Abstract B173: Preclinical characterization and antitumor efficacy of DS-5010, a highly potent and selective RET inhibitor

Background: RET gene rearrangement has been detected in several cancers including 1-2% and 50% of non-small cell lung cancer (NSCLC) and papillary thyroid carcinoma, respectively, and it is known as a driver mutation. Several US Food and Drug Administration (FDA)-approved multi-tyrosine kinase inhibitors (MTKIs) have shown inhibitory effects on RET kinase activity and have been tested in several clinical studies. However, MTKIs do not appear potent enough to show clinical benefits. The FDA-approved MTKIs have been reported to exhibit dose-limiting toxicity (DLT) at doses below those suppressing RET kinase activity. Kinase insert domain receptor (KDR) inhibition especially leads to anti-angiogenesis-related DLT such as hypertension. Thus, the development of highly potent and selective second-generation RET inhibitors is desired. DS-5010 is an orally available small-molecule RET inhibitor that shows a specific and highly potent activity against RET and gatekeeper-mutated RET (RET-GKm) and slight KDR activity. In this study, we characterized the in vitro and in vivo activities of DS-5010. Results: In biochemical assays of 106 kinases, RET and platelet-derived growth factor receptor (PDGFR) alpha/beta were inhibited more than 80% by 193 nM DS-5010. The half-maximal inhibitory concentration (IC 50 ) values of DS-5010 against RET, RET-GKm (V804L) were single digit nano-molar even under a condition of high concentration of ATP; besides it against KDR was more than 1000 nM. In a Ba/F3-RET subcutaneous tumor model, DS-5010 dosing at 10 mg/kg twice daily (bid) induced tumor regression. Moreover, DS-5010 exhibited a similar antitumor effect in a Ba/F3-RET-GKm (V804L) subcutaneous tumor model. In contrast, the FDA-approved MTKIs (cabozantinib, vandetanib, and alectinib) showed no significant antitumor effect on a Ba/F3-RET-GKm (V804L) subcutaneous tumor model. In an LC2/ad NSCLC xenograft model, which has the RET-CCDC6 fusion gene, DS-5010 dosing at 1 mg/kg thrice daily (tid) induced tumor regression. To predict acquired mutations against FDA-approved MTKIs, resistant clones were established by prolonged incubation of Ba/F3-RET cells with cabozantinib. A sequence analysis revealed that all the resistant clones possessed V804E mutation in the RET kinase domain and DS-5010 inhibited cell proliferation of Ba/F3-RET (V804E) mutation in the low nano-molar range. However, the FDA-approved MTKIs failed to show strong growth inhibitory effects (half-maximal growth inhibition [GI 50 ]: 1584-5381 nM). Conclusion: These results indicate that DS-5010 has potent in vitro and in vivo activities against RET and RET-GKm, suggesting the potential usefulness of the compound for targeted therapy of cancers with RET gene rearrangements and mutations. Moreover, its potential effectiveness against acquired MTKI-resistant cells was also demonstrated. We are currently performing investigational new drug-enabling studies of DS-5010. Citation Format: Yasuyuki Kaneta, Takahiro Komatsu, Masashi Miyamoto, Megumi Goto, Hidenori Namiki, Yoshihiro Shibata, Hideaki Kageji, Hiroaki Inagaki, Kiyoshi Nakayama, Yuichi Tominaga, Takeshi Isoyama. Preclinical characterization and antitumor efficacy of DS-5010, a highly potent and selective RET inhibitor [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr B173.