Eliminating Interference from Heterophilic Antibodies in a Two-Site Immunoassay for Creatine Kinase Mb by Using F(ab')2 Conjugate and Polyclonal Mouse IgG

Heterophilic antibodies interfere in two-site immunoassays. Our purpose was to screen for the samples containing heterophilic antibodies that react with mouse immunoglobulins and to use them to determine how to eliminate interference in various two-site immunoassays being developed in our laboratory. Of approximately 2600 samples screened, 81 had heterophilic antibodies. When creatine kinase MB (CKMB) concentration was measured with intact antibody conjugate in these 81 samples, 18 (22%) samples had apparent CKMB values significantly greater than values measured with Hybritech's "Tandem -E CKMB immunoenzymetric" assay and Corning agarose-gel electrophoresis. Adding up to 133 mg/L of polymerized IgG or up to 1666 mg/L polyclonal mouse IgG in the assay did not eliminate the interference in all the samples. However, adding F(ab')2 conjugate plus 40 mg/L of polymerized IgG or 83 mg/L of polyclonal mouse IgG eliminated the interference in all the samples. This approach was also effective in eliminating the interference in 15 samples containing 4.7-165.2 mg/L of human antimouse antibody (HAMA). Combined use of F(ab')2 conjugate and polyclonal mouse IgG is recommended to eliminate interference from heterophilic antibodies that react with murine immunoglobulins or HAMA in two-site murine-antibody-based assays.

DNA replication regulation protein Mcm7 as a marker of proliferation in prostate cancer

BACKGROUND

Recent studies have shown that minichromosome maintenance (MCM) proteins (Mcm2-7) may be useful proliferation markers in dysplasia and cancer in various tissues.

AIMS

To investigate the use of Mcm7 as a proliferation marker in 79 lymph node negative prostate cancers and compare it with Ki-67, a commonly used cell proliferation marker.

METHODS

The percentage of proliferating cells (proliferation index; PI) was calculated for basal and luminal epithelial cells in benign prostate tissue, prostatic intraepithelial neoplasia (PIN), and epithelial cells in adenocarcinoma. The PI for each biomarker was correlated with the preoperative prostate specific antigen concentration, the Gleason score, surgical resection margin status, and the AJCC pT stage for each patient.

RESULTS

The mean PIs for Ki-67 and Mcm7 were: benign luminal epithelium 0.7 and 1.2 and benign basal epithelium 0.8 and 8.2; PIN non-basal epithelium 4.9 and 10.6 and PIN basal epithelium 0.7 and 3.1; adenocarcinoma 9.8 and 22.7, respectively. Mcm7 had a significantly higher mean PI (p<0.0001) than Ki-67 for all cell categories except benign luminal epithelial cells. Mcm7 was a better discriminatory marker of proliferation between benign epithelium, PIN, and invasive adenocarcinoma (p<0.0001) than Ki-67. The drop in Mcm7 mean basal cell PI from benign epithelium to PIN epithelium was significantly larger than for Ki-67 (p<0.0001). Mcm7 had a significantly higher PI than Ki-67 at each risk level.

CONCLUSION

Mcm7 may be a useful proliferation marker in prostatic neoplasia and warrants further evaluation as a complementary tool in the diagnosis of PIN and prostate carcinoma.

Accumulation of radiolabeled anti-CEA antibody (mT84.66) in the case of multiple LS174T tumors in a nude mouse model

A comparison was made between labeled antibody accumulations in nude mice having either single or multiple human xenografts. The LS174T tumors were implanted subcutaneously. All animals were given 2 micrograms of labeled murine anti-carcinoembryonic antigen (CEA) monoclonal antibody 111In-mT84.66. Some animals were also given specific antibody pretreatment (SAP) of 200 micrograms of unlabeled mT84.66 to reduce liver accumulation of activity. In order to represent these multiple tumor examples, a simple initial-phase pharmacokinetic model was first fitted to each of the two groups (SAP and PBS treated) of single-tumor animals. Using the resultant six non-adjustable parameters as constants, the n = 1 uptake model was then used to represent tumor, liver and blood accumulations (%injected dose/organ) in the multiple-tumor animals. The model was found to be a good representation; in particular, it had far better agreement than single tumor predictions in the PBS mice. Differences between the single-tumor accumulations and those seen in multiple tumor examples were generally between two- and three-fold. The model also demonstrated that the result of SAP was to essentially eliminate the effect of liver targeting of tumor-secreted CEA. We conclude that an initial-phase one-tumor model can describe the decrease of accumulation of activity in the case of multiple tumors in nude mice in both untreated (PBS) and pretreated conditions. Implications for clinical imaging and therapy with monoclonal agents are discussed.

Chromosome mapping of the human genes encoding the MAP kinase kinase MEK1 (MAP2K1) to 15q21 and MEK2 (MAP2K2) to 7q32

Activation of the ERK mitogen-activated protein (MAP) kinase pathway has been implicated in the regulation of cell growth, differentiation and senescence. In this pathway, the MAP kinases ERK1/ERK2 are phosphorylated and activated by the dual-specificity kinases MEK1 and MEK2, which in turn are activated by serine phosphorylation by a number of MAP kinase kinase kinases. We report here the chromosomal localization of the human genes encoding the MAP kinase kinase isoforms MEK1 and MEK2. Using a combination of fluorescence in situ hybridization, somatic cell hybrid analysis, DNA sequencing and yeast artificial chromosome (YAC) clone analysis, we have mapped the MEK1 gene (MAP2K1) to chromosome 15q21. We also present evidence for the presence of a MEK1 pseudogene on chromosome 8p21. The MEK2 gene (MAP2K2) was mapped to chromosome 7q32 by fluorescence in situ hybridization and YAC clone analysis.

Identification of a high frequency of chromosomal rearrangements in the centromeric regions of prostate cancer cell lines by sequential giemsa banding and spectral karyotyping

BACKGROUND

Currently, prostate cancer (CaP) cytogenetics is not well defined, largely because of technical difficulties in obtaining primary tumor metaphases.

METHODS AND RESULTS

We examined three CaP cell lines (LNCaP, DU145, PC-3) using sequential Giemsa banding and spectral karyotyping (SKY) to search for a common structural aberration or translocation breakpoint. No consistent rearrangement common to all three cell lines was detected. A clustering of centromeric translocation breakpoints was detected in chromosomes 4, 5, 6, 8, 11, 12, 14, and 15 in DU145 and PC-3. Both these lines were found to have karyotypes with a greater level of complexity than LNCaP.

CONCLUSION

The large number of structural aberrations present in DU145 and PC-3 implicate an underlying chromosomal instability and subsequent accumulation of cytogenetic alterations that confer a selective growth advantage. The high frequency of centromeric rearrangements in these lines indicates a potential role for mitotic irregularities associated with the centromere in CaP tumorigenesis.

