Other Macromolecules Used For Delivering

boron compounds

Polylysine is another polymer having multiple reactive amino groups that has been used as a platform for the delivery of boron compounds.53,156 The protein-binding polyhedral boron derivatives, isocyanatoundecahydro-closo-dodecaborate (B12H11NCO2—), was linked to polylysine and subsequently to the anti-B16 melanoma mAb IB16-6 using two heterobifunctional linkers, SPDP and sulfo-MBS. The bioconjugate had an average of 2700 boron atoms per molecule and retained 58% of the immunoreactivity of the native antibody, as determined by a semiquantitative immuno-fluorescent assay or by ELISA. Other bioconjugates prepared by this method had greater than 1000 boron atoms per molecule of antibody and retained 40-90% of the immunoreactivity of the native antibody.53 Using another approach, site-specific linkage of boronated polylysine to the carbohydrate moieties of anti-TSH antibody resulted in a bioconjugate that had approximately 6x 103 boron atoms with retention of its immunoreactivity.156

A streptavidin/biotin system also has been developed to specifically deliver boron to tumors. Biotin was linked to a mAb and streptavidin was attached to the boron containing moiety. The indirect linking of boron to the mAb minimized loss of its immunoreactivity. BSH was attached to poly-(d-glutamate d-lysine) (poly-GL) via a heterobifunctional agent.157 This boronated poly-GL then was activated by a carbodiimide reagent and in turn reacted with streptavidin. Another approach employed a streptavidin mutant that had 20 cysteine residues per molecule. BSH was conjugated via sulfhydryl-specific bifunctional reagents to incorporate approximately 230 boron atoms/molecule.158 A closomer species with an icosahedral dodecaborate core and twelve pendant anionic mdo-7,8-carborane groups was developed as a new class of unimolecular nanovehicles for evaluation as a delivery agent for BNCT.159

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