Drug-carrier complexes, drug carriers, pharmaceutical formulations, methods of delivery drugs to an organism or tissue culture, methods of increasing the solubility of a substance, targeted carriers, drug delivery systems and implants are described. The compositions and methods of the invention include forming complexes having reversible associations between nucleotides and drugs. The compositions and methods of the invention can be employed to target drugs to cells, organisms or combinations of cells to treat and to study the underlying mechanisms of diseases, and to test drug candidates.