The puzzling uniqueness of the heterotrimeric G15 protein and its potential beyond hematopoiesis

Heterotrimeric G proteins transduce the signals of the largest family of membrane receptors (G protein-coupled receptors, GPCRs) hence triggering the activation of a wide variety of physiological responses. G15 is a G protein characterized by a number of functional peculiarities that make its signaling exceptional: 1) it can couple a variety of Gs-, Gi/o-, and Gq-linked receptors to phospholipase C activation; 2) relatively to other G proteins, it is poorly affected by beta-arrestin-dependent desensitization, the general mechanism that regulates GPCR function and 3) at the protein level, its expression is only detected in highly specific cell types (hematopoietic and epithelial cells). G15 alpha-subunit displays unique structural and biochemical properties, and is phylogenetically the most recent and divergent component of the Galphaq/11 subfamily. All these aspects shed a mysterious light on G15 biological role, which remains substantially elusive. Thus, far, G15 signaling has been analyzed in the context of hematopoiesis. Here, we highlight observations supporting the view that G15 functions may extend further beyond the immune system. In addition, we describe puzzling aspects of G15 signaling that offer a novel perspective in the understanding of its physiological role.

IFN-gamma-mediated upmodulation of MHC class I expression activates tumor-specific immune response in a mouse model of prostate cancer

De novo expression of B7-1 impaired tumorigenicity of TRAMP-C2 mouse prostate adenocarcinoma (TRAMP-C2/B7), but it did not elicit a protective response against TRAMP-C2 parental tumor, unless after in vitro treatment with IFN-gamma. TRAMP-C2 cells secrete TGF-beta and show low MHC-I expression. Treatment with IFN-gamma increased MHC-I expression by induction of some APM components and antagonizing the immunosuppressant activity of TGF-beta. Thus, immunization with TRAMP-C2/B7 conferred protection against TRAMP-C2-derived tumors in function of the IFN-gamma-mediated fine-tuned modulation of either APM expression or TGF-beta signaling. To explore possible clinical translation, we delivered IFN-gamma to TRAMP-C2 tumor site by means of genetically engineered MSCs secreting IFN-gamma.

Pichia pastoris as a host for secretion of toxic saporin chimeras

Most of the targeting moieties, such as antibody fragments or growth factor domains, used to construct targeted toxins for anticancer therapy derive from secretory proteins. These normally fold in the oxidative environment of the endoplasmic reticulum, and hence their folding in bacterial cells can be quite inefficient. For instance, only low amounts of properly folded antimetastatic chimera constituted by the amino-terminal fragment of human urokinase (ATF) fused to the plant ribosome-inactivating protein saporin could be recovered. ATF-saporin was instead secreted efficiently when expressed in eukaryotic cells protected from autointoxication with neutralizing anti-saporin antibodies. Pichia pastoris is a microbial eukaryotic host where these domains can fold into a transport-competent conformation and reach the extracellular medium. We show here that despite some host toxicity codon-usage optimization greatly increased the expression levels of active saporin but not those of an active-site mutant SAP-KQ in GS115 (his4) strain. The lack of any toxicity associated with expression of the latter confirmed that toxicity is due to saporin catalytic activity. Nevertheless, GS115 (his4) cells in flask culture secreted 3.5 mg/L of a histidine-tagged ATF-saporin chimera showing an IC(50) of 6 x 10(-11) M against U937 cells, thus demonstrating the suitability of this expression platform for secretion of toxic saporin-based chimeras.

