Use of radionuclides in cancer research and treatment

Systemic delivery and SPECT/CT in vivo imaging of 125I-labelled oncolytic adenoviral mutants in models of pancreatic cancer

Early phase clinical trials have demonstrated good therapeutic index for oncolytic adenoviruses in patients with solid tumours when administered intratumorally, resulting in local tumour elimination. Entrapment and binding of adenovirus to erythrocytes, blood factors, and neutralising antibodies have prevented efficient systemic delivery and targeting of distant lesions in the clinic. We previously generated the novel replication-selective Ad-3∆-A20T to improve tumour targeting by increasing the viral dose at distant sites. Here, we developed a protocol to directly radiolabel the virus for rapid and sensitive detection by single-photon emitted computed tomography (SPECT/CT) providing a convenient method for determining biodistribution following intravenous administration in murine models. Longitudinal whole-body scans, demonstrated efficient viral uptake in pancreatic Suit-2 and Panc04.03 xenografts with trace amounts of ¹²⁵I-Ad-3∆-A20T up to 48 h after tail vein delivery. Hepatic and splenic radioactivity decreased over time. Analysis of tissues harvested at the end of the study, confirmed potency and selectivity of mutant viruses. Ad-3∆-A20T-treated animals showed higher viral genome copy numbers and E1A gene expression in tumors than in liver and spleen compared to Ad5wt. Our direct radiolabeling approach, allows for immediate screening of novel oncolytic adenoviruses and selection of optimal viral genome alterations to generate improved mutants.

Radionuclide-Labeled Peptides for Imaging and Treatment of CXCR4- Overexpressing Malignant Tumors

Malignant tumors are a major cause of death. The lack of methods that provide an early diagnosis and adequate treatment of cancers is the main obstacle to precision medicine. The C-X-C chemokine receptor 4 (CXCR4) is overexpressed in various tumors and plays a key role in tumor pathogenesis. Therefore, CXCR4-targeted molecular imaging can quickly and accurately detect and quantify CXCR4 abnormalities in real time. The expression level and activation status of CXCR4 are very important for screening susceptible populations and providing an accurate diagnosis and optimal treatment. In view of the fact that radionuclide-labeled peptides have become widely used for the diagnosis and treatment of tumors, this manuscript reviews the potential of different radionuclide-labeled peptide inhibitors for the targeted imaging of CXCR4- positive tumors and targeted treatment. The article also discusses the specificity and in vivo distribution of radionuclide-labeled peptide inhibitors, and translation of these inhibitors to the clinic.

Fluorescent gallium and indium bis(thiosemicarbazonates) and their radiolabelled analogues: synthesis, structures and cellular confocal fluorescence imaging investigations

New fluorescent and biocompatible aromatic Ga(III)- and In(III)-bis(thiosemicarbazonato) complexes for dual mode optical and PET or SPECT molecular imaging have been synthesised via a synthetic method based on transmetallation reactions from Zn(II) precursors. Complexes have been fully characterised in the solid state by single crystal X-ray diffraction and in solution by spectroscopic methods (UV/Vis, fluorescence, (1)H and (13)C{(1)H} NMR). The bis(thiosemicarbazones) radiolabelled rapidly in high yields under mild conditions with (111)In (a gamma and Auger emitter for SPECT imaging and radiotherapy with t(1/2) = 2.8 d) and (68)Ga (a generator-available positron emitter for PET imaging with t(1/2) = 68 min). Cytotoxicity and biolocalisation studies using confocal fluorescence imaging and fluorescence lifetime imaging (FLIM) techniques have been used to study their in vitro activities and stabilities in HeLa and PC-3 cells to ascertain their suitability as synthetic scaffolds for future multimodality molecular imaging in cancer diagnosis and therapy. The observation that the indium complexes show certain nuclear uptake could be of relevance towards developing (111)In therapeutic agents based on Auger electron emission to induce DNA damage.