Comparison of dynamic FDG-microPET study in a rabbit turpentine-induced inflammatory model and in a rabbit VX2 tumor model

Rational development of radiopharmaceuticals for HIV-1

The global battle against HIV-1 would benefit from a sensitive and specific radiopharmaceutical to localize HIV-infected cells. Ideally, this probe would be able to identify latently infected host cells containing replication competent HIV sequences. Clinical and research applications would include assessment of reservoirs, informing clinical management by facilitating assessment of burden of infection in different compartments, monitoring disease progression and monitoring response to therapy. A "rational" development approach could facilitate efficient identification of an appropriate targeted radiopharmaceutical. Rational development starts with understanding characteristics of the disease that can be effectively targeted and then engineering radiopharmaceuticals to hone in on an appropriate target, which in the case of HIV-1 (HIV) might be an HIV-specific product on or in the host cell, a differentially expressed gene product, an integrated DNA sequence specific enzymatic activity, part of the inflammatory response, or a combination of these. This is different from the current approach that starts with a radiopharmaceutical for a target associated with a disease, mostly from autopsy studies, without a strong rationale for the potential to impact patient care. At present, no targeted therapies are available for HIV latency, although a number of approaches are under study. Here we discuss requirements for a radiopharmaceutical useful in strategies targeting persistently infected cells. The radiopharmaceutical for HIV should be developed based on HIV biology, studied in an animal model and then in humans, and ultimately used in clinical and research settings.

Longitudinal PET imaging of muscular inflammation using 18F-DPA-714 and 18F-Alfatide II and differentiation with tumors

AIM

(18)F-DPA-714 is a PET tracer that recognizes macrophage translocator protein (TSPO), and (18)F-Alfatide II ((18)F-AlF-NOTA-E[PEG4-c(RGDfk)]2) is specific for integrin αvβ3. This study aims to apply these two tracers for longitudinal PET imaging of muscular inflammation, and evaluate the value of (18)F-DPA-714 in differentiating inflammation from tumor.

METHODS

RAW264.7 mouse macrophage cells were used for cell uptake analysis of (18)F-DPA-714. A mouse hind limb muscular inflammation model was established by intramuscular injection of turpentine oil. For the inflammation model, PET imaging was performed at different days using (18)F-DPA-714 and (18)F-Alfatide II. The specificity of the imaging probes was tested by co- or pre-injection of PK11195 or unlabeled RGD (Arg-Gly-Asp) peptide. PET imaging using (18)F-DPA-714 was performed in A549, HT29, U87MG, INS-1, and 4T1 xenograft models. Immunofluorescence staining was performed to evaluate infiltrated macrophages and angiogenesis in inflammation and/or tumors.

RESULTS

Uptake of (18)F-DPA-714 in RAW264.7 cells was 45.5% at 1 h after incubation, and could be blocked by PK11195. PET imaging showed increased (18)F-DPA-714 and (18)F-Alfatide II uptake at inflammatory muscles. Peak uptake of (18)F-DPA-714 was seen on day 6 (4.02 ± 0.64 %ID/g), and peak uptake of (18)F-Alfatide II was shown on day 12 (1.87 ± 0.35 %ID/g) at 1 h p.i.. Tracer uptakes could be inhibited by PK11195 for (18)F-DPA-714 or cold RGD for (18)F-Alfatide II. Moreover, macrophage depletion with liposomal clodronate also reduced the local accumulation of both tracers. A549, HT29, U87MG, INS-1, and 4T1 tumor uptakes of (18)F-DPA-714 (0.46 ± 0.28, 0.91 ± 0.08, 1.69 ± 0.67, 1.13 ± 0.33, 1.22 ± 0.55 %ID/g at 1 h p.i., respectively) were significantly lower than inflammation uptake (All P < 0.05).

CONCLUSION

PET imaging using (18)F-DPA-714 as a TSPO targeting tracer could evaluate the dynamics of macrophage activation and infiltration in different stages of inflammatory diseases. The concomitant longitudinal PET imaging with both (18)F-DPA-714 and (18)F-Alfatide II matched the causal relationship between macrophage infiltration and angiogenesis. Moreover, we found (18)F-DPA-714 uptake in several types of tumors is significantly lower than that in inflammatory muscles, suggesting (18)F-DPA-714 PET has the potential for better differentiation of tumor and non-tumor inflammation.

Animal PET for thioacetamide-induced rat cholangiocarcinoma: a novel and reliable platform

PURPOSE

Cholangiocarcinoma (CCA) is a lethal disease afflicting many thousands of patients worldwide. We have previously developed an oral thioacetamide (TAA)-induced model of rat CCA that recapitulates the histologic progression of human CCA. Our objective was to evaluate the feasibility of animal PET in detecting CCA in the setting of the TAA rat model.

PROCEDURES

Male Sprague-Dawley rats (n = 30) were used in this study. Drinking water with TAA 300 mg/l was administered orally in 26 rats, and animal PET was performed at 20 weeks after initiation of TAA. A total of four rats served as controls. Animal PET images were acquired sequentially using both C-11 acetate and 2-deoxy-2-[F-18]fluoro-D-glucose (FDG) to determine the optimal tracer. Dynamic animal PET images were collected to assess the optimal scan time based on the highest tumor-to-liver (T/L) ratio using time-activity curves. Animal PET findings were compared lesion by lesion with the results of autoradiography and the histological data.

RESULTS

FDG animal PET images had a higher T/L ratio compared to images obtained with C-11 acetate as a marker. The optimal scan time for FDG animal PET was determined as 90 min postinjection of the tracer. This was when the T/L ratio reached its peak. Necropsy and histology confirmed the presence of TAA-induced CCA in 22 rats (84.6 %). Static animal PET images showed intense FDG uptake in 17 of the 22 tumor-bearing animals (77.3%). The average T/L ratio was 1.60 +/- 0.09. The sensitivity and specificity of animal PET in the detection of CCA were 77% (17/22) and 100% (4/4), respectively.

CONCLUSIONS

We conclude that animal PET in the setting of the TAA rat model seems to be feasible for the detection of CCA. Future translational studies are needed to confirm and expand our findings.

Optimal dual time point for FDG-PET in the differentiation of benign from malignant lung lesions: a simulation study

Dual time point imaging has been proposed as a means of improving the accuracy of Fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) in the diagnosis of lung malignancy. However, various sampling schedules have been used, which makes direct comparisons between their results difficult. It is unclear whether these schedules have the same accuracy for the diagnosis of lung malignancy, limiting the further development and adoption of these techniques. Although theoretically malignant and benign lesions show increasing difference in FDG uptake with longer uptake periods, the increasing noise due to decay may counteract this advantage and increase variability. In this paper, a method for the design of an optimal dual time point 18F-FDG PET imaging protocol has been proposed to address this issue.