Abstract 5783: Strong Antitumor Activity of ASN007, an Oral ERK1/2 Inhibitor, in PDX Tumor Models with MAP Kinase Pathway Alterations Including KRAS Mutations

Abstract The RAS/RAF/MEK pathway is frequently dysregulated in a broad range of cancers through mutations in several targets such as KRAS, NRAS, HRAS, BRAF, NF1 and receptor tyrosine kinases. Although MEK and BRAF inhibitors improve the outcome for patients with BRAF mutant melanoma and lung cancers, the duration of response is limited due to reactivation of the pathway. The extracellular-signal-regulated kinases, ERK1 and ERK2 (ERK1/2), which are downstream of MEK and BRAF kinases, serve as a key node in this crucial signaling pathway. Targeting ERK1/2 offers a promising therapeutic strategy for a broad range of cancers, particularly the ones driven by RAS mutations, and in overcoming resistance to MEK/BRAF inhibitors. Here, we present discovery and characterization of a novel orally bioavailable compound, ASN007, that showed inhibition of ERK1/2 kinases in a biochemical assay with IC50 = 2 nM for both targets. Interestingly, ASN007 displayed a much slower dissociation rate (longer target residence time) as compared to other ERK inhibitors. ASN007 inhibited the phosphorylation of ERK1/2 substrates such as RSK1, FRA1 and Elk1 in various cell lines with low nM IC50 values. ASN007 showed potent anti-proliferative activity that was selective for MAPK-pathway dependent cancer cell lines. Indeed, ASN007 showed much more robust activity against RAS mutant cell lines as compared to other ERK1/2 inhibitors. In a daily oral dosing regimen, ASN007 demonstrated strong tumor growth inhibition in BRAF, KRAS and NRAS mutant xenograft models in mice and was well tolerated at efficacious doses. Of note, ASN007 showed strong efficacy using various intermittent dosing regimens. It also showed a strong anti-tumor activity in colorectal PDX models with various KRAS mutations. Furthermore, ASN007 showed regression of tumor growth in a melanoma PDX model that was resistant to both MEK and BRAF inhibitors. In addition to the single agent activity, greater efficacy was observed when ASN007 was combined with immunotherapeutic agents such as an anti-PD-1 antibody or an IDO-1 inhibitor. ASN007 does not exhibit significant inhibition of CYP enzymes or the hERG channel. A Phase 1 trial with ASN007 in patients with BRAF and K-, H- and N-RAS mutant melanoma, colorectal, non-small lung and pancreatic cancers is being planned. Citation Format: Sanjeeva P. Reddy, Niranjan S. Rao, Roger A. Smith, Scott K. Thompson, Sarper Toker. Strong antitumor activity of ASN007, an oral ERK1/2 inhibitor, in PDX tumor models with MAP kinase pathway alterations including KRAS mutations [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5783.