Quantitation of ERK1/2 inhibitor cellular target occupancies with a reversible slow off-rate probe

Application of the Cellular Thermal Shift Assay (CETSA) to validate drug target engagement in platelets

Small molecule drugs play a major role in the study of human platelets. Effective action of a drug requires it to bind to one or more targets within the platelet (target engagement). However, although in vitro assays with isolated proteins can be used to determine drug affinity to these targets, additional factors affect target engagement and its consequences in an intact platelet, including plasma membrane permeability, intracellular metabolism or compartmentalization, and level of target expression. Mechanistic interpretation of the effect of drugs on platelet activity requires comprehensive investigation of drug binding in the proper cellular context, i.e. in intact platelets. The Cellular Thermal Shift Assay (CETSA) is a valuable method to investigate target engagement within complex cellular environments. The assay is based on the principle that drug binding to a target protein increases that protein's thermal stability. In this technical report, we describe the application of CETSA to platelets. We highlight CETSA as a quick and informative technique for confirming the direct binding of drugs to platelet protein targets, providing a platform for understanding the mechanism of action of drugs in platelets, and which will be a valuable tool for investigating platelet signaling and function.

Design, Synthesis, and Antitumor Activity Evaluation of Proteolysis-Targeting Chimeras as Degraders of Extracellular Signal-Regulated Kinases 1/2

Inhibition of the extracellular signal-regulated kinases 1/2 (ERK1/2) alone or in combination with other targets has emerged as a promising treatment strategy for a variety of human tumors. In addition to the development of inhibitors, the development of ERK1/2 degraders is an alternative approach to decrease its activity. We synthesized proteolysis-targeting chimeras (PROTACs) as effective ERK1/2 degraders, among which B1-10J showed high degradative activity, with DC50 of 102 nM and cytotoxic IC50 of 2.2 μM against HCT116 cells. Moreover, B1-10J dose-dependently inhibited tumor cell migration. Xenograft experiments in nude mice demonstrated that B1-10J inhibited HCT116 tumor cell growth and achieved significant regression of tumors at a daily dose of 25 mg/kg.

Ravoxertinib Improves Long-Term Neurologic Deficits after Experimental Subarachnoid Hemorrhage through Early Inhibition of Erk1/2

Extracellular signal-regulated kinase 1 and 2 (Erk1/2) signaling has been shown to be involved in brain injury after subarachnoid hemorrhage (SAH). A first-in-human phase I study reported that ravoxertinib hydrochloride (RAH), a novel Erk1/2 inhibitor, has an acceptable safety profile and pharmacodynamic effects. Here, we showed that the level of Erk1/2 phosphorylation (p-Erk1/2) was significantly increased in the cerebrospinal fluid (CSF) of aneurysmal subarachnoid hemorrhage (aSAH) patients who developed poor outcomes. In a rat SAH model that was produced by the intracranial endovascular perforation method, western blot observed that the level of p-Erk1/2 was also increased in the CSF and basal cortex, showing a similar trend with aSAH patients. Immunofluorescence and western blot indicated that RAH treatment (i.c.v injection, 30 min post-SAH) attenuates the SAH-induced increase of p-Erk1/2 at 24 h in rats. RAH treatment can improve experimental SAH-induced long-term sensorimotor and spatial learning deficits that are evaluated by the Morris water maze, rotarod test, foot-fault test, and forelimb placing test. Moreover, RAH treatment attenuates neurobehavioral deficits, the blood-brain barrier damage, and cerebral edema at 72 h after SAH in rats. Furthermore, RAH treatment decreases the SAH-elevated apoptosis-related factor active caspase-3 and the necroptosis-related factor RIPK1 expression at 72 h in rats. Immunofluorescence analysis showed that RAH attenuated neuronal apoptosis but not neuronal necroptosis in the basal cortex at 72 h after SAH in rats. Altogether, our results suggest that RAH improves long-term neurologic deficits through early inhibition of Erk1/2 in experimental SAH.

