Abstract B157: Preclinical evaluation of the blood-brain barrier permeability and intracranial efficacy of the next-generation RET inhibitor Vepafestinib
Authors: Odintsov Igor , Wakayama Kentaro , Zhang Tom , Iguchi Satoru , Kato Masanori , Lui Allan JW , Khodos Inna , Vojnic Morana , Giuliano Claudio , Bonifacio Annalisa , Davare Monika A , de Stanchina Elisa , Lovati Emanuela , Ladanyi Marc , Miyazaki Isao , Somwar Romel 
Published: December 2023

Background. Drug resistance and central nervous system (CNS) metastasis often hampers response to precision therapy for RET-rearranged solid tumors. Vepafestinib (Vepa) is a clinical-stage, potent and selective RET tyrosine-kinase inhibitor (TKI) with proven activity against on-target resistance mutations that arise post first-generation RET TKI. Here, we utilized an array of structural and pharmacokinetic methods to determine blood-brain barrier (BBB) permeability of vepa compared with other RET TKIs. Furthermore, we correlate BBB penetrability of RET inhibitors with in vivo efficacy in preclinical models of RET-rearranged intracranial solid tumors.

Methods. RET inhibitors were generated by rational chemical design to identify agents which penetrate BBB more effectively than currently approved RET TKIs, and with reduced efflux transporter susceptibility. Transcellular transport assays were conducted in LLC-PK1 and MDCK II cells expressing P-gp and BCRP, respectively. Brain penetrability was assessed by total (Kp) and unbound (Kp,uu) brain:plasma concentration ratios in male Balb/c mice and microdialysis studies in freely-moving male Wistar rats. Models of CNS metastasis were generated by implanting cells labelled with luciferase into the cerebellum of mice. Studies were conducted in comparison with selpercatinib (Selp), pralsetinib (Pral) and TPX-0046.

 Results. Assessment of Kp and Kp,uu parameters of analogs revealed an excellent structure-activity relationship where modification at the 6-position of the pyrrolopyrimidine core resulted in improved BBB penetrability. The analog with the most favorable physiochemical and biological properties was Vepa. Vepa showed poor susceptibility to P-gp and BCRP-mediated efflux and better CNS penetrability (Kp,uu: 1.3) and retention than Sel, Pral and TPX-0046. The ratio of the observed concentrations of Vepa in microdialysates from the prefrontal cortex, cerebrospinal fluid (CSF) and plasma free fraction was approximately 1:1:1; these ratios were maintained from 2h to 6.5h after Vepaadministration (up to 8h for CSF). Importantly, Vepa was more effective than Selp at causing regression of intracranial xenograft tumors of RET fusion-driven malignancies (lung adenocarcinoma and sarcoma), thus extending survival of tumor-bearing animals. Common first-generation RET TKI resistance mutations at the solvent front (G810A/C/S/R), gatekeeper (V804L/M), hinge (Y806C) and roof (L730Q/R) regions remained sensitive to Vepa. Vepa was more selective than Selp, Pral and TPX-0046, inhibiting only RET when profiled against a panel of 256 kinases. In contrast, Selp, Pral and TPX-0045 also inhibited VEGFR2, and 4, 11 and 39 additional kinases, respectively.

Conclusions. Vepafestinib is a structurally distinct and specific RET inhibitor, with superior brain penetration and retention kinetics. It is more effective than selpercatinib in controlling CNS disease. Vepafestinib is currently undergoing phase 1 and 2 clinical trial for patients with advanced solid tumors with RET alterations (margaRET, NCT04683250).

Citation Format: Igor Odintsov, Kentaro Wakayama, Tom Zhang, Satoru Iguchi, Masanori Kato, Allan JW Lui, Inna Khodos, Morana Vojnic, Claudio Giuliano, Annalisa Bonifacio, Monika A Davare, Elisa de Stanchina, Emanuela Lovati, Marc Ladanyi, Isao Miyazaki, Romel Somwar. Preclinical evaluation of the blood-brain barrier permeability and intracranial efficacy of the next-generation RET inhibitor Vepafestinib [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr B157.