The present invention relates to methods and compositions enhance the treatment of cancer and other proliferative diseases. In certain embodiments, the present invention provides a drug (e.g., "galectin-3 inhibitors") that inhibit the anti-apoptotic activity of galectin-3 in combination of administration of enhancing the chemotherapeutic agent toxicity. In some preferred embodiments, the combination therapy of the present invention can be used to improve the efficacy of chemotherapeutic agents that are affected by the state of the anti-apoptotic Bcl-2 protein in cells whose cytotoxicity is treated. For example, galectin-3 inhibitors can be administered in combination with a chemotherapeutic agent that interferes with cell cycle progression of cells undergoing accuracy, or unwanted proliferation of replication of DNA.