CBL and neoplasm: Nitrosylcobalamin (NO-Cbl), a nitric oxide (NO)-releasing cobalamin analog, was developed to selectively deliver cytotoxic NO to tumors through the transcobalamin II receptor (CD320).<h4>Methods</h4>NO-Cbl was evaluated across the NCI-60 tumor panel, followed by pharmacokinetic and biodistribution studies in glioblastoma-bearing rats using nitrate and cobalamin quantification in tissues, serum, and cerebrospinal fluid (CSF).