Abstract 1481: DAY101, a potent pan-RAF inhibitor with activity in preclinical models harboring MAPK pathway alterations beyond BRAF V600E mutation
Authors: Venetsanakos Eleni , Preigh Mike , Hou Jeannie , Cox Michael C. , Bender Jeremy , Blackman Sam C. 
Published: July 2021

Abstract
DAY101 (formerly TAK-580) is an oral, CNS-penetrant, selective small molecule pan-RAF kinase inhibitor that is equipotent against BRAF V600E, wildtype BRAF, and CRAF and can inhibit both RAF monomers and dimers, including BRAF fusions. KIAA1549:BRAF fusions have been identified as a key oncogenic driver for pilocytic astrocytoma (Jones et al. 2008). DAY101 has demonstrated significant activity against this fusion preclinically (Sun et al. 2017). Clinical data for DAY101 has shown a durable 63% response rate with good tolerability in children with low-grade glioma (LGG) harboring RAF fusions (Wright et al. 2020).
To explore the potential impact of DAY101 in adult solid tumors harboring specific genomic alterations beyond BRAF V600E, a panel of tumor cell lines and PDX models harboring BRAF fusions, non V600 BRAF mutations or RAS mutations were assessed for anti-proliferative activity in response to DAY101. Furthermore, hypothesis-driven MAPK pathway node inhibitor combinations were explored for potential synergy. While performing favourably in preclinical in vivo studies, DAY101 does exhibit some technical challenges in long-term in vitro assays, particularly in those that extend for more than three days. Accordingly, the tool compound TAK-632, which exhibits comparable biochemical and cellular potency to DAY101, was used alternatively as needed for in vitro assays.
Single-agent anti-proliferative activity was observed in a melanoma BRAF fusion PDX model treated with TAK-632 ex vivo, with less sensitivity observed in models beyond melanoma harboring other BRAF fusions. Ongoing combination studies with MEK inhibitors demonstrated strong synergy in PDX models harboring BRAF fusions ex vivo, as assessed by Bliss independence or other relevant scoring systems. In cell lines or PDX models harboring non V600 BRAF mutations, in vitro combination studies demonstrated strong synergy when DAY101 was combined with MEK inhibitors, as assessed by Bliss independence score. DAY101 exhibited modest single agent anti-proliferative activity in a panel of KRAS mutant cell lines in vitro and ongoing combination studies will assess potential synergy when combined with MAPK pathway node inhibitors.
DAY101 is currently in clinical development for the treatment of patients under 25 years old with LGG harboring RAF alterations, including BRAF fusions and BRAF mutations. Inhibition of both RAF monomers and dimers by DAY101 enables a broader indication selection strategy, beyond LGG and BRAF alterations. Ongoing translational work will highlight the potential utility of DAY101 in adult tumors harboring RAS or RAF alterations, both as a single agent and in hypothesis-driven combinations.
Citation Format: Eleni Venetsanakos, Mike Preigh, Jeannie Hou, Michael C. Cox, Jeremy Bender, Sam C. Blackman. DAY101, a potent pan-RAF inhibitor with activity in preclinical models harboring MAPK pathway alterations beyond BRAF V600E mutation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1481.