Which mechanism of resistance is most commonly observed in patients with BCR-ABL1-positive CML who develop resistance to dasatinib?
- A T315I 'gatekeeper' mutation in the ABL1 kinase domain that sterically prevents dasatinib binding to the ATP-binding site ✓
- B BCR-ABL1 gene amplification increasing target protein levels beyond the inhibitory capacity of dasatinib
- C Upregulation of SRC kinase family members that bypass the ABL1 signalling node
- D Loss of OCT-1 transporter expression in chronic phase CML reduces cellular dasatinib uptake
Explanation
The T315I 'gatekeeper' mutation is the most clinically significant resistance mutation across all BCR-ABL1 tyrosine kinase inhibitors (imatinib, dasatinib, nilotinib, bosutinib). Threonine-315 is the gatekeeper residue in the ABL1 ATP-binding pocket; its hydroxyl group forms a hydrogen bond with imatinib and contributes to dasatinib binding. The T315I substitution replaces threonine with isoleucine, eliminating this hydrogen bond and creating steric hindrance that prevents binding of all first- and second-generation TKIs (imatinib, nilotinib, dasatinib, bosutinib). Ponatinib, a third-generation TKI with a carbon-carbon triple bond in its structure, and asciminib (a STAMP inhibitor targeting the myristoyl pocket) were specifically designed to overcome T315I. BCR-ABL1 amplification and SRC overactivation are less common resistance mechanisms.
Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.
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