, evasion of apoptosis, and self-sufficiency in growth signals. Since many of these aspects of cancer biology are in turn the targets of novel therapies in development, molecular imaging techniques have great potential to inform trials of these new agents. The high cost of clinical drug development mandates the optimisation of early phase trial design to maximise the collection of evidence for efficacy and proof of mechanism, endpoints which have, in a number of examples, already been provided by molecular imaging. The variety provided by novel chemistry, and the availability of isotopes with varying physical properties, particularly suits PET imaging as a functional modality for application in clinical trials.

(18)F-FDG and (18)F-FLT uptake early after cyclophosphamide and mTOR inhibition in an experimental lymphoma model

To be a reliable predictor of response, tracer uptake should reflect changes in the amount of active tumor cells. However, uptake of (18)F-FDG, the most commonly used PET tracer, is disturbed by the inflammatory cells that appear early after cytotoxic therapy. The first aim of this study was to investigate whether 3'-(18)F-fluoro-3'-deoxy-l-thymidine ((18)F-FLT), a marker of cellular proliferation, is a better tracer for response assessment early after cytotoxic therapy. A second objective of this study was to investigate whether (18)F-FDG and (18)F-FLT responses were comparable early after mammalian target of rapamycin (mTOR) inhibition, as an example of proliferation-targeting therapies.

METHODS

Severe combined immunodeficient mice were subcutaneously inoculated with Granta-519 cells, a human cell line derived from a leukemic mantle cell lymphoma. Half the mice were treated with cyclophosphamide and the other half with mTOR inhibition. (18)F-FDG and (18)F-FLT uptake was evaluated by small-animal PET on day 0 (D0; before treatment), D+1, D+2, D+4, D+7, D+9, D+11, and D+14. At each time point, 2 mice of each treatment condition were sacrificed, and tumors were excised for histopathology.

RESULTS

After cyclophosphamide, (18)F-FDG and (18)F-FLT uptake decreased, with a maximum reduction of -29% for (18)F-FDG and -25% for (18)F-FLT uptake at D+2, compared with baseline. Although (18)F-FDG uptake increased from D+4 on, with a maximum on D+7, (18)F-FLT uptake remained virtually stable. Histology showed an increase in apoptotic or necrotic tumor fraction, followed by an influx of inflammatory cells. In mTOR-inhibited mice, (18)F-FDG uptake dropped until D+2 after therapy (-43%) but increased at D+4 (-27%) to form a plateau on D+7 and D+9 (-14% and -16%, respectively). Concurrently, (18)F-FLT uptake decreased to -31% on D+2, followed by an increase with a peak value of +12% on D+7, after which (18)F-FLT uptake decreased again. Cyclin D1 expression dropped from D+1 until D+4 and returned to baseline at D+7.

CONCLUSION

Because (18)F-FLT uptake is not significantly influenced by the temporary rise in inflammatory cells early after cyclophosphamide, it more accurately reflects tumor response. However, a formerly unknown temporary rise in (18)F-FLT uptake a few days after the administration of mTOR inhibition was defined, which makes it clear that drug-specific responses have to be considered when using PET for early treatment monitoring.

Microreactors for radiopharmaceutical synthesis

Multiple advantages of microfluidics have been demonstrated in the area of organic synthesis. However, only a limited number of them have found applications in radiopharmaceutical synthesis, while that is an area where the need for improvements offered by microfluidics is very significant. The need is to create an environment where all reactions involving short-lived radioisotopes such as (18)F (110 min half-life) or (11)C (20 min half-life) are rapid and high-yielding while the devices are controlled remotely. Several groups have identified the potential of microfluidics in this area and have demonstrated that various steps of conventional radiosynthesis can be replaced by microfluidic devices. However, despite promising results that stir up the interest in the scientific community, none of these inventions has found commercial applications with broad use yet. This article will review the technologies reported to date and analyze the unmet needs that will have to be addressed before microfluidic technology has a chance of becoming a viable and truly advantageous method of preparation of commercial radiopharmaceuticals. The latter mostly center around Positron Emission Tomography (PET) biomarkers.

Radiopharmaceuticals in preclinical and clinical development for monitoring of therapy with PET

This review article discusses PET agents, other than (18)F-FDG, with the potential to monitor the response to therapy before, during, or after therapeutic intervention. This review deals primarily with non-(18)F-FDG PET tracers that are in the final stages of preclinical development or in the early stages of clinical application for monitoring the therapeutic response. Four sections related to the nature of the tracers are included: radiotracers of DNA synthesis, such as the 2 most promising agents, the thymidine analogs 3'-(18)F-fluoro-3'-deoxythymidine and (18)F-1-(2'-deoxy-2'-fluoro-beta-d-arabinofuranosyl)thymine; agents for PET imaging of hypoxia within tumors, such as (60/62/64)Cu-labeled diacetyl-bis(N(4)-methylthiosemicarbazone) and (18)F-fluoromisonidazole; amino acids for PET imaging, including the most popular such agent, l-[methyl-(11)C]methionine; and agents for the imaging of tumor expression of androgen and estrogen receptors, such as 16beta-(18)F-fluoro-5alpha-dihydrotestosterone and 16alpha-(18)F-fluoro-17beta-estradiol, respectively.

