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Despite the initial promise of cancer therapies targeted against the epidermal growth factor receptor (EGFR), tumors treated with these agents eventually develop resistance. In this Review, the authors outline the complex mechanisms by which tumors become resistant to EGFR-targeted drugs and antibodies and offer insights into new strategies that might be employed to circumvent therapeutic resistance. All patients with metastatic lung, colorectal, pancreatic or head and neck cancers who initially benefit from epidermal growth factor receptor (EGFR)-targeted therapies eventually develop resistance. An increasing understanding of the number and complexity of resistance mechanisms highlights the Herculean challenge of killing tumors that are resistant to EGFR inhibitors. Our growing knowledge of resistance pathways provides an opportunity to develop new mechanism-based inhibitors and combination therapies to prevent or overcome therapeutic resistance in tumors. We present a comprehensive review of resistance pathways to EGFR-targeted therapies in lung, colorectal and head and neck cancers and discuss therapeutic strategies that are designed to circumvent resistance.

Increased intercellular tension is associated with enhanced cell proliferation and tissue growth. Here, we present evidence for a force-transduction mechanism that links mechanical perturbations of epithelial (E)-cadherin (CDH1) receptors to the force-dependent activation of epidermal growth factor receptor (EGFR, ERBB1)—a key regulator of cell proliferation. Here, coimmunoprecipitation studies first show that E-cadherin and EGFR form complexes at the plasma membrane that are disrupted by either epidermal growth factor (EGF) or increased tension on homophilic E-cadherin bonds. Although force on E-cadherin bonds disrupts the complex in the absence of EGF, soluble EGF is required to mechanically activate EGFR at cadherin adhesions. Fully quantified spectral imaging fluorescence resonance energy transfer further revealed that E-cadherin and EGFR directly associate to form a heterotrimeric complex of two cadherins and one EGFR protein. Together, these results support a model in which the tugging forces on homophilic E-cadherin bonds trigger force-activated signaling by releasing EGFR monomers to dimerize, bind EGF ligand, and signal. These findings reveal the initial steps in E-cadherin–mediated force transduction that directly link intercellular force fluctuations to the activation of growth regulatory signaling cascades.

The epidermal growth factor receptor (EGFR) is frequently mutated in human cancer 1 , 2 , and is an important therapeutic target. EGFR inhibitors have been successful in lung cancer, where mutations in the intracellular tyrosine kinase domain activate the receptor 1 , but not in glioblastoma multiforme (GBM) 3 , where mutations occur exclusively in the extracellular region. Here we show that common extracellular GBM mutations prevent EGFR from discriminating between its activating ligands 4 . Different growth factor ligands stabilize distinct EGFR dimer structures 5 that signal with different kinetics to specify or bias outcome 5 , 6 . EGF itself induces strong symmetric dimers that signal transiently to promote proliferation. Epiregulin (EREG) induces much weaker asymmetric dimers that drive sustained signalling and differentiation 5 . GBM mutations reduce the ability of EGFR to distinguish EREG from EGF in cellular assays, and allow EGFR to form strong (EGF-like) dimers in response to EREG and other low-affinity ligands. Using X-ray crystallography, we further show that the R84K GBM mutation symmetrizes EREG-driven extracellular dimers so that they resemble dimers normally seen with EGF. By contrast, a second GBM mutation, A265V, remodels key dimerization contacts to strengthen asymmetric EREG-driven dimers. Our results argue for an important role of altered ligand discrimination by EGFR in GBM, with potential implications for therapeutic targeting. Extracellular glioblastoma-associated mutations reduce the ability of the epidermal growth factor receptor to distinguish between its ligands.

