Ponatinib Is Active Against the CUX1-FGFR1 Fusion Kinase and Against Imatinib Resistance Mutations of the FIP1L1-PDGFRα Fusion Kinase and of KIT,

Abstract 3848

Imatinib (IM) was initially developed as a small molecule inhibitor of the BCR-ABL1 kinase, but also potently inhibits other oncogenic kinases, such as PDGFRβ and PDGFRα fusion proteins. IM has revolutionized the treatment of chronic myeloid leukemia (CML) and other neoplasms, but the development of IM resistant mutations has emerged as an important problem, triggering a search for novel compounds that overcome resistance. A leading third generation candidate is ponatinib, a novel multikinase inhibitor with potent activity towards BCR-ABL1, KIT, FGFR1, PDGFRα and other kinases. Importantly, ponatinib also targets numerous IM resistant BCR-ABL1 kinase domain mutations including the panresistant T315I mutation.

We investigated the effect of this compound on IM resistant kinase mutations in lymphoid/myeloid neoplasms associated with eosinophilia and rearrangements of PDGFRα and FGFR1, as well as KIT associated malignancies. Ba/F3 cells were used expressing either FIP1L1-PDGFRα, the IM resistant FIP1L1-PDGFRα-T674I mutant, the panresistant FIP1L1-PDGFRα-D842V mutant, or the novel CUX1-FGFR1 fusion. In addition, several KIT mutants were investigated. The growth of FIP1L1-PDGFRα and IM resistant FIP1L1-PDGFRα-T674I mutant expressing cells was strongly inhibited by ponatinib with IC50 values of 0,6 nM and 9 nM respectively. Also the panresistant FIP1L1-PDGFRα-D842V mutant and the novel CUX1-FGFR1 fusion responded well to ponatinib treatment with 50% growth inhibition at 154 nM and 56 nM respectively. IL3-driven growth of Ba/F3 cells was resistant to ponatinib (IC50: 2 μM). Western blot analysis confirmed the direct effect of ponatinib on the auto-phosphorylation of the PDGFRα and FGFR1 fusion proteins, as well as on the downstream signaling protein STAT5. Finally, we investigated several KIT single and double mutants and preliminary data indicate an inhibitory effect of ponatinib towards several KIT mutants.

In conclusion, our results demonstrate the in vitro activity of ponatinib against IM resistant mutants of the FIP1L1-PDGFRα fusion kinase, against the CUX1-FGFR1 fusion kinase as well as against IM resistant KIT mutations. Our data indicate that ponatinib, which is currently under investigation in phase II clinical trials for IM resistant CML, may also be active against neoplasms driven by FGFR1, PDGFR or KIT kinase activity, and able to overcome IM resistance in these malignancies.