Introduction: Application of therapeutic folate radioconjugates is a promising option for the treatment of folate receptor (FR)-positive tumors, although high uptake of radiofolates in the kidneys remains a critical issue. Recently, it was shown that enhancing the blood circulation of radiofolates results in increased tumor uptake and reduced retention of radioactivity in the kidneys. In this study, we investigated and compared the anti-tumor effects and potential long-term damage to the kidneys after application of an albumin-binding ((177)Lu-cm09), and a conventional ((177)Lu-EC0800) folate radioconjugate.
Methods: In vivo studies were performed with KB tumor-bearing nude mice. (177)Lu-EC0800 and (177)Lu-cm09 were applied at variable quantities (10-30 MBq/mouse), and the tumor growth was monitored over time. Mice without tumors were injected with the same radiofolates and investigated over eight months by determination of creatinine and blood urea nitrogen plasma levels and by measuring renal uptake of (99m)Tc-DMSA using SPECT. At the study end, the morphological changes were examined on renal tissue sections using variable staining methods.
Results: Compared to untreated controls, dose-dependent tumor growth inhibition and prolonged survival was observed in all treated mice. In line with the resulting absorbed dose, the treatment was more effective with (177)Lu-cm09 than with (177)Lu-EC0800, enabling complete tumor remission after application of ≥20MBq (≥28Gy). Application of radiofolates with an absorbed renal dose ≥23 Gy showed increased levels of renal plasma parameters and reduced renal uptake of (99m)Tc-DSMA. Morphological changes observed on tissue sections confirmed radionephropathy of variable stages.
Conclusions: (177)Lu-cm09 showed more favorable anti-tumor effects and significantly less damage to the kidneys compared to (177)Lu-EC0800 as was expected based on improved tumor-to-kidney ratios. It was demonstrated that enhancing the blood circulation time of radiofolates was favorable regarding the risk-benefit profile of a therapeutic application. These results hold promise for future translation of the albumin-binder concept to the clinics, potentially enabling FR-targeted radionuclide therapy in patients.
Keywords: (177)Lu; Albumin-binder; Kidney damage; Radiofolates; Radionephropathy; Radionuclide therapy.
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