Pharmacokinetics,tissue distribution,and in vivo antitumor effects of the antimelanoma immunotoxin ZME-gelonin

Antibody ZME-018 is directed against the gp240 glycoprotein on the surface of more than 80% of human melanoma cell lines and fresh biopsy specimens. Previous studies in our laboratory described the in vitro cytotoxicity and specificity of an immunoconjugate composed of mAb ZME-018 and the plant toxin gelonin. The present study describes the in vivo pharmacokinetics and therapeutic effects of ZME-gelonin in human xenograft/nude mouse models. Pharmacokinetic studies of¹²⁵I-labeled ZME-018 and ZME-gelonin demonstrated a shorter terminal-phase plasma half-life of the immunoconjugate than native ZME (20.6 h compared to 41.3 h). The initial volume of distribution of the ZME-gelonin was also higher compared to that of ZME alone (2.85 ml compared to 1.91 ml) suggesting an enhanced distribution of the conjugate outside the vasculature. The corresponding area under the concentration/time curve for the ZME-gelonin conjugate was 40% lower than that of ZME alone (80.8 compared to 139.6 μCi·ml^?1 x min). In nude mice bearing well-developed human tumor A375 melanoma xenografts, administration of¹²⁵I-labeled ZME and ZME-gelonin resulted in tumor-to-blood ratios of 1.9±0.5 and 1.5±0.6 respectively by 72 h. Compared with ZME, ZME-gelonin conjugate caused an increase in the content of radiolabel in kidney, spleen and liver. Treatment of nude mice bearing well-developed (150 mm³) s.c. A375-M xenografts with divided doses of ZME-gelonin, ZME, gelonin, or saline resulted in suppression of tumor growth in the immunotoxin group but virtually no retardation of tumor growth in the control groups. Using a murine model for a rapidly growing lethal metastatic human melanoma, treatment with ZME-gelonin resulted in a mean survival of 44 days, a 213% increase in mean survival time compared with the saline treatment (14.2±2 day survival). Given these encouraging results, we are proceeding with further preclinical development of this immunotoxin.     

Intratumoral anti-HuD immunotoxin therapy for small cell lung cancer and neuroblastoma

Background

Most patients with small cell lung cancer (SCLC) or neuroblastoma (NB) already show clinically detectable metastases at diagnosis and have an extremely poor prognosis even when treated with combined modalities. The HuD-antigen is a neuronal RNA-binding protein that is expressed in 100% of SCLC tumor cells and over 50% of neuroblastoma cells. The correlation between high titers of circulating anti-HuD antibodies in patients and spontaneous tumor remission suggests that the HuD-antigen might be a potential molecular target for immunotherapy.

Methods

We have constructed a new antibody-toxin compound (called BW-2) by assembling a mouse anti-human-HuD monoclonal antibody onto streptavidin/saporin complexes.

Results

We found that the immunotoxin BW-2 specifically killed HuD-positive human SCLC and NB cancer cells at very low concentrations in vitro. Moreover, intratumoral immunotoxin therapy in a nude mouse model of human SCLC (n?=?6) significantly reduced local tumor progression without causing toxicity. When the same intratumoral immunotoxin protocol was applied to an immunocompetent A/J mouse model of NB, significant inhibition of local tumor growth was also observed. In neuroblastoma allografted A/J mice (n?=?5) treated twice with intratumoral immunotoxin, significant tumor regression occurred in over 80% of the animals and their duration of tumor response was significantly prolonged.

Conclusions

Our study suggests that anti-HuD based immunotoxin therapy may prove to be an effective alternative treatment for patients with SCLC and NB.

     

Cachectin/tumor necrosis factor: production, distribution, and metabolic fate in vivo

A highly specific radioreceptor assay for cachectin/tumor necrosis factor (TNF) was utilized to measure the time course of lipopolysaccharide (LPS)-induced hormone production in rabbits. Cachectin/TNF bioactivity was monitored in the same serum samples by measuring lipoprotein lipase (LPL) suppression in 3T3-L1 cells. Cachectin/TNF is produced in large quantities by LPS-treated rabbits without priming by bacillus Calmette Guérin, C. parvum, or other agents. Nanomolar concentrations of the hormone are achieved, with peak levels occurring at 2 hr postinjection; the hormone is rapidly cleared thereafter. In separate studies, mice were used to assess the distribution and metabolic fate of cachectin/TNF. Radioiodinated hormone is cleared from the plasma with a half-life of 6 to 7 min. Studies of the tissue distribution of label after injection demonstrate that liver, kidneys, skin, and gastrointestinal tract take up most of the hormone. Electrophoretic analysis of tissues recovered from injected animals suggests that the hormone is very rapidly degraded after binding.     

