Compositions and methods useful in the treatment of certain cancers. The methods include administering, to a patient receiving an antifolate anticancer agent, methoxyamine administered in an amount sufficient to enhance or increase the effect of the antifolate anticancer agent. In part, this application is based on the recognition that certain molecules that target abasic lesions or AP sites in DNA improve, augment, or potentiate the chemotherapeutic efficacy of certain anticancer agents.