A method for treating a biological cell is disclosed. The method administers a mixture of a chemotherapeutic drug and a co-drug that facilitates delivery of the chemotherapeutic drug to the nucleus of the cell. Examples of co-drugs include cationic polymers, cationic lipids and cationic proteins. Cationic polymers include a polyethyleneimine (PEI), polylysine, a polybetaaminoester (PBAE), an ε-polylysine (EPL) including ε-poly-L-lysine (e-PLL), a polyarginine peptide, chitosan, a polyamidoamine dendrimer (PAMAM). Cationic lipids include 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP). Cationic proteins include protamine.