Isolation and characterization of the human UGT2B15 gene, localized within a cluster of UGT2B genes and pseudogenes on chromosome 4

Glucuronidation is a major pathway of androgen metabolism and is catalyzed by UDP-glucuronosyltransferase (UGT) enzymes. UGT2B15 and UGT2B17 are 95% identical in primary structure, and are expressed in steroid target tissues where they conjugate C19 steroids. Despite the similarities, their regulation of expression are different; however, the promoter region and genomic structure of only the UGT2B17 gene have been characterizedX to date. To isolate the UGT2B15 gene and other novel steroid-conjugating UGT2B genes, eight P-1-derived artificial chromosomes (PAC) clones varying in length from 30 kb to 165 kb were isolated. The entire UGT2B15 gene was isolated and characterized from the PAC clone 21598 of 165 kb. The UGT2B15 and UGT2B17 genes are highly conserved, are both composed of six exons spanning approximately 25 kb, have identical exon sizes and have identical exon-intron boundaries. The homology between the two genes extend into the 5'-flanking region, and contain several conserved putative cis-acting elements including Pbx-1, C/EBP, AP-1, Oct-1 and NF/kappaB. However, transfection studies revealed differences in basal promoter activity between the two genes, which correspond to regions containing non-conserved potential elements. The high degree of homology in the 5'-flanking region between the two genes is lost upstream of -1662 in UGT2B15, and suggests a site of genetic recombination involved in duplication of UGT2B genes. Fluorescence in situ hybridization mapped the UGT2B15 gene to chromosome 4q13.3-21.1. The other PAC clones isolated contain exons from the UGT2B4, UGT2B11 and UGT2B17 genes. Five novel exons, which are highly homologous to the exon 1 of known UGT2B genes, were also identified; however, these exons contain premature stop codons and represent the first recognized pseudogenes of the UGT2B family. The localization of highly homologous UGT2B genes and pseudogenes as a cluster on chromosome 4q13 reveals the complex nature of this gene locus, and other novel homologous UGT2B genes encoding steroid conjugating enzymes are likely to be found in this region of the genome.

Chromosomal localization of phospholipase A2 activating protein, an Ets2 target gene, to 9p21

A murine Ets2 target gene isolated by differential display cloning was identified as the phospholipase A2 activating protein (PLAA) gene. A 2.7-kb human cDNA demonstrating high homology to mouse and rat Plaa genes was then isolated and characterized. Human PLAA contains six WD-40 repeat motifs and three different protein kinase consensus domains. Fluorescence in situ hybridization (FISH) mapping placed PLAA on chromosome 9p21, a region frequently deleted in various cancers. A comprehensive mapping strategy was employed to define further the chromosomal localization of PLAA relative to CDKN2A within the 9p21 locus. Radiation hybrid mapping placed the gene 7.69 cR from WI-5735 (LOD >3.0), a marker in close proximity to CDKN2A and CDKN2B. Yeast artificial chromosome (YAC) mapping localized PLAA proximal to the CDKN2A/CDKN2B genes and to a region flanked by D9S171 and INFA commonly deleted in many neoplasms. Two YACs contained both PLAA and D9S259, a marker present in a second more proximal minimal deleted region observed in cutaneous melanoma and squamous cell lung carcinoma. Double-color fiber FISH mapping confirmed the location of PLAA centromeric to D9S171 and CDKN2A/CDKN2B. The mapping data suggest a possible tumor suppressor role for this gene.

Identification and localization of MEP1A-like sequences (MEP1AL1-4) in the human genome

The human MEP1A gene encodes the meprin alpha subunit that consists of a protease domain conserved in the astacin family of metalloendopeptidases and several C-terminal interaction domains present in other proteins. Using the alpha subunit cDNA, we identified two clones from a human P1-derived artificial chromosome (PAC) library. Fluorescence in situ hybridization (FISH) mapped both PACs (1e12, 65a14) to chromosome 6p21, confirming the MEP1A location. FISH also mapped PAC 65a14 to chromosome 13cen, and to chromosome 9 in three different regions, 9p12-13, 9q21, and 9q22. Southern blot analysis showed that sequences of PAC 65a14 and MEP1A were similar in the 3' end but different in the 5' end, revealing for the first time that the human genome may encode multiple interaction domains highly similar to those of the meprin alpha subunit. The symbols of MEP1AL1, MEP1AL2, MEP1AL3, and MEP1AL4 have been designated for MEP1A-like sequences on 9p12-13, 9q21, 9q22, and 13cen, respectively.

Intrachromosomal recombination between well-separated, homologous sequences in mammalian cells

In the present study, we investigated intrachromosomal homologous recombination in a murine hybridoma in which the recipient for recombination, the haploid, endogenous chromosomal immunoglobulin mu-gene bearing a mutation in the constant (Cmu) region, was separated from the integrated single copy wild-type donor Cmu region by approximately 1 Mb along the hybridoma chromosome. Homologous recombination between the donor and recipient Cmu region occurred with high frequency, correcting the mutant chromosomal mu-gene in the hybridoma. This enabled recombinant hybridomas to synthesize normal IgM and to be detected as plaque-forming cells (PFC). Characterization of the recombinants revealed that they could be placed into three distinct classes. The generation of the class I recombinants was consistent with a simple unequal sister chromatid exchange (USCE) between the donor and recipient Cmu region, as they contained the three Cmu-bearing fragments expected from this recombination, the original donor Cmu region along with both products of the single reciprocal crossover. However, a simple mechanism of homologous recombination was not sufficient in explaining the more complex Cmu region structures characterizing the class II and class III recombinants. To explain these recombinants, a model is proposed in which unequal pairing between the donor and recipient Cmu regions located on sister chromatids resulted in two crossover events. One crossover resulted in the deletion of sequences from one chromatid forming a DNA circle, which then integrated into the sister chromatid by a second reciprocal crossover.

Physical delineation of a 700-kb region overlapping the Looptail mutation on mouse chromosome 1

The mouse looptail (Lp) mutation is an established model for neural tube defects with homozygous Lp embryos showing an open neural tube from the caudal midbrain to the tip of the tail. Heterozygous Lp mice are characterized by a "looped-tail" and wobbly head movements. The Lp gene has been mapped to a 0.6-cM interval on mouse chromosome 1 delineated by two clusters of markers, Fcer1gamma/Usf1/D1Mit113/D1Wsu1 on the proximal side and Fcer1alpha/Spna1/D1Mit149 distally. In the present study, we have created a high-resolution physical map of the Lp genetic interval that is based on long-range restriction mapping by PFGE, fluorescence in situ hybridization analysis of interphase nuclei and extended chromatid fibers, and the assembly of a cloned contig. This contig consists of 25 independent and overlapping BAC clones and 3 YAC clones. The combined analysis indicates that the 0.6-cM genetic interval for Lp corresponds to a minimal physical interval of 700 kb that is delineated by D1Mit113 proximally (two crossovers) and Fcer1alpha distally (one crossover). The overall gene order and intergene distances for the region were determined to be D1Mit113-<150 kb-Nhlh1-250 kb-Atp1alpha2-280 kb-Fcer1alpha. Partial sequencing of BAC clones from the contig yielded 42 new STS markers for this region of mouse chromosome 1. Sequence analysis of the BAC clones and assignment of ESTs from the human transcript map to the cloned contig allowed the placement of four new transcription units within this region: Pc326, Kiaa0253, and Pea15 were positioned in the Nhlh1/Atp1alpha2 nonrecombinant interval, while Girk3 was located distal to Atp1alpha2.

Structural organization and chromosomal localization of the human Na,K-ATPase beta 3 subunit gene and pseudogene

We have cloned and characterized the Na,K-ATPase beta 3 subunit gene (ATP1B3), and a beta 3 subunit pseudogene (ATP1B3P1), from a human PAC genomic library. The beta 3 subunit gene is > 50 kb in size and is split into 7 exons. The exon/intron organization of the beta 3 subunit gene is identical to that of the Na,K-ATPase beta 3 subunit gene, indicating that these two genes evolved from a common evolutionary ancestor. Comparison of the promoter region of the human and mouse beta 3 subunit gene reveals a high degree of homology within a 300-bp segment located immediately upstream of the translation start site, suggesting that control elements that serve to regulate the cell-specific expression of the beta 3 subunit gene are likely to be located within this conserved region. Dot blot analysis of beta 3 subunit transcripts revealed expression within virtually all human tissues, while in situ hybridization showed expression of beta 3 mRNA in both neurons and glia of rat brain. Fluorescence in situ hybridization with PAC DNA clones localized ATP1B3 to the q22-->23 region of Chromosome (Chr) 3, and the beta 3 pseudogene to the p13-->15 region of Chr 2.

