Production and in vitro evaluation of no-carrier-added radio-cisplatin emitting Auger electrons

Aim/Introduction: Auger electrons (Auger e-) have the potential for therapeutic applications by inducing nanoscale physiochemical damage to biomolecules due to their short-range (2-500 nm). Although DNA is the primary target of Auger e-, it remains challenging to maximize the interaction between Auger e- and DNA. To assess the DNAdamaging efect of Auger e- released as close as possible to DNA, we focused on a platinum(Pt)-based antineoplastic drug, cisplatin, because it can form direct DNA adducts between Pt and nucleobases. Here, to evaluate the efect of Auger e- without chemical factors we radio-synthesized nocarrier-added (n.c.a.) [189, 191Pt]cisplatin (radio-cisplatin), and investigated its in vitro properties and DNA-damaging efect in cultured cells. Materials and Methods: N.c.a. radio-cisplatin was radio-synthesized by treating n.c.a. radio-PtCl42- with excess NH3 and heating the reaction mixture, and the product was isolated by preparative HPLC. As in vitro evaluation of radio-cisplatin, cellular uptake, intracellular distribution, and DNA binding were investigated, and DNA double-strand breaks (DSBs) were evaluated by immunofuorescence staining of γH2AX. Results: Our production method provided n.c.a. radio-cisplatin with a radiochemical purity of 99% at the end of synthesis. Although uptake of radio-cisplatin was low (0.6% incubated dose after 25-h incubation), approximately 20% of intracellular radio-Pt was in a nucleus, and 2% of intra-nucleus radio-Pt bound to DNA. Due to the low accumulation of radio-Pt, the frequency of cells with γH2AX foci was low (1%) in the γH2AX assays. Nevertheless, strong signals in nuclei of tumor cells treated with radio-cisplatin were found more often than with saline or nonradioactive cisplatin, suggesting Auger e- released very close to DNA cause more DSB. Conclusion: N.c.a. radio-cisplatin was successfully prepared at high radiochemical purities as an efective tool to evaluate DNA damage induced by Auger e- without chemical factors. Radio-cisplatin binding to DNA caused severe DSBs by the release of Auger e- very close to DNA without chemical damage by carriers. References:Obata, et al. Int. J. Mol. Sci. 2021, 22, 4622. Obata, et al. Sci Rep 2021, 11, 8140.EANM21(34th Annual Congress of the European Association of Nuclear Medicine