Andrea Bolognesi

Response of refractory Hodgkin's disease to monoclonal anti-CD30 immunotoxin

In Hodgkins disease, Hodgkin and Reed-Sternberg cells consistently express the antigen CD30. We investigated the possible therapeutic role of an immunotoxin prepared by covalent linking of an anti-CD30 monoclonal antibody (Ber-H2) to saporin (SO6), a type-1 ribosome-inactivating protein. The immunotoxin (0.8 mg/kg in one or two doses) was given to four patients with advanced refractory Hodgkins disease. In three, there was rapid and substantial reduction in tumour mass (50% to greater than 75%). Clinical responses were transient (6-10 weeks). In-vivo binding of the immunotoxin to tumour cells was shown by immunohistology in two patients. Antibodies to both parts of the immunotoxin developed in all patients.

CTLA‐4 is constitutively expressed on tumor cells and can trigger apoptosis upon ligand interaction

CTLA‐4 (CD152) is a cell surface receptor that behaves as a negative regulator of the proliferation and the effector function of T cells. We have previously shown that CTLA‐4 is also expressed on neoplastic lymphoid and myeloid cells, and it can be targeted to induce apoptosis. In our study, we have extended our analysis and have discovered that surface expression of CTLA‐4 is detectable by flow cytometry on 30 of 34 (88%) cell lines derived from a variety of human malignant solid tumors including carcinoma, melanoma, neuroblastoma, rhabdomyosarcoma and osteosarcoma (but not in primary osteoblast‐like cultures). However, by reverse transcriptase‐PCR, CTLA‐4 expression was detected in all cell lines. We have also found, by immunohistochemistry, cytoplasmic and surface expression of CTLA‐4 in the tumor cells of all 6 osteosarcoma specimens examined and in the tumour cells of all 5 cases (but only weakly or no positivity at all in neighbouring nontumor cells) of ductal breast carcinomas. Treatment of cells from CTLA‐4‐expressing tumor lines with recombinant forms of the CTLA‐4‐ligands CD80 and CD86 induced apoptosis associated with sequential activation of caspase‐8 and caspase‐3. The level of apoptosis was reduced by soluble CTLA‐4 and by anti‐CTLA‐4 scFvs antibodies. The novel finding that CTLA‐4 molecule is expressed and functional on human tumor cells opens up the possibility of antitumor therapeutic intervention based on targeting this molecule.

Induction of apoptosis by ribosome‐inactivating proteins and related immunotoxins

Immunotoxins have been prepared with 3 ribosome‐inactivating proteins (RIPs), namely, momordin, pokeweed anti‐viral protein from seeds (PAP‐S) and saporin, linked to the Ber‐H2 monoclonal antibody directed against the CD30 antigen of human lymphocytes. Either the RIPs or the immunotoxins induced apoptosis in the CD30+ L540 cell line, as shown by the morphological aspects of the cells, by the DNA fragmentation visible at the electrophoresis, and by the formation of DNA breaks evidenced by 2 cytofluorometric techniques (propidium‐iodide staining and fluoresceine‐isothiocyanate conjugate dUTP incorporation). The AC50 (concentration causing apoptosis in 50% of the cells) is in the range 10‐8 to 10‐7 M in the case of RIPs, and 10‐11 to 10‐10 M in the case of the immunotoxins.

Large scale chromatographic purification of ribosome-in-activating proteins

Abstract A method for the purification of type 1 (single-chain) ribosome-inactivating proteins from large amounts of starting material has been developed. The general procedure can be adapted with minor modifications to the purification of a variety of such proteins either from seeds, saporins from Saponaria officinalis , momordin from Momordica charantia , trichokirin from Trichosanthes kirilowii , the protein from Hordeum vulgaris and gelonin from Gelonium multiflorum , or from leaves, dianthins from Dianthus caryophyllus . Yields ranged from 13 mg to 2.6 g of highly purified protein per kg of starting material. The amount of time and work was substantially reduced as compared with previously described procedures, and reusable gels have been employed during all chromatographic operations.

In vitro anti-tumour activity of anti-CD80 and anti-CD86 immunotoxins containing type 1 ribosome-inactivating proteins

Immunotoxins specific for the CD80 and CD86 antigens were prepared by linking three type 1 ribosome‐inactivating proteins (RIPs), namely bouganin, gelonin and saporin‐S6, to the monoclonal antibodies M24 (anti‐CD80) and 1G10 (anti‐CD86). These immunotoxins showed a specific cytotoxicity for the CD80/CD86‐expressing cell lines Raji and L428. The immunotoxins inhibited protein synthesis by target cells with IC50s (concentration causing 50% inhibition) ranging from 0·25 to 192 pmol/l as RIPs. The anti‐CD80 immunotoxins appeared 1–2 log more toxic for target cells than the anti‐CD86 ones. Immunotoxins containing saporin and bouganin induced apoptosis of target cells. The toxicity for bone marrow haemopoietic progenitors of these conjugates was also evaluated. Bouganin and related immunotoxins at concentrations up to 100 nmol/l did not significantly affect the recovery of committed progenitors or of more primitive cells. The saporin‐containing immunotoxins at concentrations ≥ 1 nmol/l showed some toxicity on colony‐forming unit cells (CFU‐C). The expression of the CD80 and CD86 molecules is prevalently restricted to antigen‐presenting cells and is also strong on Hodgkin and Reed–Sternberg cells in Hodgkins disease. Present results suggest that immunotoxins targeting type 1 ribosome‐inactivating proteins to these antigens could be considered and further studied for the therapy of Hodgkins disease or other CD80/CD86‐expressing tumours.