Transected axons fail to regrow across anatomically complete spinal cord injuries (SCI) in adults. Diverse molecules can partially facilitate or attenuate axon growth during development or after injury 1 – 3 , but efficient reversal of this regrowth failure remains elusive 4 . Here we show that three factors that are essential for axon growth during development but are attenuated or lacking in adults—(i) neuron intrinsic growth capacity 2 , 5 – 9 , (ii) growth-supportive substrate 10 , 11 and (iii) chemoattraction 12 , 13 —are all individually required and, in combination, are sufficient to stimulate robust axon regrowth across anatomically complete SCI lesions in adult rodents. We reactivated the growth capacity of mature descending propriospinal neurons with osteopontin, insulin-like growth factor 1 and ciliary-derived neurotrophic factor before SCI 14 , 15 ; induced growth-supportive substrates with fibroblast growth factor 2 and epidermal growth factor; and chemoattracted propriospinal axons with glial-derived neurotrophic factor 16 , 17 delivered via spatially and temporally controlled release from biomaterial depots 18 , 19 , placed sequentially after SCI. We show in both mice and rats that providing these three mechanisms in combination, but not individually, stimulated robust propriospinal axon regrowth through astrocyte scar borders and across lesion cores of non-neural tissue that was over 100-fold greater than controls. Stimulated, supported and chemoattracted propriospinal axons regrew a full spinal segment beyond lesion centres, passed well into spared neural tissue, formed terminal-like contacts exhibiting synaptic markers and conveyed a significant return of electrophysiological conduction capacity across lesions. Thus, overcoming the failure of axon regrowth across anatomically complete SCI lesions after maturity required the combined sequential reinstatement of several developmentally essential mechanisms that facilitate axon growth. These findings identify a mechanism-based biological repair strategy for complete SCI lesions that could be suitable to use with rehabilitation models designed to augment the functional recovery of remodelling circuits. Stimulating the intrinsic growth capacity of neurons and providing growth-supportive substrate and chemoattraction can allow axon regrowth across anatomically complete spinal cord injuries in adult rodents.

Three-dimensional (3D) cell culture is gaining acceptance in response to the need for cellular models that better mimic physiologic tissues. Spheroids are one such 3D model where clusters of cells will undergo self-assembly to form viable, 3D tumor-like structures. However, to date little is known about how spheroid biology compares to that of the more traditional and widely utilized 2D monolayer cultures. Therefore, the goal of this study was to characterize the phenotypic and functional differences between lung tumor cells grown as 2D monolayer cultures, versus cells grown as 3D spheroids. Eight lung tumor cell lines, displaying varying levels of epidermal growth factor receptor (EGFR) and cMET protein expression, were used to develop a 3D spheroid cell culture model using low attachment U-bottom plates. The 3D spheroids were compared with cells grown in monolayer for 1) EGFR and cMET receptor expression, as determined by flow cytometry, 2) EGFR and cMET phosphorylation by MSD assay, and 3) cell proliferation in response to epidermal growth factor (EGF) and hepatocyte growth factor (HGF). In addition, drug responsiveness to EGFR and cMET inhibitors (Erlotinib, Crizotinib, Cetuximab [Erbitux] and Onartuzumab [MetMab]) was evaluated by measuring the extent of cell proliferation and migration. Data showed that EGFR and cMET expression is reduced at day four of untreated spheroid culture compared to monolayer. Basal phosphorylation of EGFR and cMET was higher in spheroids compared to monolayer cultures. Spheroids showed reduced EGFR and cMET phosphorylation when stimulated with ligand compared to 2D cultures. Spheroids showed an altered cell proliferation response to HGF, as well as to EGFR and cMET inhibitors, compared to monolayer cultures. Finally, spheroid cultures showed exceptional utility in a cell migration assay. Overall, the 3D spheroid culture changed the cellular response to drugs and growth factors and may more accurately mimic the natural tumor microenvironment.