Molecular imaging of cancer: evaluating characters of individual cancer by PET/SPECT imaging

The present status of cancer molecular imaging (MI) with nuclear medicine techniques is reviewed, highlighting the Japanese activities in this field. With the progress in MI research, including significant contributions from Japanese studies, it has become possible to noninvasively evaluate various important characters of cancer in clinical patients, such as metabolism, cellular proliferation, tumor hypoxia, and receptor expression. Tumor metabolic information is used for tumor characterization, treatment response evaluation, and prognosis prediction. Hypoxia imaging is used for treatment planning and predicting treatment response. Receptor imaging can be used for the selection of the candidate for receptor-targeted treatment. Various novel probes that can target cancer-associated antigens, various cellular growth factor receptors, tumor angiogenesis, and so on, are under development, aiming for clinical evaluation. Application of radiolabeled ligands for treatment (targeted internal radiation therapy) is another important field in which MI technique can play a critical role. MI, which can deliver the outcome of basic oncological research to the bedside, is essential translational research for improved individualized patient management, and further advances in MI studies are eagerly awaited.

[18F]Fluorothymidine positron emission tomography before and 7 days after gefitinib treatment predicts response in patients with advanced adenocarcinoma of the lung

PURPOSE

To evaluate the usefulness of 3'-deoxy-3'-[18F]fluorothymidine (FLT)-positron emission tomography (PET) for predicting response and patient outcome of gefitinib therapy in patients with adenocarcinoma of the lung.

EXPERIMENTAL DESIGN

Nonsmokers with advanced or recurrent adenocarcinoma of the lung were eligible. FLT-PET images of the thorax were obtained before and 7 days after the start of gefitinib (250 mg/d) therapy, the maximum standardized uptake values (SUVmax) of primary tumors were measured, and the percent changes in SUVmax were calculated. After 6 weeks of therapy, the responses were assessed by computed tomography of the chest.

RESULTS

Among 31 patients who were enrolled, we analyzed 28 patients for whom we had complete data. Chest computed tomography revealed partial response in 14 (50%), stable disease in 4 (14%), and progressive disease in 10 (36%) after 6 weeks of treatment. Pretreatment SUVmax of the tumors did not differ between responders and nonresponders. At 7 days after the initiation of therapy, the percent changes in SUVmax were significantly different (-36.0 +/- 15.4% versus 10.1 +/- 19.5%; P < 0.001). Decrease of > 10.9% in SUVmax was used as the criterion for predicting response. The positive and negative predictive values were both 92.9%. The time to progression was significantly longer in FLT-PET responders than nonresponders (median, 7.9 versus 1.2 months; P = 0.0041).

CONCLUSION

FLT-PET can predict response to gefitinib 7 days after treatment in nonsmokers with advanced adenocarcinoma of the lung. The change in tumor SUVmax obtained by FLT-PET seems to be a promising predictive variable.

The role of DNA synthesis imaging in cancer in the era of targeted therapeutics

Non-specific targets such as DNA and microtubules have been the mainstay of cancer therapeutics and the most effective clinical agents until a decade ago. Advances in genetics, molecular and cellular biology over the past decade led to the development of a new generation of agents that are far more specific and effective. In contrast to progress seen with therapeutic agents, general monitoring targets such as proliferation imaging are just gaining momentum and targeted imaging is still in its infancy. In these paradoxical times, this review assesses the role of proliferation imaging in monitoring the efficacy of targeted therapeutics.

A theoretical framework for prescribing radiotherapy dose distributions using patient-specific biological information

We present a formalism for using functional imaging both to derive patient-specific radiobiological properties and consequently to prescribe optimal nonuniform radiotherapy dose distributions. The ability to quantitatively assess the response to an initial course of radiotherapy would allow the derivation of radiobiological parameters for individual patients. Both an iterative optimization and an analytical approach to this problem were investigated and illustrated by application to the linear-quadratic model of cell killing using simulated parametric data for a modeled tumor. Potential gains in local control were assessed by comparing uniform dose distributions with optimized dose distributions of equal integral dose. The effect on local prescribed dose of variations in effective radiosensitivity, tumor burden, and proliferation rate was investigated, with results suggesting that dose variations would be significant but clinically achievable. The sensitivity of derived parameters to image noise and the effect of varying the initial fractionation and imaging schedule were assessed. The analytical approach proved remarkably robust, with 10% image noise resulting in dose errors of approximately 1% for a clinically relevant set of parameters. Potential benefits were demonstrated by using this formalism to prescribe nonuniform dose distributions for model tumors using a range of literature-derived parameters. The redistribution of dose improved tumor control probability by factors between 1.03 and 4.27 for a range of model tumors.

Targeted molecular imaging in oncology: focus on radiation therapy

Anatomically based technologies (computed tomography scans, magnetic resonance imaging, and so on) are in routine use in radiotherapy for planning and assessment purposes. Even with improvements in imaging, however, radiotherapy is still limited in efficacy and toxicity in certain applications. Further advances may be provided by technologies that image the molecular activities of tumors and normal tissues. Possible uses for molecular imaging include better localization of tumor regions and early assay for the radiation response of tumors and normal tissues. Critical to the success of this approach is the identification and validation of molecular probes that are suitable in the radiotherapy context. Recent developments in molecular-imaging probes and integration of functional imaging with radiotherapy are promising. This review focuses on recent advances in molecular imaging strategies and probes that may aid in improving the efficacy of radiotherapy.