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Biomedical subjects

M J Mattes

Publications and source records attributed to M J Mattes.

At least 37 records · Page 2Linked to original sources
PubMed1997

Advantage of residualizing radiolabels for an internalizing antibody against the B-cell lymphoma antigen, CD22.

LL2 is an anti-CD22 pan-B-cell monoclonal antibody which, when radiolabeled, has a high sensitivity for detecting B-cell, non-Hodgkin's lymphoma (NHL), as well as an antitumor efficacy in therapeutic applications. The aim of this study was to determine whether intracellularly retained radiolabels have an advantage in the diagnosis and therapy of lymphoma with LL2. In vitro studies showed that iodinated LL2 is intracellularly catabolized, with a rapid release of the radioiodine from the cell. In contrast, residualizing radiolabels, such as radioactive metals, are retained intracellularly for substantially longer. In vivo studies were performed using LL2-labeled with radioiodine by a non-residualizing (chloramine-T) or a residualizing method (dilactitol-tyramine, DLT), or with a radioactive metal (111In). The biodistribution of a mixture of 125I (non-residualizing chloramine-T compared to residualizing DLT), 111In-labeled LL2 murine IgG2a or its fragments [F(ab')2, Fab'], as well as its humanized, CDR-grafted form, was studied in nude mice bearing the RL human B-cell NHL cell line. Radiation doses were calculated from the biodistribution data according to the Medical International Radiation Dose scheme to assess the potential advantage for therapeutic applications. At all assay times, tumor uptake was higher with the residualizing labels (i.e., 111In and DLT-125I) than with the non-residualizing iodine label. For example, tumor/blood ratios of 111In-labeled IgG were 3.2-, 3.5- and 2.8-fold higher than for non-residualizing iodinated IgG on days 3, 7 and 14, respectively. Similar results were obtained for DLT-labeled IgG and fragments with residualized radiolabels. Tumor/organ ratios also were higher with residualizing labels. No significant differences in tumor, blood and organ uptake were observed between murine and humanized LL2. The conventionally iodinated anti-CD20 antibody, 1F5, had tumor uptake values comparable to those of iodinated LL2, the uptake of both antibodies being strongly dependent on tumor size. These data suggest that, with internalizing antibodies such as LL2, labeling with intracellularly retained isotopes has an advantage over released ones, which justifies further clinical trials with residualizing 111In-labeled LL2 for diagnosis, and residualizing 131I and 90Y labels for therapy.

Animals↗
PubMed1997

Advantage of a residualizing iodine radiolabel for radioimmunotherapy of xenografts of human non-small-cell carcinoma of the lung.

UNLABELLED: Attachment of 131I to MAbs through adducts such as dilactitol-tyramine (DLT), which remain lysosomally trapped after catabolism of the labeled MAb, can greatly increase the residence time of the radiolabel at the tumor site. Our previous studies demonstrated a marked increase in accretion of 131I in a human lung-cancer xenograft model, using 131I-DLT in comparison to 131I linked to MAb by the conventional chloramine-T methodology. METHODS: In this study, biodistribution experiments were performed to evaluate the effect of protein dose on the accretion of 131I-DLT-labeled MAb RS11 in tumor and nontumor tissues, and in vivo radioimmunotherapy experiments compared the effect of single injections of 131I-DLT-labeled MAb RS11 to conventional 131I-labeled RS11 and an untreated control group. RESULTS: Dosimetry calculations based on the biodistribution data indicate only small changes in absorbed dose-to-tumor and nontumor tissues with increasing protein dose up to 100 micrograms, with a predicted absorbed dose to tumor of from 21,000 to 25,000 cGy/mCi. A single dose of 100 microCi of 131I-DLT-RS11 was found to cause tumor regression. At 7 wk postinjection of the radiolabeled MAbs, tumor volume in 73% of the animals administered 131I-DLT-labeled RS11 remained smaller than at the time of MAb injection. This is compared to 14% of the tumors in the conventionally labeled 131I-RS11 group and none in the untreated group. CONCLUSION: The use of the residualizing radiolabel DLT provides a therapeutic advantage in comparison to conventional 131I-labeled RS11.

