Carboranyl-porphyrazines and derivatives for boron neutron capture therapy: From synthesis to in vitro tests

• Soft cyclotetramerization of carboranyl(alkylthio)maleonitriles affords carboranyl(alkylthio)porphyrazines.
• Carboranyl(alkylthio)porphyrazines/liposome adducts are structurally and chemically stable.
• Carboranyl(alkylthio)porphyrazines/liposome adducts introduce large B amounts into cancerous cells.

The recent advances in the synthesis of highly boronated porphyrazines and tetrabenzoporphyrazines (phthalocyanines) are reviewed, together with an analysis of their relevant physical and chemical properties. It is also shown how liposomes of variable lipid formulation and polarity can be efficiently loaded with carboranyl-porphyrazines, opening a perspective to the use of these supramolecular adducts as boron carriers for application in boron neutron capture therapy (BNCT). In particular, the remarkable chemical and structural stability of the loaded liposomal vectors, evaluated through state-of-art physico-chemical techniques, suggests that the carboranyl-porphyrazine/liposome adducts can effectively and selectively enter the membrane of cancerous cells. This has been explicitly checked by in vitro tests on model colon carcinoma cell cultures, showing that carboranyl-porphyrazines are incorporated in the cancerous cells at a high ratio, especially if liposome carriers with a cationic formulation are used. This behavior, together with the observed very low toxicity, makes polycarboranyl-porphyrazines suited for application in BNCT.

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