A potent and specific immunotoxin for tumor cells expressing disialoganglioside GD2

Summary Monoclonal antibody 14G2a (anti-GD₂) reacts with cell lines and tumor tissues of neuroectodermal origin that express disialoganglioside GD₂. mAb 14G2a was coupled to the ribosome-inactivating plant toxin gelonin with the heterobifunctional cross-linking reagentN-succinimidyl-3(2-pyridyldithio)propionate. The activity of the immunotoxin was assessed by a cell-free translation assay that confirmed the presence of active gelonin coupled to 14G2a. Data from an enzyme-linked immunosorbent assay demonstrated the specificity and immunoreactivity of the 14G2a-gelonin immunotoxin, which was identical to that of native 14G2a. Assays for complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC) revealed that these functional properties of the native 14G2a antibody were also preserved in the 14G2a-gelonin immunotoxin. The gelonin-14G2a immunotoxin was directly cytotoxic to human melanoma (A375-M and AAB-527) cells and was 1000-fold more active than native gelonin in inhibiting the growth of human melanoma cells in vitro. The augmentation of tumor cell killing of 14G2a-gelonin immunotoxin was examined with several lysosomotropic compounds. Chloroquine and monensin, when combined with 14G2a-gelonin immunotoxin, augmented its cytotoxicity more than 10-fold. Biological response modifiers such as tumor necrosis factor and interferon and chemotherapeutic agents such as cisplatinum andN,N-bis(2-chloroethyl)-N-nitrosourea (carmustine) augmented the cytotoxicity of 14G2a-gelonin 4- to 5-fold. The results of these studies suggest that 14G2a-gelonin may operate directly by both cytotoxic efforts and indirectly by mediating both ADCC and CDC activity against tumor cells; thus it may prove useful in the future for therapy of human neuroectodermal tumors.Research conducted, in part, by the Clayton Foundation for Research     

Combination Treatments with the PKC Inhibitor,Enzastaurin, Enhance the Cytotoxicity of the Anti-Mesothelin Immunotoxin,SS1P

Activated protein kinase C (PKC) contributes to tumor survival and proliferation, provoking the development of inhibitory agents as potential cancer therapeutics. Immunotoxins are antibody-based recombinant proteins that employ antibody fragments for cancer targeting and bacterial toxins as the cytotoxic agent. Pseudomonas exotoxin-based immunotoxins act via the ADP-ribosylation of EF2 leading to the enzymatic inhibition of protein synthesis. Combining PKC inhibitors with the immunotoxin SS1P, targeted to surface mesothelin, was undertaken to explore possible therapeutic strategies. Enzastaurin but not two other PKC inhibitors combined with SS1P to produce synergistic cell death via apoptosis. Mechanistic insights of the synergistic killing centered on the complete loss of the prosurvival Bcl2 protein, Mcl-1, the loss of AKT and the activation of caspase 3/7. Synergy was most evident when cells exhibited resistance to the immunotoxin alone. Further, because PKC inhibition by itself was not sufficient to enhance SS1P action, enzastaurin must target other kinases that are involved in the immunotoxin pathway.     

In vivo cytotoxic efficacy of immunotoxins prepared from anti-CD5 antibody linked to ricin A-chain

Summary The antitumoral efficacy of various anti-CD5 immunotoxins, prepared with whole monoclonal antibody (mAb), F(ab)₂ or Fab fragment linked to native ricin A-chain (RTA) or partially deglycosylated ricin A-chain (dRTA), was examined in vivo in ascitic nude mice bearing a large burden of Ichikawa human tumour cells. We first demonstrated that after systemic administration of IgG-RTA or F(ab)₂-dRTA, the cytotoxic activity of immunotoxin molecules specifically bound to tumour cells was preserved. Secondly we showed, by using different immunotoxins with various targeting capacities, that their cytotoxic effect in vivo was related to the number of immunotoxin molecules bound per cell. However, even when antigen saturation was achieved after i.p. injection, the cytotoxic effect did not exceed 53% of the tumour burden. By contrast, when the immunotoxin was administered i.p. or i.v. with the enhancer monensin conjugated to human serum albumin and injected i.p., 90% of the tumour cells were killed. This potentiating effect was demonstrated even when the tumour localisation was as low as 5% of the saturation level. Such an effect could be completely prevented by addition of unconjugated monoclonal antibody, demonstrating the specificity of the immunotoxin-induced cytotoxicity in the presence of the enhancer. However this enhancement was demonstrated whatever the route of immunotoxin administration, i.p. or i.v., but was only observed when the enhancer was injected i.p. and not i.v.. These results emphasize the importance of optimizing the therapeutic course to improve the antitumoral efficacy of immunotoxins.     