Animals↗
PubMed1997

Manipulation of blood clearance to optimize delivery of residualizing label-antibody conjugates to tumor cells in vivo.

UNLABELLED: We have attempted to improve the therapeutic index of radioimmunotherapy by manipulating the blood clearance rate and the catabolism of the radiolabel. The general strategy is to allow the antibody (Ab) to circulate in the blood for 2-3 days, then to clear it rapidly by a method that delivers the Ab to hepatocytes. In addition, the radiolabel selected has two key properties: it is a residualizing label (which is lysosomally trapped after catabolism), so it is retained well by tumor cells, but is excreted rapidly by hepatocytes into bile. METHODS: In initial experiments, three residualizing radiolabels were tested for their rate of excretion after specific delivery in vivo to either hepatocytes, via galactosylated Ab, or Kupffer cells, via immune complexes. A label showing rapid biliary excretion only after delivery to hepatocytes, (111)In-benzyl-diethylenetriamine tetraacetic acid, was then used for radioimmunodetection in a protocol of delayed rapid blood clearance in which clearance was by hepatocytes. This was achieved by using galactosylated Ab, combined with temporary inhibition of the asialo-glycoprotein receptor on hepatocytes. Ab RS11 and the lung adenocarcinoma Calu-3 xenograft in nude mice were used. Control experiments were performed with a conventional 125I label and with 125I-dilactitol-tyramine. RESULTS: Indium-benzyl-diethylenetriamine tetraacetic acid was identified as a label that was excreted more rapidly from hepatocytes than from Kupffer cells, by biliary excretion. Using this radiolabel with delayed rapid blood clearance, very high tumor/blood ratios were obtained, 166:1 at day 3, but tumor/normal tissue ratios for other tissues were not as high. There appeared to be some uptake of the radiolabel by all normal tissues tested, including the lungs and muscle. Dosimetry calculations suggested that the therapeutic index was no better than with a simple Ab injection. CONCLUSION: Antibody catabolism can be directed towards either hepatocytes or Kupffer cells, and this difference can strongly affect the excretion rate of radiolabels, since only hepatocytes can excrete degradation products into bile. Processing will also depend on the particular radiolabel. These factors are particularly important for protocols involving delayed rapid blood clearance, since liver uptake is so rapid. The methods described should stimulate other approaches of manipulating Ab blood clearance and radiolabel catabolism to achieve improved therapeutic results.

Animals↗
PubMed1996

Internalization and catabolism of radiolabelled antibodies to the MHC class-II invariant chain by B-cell lymphomas.

The fate of antibody (Ab) LL1, which reacts with the invariant chain (Ii) subunit of the immature MHC class-II antigen (CD74) after binding to the surface of B-cell lymphomas was investigated. This Ab was internalized and catabolized very rapidly, much faster than other Abs that are considered to be rapidly internalized, such as CD19, CD22 and anti-(transferrin receptor). Such internalization did not depend on Ab cross-linking. The capacity of this uptake process was determined in long-term experiments by increasing the Ab concentration: in 1 day, approx. 8 x 10(5) Ab molecules per cell were catabolized. This analysis was facilitated by the use of radiolabels that are trapped within cells after catabolism of the Abs to which they were conjugated. If the Ab is a reliable marker for the Ii antigen, which is likely, we can conclude that Ii directed to the cell surface appears to be sufficient, indeed more than sufficient, to account for the cell content of mature class-II molecules.

Antibodies↗
PubMed1996

Antibody penetration of tumor GS-7 xenografts in nude mice: a model for mucinous adenocarcinoma of the colon.

