The human EGF receptor as a target for cancer therapy: six new rat mAbs against the receptor on the breast carcinoma MDA-MB 468

Using the breast carcinoma cell line MDA-MB 468 as immunogen, we have produced six new rat monoclonal antibodies (mAbs) against the human EGF receptor (EGFR) and are investigating their use for diagnostic and therapeutic applications in cancer patients whose tumours overexpress these receptors. The mAbs (three IgG2b and one each of IgG2a, IgG1 and IgA) were selected on the basis that they bound to the extracellular domain of the EGFR and blocked growth factor-receptor interaction. Competitive assays showed that, with the exception of antibody ICR65, the mAbs bound to one of two distinct epitopes on the external domain of the EGFR. ICR65, however, cross-reacted with mAbs binding to both epitopes. All of the mAbs immunoprecipitated the 170 kDa glycoprotein from cells expressing the EGFR but not the 185 kDa product of the related c-erbB-2 proto-oncogene. Unlike EGF and TGF alpha none of the mAbs stimulated the growth of quiescent human foreskin fibroblasts but they inhibited the EGF and TGF alpha induced growth stimulation of these cells in vitro. When tested for their effect on tumour cells the mAbs were found to inhibit the growth in vitro of a number of human tumours that overexpressed the EGFR (e.g. HN5, HN6, HN15, A431, MDA-MB 468) but they were without effect on tumour cell lines expressing low or undetectable amounts of the receptor. Our initial results indicate that this new generation of antibodies which bind with high affinity to the EGFR, block growth factor-receptor interaction and inhibit the growth of human squamous carcinoma cell lines overexpressing the receptor have potential for clinical application.

c-erbB2 protein overexpression in breast cancer as a target for PET using iodine-124-labeled monoclonal antibodies

ICR 12, one of a panel of rat monoclonal antibodies recognizing the external domain of the human c-erb B2 proto-oncogene product, (Styles, 1990) was chosen as a candidate for radiolabeling with 124I for positron emission tomography of selected patients with breast cancer. By using N-bromosuccinimide (NBS), optimal labeling conditions were established using 125I. The labeling efficiency was determined using instant thin-layer chromatography (ITLC) and gel filtration (HPLC). The antibody was then labeled with the positron emitter 124I, and a labeling efficiency of 96% and immunoreactivity of 80%-90% was obtained. The product was stable, with less than 5% of the radiolabel being eluted after six days storage in plasma at 37 degrees C. Immunolocalization studies were performed in athymic mice bearing human breast carcinoma xenografts overexpressing the c-erb B2 gene product using as controls 125I labeled isotype-matched rat antibody, and antigen-negative tumors. Good uptake of 124I-labeled ICR12 was obtained in c-erb B2 expressing tumors (up to 12% injected dose per gram at intervals up to 120 hr), with localization indices of 3.4-6.2. Tumor xenografts of 6 mm diameter were successfully imaged with high resolution at 24, 48 and 120 hr using the RMH/ICR MUP-PET camera. We suggest that 124I-labeled ICR12 is a suitable agent to image and quantify immunolocalization in patients whose tumors overexpress the c-erb B2 proto-oncogene product.

Rat monoclonal antibodies to the external domain of the product of the C-erbB-2 proto-oncogene

With the breast carcinoma cell line BT 474 used as a source of antigen, four rat monoclonal antibodies (MAbs) (3 IgG2a and I IgA) have been prepared against the external domain of the product of the c-erbB-2 proto-oncogene. All 4 antibodies stain frozen sections of tissues that over-express the product of the c-erbB-2 proto-oncogene, and competitive binding assays showed that the antibodies recognized 2 non-overlapping epitopes. Representative antibodies from the two groups (ICR12 and 13) were shown to specifically immunoprecipitate a 190 kDa protein from 35S-methionine-labelled breast carcinoma cells where the c-erbB-2 is amplified (BT 474 and MDA-MB 361). Two of the antibodies (ICR12 and ICR17) bind to the denatured antigen in Western blots and ICR12 stains formolsaline-fixed sections of breast carcinoma tissue that over-expresses the product of the c-erbB-2 proto-oncogene. These antibodies should be useful not only for immunocytochemical diagnoses but also for radio-immunoscintigraphic and therapeutic applications.