The prostate specific membrane antigen regulates the expression of IL-6 and CCL5 in prostate tumour cells by activating the MAPK pathways

The interleukin-6 (IL-6) and the chemokine CCL5 are implicated in the development and progression of several forms of tumours including that of the prostate. The expression of the prostate specific membrane antigen (PSMA) is augmented in high-grade and metastatic tumors. Observations of the clinical behaviour of prostate tumors suggest that the increased secretion of IL-6 and CCL5 and the higher expression of PSMA may be correlated. We hypothesized that PSMA could be endowed with signalling properties and that its stimulation might impact on the regulation of the gene expression of IL-6 and CCL5. We herein demonstrate that the cross-linking of cell surface PSMA with specific antibodies activates the small GTPases RAS and RAC1 and the MAPKs p38 and ERK1/2 in prostate carcinoma LNCaP cells. As downstream effects of the PSMA-fostered RAS-RAC1-MAPK pathway activation we observed a strong induction of NF-κB activation associated with an increased expression of IL-6 and CCL5 genes. Pharmacological blockade with specific inhibitors revealed that both p38 and ERK1/2 participate in the phenomenon, although a major role exerted by p38 was evident. Finally we demonstrate that IL-6 and CCL5 enhanced the proliferative potential of LNCaP cells synergistically and in a dose-dependent manner and that CCL5 functioned by receptor-mediated activation of the STAT5-Cyclin D1 pro-proliferative pathway. The novel functions attributable to PSMA which are described in the present report may have profound influence on the survival and proliferation of prostate tumor cells, accounting for the observation that PSMA overexpression in prostate cancer patients is related to a worse prognosis.

Chemical conjugation of ΔF508-CFTR corrector deoxyspergualin to transporter human serum albumin enhances its ability to rescue Cl−channel functions

The most common mutation of the cystic fibrosis (CF) gene, the deletion of Phe508, encodes a protein (ΔF508-CFTR) that fails to fold properly, thus mutated ΔF508-cystic fibrosis transmembrane conductance regulator (CFTR) is recognized and degraded via the ubiquitin-proteasome endoplasmic reticulum-associated degradation pathway. Chemical and pharmacological chaperones and ligand-induced transport open options for designing specific drugs to control protein (mis)folding or transport. A class of compounds that has been proposed as having potential utility in ΔF508-CFTR is that which targets the molecular chaperone and proteasome systems. In this study, we have selected deoxyspergualin (DSG) as a reference molecule for this class of compounds and for ease of cross-linking to human serum albumin (HSA) as a protein transporter. Chemical cross-linking of DSG to HSA via a disulfide-based cross-linker and its administration to cells carrying ΔF508-CFTR resulted in a greater enhancement of ΔF508-CFTR function than when free DSG was used. Function of the selenium-dependent oxidoreductase system was required to allow intracellular activation of HSA-DSG conjugates. The principle that carrier proteins can deliver pharmacological chaperones to cells leading to correction of defective CFTR functions is therefore proven and warrants further investigations.

MPB-07 reduces the inflammatory response to Pseudomonas aeruginosa in cystic fibrosis bronchial cells

Chronic lung inflammation in cystic fibrosis (CF) is specifically characterized by predominant endobronchial neutrophil infiltrates, colonization by Pseudomonas aeruginosa, and elevated levels of cytokines and chemokines, first of all IL-8. The extensive inflammatory process in CF lungs is the basis of progressive tissue damage and is largely considered detrimental, making antiinflammatory approaches a relevant therapeutic target. This neutrophil-dominated inflammation seems to be related to an excessive proinflammatory signaling, originating from the same surface epithelial cells expressing the defective CF transmembrane conductance regulator (CFTR) protein, although the underlying mechanisms have not been completely elucidated. To investigate the relationship between defective CFTR and the inflammatory response to P. aeruginosa in CF airway cells, we studied the effect of the DeltaF508 CFTR corrector, benzo(c)quinolizinium (MPB)-07 (Dormer et al., J Cell Science 2001;114:4073-4081). CF bronchial epithelial IB3-1 and CuFi-1 cells overproduced the inflammatory molecules, IL-8 and intercellular adhesion molecule (ICAM)-1, in response to P. aeruginosa, compared with the wild-type, CFTR-expressing bronchial cells, S9, and NuLi-1 cells. In both IB3-1 and CuFi-1 cells, the corrector MPB-07 dramatically reduces the IL-8 and ICAM-1 mRNA expression elicited by P. aeruginosa infection. Correction of CFTR-dependent Cl- efflux was confirmed in MPB-07-treated IB3-1 and CuFi-1 cells. In conclusion, the DeltaF508 CFTR corrector MPB-07 produces an antiinflammatory effect in CF bronchial cells exposed to P. aeruginosa in vitro.

