Abstract P233: TAS0953/HM06 is effective in preclinical models of diverse tumor types driven by RET alterations
Authors: Odintsov Igor , Kurth Renate I. , Ishizawa Kota , Delasos Lukas , Lui Allan J.W. , Khodos Inna , Hagen Connor J. , Chang Qing , Mattar Marissa S. , Vojnic Morana , Kunte Siddharth , Bonifacio Annalisa , Giuliano Claudio , De Stanchina Elisa , Cheng Emily , Lovati Emanuela , Ladanyi Marc , Somwar Romel 
Published: December 2021

Abstract
Fusions involving RET receptor tyrosine kinase are a common driver of tumors across different tissue types, such as lung, thyroid, colorectal, soft tissue and others. TAS0953/HM06 (hereby referred to as HM06) is a novel 2ndgeneration RET-specific inhibitor that is effective against RET solvent front (G810) and gatekeeper (V804) mutations. Here, we evaluated the efficacy of HM06 in lung and thyroid carcinomas, and soft-tissue sarcoma cell lines and PDXs derived from RET inhibitor-naive tumor samples or from tumors with acquired resistance to selpercatinib. HM06 was more effective than the RET multi-kinase inhibitors cabozantinib and vandetanib, and as effective as selpercatinib and pralsetinib in inhibiting growth of patient-derived and isogenic lung, thyroid and sarcoma cell lines (IC50=0.02-0.1 µM) harboring different RET fusions (KIF5B-RET, CCDC6-RET, TRIM33-RET, SPECCL1-RET) or activating mutations (RET C634W). Growth of non-tumor cells was up to 80-fold less sensitive to HM06 (IC50= 1.6 µM). Treatment of RET fusion-positive lung cancer cells with HM06 resulted in a dose-dependent inhibition of RET phosphorylation (Y905 and Y1062) and the downstream effectors AKT, ERK1/2, p70S6K and S6. Caspase 3/7 activity and markers of apoptosis (BIM, cleaved PARP) were induced by HM06 to a similar extent as pralsetinib and selpercatinib (dose range: 0.05-1 µM). HM06 induced changes in the core mediators of cell cycle regulation (upregulation of p27, downregulation of CCND1) and suppressed expression of MYC and ETV5. In vivo, HM06 blocked tumor growth and/or induced regression of up to 65% in seven patient-derived xenograft (PDX) models with RET fusions (five NSCLC PDXs, one sarcoma PDX and one NSCLC cell-line xenograft) to a similar extent as pralsetinib and selpercatinib. However, 6 weeks after cessation of treatment of the SPECCL1-RET-driven sarcoma PDX model, growth of tumors treated with HM06 was suppressed completely, whereas 3/5 pralsetinib-treated tumors and 1/5 selpercatinib-treated tumor regrew. Combination of HM06 and the MET inhibitor capmatinib effectively blocked growth of PDX tumors in a model that was derived from a patient sample that expressed RET fusion and METamplification, and was resistant to selpercatinib. These results suggest that HM06 may be an effective therapy for RET-driven tumors in a tissue-type agnostic manner and can effectively address common on-target and off-target resistance mechanisms such as RET G810X and V804X mutations. HM06 is currently in a phase 1 and 2 clinical trial for patients with advanced solid tumors with RET gene abnormalities (margaRET, NCT 04683250).
Citation Format: Igor Odintsov, Renate I. Kurth, Kota Ishizawa, Lukas Delasos, Allan J.W. Lui, Inna Khodos, Connor J. Hagen, Qing Chang, Marissa S. Mattar, Morana Vojnic, Siddharth Kunte, Annalisa Bonifacio, Claudio Giuliano, Elisa De Stanchina, Emily Cheng, Emanuela Lovati, Marc Ladanyi, Romel Somwar. TAS0953/HM06 is effective in preclinical models of diverse tumor types driven by RET alterations [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P233.