Therapeutic potential of EGFR-related protein, a universal EGFR family antagonist

Translational research of a novel humanized epidermal growth factor receptor-related protein: a putative inhibitor of pan-ErbB

PURPOSE

The ErbB family members are protein tyrosine kinases, which play a crucial role in the signal transduction pathways that regulate key cellular functions. Overexpression of the ErbB family members is associated with oncogenicity, metastatic potential, cell proliferation, apoptosis, angiogenesis, and prognosis in cancer. Molecular-targeted therapies centered on the ErbB signaling pathway are the currently promising anti-cancer therapies.

METHODS

We reviewed the literature to summarize the current knowledge of epidermal growth factor receptor (EGFR)-related protein (ERRP) and determine the potential of this protein to be translated into a molecular-targeting treatment for cancer.

RESULTS

ERRP isolated from rat gastroduodenal mucosa is a pan-ErbB inhibitor that targets multiple members of the ErbB family both in vitro and in vivo. Sequestration of ErbB ligands by ERRP results in the formation of inactive ErbB heterodimers and subsequent attenuation of signaling pathways activated by ErbB. We suggest a strategy to develop a humanized ERRP protein based on activity of rat EERP in vitro.

CONCLUSIONS

As rat ERRP protein is expected to generate an immune response in humans, we propose a hypothesis that a humanized version of ERRP has potential therapeutic value for cancer patients.

EGFR(s) in aging and carcinogenesis of the gastrointestinal tract

Cells of the gastrointestinal (GI) mucosa are subject to a constant process of renewal which, in normal adults, reflects a balance between the rates of cell production and cell loss. Detailed knowledge of these events is, therefore, essential for a better understanding of the normal aging processes as well as many GI diseases, particularly malignancy, that represent disorders of tissue growth. In general, many GI dysfunctions, including malignancy, increase with advancing age, and aging itself is associated with alterations in structural and functional integrity of the GI tract. Although the regulatory mechanisms for age-related increase in the incidence of GI-cancers are yet to be fully delineated, recent evidence suggests a role for epidermal growth family receptors and its family members {referred to as EGFR(s)} in the development and progression of carcinogenesis during aging. The present communication discusses the involvement of EGFR(s) in regulating events of GI cancers during advancing age and summarizes the current available therapeutics targeting these receptors. The current review also describes the effectiveness of ErbB inhibitors as well as combination therapies. Additionally, the involvement of GI stem cells in the development of the age-related rise in GI cancers is emphasized.

Novel EGF pathway regulators modulate C. elegans healthspan and lifespan via EGF receptor, PLC-gamma, and IP3R activation

Improving health of the rapidly growing aging population is a critical medical, social, and economic goal. Identification of genes that modulate healthspan, the period of mid-life vigor that precedes significant functional decline, will be an essential part of the effort to design anti-aging therapies. Because locomotory decline in humans is a major contributor to frailty and loss of independence and because slowing of movement is a conserved feature of aging across phyla, we screened for genetic interventions that extend locomotory healthspan of Caenorhabditis elegans. From a group of 54 genes previously noted to encode secreted proteins similar in sequence to extracellular domains of insulin receptor, we identified two genes for which RNAi knockdown delayed age-associated locomotory decline, conferring a high performance in advanced age phenotype (Hpa). Unexpectedly, we found that hpa-1 and hpa-2 act through the EGF pathway, rather than the insulin signaling pathway, to control systemic healthspan benefits without detectable developmental consequences. Further analysis revealed a potent role of EGF signaling, acting via downstream phospholipase C-gammaplc-3 and inositol-3-phosphate receptor itr-1, to promote healthy aging associated with low lipofuscin levels, enhanced physical performance, and extended lifespan. This study identifies HPA-1 and HPA-2 as novel negative regulators of EGF signaling and constitutes the first report of EGF signaling as a major pathway for healthy aging. Our data raise the possibility that EGF family members should be investigated for similar activities in higher organisms.