Detection of ricin and other ribosome-inactivating proteins by an immuno-polymerase chain reaction assay

Ribosome-inactivating proteins (RIPs) are plant proteins with enzymatic activity, classified as type 1 (single chain) or type 2 (two chains). They are identified as rRNA N-glycosidases (EC 3.2.2.22) and cause an irreversible inhibition of protein synthesis. Among type 2 RIPs, there are potent toxins (ricin is the best known) that are considered as potential biological weapons. The development of a fast and sensitive method for the detection of biological agents is an important tool to prevent or deal with the consequences of intoxication. In this article, we describe a very sensitive immuno-polymerase chain reaction (IPCR) assay for the detection of RIPs-a type 1 RIP (dianthin) and a type 2 RIP (ricin)-that combines the specificity of immunological analysis with the exponential amplification of PCR. The limit of detection (LOD) of the technique was compared with the LODs of the conventional immunological methods enzyme-linked immunosorbent assay (ELISA) and fluorescent immunosorbent assay (FIA). The LOD of IPCR was more than 1 million times lower than that of ELISA, allowing the detection of 10 fg/ml of dianthin and ricin. The possibility to detect ricin in human serum was also investigated, and a similar sensitivity was observed (10 fg/ml). IPCR appears to be the most sensitive method for the detection of ricin and other RIPs.

A fluorescence-based assay for the reductase activity of protein disulfide isomerase

We report on a new spectrofluorimetric assay for the measurement of reductase activity of proteins belonging to the superfamily of thioredoxins such as protein disulfide isomerase (PDI). The assay relies on the preparation of a fluorescence-quenched substrate easily accessible in two steps through functional group transformations of the peptide Gly-Cys-Asp. In the first step fluorescein isothiocyanate is linked to the Gly-NH(2) terminus and in the second step the Cys-SH groups are converted into a disulfide bond. Both intermediate and final substrate have been fully characterized by mass spectrometric and nuclear magnetic resonance measurements. Dimethyl sulfoxide is here reported to be a mild oxidizing agent allowing us to obtain in good overall yield the assay substrate in a single synthetic step. A reliable estimation of PDI reductase activity is obtained via the detection of a strong fluorescence enhancement after enzymatic reduction. Moreover, our assay provides further support for the key role played by thioredoxin reductase in enabling disulfide reductase activity of PDI.

Apical Transport and Folding of Prostate-specific Membrane Antigen Occurs Independent of Glycan Processing

Prostate-specific membrane antigen (PSMA) is an integral cell-surface membrane glycoprotein that is overexpressed in prostate carcinomas rendering it an appropriate target for antibody-based therapeutic strategies. The biosynthesis of PSMA in transfected COS-1 cells reveals a slow conversion of mannose-rich to complex glycosylated PSMA compatible with slow transport kinetics from the endoplasmic reticulum to the Golgi. Importantly, mannose-rich PSMA persists as a trypsin-sensitive protein throughout its entire life cycle, and only Golgi-located PSMA glycoforms acquire trypsin resistance. This resistance, used here as a tool to examine correct folding, does not depend on the type of glycosylation, because different PSMA glycoforms generated in the presence of inhibitors of carbohydrate processing in the Golgi are also trypsin resistant. The conformational transition of PSMA to a correctly folded molecule is likely to occur in the Golgi and does not implicate ER molecular chaperones, such as BiP. We show here that PSMA is not only heavily N-but also O-glycosylated. The question arising is whether glycans, which do not play a role in folding of PSMA, are implicated in its transport to the cell surface. Neither the cell-surface expression of PSMA nor its efficient apical sorting in polarized Madin-Darby canine kidney cells are influenced by modulators of N- and O-glycosylation. The acquisition of folding determinants in the Golgi, therefore, is an essential prerequisite for protein trafficking and sorting of PSMA and suggests that altered or aberrant glycosylation often occurring during tumorigenesis has no regulatory effect on the cell-surface expression of PSMA.