A specific and potent immunotoxin composed of antibody ZME-018 and the plant toxin gelonin

Murine monoclonal antibody ZME-018 recognizes a 240 Kda glycoprotein present on the surface of most human melanoma cells and on over 80% of human biopsy specimens tested. Gelonin is a ribosome-inactivating plant toxin similar in nature and rivaling the activity of ricin A chain. ZME-018 was coupled to purified gelonin using the reagents SPDP and 2-iminothiolane. The ZME-gelonin conjugate was purified by S-300 Sephacryl and Blue Sepharose chromatography, removing unreacted gelonin and antibody, respectively. PAGE analysis showed that ZME was coupled to 1, 2, or 3 gelonin molecules. The ZME-gelonin conjugate was 10(6)-fold more active than gelonin itself in inhibiting the growth of log-phase human melanoma cells in culture. The immunoconjugate was not cytotoxic to antigen negative T-24 (human bladder carcinoma) cells. Treatment of melanoma cells with recombinant IFN-alpha or TNF substantially augmented the cytotoxicity of the immunoconjugate while treatment with IFN-gamma had a minor effect. Using the human tumor colony assay of melanoma cells obtained from fresh biopsy specimens, greater than 90% growth suppression was observed in 2 of 4 samples tested at a concentration of 250 ng/ml. In addition, 25% growth suppression was observed with a third sample tested, and no growth suppression was observed in 1 sample. Thus, clonogenic melanoma cells are sensitive in vitro to the cytotoxic activity of this immunotoxin at concentrations which we presume are pharmacologically relevant.     

Targeting tumor-associated macrophages in an experimental glioma model with a recombinant immunotoxin to folate receptor β

Tumor-associated macrophages (TAMs) are frequently found in glioblastomas and a high degree of macrophage infiltration is associated with a poor prognosis for glioblastoma patients. However, it is unclear whether TAMs in glioblastomas promote tumor growth. In this study, we found that folate receptor β (FRβ) was expressed on macrophages in human glioblastomas and a rat C6 glioma implanted subcutaneously in nude mice. To target FRβ-expressing TAMs, we produced a recombinant immunotoxin consisting of immunoglobulin heavy and light chain Fv portions of an anti-mouse FRβ monoclonal antibody and Pseudomonas exotoxin A. Injection of the immunotoxin into C6 glioma xenografts in nude mice significantly depleted TAMs and reduced tumor growth. The immunotoxin targeting FRβ-expressing macrophages will provide a therapeutic tool for human glioblastomas.     

High-dose,unlabeled, nonspecific antibody pretreatment: influence on specific antibody localization to human melanoma xenografts

Summary Nonspecific uptake of radiolabeled monoclonal antibodies in normal tissues is a significant problem for tumor imaging. A potential means of decreasing nonspecific antibody binding is to blockade nonspecific antibody binding sites by predosing with cold, nonspecific isotypematched antibody, before injecting specific antibody. Nontumor-specific murine monoclonal antibody LK2H10 (IgG1) or Ab-1 (IgG2a) was given i.v. at doses of 0 to 3.5 mg to nude mice with xenografts of human melanoma. These mice were then given i.v. 4 g of ¹³¹I anti-high molecular weight antigen of melanoma (HMWMAA) monoclonal antibody 763.24T (IgG1) or 225.28S (IgG2a), respectively. These mice were also given a tracer dose of ¹²⁵I LK2H10 or Ab-1, respectively. Specific tumor uptake of anti-HMWMAA antibodies was see in all cases. No drop in tumor or nontumor uptake was demonstrated for either of the tumor-specific or nonspecific monoclonal antibodies due to nonspecific monoclonal antibody pretreatment. These data suggest that high doses of isotype-matched unlabeled nonspecific monoclonal antibody given before ¹³¹I tumor-specific monoclonal antibody, will not enhance tumor imaging. Present address: Hybritech, San Diego, CA, USA     