Ber-H2 (anti-CD30)-saporin immunotoxin : a new tool for the treatment of Hodgkin's disease and CD30+ lymphoma : in vitro evaluation

An immunotoxin containing an anti‐CD30 monoclonal antibody (Ber‐H2) and saporin, a ribosome‐inactivating protein type 1, is described. It specifically inhibits protein synthesis by Hodgkin derived target cell lines with a very high efficiency (IC50 ranging from 5 × 10–12 M to 5.10∼14 M, assaporin), while irrelevant immunotoxins do not. Present results suggest that this immunotoxin could be used for in vivo therapy as well as for ex vivo bone marrow purging in Hodgkins disease and CD304+ lymphomas.

Activities associated with the presence of ribosome‐inactivating proteins increase in senescent and stressed leaves

The ribosome‐inactivating proteins (RIPs) from Hura crepitans and Phytolacca americana release adenine from herring sperm DNA. Leaf extracts from these plants show the same enzymatic activities as the RIPs. The translation inhibitory activity and the activity on DNA are both increased in the leaves of both plants during senescence or when subjected to heat or osmotic stress. It is proposed that a physiological role of RIPs could be to intervene in the death of plant cells.

Pathophysiology of circulating xanthine oxidoreductase: new emerging roles for a multi-tasking enzyme.

The enzyme xanthine oxidoreductase (XOR) catalyses the last step of purine degradation in the highest uricotelic primates as a rate-limiting enzyme in nucleic acid catabolism. Although XOR has been studied for more than a century, this enzyme continues to arouse interest because its involvement in many pathological conditions is not completely known. XOR is highly evolutionarily conserved; moreover, its activity is very versatile and tuneable at multiple-levels and generates both oxidant and anti-oxidant products. This review covers the basic information on XOR biology that is essential to understand its enzymatic role in human pathophysiology and provides a comprehensive catalogue of the experimental and human pathologies associated with increased serum XOR levels. The production of radical species by XOR oxidase activity has been intensively studied and evaluated in recent decades in conjunction with the cytotoxic consequences and tissue injuries of various pathological conditions. More recently, a role has emerged for the activity of endothelium-bound enzymes in inducing the vascular response to oxidative stress, which includes the regulation of pro-inflammatory and pro-thrombotic activities of endothelial cells. The possible physiological functions of circulating XOR and the products of its enzyme activity are presented here together with their implications in cardiovascular and metabolic diseases.

Purification and properties of new ribosome-inactivating proteins with RNA N-glycosidase activity

Ribosome-inactivating proteins (RIPs) similar to those already known (Stirpe & Barbieri (1986) FEBS Lett. 195, 1-8) were purified from the seeds of Asparagus officinalis (two proteins, asparin 1 and 2), of Citrullus colocynthis (two proteins, colocin 1 and 2), of Lychnis chalcedonica (lychnin) and of Manihot palmata (mapalmin), from the roots of Phytolacca americana (pokeweed antiviral protein from roots, PAP-R) and from the leaves of Bryonia dioica (bryodin-L). The two latter proteins can be considered as isoforms, respectively, of previously purified PAP, from the leaves of P. americana, and of bryodin-R, from the roots of B. dioica. All proteins have an Mr at approx, 30,000, and an alkaline isoelectric point. Bryodin-L, colocins, lychnin and mapalmin are glycoproteins. All RIPs inhibit protein synthesis by a rabbit reticulocyte lysate and phenylalanine polymerization by isolated ribosomes and alter rRNA in a similar manner as the A-chain of ricin and related toxins (Endo et al. (1987) J. Biol. Chem. 262, 5908-5912).

Internalization and recycling of ALCAM/CD166 detected by a fully human single-chain recombinant antibody

Activated leukocyte cell adhesion molecule (ALCAM/CD166), a member of the immunoglobulin superfamily with five extracellular immunoglobulin-like domains, promotes heterophilic (ALCAM-CD6) and homophilic (ALCAM-ALCAM) cell-cell interactions. Here we describe a fully human single-chain antibody fragment (scFv) directed to ALCAM/CD166. We selected the I/F8 scFv from a phage display library of human V-gene segments by cell panning and phage internalization into IGROV-I human ovary carcinoma cells. The I/F8 specificity was identified as ALCAM/CD166 by matrix-assisted laser desorption/ionisation time-of-flight (MALDI-TOF) peptide mass fingerprinting of the I/F8-immunoprecipitated protein. The I/F8 scFv reacts with the human, monkey and murine ALCAM/CD166 molecule, indicating that the recognized epitope is highly conserved. The I/F8 scFv completely abolished binding of both ALCAM/Fc and CD6/Fc soluble ligands, whereas it did not compete with the anti-ALCAM/CD166 murine monoclonal antibodies J4-81 and 3A6 and therefore recognizes a different epitope. Engagement through I/F8 scFv, 3A6 monoclonal antibody or CD6/Fc ligand induced ALCAM/CD166 internalization, with a kinetics slower than that of transferrin in the same cells. Newly internalized I/F8-ALCAM complexes colocalized with clathrin but not with caveolin and we demonstrated, using surface biotinylation and recycling assays, that endocytosed ALCAM/CD166 recycles back to the cell surface. Such an endocytic pathway allows the efficient delivery of an I/F8 scFv-saporin immunotoxin into tumor cells, as the conjugates are able to selectively kill cell lines expressing ALCAM/CD166. Altogether these data provide evidence of the suitability of the I/F8 scFv for further functional analysis of ALCAM/CD166 and intracellular delivery of effector moieties.