Transplanted Murine Tumours SPECT Imaging with 99mTc Delivered with an Artificial Recombinant Protein

99mTc is a well-known radionuclide widely used and readily available for medical imaging. Despite this, the 99mTc isotope is rarely utilized for tumour imaging due to the lack of agents that can selectively deliver it to tumours. However, the use of immunologically compatible recombinant proteins, which combine metal-binding sites and tumour-specific ligands, shows promise for utilizing 99mTc in the early detection of tumours. To illustrate this, a protein called E1b, containing a metal binding center with ELP repeats, tumour-specific ligands recognizing integrin αvβ3 and nucleolin, as well as a short Cys-rich sequence, was artificially designed. This protein was produced in E. coli and purified to homogeneity using metal-chelate chromatography. In experiments, C57Bl/6 and Balb/C mice with subcutaneously grafted lung carcinoma (LLC) or mammary gland adenocarcinoma (Ca755, EMT6, or 4T1) were used to test 99mTc-E1b selectivity and the kinetics of isotope retention. The mice were intravenously injected with approximately 80 MBq of 99mTc in complex with E1b, which had been freshly purified using gel-chromatography. The biodistribution of the labeled protein was then studied using the SPECT/CT imaging method within 24 h. The ratio of radionuclide distribution in the tumour versus the adjacent normal tissue (T/N) steadily increased over the 24-h period, reaching 15.7±4.2 for EMT6, 16.5±3.8 for Ca755, 6.7±4.2 for LLC, and 7.5±3.1 for 4T1.