Abstract 3581: Rapid conversion to resistance, of a colon PDX with ret-fusion, by ponatinib treatment could potentially be attributed to the introduction of the gate keeper mutation V804M
Authors: Yang Mengmeng , Cai Jie , Guo Sheng , Wery Jean-Pierre , Li Henry Qixiang 
Published: August 2015

Abstract
RET encodes a receptor tyrosine kinase (RTK) involved in cellular mechanisms of proliferation, migration and differentiation. RET fusions with different genes at 10q11.2 result in constitutively activation and drive tumor development in various cancers: 10-20% of sporadic papillary thyroid cancer1, spitzoid neoplasms, CMML and 1% of lung adenocarcinomas2,3. RET fusions have been suggested to be important therapeutic targets. Ponatinib, a multi-kinase inhibitor, was approved for the treatment of Ph+ chronic myeloid leukemia (CML) and acute lymphoblast leukemia (ALL), including CML with T315I/imatinib-resistance. Ponatinib has recently been found to potently inhibit the common NSCLC fusion variant, KIF5B-RET at clinically-achievable concentrations.
We have established large collection of colorectal patient derived xenografts (PDXs)4,5. Two of the poorly differentiated adenocarcinoma, CR1520 and CR2518, contain two different chromosome 10 in-frame RET-fusions, CCDC6-RET (CR2518) and NCOA4-RET (CR1520), as revealed by RNAseq and Sanger Sequencing6. Both models have also demonstrated over-expressing ret gene at mRNA levels. More importantly, they both responded Ponatinib significantly along with dephosphorylation of RET and downstream AKT, confirming these two types of Ret fusions as oncogenic drivers in these two models6. In addition, we also observed that Ponatinib treatment also rapidly drives CR2518 into its resistance (The resistant derivative is called CR2545). To investigate the underlying mechanism of the resistance, we performed RNAseq analysis of CR2545, which revealed retaining of the ret-fusion, but also the introduction of a previously described gate-keeper mutation, V804M, at ret kinase domain. V804M, a mutation frequently found in familial medullary thyroid carcinoma (FMTC), introduces bulky amino acid at position 804 and found to resistant to vandetanib. This may contribute to the resistance. However, this notion apparently contradicts to the previous observation/claim that V804M is sensitive to Ponatinib7, and ponatinib should be used to treat RET-V804M/L cancers. It is possible that the described V804M containing vandetanib resistant cells are sensitive to ponatinib, but via a non-RET mechanism for the multi-kinase inhibition nature of ponatinib; or in our case, there are other non-RET Ponatinib resistant mechanisms been introduced in CR2545 where RET is no longer the key oncogenic driver. We are currently testing other RET inhibitors and also assessing pharmacodanamic (PD) parameters to further investigate RET resistant mechanism. The further findings from the ongoing studies will be presented at the meeting.
Citation Format: Mengmeng Yang, Jie Cai, Sheng Guo, Jean-Pierre Wery, Henry Qixiang Li. Rapid conversion to resistance, of a colon PDX with ret-fusion, by ponatinib treatment could potentially be attributed to the introduction of the gate keeper mutation V804M. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3581. doi:10.1158/1538-7445.AM2015-3581