Constitutive activation of p38 and ERK1/2 MAPKs in epithelial cells of myasthenic thymus leads to IL-6 and RANTES overexpression: effects on survival and migration of peripheral T and B cells

Myasthenia gravis (MG) is an autoimmune disease of neuromuscular junctions where thymus plays a pathogenetic role. Thymectomy benefits patients, and thymic hyperplasia, a lymphoid infiltration of perivascular spaces becoming site of autoantibody production, is recurrently observed. Cytokines and chemokines, produced by thymic epithelium and supporting survival and migration of T and B cells, are likely to be of great relevance in pathogenesis of thymic hyperplasia. In thymic epithelial cell (TEC) cultures derived "in vitro" from normal or hyperplastic age-matched MG thymuses, we demonstrate by gene profiling analysis that MG-TEC basally overexpress genes coding for p38 and ERK1/2 MAPKs and for components of their signaling pathways. Immunoblotting experiments confirmed that p38 and ERK1/2 proteins were overexpressed in MG-TEC and, in addition, constitutively activated. Pharmacological blockage with specific inhibitors confirmed their role in the control of IL-6 and RANTES gene expression. According to our results, IL-6 and RANTES levels were abnormally augmented in MG-TEC, either basally or upon induction by adhesion-related stimuli. The finding that IL-6 and RANTES modulate, respectively, survival and migration of peripheral lymphocytes of myasthenic patients point to MAPK transcriptional and posttranscriptional abnormalities of MG-TEC as a key step in the pathological remodelling of myasthenic thymus.

N-terminal deletion affects catalytic activity of saporin toxin

Single-chain ribosome inactivating proteins (RIPs) are cytotoxic components of macromolecular pharmaceutics for immunotherapy of cancer and other human diseases. Saporin belongs to a family of single-chain RIPs sharing sequence and structure homology. In a preliminary attempt to define an active saporin polypeptide of minimum size we have generated proteins with deletions at the N-terminus and at the C-terminus. An N-terminal (sapDelta1-20) deletion mutant of saporin displayed defective catalytic activity, drastically reduced cytotoxicity but increased ability to interact with liposomes inducing their permeabilization at low pH. A C-terminal (sapDelta239-253) deletion mutant showed instead a moderate reduction in cytotoxic activity. A substantial alteration of secondary structure was evidenced by Fourier transformed infrared spectroscopy (FTIR) in the sapDelta1-20 mutant. It can be hypothesized that the defective functions of sapDelta1-20 are due to alterations of its spatial configuration.

Peptide analogues of a T-cell epitope of ricin toxin A-chain prevent agonist-mediated human T-cell response

The clinical efficacy of immunotoxins (IT) containing ricin toxin A-chain (RTA) can be drastically reduced by anti-toxin-neutralizing antibodies developed by patients. Strategies aimed at epitope-specific modulation of the immune response must be therefore set up to broaden the clinical applicability of RTA-based IT. Prevention or reduction of humoral immune responses against RTA could be achieved by peptide-based down-modulating strategies. Peptide analogues were investigated as candidate antagonist altered peptide ligands (APL) considering the sequence of a previously identified dominant T-cell epitope of RTA (i.e. I175-E185) presented in the context of the HLA-DRB1*03011 allele. Alanine-substituted peptides provided information on the role of individual residues of the wild-type peptide and allowed to identify one antagonist APL corresponding to the double-mutant peptide E177A/A178D. The analogue E177A/A178D not only prevented the agonist from stimulating anti-RTA human T-cell clones but also failed to induce down-regulation of surface-expressed TCR, thus suggesting its possible use for in vivo immune modulation of anti-RTA responses.