Chromosomal localization, structure, and regulation of the UGT2B17 gene, encoding a C19 steroid metabolizing enzyme

UGT2B17 is a UDP-glucuronosyltransferase enzyme expressed in several extrahepatic steroid target tissues, including the human prostate, where it glucuronidates C19 steroids such as dihydrotestosterone (DHT), androsterone (ADT), and androstane-3alpha, 17beta-diol (3alpha-diol). To determine if UGT2B17 is regulated by physiological effectors of the human prostate, DHT and epidermal growth factor (EGF) were demonstrated to specifically down-regulate the steady-state levels of UGT2B17 transcript and protein in LNCaP cells (Guillemette et al., 1997). These results implicate regulation of UGT2B17 at the level of gene transcription, therefore, a P-1-derived artificial chromosome (PAC) clone of 120 kb containing the entire UGT2B17 gene was isolated. The gene is comprised of six exons spanning approximately 30 kb, and fluorescence in situ hybridization of the UGT2B17 PAC clone to normal human lymphocyte chromosomes, mapped the gene to chromosome 4q13. To determine if the 5'-flanking DNA of the UGT2B17 gene is sufficient to confer gene expression, a 2,942-bp fragment was subcloned into a luciferase reporter plasmid and yielded an activity of 25-fold over background when transfected in LNCaP cells. However, transfection of the construct into HK-293, MCF-7, JEG-3, and HepG2 cells yielded only a moderate activity of two- to five-fold over background. Treatment of transfected LNCaP cells with 10 nM R1881, a nonmetabolizable analog of DHT, and 10 ng/ml EGF decreased the luciferase activity by 60%. This suggests that at least part, if not all, of the inhibitory effect of EGF and DHT on UGT2B17 is at the level of transcription. Progressive 5' deletions of the UGT2B17 5'-flanking region in the luciferase constructs alleviated the inhibition by R1881 and EGF, and revealed several potential responsive elements that may confer the observed regulation of the UGT2B17 gene. This study demonstrates regulation of the UGT2B17 gene by physiological effectors of the human prostate and supports the hypothesis that UGT enzymes are involved in steroid metabolism in extrahepatic tissues.

Cloning, structural organization, and chromosomal mapping of the human phenol sulfotransferase STP2 gene

Phenol- and monoamine-metabolizing sulfotransferases (STP and STM, respectively) are members of a superfamily of enzymes that add sulfate to a variety of xenobiotics and endobiotics containing hydroxyl or amino functional groups. To characterize related sulfotransferase genes further, we used extra-long PCR (XL-PCR) to generate three distinct sizes of amplification products from human genomic DNA or from genomic phage library clones, each of which contained sulfotransferase gene sequences. One of the PCR fragments contained a new sulfotransferase gene, STP2, corresponding to a recently published cDNA clone that encodes a sulfotransferase with catalytic specificity distinct from that of the previously described STP1 and STM. Additional upstream sequence information was obtained using a second STP2-specific XL-PCR-based approach. The STP2 gene is composed of eight exons and seven introns, with exon sizes ranging from 95 to 181 bp. Protein-coding exon lengths and locations of the splice junctions were identical to those in both the STM gene and an STP2 gene published independently by another group recently. The STP2 gene maps to a chromosomal location (16p11.2-p12) that is the same as that previously determined for both STP1 and STM. The characterization of the STP2 gene provides further insight into the organization, regulation, and multiplicity of the sulfotransferase supergene family.

Requirements for ectopic homologous recombination in mammalian somatic cells

Ectopic recombination occurs between DNA sequences that are not in equivalent positions on homologous chromosomes and has beneficial as well as potentially deleterious consequences for the eukaryotic genome. In the present study, we have examined ectopic recombination in mammalian somatic (murine hybridoma) cells in which a deletion in the mu gene constant (Cmu) region of the endogenous chromosomal immunoglobulin mu gene is corrected by using as a donor an ectopic wild-type Cmu region. Ectopic recombination restores normal immunoglobulin M production in hybridomas. We show that (i) chromosomal mu gene deletions of 600 bp and 4 kb are corrected less efficiently than a deletion of only 2 bp, (ii) the minimum amount of homology required to mediate ectopic recombination is between 1.9 and 4.3 kb, (iii) the frequency of ectopic recombination does not depend on donor copy number, and (iv) the frequency of ectopic recombination in hybridoma lines in which the donor and recipient Cmu regions are physically connected to each other on the same chromosome can be as much as 4 orders of magnitude higher than it is for the same sequences located on homologous or nonhomologous chromosomes. The results are discussed in terms of a model for ectopic recombination in mammalian somatic cells in which the scanning mechanism that is used to locate a homologous partner operates preferentially in cis.

Primary structure, expression and chromosomal locus of a human homolog of rat ERK3

We report the cloning and characterization of a human cDNA encoding a novel homolog of rat extracellular signal-regulated kinase 3 (ERK3). The cDNA encodes a predicted protein of 721 amino acids which shares 92% amino acid identity with rat ERK3 over their shared length. Interestingly, the human protein contains a unique extension of 178 amino acids at its carboxy terminal extremity. The human ERK3 protein also displays various degrees of homology to other members of the MAP kinases family, but does not contain the typical TXY regulatory motif between subdomains VII and VIII. Northern blot analysis revealed that ERK3 mRNA is widely distributed in human tissues, with the highest expression detected in skeletal muscle. The human ERK3 gene was mapped by fluorescence in situ hybridization to chromosome 15q21, a region associated with chromosomal abnormalities in acute nonlymphoblastic leukemias. This information should prove valuable in designing studies to define the cellular function of the ERK3 protein kinase.

Human cardiotrophin-1: protein and gene structure, biological and binding activities, and chromosomal localization

Cardiotrophin-1 (CT-1) is a new member of the interleukin-6 cytokine family that was identified from a mouse embryoid body cDNA library by expression cloning. Mouse CT-1 induces features of hypertrophy in neonatal rat cardiac myocytes and binds to and activates the leukaemia inhibitory factor/gp130 receptor complex. In this work we report the isolation and characterization of cDNA and genomic clones encoding human CT-1. These clones encode a 201 amino acid protein that is 80% identical to the mouse protein. Human CT-1 produced by transfection of the cDNA clones into mammalian cells induces the hypertrophy of neonatal rat cardiac myocytes. Human and mouse CT-1 bind to the leukaemia inhibitory factor receptor on both human and mouse cell lines indicating a lack of species specificity. No binding to the human oncostatin M specific receptor was detected. A 1.7 kb CT-1 mRNA is expressed in adult human heart, skeletal muscle, ovary, colon, prostate and testis and in fetal kidney and lung. The coding region of CT-1 is contained on three exons and is located on human chromosome 16p11.1-16p11.2.

Allelic fusion of DNA topoisomerase II alpha and retinoic acid receptor alpha genes in adriamycin-resistant p388 murine leukemia revealed by fluorescence in situ hybridization

Fluorescence in situ hybridization (FISH) analysis of metaphase and decondensed free chromatin fibers from Adriamycin (ADR)-sensitive and ADR-resistant murine cells demonstrated a close juxtaposition of topoisomerase II alpha (Top2a) and retinoic acid receptor alpha (Rara) genes in adjacent chromatin in the drug-resistant cells, and a close but separate genetic proximity in normal murine chromatin. This provides physical evidence that the chromosome 11 allelic rearrangement resulting in a chimeric truncated Top2a/Rara transcript in the ADR-resistant cells is due to a novel fusion of the Topo2a and Rara genes. This is the first description of a Rara gene disruption in cells selected for antineoplastic drug resistance.

