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Introduction: Targeted α-particle therapy agents have shown promising responses in patients who have developed resistance to β - -particle emitting radionuclides, albeit off-target toxicity remains a concern. Astatine-211 emits only one α-particle per decay and may alleviate the toxicity from α-emitting daughter radionuclides. Previously, we developed the low-molecular-weight PSMA-targeted agent [ 211 At]L3-Lu that showed suitable therapeutic efficacy and was well tolerated in mice. Although [ 211 At]L3-Lu had good characteristics, we now have evaluated a closely related analogue, [ 211 At]YF2, to determine the better molecule for clinical translation., Methods: The tin precursors and unlabeled iodo standards for [ 211 At]YF2 and [ 211 At]L3-Lu each were synthesized and a new one-step labeling method was developed to produce [ 211 At]YF2 and [ 211 At]L3-Lu from the respective tin precursor. RCY and RCP were determined using RP-HPLC. Cell uptake, internalization and in vitro cell-killing (MTT) assays were performed on PSMA + PC-3 PIP cells in parallel experiments to compare [ 211 At]YF2 and [ 211 At]L3-Lu directly. A paired-label biodistribution study was performed in athymic mice with subcutaneous PSMA-positive PC-3 PIP xenografts as a head-to-head comparison of [ 131 I]YF2 and [ 125 I]L3-Lu. The tissue distribution of [ 211 At]YF2 and [ 211 At]L3-Lu were determined individually in the same animal model., Results: The syntheses of tin precursors and unlabeled iodo standards were accomplished in reasonable yields. A streamlined and scalable radiolabeling method (1 h total synthesis time) was developed for the radiosynthesis of both [ 211 At]YF2 and [ 211 At]L3-Lu with 86 ± 7 % (n = 10) and 87 ± 5 % (n = 7) RCY, respectively, and > 95 % RCP for both. The maximum activity of [ 211 At]YF2 produced to date was 666 MBq. An alternative method that did not involve HPLC purification was developed that provided similar RCY and RCP. Significantly higher cell uptake, internalization and cytotoxicity was seen for [ 211 At]YF2 compared with [ 211 At]L3-Lu. Significantly higher uptake and longer retention in tumor was seen for [ 131 I]YF2 than for co-administered [ 125 I]L3-Lu, while considerably higher renal uptake was seen for [ 131 I]YF2. The biodistribution of [ 211 At]YF2 was consistent with that of [ 131 I]YF2., Conclusion: [ 211 At]YF2 exhibited higher cellular uptake, internalization and cytotoxicity than [ 211 At]L3-Lu on PSMA-positive PC3 PIP cells. Likewise, higher uptake and longer retention in tumor was seen for [ 211 At]YF2. Experiments to evaluate the dosimetry and therapeutic efficacy of [ 211 At]YF2 are under way., Competing Interests: Declaration of competing interest Ganesan Vaidyanathan, Martin Pomper and Michael Zalutsky are co-inventors on a patent related to the labeled PSMA inhibitors described in this study and discussed in this publication. They are entitled to royalty distributions related to this technology, which was originally licensed by Precision Molecular, Inc. and now transferred to z-alpha, Inc. Martin Pomper and Michael Zalutsky are co-founders and paid consultants of z-alpha and are minority shareholders via stock options. No other potential competing interests related to this work are reported., (Copyright © 2024 Elsevier Inc. All rights reserved.)

We report on new measurements establishing the existence of low-lying isomeric states in ^{136}Cs using γ rays produced in ^{136}Xe(p,n)^{136}Cs reactions. Two states with O(100)  ns lifetimes are placed in the decay sequence of the ^{136}Cs levels that are populated in charged-current interactions of solar neutrinos and fermionic dark matter with ^{136}Xe. Xenon-based experiments can therefore exploit a delayed-coincidence tag of these interactions, greatly suppressing backgrounds to enable spectroscopic studies of solar neutrinos and dark matter.

Two samples, one of natural iridium and the other of enriched 193 Ir, were irradiated with a monoenergetic neutron beam of energy 6.0 MeV at the Triangle Universities Nuclear Laboratory. The product of the 193 Ir [Formula: see text] Ir reaction was determined by means of measuring X-rays following electron conversion of the isomeric state at 80.2 keV in 193 Ir. The cross section for inelastic neutron scattering is reported disagreeing with the literature data., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 The Author(s). Published by Elsevier Ltd.. All rights reserved.)