Dynamic Evolution of Ponatinib Resistant BCR-ABL1 T315 and Compound Mutations
Authors: Chen Jiaqi , Liu Hongxing , Wang Fang , Zhang Yang , Chen Xue , Nie Daijing , Li Yu , Tan Yincheng , Xu Yuanli , Ma Xiaoli 
Published: November 2019

The third-generation tyrosine kinase inhibitor (TKI) ponatinib exhibits activity against all common BCR-ABL1 kinase domain (KD) single mutations, including the highly resistant gatekeeper T315I. However, the drug response is variable and the clinical resistance mutations may still befall with few reports to date. We performed next-generation sequencing (NGS) detection of BCR-ABL1 KD mutations in sequential samples of three BCR-ABL1-positive leukemia patients who developed clinical resistance to ponatinib, to explore the dynamic evolution of ponatinib mutations.
Case 1 was diagnosed as chronic myeloid leukemia (CML) chronic phase when he was 29 years old in 2009. His maintenance therapies were imatinib and dasatinib for seven years and then replaced with ponatinib due to the blast crisis of CML and the T315I mutation with variant allele frequency (VAF) of 46%. He did not achieved molecular remission after attempting multiple combined chemotherapy and TKIs including ponatinib, with the T315I mutation persists and eventually increases to VAF of 97%. He was then was medicated with a combined chemotherapy plus dasatinib and ponatinib. But NGS KD mutation investigation showed multiple T315I compound mutations, T315M and T315I mutations six months later. The patients went through salvage allogenic hemopoietic stem cell transplantation (allo-HSCT), and the above polyclonal and compound mutations were still carried after transplantation. Finally, Q252H/T315I (VAF,50%) became the dominant clone, and ponatinib and HQP1351 (domestic TKI designed for T315I) were ineffective for this compound mutation (Figure a).
A similar dynamic evolution to the BCR-ABL1 KD mutation of Case1 also occurred in case 2. The 7-year-old boy was diagnosed with BCR-ABL1-positive acute B-lymphocytic leukemia (Ph+B-ALL) in April 2014. NGS results showed that he had D276G (7%), F311I (27%) and F317L (31%) polyclonal mutations in BCR-ABL1 KD after 18 months of imatinib administration which were subsequently treated with ponatinib. After 5 months of treatment with ponatinib, F311I and F317L mutations disappeared, but G250E (5%) and D276G/T315L (4%) compound mutation appeared; subsequent progression to D276G/T315L (32%), G250W/E255V/F311I (4%) and F311I/T315I (58%) polyclonal compound mutations; long induction chemotherapy combined with ponatinib treatment remained unresolved, and finally there was only D276G/T315L compound mutation (VAF, 100%, figure b and d). Notably, a rare mutation T315L (c.943_945delinsCTC/p.T315L) appeared in the BCR-ABL1 KD. D276G is known to be sensitive to various TKIs, so we speculate that ponatinib is ineffective for the T315L mutation.
Case 3 was a 46-year-old woman who diagnosed with Ph+B-ALL in July 2018. The Q252H (20%) and T315I (44%) double mutations appeared after oral administration of imatinib for 2 months, and then switched to ponatinib for remission. After 8 months, the bone marrow and peripheral blood samples showed not only the T315I/F359V compound mutation (VAF, 90% and 94%), but also the T315L mutation (VAF, 5% and 6%, c.943_944AC>CT/p.T315L). The clinician combined her BCR-ABL1 KD mutation and condition, ponatinib was discontinued. After 1 month of chemotherapy combined with dasatinib, the patient's condition improved, but the BCR-ABL1 KD mutation progressed to T315L (18%, figure c and e) and T315I/F359V compound mutation (76%). She eventually died from severe pulmonary infection and sepsis.
NGS analysis identify KD mutation with sensitivity about 2%, and can also distinguish between compound and polyclonal mutations. All of the ultimately dominant ponatinib resistant mutations (Q252H/T315I, D276G/T315L, and T351I/F359V) in these three cases were T315 compound mutations derived from the T315I or other original mutation with additional mutation event. The T315L/M mutations and compound mutations collaborated by T315 and other KD mutations may confer the major component of ponatinib resistance. The dynamic resistant mutation in these three patients adds to the currently less content compendium of ponatinib clinical resistance. All of the three patients encountered ponatinib toxic side effects and had to discontinue or reduce the dose, which also confer favorable opportunity for the development of drug-resistant mutations.
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Disclosures
No relevant conflicts of interest to declare.