Application of the cross-organ beta dose method for tissue dosimetry in tumor-bearing mice treated with a 90Y-labeled immunoconjugate

BACKGROUND

Radioimmunotherapy of nude mice bearing human tumor xenografts using 90Y-labeled monoclonal antibodies has resulted in slower tumor growth, decreased tumor burden, and increased survival times. Dosimetry estimates in the murine model usually were based on biodistribution data and standard Medical Internal Radiation Dose approaches. A new dosimetric model for the mouse that takes into consideration the small dimensions, mass, and proximity of murine organs has been developed based on self-organ absorbed and cross-organ doses.

METHODS

Nude mice bearing carcinoembryonic antigen-expressing WiDr human colon cancer xenografts were injected with 240 microCi 90Y-anti-carcinoembryonic-antigen monoclonal antibodies and then killed at 12, 24, 72, 120, and 168 hours. Tumors and major organs were removed, weighed, and counted on a gamma counter. Using the resulting biodistribution data, the radiation doses to tumor and normal organs were calculated using the new dosimetric model for the mouse.

RESULTS

Three organs (the liver, kidneys, and large bowel) directly received > 50% of the total absorbed beta dose from radioactivity. Lungs, stomach, and marrow received the highest percentage (70-75%) of the total absorbed dose from adjacent organs. Tumor absorbed dose, estimated with the new dosimetric model, was three times less than that obtained with a MIRD-style calculation without correction for self-absorbed and cross-organ doses.

CONCLUSIONS

The new dosimetric model, which accounts more accurately for self-organ absorbed and cross-organ beta dose fraction, allows the calculation of tumor and organ doses in the murine model. Accurate estimation of radiation doses to tumor and critical organs, such as the marrow, spleen and kidneys, is important in determining the efficacy and toxicity of radioimmunotherapy regimens in animals and in subsequent human applications.

A method including edge effects for the estimation of radioimmunotherapy absorbed doses in the tumor xenograft model

The temporal relationship of radiolabeled monoclonal antibody (Mab) uptake to tumor size in a nude mouse human colon cancer xenograft model (LS174T) was evaluated as an aid to developing a method for estimation of radioimmunotherapy absorbed dose. Tumors of heterogeneous size were treated with 4.4 MBq (120 microCi) of 90Y-labeled anti-Carcinoembryonic Antigen Mab (90Y-ZCE025). Regression analysis demonstrated an inverse log-log relationship of antibody uptake (%ID/g) to tumor mass in four time intervals investigated (N > 10 points/interval):12-24 h, 2-3 d, 5-7 d, and 10-14 d. Curves of predicted radionuclide concentration vs time were then constructed for a range of constant tumor sizes. Xenograft radiation dose was obtained by temporal integration of each curve and application of appropriate dose estimation formulas. For each assumed tumor mass, an edge correction for loss of beta energy outside the target volume was applied assuming a spherical tumor shape. Estimated average absorbed doses were found to vary only from 13.8-10.3 Gy for a 20-fold change in tumor sizes (0.1-2.0 g, respectively). Such constancy of dose may explain xenograft stasis observed by our group in earlier experiments at this level of administered 90Y activity.

A mouse model for calculating cross-organ beta doses from yttrium-90-labeled immunoconjugates

BACKGROUND

The organs of laboratory mice used in radioimmunotherapy experiments are relatively small compared to the ranges of high-energy yttrium-90 (Y-90) beta particles. Current Medical Internal Radiation Dose (MIRD) dosimetry methods do not account for beta energy that escapes an organ. A dosimetry model was developed to provide more realistic dose estimates for organs in mice who received Y-90-labeled antibodies by accounting for physical and geometric factors, loss of beta dose due to small organ sizes, and cross-organ doses.

METHODS

The dimensions, masses, surface areas, and overlapping areas of different organs of 10 athymic nude mice, each weighing approximately 25 g, were measured to form a realistic geometric model. Major organs in this model include the liver, spleen, kidneys, lungs, heart, stomach, small intestine, large intestine, thyroid, pancreas, bone, marrow, and carcass. A subcutaneous tumor mass also was included in the model. By accounting for small organ absorbed fractions and cross-organ beta doses, the MIRD methodology was extended from humans to mice for beta dose calculations.

RESULTS

Absorbed fractions of beta energy were calculated using the Berger's point kernels and the electron transport code EGS4. Except for the tumor and carcass, the self-organ absorbed fractions ranged from 15% to 20% in smaller organs (the marrow and thyroid) to 65%-70% in larger organs (the liver and small intestine). Cross-organ absorbed fractions also were calculated from estimates of the overlapping surface areas between organs.

CONCLUSION

The mathematic mouse model presented here provides more realistic organ dosimetry of radiolabeled monoclonal antibodies in the nude mouse, which should, in turn, contribute to a better understanding of the correlation of biodistribution study results and organ-tumor toxicity information.

Pharmacokinetics of an anti-carcinoembryonic antigen monoclonal antibody conjugated to a bifunctional transition metal carborane complex (venus flytrap cluster) in tumor-bearing mice

An anticarcinoembryonic antigen (CEA) monoclonal antibody, T84.66, has been conjugated to a metallocarborane complex (Venus flytrap cluster, VFC) containing 57Co. This radioimmunoconjugate, 57Co-VFC-T84.66, retained > 90% immunoreactivity, was stable in serum (7 days) and demonstrated good localization in LS174T tumor xenografts. Pharmacokinetics of 57Co-VFC-T84.66 in tumor-bearing mice were compared to T84.66 Mab conjugated with either DTPA or its benzylisothiocyanate derivative (BzDTPA) labeled with 111In. Whole-body half-life for VFC-T84.66 was less (t1/2 = 62 hr) than that for either DTPA-T84.66 (t1/2 = 157 hr) or BzDTPA-T84.66 (t1/2 = 167 hr). Blood clearance was similar for all three radioimmunoconjugates (t1/2 = 22 hr). Hepatic uptake of the radiolabel was rapid and remained constant for 7 days for both DTPA radioimmunoconjugates (DTPA radioimmunoconjugate = 13.7 +/- 1.5 %ID/g; BzDTPA radioimmunoconjugate = 10.4 +/- 1.7%ID/g). For VFC, however, liver radioactivity decreased from 19.1 +/- 0.6%ID/g at 1 hr to 0.9 +/- 0.1 %ID/g 7 days postinjection, suggesting a possible role for VFC radioimmunoconjugate in the imaging and therapy of liver metastases.

Comparison of radioimmunotherapy and external beam radiotherapy in colon cancer xenografts

Radioimmunotherapy and external beam radiotherapy were compared in a nude mouse human colon cancer model. Radioimmunotherapy was delivered by intraperitoneal injection of 90Y-labeled anticarcinoembryonic antigen monoclonal antibody (anti-CEA MAB). Single fraction external beam radiotherapy was delivered using a 60Co teletherapy unit. Control groups received saline, unlabeled anti-CEA monoclonal antibody and labeled nonspecific monoclonal antibody. Subcutaneous CEA-expressing LS174T human colon carcinoma tumors were measured over time. Tumor growth suppression was expressed as delay to reach 2g compared to saline controls. Unlabeled anti-CEA monoclonal antibody and labeled nonspecific monoclonal antibody had no effect. External beam radiotherapy of 300, 600, 1000 and 2000 cGy produced growth delays of 3, 12, 17, and 22 days, respectively. Radioimmunotherapy with 120 microCi, 175 microCi, and 225 microCi resulted in growth delays of 20, 34, and 36 days. Estimated absorbed tumor dose was 1750 cGy in the 120 microCi group. Similar comparisons were done with the more radioresistant WiDr human colon carcinoma cell line. External beam radiotherapy doses of 400, 800, 1200, and 1600 cGy resulted in growth delays of 6, 21, 36 and 48 days, respectively. Radioimmunotherapy of 120 microCi and 175 microCi resulted in growth delays of 9 and 19 days, respectively. The 120 microCi dose delivered an estimated absorbed tumor dose of 1080 cGy to WiDr tumors. In summary, for the radiosensitive LS174T line, radioimmunotherapy produced biologic effects that were comparable to a similar dose of single fraction external beam radiotherapy. For the more radioresistant WiDr tumor, radioimmunotherapy produced a biologic effect which was less than a similar dose of single fraction external beam radiotherapy. These studies suggest that a tumor's response to radioimmunotherapy relative to that of external beam radiotherapy is, in part, dependent on tumor radiosensitivity and repair capacity.