An immunotoxin for the treatment of T-acute lymphoblastic leukemic meningitis: studies in rhesus monkeys

Summary Monoclonal antibody WT1 (anti-CD7), conjugated to ricin A chain, was administered intrathecally to rhesus monkeys to test its suitability for use in the therapy of leukemic meningitis. The WT1-SMPT-dgRTA conjugate was cytotoxic to CEM (T-lymphoblastic leukemia) cells in vitro with an ID₅₀ of 53 pM. Immunoperoxidase testing showed no binding of WT1 to normal human tissues other than lymph nodes. Thirteen animals received one or more intrathecal 60-g doses of WT1-SMPT-dgRTA. All monkeys receiving repeated doses developed a cerebrospinal fluid (CSF) pleocytosis (primarily eosinophils), which was generally resolving by 3–4 weeks after therapy. Pharmacokinetic studies showed a half-life of 99 min, consistent with CSF clearance by bulk flow. Peak CSF immunotoxin concentrations exceeded the ID₅₀ for CEM cells by more than 2 log units and a concentration exceeding the ID₅₀ was maintained for as long as 24 h. All eight monkeys receiving repeated doses of immunotoxin developed serum antibodies against both WT1 and ricin A chain. In six of these monkeys antibodies were also present in the CSF. Both anti-WT1 and anti-(ricin A chain) antibodies were able to inhibit in vitro cytotoxicity of the immunotoxin for CEM cells; however, only anti-WT1 antibodies could block immunotoxin binding to the cell surface. No monkey developed anti-immunotoxin antibodies fewer than 7 days after the initiation of therapy, suggesting that repeated doses could be administered for up to 1 week without inhibition of clinical activity.     

Effects of BCL-2 overexpression on the sensitivity of MCF-7 breast cancer cells to ricin, diphtheria and Pseudomonas toxin and immunotoxins

Immunotoxins are presently being evaluated as novel agents for cancer therapy. The direct mechanism by which immunotoxins kill cancer cells is inhibition of protein synthesis, but cytotoxicity due to induction of apoptosis has also been observed with these agents. Some cancers that express high levels of BCL-2 are relatively resistant to apoptosis inducing agents. It is therefore important to determine to what degree the toxicity of ricin, diphtheria toxin, Pseudomonas exotoxin and Pseudomonas exotoxin derived immunotoxins towards cancer cells can be attributed to inhibition of protein synthesis, and to what degree to subsequent induction of apoptosis. We compared the sensitivity of MCF-7 breast cancer cells that were stably transfected with a BCL-2 expression plasmid and thus protected against apoptosis and of MCF-7 cells transfected with a control plasmid towards ricin, diphtheria and Pseudomonas toxin, a Pseudomonas toxin-derived immunotoxin (LMB-7) and tumour necrosis factor (TNF). We found that BCL-2 mediated inhibition of apoptosis renders the cells almost completely resistant (1000-fold) to tumour necrosis factor, but the same cells were only 3–10 fold more resistant to cytotoxicity induced by immunotoxin LMB-7 as well as Pseudo-monas exotoxin, diphtheria toxin and ricin. We next studied several leukaemia cell lines with variable levels of BCL-2 expression and found them quite sensitive to a Pseudomonas exotoxin containing immunotoxin independent of the level of BCL-2. Our data indicate that although BCL-2 overexpression can have a modest effect on sensitivity to an immunotoxin, cell lines derived from patients are still very sensitive to immunotoxins.     

