Helmout Modjtahedi

Epidermal growth factor receptor inhibitors in cancer treatment: advances, challenges and opportunities

Aberrant expression of the epidermal growth factor receptor (EGFR) system has been reported in a wide range of epithelial cancers. In some studies, this has also been associated with a poor prognosis and resistance to the conventional forms of therapies. These discoveries have led to the strategic development of several kinds of EGFR inhibitors, five of which have gained US Food and Drug Administration approval for the treatment of patients with non-small-cell lung cancer (gefitinib and erlotinib), metastatic colorectal cancer (cetuximab and panitumumab), head and neck (cetuximab), pancreatic cancer (erlotinib) and breast (lapatinib) cancer. Despite these advances and recent studies on the predictive value of activating EGFR mutation and KRAS mutations with response in non-small-cell lung cancer and colon cancer patients, there is currently no reliable predictive marker for response to therapy with the anti-EGFR monoclonal antibodies cetuximab and panitumumab or the small molecule EGFR tyrosine kinase inhibitors gefitinib and erlotinib. In particular, there has been no clear association between the expression of EGFR, determined by the US Food and Drug Administration-approved EGFR PharmDX kit, and response to the EGFR inhibitors. Here, we discuss some of the controversial data and explanatory factors as well as future studies for the establishment of more reliable markers for response to therapy with EGFR inhibitors. Such investigations should lead to the selection of a more specific subpopulation of cancer patients who benefit from therapy with EGFR inhibitors, but equally to spare those who will receive no benefit or a detrimental effect from such biological agents.

Overexpression of epidermal growth factor receptor in human head and neck squamous carcinoma cell lines correlates with matrix metalloproteinase‐9 expression and in vitro invasion

Numerous reports have shown an association between overexpression of the epidermal growth factor receptor (EGFR), and poor prognosis in head and neck squamous cell carcinomas (HNSCC), however, the underlying mechanisms are still unclear. In the present study, we set out to determine whether EGFR expression was associated with in vitro invasive capacity in a panel of four established and ten newly derived HNSCC lines. Ten of the cell lines expressed high levels of EGFR as determined by a ligand‐binding assay and dot blot analysis, whereas the remaining four showed weak overexpression or normal levels of EGFR. The ability of cells to invade through Matrigel was found to be higher in the EGFR overexpressing cell lines (p < 0.0001). Expression levels of matrix metalloproteinases (MMP‐1, MMP‐2, MMP‐3, MMP‐7, MMP‐9, MMP‐10, MMP‐11, MMP‐13, MT1‐MMP) and tissue inhibitors of MMP (TIMP‐1, TIMP‐2) were evaluated by semiquantitative RT‐PCR, substrate zymography and western blot. We found a strong positive correlation between EGFR levels and the expression of MMP‐9 mRNA (r2 = 0.95; p < 0.0001), MMP‐9 enzyme activity (r2 = 0.8099; p < 0.0001) and an inverse correlation with TIMP‐1 (r2 = 0.48; p = 0.0059). In six selected HNSCC lines, in vitro invasion was assayed in the presence of an anti‐EGFR monoclonal antibody, ICR62. A significant reduction of invasion in four selected EGFR‐overexpressing cell lines was found with 30 nM ICR62 (from 50% to 70%; p < 0.001) but there was no effect in two cell lines with normal EGFR levels. Our results show that the in vitro invasive phenotype of HNSCC lines correlates with high EGFR and MMP‐9 expression, and it is therefore suggested that the EGFR signaling pathway might play an important role in the invasive behavior of HNSCC via specific upregulation of MMP‐9 and downregulation of TIMP‐1. Int. J. Cancer 86:307–317, 2000.

Vascular endothelial growth factor family members are differentially regulated by c-erbB signaling in head and neck squamous carcinoma cells.