Eliminating interference from heterophilic antibodies in a two-site immunoassay for creatine kinase MB by using F(ab')2 conjugate and polyclonal mouse IgG

Heterophilic antibodies interfere in two-site immunoassays. Our purpose was to screen for the samples containing heterophilic antibodies that react with mouse immunoglobulins and to use them to determine how to eliminate interference in various two-site immunoassays being developed in our laboratory. Of approximately 2600 samples screened, 81 had heterophilic antibodies. When creatine kinase MB (CKMB) concentration was measured with intact antibody conjugate in these 81 samples, 18 (22%) samples had apparent CKMB values significantly greater than values measured with Hybritech's "Tandem -E CKMB immunoenzymetric" assay and Corning agarose-gel electrophoresis. Adding up to 133 mg/L of polymerized IgG or up to 1666 mg/L polyclonal mouse IgG in the assay did not eliminate the interference in all the samples. However, adding F(ab')2 conjugate plus 40 mg/L of polymerized IgG or 83 mg/L of polyclonal mouse IgG eliminated the interference in all the samples. This approach was also effective in eliminating the interference in 15 samples containing 4.7-165.2 mg/L of human antimouse antibody (HAMA). Combined use of F(ab')2 conjugate and polyclonal mouse IgG is recommended to eliminate interference from heterophilic antibodies that react with murine immunoglobulins or HAMA in two-site murine-antibody-based assays.

Gamma-interferon enhancement of carcinoembryonic antigen expression in human colon carcinoma xenografts

Athymic nu/nu mice bearing a subcutaneous human colon cancer xenograft (WiDr, low CEA expression) were treated with gamma-interferon (gamma IFN) at varying doses, frequencies, and periods of duration. CEA content (micrograms/g) and uptake of radiolabeled anti-CEA monoclonal antibody (MAB) (percent injected dose per gram, % ID/g) were measured at 48 h following administration of the MAB, The optimal enhancement of tumor CEA content and tumor localization of [111In] anti-CEA monoclonal antibody (MAB) was seen at gamma IFN doses of 100,000 U i.p. every 8 h for 4 days (4.7 micrograms/g; 29% ID/g) compared to control animals (0.9 micrograms/g; 10% ID/g). The effects of gamma IFN on CEA content and MAB localization were less pronounced when administered (a) at lower doses: 5,000 to 50,000 U i.p. every 8 h, (b) at varying frequencies: 300,000 U/day delivered in divided doses every 4 or 24 h, or (c) for varying periods: 2 or 6 days of therapy. In each case, the biologic effects on tumor CEA content and uptake of [111In]MAB correlated closely with the serum gamma IFN level. Therefore, we conclude that enhancement of in vivo CEA expression by gamma IFN may have clinical relevance for tumor imaging and therapy using radiolabeled monoclonal antibodies.

Carboranyl peptide-antibody conjugates for neutron-capture therapy: preparation, characterization, and in vivo evaluation

Two model peptides rich in boron and prepared by Merrifield syntheses, dansyl.(nido-CB)2, (1) and dansyl.(nido-CB)10.Lys.Ac (2), where nido-CB represents the alpha-amino acid [nido-7-CH3-8-(CH2)3CH-(NH2)COOH-7,8-C2B9H10]-, were conjugated with the anti-CEA mAb T84.66 using peptide active ester reagents. The dansyl groups provided a means of fluorimetric analysis of mAb conjugates which was augmented by conventional amino acid analyses for nido-CB. The conjugate of 1 contained an average of 63 B atoms per mAb molecule. The mAb conjugate of 2 was chromatographically separated into a strongly fluorescent high molecular weight aggregated fraction (HMW) and a less intensely fluorescent monomeric fraction. Both fractions retained immunoreactivity. The HMW species contained an average of ca. 490 B atoms/mAb molecule, as determined by amino acid analysis. Biodistribution data were collected using nude mice bearing LS174T xenografts and 125I-labeled mAb conjugates. While the lightly B-loaded dipeptide conjugate gave biodistribution results which resembled those of native T84.66 mAb, the undecapeptide conjugate displayed greatly enhanced liver uptake and decreased tumor accretion. These results suggest that as the boron-containing burden on the supporting immunoprotein is greatly increased, as in the case of the T84.66-2 conjugate, loss of circulating conjugate to liver effectively competes with the desired tumor localization. Means which might be taken to circumvent this difficulty have been described elsewhere (ref 15).

Effects of recombinant human gamma-interferon on carcinoembryonic antigen expression of human colon cancer cells

The effects of human recombinant gamma-interferon (gamma-IFN) on the levels of carcinoembryonic antigen (CEA) expression were investigated in vitro in three human colon adenocarcinoma cell lines (WiDr, HT29, and SW403). Subconfluent cultures were exposed continuously to IFN at concentrations of 1-1,000 antiviral units/ml for up to 6 consecutive days. IFN resulted in a significant increase in CEA levels when assayed by cellular enzyme-linked immunosorbent assay (ELISA), with higher concentrations and longer exposure times resulting in greater CEA enhancement. A three to five-fold enhancement of CEA was observed after 5-6 days of continuous exposures at concentrations of 100-1,000 antiviral units/ml. CEA levels returned to baseline over a 4-day period after discontinuation of IFN. Levels of IFN that resulted in CEA enhancement also resulted in cell growth inhibition, with a direct correlation observed. Flow cytometric studies, which evaluated changes in CEA membrane expression of only the viable cells remaining after IFN exposure, gave similar results to cellular ELISA. Quantitative CEA ELISA, which quantitated changes in total cellular CEA content, demonstrated greater increase in CEA than predicted by cellular ELISA. Continuous IFN exposures for 5-6 days at 1,000 U/ml led to a 96-, 26-, and 5-fold increase in total CEA for the WiDr, HT29, and SW403 cell lines, respectively. WiDr cells exposed to daily 6-h IFN pulses demonstrated intermediate increases in CEA compared with cells exposed continuously to IFN.(ABSTRACT TRUNCATED AT 250 WORDS)

Interferon enhancement of radioimmunotherapy for colon carcinoma

Recombinant human gamma-interferon (IFN-gamma) has recently been shown to enhance localization of radiolabeled monoclonal antibodies (MAb) to human colon carcinoma xenografts in athymic mice. The present study investigates the ability of gamma-interferon to enhance radioimmunotherapy of a low carcinoembryonic antigen-expressing human colon cancer (WiDr) in athymic mice. Growth curve analysis, antibody localization, and dose estimation studies were performed. A significant tumor growth delay, measured as the time to reach 1.0 g, was noted for animals receiving specific anti-carcinoembryonic antigen 90Y-MAb (ZCE025, 120 microCi) plus IFN-gamma (61.8 days) as compared to animals that received specific 90Y-MAb with phosphate-buffered saline (34.9 days; P less than 0.005). IFN-gamma (100,000 units) was given i.p. every 8 h for 2 days before and 4 days after 90Y-MAb therapy. The time required to reach 1.0 g for animals treated with nonspecific 90Y-MAb (ZME018) was significantly less either with (38.3 days) or without (34.4 days) IFN-gamma. The difference was more apparent when compared to animals receiving IFN-gamma alone (30.0 days) or phosphate-buffered saline alone (28.9 days; P less than 0.001). Increased antibody localization in the tumors of animals treated with IFN-gamma plus specific 90Y-MAb (43.2% injected dose/g) was seen in comparison to animals treated with specific 90Y-MAb without IFN-gamma (18.2% injected dose/g). The estimate of radiation dose delivered to the tumors, based on biodistribution data over time, revealed significantly higher levels in animals treated with specific 90Y-MAb with IFN-gamma (2477 cGy) compared to animals treated without IFN-gamma (1217 cGy). These results provide support for the use of gamma-interferon as an immunomodulating agent prior to radioimmunotherapy.

