Production and synthesis of a novel 191Pt-labeled platinum complex and evaluation of its biodistribution in healthy mice.

We previously reported that our sugar-conjugated platinum complex (cis-dichloro [(2-fluoro-α-d-glucopylanosidyl) propane-1,3-diamine] platinum: FGC-Pt) has low toxicity and tumor growth inhibitory effect comparable to that of cisplatin. We focused on radioactive Pt isotopes in order to analyze the kinetics of FGC-Pt using gamma-ray imaging techniques, assuming that FGC-Pt could be used for chemotherapy in the future. Therefore, in this study, we aimed to develop a non-invasive method to analyze the biodistribution of FGC-Pt using 191Pt-labeled FGC-Pt ([191Pt]FGC-Pt). 191Pt was produced via the (n,2n) reaction induced by accelerator neutrons. [191Pt]FGC-Pt was prepared using two different methods. In the first method, [191Pt]FGC-Pt (method A) was obtained through the accelerator neutron irradiation of FGC-Pt. In the second method, [191Pt]FGC-Pt (method B) was synthesized using [191Pt]K2PtCl4, which was obtained by the accelerator neutron irradiation of K2PtCl4. Highly purified [191Pt]FGC-Pt was obtained using the latter method, which suggests that the synthetic method using a 191Pt-labeled platinum reagent is suitable for the radioactivation of platinum complexes. We also aimed to investigate whether a significant correlation existed between the biodistribution of FGC-Pt and [191Pt]FGC-Pt in healthy mice 24 h after tail vein administration. FGC-Pt and [191Pt]FGC-Pt were similarly distributed in healthy mice, with a higher accumulation in the liver and kidney 24 h post injection. In addition, a significant correlation (p < 0.05, r = 0.92) between the 191Pt radioactivity concentration (%ID/g (gamma counter)) and platinum concentration (%ID/g (ICP-MS)) was observed in 13 organs. These results suggest that 191Pt-labeled compounds, synthesized using radioactive platinum reagents, can be used to confirm the biodistribution of platinum compounds. Our study on the biodistribution of [191Pt]FGC-Pt is expected to contribute to the development of novel platinum-based drugs in the future.

Synthesis and Biological Evaluation of a Novel Sugar-Conjugated Platinum(II) Complex Having a Tumor-Targeting Effect.

We designed and synthesized a novel platinum complex conjugated with 2-fluorinated 2-deoxyglucoside, named FGC-Pt, to capitalize on the Warburg effect and metabolic trapping properties of [18F]2-deoxy-2-fluoro-d-glucose ([18F]FDG). Then, we conducted comprehensive in vitro and in vivo studies to evaluate the effects of FGC-Pt. In vitro cytotoxicity assays using HeLa cells revealed that FGC-Pt exhibited concentration-dependent cytotoxicity, even though its cytotoxic effect was less pronounced than that of cisplatin. In the evaluation of in vivo biodistribution in mice, platinum concentration in tumors and major organs (muscle, bone, blood, liver, and kidney) and the ratio of platinum concentration in tumors to major organs following the tail vein injection of FGC-Pt and cisplatin suggest that FGC-Pt is more retained in tumors than in other organs and tends to accumulate in tumors more than cisplatin. Furthermore, an in vivo assessment of the antitumor effect conducted in A549 cell-bearing mice demonstrated that FGC-Pt possesses substantial potential as an antitumor agent. It exhibited a tumor growth-inhibitory effect comparable to that of cisplatin while inducing lower toxicity, as evidenced by lower weight loss after administration. Herein, we successfully produced a novel compound with a tumor-growth-inhibitory effect comparable to that of cisplatin and low toxicity.