Radiolabelled FGF-2 for Imaging Activated Fibroblasts in the Tumor Micro-Environment.

Tumor associated fibroblasts (TAFs) play a key role in tumor growth and metastatization. TAFs overexpress different biomarkers that are usually expressed at low levels in physiological conditions. Among them are the fibroblast growth factor receptors (FGFRs) that bind the fibroblast growth factors (FGFs). In particular, the overexpression of FGFR-2c in tumors has been associated with advanced clinical stages and increased metastatization. Here, we developed a non-invasive tool to evaluate, in vivo, the expression of FGFR-2c in metastatic cancer. This is based on 99mTc-labelled FGF-2. METHODS: 99mTc-FGF-2 was tested in vitro and in vivo in mice bearing allografts of sarcoma cells. Images of 99mTc-FGF-2 were acquired using a new portable high-resolution ultra-sensitive gamma camera for small animal imaging. RESULTS: FGF-2 was labeled with high specific activity but low labelling efficiency, thus requiring post-labeling purification by gel-filtration chromatography. In vitro binding to 2C human keratinocytes showed a Kd of 3.36 × 10-9 M. In mice bearing J774A.1 cell allografts, we observed high and rapid tumor uptake of 99mTc-FGF-2 with a high Tumor/Blood ratio at 24 h post-injection (26.1 %ID/g and 12.9 %ID) with low kidney activity and moderate liver activity. CONCLUSIONS: we labeled FGF-2 with 99mTc and showed nanomolar Kd in vitro with human keratinocytes expressing FGF-2 receptors. In mice, 99mTc-FGF-2 rapidly and efficiently accumulated in tumors expressing FGF-2 receptors. This new radiopharmaceutical could be used in humans to image TAFs.

Three-Dimensional In Vitro Tumor Spheroid Models for Evaluation of Anticancer Therapy: Recent Updates.

Advanced tissue engineering processes and regenerative medicine provide modern strategies for fabricating 3D spheroids. Several different 3D cancer models are being developed to study a variety of cancers. Three-dimensional spheroids can correctly replicate some features of solid tumors (such as the secretion of soluble mediators, drug resistance mechanisms, gene expression patterns and physiological responses) better than 2D cell cultures or animal models. Tumor spheroids are also helpful for precisely reproducing the three-dimensional organization and microenvironmental factors of tumors. Because of these unique properties, the potential of 3D cell aggregates has been emphasized, and they have been utilized in in vitro models for the detection of novel anticancer drugs. This review discusses applications of 3D spheroid models in nuclear medicine for diagnosis and therapy, immunotherapy, and stem cell and photodynamic therapy and also discusses the establishment of the anticancer activity of nanocarriers.

Methods for Radiolabeling Nanoparticles (Part 3): Therapeutic Use.

Following previously published systematic reviews on the diagnostic use of nanoparticles (NPs), in this manuscript, we report published methods for radiolabeling nanoparticles with therapeutic alpha-emitting, beta-emitting, or Auger's electron-emitting isotopes. After analyzing 234 papers, we found that different methods were used with the same isotope and the same type of nanoparticle. The most common type of nanoparticles used are the PLGA and PAMAM nanoparticles, and the most commonly used therapeutic isotope is 177Lu. Regarding labeling methods, the direct encapsulation of the isotope resulted in the most reliable and reproducible technique. Radiolabeled nanoparticles show promising results in metastatic breast and lung cancer, although this field of research needs more clinical studies, mainly on the comparison of nanoparticles with chemotherapy.

Current Status of SPECT Radiopharmaceuticals for Specific Bacteria Imaging.

Imaging infection still represents a challenge for researchers. Despite nuclear medicine (NM) offers valuable tools able to discriminate between infections and inflammation, there is an unmet clinical need to develop new strategies able to specifically target the causative pathogen, to select the best antimicrobial treatment for each patient and to accurately assess therapeutic efficacy. These aspects are commonly addressed by microbiology or histology but the diagnosis often relies on invasive procedures that are prone to contamination or sample bias and do not reflect the spatial heterogeneity of the infective process. Therefore, in the era of personalized medicine and treatment, a lot of efforts are in play to improve a personalized diagnosis. Molecular imaging is an ideal candidate for this purpose and, indeed, research is going fast to this direction aiming to find more selective and proper antimicrobial treatments and to overcome broad-spectrum antibiotic use, which still represents the major cause of bacterial drug-resistance. Several approaches for specifically image bacteria have been proposed and provided encouraging perspectives in preclinical studies. Nevertheless, the majority of these promising approaches are still confined in "bench stages" and crucial issues still need to be addressed before their translation in clinical practice. This review will focus on radiolabeled antibiotics for SPECT imaging of bacteria, their mechanisms of action, their potentiality and limitations for "bed-side" applications.

