The constitutively active tyrosine kinase BCR-Abl has been implicated as the underlying cause of chronic myeloid leukemia (CML). Current treatments for CML patients focus on the long-term use of imatinib, a small-molecule tyrosine kinase inhibitor (TKI) targeting the ATP binding site of BCR-Abl, but the response is not sustained for a number of patients due to point mutations that develop in the drug-binding region. Second- and third-generation ATP-competitive inhibitors have been developed to override imatinib resistance, but none of them exhibits inhibitory activity against T315I mutated BCR-Abl (Quintas-Cardama et al, 2007). Therefore, therapeutic approaches that target regions distant from the ATP cleft may be a promising strategy to overcome the emerging drug-resistance. In this study, a new class of substrate-based Abl kinase inhibitors targeting the ligand binding site was developed by grafting modified substrates onto the cyclotide scaffold to improve the stability and therapeutic efficacy of the inhibitor. Disulfide-rich cyclic peptides within the cyclotide family have been shown to possess extraordinary stability against enzymatic, chemical and thermal degradation (Colgrave & Craik, 2004). The exceptional stability combined with the possibility to accommodate different loop sequences without disturbing the overall peptide fold point towards potential pharmaceutical applications of cyclotides. A cell-penetrating cyclotide, MCoTI-II (Cascales et al, 2011; Greenwood et al, 2007), was employed as the scaffold for our grafting study. One of the grafted peptides showed significant Abl kinase inhibition in the low micromolar range in vitro. More importantly, the MCoTI-II mutant displayed enzymatic stability and cell penetrating properties inherited from its parent scaffold. The results suggest that this approach can be applied to develop stable, non-toxic peptide-based kinase inhibitors towards various disease-linked kinases.