928P Phase I dose-expansion (part II) study of ISU104 (a novel anti-ErbB3 monoclonal antibody) alone and combination with cetuximab (CET), in patients (pts) with recurrent/metastatic (R/M) head and neck squamous cell carcinoma (HNSCC)

ERBB3 targeting: A promising approach to overcoming cancer therapeutic resistance

Human epidermal growth factor receptor-3 (ERBB3) is a member of the ERBB receptor tyrosine kinases (RTKs) and is expressed in many malignancies. Along with other ERBB receptors, ERBB3 is associated with regulating normal cell proliferation, apoptosis, differentiation, and survival, and has received increased research attention for its involvement in cancer therapies. ERBB3 expression or co-expression levels have been investigated as predictive factors for cancer prognosis and drug sensitivity. Additionally, the association between the elevated expression of ERBB3 and treatment failure in cancer therapy further established ERBB3-targeting therapy as a crucial therapeutic approach. This review delves into the molecular mechanisms of ERBB3-driven resistance to targeted therapeutics against ERBB2 and EGFR and other signal transduction inhibitors, endocrine therapy, chemotherapy, and radiotherapy. Using preclinical and clinical evidence, we synthesise and explicate how various aspects of aberrant ERBB3 activities-such as compensatory activation, signal crosstalk interactions, dysregulation in the endocytic pathway, mutations, ligand-independent activation, intrinsic kinase activity, and homodimerisation-can lead to resistance development and/or treatment failures. Several ERBB3-directed monoclonal antibodies, bispecific antibodies, and the emerging antibody-drug conjugate demonstrate encouraging clinical outcomes for improving therapeutic efficacy and overcoming resistance, especially when combined with other anti-cancer approaches. More research efforts are needed to identify appropriate biomarkers tailored for ERBB3-targeted therapies.

HER3: Toward the Prognostic Significance, Therapeutic Potential, Current Challenges, and Future Therapeutics in Different Types of Cancer

Human epidermal growth factor receptor 3 (HER3) is the only family member of the EGRF/HER family of receptor tyrosine kinases that lacks an active kinase domain (KD), which makes it an obligate binding partner with other receptors for its oncogenic role. When HER3 is activated in a ligand-dependent (NRG1/HRG) or independent manner, it can bind to other receptors (the most potent binding partner is HER2) to regulate many biological functions (growth, survival, nutrient sensing, metabolic regulation, etc.) through the PI3K-AKT-mTOR pathway. HER3 has been found to promote tumorigenesis, tumor growth, and drug resistance in different cancer types, especially breast and non-small cell lung cancer. Given its ubiquitous expression across different solid tumors and role in oncogenesis and drug resistance, there has been a long effort to target HER3. As HER3 cannot be targeted through its KD with small-molecule kinase inhibitors via the conventional method, pharmaceutical companies have used various other approaches, including blocking either the ligand-binding domain or extracellular domain for dimerization with other receptors. The development of treatment options with anti-HER3 monoclonal antibodies, bispecific antibodies, and different combination therapies showed limited clinical efficiency for various reasons. Recent reports showed that the extracellular domain of HER3 is not required for its binding with other receptors, which raises doubt about the efforts and applicability of the development of the HER3-antibodies for treatment. Whereas HER3-directed antibody-drug conjugates showed potentiality for treatment, these drugs are still under clinical trial. The currently understood model for dimerization-induced signaling remains incomplete due to the absence of the crystal structure of HER3 signaling complexes, and many lines of evidence suggest that HER family signaling involves more than the interaction of two members. This review article will significantly expand our knowledge of HER3 signaling and shed light on developing a new generation of drugs that have fewer side effects than the current treatment regimen for these patients.

HER3 in cancer: from the bench to the bedside

The HER3 protein, that belongs to the ErbB/HER receptor tyrosine kinase (RTK) family, is expressed in several types of tumors. That fact, together with the role of HER3 in promoting cell proliferation, implicate that targeting HER3 may have therapeutic relevance. Furthermore, expression and activation of HER3 has been linked to resistance to drugs that target other HER receptors such as agents that act on EGFR or HER2. In addition, HER3 has been associated to resistance to some chemotherapeutic drugs. Because of those circumstances, efforts to develop and test agents targeting HER3 have been carried out. Two types of agents targeting HER3 have been developed. The most abundant are antibodies or engineered antibody derivatives that specifically recognize the extracellular region of HER3. In addition, the use of aptamers specifically interacting with HER3, vaccines or HER3-targeting siRNAs have also been developed. Here we discuss the state of the art of the preclinical and clinical development of drugs aimed at targeting HER3 with therapeutic purposes.