Present status and future trends in molecular imaging of lymphocytes.

Immune system is emerging as a crucial protagonist in a huge variety of oncologic and non-oncologic conditions including response to vaccines and viral infections (such as SARS-CoV-2). The increasing knowledge of molecular biology underlying these diseases allowed the identification of specific targets and the possibility to use tailored therapies against them. Immunotherapies and vaccines are, indeed, more and more used nowadays for treating infections, cancer and autoimmune diseases and, therefore, there is the need to identify, quantify and monitor immune cell trafficking before and after treatment. This approach will provide crucial information for therapy decision-making. Imaging of B and T-lymphocytes trafficking by using tailored radiopharmaceuticals proved to be a successful nuclear medicine tool. In this review, we will provide an overview of the state of art and future trends for "in vivo" imaging of lymphocyte trafficking and homing by mean of specific receptor-tailored radiopharmaceuticals.

Methods for Radiolabelling Nanoparticles: SPECT Use (Part 1).

The use of nanoparticles (NPs) is rapidly increasing in nuclear medicine (NM) for diagnostic and therapeutic purposes. Their wide use is due to their chemical-physical characteristics and possibility to deliver several molecules. NPs can be synthetised by organic and/or inorganic materials and they can have different size, shape, chemical composition, and charge. These factors influence their biodistribution, clearance, and targeting ability in vivo. NPs can be designed to encapsulate inside the core or bind to the surface several molecules, including radionuclides, for different clinical applications. Either diagnostic or therapeutic radioactive NPs can be synthetised, making a so-called theragnostic tool. To date, there are several methods for radiolabelling NPs that vary depending on both the physical and chemical properties of the NPs and on the isotope used. In this review, we analysed and compared different methods for radiolabelling NPs for single-photon emission computed tomography (SPECT) use.

Methods for Radiolabelling Nanoparticles: PET Use (Part 2).

The use of radiolabelled nanoparticles (NPs) is a promising nuclear medicine tool for diagnostic and therapeutic purposes. Thanks to the heterogeneity of their material (organic or inorganic) and their unique physical and chemical characteristics, they are highly versatile for their use in several medical applications. In particular, they have shown interesting results as radiolabelled probes for positron emission tomography (PET) imaging. The high variability of NP types and the possibility to use several isotopes in the radiolabelling process implies different radiolabelling methods that have been applied over the previous years. In this review, we compare and summarize the different methods for NP radiolabelling with the most frequently used PET isotopes.

Synthesis and Biodistribution of 99mTc-Labeled PLGA Nanoparticles by Microfluidic Technique.

The aim of present study was to develop radiolabeled NPs to overcome the limitations of fluorescence with theranostic potential. Synthesis of PLGA-NPs loaded with technetium-99m was based on a Dean-Vortex-Bifurcation Mixer (DVBM) using an innovative microfluidic technique with high batch-to-batch reproducibility and tailored-made size of NPs. Eighteen different formulations were tested and characterized for particle size, zeta potential, polydispersity index, labeling efficiency, and in vitro stability. Overall, physical characterization by dynamic light scattering (DLS) showed an increase in particle size after radiolabeling probably due to the incorporation of the isotope into the PLGA-NPs shell. NPs of 60 nm (obtained by 5:1 PVA:PLGA ratio and 15 mL/min TFR with 99mTc included in PVA) had high labeling efficiency (94.20 ± 5.83%) and >80% stability after 24 h and showed optimal biodistribution in BALB/c mice. In conclusion, we confirmed the possibility of radiolabeling NPs with 99mTc using the microfluidics and provide best formulation for tumor targeting studies.