To update key recommendations of the American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) human epidermal growth factor receptor 2 (HER2) testing in breast cancer guideline. Based on the signals approach, an Expert Panel reviewed published literature and research survey results on the observed frequency of less common in situ hybridization (ISH) patterns to update the recommendations. Two recommendations addressed via correspondence in 2015 are included. First, immunohistochemistry (IHC) 2+ is defined as invasive breast cancer with weak to moderate complete membrane staining observed in >10% of tumor cells. Second, if the initial HER2 test result in a core needle biopsy specimen of a primary breast cancer is negative, a new HER2 test may (not \"must\") be ordered on the excision specimen based on specific clinical criteria. The HER2 testing algorithm for breast cancer is updated to address the recommended workup for less common clinical scenarios (approximately 5% of cases) observed when using a dual-probe ISH assay. These scenarios are described as ISH group 2 ( HER2/chromosome enumeration probe 17 [CEP17] ratio ≥2.0; average HER2 copy number <4.0 signals per cell), ISH group 3 ( HER2/CEP17 ratio <2.0; average HER2 copy number ≥6.0 signals per cell), and ISH group 4 ( HER2/CEP17 ratio <2.0; average HER2 copy number ≥4.0 and <6.0 signals per cell). The diagnostic approach includes more rigorous interpretation criteria for ISH and requires concomitant IHC review for dual-probe ISH groups 2 to 4 to arrive at the most accurate HER2 status designation (positive or negative) based on combined interpretation of the ISH and IHC assays. The Expert Panel recommends that laboratories using single-probe ISH assays include concomitant IHC review as part of the interpretation of all single-probe ISH assay results.

Key Points The ERBB system consists of four receptors (ERBB1–4), two of which, ERBB2/HER2 and ERBB3 are non-autonomous. All four ERBB proteins form functional dimers after activation by epidermal growth factor (EGF)-family growth factors. Recent advances in structural analysis of the receptors has revealed the mechanism of receptor dimerization, and together with the results of gene targeting in mice provide an explanation for the critical role of ERBB2/HER2 in human cancer. Misregulated activation of ERBB receptors has been widely associated with human malignancies, and a number of drugs that target these receptors are in clinical use. ∼25,000 scientific papers relate to ERBB-receptor signalling, in which hundreds of receptor interactions are described, forcing investigators to take a systems view of the network. Definitions from the field of systems biology apply to the ERBB network, which is described as a robust information-processing system, with a bow-tie structure, to which we apply principles of modularity, redundancy, bistability, system controls and buffering. Fragility of the system is a necessary trade-off of its robustness, a principle we exemplify when dealing with clinically approved, as well as experimental, cancer therapeutics. Future analysis of the ERBB network might depend on establishing common experimental conditions, which will allow synergistic interactions between experimentalists and theoreticians in the field. The ERBB network is one of the most studied areas in signal transduction, and it exemplifies the pathogenic power of aberrant signalling. Systems-level modelling and an understanding of the network's circuitry, robustness and controls will enable the development of novel cancer therapies. Signalling through the ERBB/HER receptors is intricately involved in human cancer and already serves as a target for several cancer drugs. Because of its inherent complexity, it is useful to envision ERBB signalling as a bow-tie-configured, evolvable network, which shares modularity, redundancy and control circuits with robust biological and engineered systems. Because network fragility is an inevitable trade-off of robustness, systems-level understanding is expected to generate therapeutic opportunities to intercept aberrant network activation.

