Blood–brain barrier (BBB) toxicity and permeability assessment after L-(4-10Boronophenyl)alanine, a conventional B-containing drug for boron neutron capture therapy, using an in vitro BBB model

• BBB permeability and toxicity of L-10BPA were determined using an in vitro BBB model.
• The three-dimensional BBB coculture consisted of brain capillary endothelial and glial cells.
• Lack of toxic effects of L-10BPA, accompanied by low brain penetration, was found.
• Nevertheless, post-exposure cellular stress phenomenon was observed.
• This approach provides a useful early safety assessment model for new drug screening.

Since brain tumours are the primary candidates for treatment by Boron Neutron Capture Therapy, one major challenge in the selective drug delivery to CNS is the crossing of the blood–brain barrier (BBB). The present pilot study investigated (i) the transport of a conventional B-containing product (i.e., L-(4-10Boronophenyl)alanine, L-10BPA), already used in medicine but still not fully characterized regarding its CNS interactions, as well as (ii) the effects of the L-10BPA on the BBB integrity using an in vitro model, consisting of brain capillary endothelial cells co-cultured with glial cells, closely mimicking the in vivo conditions. The multi-step experimental strategy (i.e. Integrity test, Filter study, Transport assay) checked L-10BPA toxicity at 80 µg Boron equivalent/ml, and its ability to cross the BBB, additionally by characterizing the cytoskeletal and TJ’s proteins by immunocytochemistry and immunoblotting.In conclusion, a lack of toxic effects of L-10BPA was demonstrated, nevertheless accompanied by cellular stress phenomena (e.g. vimentin expression modification), paralleled by a low permeability coefficient (0.39±0.01×10−3 cm min−1), corroborating the scarce probability that L-10BPA would reach therapeutically effective cerebral concentration. These findings emphasized the need for novel strategies aimed at optimizing boron delivery to brain tumours, trying to ameliorate the compound uptake or developing new targeted products suitable to safely and effectively treat head cancer. Thus, the use of in vitro BBB model for screening studies may provide a useful early safety assessment for new effective compounds.