Anti-TNFα therapy in rheumatoid arthritis and autoimmunity

The aim of the study was to evaluate a panel of autoantibodies in patients affected by rheumatoid arthritis (RA) treated with anti-TNFalpha blockers, and to consider a different autoantibody induction effect by infliximab and etanercept; and in addition to evaluate in these cases a relationship between antinuclear antibody (ANA) titre and both C-reactive protein (CRP) and Blys levels. Fifty-four patients (8 men, 46 women, mean age 51.4 years, mean duration of disease 13.6 years) affected by refractory RA were treated with anti-TNFalpha blockers for 12 consecutive months; 43 patients were given infliximab and 11 etanercept. At baseline and every 4 months a panel of autoantibodies consisting of rheumatoid factor, antinuclear, anti-double-stranded DNA, anti-ENA, anti-mitochondrial, anti-thyroid and anti-neutrophil cytoplasmic antibodies (ANCA) was tested. At the same time CRP level was measured. Blys level was determined at baseline and after 1 year in five cases that developed a strong positivity for ANA during infliximab therapy. In 41 cases (95.3%) treated with infliximab, ANA were detected on at least one occasion, and in almost half of these cases the titre was very high, equal to or higher than 1:1.280. On the other hand, patients treated with etanercept presented ANA positivity in a lower percentage of cases and at a low titre. No correlation was found between ANA titre and CRP level; Blys level did not present a constant trend in patients who developed a very high positivity for ANA. Anti-double-stranded DNA, anti-thyroid or ANCA were found only in a few patients, in the absence of a clinical picture indicative of systemic lupus erythematosus, autoimmune thyroiditis or ANCA-associated vasculitis. A different incidence of ANA positivity was found in infliximab- and etanercept-treated RA patients; this finding might be due to the partially different method of inhibition of TNFalpha between the two drugs. Both CRP and Blys do not seem to participate in this phenomenon. Other autoantibodies were detected in a few patients, but no case of onset of new autoimmune disorders was observed.

A dominant linear B-cell epitope of ricin A-chain is the target of a neutralizing antibody response in Hodgkin's lymphoma patients treated with an anti-CD25 immunotoxin

Hodgkin's lymphoma patients treated with an anti-CD25 Ricin toxin A-chain (RTA)-based Immunotoxin (RFT5.dgA) develop an immune response against the toxic moiety of the immunoconjugate. The anti-RTA antibody response of 15 patients showing different clinical features and receiving different total amounts of RFT5.dgA was therefore studied in detail, considering antibody titre, IgG and IgM content, average binding efficacy and ability to inhibit in vitro the cytotoxicity of a RTA-based Immunotoxin. No correlations were found between these parameters and the clinical features of the patients or the total amount of Immunotoxin administered. However, using a peptide scan approach we have identified a continuous epitope recognized by all patients studied, located within the stretch L161-I175 of the RTA primary sequence, close to a previously identified T-cell epitope. The ability of anti-L161-I175 antibodies to recognize folded RTA and to affect the biological activity of RTA by inhibiting RTA-IT cytotoxicity in vitro revealed that they may exert an important role in IT neutralization in vivo. Discovery of RTA immunodominant epitopes which are the target of anti-RTA immune response may lead to the development of immunomodulating strategies and to more successful treatment schedules.

Immunotoxins and Other Conjugates: Preparation and General Characteristics

Targeted toxins represent an invaluable tool offering a wide range of potential applications, both in experimental models and in the clinics. Here we will review several aspects related to the preparation and properties of carrier molecule-toxin heteroconjugates and fusion toxins.