Pharmacokinetic studies of radiolabelled rat monoclonal antibodies recognising syngeneic sarcoma antigens. II. Effect of host age and immune status

In the preceding paper it was suggested that the tumour localisation of 125I-labelled syngeneic rat monoclonal antibodies (mAbs) may be limited in immunocompetent hosts by the presence of competing endogenous serum antibodies. In syngeneic congenitally athymic (nu/nu) and cyclosporin-A-treated rats (both of which fail to mount immune responses to tumour antigens) increased uptake of mAbs in tumour tissue was obtained compared with that in immunocompetent animals. However, in the case of IgG2b and IgG1 mAbs, this appeared to be due primarily to enhanced "non-specific" localisation mediated by Fc binding, since it was abolished by the use of F(ab')2 fragments with two out of three mAbs tested. Normal tissue distribution was also influenced by host immune status: in nu/nu rats the uptake of IgG2b mAbs in the spleen was up to fivefold higher than that previously found in normal animals and the levels in liver were also increased. This effect was not seen in cyclosporin-A-treated hosts, suggesting that the reticuloendothelial system of congenitally athymic animals contains cells with enhanced IgG2b-FcR activity. This hypothesis was strengthened by the observation that splenic uptake was reduced by either the use of F(ab')2 fragments, or prior "blockade" of Fc receptors by "cold competition" with excess unlabelled IgG2b mAbs. This blockade could not be effected by mAbs of any other isotype or by IgG2b F(ab')2 fragments. The former manoeuvre resulted in higher tumour specificity ratios but usually at the expense of reduced levels of tumour associated radiolabelled mAb. The latter was found to increase "absolute" tumour localisation by up to 35%. In an attempt to characterise further and compare the Fc receptor activity of intratumour and intrasplenic host cells. The distribution of IgG2b mAbs was assayed in 3-week, 8-week and 12-week-old rats. We were able operationally to distinguish the activity of these two categories of cells, suggesting that they represent either different lineages or differentially activated subpopulations: the splenic IgG2b binding was fully expressed in weanling nu/nu rats whereas the FcR activity of cells infiltrating MC24 sarcoma was limited in 3-week-old compared with 8-12-week-old hosts. A further difference was apparent in the subclass "preference" of FcR binding: in immunodeprived rats both IgG1 and IgG2b mAbs were able to bind to tumour-infiltrating host cells, but uptake of IgG1 mAbs in the spleen was always low and not reduced further by the use of F(ab')2 fragments.(ABSTRACT TRUNCATED AT 400 WORDS)

Pharmacokinetic studies of radiolabelled rat monoclonal antibodies recognising syngeneic sarcoma antigens. I. Comparison of IgG subclasses

The object of our current investigations is to explore the potential of antibodies for localisation and treatment of disseminated disease, using as a model rat monoclonal antibodies (mAbs) raised against syngeneic tumour-specific antigens. As part of this study, antibodies of differing isotypes with specificity for either HSN or MC24 sarcoma were labelled with 125iodine and injected intravenously into normal rats or those bearing paired tumours in contralateral flanks. The blood clearance rates of the radiolabelled antibodies were found to be influenced by immunoglobulin subclass (IgG2b greater than IgG2a greater than IgG1) and to be increased non-specifically by the presence of growing tumours. The tumour and normal tissue distributions of the antibodies tested were also found to vary according to their apparent degree of interaction with host Fc-receptor-bearing cells, to the extent that tumour specificity in vitro was not necessarily reflected in selectivity of localisation in vivo. Three IgG2b monoclonal antibodies showed preferential uptake in the spleens of syngeneic rats and non-specific accumulation in tumours. This effect was not observed with antibodies of IgG2a or IgG1 subclass, and was abolished by the use of IgG2b F(ab')2 preparations. In spite of the use of immunoglobulin fragments, varying the assay time and testing tumours of different sizes, specific tumour localisation was low with all seven monoclonal antibodies tested. The maximum uptake achieved was less than 1% of the injected dose of antibody per gram of tumour. Much higher levels of antibody localisation have been reported for human tumour xenografts growing in nude mice, but these are rarely achieved in other systems. We propose that the use of autologous monoclonal antibodies recognising tumour-associated antigens of relatively low epitope density in syngeneic hosts provides a valid alternative model in which to investigate the factors limiting more effective, specific immunolocalisation of malignant disease.

