2019: Dual-mechanism ERK1/2 inhibitors exploit a distinct binding mode to block phosphorylation and nuclear accumulation of ERK1/2

Summary
The RAS-regulated RAF-MEK1/2-ERK1/2 signalling pathway is frequently deregulated in cancer due to activating mutations of growth factor receptors, RAS or BRAF. Both RAF and MEK1/2 inhibitors are clinically approved and various ERK1/2 inhibitors (ERKi) are currently undergoing clinical trials. To date ERKi display two distinct mechanisms of action (MoA); catalytic ERKi solely inhibit ERK1/2 catalytic activity, whereas dual mechanism ERKi additionally prevent the activating phosphorylation of ERK1/2 at its T-E-Y motif by MEK1/2. These differences may impart significant differences in biological activity because T-E-Y phosphorylation is the signal for nuclear entry of ERK1/2, allowing them to access many key transcription factor targets. Here, we characterised the MoA of five ERKi and examined their functional consequences in terms of ERK1/2 signalling, gene expression and antiproliferative efficacy. We demonstrate that catalytic ERKi promote a striking nuclear accumulation of p-ERK1/2 in KRAS mutant cell lines. In contrast, dual mechanism ERKi exploit a distinct binding mode to block ERK1/2 phosphorylation by MEK1/2, exhibit superior potency and prevent the nuclear accumulation of ERK1/2. Consequently, dual-mechanism ERKi exhibit more durable pathway inhibition and enhanced suppression of ERK1/2-dependent gene expression compared to catalytic ERKi, resulting in increased efficacy across BRAF and RAS mutant cell lines.

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Dual-mechanism ERK1/2 inhibitors exploit a distinct binding mode to block phosphorylation and nuclear accumulation of ERK1/2

A novel ERK inhibitor has potent activity in NRAS-mutant melanoma cancer models

Introduction

  • NRAS mutations occur in 15-20% of mutant melanoma cancer patients. Currently there is no approved therapy for NRAS-mutant melanoma, an indication which is associated with aggressive clinical outcome and a poor prognosis.
  • The NRAS mutation leads to constitutive activation of the MAPK pathway. ERK is the primary downstream effector of MAPK and its direct inhibition may provide an attractive therapeutic approach for the treatment of NRAS-mutant
    melanoma.
  • As previously described, using fragment-based drug discovery we have identified a novel and selective inhibitor of ERK which inhibits in vitro ERK catalytic activity as well as ERK phosphorylation1.
  • Here, we demonstrate the in vitro and in vivo activity of a novel, highly potent, elective ERK inhibitor in models of NRAS-mutant melanoma.

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A novel ERK inhibitor has potent activity in NRAS-mutant melanoma cancer models

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

Summary
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