A new cell line derived from a human adenocarcinoma of the colon, GS-7, was propagated as a s.c. tumor in nude mice. This tumor histologically is a mucinous adenocarcinoma (also designated mucoid or colloid) with characteristic large mucin pools that are not lined by an epithelial layer but may contain scattered, randomly distributed cancer cells. Ten to 20% of human colorectal adenocarcinomas are of this histological type, but rapidly growing xenografts with this histology have been rarely used experimentally. This tumor, therefore, constitutes a useful model for similar human tumors. The mucin pools contain large amounts of carcinoembryonic antigen and tumor-associated glycoprotein 72, and the cells express epithelial glycoprotein 2 on their surface. The ability of antibodies injected i.v. to penetrate this tumor was investigated, using both biotinylated and radioiodinated antibodies (Abs). The results demonstrate that Abs can effectively penetrate the mucin pools, and that large amounts of Ab can localize there. This tumor type may have advantages as a target for certain forms of experimental immunotherapy.

Adenocarcinoma, Mucinous↗
PubMed1996

Processing of antibodies bound to B-cell lymphomas and other hematological malignancies.

In an attempt to recognize general patterns in the processing of Abs (antibodies) bound to the surface of tumor cells, eight monoclonal antibodies were tested on 10 hematological malignancies of various histological types. The results were compared with previous findings obtained with carcinomas, melanomas, and gliomas, using some of the same antibodies. The data demonstrated that some B-cell lymphomas appear to be unusual in that Abs were unable to bind to them irreversibly; except for those Abs that were rapidly internalized, none of the Abs tested was able to bind irreversibly to the B-cell lymphomas Raji or RL. In contrast, most Abs bound irreversibly to the tumors of other histological types, including other hematological tumors. Irreversible Ab binding to B-cell lymphomas was achieved by cross-linking the Abs on the cell surface. Such differences between cell lines may be due to differences in the supramolecular structure of the surface membrane, which affect the frequency or stability of bivalent Ab binding. The Ab binding interaction could not be described in terms of "functional affinity." These results may lead to improvements in the use of Abs for tumor immunotherapy and for other purposes.

Animals↗
PubMed1996

Rabbit complement lyses tumor cells without massive C3 deposition.

These experiments were performed to determine why rabbit complement lyses tumor cells very efficiently, while not having particularly strong activity in hemolytic assays or in any other complement assay. The target cells used were human tumor cells coated with three different mouse IgG(2a) monoclonal antibodies, and complement from 5 mammalian species were tested. In antibody titration experiments, rabbit complement was found to lyse target cells at a relatively low antibody concentration, insufficient to allow lysis by complement of other species. Since this result was still observed after absorption of rabbit serum with target cells, the potency of rabbit complement cannot be attributed to the presence of natural antibodies. We then assayed C3 deposition on target cells, using two types of (125)I-labeled anti-C3 Abs to measure C3 deposition: goat antibodies specific for C3 of the human, guinea pig, rabbit, rat or mouse, and chicken antibodies to human C3 which cross-react with C3 of other mammals. Unexpectedly, complement of the human, rat, guinea pig, and BUB mouse deposited large amounts of C3 on the surface of target cells, while rabbit complement deposited 100-1,000 fold less. We discuss the possible reasons that C3 deposition does not correlate with cytotoxicity, and may indeed be inversely related. These data indicate that there is a fundamental difference in the complement cascade between rabbits and the other species tested. The potent lytic activity of rabbit complement is likely to be related to this difference, although the mechanism is not yet understood.

Animals↗
PubMed1995

On the validity of "functional affinity" determination for antibodies binding to cell surface antigens or other polyvalent antigens.