A transition metal complex (Venus flytrap cluster) for radioimmunodetection and radioimmunotherapy

A novel transition metal complex, Venus flytrap cluster (VFC), is described for the preparation of radio-labeled antibodies. VFC contained 57Co, which was held tightly between the faces of two covalently bridged carborane ligands by cluster bonding of the metal with appropriate ligand orbitals. Anti-carcinoembryonic antigen monoclonal antibody T84.66 was conjugated to 57Co-VFC with full retention of immunological activity. Biodistribution studies in nude mice bearing carcinoembryonic antigen-producing tumors showed excellent tumor localization of 57Co-VFC-T84.66. The accumulation of radionuclide in normal liver was low and independent of dose, which may reflect the stability of the radionuclide complex. These results presage the use of VFC systems for binding transition metals that are clinically useful for radioimmunodiagnosis and radioimmunotherapy.

Localization of intraperitoneal xenografts of human colon cancer by radiolabeled anti-CEA antibodies

An intraperitoneal xenograft tumor model was developed in the nude mouse to represent advanced colorectal disease in the human patient. Intraperitoneal (ip) and subcutaneous (sc) tumor xenografts were successfully localized by indium 111-labeled anti-carcinoembryonic antigen monoclonal antibodies (Indacea) administered intravenously (IV) or intraperitoneally (IP). In the sc model, tumor uptake (% injected dose per g of tumor tissue--%ID/g) was significantly improved at 72 hours postinjection when Indacea was administered IP (44.01 +/- 1.94 vs. 33.74 +/- 0.87, P less than 0.005). In the ip model, tumor uptake at 72 hours was improved with IP Indacea (28.23 +/- 5.42 vs. 19.36 +/- 5.50, P less than 0.01) and the tumor to blood ratio was significantly improved for IP Indacea (17.83 +/- 2.95 vs. 8.45 +/- 1.38, P less than 0.01). Tumor mass was not a contributing factor in these differences. This study demonstrates that ip xenografts can be successfully imaged using radiolabeled antibodies and that the IP route of administration results in better tumor uptake of the antibody in ip lesions.

Radioimmunotherapy of human colon cancer in nude mice

Nude mice bearing subcutaneous human colon cancer xenografts (LS174T) were treated with 120 microCi of yttrium 90-labeled anti-carcinoembryonic antigen monoclonal antibodies (specific therapy), 120 microCi of 90Y-labeled anti-melanoma monoclonal antibodies (nonspecific therapy), or phosphate-buffered saline solution (no treatment control). Mean (+/- SD) tumor growth rates (percent increase per day) over the first 30 days of the study were as follows: 0.6% +/- 0.2% per day (specific therapy); 17.7% +/- 5.7% per day (nonspecific therapy); and 30.5% +/- 4.2% per day (control). In all three groups, tumors over 1 g had similar doubling times (5.74 +/- 0.71 d). Specific therapy caused a lag in tumor growth corresponding to a 3-logarithm cell kill. Estimated tumor dose of radiation obtained by tissue analysis was 34 and 14 Gy for specific and nonspecific therapy, respectively. In conclusion, 120 microCi of 90Y-labeled anti-carcinoembryonic antigen monoclonal antibodies was effective in suppressing growth of human colon cancer xenografts. Clinical studies with this preparation are recommended.

Presurgical imaging with indium-labeled anti-carcinoembryonic antigen for colon cancer staging

Over a 4-year period, 108 patients with known or suspected colorectal cancer were studied by radioimmunoconjugate scintigraphy prior to operative procedures. Study subjects received 0.2 to 40 mg i.v. of murine anti-carcinoembryonic antigen monoclonal antibody labeled with 2-5 mCi of 111In (Indacea). Resected tissues were analyzed for 111In and carcinoembryonic antigen content. Tumor, liver, and draining lymph nodes had over 10% injected dose/kg compared to less than 2.5% injected dose/kg for other normal tissues. Primary tumors that were successfully imaged were significantly larger and had higher 111In and carcinoembryonic antigen content. In 54 patients, primary tumors were visualized with a sensitivity of 78%. Hepatic metastases (58 patients) were visualized as negative filling defects (sensitivity, 45%). Extrahepatic (intraabdominal) metastases (25 patients) were visualized (sensitivity, 48%) as areas of increased uptake. Extraabdominal metastases were uncommon (10 patients; sensitivity, 80%). Of 56 patients with known or suspected hepatic metastases who presented with no evidence of extrahepatic disease by conventional tests (X-ray, computerized tomographic scan), 20 (36%) were documented to have extrahepatic metastases at exploratory surgery and 10 of these (50%) had the extrahepatic disease localized by the Indacea scan. The management of these 10 patients was, or could have been, modified by the scan findings and unnecessary surgery eliminated.

Role of bone marrow transplantation in 90Y antibody therapy of colon cancer xenografts in nude mice

The efficacy of bone marrow transplantation (BMT) for the prevention of 90Y toxicity and extension of survival in nude mice with i.p. LS174T carcinomatosis was evaluated. 90Y-labeled monoclonal antibody (MAB) directed against carcinoembryonic antigen (90Y-anti-CEA MAB) at a dose of 120 microCi caused no deaths due to treatment toxicity and increased the duration of animal survival. No long term cures were obtained in these mice. At doses of 160 microCi or more 90Y-anti-CEA MAB led to hematological deaths. Nude mice were given i.p. injections of 10(6) LS174T tumor cells on day 0. On day 7 the mice received 90Y-anti-CEA MAB i.p. at doses of 120-225 microCi. Syngeneic bone marrow cells (10(7) cells) were then injected i.v. into the mice at 1, 3, 5, 7, 10, or 14 days following 90Y treatment. In the absence of BMT, toxic deaths for animals given 175 microCi 90Y were 11 of 24 (46%) with a median survival of 17 days and 13 of 20 (65%) for animals given 225 microCi 90Y with a median survival of 14 days. Animals receiving the same two doses of 90Y and given BMT 5 days following the 90Y treatment showed 0 of 24 (0%) and 0 of 54 (0%) toxicity deaths, respectively. The optimal time of BMT in relation to 90Y therapy was dependent upon the dose of 90Y-anti-CEA MAB (225 microCi, 3-5 days; 175 microCi, 5-14 days). The mean survival in tumor bearing animals was extended from 31.7 +/- 1.2 (SE) to 45.3 +/- 2.0 days by treatment with 120 microCi of 90Y-anti-CEA MAB. By increasing the dose of 90Y-anti-CEA MAB to 225 microCi and undertaking BMT 5 days later the mean survival was further extended to 63.2 +/- 3.6 days (P less than 0.005). BMT administered at the optimal times can prevent toxic deaths and facilitates higher, more effective doses of tumor specific 90Y-MAB.

