The use of polyhedral boron hydrides for cancer treatment is traditionally connected with boron neutron capture therapy. More recently, polyhedral borate anions were proposed as carriers of radionuclide label for targeted radionuclide therapy and diagnostics of cancer. Some metal derivatives of carboranes were found to demonstrate significant antitumor activity themselves. This review is designed to highlight the recent work concerning various fields of potential application of polyhedral boron compounds in anticancer diagnostics and therapy.

The 1 : 2 condensation of dibutyltin(IV) oxide with 1,2-carborane-9-carboxylic acid resulted in bis(1,2-dicarba-closo-dodecaborane-9-carboxylato)di-n-butyltin (1), the first carborane-based organotin compound where the carborane cage is linked to the carboxylic moiety via a boron atom. The structure of 1, characterized by 1 H, 11 B, 13 C, 119 Sn NMR spectroscopy and X-ray diffraction, was shown to correspond to bis(1,2-dicarba-closo-dodecaborane-9-carboxylato)di-n-butyltin. Compound 1 was screened in vitro against seven tumour cell lines of human origin and was found to be significantly more active than 5-fluorouracil, cis-platin and carboplatin but less active than methotrexate and doxorubicin.

X-ray diffraction studies reveal the structure of {[(2-CsH5-1,2-C2BloHlo-I-COO)Bu2Sn]20}2, 1, to conform to the common motif found for {[(R'COO)R2Sn]20}2 compounds. The dimer features a central Bu4Sn202 unit (two-fold symmetry) with the two Bu2Sn groups being linked via bridging oxygen atoms, each of which also carries an exocyclic Bu2Sn moiety. The two pairs of exo-and endo-cyclic tin atoms are each linked via an almost symmetrically bridging carboxylate ligand and the two remaining ligands coordinate an exocyclic tin atom only, in the monodentate mode. The in vitro anti-tumour activity of 1, determined against a variety of cell lines, is compared with those of the corresponding 2-methylcarboranylacetate, derivative 2, and with clinically used compounds.

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The review summarizes our results and data published in the literature on the synthesis and antitumor activity of metal containing carboranes. Carboranyl derivatives of platinum and tin and some metallacarboranes exhibit activity against malignant tumors.