ErbB-inhibitory protein: a modified ectodomain of epidermal growth factor receptor synergizes with dasatinib to inhibit growth of breast cancer cells

Many solid tumors, including breast cancer, show increased activation of several growth factor receptors, specifically epidermal growth factor receptor (EGFR) and its family members as well as c-Src, a nonreceptor tyrosine kinase that promotes proliferation, inhibits apoptosis, and induces metastasis. We hypothesize that inhibition of c-Src and EGFRs will be an effective therapeutic strategy for triple-negative breast cancer. To test our hypothesis, we used a c-Src-specific inhibitor dasatinib (BMS-354825; Bristol-Myers Squibb) and our newly developed ErbB-inhibitory protein (EBIP), a potential pan-ErbB inhibitor, in breast cancer cells. EBIP is composed of 1 to 448 amino acids of the ectodomain of human EGFR to which the 30-amino acid epitope (known as "U" region) of rat EGFR-related protein is fused at the COOH-terminal end. The combination of dasatinib and EBIP was found to be highly effective in inhibiting the growth of four different breast cancer cells (MDA-MB-468, SKBr-3, MDA-MB-453, and MDA-MB-231) that express different levels of EGFRs. In EGFR-overexpressing MDA-MB-468 cells, the combination, but not monotherapy, markedly stimulated apoptosis mediated by caspase-9 and caspase-8 and attenuated activation of EGFR and Src as well as tyrosine kinase activity. EBIP also inhibited heregulin-induced activation of HER-2 and HER-3 in MDA-MB-453 breast cancer cells. The combination therapy was highly effective in suppressing tumor growth ( approximately 90% inhibition) in MDA-MB-468-derived xenografts in severe combined immunodeficient mice. The latter could be attributed to induction of apoptosis. We conclude that combining dasatinib and EBIP could be an effective therapeutic strategy for breast cancer by targeting EGFRs and Src signaling.

Cell cycle and apoptosis regulatory protein-1: a novel regulator of apoptosis in the colonic mucosa during aging

Although the regulatory mechanisms for the age-related rise in proliferation and reduction in apoptosis in the colonic mucosa are yet to be fully delineated, we have demonstrated that these events are associated with increased expression and activation of epithelial growth factor receptor (EGFR)/ErbB-1 and some of its receptor family members (EGFRs), indicating their involvement in these processes. However, the downstream signaling events of EGFR and/or its family members regulating age-related changes in mucosal proliferation and apoptosis remain to be delineated. Cell cycle and apoptosis regulatory protein-1 (CARP-1), a novel growth signaling regulator that we isolated, participates in EGFR-dependent signaling. In the current investigation, we examined the involvement of CARP-1 in colonic mucosal growth-related processes during aging. We report that the age-related reduction in apoptosis in the colonic mucosa is associated with increased expression and tyrosine phosphorylation of not only EGFR but also ErbB-2 and ErbB-3. In contrast, protein and mRNA levels of CARP-1 as well as tyrosine phosphorylation of CARP-1 are decreased. Additionally, we have observed that administration of wortmannin, an inhibitor of phosphatidylinositol 3-kinase activity that accelerates apoptosis in the colonic mucosa of aged rats, causes a marked increase in expression and tyrosine phosphorylation of CARP-1. The age-related decline in CARP-1 expression could partly be attributed to increased methylation of the CARP-1 promoter. Taken together, our data suggest that not only EGFR but also its other members are involved in regulating colonic mucosal growth during aging and that CARP-1 may play a crucial role in transducing EGFRs signals.

Regression of early and intermediate stages of colon cancer by targeting multiple members of the EGFR family with EGFR-related protein

A role of the epidermal growth factor receptor (EGFR) family has been suggested in colon cancer etiology, progression, and/or severity. Our recently identified pan-erbB inhibitor EGFR-related protein (ERRP) targets EGFRs by attenuating their activation and subsequent signaling leading to cellular growth inhibition. In the present study, we evaluated the therapeutic effectiveness of ERRP on early and intermediate stages of colon cancer by examining regression of chemically induced aberrant crypt foci (ACF) in the colon of CF1 mice and intestinal adenomas in APC(Min+/-) (Min) mice. After formation of ACF or adenomas, the mice were injected (i.p.) with ERRP (50 microg/mouse) for 10 consecutive days. This treatment significantly reduced the number of ACF from 25.0 +/- 3.0 (controls) to 14.9 +/- 1.6 (ERRP-treated; P = 0.011) and also reduced their size (P < 0.01). In Min mice, ERRP caused the regression of adenomas throughout the small intestine (P < 0.05) and reduced their size (P < 0.001). This could partly be attributed to inhibition of proliferation and stimulation of apoptosis in the intestinal mucosa and was associated with decreased activation of several EGFR family members, suppression of downstream effector nuclear factor kappaB and down-regulation of cyclooxygenase-2. ERRP-induced attenuation of EGFR activation could be due to increased sequestration of the ligand(s) by ERRP, rendering them unavailable for binding to and activation of the receptor. In conclusion, our data show that ERRP is effective in regressing both early and intermediate intestinal lesions and could be an effective therapeutic agent for colon cancer.

