Abstract 4763: The tyrosine kinase inhibitor axitinib targets T315I gatekeeper-mutant Philadelphia chromosome-positive leukemias in vitro and in vivo
Authors: Pemovska Tea , Kontro Mika , Repasky Gretchen A. , Porkka Kimmo , Wennerberg Krister 
Published: May 2015

Abstract
The use of ABL1 kinase inhibitors has dramatically improved the outcome for chronic myeloid leukemia (CML) and Philadelphia-positive (Ph+) acute lymphoblastic leukemia (ALL) patients. However, resistance after treatment still poses a major clinical challenge. The most common resistance mechanism following treatment with first or second line therapy is the occurrence of a T315I mutation in the kinase domain of BCR-ABL1. Only one clinically available ABL1 inhibitor, ponatinib, has been shown to target this gatekeeper mutation, but has recently been associated with significant adverse effects. Hence, there is an unmet need for new and improved therapies for patients with T315I BCR-ABL1 leukemias.
In this study we set out to functionally and molecularly profile BCR-ABL1 T315I-driven CML/Ph+ALL patient samples to understand the disease pathogenesis and identify novel therapies with a drug sensitivity and resistance testing (DSRT) platform covering 306 approved and investigational oncology compounds. Mononuclear cells isolated from patient bone marrow were plated with drugs on 384-well plates. Each compound was tested for its effect on cell growth and survival in a 10,000-fold concentration range enabling the generation of dose response curves and by comparing to healthy donor mononuclear cells, selective drug sensitivity scores (sDSS).
Ex vivo DSRT results of one CML and two Ph+ALL patient samples with the T315I mutation revealed a marked and specific sensitivity (IC50 30-40nM) to the tyrosine kinase inhibitor axitinib, originally developed as a VEGFR inhibitor. Strikingly, sensitivity to axitinib was higher in these T315I positive patient samples than in T315I negative CML or ALL patient samples or any other leukemic samples. Supporting the notion that axitinib is a direct T315I BCR-ABL1 inhibitor we observed that Ba/F3 cells transformed with T315I BCR-ABL1 were sensitive to axitinib while the same cells transformed with wild type BCR-ABL1 were not. Finally, we discovered that axitinib has been described to have selective binding towards T315I ABL1 compared to the wild type kinase (Kd 1.5 nM vs. 36 nM, respectively, Davis et al. 2011, Nat. Biotechnol. 29:1046-1051). Based on this information, the T315I CML patient mentioned above was compassionately treated with axitinib for 2 weeks resulting in a rapid 4-fold reduction of the mutated transcript levels in blood suggesting targeted in vivo activity of the drug.
In summary, we demonstrated that axitinib is a potent BCR-ABL1 T315I inhibitor both in vitro and in vivo. In light to the fact that axitinib is currently approved as a second line therapy for renal cell carcinoma and is well tolerated in patients, there is an opportunity to repurpose axitinib for Ph+ leukemia patients with T315I mutations with significantly shorter clinical development time.
Citation Format: Tea Pemovska, Mika Kontro, Gretchen A. Repasky, Kimmo Porkka, Krister Wennerberg. The tyrosine kinase inhibitor axitinib targets T315I gatekeeper-mutant Philadelphia chromosome-positive leukemias in vitro and in vivo. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4763. doi:10.1158/1538-7445.AM2014-4763