Aberrant expression of tyrosine kinases such as c-erbB and EGFR contributes to the progression of head and neck squamous cell carcinomas (HNSCCs). One mechanism may be potentiation of angiogenesis, since upregulation of vascular endothelial growth factor (VEGF) expression by activation of epidermal growth factor receptor (EGFR) and/or c-erbB-2 has been described. Firstly, we demonstrated expression of all 4 members of the VEGF family in a panel of 15 HNSCC cell lines which over-express one or more c-erbB receptors. We then explored the regulatory roles of three major ligands with different selectivity of binding to c-erbB receptors (namely transforming growth factor-α (TGF-α), betacellulin (BTC) and heregulin-β1 (HRG-β1)) on VEGF-A, B, C and D expression in selected HNSCC lines. Using semi-quantitative reverse transcription-PCR, we showed that all three c-erbB ligands up-regulated VEGF-A mRNA (all isoforms) and VEGF-C (BTC max at 1–10 nM; TGF-α and HRG-β1 max at 10–100 nM) but had no effect on VEGF-B. Interestingly, all ligands simultaneously down-regulated the expression of VEGF-D mRNA. A monoclonal antibody (mAb) which blocks EGFR ligand binding (ICR62) down-regulated the basal levels of VEGF-A (all isoforms) and VEGF-C, had no detectable effects on VEGF-B and increased VEGF-D. ICR62 also reversed the effects of all three erbB ligands (TGF-α, BTC and HRG-β1) on VEGF-A, VEGF-C and VEGF-D expression. An anti-c-erbB-2 mAb (ICR12) showed similar effects on basal or ligand-modulated expression of VEGF in these cell lines, although to a lesser extent. Our results reveal that the four VEGF genes are regulated by c-erbB signaling pathways in a strikingly different manner, suggesting that they serve distinct, although perhaps complimentary (VEGF-A and VEGF-C) or antagonistic (VEGF-D) functions. The EGFR and c-erbB-2 signaling pathway(s) plays a role in VEGF regulation in HNSCC, although EGFR would appear to be dominant in this cell type.

The role of c-erbB receptors and ligands in head and neck squamous cell carcinoma

c-erbB receptor signalling induces pleiotropic responses and influences several biological functions involved in the pathogenesis and progression of HNSCC. Aberrant expression of multiple c-erbB receptors and ligands is frequently observed in tumour cells. EGFR appears to be a dominant factor controlling the malignant phenotype in HNSCC at least in part via regulation of molecules involved in invasive and angio-/lymphangiogenic processes. Although c-erbB-2 is an orphan receptor, the formation of heterodimer complexes appears to be an important mechanism for inter-receptor activation and synergistic signal transduction. The roles of c-erbB-3 and c-erbB-4 in HNSCC progression are less clear. However, their ability to form heterodimers with other c-erbB family members enhances proliferation and invasion in HNSCC cells. At least two major downstream signalling pathways, MAPK and PI3K, are involved in the transcriptional regulation of proteases and cytokines implicated in invasion and angiogenesis. Studies using clinical specimens confirmed experimental data that co-operative signalling of c-erbB receptors may play a significant role in the pathogenesis of HNSCC. Most therapeutic studies in HNSCC so far have focused on the strategies targeting of EGFR. Due to the complexity of the system both at the receptor and ligand levels and the integrated biological functions of the c-erbB family in HNSCC, the effect of combined c-erbB blockade (or their downstream signalling pathways) on HNSCC progression should be explored.

Targeting of cells expressing wild‐type EGFR and type‐III mutant EGFR (EGFRvIII) by anti‐EGFR MAb ICR62: A two‐pronged attack for tumour therapy

With a view to their use in cancer therapy, we have produced rat monoclonal antibodies (MAbs) directed against 5 distinct epitopes (A–E) on the external domain of the wild‐type human EGF receptor (EGFR). Here, we have investigated the relative binding and anti‐tumour activity of our anti‐EGFR MAbs against HC2 20d2/c cells, which have been engineered to overexpress the type‐III mutated form of the human EGFR (EGFRvIII). We found that anti‐EGFR MAbs that are the most effective antagonists of EGFR ligands (e.g., ICR16, ICR62 and ICR80) also bind to cells that overexpress the EGFRvIII. Although these antibodies are potent inhibitors of the growth of cells which express wild‐type EGFR, they did not directly inhibit the growth in vitro of EGFRvIII expressing HC2 20d2/c cells, or the constitutive tyrosine kinase activity of this receptor. However, in the presence of human peripheral blood mononuclear cells (PBMC), the rat IgG2b MAb ICR62 induced strong antibody‐dependent cell‐mediated cytotoxicity (ADCC) against HC2 20d2/c cells in culture. Interestingly, MAb ICR62 also inhibited very effectively experimental lung metastases of HC2 20d2/c cells in athymic nude mice. Our results suggest that anti‐EGFR MAb ICR62, which binds to the EGFRvIII, may have potential in the treatment of tumors which overexpress the EGFRvIII via immunological mechanisms such as ADCC. Since tumours that are EGFRvIII positive may also overexpress the wild‐type EGFR, the use of anti‐EGFR MAbs that target both wild‐type and mutant receptors may have advantages over those that target only1form.

