Tumor Growth Suppression and Enhanced Radioresponse by an Exogenous Epidermal Growth Factor in Mouse Xenograft Models with A431 Cells

Receptor Elimination by E3 Ubiquitin Ligase Recruitment (REULR): A Targeted Protein Degradation Toolbox

In recent years, targeted protein degradation (TPD) of plasma membrane proteins by hijacking the ubiquitin proteasome system (UPS) or the lysosomal pathway has emerged as a novel therapeutic avenue in drug development to address and inhibit canonically difficult targets. While TPD strategies have been successful in targeting cell surface receptors, these approaches are limited by the availability of suitable binders to generate heterobifunctional molecules. Here, we present the development of a nanobody (VHH)-based degradation toolbox termed REULR (Receptor Elimination by E3 Ubiquitin Ligase Recruitment). We generated human and mouse cross-reactive nanobodies against five transmembrane PA-TM-RING-type E3 ubiquitin ligases (RNF128, RNF130, RNF167, RNF43, and ZNRF3), covering a broad range and selectivity of tissue expression, with which we characterized the expression in human and mouse cell lines and immune cells (PBMCs). We demonstrate that heterobifunctional REULR molecules can enforce transmembrane E3 ligase interactions with a variety of disease-relevant target receptors (EGFR, EPOR, and PD-1) by induced proximity, resulting in effective membrane clearance of the target receptor at varying levels. In addition, we designed E3 ligase self-degrading molecules, "fratricide" REULRs (RNF128, RNF130, RENF167, RNF43, and ZNRF3), that allow downregulation of one or several E3 ligases from the cell surface and consequently modulate receptor signaling strength. REULR molecules represent a VHH-based modular and versatile "mix and match" targeting strategy for the facile modulation of cell surface proteins by induced proximity to transmembrane PA-TM-RING E3 ligases.

DNA damage alters EGFR signaling and reprograms cellular response via Mre-11

To combat the various DNA lesions and their harmful effects, cells have evolved different strategies, collectively referred as DNA damage response (DDR). The DDR largely relies on intranuclear protein networks, which sense DNA lesions, recruit DNA repair enzymes, and coordinates several aspects of the cellular response, including a temporary cell cycle arrest. In addition, external cues mediated by the surface EGF receptor (EGFR) through downstream signaling pathways contribute to the cellular DNA repair capacity. However, cell cycle progression driven by EGFR activation should be reconciled with cell cycle arrest necessary for effective DNA repair. Here, we show that in damaged cells, the expression of Mig-6 (mitogen-inducible gene 6), a known regulator of EGFR signaling, is reduced resulting in heightened EGFR phosphorylation and downstream signaling. These changes in Mig-6 expression and EGFR signaling do not occur in cells deficient of Mre-11, a component of the MRN complex, playing a central role in double-strand break (DSB) repair or when cells are treated with the MRN inhibitor, mirin. RNAseq and functional analysis reveal that DNA damage induces a shift in cell response to EGFR triggering that potentiates DDR-induced p53 pathway and cell cycle arrest. These data demonstrate that the cellular response to EGFR triggering is skewed by components of the DDR, thus providing a plausible explanation for the paradox of the known role played by a growth factor such as EGFR in the DNA damage repair.

Biased signaling downstream of epidermal growth factor receptor regulates proliferative versus apoptotic response to ligand

Inhibition of epidermal growth factor receptor (EGFR) signaling by small molecule kinase inhibitors and monoclonal antibodies has proven effective in the treatment of multiple cancers. In contrast, metastatic breast cancers (BC) derived from EGFR-expressing mammary tumors are inherently resistant to EGFR-targeted therapies. Mechanisms that contribute to this inherent resistance remain poorly defined. Here, we show that in contrast to primary tumors, ligand-mediated activation of EGFR in metastatic BC is dominated by STAT1 signaling. This change in downstream signaling leads to apoptosis and growth inhibition in response to epidermal growth factor (EGF) in metastatic BC cells. Mechanistically, these changes in downstream signaling result from an increase in the internalized pool of EGFR in metastatic cells, increasing physical access to the nuclear pool of STAT1. Along these lines, an EGFR mutant that is defective in endocytosis is unable to elicit STAT1 phosphorylation and apoptosis. Additionally, inhibition of endosomal signaling using an EGFR inhibitor linked to a nuclear localization signal specifically prevents EGF-induced STAT1 phosphorylation and cell death, without affecting EGFR:ERK1/2 signaling. Pharmacologic blockade of ERK1/2 signaling through the use of the allosteric MEK1/2 inhibitor, trametinib, dramatically biases downstream EGFR signaling toward a STAT1-dominated event, resulting in enhanced EGF-induced apoptosis in metastatic BC cells. Importantly, combined administration of trametinib and EGF also facilitated an apoptotic switch in EGFR-transformed primary tumor cells, but not normal mammary epithelial cells. These studies reveal a fundamental distinction for EGFR function in metastatic BC. Furthermore, the data demonstrate that pharmacological biasing of EGFR signaling toward STAT1 activation is capable of revealing the apoptotic function of this critical pathway.

Efficacy of combined icotinib and pemetrexed in EGFR mutant lung adenocarcinoma cell line xenografts

Background

The combination of EGFR tyrosine kinase inhibitors (TKIs) and chemotherapy is thought to increase treatment efficacy in non‐small‐cell lung cancer (NSCLC). This study investigated the efficacy and potential mechanisms of different combined modes of icotinib plus pemetrexed in EGFR‐mutant lung adenocarcinoma cell line xenograft models.

