[en] Trithiol chelates are suitable for labeling radioarsenic (⁷²As: 2.49 MeV β⁺, 26 h; ⁷⁷As: 0.683 MeV β^-, 38.8 h) to form potential theranostic radiopharmaceuticals for PET imaging and therapy. In this paper, to investigate the in vivo stability of trithiol chelates complexed with no carrier added (nca) radioarsenic, a bifunctional trithiol chelate was developed, and conjugated to bombesin(7–14)NH₂ as a model peptide. A trithiol-BBN(7–14)NH₂ bioconjugate and its arsenic complex were synthesized and characterized. The trithiol-BBN(7–14)NH₂ conjugate was radiolabeled with ⁷⁷As, its in vitro stability assessed, and biodistribution studies were performed in CF-1 normal mice of free [⁷⁷As]arsenate and ⁷⁷As-trithiol- BBN(7–14)NH₂. The trithiol-BBN(7–14)NH₂ conjugate, its precursors and its As-trithiol-BBN(7–14)NH₂ complex were fully characterized. Radiolabeling studies with nca ⁷⁷As resulted in over 90% radiochemical yield of ⁷⁷As-trithiol-BBN, which was stable for over 48 h. Biodistribution studies were performed with both free [⁷⁷As]arsenate and Sep-Pak® purified ⁷⁷As-trithiol-BBN(7–14)NH₂. Compared to the fast renal clearance of free [⁷⁷As]arsenate, ⁷⁷As-trithiol-BBN(7–14)NH₂ demonstrated increased retention with clearance mainly through the hepatobiliary system, consistent with the lipophilicity of the ⁷⁷As-trithiol-BBN(714)NH₂ complex. Finally, the combined in vitro stability of ⁷⁷As-trithiol-BBN(7–14)NH₂ and the biodistribution results demonstrate its high in vivo stability, making the trithiol a promising platform for developing radioarsenic-based theranostic radiopharmaceuticals.