The human EGF receptor as a target for cancer therapy: six new rat mAbs against the receptor on the breast carcinoma MDA-MB 468

Using the breast carcinoma cell line MDA-MB 468 as immunogen, we have produced six new rat monoclonal antibodies (mAbs) against the human EGF receptor (EGFR) and are investigating their use for diagnostic and therapeutic applications in cancer patients whose tumours overexpress these receptors. The mAbs (three IgG2b and one each of IgG2a, IgG1 and IgA) were selected on the basis that they bound to the extracellular domain of the EGFR and blocked growth factor-receptor interaction. Competitive assays showed that, with the exception of antibody ICR65, the mAbs bound to one of two distinct epitopes on the external domain of the EGFR. ICR65, however, cross-reacted with mAbs binding to both epitopes. All of the mAbs immunoprecipitated the 170 kDa glycoprotein from cells expressing the EGFR but not the 185 kDa product of the related c-erbB-2 proto-oncogene. Unlike EGF and TGF alpha none of the mAbs stimulated the growth of quiescent human foreskin fibroblasts but they inhibited the EGF and TGF alpha induced growth stimulation of these cells in vitro. When tested for their effect on tumour cells the mAbs were found to inhibit the growth in vitro of a number of human tumours that overexpressed the EGFR (e.g. HN5, HN6, HN15, A431, MDA-MB 468) but they were without effect on tumour cell lines expressing low or undetectable amounts of the receptor. Our initial results indicate that this new generation of antibodies which bind with high affinity to the EGFR, block growth factor-receptor interaction and inhibit the growth of human squamous carcinoma cell lines overexpressing the receptor have potential for clinical application.

Immunotherapy of human tumour xenografts overexpressing the EGF receptor with rat antibodies that block growth factor-receptor interaction

Athymic mice bearing xenografts of human tumours that overexpress the receptor (EGFR) for EGF and TGF alpha have been used to evaluate the therapeutic potential of three new rat monoclonal antibodies (mAbs) directed against two distinct epitopes on the extracellular domain of the human EGFR. The antibodies, ICR16 (IgG2a), ICR62 (IgG2b) and ICR64 (IgG1), have been shown (Modjtahedi et al., 1993) to be potent inhibitors of the growth in vitro of a number of human squamous cell carcinomas because they block receptor-ligand interaction. When given i.p. at 200 micrograms dose, the three antibodies were found to induce complete regression of xenografts of the HN5 tumour if treatment with antibody commenced at the time of tumour implantation (total doses: ICR16, 3.0 mg; ICR62, 1.2 mg; ICR64, 2.2 mg). More importantly when treatment was delayed until the tumours were established (mean diam. 0.5 cm) both ICR16 and ICR62 induced complete or almost complete regression of the tumours. Furthermore, treatment with a total dose of only 0.44 mg of ICR62 was found to induce complete remission of xenografts of the breast carcinoma MDA-MB 468, but ICR16 was less effective at this dose of antibody and only 4/8 tumours regressed completely. ICR16 and ICR62 were poor inhibitors of the growth in vitro of the vulval carcinoma A431, but both induced a substantial delay in the growth of xenografts of this tumour and 4/8 tumours regressed completely in the mice treated with ICR62 (total dose 2.2 mg). Although ICR16 and ICR64 were more effective than ICR62 as growth inhibitors in vitro, ICR62 was found to be substantially better at inducing regression of the tumour xenografts due perhaps to additional activation of host immune effector functions by the IgG2b antibody. We conclude that these antibodies may be useful therapeutic agents that can be used alone without conjugation to other cytotoxic moieties.

Antitumor activity of combinations of antibodies directed against different epitopes on the extracellular domain of the human EGF receptor.

