Radiobiological mechanisms of radium-223 dichloride: a nonclinical study

This study aimed to elucidate the radiobiological mechanisms of radium-223 dichloride ([223Ra]RaCl2)—an FDA-approved agent for metastatic castration-resistant prostate cancer—by investigating its in vitro and in vivo toxic effects. Using both the CCK8 and clonogenic assays, our in vitro experiments evaluated the inhibition of cell proliferation in response to variations in applied activity and exposure duration in human cancer cell lines (MDA-MB-231, BxPC3, A549, and PC3) as well as in rat pancreatic cancer cells (AR42J). Molecular analyses utilizing SDS-PAGE characterized the activation of specific cell death pathways. Additionally, an in vivo investigation employing intravenous administration further examined the systemic toxicity of [223Ra]RaCl2 by monitoring animal mortality, body weight, and hematological parameters following treatment with varying activity levels (74, 148, and 222 kBq/head). [223Ra]RaCl2 significantly inhibited cell proliferation in an applied activity- and time-dependent manner in human cancer cell lines, whereas AR42J cells showed relative resistance. Molecular findings revealed that BxPC3 cells underwent apoptosis via caspase-3 cleavage; PC3 cells experienced pyroptosis marked by gasdermin E (GSDME) activation and caspase-7 cleavage; and MDA-MB-231 cells exhibited enhanced PARP-1 activation indicative of DNA double-strand breaks. In vivo, treated animals demonstrated significant differences in mortality, body weight, and hematological parameters compared to controls, mirroring myelosuppressive effects typical of radiotherapy. The findings provide critical insights into the differential cytotoxic mechanisms of [223Ra]RaCl2 across various cancer cell types and highlight its systemic toxicity in vivo. This improved understanding may facilitate the development of safer and more effective therapeutic radiopharmaceuticals based on [223Ra]RaCl2.