2018 AACR: A novel ERK1/2 inhibitor has potent activity in KRAS-mutant non-small cell lung cancer models

Non-small cell lung cancer (NSCLC) molecular profiling is a key factor in treatment selection. Although, patients with NSCLC tumors harboring EGFR or ALK mutations can benefit from personalized therapies, there are currently no approved targeted therapies for KRAS mutant tumors which occur in 25% to 30% of patients with NSCLC. The constitutive activation of the MAPK pathway in these tumors provides a rationale for targeting effectors such as MEK1/2 (MEK) or ERK1/2 (ERK). Inhibitor of MEK kinase have been tested clinically in KRAS-mutant NSCLC but results have been disappointing, possibly because compensatory signalling such as the reactivation of ERK is triggered following the inhibition of MEK, leading to cancer cell survival. Therefore, targeting ERK directly represents an attractive therapeutic approach. As previously described, we have developed a novel, potent and selective ERK inhibitor identified by fragment-based drug discovery which has potent activity in vitro and in vivo. Here, we demonstrate the activity of this lead compound in KRAS-mutant NSCLC models.
Our novel ERK inhibitor was tested in a panel of 440 human cancer cell lines of which the KRAS NSCLC population was identified as particularly sensitive. 62% of the KRAS-mutant NSCLC cell lines tested, exhibited antiproliferative IC50s ranging from 1 nM to 500 nM. This lead compound also inhibited ERK downstream signalling in KRAS NSCLC models both in vitro and in vivo. Indeed, the phosphorylation level of the ERK substrate, RSK, was strongly decreased in HCC-44 and Calu-6 xenograft tumors 2h after the oral administration of the lead compound at 50 mg/kg. Levels of pRSK remained below those of untreated tumors for up to 16h in HCC-44 tumors and 24h in Calu-6 tumors. We also confirmed that, the ERK inhibitor conferred a decrease in phosphorylation of ERK itself in both models. The inhibition of ERK signalling corresponded to significant anti-tumour activity in these models with a daily oral administration of 50 mg/kg compound leading to significant tumor regression in subcutaneous models of HCC-44 (18.3% T/C) and Calu-6 (8.9% T/C) xenograft tumors.
This work demonstrates the in vitro and in vivo activity of a novel, highly potent, selective ERK inhibitor in models of KRAS-mutant NSCLC. These data support the further optimisation of this series of compounds for clinical development.

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A novel ERK1/2 inhibitor has potent activity in KRAS-mutant non-small cell lung cancer models