Immunoconjugates made of an anti-EGF receptor monoclonal antibody and type 1 ribosome-inactivating proteins from Saponaria ocymoides or Vaccaria pyramidata

Abstract

Summary The present paper describes two immunoconjugates consisting of an anti-epidermal growth factor receptor (EGFR) monoclonal antibody (MAb), named Mint5, covalently linked to the type 1 ribosome-inactivating proteins (RlPs) ocymoidine (Ocy) and pyramidatine (Pyra) from Saponaria ocymoides and Vaccaria pyramidata respectively. Both antibody and toxins are shown to retain their respective biological properties upon chemical conjugation. The immunoconjugates exert specific inhibition of EGFR expressing target cell proliferation and protein synthesis in in vitro assays and also inhibit the growth of grafted human tumour cells in nude mice.Keywords: immunoconjugate; anti-epidermal growth factor receptor; ocymoidine; pyramidatineThe clinical use of immunotoxins for the treatment of cancer is currently under evaluation worldwide. The therapeutic potentiality of immunotoxins and preclinical and clinical results over the last 20 years have been reviewed recently (Thrush et al, 1996), indicating that, although immunotoxins seem promising for systemic therapy of haematological malignancies, a number of different problems still need to be solved, especially for the treatment of solid tumours. In particular, the refining of dose regimen and administration route, the combination with chemotherapy and the reduction of immunogenicity are the major goals of future research. In this paper, we describe the preparation of two new immunoconjugates made of an anti-epidermal growth factor receptor monoclonal antibody, named MintS, chemically linked to either ocymoidine or pyramidatine, toxins from Saponaria ocymoides and Vaccaria pyramidata respectively.The epidermal growth factor (EGF) and its receptor play a critical role in the growth and regulation of many normal and malignant cell types. EGFR overexpression is a common feature in most carcinomas and correlates with poor prognosis (Fox et al, 1994).The potential value of EGFR as a target for the diagnosis and therapy of human tumours has been recognized for several years, and the use of anti-EGFR monoclonal antibodies may provide therapeutic tools in the treatment of tumours overexpressing the receptor (Ennis et al, 1991).Moreover, immunoconjugates of EGFR-specific monoclonal antibodies to either gelonin (Ozawa et al, 1989) or ricin A chain (Masui et al, 1989) were shown to reduce the growth of human tumour cells transplanted into athymic mice.

Sapovaccarin-S1 and -S2, Two Type I RIP Isoforms from the Seeds of Saponaria vaccaria L.

“…with a size of approximately 28 kDa and an isoelectric point (pI) of 9.5 and could identify its 30 N-terminal amino acids [ 5 ]. In 1997, the isolated RIP was used for immunoconjugate construction and successful inhibition of tumor growth in mice by these immunotoxins was demonstrated [ 26 ]. The full amino acid sequence, however, has never been published.…”

Synergistic Antitumor Activity from Two-Stage Delivery of Targeted Toxins and Endosome-Disrupting Nanoparticles

“…9−12 A few molecules of such toxins in the cytosol are sufficient to kill a cell, 5,10,11 and this high lethality has made these molecules candidate anticancer therapeutics. However, by themselves, type I toxins such as gelonin lacking any cell-binding or cytoplasmic delivery domains are limited by their inability to cross the plasma membrane at therapeutically useful levels.…”

Convergent Potency of Internalized Gelonin Immunotoxins across Varied Cell Lines, Antigens, and Targeting Moieties

“…Like CEA, EGFR is a well established cancer-associated antigen. EGFR has also been used as a target for designed immunotoxins (29,30). Previous studies have suggested that antigens displaying similar expression levels but different internalization rates can lead to profoundly different immunotoxin potencies (6).…”