Immunological detection of DNA damage caused by melphalan using monoclonal antibodies

Immunological detection of melphalan adducts on DNA should permit new types of clinical and experimental investigations. Five cloned rat hybridoma cell lines were derived, each producing an antibody that bound to DNA alkylated with melphalan (phenylalanine mustard) but not to normal DNA. Further characterization of one melphalan specific antibody (MP5/73) used a competitive fluorogenic enzyme-linked immunoabsorbent assay. Using denatured DNA, 50% inhibition of antibody binding was caused by 30 fmol of total melphalan adducts (determined using radioactive melphalan) per assay well. Denatured control DNA caused 16 to 24% inhibition at 45 micrograms (130 nmol)/well, the maximum concentration tested. Adducts on RNA behaved similarly to those on denatured DNA. Adducts on native DNA caused 50% inhibition at 272 to 1335 fmol/well dependent upon alkylation frequency and sonication treatment. Native control DNA caused no detectable inhibition at 45 micrograms/well. The adducts recognized by the antibody were thermo- and alkali labile. Denaturation of the alkylated DNA by moderate heating in the presence of 75% formamide gave 50% inhibition at 50 fmol/well, indicating that only 5% of the recognized adducts could bind antibody in native DNA.

Vaccination with syngeneic monoclonal anti-idiotype protects against a tumour challenge

Rat X rat hybridomas secreting monoclonal anti-idiotypic antibodies have been prepared from Hooded rats immunized with two tumour-reactive, syngeneic monoclonal antibodies 11/160 and M10/76 (specific, respectively, for the Hooded rat sarcomata HSN and MC24). The hybridomas were selected on the basis that the secreted antibodies competed with antigen for binding to the immunizing idiotype. One monoclonal anti-idiotype (HIM/1/230, gamma 2a isotype) that recognizes an antigen-binding site idiotope of antibody 11/160 has been found to substitute for antigen. Hooded rats vaccinated by three challenges with HIM/1/230 produce serum Ab3 that is indistinguishable in antigen specificity from the 11/160 Ab1, and show reduced tumour take following an i.v. challenge with 10(6) HSN cells. The response to vaccination with anti-idiotype was both qualitatively and quantitatively dependent on the mode of immunization. High titre 11/160-like Ab3 was generated only when the vaccine contained Freund's adjuvant, whereas resistance to tumour challenge was found only in animals vaccinated with anti-idiotype in the absence of adjuvant.

An ineffective monoclonal antibody-ricin A chain conjugate is converted to a tumouricidal agent in vivo by subsequent systemic administration of ricin B chain

