C11-acetate and F-18 FDG PET for men with prostate cancer bone metastases: relative findings and response to therapy

Synthesis of oncological [11C]radiopharmaceuticals for clinical PET

Positron emission tomography (PET) is a nuclear medicine modality which provides quantitative images of biological processes in vivo at the molecular level. Several PET radiopharmaceuticals labeled with short-lived isotopes such as (18)F and (11)C were developed in order to trace specific cellular and molecular pathways with the aim of enhancing clinical applications. Among these [(11)C]radiopharmaceuticals are N-[(11)C]methyl-choline ([(11)C]choline), l-(S-methyl-[(11)C])methionine ([(11)C]methionine) and 1-[(11)C]acetate ([(11)C]acetate), which have gained an important role in oncology where the application of 2-[(18)F]fluoro-2-deoxy-d-glucose ([(18)F]FDG) is suboptimal. Nevertheless, the production of these radiopharmaceuticals did not reach the same level of standardization as for [(18)F]FDG synthesis. This review describes the most recent developments in the synthesis of the above-mentioned [(11)C]radiopharmaceuticals aiming to increase the availability and hence the use of [(11)C]choline, [(11)C]methionine and [(11)C]acetate in clinical practice.

Modern Detection of Prostate Cancer's Bone Metastasis: Is the Bone Scan Era Over?

Prostate cancer cells have an exquisite tropism for bone, which clinically translates into the highest rate of bone metastases amongst male cancers. Although in the latest years there has been an active development of new "bone targeted" therapies, modern diagnostic techniques for bone metastases still relies mostly on (99m)Tc bone scanning (BS) and plain X-ray. BS dramatically lacks specificity and sensitivity. Recent publications using modern imaging technologies have clearly pinpointed that BS grossly underestimates the true prevalence of bone metastasis. In addition BS does not allow tumour measurement and is, therefore, not appropriate to monitor response to therapy. This might be extremely important in patients harbouring high-risk localized disease that are eventually candidate for local therapy. Here we reviewed what are the emerging imaging strategies that are likely to supplant BS and to what extent they can be used in the clinic already.

FDG PET/CT demonstration of pancreatic metastasis from prostate cancer

We report the hybrid FDG PET/CT appearance of a biopsy-proven pancreatic metastasis from prostate cancer in a man with castrate-resistant metastatic disease. The common sites of metastases from prostate cancer are bone and locoregional lymph nodes. Pancreas is an atypical location of metastasis from prostate cancer. PET/CT in this case helped with the targeted pathologic confirmation to differentiate primary pancreatic tumor from an unusual metastasis from prostate cancer which in turn impacted the clinical management.

Androgen-independent molecular imaging vectors to detect castration-resistant and metastatic prostate cancer

Prostate-specific promoters are frequently employed in gene-mediated molecular imaging and therapeutic vectors to diagnose and treat castration-resistant prostate cancer (CRPC) that emerges from hormone ablation therapy. Many of the conventional prostate-specific promoters rely on the androgen axis to drive gene expression. However, considering the cancer heterogeneity and varying androgen receptor status, we herein evaluated the utility of prostate-specific enhancing sequence (PSES), an androgen-independent promoter in CRPC. The PSES is a fused enhancer derived from the prostate-specific antigen (PSA) and prostate-specific membrane antigen gene regulatory region. We augmented the activity of PSES by the two-step transcriptional amplification (TSTA) system to drive the expression of imaging reporter genes for either bioluminescent or positron emission tomography (PET) imaging. The engineered PSES-TSTA system exhibits greatly elevated transcriptional activity, androgen independency, and strong prostate specificity, verified in cell culture and preclinical animal experimentations. These advantageous features of PSES-TSTA elicit superior gene expression capability for CRPC in comparison with the androgen-dependent PSA promoter-driven system. In preclinical settings, we showed robust PET imaging capacity of PSES-TSTA in a castrated prostate xenograft model. Moreover, intravenous administrated PSES-TSTA bioluminescent vector correctly identified tibial bone marrow metastases in 9 of 9 animals, whereas NaF- and FDG-PET was unable to detect the lesions. Taken together, this study showed the promising utility of a potent, androgen-independent, and prostate cancer-specific expression system in directing gene-based molecular imaging in CRPC, even in the context of androgen deprivation therapy.

Do androgens control the uptake of 18F-FDG, 11C-choline and 11C-acetate in human prostate cancer cell lines?

PURPOSE

The aim of this study was to evaluate the impact of androgen ablation therapy in different prostate cancer (PCa) cell lines--reflecting different stages of the disease--on (18)F-fluorodeoxyglucose (FDG), 11C-choline and 11C-acetate uptake.

METHODS

Uptake experiments were performed in androgen-sensitive (LNCaP, PC346C) and independent cell lines (22Rv1, PC346DCC, PC-3) as well as in a benign prostatic hyperplasia (BPH-1) cell line. Tracer uptake was assessed under androgen ablation. Results of the cancer cell lines were normalized to those of BPH-1. To evaluate the effect of androgen on the uptake of 18F-FDG, 11C-choline and 11C-acetate in PCa cell lines, 10(-8) M R1881, 10(-10) M R1881, the combination of 10(-10) M R1881 plus 10(-6) M Casodex or 10(-6) M Casodex alone were added in parallel cell cultures 1 day before uptake experiments. Uptake in androgen-supplemented cell cultures was compared to the uptake under androgen deprivation. Uptake was corrected for cell number using protein content.

RESULTS

Compared to BPH-1, a higher 18F-FDG uptake was observed only in PC346C cells, whereas a higher 11C-choline and markedly increased 11C-acetate uptake was seen in all cancer cell lines. Androgens significantly modulated the uptake of 18F-FDG in LNCaP, PC346C and 22Rv1 cells, and of 11C-choline in the PC346C and 22Rv1 cell line. No androgenic effect on 11C-choline and 18F-FDG uptake was observed in PC-3 and PC346DCC cells. 11C-Acetate uptake was independent of androgen status in all PCa cell lines studied.

CONCLUSION

18F-FDG uptake in PCa cell lines showed the highest variability and strongest androgen effect, suggesting its poor potential for metabolic imaging of advanced PCa. In contrast to 18F-FDG and 11C-choline, 11C-acetate uptake was unaffected by androgens and thus 11C-acetate seems best for monitoring PCa progression.

Role of glutamine in cancer: therapeutic and imaging implications

Metabolic imaging has great clinical potential in cancer because perturbations of metabolism are common hallmarks of malignant cellular transformation. Novel imaging strategies focused on glutamine could provide a valuable complement to (18)F-FDG PET, because glutamine complements glucose in the metabolic platforms that support tumor growth at the cellular level. Furthermore, recent work has demonstrated that distinct aspects of glutamine metabolism are under the control of oncogenes and tumor suppressors. It is plausible that imaging glutamine metabolism could predict both the presence of specific transforming mutations in the tumor and the sensitivity to therapeutic agents designed to target glutamine use. Here, we review the essential aspects of glutamine metabolism in cancer cells and discuss opportunities for imaging in cancer patients.