Comparison of multiple anti-CEA immunotoxins active against human adenocarcinoma cells

Summary Anti-carcinoembryonic antigen (CEA) immunotoxins constructed with multiple anti-CEA antibodies (goat and baboon polyclonal, and three murine monoclonal antibodies) by covalently linking them to the A chain of ricin via a disulfide bond all function as potent and specific toxins for CEA-bearing cells, suggesting that the CEA molecule is capable of directing productive internalization of ricin A chain. The high potency of anti-CEA immunotoxins apparently makes addition of ricin B chain unnecessary for high toxic efficiency, as in some other systems, because presence of the B chain reduces target cell specificity. Several characteristics of the immunotoxins which might account for their cytotoxic potency were studied. Equilibrium association constants of the goat, baboon, and murine monoclonal C-19 antibodies with fluid-phase CEA were determined by using Langmuir plots and were found to be 8.79, 6.61, and 8.13×10⁹ M ^–1, respectively, indicating the high and similar affinities of the three antibodies toward CEA. Radioimmunoassay binding studies of the three immunotoxins with ¹²⁵I-CEA showed that the antibody portions of the molecules retained the ability to form complexes with CEA after conjugation to ricin A chain. The maximum number of anti-CEA antibody molecules bound per cell, as demonstrated by ¹¹¹In-labeled C-19 binding assays with CEA-bearing cell lines, varied from 2.65×10⁵ per cell for HT29 to 2.01×10⁶ for LoVo, with an intermediate value of 1.17×10⁶ per cell for WiDr. Cytotoxicity of the immunotoxins was assessed by inhibition of protein synthesis and expressed as a median inhibitory dose (ID₅₀). Comparison of the ID₅₀'s of each immunotoxin on the three cell lines has shown that the immunotoxin made of the monoclonal C-19 antibody is in general 6 to 7 times more cytotoxic than the goat and baboon antibody immunotoxins. The affinity of CEA-antibody binding is probably an important, but not a sole factor in determining the immunotoxin potency. The fact that the antibodies with very similar affinity toward fluid phase CEA make immunotoxins of different potency might indicate that interactions with membrane-bound CEA are more complex and/or the efficiency of internalization of various immunotoxins is different. An important factor in immunotoxin action appears to be the CEA content in target adenocarcinoma cells.Supported in part by the NIH BRSG grant SO7RRO5712, the American Cancer Society, Mass. Div. Research Grant 1543-C-1, and by the Aid for Cancer Research (Boston) award to L. V. L., and by RO1 CA 29160 and RO1 CA 39748 grants to T. W. G.     

Lack of cell-cycle-specific effects of recombinant tumor necrosis factor in vivo

Several in vitro studies have demonstrated that tumor cells arrested in the G2 and M phases of the cell cycle expressed an increased sensitivity to the tumor necrosis factor (TNF). The scope of the present study was to investigate whether this cycle dependence of TNF effects also exists in vivo. The experiments were performed by using the Lewis lung carcinoma (LLC), which had been allotransplanted to nude mice. In order to induce delays of the tumor cell cycle in G2, the animals were treated with etoposide (40 mg/kg body weight i.p.) or with local radiation (15 Gy), each increasing the G2 fraction of the LLC from 10% to 35% and 50% respectively. For combination therapy with recombinant (r)TNF, the tumor was transplanted to four groups of six mice each, one of them serving as a control group the others being treated either with a G2 inductor alone, with rTNF alone, or with rTNF and a G2 inductor combined. Administration of rTNF (125 or 250 g/kg body weight i.v.) was always carried out 24 h after therapy with etoposide or radiation when the maximum of G2 accumulation had developed. The growth behavior of the treated tumors revealed that the response of the LLC to rTNF in vivo was not improved by pretreatment with a G2 inductor and, thus, obviously lacked cell-cycle specificity. It is supposed that direct interactions of TNF with the tumor cells, which are a basic requirement for cell-cycle-linked phenomena, play a minor role in the therapeutic outcome of the LLC under in vivo conditions.     

Discovery and characterization of COVA322, a clinical-stage bispecific TNF/IL-17A inhibitor for the treatment of inflammatory diseases

Biologic treatment options such as tumor necrosis factor (TNF) inhibitors have revolutionized the treatment of inflammatory diseases, including rheumatoid arthritis. Recent data suggest, however, that full and long-lasting responses to TNF inhibitors are limited because of the activation of the pro-inflammatory T_H17/interleukin (IL)-17 pathway in patients. Therefore, dual TNF/IL-17A inhibition is an attractive avenue to achieve superior efficacy levels in such diseases. Based on the marketed anti-TNF antibody adalimumab, we generated the bispecific TNF/IL-17A-binding FynomAb COVA322. FynomAbs are fusion proteins of an antibody and a Fyn SH3-derived binding protein. COVA322 was characterized in detail and showed a remarkable ability to inhibit TNF and IL-17A in vitro and in vivo. Through its unique mode-of-action of inhibiting simultaneously TNF and the IL-17A homodimer, COVA322 represents a promising drug candidate for the treatment of inflammatory diseases. COVA322 is currently being tested in a Phase 1b/2a study in psoriasis (ClinicalTrials.gov Identifier: NCT02243787).     