Radioimmunotherapy of human colon carcinomatosis xenograft with 90Y-ZCE025 monoclonal antibody: toxicity and tumor phenotype studies

Monoclonal antibody ZCE025 recognizes an epitope of the carcinoembryonic molecule (CEA). We have shown that when linked to 90Y, its localization in the tumor was sufficient to result in a significant tumoricidal effect in human colon carcinomatosis grown in the peritoneum of athymic mice. Intraperitoneal tumors were present 7 days after inoculation of the CEA-producing human colon carcinoma cell line LS174T, when the mice received i.p. injections with 40 to 160 microCi of 90Y-labeled ZCE025 or 96.5c (nonspecific monoclonal antibody). The animals that were autopsied 12 days after treatment displayed a significant (P less than 0.001) inhibition of tumor growth when compared to the control animals that received no treatment or similar doses of nonspecific monoclonal antibody. Microscopically, the treated tumors showed extensive radiation effect and they became progressively necrotic until only a rim of viable tissue remained in the periphery of the nodules. CEA expression was practically absent on the newly grown nodules that began to appear 3 weeks after therapy, and remained so 6 weeks thereafter. In contrast, over 80% of the tumor cells from the untreated animals expressed CEA. There was no mortality due to treatment; however, the hematopoietic organs were markedly depleted at the higher doses. The marrow and the spleen recovery began 2 weeks after treatment, and it was completed by the 4th week. No evidence of toxicity was present in any of the other organs examined. These studies suggest that 90Y-ZCE025 therapy results in clonal selection of cells lacking or minimally expressing CEA. The inherent implications of these findings are discussed.

Estimation of monoclonal antibody-associated 90Y activity needed to achieve certain tumor radiation doses in colorectal cancer patients

In these measurements, we quantitated, via surgical samples, human primary tumor uptake of the anti-carcinoembryonic antigen monoclonal antibody T84.66. Uptake was measured in units of percentage of injected dose/kg with 111In as the radiolabel. All 11 colorectal lesions were nonnecrotic and were visualized upon scanning. Tumor volume was calculated using the three orthogonal dimensions as described by pathology. Uptake mean +/- SD was 6.55 +/- 3.55% injected dose/kg with a range of 1.2 to 10.4% injected dose/kg. Lesion mean volume was 36 cm3 with a range of 1.5 to 304 cm3. Using mean values, assuming no biological clearance and that the biodistribution of the monoclonal is independent of its radiolabel, the predicted human tumor 90Y beta dose was 0.12 Gy/mCi. Therefore a 10-Gy tumor dose would require 83 mCi of i.v. activity. Using least and highest uptake results, requisite activity values were 3-fold larger and smaller respectively. Thus, there was approximately an order of magnitude variation in the amount of 90Y predicted to achieve a given tumor dose in colorectal cancer patients. Murine and human uptake values were consistent if lesion mass and carcinoembryonic antigen content were taken into account.

Mechanism of decreasing liver uptake of 111In-labeled anti-carcinoembryonic antigen monoclonal antibody by specific antibody pretreatment in tumor bearing mice

The purpose of this study was to examine the mechanism of specific antibody pretreatment for reduction of liver uptake of 111In-labeled monoclonal antibody (MAB). Previous work with an anti-carcinoembryonic antigen (CEA) MAB (T84.66) and LS174T human colon cancer xenografts in nude mice has shown that giving a high dose (0.2 mg) of unlabeled T84.66 in conjunction with the same MAB (T84.66) labeled with 111In (Indacea) significantly lowered the liver uptake of 111In. High performance liquid chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis were used to assess the radiolabeled components in serum and liver at different times following administration of Indacea in normal and tumor bearing mice. In serum the 111In remained associated with the IgG in both tumor bearing and non-tumor bearing mice. Liver uptake of 111In in mice without tumor was low (8-12% injected dose/g) and both IgG and a low molecular weight metabolite were found in the liver homogenates. Liver uptake in tumor bearing mice increased dramatically (15-40% injected dose/g) with size of tumor and in addition to the IgG and low molecular weight components, a high molecular weight compound was identified. Administration of CEA: Indacea complexes to non-tumor bearing mice produced the same high pressure liquid chromatography and gel patterns as those seen in mice with large (greater than 1 g) tumors. Liver homogenates from tumor bearing mice given specific antibody pretreatment showed the same patterns seen with non-tumor bearing mice (no high molecular weight peak). In conclusion, CEA:Indacea complexes are formed in tumor bearing mice and rapidly cleared by the liver. Specific antibody pretreatment results in the production of unlabeled CEA:MAB complexes causing a reduction in the formation of CEA:Indacea complexes and a lower liver uptake of 111In.

Mechanisms of tissue uptake and metabolism of radiolabeled antibody--role of antigen: antibody complex formation

Scintigraphic studies in animals and in humans have demonstrated uptake of radiolabeled antibody by both normal and tumor tissue. Normal tissues most commonly visualized are blood, liver, spleen, kidneys, lymph nodes, bone, and thyroid. A number of factors have been demonstrated to affect the uptake by normal and tumor tissue, including radioisotope properties, immunoglobulin characteristics, antibody specificity, tumor size, vascular permeability, and antigen expression. Clarification of the mechanisms of tumor and normal tissue uptake depends upon comparison of scintigraphic findings with analysis of tissue for such factors as radioactivity, antigen content, and tumor size. One of the major limitations of 111In labeled monoclonal antibody imaging has been extensive 111In uptake by histologically normal liver, especially in a host bearing a large tumor mass. By high performance liquid chromatography and sodium dodecyl sulfate-polyacrylamide-gel electrophoresis analysis of liver and blood it can be demonstrated that much of the liver uptake is related to the formation of antigen:antibody complexes. The normal liver intensity can be decreased by inhibition of radiolabeled complex formation. Understanding of the mechanisms of tissue uptake, both normal and tumor, and of radiolabeled antibody metabolism is crucial to the rational planning and use of radioimmunoconjugates for tumor imaging and treatment. Animal and human studies complement one another in examination of these mechanisms.

The effects of hyperthermia on tumor carcinoembryonic antigen expression

The effects of hyperthermia on carcinoembryonic antigen (CEA) expression were investigated. The human colon adenocarcinoma cell line, LS174T, was heated in vitro for 42 degrees C/1 hr, 43 degrees C/1 hr, or 45 degrees C/30 min. Carcinoembryonic antigen membrane expression was assayed by live cell radioimmunoassay 0-6 days after heating. A heat exposure of 45 degrees C/30 min resulted in an initial decrease in carcinoembryonic antigen membrane expression 1 day post-heating followed by a 2-3 fold increase which peaked 3 days post-heating. Carcinoembryonic antigen expression began returning to normal by the sixth day. Heat exposures of 42 degrees C/1 hr and 43 degrees C/1 hr also resulted in increased carcinoembryonic antigen expression but this increase was of lesser magnitude and of shorter duration. Carcinoembryonic antigen shed into the medium, as measured by enzyme immunoassay, also increased after heating in a temperature-dependent fashion. Flow cytometry analysis demonstrated that cells in all phases of the cell cycle expressed this increase. We conclude that hyperthermia results in significant changes in carcinoembryonic antigen membrane expression and shedding. The implications that these findings have with regards to clinical hyperthermia and radioimmunotherapy are discussed.

Antigenic sites in carcinoembryonic antigen

The epitope reactivities of 52 well-characterized monoclonal antibodies (Mabs) against carcinoembryonic antigen from 11 different research groups were studied using competitive solid-phase immunoassays. About 60% of all possible combinations of Mabs as inhibitors and as the primary binding antibody were investigated. The inhibition data were analyzed by a specially developed computer program "EPITOPES" which measures concordance and discordance in inhibition patterns between Mabs. The analysis showed that 43 of the 52 Mabs (83%) could be classified into one of five essentially noninteracting epitope groups (GOLD 1-5) containing between four and 15 Mabs each. The epitopes recognized by the Mabs belonging to groups 1 to 5 were peptide in nature. With one or two possible exceptions non-classifiable Mabs were either directed against carbohydrate epitopes (4 Mabs) or were inactive in the tests used. Within epitope groups GOLD 1, 4, and 5 two partially overlapping subgroups were distinguished. Mabs with a high degree of carcinoembryonic antigen specificity generally belonged to epitope groups GOLD 1 and 3.

