Comparative Analysis between [(18)F]Fludarabine-PET and [(18)F]FDG-PET in a Murine Model of Inflammation

FDG-PET/CT in the Monitoring of Lymphoma Immunotherapy Response: Current Status and Future Prospects

Cancer immunotherapy has been extensively investigated in lymphoma over the last three decades. This new treatment modality is now established as a way to manage and maintain several stages and subtypes of lymphoma. The establishment of this novel therapy has necessitated the development of new imaging response criteria to evaluate and follow up with cancer patients. Several FDG PET/CT-based response criteria have emerged to address and encompass the various most commonly observed response patterns. Many of the proposed response criteria are currently being used to evaluate and predict responses. The purpose of this review is to address the efficacy and side effects of cancer immunotherapy and to correlate this with the proposed criteria and relevant patterns of FDG PET/CT in lymphoma immunotherapy as applicable. The latest updates and future prospects in lymphoma immunotherapy, as well as PET/CT potentials, will be discussed.

First-in-Man Noninvasive Initial Diagnostic Approach of Primary CNS Lymphoma Versus Glioblastoma Using PET With 18 F-Fludarabine and l -[methyl- 11 C]Methionine

OBJECTIVES

This study sought to assess 18 F-fludarabine ( 18 F-FLUDA) PET/CT's ability in differentiating primary central nervous system lymphomas (PCNSLs) from glioblastoma multiformes (GBMs).

PATIENTS AND METHODS

Patients harboring either PCNSL (n = 8) before any treatment, PCNSL treated using corticosteroids (PCNSLh; n = 10), or GBM (n = 13) were investigated with conventional MRI and PET/CT, using 11 C-MET and 18 F-FLUDA. The main parameters measured with each tracer were SUV T and T/N ratios for the first 30 minutes of 11 C-MET acquisition, as well as at 3 different times after 18 F-FLUDA injection. The early 18 F-FLUDA uptake within the first minute of injection was equally considered, whereas this parameter was combined with the later uptakes to obtain R FLUDA 2 and R FLUDA 3 ratios.

RESULTS

No significant differences in 11 C-MET uptakes were observed among PCNSL, PCNSLh, and GBM. With 18 F-FLUDA, a clear difference in dynamic GBM uptake was observed, which decreased over time after an early maximum, as compared with that of PCNSL, which steadily increased over time, PCNSLh exhibiting intermediate values. The most discriminative parameters consisting of R FLUDA 2 and R FLUDA 3 integrated the early tracer uptake (first 60 seconds), thereby provided 100% specificity and sensitivity.

CONCLUSIONS

18 F-FLUDA was shown to likely be a promising radiopharmaceutical for differentiating PCNSL from other malignancies, although a pretreatment with corticosteroids might compromise this differential diagnostic ability. The diagnostic role of 18 F-FLUDA should be further investigating, along with its potential of defining therapeutic strategies in patients with PCNSL, while assessing the treatments' effectiveness.

Novel Al18F-NOTA-Conjugated Lactam-Cyclized α-Melanocyte-Stimulating Hormone Peptides with Enhanced Melanoma Uptake

