Compounds and pharmaceutical formulations containing these compounds are described. Also described are methods of making and using the compounds. The compounds include nucleobases, nucleobase analogues, or combinations thereof. In one embodiment, a nucleobase analogue is combined with doxorubicin and encapsulated within a liposome for use in inhibiting or preventing the growth of cancer cells. Further described are pharmaceutical compositions containing two or more therapeutically active agents encapsulated within a vesicle, such as a liposome, wherein the molar ratio of the agents provides a synergistic therapeutic effect.