A widely used method of comparing different antibodies (Abs) is to determine their "functional affinities." This value is supposedly a constant that reflects the basic binding interaction between antibody and antigen and, if it is determined under standard conditions, allows the comparison of Abs used by different laboratories. However, I present here both theoretical and experimental evidence that, for Abs binding bivalently, functional affinity determinations seem to be invalid. Experimental data were obtained with erythrocyte targets, to eliminate interference due to the internalization or catabolism of bound Ab, but similar results have been obtained with tumor target cells. Several fundamental discrepancies between the theoretical expectations and the actual values obtained were demonstrated, all of which can be attributed to the effects of bivalent binding. One discrepancy is that the functional affinity determined did not equal the ratio of the rate constants for association and dissociation. A second is that the functional affinity was not a constant but, rather, depended on trivial experimental conditions, such as the volume of incubation. In addition, it has been recognized previously that functional affinity is affected strongly by the structure of a multivalent antigen and, in particular, by any change that makes it more or less likely that an Ab will bind bivalently. The value of other methods of comparing the avidity of different Abs is discussed. In many situations, Ab binding can be considered predominantly irreversible for practical purposes.

Antibody Affinity↗
PubMed1995

Lysine-directed radioiodination of proteins with a cyanuric chloride derivative of aminofluorescein.

Protein radioiodination via iodo-5-([4,6-dichlorotria- zin-2-yl]amino)fluorescein(DTAF), a cyanuric chloride derivative of aminofluorescein, was characterized. Commercially available DTAF was iodinated by the Iodogen reaction and then conjugated to IgC antibodies in a 4-h incubation in borate buffer, pH 9.0. With low amounts of protein, 10 micron, molar ratios of iodine:IgC of nearly 1:1 were obtained. With 25 micron protein, which was used routinely, 15-20% efficiency of (125)I incorporation was obtained. Polylysine was labeled efficiently, and labeling was inhibited by ethanolamine, which is consistent with previous data indicating that conjugation is to amino in the protein. A low level of aggregates, primarily dimers, was generated. This procedure is a simple, inexpensive method to test the advantage of lysine-directed protein iodination, with proteins for which oxidative iodination is unsuitable. Abs labeled with DTAF retained strong antigen-binding activity, and, in the case of one Ab, were much more active than the chloramine T-labeled Ab. Catabolic products of iodo-DTAF conjugates, produced after internalization and degradation of Ab bound to the cell surface, were retained within some but not all human carcinoma cell lines.

Fluorescein↗
PubMed1995

Effects of radiolabeling monoclonal antibodies with a residualizing iodine radiolabel on the accretion of radioisotope in tumors.

The effect of using a "residualizing" iodine radiolabel, dilactitol-iodotyramine, for radioimmunolocalization of antibodies to tumors was investigated. This tracer is designed to be lysosomally trapped after catabolism of the labeled antibody. mAbs RS7 and RS11 were used for in vivo and in vitro studies on the uptake and retention of radioisotope into tumor cells. Both are murine IgG1 mAbs with pancarcinoma reactivity, which react with integral membrane glycoproteins. mAb RS7 has been shown to be relatively rapidly catabolized by the antigen-bearing cell line Calu-3, whereas RS11 is catabolized more slowly in the same cells. An 111In- or 88Y-p-isothiocyanatobenzyl-diethylenetriamine pentaacetic acid conjugate was also tested because these radiometals are known to be lysosomally trapped, and iodination via chloramine T was used to provide a baseline. In vitro, a substantial increase in retention of the label by cells was observed when the dilactitol-tyramine DLT- or 111In-labeled mAbs were used, and the improvement gained by the use of these residualizing labels was greater with the use of the rapidly catabolized mAb (RS7) than it was with the more slowly catabolized mAb (RS11). In biodistribution studies in nude mice bearing Calu-3 tumor xenografts, a dramatic improvement in the tumor accretion of the radiolabel was seen with the use of the 131I-labeled DLT- or 88Y-labeled mAbs. For example, at day 7 the percentage of injected dose/g in the tumor was 5.54 +/- 1.47% (SD), 38.06 +/- 8.04%, and 43.18 +/- 19.50% for the conventionally iodinated, DLT- and 88Y-labeled RS7, respectively. Dosimetry calculations performed on the biodistribution data predict increases of approximately 8- and 4-fold in the absorbed dose to tumor with the use of 131I-labeled DLT- and 90Y-labeled mAbs, respectively, compared to the conventional 131I. In contrast to in vitro findings, these results were similar for both RS7 and RS11, suggesting that the use of DLT may be advantageous for most of the mAbs binding to the cell surface, including antibodies that are catabolized relatively slowly. The advantage of 131I-labeled DLT over 90Y is due to the longer physical half-life of the 131I.

