Polypeptide conjugate binders that discriminate between two isoforms of human carbonic anhydrase in human blood.

Two binder candidates 4-C37L34-B and 3-C15L8-B from a 16-membered set of 42-residue polypeptide conjugates designed to bind human carbonic anhydrase II (HCAII), were shown to bind HCAII with high affinity in a fluorescence-based screening assay. Two carbonic anhydrase isoforms with 60 % homology exist in human blood with HCAI being present in five- to sevenfold excess over HCAII. The ability of the binders to discriminate between HCAI and HCAII was evaluated with regard to what selectivity could be achieved by the conjugation of polypeptides from a 16-membered set to a small organic molecule that binds both isoforms with similar affinities. The polypeptide conjugate 4-C37L34-B bound HCAII with a K(D) of 17 nM and HCAI with a K(D) of 470 nM, that is, with a 30-fold difference in affinity. The corresponding dissociation constants for the complexes formed from 3-C15L8-B and the two carbonic anhydrases were 60 and 390 nM, respectively. This demonstration of selectivity between two very similar proteins is striking in view of the fact that the molecular weight of each one of the conjugate molecules is little more than 5000, the fold is unordered, and the polypeptide sequences were designed de novo and have no prior relationship to carbonic anhydrases. The results suggest that synthetic polypeptide conjugates can be prepared from organic molecules that are considered to be weak binders with low selectivity, yielding conjugates with properties that make them attractive alternatives to biologically generated binders in biotechnology and biomedicine.

Xylose as a carrier for boron containing compounds.

A xylosylated carborane was synthesized by standard carbohydrate methodology and tested on normal HFL-1 cells as well as transformed T24 cells. The xylosylated carborane initiated glycosaminoglycan (GAG) synthesis in both cell lines and treatment with the carborane gave a pronounced translocation of proteoglycans to the nuclei of T24 cells. However, most of the boron-containing compounds were secreted to the medium. We conclude that xylosides carrying carboranes are not suitable for boron neutron capture therapy (BNCT) for T24 cells. However, the uptake of boron-containing xyloside, the GAG priming capacity, and the nuclear translocation of glypican-1 make this xyloside a candidate for further investigation for selectivity toward other tumor cell lines.