A carcinoembryonic antigen‐directed immunotoxin built by linking a monoclonal antibody to a hemolytic toxin

Abstract

Hybrid molecules prepared by linking toxins to monoclonal antibodies (MAbs) are cytotoxic to cells bearing the target antigen. The toxin most widely used has been the plant toxin ricin as the toxic component, which inhibits protein synthesis at the ribosome level. Immunotoxins based on membrane-active, hemolytic toxins can be a useful alternative when directed towards antigens which do not mediate internalization, as is the case for most carcinoma antigens. We present an alternative for toxic components using a hemolytic toxin acting at the membrane level, due to its phospholipase activity. The hemolytic toxin (HT), isolated from the sea anemone Stoichactis helianthus, has been conjugated to a MAb directed against carcinoembryonic antigen (CEA), by means of an artificial disulphide bridge. The hybrid alpha CEA-HT exhibits no hemolytic activity unless it is reduced. It is toxic for cells (MDA-MB-134) expressing CEA and not toxic for cells (MDA-MB-231) not bearing CEA. An excess of free antibody reverses toxicity.

The anticancer effects of actinoporin RTX-A from the sea anemone Heteractis crispa (=Radianthus macrodactylus)

“…The results shown in Table 1 indicated that RTX-A demonstrated potent cytotoxic activity (IC 50 = 1–5 nM) against human caner cell lines, including HL-60, MDA-MB-231, HeLa, THP-1, and SNU-C4. The active concentrations of RTX-A, 10 −9 M, agree with the values of the cytotoxicity obtained earlier for the α-PFT of the actinoporin family, ranging from 10 −10 to 10 −7 M, according to reviewed data (Alvarez et al, 2009; Avila et al, 1988; Avila et al, 1989; Tejuca et al, 2004). …”

Interaction of the Eukaryotic Pore-forming Cytolysin Equinatoxin II with Model Membranes: 19F NMR Studies

“…Indeed, the potency and properties of these cytolysins have prompted their evaluation as the toxic component of chimeric proteins targeted at tumour cells 8,9 and human parasites. 10 The nature of their interaction with lipids in bilayer membranes and the specific role of sphingomyelin in pore formation are not understood at the molecular level.…”

Evolution of the Cytolytic Pore-Forming Proteins (Actinoporins) in Sea Anemones

“…Actinoporins have been used to elucidate cell membrane dynamics and to investigate pharmaceutically relevant biomedical applications [21,22,23,24]. Several residues have been manipulated to identify functionally important regions within the protein [25], revealing an aromatic-rich region that forms the phosphocholine (POC) binding site, with a single amino acid residue (W112 in Equinatoxin II (EqII)) taking on a key role in initiating sphingomyelin recognition and pore formation [11,26,27].…”