A small molecule inhibitor of HER3: a proof-of-concept study

Abstract

Despite being catalytically defective, pseudokinases are typically essential players of cellular signalling, acting as allosteric regulators of their active counterparts. Deregulation of a growing number of pseudokinases has been linked to human diseases, making pseudokinases therapeutic targets of interest. Pseudokinases can be dynamic, adopting specific conformations critical for their allosteric function. Interfering with their allosteric role, with small molecules that would lock pseudokinases in a conformation preventing their productive partner interactions, is an attractive therapeutic strategy to explore.  As a well-known allosteric activator of EGFR family members, and playing a major part in cancer progression, the pseudokinase HER3 is a relevant context in which to address the potential of pseudokinases as drug targets for the development of allosteric inhibitors. In this proof-of-concept study, we developed a multiplex, medium throughput thermal-shift assay screening strategy to assess over 100,000 compounds and identify selective small molecule inhibitors that would trap HER3 in a conformation which is unfavourable for the formation of an active HER2-HER3 heterodimer. As a proof-of-concept compound, AC3573 bound with some specificity to HER3 and abrogated HER2-HER3 complex formation and downstream signalling in cells. Our study highlights the opportunity to identify new molecular mechanisms of action interfering with the biological function of pseudokinases.

There’s more to death than life: Noncatalytic functions in kinase and pseudokinase signaling

“…The formation of an active dimer with HER2 whereby HER3 allosterically activates HER2 is inherent to its function. Stemming from DSF-based screening, a small-molecule binder of HER3 (AC3573) with marked selectivity over HER2 has been identified ( 100 ). Importantly, AC3573 antagonizes signaling by decreasing heterodimer formation, in contrast with another ATP-competitive inhibitor, bosutinib, which can promote active dimers ( 101 ).…”

A preclinical model of patient-derived cerebrospinal fluid circulating tumor cells for experimental therapeutics in leptomeningeal disease from melanoma

“…Since ErbB3 is sometimes regarded as “undruggable’ due to its lack of phosho-activity, 47 allosteric inhibitors were recently developed to prevent ErbB3 from dimer signaling. 48 In another study, bi-specific antibody for IGF1R and ErbB3 was tested in preclinical models of pancreatic cancer. 49 Further investigation is currently underway in our lab to investigate ErbB3’s role in LMD.…”

Targeting the Non-Catalytic Functions: a New Paradigm for Kinase Drug Discovery?

“…21 In 2020, Colomba and coworkers also discovered that AC3573 (2, Figure 1) could selectively bind to HER3 and block HER3−HER2 heterodimerization in cells. 22 The Kinase Suppressor of Ras (KSR) is another well-studied pseudokinase featured with an arginine residue in the conserved β3-lysine position, and histidine− lysine−aspartic acid at the beginning of the catalytic loop instead of histidine−arginine−aspartic acid or tyrosine− arginine−aspartic acid for most active protein kinases. 23 KSR plays an essential role in Ras/mitogen-activated protein kinase (MAPK) signaling by acting as a molecular scaffold to assemble the MAPK signaling modules.…”

“…The compound also potently suppressed HER3-dependent cell growth at submicromolar concentrations . In 2020, Colomba and co-workers also discovered that AC3573 ( 2 , Figure ) could selectively bind to HER3 and block HER3–HER2 heterodimerization in cells . The Kinase Suppressor of Ras (KSR) is another well-studied pseudokinase featured with an arginine residue in the conserved β3-lysine position, and histidine–lysine–aspartic acid at the beginning of the catalytic loop instead of histidine–arginine–aspartic acid or tyrosine–arginine–aspartic acid for most active protein kinases .…”