Immunolesioning of Glutamate Receptor GluR1-Containing Neurons in the Rat Neostriatum Using a Novel Immunotoxin

1. To investigate the potency of a novel immunotoxin that is specific for glutamate receptor GluR1, a subunit of the -amino-3-hydroxy-5-methyl-4-isoxazole-propionate (AMPA)-type receptor channel, immunolesioning was performed.2. A ribosome-inactivating protein, trichosanthin (TCS), was isolated and conjugated to the goat anti-rabbit IgG antibody molecule. The anti-rabbit antibody–TCS complex was preincubated with GluR1-specific rabbit antibody to produce a GluR1-specific immunotoxin. The immunotoxin was unilaterally administered into either the neostriatum or the lateral ventricle of rats.3. Immunoreactivity for GluR1 or GluR4 was revealed in perfuse-fixed sections of the neostriatum obtained from the lesioned and control animals by immunocytochemistry. After ventricular or striatal injections of the immunotoxin, depletions of GluR1-immunoreactive neurons, the presumed GABAergic interneurons in the neostriatum, were found. Depletions of GluR4-immunoreactive perikarya, the presumed same subpopulation of striatal interneurons, were also found. In addition, no change in the pattern of distribution of immunoreactivity for GluR2 or glial fibrillary acidic protein was found in the lesioned neostriatum. These results indicate that the novel GluR1 immunotoxin is potent and specific.4. In addition, striatal application of the immunotoxin caused a greater depletion in the number of GluR1-immunoreactive neurons. The present results also indicate that the route of immunotoxin application may be important in producing specific lesions.     

Antitumour activity of a sterically blocked ricin immunotoxin on a human colorectal adenocarcinoma grafted subcutaneously in nude mice

Summary We prepared a ricin-antibody conjugate, lacking the ability to bind the galactosidic residues of Sepharose 6B, a so-called blocked immunotoxin. The monoclonal antibody AR-3 was cross-linked to ricin through a thioether bond. Further studies showed that the immunoconjugate suppressed the tumour growth of HT-29 cells in intraperitoneally grafted nude mice, without showing any undesirable ricin toxicity.In this work, to demonstrate the therapeutic activity of the AR-3—ricin conjugate injected into mice bearing subcutaneous tumour, we first evaluated its pharmacokinetic behaviour and biodistribution. The behaviour of the immunoconjugate injected intravenously was almost intermediate between that of the antibody and ricin. Moreover, when the immunotoxin was intravenously administered to nude mice bearing subcutaneous tumour, no therapeutic effects appeared, in accordance with the relatively low permeability of the immunotoxin from the blood to the skin. In contrast, peritumoral treatment produced a strong reduction of the neoplastic nodules without substantial regrowth of the malignant cells. This result was also achieved when the immunotoxin treatment was performed on a well-established tumour. This finding was strictly related to the specificity of the immunoconjugate, since the analogous treatment with an irrelevant immunotoxin showed therapeutic failure.     

Species-specific TNF induction of thymocyte proliferation

Summary Recombinant murine (rMu) tumor necrosis factor (TNF), in a standard comitogenic assay with phytohemagglutinin, induced murine thymocyte proliferation, while up to 10,000-fold higher concentrations of recombinant human TNF did not. The induction of thymocyte proliferation was dependent upon TNF concentration in a biphasic manner. Thus, 100 to 1000 units/ml TNF were near optimal while concentrations 1,000 units/ml caused apparent down regulation. The effect was abrogated by neutralizing antibody to rMu-TNF but not by neutralizing antibody to rMu-interleukin 1 or . The rMu-TNF did not induce proliferation of the mature murine T-helper cell line, D10.G4.1, in the presence of mitogen. Taken together the results indicate that TNF, in a strictly species-specific manner, can regulate thymocyte proliferation independently of interleukin 1.Supported in part by Asahi Chemical Industry Co., Inc. and by USPHS Grants CA-24538, CA-15142 and CA-09072 awarded by the National Cancer Institute, Department of Health and Human Services     

Comparison of the cytotoxic potency of T101 Fab, F(ab')2 and whole IgG immunotoxins

