Abstract 2091: Identification of a highly potent, selective and orally available RET inhibitor with antitumor efficacy in RET-dependent tumor models.

Proceedings: AACR 104th Annual Meeting 2013; Apr 6-10, 2013; Washington, DC The RET proto-oncogene encodes a receptor tyrosine kinase that is mainly expressed in neural crest-derived tissues where it plays an important role in cell differentiation, growth and survival. Germline activating point mutations of RET are associated with multiple endocrine neoplasia type 2 (MEN2), an inherited cancer syndrome characterized by development of medullary thyroid carcinoma (MTC), pheochromocytoma and parathyroid hyperplasia and are present in circa 50% of sporadic cases of MTC. More recently, a chromosomal rearrangement of the RET gene was identified in a subset of lung adenocarcinomas (1-2%) which is reported to result in expression of a fusion protein containing constitutively active RET kinase domain fused to the N-terminal portion of the kinesin KIF5B. We recently presented data on NMS-173, a very potent RET inhibitor characterized by an excellent in vivo activity profile upon i.v. administration. Here we describe the identification and the preclinical characterization of NMS-616, a novel analogue belonging to the same chemical class, suitable for oral administration. NMS-616 is a highly potent (IC50: 2 nM), ATP competitive RET inhibitor, characterized by high selectivity when tested against a panel of more than 50 kinases. NMS-616 potently blocked proliferation of MTC cell lines, such as the TT human cell line, which endogenously harbours constitutively activated RET, concomitant with abrogation of RET autophosphorylation and signaling pathway activation. The compound also inhibited the IL-3 independent proliferation of RET-driven Ba/F3 cells, with down-modulation of RET autophosphorylation and downstream signalling pathways. NMS-616 is characterized by a good in vitro ADME profile and in vivo pharmacokinetic parameters in the mouse, including oral bioavailability. When tested in vivo in a murine subcutaneous xenograft model employing TT cells, NMS-616 displayed dose-dependent tumor growth inhibition following daily oral administration at 50 and 100 mg/Kg, with tumor regression observed at both dose levels. In addition ex vivo analysis demonstrated dose-dependent target modulation following a single administration and the maintenance of RET phosphorylation inhibition for at least 24 hours. Citation Format: Elena Ardini, Patrizia Banfi, Francesca Quartieri, Paolo Polucci, Nilla Avanzi, Dario Ballinari, Laura Mancini, Edward Felder, Daniele Donati, Arturo Galvani, Enrico Pesenti, Antonella Isacchi, Maria Menichincheri. Identification of a highly potent, selective and orally available RET inhibitor with antitumor efficacy in RET-dependent tumor models. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2091. doi:10.1158/1538-7445.AM2013-2091