The purpose of this study was to evaluate the effect of linker on tumor targeting and biodistribution of Al18F-NOTA-PEG2Nle-CycMSHhex {Al18F-1,4,7-triazacyclononane-1,4,7-triyl-triacetic acid-poly(ethylene glycol)-Nle-c[Asp-His-DPhe-Arg-Trp-Lys]-CONH2} and Al18F-NOTA-AocNle-CycMSHhex {Al18F-NOTA-8-aminooctanoic acid-Nle-CycMSHhex} on melanoma-bearing mice. NOTA-PEG2Nle-CycMSHhex and NOTA-AocNle-CycMSHhex were synthesized using fluorenylmethoxycarbonyl (Fmoc) chemistry. The melanocortin-1 (MC1) receptor binding affinities of the peptides were determined on B16/F10 melanoma cells. The biodistribution of Al18F-NOTA-PEG2Nle-CycMSHhex and Al18F-NOTA-AocNle-CycMSHhex was determined on B16/F10 melanoma-bearing C57 mice. The melanoma imaging property of Al18F-NOTA-PEG2Nle-CycMSHhex was further examined on B16/F10 melanoma-bearing C57 mice because of its higher melanoma uptake and lower renal uptake than that of Al18F-NOTA-AocNle-CycMSHhex. The IC50 values of NOTA-PEG2/AocNle-CycMSHhex were 1.24 ± 0.07 and 2.75 ± 0.48 nM on B10/F10 cells. Al18F-NOTA-PEG2Nle-CycMSHhex and Al18F-NOTA-AocNle-CycMSHhex were readily prepared with more than 55% of radiolabeling yields and displayed melanocortin-1 receptor (MC1R)-specific binding on B16/F10 cells. Al18F-NOTA-PEG2Nle-CycMSHhex exhibited higher tumor uptake and lower kidney and liver uptake than Al18F-NOTA-AocNle-CycMSHhex at 1 and 2 h post injection. The tumor and renal uptakes of Al18F-NOTA-PEG2Nle-CycMSHhex were 17.44 ± 0.76 and 2.07 ± 0.43% ID/g at 1 h post injection, respectively. Al18F-NOTA-PEG2Nle-CycMSHhex showed the high tumor to normal organ uptake ratios after 1 h post injection. The B16/F10 melanoma lesions could be clearly visualized by positron emission tomography (PET) using Al18F-NOTA-PEG2Nle-CycMSHhex as an imaging probe at 1 and 2 h post injection. Overall, high tumor uptake, low kidney and liver uptake, and fast urinary clearance of Al18F-NOTA-PEG2Nle-CycMSHhex highlighted its potential as an MC1R-targeted imaging probe for melanoma detection.

Highly Efficient Separation of Ultratrace Radioactive Copper Using a Flow Electrolysis Cell

Preparing compounds containing the radioisotope ⁶⁴Cu for use in positron emission tomography cancer diagnostics is an ongoing area of research. In this study, a highly efficient separation method to recover ⁶⁴Cu generated by irradiating the target ⁶⁴Ni with a proton beam was developed by employing a flow electrolysis cell (FE). This system consists of (1) applying a reduction potential for the selective adsorption of ⁶⁴Cu from the target solution when dissolved in HCl and (2) recovering the ⁶⁴Cu deposited onto the carbon working electrode by desorbing it from the FE during elution with 10 mmol/L HNO₃, which applies an oxidation potential. The ⁶⁴Cu was selectively eluted at approximately 30 min under a flow rate of 0.5 mL/min from the injection to recovery. The newly developed flow electrolysis system can separate the femtomolar level of ultratrace radioisotopes from the larger amount of target metals as an alternative to conventional column chromatography.

Smart-Polypeptide-Coated Mesoporous Fe3O4 Nanoparticles: Non-Interventional Target-Embolization/Thermal Ablation and Multimodal Imaging Combination Theranostics for Solid Tumors

Tumor theranostics hold great potential for personalized medicine in the future, and transcatheter arterial embolization (TAE) is an important clinical treatment for unresectable or hypervascular tumors. In order to break the limitation, simplify the procedure of TAE, and achieve ideal combinatorial theranostic capability, here, a kind of triblock-polypeptide-coated perfluoropentane-loaded mesoporous Fe₃O₄ nanocomposites (PFP-m-Fe₃O₄@PGTTCs) were prepared for non-interventional target-embolization, magnetic hyperthermia, and multimodal imaging combination theranostics of solid tumors. The results of systematic animal experiments by H22-tumor-bearing mice and VX2-tumor-bearing rabbits in vivo indicated that PFP-m-Fe₃O₄@PGTTC-6.3 has specific tumor accumulation and embolization effects. The tumors' growth has been inhibited and the tumors disappeared 4 weeks and ≤15 days post-injection with embolization and magnetic hyperthermia combination therapy, respectively. The results also showed an excellent effect of magnetic resonance/ultrasound/SPECT multimodal imaging. This pH-responsive non-interventional embolization combinatorial theranostics system provides a novel embolization and multifunctional theranostic candidate for solid tumors.

