Imatinib resistance in CML most commonly arises from T315I point mutation in BCR-ABL. Ponatinib is specifically designed to overcome T315I resistance because:

• A Ponatinib has a carbon-carbon triple bond (alkyne) linker that allows accommodation in the modified ATP-binding site of T315I mutant BCR-ABL without steric clash with the bulky isoleucine ✓
• B Ponatinib is a type I TKI that binds the active DFG-in conformation not blocked by the T315I gatekeeper mutation
• C Ponatinib inhibits mutant BCR-ABL by covalently binding a cysteine residue outside the ATP-binding site
• D Ponatinib bypasses BCR-ABL inhibition by directly targeting downstream RAS-MAPK signaling

Explanation

The T315I mutation substitutes threonine-315 (a critical hydrogen bond contact site for most TKIs) with bulky isoleucine, creating steric clashes that prevent imatinib, dasatinib, and nilotinib from binding. Ponatinib's structure incorporates a carbon-carbon triple bond (ethynyl/alkyne) linker between the two aryl rings, creating a compact linear geometry that fits past the isoleucine side chain without steric conflict, while still forming the necessary contacts with the ATP-binding site. This rational structural design allows ponatinib to inhibit T315I and all other known point mutations in BCR-ABL. STAMP inhibitors (asciminib) address T315I by binding the myristoyl pocket allosterically.

Reference: KD Tripathi, Essentials of Medical Pharmacology, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.