Reductive activation of ricin and ricin A-chain immunotoxins by protein disulfide isomerase and thioredoxin reductase

Intracellular activation of ricin and of the ricin A-chain (RTA) immunotoxins requires reduction of their intersubunit disulfide(s). This crucial event is likely to be catalyzed by disulfide oxidoreductases and precedes dislocation of the toxic subunit to the cytosol. We investigated the role of protein disulfide isomerase (EC 5.3.4.1, PDI), thioredoxin (Trx), and thioredoxin reductase (EC 1.8.1.9, TrxR) in the reduction of ricin and of a ricin A-chain immunotoxin by combining enzymatic assays, SDS-PAGE separation and immunoblotting. We found that, whereas PDI, Trx, and TrxR used separately were unable to directly reduce ricin and the immunotoxin, PDI and Trx in the presence of TrxR and NADPH could reduce both ricin and immunotoxin in vitro. PDI functioned only after pre-incubation with TrxR and the reductive activation of ricin was more efficient in the presence of glutathione. Similar results were obtained with microsomal membranes or crude cell extracts. Pre-incubation with the gold(I) compound auranofin, which irreversibly inactivates TrxR, resulted in a dose-dependent inhibition of ricin and immunotoxin reduction. Reductive activation of ricin and immunotoxin decreased or was abolished in microsomes depleted of TrxR and in cell extracts depleted of both PDI and Trx. Pre-incubation of U-937, Molt-3, Jurkat, and DU145 cells with auranofin significantly decreased ricin cytotoxicity with respect to mock-treated controls (P<0.05). Conversely, auranofin failed to protect cells from the toxicity of pre-reduced ricin which does not require intracellular reduction of disulfide between the two ricin subunits. We conclude that TrxR, by activating disulfide reductase activity of PDI, can ultimately lead to reduction/activation of ricin and immunotoxin in the cell.

Anti-tumor effects of toxins targeted to the prostate specific membrane antigen

BACKGROUND

There is presently no effective therapy for relapsing, metastatic, androgen-independent prostate cancer. Immunotherapy with monoclonal antibody-vehicled toxins (Immunotoxins, ITs) may be a promising novel treatment option for the management of prostate cancer in these cases.

METHODS

Three anti-prostate specific membrane antigen (anti-PSMA) monoclonals (J591, PEQ226.5, and PM2P079.1) were cross-linked to ricin A-chain (RTA; native or recombinant), and their cytotoxic effects were investigated in monolayer and three-dimensional (3-D) cell cultures of prostate carcinoma cells (LNCaP).

RESULTS

The various Immunotoxins showed effects in the nanomolar range (IC(50s) of 1.6-99 ng/ml) against PSMA+ cells (IC(50) being the concentration inhibiting 50% cell proliferation or protein synthesis). PSMA(-) cell lines were 62- to 277-fold less sensitive to anti-PSMA ITs, evidencing an appreciable therapeutic window. Treatment with J591-smpt-nRTA (0.35-31.7ng/ml) resulted in complete eradication of 3-D tumor micromasses or in 1.46- to 0.35-log reduction of target cells number, depending on the dose.

CONCLUSION

Anti-PSMA ITs appear to be promising for use in the eradication of small prostate tumor cell aggregates present in tissues and in the bone marrow.

Human MBP-specific T cells regulate IL-6 gene expression in astrocytes through cell-cell contacts and soluble factors

One of the distinctive features of multiple sclerosis (MS) attacks is homing to the CNS of activated T cells able to orchestrate humoral and cell-based events, resulting in immune-mediated injury to myelin and oligodendrocytes. Of the complex interplay occurring between T cells and CNS constituents, we have examined some aspects of T-cell interactions with astrocytes, the major components of the glial cells. Specifically, we focused on the ability of T cells to regulate the gene expression of interleukin-6 (IL-6) in astrocytes, based on previous evidence showing the involvement of this cytokine in CNS disorders. We found that T-cell adhesion and T-cell soluble factors induce IL-6 gene expression in U251 astrocytes through distinct signaling pathways, respectively, resulting in the activation of NF-kappaB and IRF-1 transcription factors. In a search for effector molecules at the astrocyte surface, we found that alpha3beta1 integrins play a role in NF-kappaB activation induced by T-cell contact, whereas interferon-gamma (IFN-gamma) receptors dominate in IRF-1 induction brought about by T-cell-derived soluble factors. Similar phenomena were observed also in normal fetal astrocyte cultures. We therefore propose that through astrocyte induction, T cells may indirectly regulate the availability of a cytokine which is crucial in modulating fate and behavior of cell populations involved in the pathogenesis of MS inflammatory lesions.

