Abstract

RRx-001, has shown promise as a novel cancer therapeutic agent. The disposition of RRx-001 was evaluated in vitro and after intravenous (iv) administration to rats. At both 24 and 168 h after a single iv administration of ¹⁴C-RRx-001 (10 mg/kg), the majority of radiolabel was in the blood. The recovery of label in excreta was quite low, but the major route of radiolabel excretion was via the kidney, with approximately 26% in the urine by the first 8 h and decreasing amounts in all subsequent collections to a total of 36.3% by 168 h. The partitioning of total radioactivity in red blood cells (RBC) and plasma was determined following in vitro addition to human, rat, dog and monkey whole blood at 1 and 20 μM. In rat, at 30 min about 75% of the radioactivity is associated with RBC and 25% with plasma. In human, at 30 min about 25% of the radioactivity is associated with RBC and 75% with plasma. Analysis by LC/radiodetection/MS showed that ¹⁴C-RRx-001 reacted rapidly with whole blood to give four major soluble metabolites - the GSH and Cys adducts of RRx-001 (M1 and M2) and the corresponding mononitro GSH and Cys adducts (M3 and M4). Human hemoglobin was incubated with cold RRx-001 in buffer and a standard proteomics protocol used to separate and identify the tryptic peptides. Standard peptide collision induced fragment ions supported the structure of the peptide GTFATLSELHCDK with the alkylation on the Cys-93 locus of the Hb beta chain.