Mechanisms of curcumin- and EGF-receptor related protein (ERRP)-dependent growth inhibition of colon cancer cells

Numerous dietary and pharmacological agents have been proposed as alternative strategies for treatment and prevention of colorectal cancer. Curcumin, an active ingredient of turmeric, that inhibits growth of malignant neoplasms, has a promising role in the prevention and treatment of colorectal cancer. EGF-R related protein (ERRP), a recently identified pan-erbB inhibitor, is a potential therapeutic agent for colorectal cancer. Here we examine whether curcumin together with ERRP will cause a greater inhibition of growth of colon cancer cells than either agent alone and the mechanisms of this inhibition. Human colon cancer HCT-116 or HT-29 cells were incubated with increasing doses of curcumin (up to 10 microM) or ERRP (up to 5 microg/ml), or a combination of both for 48 h. We observed that the cell growth inhibition and stimulation of apoptosis in response to the combinatorial treatment was significantly greater than that caused by either agent alone. These changes were associated with decreased activation (tyrosine phosphorylation) of EGFR, ErbB-2, ErbB-3, and/or IGF-1R. Whereas curcumin inhibited constitutive activation of both EGFR and IGF-1R, ERRP decreased activation of EGFR, ErbB-2, and ErbB-3 but had no effect on IGF-1R. Further, the combination therapy caused a greater attenuation of downstream effectors such as NF-kappaB, Akt and BAD activation, and down-regulation of procaspase-3 than that noted with either agent alone. The superior effects of the combinatorial treatment could partly be attributed to inhibition of constitutive activation of EGFRs and IGF-1R signaling pathways.

Emerging therapies in gastrointestinal cancers

Members of the receptor tyrosine kinase family, that include EGFR, ErbB-2/HER-2, ErbB-3/HER-3 and ErbB-4/HER-4, are frequently implicated in experimental models of epithelial cell neoplasia as well as in human cancers. Therefore, interference with the activation of these growth factor receptors represents a promising strategy for development of novel and selective anticancer therapies. Indeed, a number of inhibitors that target either EGFR or HER-2, with the exception of a few that target both; have been developed for treatment of epithelial cancers. Since most solid tumors express different ErbB receptors and/or their ligands, identification of inhibitor(s), targeting multiple EGFR family members may provide a therapeutic benefit to a broader patient population. Here we describe the significance of an ErbB family of receptors in epithelial cancers, and summarize different available therapeutics targeting these receptors. It also emphasizes the need to develop pan-ErbB inhibitors and discusses EGF-Receptor Related Protein, a recently isolated negative regulator of EGFR as a potential pan-ErbB therapeutic for a wide variety of epithelial cancers.

Antitumor activity of epidermal growth factor receptor-related protein is mediated by inactivation of ErbB receptors and nuclear factor-kappaB in pancreatic cancer

The erbB family of receptor tyrosine kinases plays critical roles in human cancers, including pancreatic cancer. Discovering a specific agent, which targets multiple members of the erbB family, would be important in pancreatic cancer therapy. Recently, we isolated a novel negative regulator of epidermal growth factor receptor (EGFR), termed EGFR-related protein (ERRP), whose expression attenuates EGFR activation. In the current study, we examined the effects of recombinant ERRP on the growth and ligand-induced activation of multiple members of erbB family in three pancreatic cancer cell lines that express varying levels of EGFR and other member(s) of its family, specifically HER-2. Additionally, we compared the growth inhibitory effect of ERRP with that of Erbitux or Herceptin. Our results showed that ERRP is most effective in inhibiting proliferation of BxPC-3, HPAC, and PANC-1 pancreatic cancer cells. ERRP also inhibited ligand-induced activation of EGFR, HER-2, and HER-3 (ErbB3). In contrast, Erbitux and Herceptin only partially or modestly inhibited activation of EGFR, HER-2, and HER-3. Most importantly, ERRP was found to inhibit pancreatic tumor growth in a severe combined immunodeficient mouse xenograft model. The antitumor activity of ERRP correlates well with tumor differentiation and down-regulation of nuclear factor-kappaB activity. In summary, our results suggest that ERRP is an effective pan-erbB inhibitor, which could be a potential therapeutic agent for pancreatic cancers expressing different levels and subclasses of erbB family of proteins.