Identification of ricin A-chain HLA class II-restricted epitopes by human T-cell clones

The identification of ricin toxin A-chain (RTA) epitopes and the molecular context in which they are recognized will allow strategies to be devised that prevent/suppress an anti-RTA immune response in patients treated with RTA-based immunotoxins. RTA-specific human T-cell lines and T-cell clones were produced by in vitro priming of PBMC. The T-cell clones used a limited set of Vbeta chains (Vbeta1, Vbeta2 and Vbeta8) to recognize RTA epitopes. The use of RTA deletion mutants demonstrated that T-cell lines and T-cell clones from three out of four donors responded to RTA epitopes within the domain D124-Q223, whereas one donor recognized the region I1-D124. The response to RTA peptides of T-cell lines and T-cell clones from two donors allowed the identification of immunogenic segments (D124-G140 and L161-T190) recognized in the context of different HLA-DRB1 alleles (HLA-DRB1*0801, and HLA-DRB1*11011 and B1*03011, respectively). The response to L161-T190 was investigated in greater detail. We found that the HLA-DRB1*03011 allele presents a minimal epitope represented by the sequence I175-Y183 of RTA, whereas the HLA-DRB1*11011 allele presents the minimal epitope M174-I184. RTA peptides and an I175A RTA point mutant allowed us to identify I175 as a crucial residue for the epitope(s) recognized by the two HLA-DRB1 alleles. Failure of T-cell clones to recognize ribosome inactivating proteins (RIPs) showing sequences similar but not identical to RTA further confirmed the role of I175 as a key residue for the epitope recognized in the context of HLA-DRB1*11011/03011 alleles.

Pharmacokinetics of intrathecal transferrin-ricin a chain immunotoxin

We have studied the pharmacokinetics of an anti-transferrin receptor immunotoxin following intrathecal (i.t.) and intravenous (i.v.) bolus inoculation in healthy rats. After i.t. inoculation of 4.9 microg transferrin-ricin A-chain (Tfn-RTA) we have measured the immunotoxin concentration in the cerebrospinal fluid (CSF), in the brain tissue and in the peripheral blood. After i.v. administration of 4.9 microg Tfn-RTA the concentration of Tfn-RTA immunotoxin was evaluated in the peripheral blood. We found that the clearance of Tfn-RTA from the CSF is rapid (9.1 microLmin(-1)), the immunotoxin then diffuses into the brain tissue and in the peripheral blood where it reaches concentrations below the MTC50 (Minimum Toxin Concentration 50%). The rate of immunotoxin elimination from the peripheral blood following either i.v. or i.t. administration are similar (kel = 0.0021 min(-1) vs. 0.0025 min(-1)). Thus, in the healthy rat the immunotoxin does not accumulate following i.t. inoculation, reaching non toxic concentrations in the brain tissue and in the peripheral blood, whereas in the CSF as well as at the interface CSF/brain tissue the immunotoxin may reach potentially therapeutic concentrations. In conclusion we believe that the i.t. inoculation of an immunotoxin could be considered a potentially useful route of administration in the treatment of leptomeningeal carcinomatosis.

Effect of therapeutic macromolecules in spheroids

Recent advances in biotechnology have allowed the production of new types of macromolecular therapeutic agents (antibodies, immunotoxins, cytokines, extracellular matrix molecule (ECM) proteins, vectors) that may eventually find broad clinical applications in the treatment of human tumors and other diseases. The model of the Multicellular Tumor Spheroids (MTS) represents a valuable tool to test the therapeutic potential of these new pharmacologic agents in a 3-D context. Specific questions pertaining to the behaviour in a 3-D setting of some of the macromolecules under evaluation for in vivo applications can also be addressed in the MTS model (e.g. 'binding site barrier', role of cell-cell and cell-ECM interactions). This paper reviews the most significant contributions regarding the delivery of macromolecules to MTS, the penetration and therapeutic effects of antibodies, radiolabelled antibodies, immunotoxins and other macromolecular compounds.

