Selective blood–brain barrier penetration and tumor targeting of nitrosylcobalamin in glioblastoma: Pharmacokinetics, tissue distribution, and synergistic activity with trail and temozolomide

ABSTRACT

Background: Glioblastoma multiforme (GBM) remains a lethal brain tumor characterized by poor response to chemotherapy and limited blood–brain barrier (BBB) permeability. 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).

Methods: 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). Synergistic activity with TRAIL or temozolomide was assessed in human U87 and D54 glioma cells using SRB assays and Chou–Talalay analysis.

Results: NO-Cbl showed broad antitumor activity in vitro, with central nervous system tumor cell lines displaying intermediate sensitivity (mean ID₅₀ = 17.6 µM). In vivo, NO-Cbl effectively crossed the BBB, with tumor nitrate levels peaking at 20.4 nmol/g at 30 min and remaining elevated at 24 h, confirming tumor-selective accumulation. Serum nitrate exhibited a rapid half-life (4–5 h), while serum and CSF B12 showed slower and variable clearance (21–26 h and 11–12 h, respectively). In glioma cell lines, NO-Cbl synergized with TRAIL and temozolomide (TMZ) (combination index < 1.0), enhancing antiproliferative effects and suggesting potential to overcome resistance mechanisms.

Conclusion: This pilot study demonstrates that NO-Cbl crosses the BBB, accumulates selectively in brain tumor tissue, and synergizes with established and experimental glioblastoma therapies. These findings establish a translational foundation for developing cobalamin-based therapeutics as a novel treatment strategy for glioblastoma.