An immunotoxin comprising a tumour-specific monoclonal antibody (11/160) coupled to ricin A chain, although inactive in in vitro cytotoxicity assays against HSNtc sarcoma target cells, was found to be capable of significant tumouricidal activity in syngeneic rats if potentiated by ricin B chain. The 11/160-ricin A, when bound to tumour cells prior to their inoculation, led to a slight inhibition of tumour growth s.c. compared with untreated sarcoma cells or those coated with antibody alone. However, all tumours in these groups developed progressively (69/69), whereas in those rats receiving 15 micrograms or 150 micrograms ricin B chain i.v. 5 min after tumour cell inoculation, the 'take rate' was reduced to 75% and 30% respectively, and significantly longer latent periods were evident for those tumours which did develop. Ricin B chain similarly inhibited, in a dose-dependent manner, the lung colonisation potential of 11/160-ricin A coated HSNtc cells. No effects were obtained if the B chain treatment followed inoculation of untreated or antibody-coated cells, suggesting that systemically administered B chain is capable of gaining access to and activating antibody-ricin A chain conjugates bound to the surface of syngeneic sarcoma cells in lung or subcutaneous sites. Tumour inhibition was obtained in some instances with intervals of up to 24 h between inoculation of conjugate-coated tumour cells and B chain. Experiments are in progress to determine if such potentiation may be feasible in a therapeutic rather than a prophylactic setting using this syngeneic solid tumour system.

The shedding of viable cells into the local lymph by tumours growing in the gut of rats

Suspensions of syngeneic sarcoma cells were injected into the Peyer's patches of rats from which the mesenteric nodes had been removed. By later cannulating the thoracic duct of such rats it was possible to collect peripheral intestinal lymph that had come directly from the tumour bearing area without being filtered through a regional node. The number of viable tumour cells in the lymph coming from the tumours was monitored by culturing the whole lymph cells in a limiting dilution assay. The tumours grew to a diameter of approximately 1 cm in 25 days and during this time tumour cells were present in the lymph at a ratio of approximately 1 tumour cell per 10(5) lymph cells. In euthymic rats this number declined as the immune response developed. In athymic rats the number increased by approximately 10 fold during the experiments. It was concluded that the shedding of viable cells parallels the linear, not the volumetric dimensions of the tumour.

The production of hybridomas from the gut associated lymphoid tissue of tumour bearing rats. I. Mesenteric nodes as a source of IgG producing cells

Rat X rat hybridomas secreting antibodies with tumour specificity have been prepared using cells from the mesenteric nodes of rats bearing syngeneic sarcomata in their Peyer's patches. The antibodies obtained, which embraced all of the major immunoglobulin classes, varied in cellular reactivity from the individually tumour specific to cross-reactive with both normal and tumour cells. Several IgA producing hybridomas were prepared using this protocol but IgG secretors were obtained more frequently and they accounted for about half of the specific hybridomas. Specific IgG producers were found to predominate also when hybridomas were prepared from the mesenteric nodes of a rat immunized by injection of horseradish peroxidase into the Peyer's patches. Comparison of these data with our earlier results using spleen cells taken from rats that were either hyperimmunized with, or were bearing the same tumours in the leg, show that mesenteric nodes draining a tumour growing in the Peyer's patches are a much better source specific IgG producing B cells.

The production of hybridomas from the gut associated lymphoid tissue of tumour bearing rats. II. Peripheral intestinal lymph as a source of IgA producing cells

Peripheral intestinal lymph afferent to the mesenteric nodes has been collected from rats bearing syngeneic sarcomata in their Peyer's patches and the B cells used to produce rat X rat hybridomas. Analysis of the hybridoma supernatants by radioimmunoassay for the presence of immunoglobulins, showed that hybridomas secreting IgA predominated. Eleven out of the 15 hybridomas selected for antibody binding to cells of the immunising tumour secreted IgA antibodies, and six of these were tumour specific. Efferent mesenteric lymph (i.e. normal thoracic duct lymph), on the other hand, was found to be a poor source of B cells for hybridoma production and no specific IgA secreting hybridomas were obtained. The high yield of IgA secreting hybridomas obtained shows that peripheral intestinal lymph is a better source of IgA committed B cells than are the mesenteric nodes or thoracic duct lymph. We conclude that the IgA producing cells in the latter tissues are too far along the differentiation pathway to plasma cells to undergo successful somatic cell fusion.