The receptor (EGFR) for epidermal growth factor (EGF) and transforming growth alpha (TGFα) is often overexpressed in certain types of human malignancy and high levels of expression of the receptor and/ or coexpression of growth factors. EGF and TGFα have also been correlated with poor prognosis in many patients. We have produced a number of rat monoclonal antibodies (MAbs) against four distinct epitopes on the external domain of the EGF receptor and are currently evaluating their potential for therapeutic use. Nine of these of MAbs were found to inhibit the binding of TGF and EGF to the receptor on tumor cells and these MAbs were able to inhibit the growth in vitro and in vivo of tumor cells that overexpress the EGF receptor. Here, we describe the results of experiments to determine the antitumor activity of combination treatment with two antibodies directed against separate epitopes on the external domain of human EGFR. Our results showed that treatment of human tumor xenografts with a combination of two anti-EGFR MAbs that bind to two distinct epitopes on the external domain of EGF receptor was not as effective as treatment with ICR62 alone, which binds to epitope C on the EGFR and is of IgG2b isotype. A phase I clinical trial with antibody ICR62 is currently underway in Royal Marseden Hospital (UK) in patients with head and neck and lung carcinomas.

The expression of p53, c-erbB-1 and c-erbB-2 molecules and their correlation with prognostic markers in patients with head and neck tumors

Molecular prognostic and predictive factors have extensively been studied in different cancers during the past decades, some of which were found to be useful in diagnosis, follow up or even treatment of some malignant tumors. To assess the significance of c-erbB-1, c-erbB-2 and p53 expression in head and neck tumors among Iranian patients and their correlation with known prognostic factors, samples from 53 patients with squamous cell carcinomas of larynx and tongue were studied immunohistochemically. Strong immunoreactivity of c-erbB-1, c-erbB-2 and p53 was observed in 37 (70%), 40 (76%) and 37 (70%) of cases, respectively. The coexpression of these molecules was detected in 27 (50.9%) samples. Neither histological grading nor nodal involvement revealed correlation with c-erbB-1 and/or c-erbB-2 expression. No correlation was found between p53 expression and histological grade. However, a significant positive association was observed between p53 expression and nodal involvement. This data, which is the first report on head and neck squamous cell carcinomas (HNSCC) in Iran, indicates the significance of p53 protein expression which may result from p53 tumor suppressor gene inactivation in lymph node metastasis of HNSCC among Iranian patients.

Anti‐EGFR monoclonal antibodies which act as EGF, TGFα, HB‐EGF and BTC antagonists block the binding of epiregulin to EGFR‐expressing tumours

Epiregulin is the newest member of the epidermal growth factor (EGF) family of ligands that was isolated from conditioned medium of the murine fibroblast‐derived tumour cell line NIH3T3/T7. Here, using a panel of anti‐EGFR receptor (EGFR) monoclonal antibodies (MAbs) directed against 4 distinct epitopes on the external domain of the receptor, we have investigated the importance of the EGFR in transmitting the biological action of epiregulin. We found that MAb ICR9, which enhances the binding of EGF, TGFα, HB‐EGF and betacellulin to the EGFR, also increases the binding of 125I‐epiregulin to a number of EGFR‐expressing tumour cell lines, including EJ, SKBR3, SKOV3, MDA‐MB468 and HN5. In addition, anti‐EGFR MAbs ICR15, ICR16, ICR61, ICR62 and ICR80, which block the binding of 125I‐EGF to the EGFR, inhibit the binding of 125I‐epiregulin to these tumour cell lines. Like EGF, we found that both the epiregulin‐induced growth inhibition of HN5 and MDA‐MB468 cells and tyrosine phosphorylation of the 170 kDa EGFR on HN5 cells are reversed in the presence of anti‐EGFR MAbs ICR62 and ICR80. Surprisingly and unlike 125I‐EGF, radiolabelled epiregulin bound very poorly to human bladder carcinoma EJ cells and its binding to SKOV3 cells was not inhibited efficiently in the presence of blocking antibodies. We conclude that the EGFR plays an important role in transmitting the biological action of epiregulin and that these effects could be blocked in the presence of anti‐EGFR MAbs. The low level of binding of epiregulin compared with EGF to EJ cells suggests that the EGFR may not be the primary receptor for epiregulin. Int. J. Cancer 75:310–316, 1998.