FDG-PET/CT in Lymphoma: Where Do We Go Now?

18F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDG-PET/CT) is an essential part of the management of patients with lymphoma at staging and response evaluation. Efforts to standardize PET acquisition and reporting, including the 5-point Deauville scale, have enabled PET to become a surrogate for treatment success or failure in common lymphoma subtypes. This review summarizes the key clinical-trial evidence that supports PET-directed personalized approaches in lymphoma but also points out the potential place of innovative PET/CT metrics or new radiopharmaceuticals in the future.

Hyperpolarized 13 C magnetic resonance imaging for noninvasive assessment of tissue inflammation

Inflammation is a central mechanism underlying numerous diseases and incorporates multiple known and potential future therapeutic targets. However, progress in developing novel immunomodulatory therapies has been slowed by a need for improvement in noninvasive biomarkers to accurately monitor the initiation, development and resolution of immune responses as well as their response to therapies. Hyperpolarized magnetic resonance imaging (MRI) is an emerging molecular imaging technique with the potential to assess immune cell responses by exploiting characteristic metabolic reprogramming in activated immune cells to support their function. Using specific metabolic tracers, hyperpolarized MRI can be used to produce detailed images of tissues producing lactate, a key metabolic signature in activated immune cells. This method has the potential to further our understanding of inflammatory processes across different diseases in human subjects as well as in preclinical models. This review discusses the application of hyperpolarized MRI to the imaging of inflammation, as well as the progress made towards the clinical translation of this emerging technique.

[18F]-Fludarabine for Hematological Malignancies

With the emergence of PET/CT using ¹⁸F-FDG, molecular imaging has become the reference for lymphoma lesion detection, tumor staging, and response assessment. According to the response in some lymphoma subtypes it has also been utilized for prognostication of disease. Although ¹⁸F-FDG has proved useful in the management of patients with lymphoma, the specificity of ¹⁸F-FDG uptake has been critically questioned, and is not without flaws. Its dependence on glucose metabolism, which may indiscriminately increase in benign conditions, can affect the ¹⁸F-FDG uptake in tumors and may explain the causes of false-positive imaging data. Considering these drawbacks, ¹⁸F-fludarabine, an adenine nucleoside analog, was developed as a novel PET imaging probe. An efficient and fully automated radiosynthesis has been implemented and, subsequently preclinical studies in xenograft murine models of hematological maligancies (follicular lymphoma, CNS lymphoma, multiple myeloma) were conducted with this novel PET probe in parallel with ¹⁸F-FDG. The results demonstrated several crucial points: tumor-specific targeting, weaker uptake in inflammatory processes, stronger correlation between quantitative values extracted from [¹⁸]F-fludarabine and histology when compared to ¹⁸F-FDG-PET, robustness during immunotherapy with rituximab, divergent responses between CNS lymphoma and glioblastoma (GBM). All these favorable findings permitted to establish a “first in man” study where 10 patients were enrolled. In DLBCL patients, increased uptake was observed in sites considered abnormal by CT and [¹⁸F]FDG; in two patients discrepancies were observed in comparison with ¹⁸F-FDG. In CLL patients, the uptake coincided with sites expected to be involved and displayed a significant uptake in hematopoietic bone marrow. No uptake was observed, whatever the disease group, in the cardiac muscle and brain. Moreover, its mean effective dose was below the effective dose reported for ¹⁸F-FDG. These preclinical and clinical findings revealed a marked specificity of ¹⁸F-fludarabine for lymphoma tissues. Furthermore, it might well be a robust tool for correctly quantifying the disease, in the presence of confounding inflammatory processes, thus avoiding false-positive results, and an innovative approach for imaging hematological malignancies.