Methods

Nude mice were subcutaneously injected with EGFR‐mutant human lung adenocarcinoma cells (HCC827) and randomized into six treatment groups. Tumor xenograft volumes were monitored and recorded. Microvessel density (MVD) and proliferation and apoptosis rates were evaluated with CD34 positive cell counting, and Ki‐67 and caspase‐3 scores, respectively, and determined via immunohistochemistry. Thymidylate synthase (TS), EGFR, and downstream signaling molecule expression was detected by Western blotting.

Results

The volume and weight of tumor xenografts in the sequential pemetrexed followed by icotinib (Pem‐Ico) group and the concurrent icotinib and pemetrexed (Ico + Pem) group were significantly smaller than those in the control, pemetrexed (Pem), icotinib (Ico), and sequential icotinib followed by pemetrexed (Ico‐Pem) groups. Compared to other groups, a decrease in the MVD and proliferation rate and an increase in the apoptosis rate were observed in the Pem‐Ico and Ico + Pem groups. TS expression and EGFR, AKT, and MAPK phosphorylation were significantly reduced in the Pem‐Ico or Ico + Pem groups.

Conclusions

Pem‐Ico had additive antitumor activity in vivo, similar to Ico + Pem, both of which are suggested as potentially optimized strategies for treating EGFR‐mutant lung adenocarcinoma.

Epidermal Growth Factor Enhances Cellular Uptake of Polystyrene Nanoparticles by Clathrin-Mediated Endocytosis

The interaction between nanoparticles and cells has been studied extensively, but most research has focused on the effect of various nanoparticle characteristics, such as size, morphology, and surface charge, on the cellular uptake of nanoparticles. In contrast, there have been very few studies to assess the influence of cellular factors, such as growth factor responses, on the cellular uptake efficiency of nanoparticles. The aim of this study was to clarify the effects of epidermal growth factor (EGF) on the uptake efficiency of polystyrene nanoparticles (PS NPs) by A431 cells, a human carcinoma epithelial cell line. The results showed that EGF enhanced the uptake efficiency of A431 cells for PS NPs. In addition, inhibition and localization studies of PS NPs and EGF receptors (EGFRs) indicated that cellular uptake of PS NPs is related to the binding of EGF-EGFR complex and PS NPs. Different pathways are used to enter the cells depending on the presence or absence of EGF. In the presence of EGF, cellular uptake of PS NPs is via clathrin-mediated endocytosis, whereas, in the absence of EGF, uptake of PS NPs does not involve clathrin-mediated endocytosis. Our findings indicate that EGF enhances cellular uptake of PS NPs by clathrin-mediated endocytosis. This result could be important for developing safe nanoparticles and their safe use in medical applications.

Efficacy of radiotherapy for the treatment of cystic echinococcosis in naturally infected sheep

BACKGROUND

Radiotherapy is commonly used to treat cancers. To date, there has been no study focusing on the effects of radiotherapy on hydatid disease in large animals. In this study, we aim to investigate the efficiency and safety of radiotherapy for treating hydatid disease caused by Echinococcus granulosus in naturally infected sheep.

METHODS

Ultrasound was used to screen naturally infected sheep in an echinococcosis endemic area in Xinjiang, China. A computer tomography (CT) scan confirmed the presence of hydatid cysts. Twenty sheep naturally infected with E. granulosus in the liver and/or lungs were randomly assigned into four groups receiving no irradiation, or X-ray irradiation of low (30 Gy), medium (45 Gy), and high dose (60 Gy), respectively. After three months of radiotherapy, a CT scan was performed to measure the changes in the cysts. The hepatic parasite cysts and host tissues were collected for histology and gene expression analysis.

RESULTS

In the animals subject to irradiation, no significant differences were observed in their appetite, daily activities, and weight before and after radiotherapy. Severe calcification was noticed in the cysts subject to a high dose of radiation compared with the groups subject to low and medium doses. Hematoxylin and eosin staining showed that irradiation contributed to the damage of the cyst structure and nucleus in the germinal layers. Quantitative PCR demonstrated that expression of TPX and HSP70 significantly decreased in a dose-dependent manner (P < 0.05). The expression of the EPC1 decreased in the medium- and high-dose groups compared with the low-dose group (P < 0.05). Meanwhile, the expression of radiation-related apoptosis genes caspase-3 and Gadd45 decreased with an increase in the irradiation dose.

CONCLUSIONS

Radiotherapy is an option with satisfactory efficiency and safety for treating cystic echinococcosis in sheep with partial response or stable disease at month 3. In future, inhibition of cystic activity using radiotherapy may serve as a new regimen for treating hydatid disease.

The paradoxical functions of EGFR during breast cancer progression

The epidermal growth factor receptor (EGFR) is one of the most well-studied signaling pathways in cancer progression. As a result, numerous therapeutics including small-molecule inhibitors and monoclonal antibodies have been developed to target this critical oncogenic driver. Several of these EGFR inhibitors (EGFRi) have been evaluated in metastatic breast cancer, as high-level EGFR expression in primary tumors correlates with the highly aggressive basal-like phenotype and predicts for poor patient prognosis. Surprisingly, these trials have been unanimously unsuccessful at improving patient outcomes. Numerous factors, such as lack of proper patient selection may have contributed to the failure of these trials. However, recent findings suggest that there are fundamental changes in EGFR signaling that take place during primary tumor invasion, dissemination and ultimate metastasis of breast cancer cells. Herein, we review the outcomes of EGFR-targeted clinical trials in breast cancer and explore our current understanding of EGFR signaling within primary mammary tumors and how these events are altered in the metastatic setting. Overall, we put forth the hypothesis that fundamental changes in EGFR signaling between primary and metastatic tumors, a process we term the 'EGFR paradox,' contribute to the clinically observed inherent resistance to EGFRi. Furthermore, this hypothesis introduces the possibility of utilizing EGFR agonism as a potential therapeutic approach for the treatment of metastatic breast cancer.