The in vitro killing of the human CEM cell line was studied by using ricin A-chain immunotoxins constructed with either the whole IgG or the Fab and F(ab')2 fragments of the same T101 (anti-CD5) antibody. In the presence of ammonium chloride as an activator, the "whole" immunotoxin as well as the "fragment" immunotoxins did not show any significant difference in the cell killing efficacy. In contrast, without the activator, the efficacy of the T101 immunotoxin was greatly improved when fragments were used. Indeed, at a saturating dose, a cytoreduction of three orders of magnitude was obtained with the fragment immunotoxins vs less than one order of magnitude for the whole immunotoxin, as assessed in a clonogenic assay. This enhancing effect was related to better cell killing kinetics, because with a similar amount of A-chain molecules bound per cell, T101 fragment immunotoxins achieved a twofold faster protein synthesis inactivation rate than the corresponding whole IgG immunotoxin. No significant difference in activity was shown between monovalent (Fab) and divalent (F(ab')2) forms of fragment immunotoxins. The observation that T101 fragment immunotoxins were more potent than intact immunotoxins was extended to another fragment immunotoxin constructed with an antibody (F111.98) directed against a different epitope of the CD5 Ag. In another model (anti-CD22 1G11 antibody on Raji cells), the fragment immunotoxin did not show any superiority over the IgG immunotoxin which was by itself very potent, strongly suggesting an Ag-dependent phenomenon.     

Influence of antibody protein dose on therapeutic efficacy of radioiodinated antibodies in nude mice bearing GW-39 human tumor

Summary The biodistributions of three¹³¹I-labeled murine monoclonal antibodies, NP-4 and Immu-14 anti-(carcinoembryonic antigen), and Mu-9 anti-(colon-specific antigen p), were determined at antibody protein doses varying from 1 µg to 1000 µg in nude mice with small (0.1–0.4 g) GW-39 human colonic cancer xenografts. For each antibody, the percentage of the injected dose per gram of tumor and tumor/nontumor ratios were constant over a wide protein dose range. However, at high protein doses (above 100 µg for NP-4 and Immu-14) the percentage of the injected dose per gram of tumor and tumor/nontumor ratios decreased. Assuming that the uptake of a control anti-(-fetoprotein) antibody represents the amount of antibody that accumulates in the tumor nonspecifically (i.e., antigen-independently), it could be shown that for each antibody the amount of antibody protein that accumulates in the tumor specifically, increases linearly with the protein dose, reaching a plateau level at the highest doses tested. The growth inhibition of GW-39 tumor transplants in nude mice treated with¹³¹I-labeled antibody at either low or high antibody protein dose was compared. These experiments indicated that, in this experimental model, enhanced antibody protein dose may decrease the therapeutic efficacy of radioiodinated antibodies. It is suggested that heterogeneous distribution at low protein dose, with intense localization around the blood vessels, may enhance the tumoricidal effect of radioantibodies.Supported in part by USPHS grants CA 39 841 and CA 37 895, National Institutes of Health and Human ServicesResearch fellow of the Dutch Cancer Society     

Characterization of tumor-necrosis-factor-gene-transduced tumor-infiltrating lymphocytes from ascitic fluid of cancer patients: analysis of cytolytic activity,growth rate,adhesion molecule expression and cytokine production

We characterized tumor-infiltrating lymphocytes (TIL) from ascites of patients with ovarian or pancreatic cancer in which the human tumor necrosis factor (TNF) gene was successfully transduced with retrovirus vector. The TNF-gene-transduced TIL (TNF-TIL) from these patients showed a higher level of TNF production and higher cytotoxic activity against K562 and Daudi cells than did neomycin-phosphotransferase-gene-transduced TIL (neo-TIL). Of these TIL preparations, only that from pancreatic cancer was further characterized since it was collected in a relatively large amount. In spite of the fact that the autologous tumor cells showed resistance to soluble TNF, the TNF-TIL clearly demonstrated enhanced cytotoxicity against them as compared with neo-TIL. The enhanced cytotoxicity was ascribed to autocrine effects of secreted TNF on TIL, which included augmentation of adhesion molecule (CD2 and CD11a) and interleukin-2 receptor expression, and elevation of production of interferon , lymphotoxin and granulocyte/macrophage-colonystimulating factor and its paracrine effect on target cells to facilitate them to be more susceptible to TIL.