Recurrent oral ulcer (ROU) is a common oral mucosal disease with recurrent ulcerative lesions. Shuanghuanglian Oral liquid is a traditional Chinese medicine preparation widely used to treat oral ulcers. This study aimed to explore the effect of Shuanghuanglian oral liquid on the epidermal growth factor (EGF) level in saliva and serum inflammatory factors in patients with recurrent oral ulcers to provide a certain reference for clinical treatment. A retrospective analysis of 90 ROU patients from 2018 to 2021 was divided into an observation group (n=45) and a control group (n=45). All patients were recruited from Kunming Stomatological Hospital North Downtown Campus. The control group used a mouthwash containing chlorhexidine, while the observation group used the same mouthwash with an additional topical application of Shuanghuanglian. The EGF level in saliva, serum inflammatory factor, clinical efficacy, pain and quality of life scores, recurrence rate, and incidence of adverse reactions were observed in the two groups. After treatment, EGF (RR 0.41, 95%CI 0.15-0.73, P < .001), tumor necrosis factor-α (TNF-α) (RR 0.68, 95%CI 0.53-0.77, P = .003), interleukin-10 (IL-10) (RR 0.64, 95%CI 0.48-0.75, P < .001), and C-reactive protein (CRP) (RR 0.52, 95%CI 0.35-0.65, P < .001) in observation group were significantly lower than those in the control group; The total effective rate of the observation group was significantly higher than that of the control group (RR 0.85, 95%CI 0.44-0.95, P = .02); Visual analogue scale (VAS) (RR 0.48, 95%CI 0.35-0.68, P < .001) and Oral Health Rating Scale (OHIP-4) scores (RR 0.61, 95%CI 0.47-0.84, P < .001)of observation group were significantly lower than those of control group after treatment; The incidence of total adverse reactions (RR 0.73, 95%CI 0.61-0.86, P = .011) and the recurrence rate at 6 months after treatment in the observation group were significantly lower than those in the control group (RR 0.78, 95%CI 0.69-0.91, P = .015). Shuanghuanglian oral liquid has a remarkable effect on patients with ROU by reducing the levels of EGF and inflammatory factors in patients, reducing the pain degree of patients, improving the oral health of patients, improving the quality of life of patients, and reducing the incidence of adverse reactions and the recurrence rate of patients to a certain extent.

The epidermal growth factor receptor (EGFR) is a receptor tyrosine kinase that is commonly upregulated in cancers such as in non-small-cell lung cancer, metastatic colorectal cancer, glioblastoma, head and neck cancer, pancreatic cancer, and breast cancer. Various mechanisms mediate the upregulation of EGFR activity, including common mutations and truncations to its extracellular domain, such as in the EGFRvIII truncations, as well as to its kinase domain, such as the L858R and T790M mutations, or the exon 19 truncation. These EGFR aberrations over-activate downstream pro-oncogenic signaling pathways, including the RAS-RAF-MEK-ERK MAPK and AKT-PI3K-mTOR pathways. These pathways then activate many biological outputs that are beneficial to cancer cell proliferation, including their chronic initiation and progression through the cell cycle. Here, we review the molecular mechanisms that regulate EGFR signal transduction, including the EGFR structure and its mutations, ligand binding and EGFR dimerization, as well as the signaling pathways that lead to G1 cell cycle progression. We focus on the induction of CYCLIN D expression, CDK4/6 activation, and the repression of cyclin-dependent kinase inhibitor proteins (CDKi) by EGFR signaling pathways. We also discuss the successes and challenges of EGFR-targeted therapies, and the potential for their use in combination with CDK4/6 inhibitors.

In addition to maintaining immune tolerance, FOXP3 + regulatory T (T reg ) cells perform specialized functions in tissue homeostasis and remodelling 1 , 2 . However, the characteristics and functions of brain T reg cells are not well understood because there is a low number of T reg cells in the brain under normal conditions. Here we show that there is massive accumulation of T reg cells in the mouse brain after ischaemic stroke, and this potentiates neurological recovery during the chronic phase of ischaemic brain injury. Although brain T reg cells are similar to T reg cells in other tissues such as visceral adipose tissue and muscle 3 – 5 , they are apparently distinct and express unique genes related to the nervous system including Htr7 , which encodes the serotonin receptor 5-HT 7 . The amplification of brain T reg cells is dependent on interleukin (IL)-2, IL-33, serotonin and T cell receptor recognition, and infiltration into the brain is driven by the chemokines CCL1 and CCL20. Brain T reg cells suppress neurotoxic astrogliosis by producing amphiregulin, a low-affinity epidermal growth factor receptor (EGFR) ligand. Stroke is a leading cause of neurological disability, and there are currently few effective recovery methods other than rehabilitation during the chronic phase. Our findings suggest that T reg cells and their products may provide therapeutic opportunities for neuronal protection against stroke and neuroinflammatory diseases. In a mouse model of ischaemic stroke, regulatory T cells infiltrate the injured brain in response to the chemokines CCL1 and CCL20 and suppress excessive astrogliosis via the production of amphiregulin.