Kits and methods for treating cancer comprising administration of a gliadin peptide to a patient are disclosed herein. A kit according to the invention comprises a pharmaceutical composition comprising a gliadin peptide and instructions for administering the peptide to a patient. The kit may further comprise a pharmaceutical composition comprising at least one chemotherapeutic agent such as a receptor tyrosine kinase inhibitor and instructions for co-administering the compounds. A method of treating cancer according to the invention comprises administering a gliadin peptide to a patient and may further comprise co-administering at least one chemotherapeutic agent such as a receptor tyrosine kinase inhibitor. Co-administration of a gliadin peptide and receptor tyrosine kinase inhibitor to a patient with cancer is effective to decrease or prevent resistance of the cancer to the receptor tyrosine kinase inhibitor.