Provided herein are polypeptides containing stabilized therapeutic peptides related to KRAS guanidine exchange factor (SOS1). Also provided are compositions containing these polypeptides and methods of using such peptides in the treatment of cancer that includes administering to a subject one of the polypeptides. This disclosure relates to structurally stabilized therapeutic peptides related to KRAS guanidine exchange factor (SOS1), and methods of using such peptides in the treatment of cancer.