Adenocarcinoma↗
PubMed1994

Processing of antibody-radioisotope conjugates after binding to the surface of tumor cells.

BACKGROUND: Previous experiments indicated that most antibodies binding to cell surface antigens are internalized gradually and degraded within lysosomes, with a half-life of degradation of approximately 1 day, for most antibodies. The research discussed in this article extended our studies to eight additional antibodies reacting with six different antigens, including three antigens anchored in the membrane by glycosyl-phosphatidylinositol. The authors also tested antibodies labeled with 111indium, as well as 125iodine, to determine whether different radiolabels would be processed differently. METHODS: Antibodies were radiolabeled with 125I or with 111In bound to benzyl-DTPA. After binding to the surface of tumor cells in vitro, excess antibody was washed away, and the fate of the radiolabel was investigated over periods of 3-7 days. Radiolabel released into the supernatant or retained by the cells was analyzed to determine whether it was still on intact antibody. RESULTS: In 13 of the 15 antibodies that were tested, a similar pattern of irreversible binding and gradual catabolism was observed. Iodine conjugated to antibodies was released rapidly from the cell after antibody catabolism. In contrast, the 111In was retained within the cell much longer than 125I, with the rate of degradation and release into the medium being at least fivefold slower. More than 50% of the bound 111In was still present on the cells after 7 days. Biochemical analysis of the retained 111In extracted cells after 4-6 days demonstrated that it was no longer associated with antibodies and was in a low molecular weight form, probably still associated with the chelator benzyl-DTPA. CONCLUSIONS: Different radiolabels are processed by tumor cells differently, after catabolism of the antibody to which they originally were conjugated. The data suggest that the prolonged retention of 111In, relative to that of 125I, is due not to deiodination of iodine conjugates, but rather to intracellular retention of catabolic products containing 111In, perhaps within lysosomes. The use of radioisotopes that are retained within cells after antibody internalization and degradation may improve both radioimmunodetection and radioimmunotherapy of cancer.

Antibodies, Monoclonal↗
PubMed1994

SCLC-cluster-2 antibodies detect the pancarcinoma/epithelial glycoprotein EGP-2.

Analysis of the antibodies submitted to the 3 International Workshops on Small Cell Lung Cancer Antigens has resulted in the identification of 15 clusters of antibody reactivity. One of these clusters, named SCLC cluster 2, is characterized by reactivity against an epithelium-associated 38 kDa membrane glycoprotein. SCLC cluster 2, and a number of other antibodies with reportedly similar reactivities, were shown to recognize a protein encoded by the GA733-2 gene, whereas the newly defined SCLC cluster 13 antibodies react with the GA733-1 gene product. We propose to call the antigen detected by SCLC-cluster-2 antibodies "epithelial glycoprotein 2" (EGP-2), and the epithelium-associated glycoprotein recognized by antibodies clustered in SCLC cluster 13 (see elsewhere in this volume) "epithelial glycoprotein 1" (EGP-1). A short overview of the characteristics of both proteins and the applications of anti-EGP-2 antibodies is presented.

Animals↗
PubMed1994

Characterization of cluster 13: the epithelial/carcinoma antigen recognized by MAb RS7.