Clearance of antibodies from rat sarcoma cell surfaces. Rate of clearance of alloantibodies depends on antibody isotype

The influence of antibody isotype on the lifetime of complexes involving cell surface antigens of the rat fibrosarcoma HSN.TC has been investigated using direct binding and competitive RIAs to monitor the antibodies. Alloantibodies of the IgG class that had bound to the cells during a 1-hr exposure to antiserum were cleared subsequently from the cell surface by an active process involving two distinct phases. Between 30 and 70% of these antibodies were lost in the first 10 hr but the antibodies remaining were cleared more slowly with half-lives ranging from 20 to 40 hr. Antibodies of the IgM class, however, and those that could bind Clq and initiate the complement cascade were cleared rapidly with half-lives of less than 3 hr. Analysis of total cell-associated immunoglobulin showed that the disappearance from the cell surface was not a consequence of intracellular accumulation of antibody but was caused by the release of the antibody in a degraded form. The surface expression of the majority of the alloantigens involved was not affected by continuous exposure to antibody although modulation of a subpopulation of antigens could not be excluded. These results suggest that the clearance of alloantibodies involved their internalization and degradation and that antibodies capable of forming multimeric complexes were cleared rapidly. Some of the IgG-containing complexes, however, exhibited extended lifetimes at the cell surface, suggesting that either they were not internalized or they were recycled between the cell interior and the plasma membrane.

Monoclonal antibodies to rat sarcomata. I. Immunization procedures and source of lymphoid cells for hybridoma production

Hybridomas secreting monoclonal antibodies with specificity for Hooded rat fibrosarcomata have been obtained by fusion of the rat myeloma Y3 Ag 1.2.3. (Galfre, Milstein & Wright, 1979) with cells taken from spleens or lymph nodes of immunized syngeneic and allogeneic donors. Two of the monoclonal antibodies, both derived from he spleens of tumour bearers, showed specificity for individual tumours one for MC24 (M10/76) and the other for HSNTC (11/160). These two antibodies had a long half-life in the blood when injected intravenously showing that they had a low affinity for normal tissue antigens. Monoclonal antibodies exhibiting broad tumour specificity or extensive cross-reactivity with normal cells were secreted by many of the hybridomas derived from both syngeneic and allogeneic rats that had been hyperimmunized with tumour cells. These results are discussed in relation to the production of monoclonal anti-tumour antibodies for use in experimental therapy.

Production of IgA secreting hybridomas: a monoclonal rat antibody of the IgA class with specificity for RT1c

We report a method for the production of rat hybridomas secreting IgA antibodies with biological activity. By fusing the rat myeloma Y3.AG.1.2.3 with mesenteric lymph node cells taken from animals that had been immunised via the Peyer's patches with allogeneic cells we have obtained a hybridoma secreting monoclonal antibodies of the IgA class with specificity for RT1c.

Syngeneic antitumour antibodies in rats: clearance of cell-bound antibody in vivo and in vitro

Hooded Lister/Cbi rats bearing the HSN.TC fibrosarcoma produced a high-titre non-complement-binding IgG antibody, and tests in vitro indicated that the syngeneic antibody was specific for this tumour. About 1.4 X 10(5) antibody molecules were bound per cell, a figure one eighth that for cells treated with a high-titre allo-antiserum. When tumour-bearer serum was passively transferred into congenitally athymic rats bearing the HSN.TC tumour the antibody was absorbed out specifically, by comparison with control animals or athymic rats bearing an unrelated tumour that was also syngeneic in Hooded rats. The kinetics of loss of antibody from the surface of HSN.TC cells has been monitored in vitro and the antibody has been found to have an extended half-life at the cell surface (greater than 40 h).

Reversible suppression of allo-antibody production by cyclosporin A

Treatment of rats with 25 mg/kg/day of cyclosporin A suppressed their immune response to skin allografts. Withdrawal of cyclosporin A treatment led to complete recovery of specific immune responsiveness and the time taken for recovery was independent of the duration of treatment. Titration of the dose of cyclosporin A administered in vivo indicated that doses of 12 mg/kg/day or less were not fully immunosuppressive.