Targeting Extracellular Signal-Regulated Protein Kinase 1/2 (ERK1/2) in Cancer: An Update on Pharmacological Small-Molecule Inhibitors

Extracellular signal-regulated protein kinase 1/2 (ERK1/2), the only known substrate of MEK1/2, is located downstream of the RAS-RAF-MEK-ERK (MAPK) pathway and is associated with the abnormal activation and poor prognosis of cancer. To date, several small-molecule inhibitors of RAS, RAF, and MEK have been reported to make rapid advances in cancer therapy; however, acquired resistance still occurs, thereby weakening the therapeutic efficacy of these inhibitors. Recently, selective inhibition of ERK1/2 has been regarded as a potential cancer therapeutic strategy that can not only effectively block the MAPK pathway but also overcome drug resistance caused by upstream mutations in RAS, RAF, and MEK. Herein, we summarize the oncogenic roles, key signaling network, and the single- and dual-target inhibitors of ERK1/2 in preclinical and clinical trials. Together, these inspiring findings shed new light on the discovery of more small-molecule inhibitors of ERK1/2 as candidate drugs to improve cancer therapeutics.

Identification of cell type-specific correlations between ERK activity and cell viability upon treatment with ERK1/2 inhibitors

Increased MAPK signaling is a hallmark of various cancers and is a central regulator of cell survival. Direct ERK1/2 inhibition is considered a promising approach to avoid ERK1/2 reactivation caused by upstream kinases BRAF, MEK1/2, and KRAS, as well as by receptor tyrosine kinase inhibitors, but the dynamics and selectivity of ERK1/2 inhibitors are much less studied compared with BRAF or MEK inhibitors. Using ERK1/2 and downstream kinase ELK1 reporter cell lines of lung cancer (H1299; NRAS^Q61K), colon cancer (HCT-116; KRAS^G13D), neuroblastoma (SH-SY5Y), and leukemia (U937), we examined the relationship between ERK inhibition and drug-induced toxicity for five ERK inhibitors: SCH772984, ravoxertinib, LY3214996, ulixertinib, and VX-11e, as well as one MEK inhibitor, PD0325901. Comparing cell viability and ERK inhibition revealed different ERK dependencies for these cell lines. We identify several drugs, such as SCH772984 and VX-11e, which induce excessive toxicity not directly related to ERK1/2 inhibition in specific cell lines. We also show that PD0325901, LY3214996, and ulixertinib are prone to ERK1/2 reactivation over time. We distinguished two types of ERK1/2 reactivation: the first could be reversed by adding a fresh dose of inhibitors, while the second persists even after additional treatments. We also showed that cells that became resistant to the MEK1/2 inhibitor PD0325901 due to ERK1/2 reactivation remained sensitive to ERK1/2 inhibitor ulixertinib. Our data indicate that correlation of ERK inhibition with drug-induced toxicity in multiple cell lines may help to find more selective and effective ERK1/2 inhibitors.

Evaluation of FOXO1 Target Engagement Using a Single-Cell Microfluidic Platform

The cellular thermal shift assay (CETSA) has been used extensively since its introduction to study drug-target engagement within both live cells and cellular lysate. This has proven to be a useful tool in early stage drug discovery and is used to study a wide range of protein classes. We describe the application of a single-cell CETSA workflow within a microfluidic affinity capture (MAC) chip. This has enabled us to quantitatively determine the active FOXO1 single-molecule count and observe FOXO1 stabilization and destabilization in the presence of three small molecule inhibitors, including demonstrating the determination of EC₅₀. The successful use of the MAC chip for single-cell CETSA paves the way for the study of precious clinical samples owing to the low number of cells needed by the chip. It also provides a useful tool for studying any underlying population heterogeneity that exists within a cellular system, a feature that is usually masked when conducting ensemble measurements.

Covalent Small Molecule Immunomodulators Targeting the Protease Active Site

Cells of the immune system utilize multiple proteases to regulate cell functions and orchestrate innate and adaptive immune responses. Dysregulated protease activities are implicated in many immune-related disorders; thus, protease inhibitors have been actively investigated for pharmaceutical development. Although historically considered challenging with concerns about toxicity, compounds that covalently modify the protease active site represent an important class of agents, emerging not only as chemical probes but also as approved drugs. Here, we provide an overview of technologies useful for the study of proteases with the focus on recent advances in chemoproteomic methods and screening platforms. By highlighting covalent inhibitors that have been designed to target immunomodulatory proteases, we identify opportunities for the development of small molecule immunomodulators.