Cluster 13 was defined by 2 independently derived murine monoclonal antibodies (MAbs), RS7 (IgG1) and MR54 (IgG2a), which were raised against human squamous-cell carcinoma of the lung and a human ovarian-carcinoma cell line, respectively. Immunologic and biochemical evidence demonstrated that RS7 and MR54, as well as 2 additional MAbs, MR6 (IgG2a) and MR23 (IgG1), generated in the same fusion as MR54, recognize the same antigen, a 46- to 48-kDa glycoprotein. Evaluation of the expression of antigen on the surface of tumor cell lines, Western blotting analyses, competitive binding studies, and double-determinant ELISA assays, support this conclusion. Two distinct epitopes are defined by these MAbs. In order to further characterize this antigen, amino-acid-sequence analyses were performed on peptides derived from antigen purified by affinity chromatography with MAb RS7. The sequence data obtained from 2 peptides, which were independently generated by CNBr cleavage and trypsin digestion respectively indicated identity to GA733-1. The GA733-1 genomic DNA sequence predicted a type-1 membrane protein of 35 kDa, with 4 potential N-linked glycosylation sites. The GA733-1 protein product has not been identified previously, and MAbs to this tumor-associated antigen were not previously known.

Amino Acid Sequence↗
PubMed1994

The fate of antibodies and their radiolabels bound to tumor cells in vitro: the effect of cross-linking at the cell surface and of anti-idiotype antibodies.

In order to obtain rapid blood clearance of circulating antibodies (Ab) at a desired time, cross-linking reagents such as second Ab are often employed. Such reagents will generally bind to Ab located at the tumor site as well as free Ab, and we therefore investigated whether the cross-linking of Ab bound to the surface of tumor cells affects the processing of those Ab. Cross-linking was induced in various ways: a polyclonal second Ab [rabbit anti-(mouse IgG)], a monoclonal rat anti-(mouse IgG constant region) Ab, and streptavidin used in conjunction with a biotinylated first Ab. Processing was followed for 3 days, to allow nearly all of the bound Ab to reach its ultimate fate. Results depended strongly on the particular first Ab used. Two basic effects were observed. First, the second Ab efficiently prevented the early dissociation of intact Ab from the cell; once the second Ab bound, there was virtually no dissociation of the primary Ab bound to the cells. For most Ab, where only a small proportion of bound Ab dissociated intact, this effect was relatively small. However, for an unusual Ab, where the majority dissociated intact (L6) the effect of a second Ab in prolonging Ab retention by the cell was dramatic. Second, cross-linking sometimes resulted in markedly accelerated internalization and degradation of the bound Ab, coupled with the release of degradation products into the medium. This process resulted in much shorter retention of the radioisotope by the cell. If a "residualizing" radiolabel was used, 125I-dilactitoltyramine, which is probably trapped within lysosomes after Ab catabolism, the effect of the second Ab in accelerating loss from the cell was largely prevented. We also tested anti-idiotype Ab as cross-linking reagents. In addition to testing anti-idiotype Ab known to react with the cell-bound primary Ab, we also tested anti-idiotype Ab not expected to bind to cell-bound Ab, initially as a negative control. Unexpectedly, all anti-idiotype Ab tested induced rapid release of the primary Ab from the cell. This effect was similar to the effect of a large excess of unlabeled Ab, and we attribute it to the blocking of the free binding site of a "wobbling" Ab, which prevents its rebinding to a second antigen molecule. We conclude that the use of selected anti-idiotype Ab to clear circulating Ab, while not reacting with cell-bound Ab, must be done cautiously.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Internalization of an intact doxorubicin immunoconjugate.