Genetic grafting of membrane-acting peptides to the cytotoxin dianthin augments its ability to de-stabilize lipid bilayers and enhances its cytotoxic potential as the component of transferrin-toxin conjugates

Three chimeric proteins were obtained by fusing together the dianthin gene and DNA fragments encoding for the following membrane-acting peptides: the N-terminus of protein G of the vesicular stomatitis virus (KFT25), the N terminus of the HA2 hemagglutinin of influenza virus (pHA2), and a membrane-acting peptide (pJVE). Chimeric dianthins (KFT25DIA, pHA2DIA and pJVEDIA) retained full enzymatic activity in cell-free assays and showed increased ability to induce pH-dependent calcein release from large unilamellar vesicles (LUVs). pHA2DIA and pJVEDIA also showed faster kinetics of interaction with LUVs, while KFT25DIA and pHA2DIA displayed a reduced cytotoxicity as compared to wild-type dianthin. Conjugates made by chemically cross-linking KFT25DIA or pJVEDIA and human transferrin (Tfn) showed greater cell-killing efficiency than conjugates of Tfn and wild-type dianthin. As a consequence, by fusion of membrane-acting peptides to the dianthin sequence the specificity factor (i.e., the ratio between non-specific and specific toxicity) of Tfn-KFT25DIA, Tfn-pHA2DIA and Tfn-pJVEDIA was increased with respect to that of Tfn-based conjugates made with wild-type dianthin. Taken together, our results suggest that genetic fusion of membrane-acting peptides to enzymatic cytotoxins results in the acquisition of new physico-chemical properties exploitable for designing new recombinant cytotoxins and to tackle cell-intoxication mechanisms.

Adhesion of immature and mature T cells induces in human thymic epithelial cells (TEC) activation of IL-6 gene trascription factors (NF-kappaB and NF-IL6) and IL-6 gene expression: role of alpha3beta1 and alpha6beta4 integrins

T cell precursors homed to thymus develop in close contact with stromal cells. Among them, thymic epithelial cells (TEC) are known to exert dominant roles in their survival and functional shaping. Key molecules mediating TEC/thymocytes interactions include cytokines and growth factors secreted by the two cell types and adhesion receptors mediating cell contact. Signaling events triggered in thymocytes by adhesion to epithelial cells have been extensively investigated, whereas little is known on the opposite phenomenon. We have previously investigated this issue in a co-culture system composed of TEC cultures derived from human normal thymus and heterologous thymocytes. We demonstrated that thymocytes adhere to TEC involving beta1 and beta4 integrins and induce the clustering of alpha3beta1 and alpha6beta4 heterodimers at the TEC surface. In addition thymocyte adhesion was followed by activation of NF-kappaB and NF-IL6 gene transcription factors and enhanced IL-6 production. The two latter phenomena were reproduced by the cross-linking of the alpha3, alpha6, beta1 and beta4 integrins, thus implying that the alpha3beta1 and alpha6beta4 heterodimers can signal during thymocyte adhesion. We have extended our previous work investigating in the same experimental setting the inducing activity of non stimulated or activated policlonal or clonal mature T cells as representative of the more mature thymocyte subset. We found that adhesion of unstimulated T cell i) involved beta1, but not beta4 integrin functions at the surface ii) induced the clustering of alpha3beta1, but not alpha2beta1 heterodimers at the TEC surface and iii) up-regulated the nuclear binding activity of NF-kappaB transcription factor and the IL-6 secretion. We propose that alpha3beta1 and alpha6beta4 heterodimers are induced to cluster at the TEC surface recognizing yet unknown cellular ligands differentially expressed during T cell development.