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

Abstract

(Santon et al., 1986;Ozanne et al., 1986;Velu et al., 1987; Difore et al., 1987;Harris et al., 1990). In addition, some of these tumours produce ligands for the receptor and it has been suggested that an autocrine mechanism is involved in progression of cancers of this type (Sporn & Roberts 1985;Imanishi et al., 1988;Nistar et al., 1988; Dernyck 1990;Tateishi et al., 1990;Yoshida et al., 1990; Morishige et al., 1991). Over-expression of the EGFR by tumour cells, compared to their normal counterparts, has been reported for a number of squamous cell carcinomas (e.g. Cowley et Hendler et al., 1984;Sainsbury et al., 1985;Gullick et al., 1986) and this in turn was also correlated to poor prognosis in patients with some of these carcinomas (reviewed by Gullick, 1991 We have reported (Modjtahedi, et al., 1992) the preparation and properties of ten rat mAbs that bind to three distinct epitopes (A,B,C) on the external domain of the EGFR using as immunogen the human squamous cell carcinoma HN5. While all of the mAbs against epitopes B and C blocked the binding of EGF and TGFa to the receptor on a number of squamous carcinoma cell lines the antibodies against epitope C were an order of magnitude better than the others at inhibiting cell growth. The best antibody, ICR16, inhibited completely the growth of HN5 cells in vitro at antibody concentrations above 1 nM. However, none of the antibodies was of the IgG2b isotype and therefore would not be expected to interact efficiently with the host immune effector functions in rat, mouse or man. Since our intention is to test the effectiveness of antibodies in the clinic we report here the preparation of a second series of antibodies using as immunogen the EGFR over-expressing breast carcinoma (Filmus et al., 1985) searching particularly for IgG2b antibodies with growth inhibitory properties. Materials and methods Cell lines

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

“…Indeed, we have found that culture supernatants of A43 1 cells effectively block the binding of all of the rat antibodies to the receptor for EGF (Modjtahedi et al, 1993). The success of treatment clearly depends on antigen density and the results obtained with the SKOV 3 xenografts suggest that too few receptors were present to permit effective immune destruction.…”

“…We have shown (Modjtahedi et al, 1993 see accompanying paper) that a number of rat antibodies raised against the external domain of the human receptor for EGF were potent inhibitors of the growth in vitro of tumour cells that overexpress this receptor. In this paper we demonstrate that three of these antibodies, ICR16 (IgG2a), ICR62 (IgG2b) and ICR64 (IgG1) were also very effective inhibitors of the growth in athymic mice of several tumours that overexpress the EGFR.…”

“…Rat monoclonal antibodies ICR16 (IgG2a), ICR62 (IgG2b) and ICR64 (IgGI) that are directed against the external domain of the human receptor for EGF were prepared and purified from ascites as described in the preceding paper (Modjtahedi et al, 1993). Isotype matched monoclonal antibodies were used as controls namely, ALN/l 1/53 (IgG2a) and 11/160 (IgG2b), that are directed against a specific antigen on the rat sarcoma HSN (Dean et al, 1984) ( ± s.d.).…”

“…The antibodies, ICR16 (IgG2a), ICR62 (IgG2b) and ICR64 (IgGl), 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.…”

Phase I trial and tumour localisation of the anti-EGFR monoclonal antibody ICR62 in head and neck or lung cancer

“…Our aim was to obtain a diverse population of antibodies that bound to distinct epitopes on the EGFR and which were of different isotype in order to select the best MAb or combination of MAbs for therapeutic and diagnostic use. Of these, the IgG2b MAb ICR62 was prominent in that it (a) effectively blocks the binding of EGF, TGF-ai, and HB-EGF to EGFR; (b) inhibits the growth of EGFR-overexpressing tumour cell lines in vitro (Modjtahedi et al, 1993a;; and (c) was the most effective antibody in our MAb library for eradicating such tumours in athymic mice (Modjtahedi et al, 1993b;Dean et al, 1994). We have also reported recently that antibodies to the EGFR that inhibit the growth of EGFR-overexpressing tumours do so by inducing terminal differentiation and that a further therapeutic effect may be obtained via immunological mechanisms with rat IgG2b MAbs such as ICR62 .…”