An immunoconjugate between doxorubicin and anti-(carcinoembryonic antigen) (CEA) was prepared by using aminodextran (M(r) = 40,000) as the intermediate carrier, and the carbohydrate moiety of the antibody as the linking site. The resulting immunoconjugate was subjected to an in vitro evaluation for the internalization on the target cells (Lo Vo), and compared to that of unconjugated antibody, as well as the cellular uptake of unconjugated doxorubicin. The internalization was evaluated microscopically by following the translocation of the red fluorescence of doxorubicin and the green fluorescence of the fluorescein-isothiocyanate-labeled goat anti-(mouse Ig) antibody, which visualizes the location of the primary mouse antibody. Anti-CEA monoclonal antibody (NP-4) was found to internalize into Lo Vo cells. The immunoconjugate made with this antibody was similarly internalized, and the doxorubicin was found to distribute with the primary antibody. The cell surface and cytoplasm were the major compartments of their distribution. These results indicate that the drug molecules were indeed delivered into the cells by the antibody as an intact conjugate. Unconjugated doxorubicin, on the contrary, was quickly absorbed by the cells and concentrated in the nucleus within 30 min, and never showed a distribution in the cytoplasm or cell membrane as in the nucleus by this procedure. The intermediate drug conjugate, doxorubicin-dextran, did not show internalization. The internalization of NP-4 antibody (or the doxorubicin conjugate) was also confirmed by studying the intracellular catabolism of the cell-bound antibody (or conjugate). The release of the degraded antibody by the cells, as differentiated by trichloroacetic acid precipitation techniques, was considered an indication of internalization. Lysosomes were involved in the degradation, since the process was markedly inhibited in the presence of the lysosomal enzyme inhibitor, ammonium chloride.

Antibodies, Monoclonal↗
PubMed1994

Localization of complement-fixing cytotoxic monoclonal antibodies to subcutaneous tumors and liver metastases in a syngeneic immunocompetent rat colon carcinoma model.

To study the immune effects of complement-fixing cytotoxic monoclonal antibodies (mAbs) in a syngeneic immunocompetent animal model, mouse mAbs reactive with the transplantable rat colon carcinoma K12/TRb were generated. This system was used in part because rats have a complement system superior to that of mice. Seven murine IgG mAbs that reacted strongly with cell surface determinants of the K12/TRb rat colon carcinoma cell line were produced by immunizing MRL/Mp-1pr/1pr autoimmune mice, known to produce an increased amount of complement-fixing IgG2a and IgG3 immune cytotoxic antibodies, with K12/TRb cells. These mAbs were screened for their specificity of reaction, and two of these mAbs were extensively tested for their ability to lyse cells in vitro and localize to K12/TRb tumors in syngeneic BD IX rats. IgG2a mAbs 27-3 and 61-5 were able to mediate both complement and lymphocyte cytotoxicity in vitro and localize to subcutaneous tumors and liver metastases in this immunocompetent rat model.

Animals↗
PubMed1994

The processing and fate of antibodies and their radiolabels bound to the surface of tumor cells in vitro: a comparison of nine radiolabels.

UNLABELLED: Processing radiolabeled degradation products is the key factor affecting retention of antibodies within the cell. In this study, we have analyzed the processing of antibodies labeled in nine different ways. METHODS: Antibodies were labeled with three different radioisotopes and seven different forms of 125I. Eight of the radiolabels (except 188Re) were conjugated to the same antibody, MA103, and tested on the renal carcinoma cell line SK-RC-18 and/or the ovarian carcinoma cell line SK-OV-6. Rhenium conjugation utilized the antibody RS7, the target cell line ME180 and three of the other radiolabels were also tested with this antibody-target cell combination for comparison. RESULTS: Iodine conjugated to antibodies by conventional methods was rapidly released from the cell after antibody catabolism. In contrast, iodinated moieties, such as dilactitol-tyramine and inulin-tyramine were retained within cells four to five times longer. CONCLUSIONS: The use of radiolabels that are trapped within cells after antibody catabolism can potentially increase the dose of radiation delivered to the tumor, from the same amount of radioactivity deposited by a factor of four or five. The prolonged retention of 111In relative to 125I is not due to deiodination of iodine conjugates, but rather to intracellular retention of catabolic products containing 111In, perhaps within lysosomes.

Acetylgalactosamine↗