The invention provides a pharmaceutical composition comprising (a) a compound of the formula (1), wherein R1, R2, R3 and R4 are substituents, at least one of which contains a carborane cluster； and M is selected from two hydrogen ions and one or two metal ions, wherein any metal ions present are charge-balanced by one or more counter ions； and (b) a vehicle comprising: (i) dimethylacetamide as solvent； and (ii) a co-solvent comprising one or more of tetraglycol； propylene glycol； polyethylene glycol； and a non-ionic surfactant. The pharmaceutical compositions are useful as radiation sensitizers in radiation treatment of cancers.
