The present invention relates to pharmaceutically acceptable salts of conjugates comprising a chemotherapeutic drug and an amino acid or a derivative thereof, which are readily taken up by a target cell and reduce side effects induced by the chemotherapeutic drug. In particular, the present invention relates to pharmaceutically acceptable salts of conjugates comprising cytidine analog drugs and aspartic or glutamic acid and analogs thereof, pharmaceutical compositions comprising these conjugates and use thereof for the treatment of cancer or a pre-cancer condition or disorder.