[18F]Fludarabine-PET as a promising tool for differentiating CNS lymphoma and glioblastoma: Comparative analysis with [18F]FDG in human xenograft models

This paper investigated whether positron emission tomography (PET) imaging with [¹⁸F]fludarabine ([¹⁸F]FDB) can help to differentiate central nervous system lymphoma (CNSL) from glioblastoma (GBM), which is a crucial issue in the diagnosis and management of patients with these aggressive brain tumors. Multimodal analyses with [¹⁸F]fluorodeoxyglucose ([¹⁸F]FDG), magnetic resonance imaging (MRI) and histology have also been considered to address the specificity of [¹⁸F]FDB for CNSL. Methods: Nude rats were implanted with human MC116 lymphoma-cells (n = 9) or U87 glioma-cells (n = 4). Tumor growth was monitored by MRI, with T2-weighted sequence for anatomical features and T1-weighted with gadolinium (Gd) enhancement for blood brain barrier (BBB) permeability assessment. For PET investigation, [¹⁸F]FDB or [¹⁸F]FDG (~11 MBq) were injected via tail vein and dynamic PET images were acquired up to 90 min after radiotracer injection. Paired scans of the same rat with the two [¹⁸F]-labelled radiotracers were investigated. Initial volumes of interest were manually delineated on T2w images and set on co-registered PET images and tumor-to-background ratio (TBR) was calculated to semi-quantitatively assess the tracer accumulation in the tumor. A tile-based method for image analysis was developed in order to make comparative analysis between radiotracer uptake and values extracted from immunohistochemistry staining. Results: In the lymphoma model, PET time-activity curves (TACs) revealed a differential response of [¹⁸F]FDB between tumoral and healthy tissues with average TBR varying from 2.45 to 3.16 between 5 to 90 min post-injection. In contrast, [¹⁸F]FDG demonstrated similar uptake profiles for tumoral and normal regions with TBR varying from 0.84 to 1.06 between these two time points. In the glioblastoma (GBM) model, the average TBRs were from 2.14 to 1.01 for [¹⁸F]FDB and from 0.95 to 1.65 for [¹⁸F]FDG. Therefore, inter-model comparisons showed significantly divergent responses (p < 0.01) of [¹⁸F]FDB between lymphoma and GBM, while [¹⁸F]FDG demonstrated overlap (p = 0.04) between the groups. Tumor characterization with histology (based mainly on Hoechst and CD79), as well as with MRI was overall in better agreement with [¹⁸F]FDB-PET than [¹⁸F]FDG with regard to tumor selectivity. Conclusions: [¹⁸F]FDB-PET demonstrated considerably greater specificity for CNSL when compared to [¹⁸F]FDG. It also permitted a more precise definition of target volume compared to contrast-enhanced MRI. Therefore, the potential of [¹⁸F]FDB-PET to distinguish CNSL from GBM is quite evident and will be further investigated in humans.

[18F]Fludarabine-PET in a murine model of multiple myeloma

Purpose

Multiple myeloma (MM) is a haematological malignancy that affects plasma cells in the bone marrow. Recently, [¹⁸F]fludarabine has been introduced as an innovative PET radiotracer for imaging lymphoma. It demonstrated a great potential for accurate imaging of lymphoproliferative disorders. With the goal to question the usefulness of [¹⁸F]fludarabine-PET in other haematological diseases, an in vivo MM model was investigated.

Methods

RPMI8226-GFP-Luc MM cells expressing the green fluorescent protein (GFP) as well as the luciferase reporter (Luc) were derived from the parental RPMI8226 cells. They were injected subcutaneously into the flank of nude mice. Myeloma tumour growth was followed using bioluminescence-based imaging (BLI) and characterised by immunohistochemistry (IHC). The tumour specificity of [¹⁸F]fludarabine was evaluated and compared to [¹⁸F]FDG.

Results

The tumoural uptake of [¹⁸F]FDG was greater than that of [¹⁸F]fludarabine. However, the quantitative data extracted from IHC stainings were in better agreement with [¹⁸F]fludarabine, when compared to [¹⁸F]FDG. The relationship between the tumoural uptake of [¹⁸F]-labelled tracers and the BLI quantitative data was also in favour of [¹⁸F]fludarabine.

Conclusion

Our results suggest that [¹⁸F]fludarabine-PET might represent an alternative and perhaps more specific modality for MM imaging when compared to [¹⁸F]FDG. Nevertheless, more investigations are required to extend this conclusion to humans.