Effect of yttrium-90-labeled anti-carcinoembryonic antigen monoclonal antibody on the morphology and phenotype of human tumors grown as peritoneal carcinomatosis in athymic mice

Grossly visible peritoneal carcinomatosis resembling that seen in man was produced in athymic mice 7 days after intraperitoneal injection of 8 x 10(5) cells of the carcinoembryonic antigen (CEA)-producing human colon carcinoma cell line LS174T. The mice received intraperitoneal injections of 40 to 160 microCi of yttrium-90 (90Y)-labeled anti-CEA monoclonal antibody (MAb). When the mice were killed 12 days after injection, a significant inhibition of tumor growth, ranging from 40% to 95%, was observed in the treated animals when compared to the growth of tumors in the untreated animals (P less than 0.001). No mortality secondary to the therapy was seen. The bone marrow was depleted significantly at the higher doses of labeled MAb, but total recovery was observed 4 weeks after treatment. Histologically, the treated tumors showed extensive radiation effects early in the posttherapy period and massive necrosis at later times. Minute foci of viable tumor remained in the periphery. New tumor outgrowths with histologic features similar to those in the untreated controls began to appear 3 weeks after therapy. The CEA expression of the treated tumors was similar to that of the untreated controls during the early posttreatment period, diminishing progressively as the tumors became necrotic. Newly grown tumor nodules in the treated animals lacked significant CEA expression both initially and at later times. Our studies suggest that therapy with 90Y-anti-CEA MAb therapy results in selection of tumor clones lacking CEA, and that a single large dose of 90Y-MAb should be more effective than multiple fractions of smaller doses.

Effect of specific antibody pretreatment on liver uptake of 111In-labeled anticarcinoembryonic antigen monoclonal antibody in nude mice bearing human colon cancer xenografts

Administration of a large dose (0.2 mg) of unlabeled specific anticarcinoembryonic antigen (anti-CEA) monoclonal antibody (MAB) to nude mice bearing LS174T human colon cancer xenografts significantly decreased normal liver uptake of 111In-labeled anti-CEA MAB (Indacea). Mice bearing tumors of approximately 1 g showed liver accumulation of indium-111 at 48 h following injection of 2 micrograms/10 microCi Indacea of 33.8 +/- 1.5% injected dose per gram (%ID/g) (N = 25). Treatment with 0.2 mg unlabeled anti-CEA MAB reduced this to 8.9 +/- 0.5% ID/g (N = 22; P less than 0.001). The dose of pretreatment was found to be critical. Increasing the amount of unlabeled MAB to 2.0 mg did not significantly improve the liver level of indium-111, but did compromise the tumor uptake of Indacea (15.9 +/- 1.3 versus 12.4 +/- 0.4% ID/g; P less than 0.05). Lowering the dose of pretreatment 10-fold resulted in increased (P less than 0.001) liver uptake of the label (26.5 +/- 2.8% ID/g). The unlabeled anti-CEA MAB treatment given as a single dose or fractionated over several days gave the same results. The decrease in liver uptake was the same for i.v. administration of the unlabeled MAB given 1 week prior to Indacea injection or mixed together with Indacea. With i.p. administration, simultaneous injection of the unlabeled MAB with Indacea was not as effective as pretreatment (20 min to 7 days) in decreasing the liver uptake of 111In (P less than 0.05). Epitope specificity and affinity were shown to be important considerations in the choice of MAB combinations used for pretreatment and imaging. Pretreatment with nonspecific MAB was ineffective in decreasing liver uptake of Indacea.

The effects of tumor mass, tumor age, and external beam radiation on tumor-specific antibody uptake

The effects of external beam radiation on tumor uptake of radiolabeled monoclonal antibody were investigated. Nude mice bearing carcinoembryonic antigen (CEA)-producing subcutaneous human tumor xenografts (LS174T) were irradiated (60Co) with a single fraction of 0, 2 or 20 Gy, 6 or 11 days after tumor inoculation. An Indium-111 labeled anti-CEA monoclonal antibody (T84.66) was injected 1-2 hrs after irradiation. Biodistribution studies performed at 48 hrs showed a statistically significant (p less than 0.01) inverse correlation between tumor mass and tumor antibody uptake. Tumor age was also a significant factor with 11 day old tumors having significantly less uptake (p less than 0.0001) compared to 6 day old tumors for a given mass. Radiation increased tumor antibody uptake only in those tumors where growth inhibition also occurred. Multiple regression analysis showed that this inverse correlation between tumor mass and antibody uptake was the same for irradiated and nonirradiated tumors. We conclude that, in this model system, radiation does not act independently to enhance tumor antibody deposition. Radiation's primary effect is to reduce tumor mass, with mass reduction then resulting in an increase in antibody uptake. The clinical implications of this study are discussed.

Prolongation of survival of nude mice bearing human colon cancer. Treatment with yttrium 90-labeled anti-carcinoembryonic antigen antibody

Nude mice bearing diffuse intraperitoneal carcinomatosis of the human colon cancer cell line LS174T were treated with an anti-carcinoembryonic antigen monoclonal antibody (MAB) that was labeled with yttrium 90 (90Y-ZCE025). Control animals were either untreated or treated with nonspecific 90Y-MAB (90Y-96.5c). The median survival (MS) for untreated animals was 26 days. The MS for specific and nonspecific therapy that consisted of 120 microCi of 90Y-MAB was 69 and 34 days, respectively. No significant improvement in the MS was observed with a second 120-microCi administration of 90Y-MAB given two weeks later. A decreased MS was observed with 80 microCi of 90Y-MAB given every four days for three cycles. In each category, specific therapy had a significant advantage over nonspecific therapy in increased effectiveness and decreased toxicity. The 90Y-ZCE025 therapy gave an increased life span of almost 200%. The therapeutic effects with different dosing regimens have important implications for treatment planning.

Impact of radiolabeled antibody imaging on management of colon cancer

One hundred patients with known or suspected colorectal cancer were studied by radioimmunoconjugate scintigraphy prior to operation. Study subjects received murine monoclonal anticarcinoembryonic antigen labeled with indium 111 (Indacea). Sensitivity of imaging was 76 percent for primary tumors, 44 percent for hepatic metastases, 38 percent for extrahepatic abdominal metastases, and 78 percent for extraabdominal metastases. Seventeen of 46 patients (37 percent) with known or suspected hepatic metastases and no evidence of extrahepatic disease by conventional imaging methods had extrahepatic metastases at exploratory surgery. Nine of the 17 patients had disease accurately predicted by the Indacea scanning. The management of each of these nine patients was, or could have been, modified by the scan findings and unnecessary surgery eliminated. A number of patients without post-operative disease had an unexplained increase in plasma carcinoembryonic antigen level due to production of human antimouse antibody. The addition of excess mouse immunoglobulin to the plasma prior to assay blocked this artifactual increase.

Artifactual CEA elevation due to human anti-mouse antibodies

Retrospective analysis of 108 patients who received indium 111-labeled murine monoclonal antibodies for imaging of cancer was performed. Most patients had operative procedures for colorectal carcinoma following completion of scintiscanning. Eleven patients had markedly elevated carcinoembryonic antigen (CEA) levels postoperatively without evidence of residual or recurrent disease. The laboratory method of measuring CEA levels was a commercially available double mouse monoclonal antibody enzyme immunoassay. It was postulated that the unexplained elevation of CEA was a reflection of the presence of human anti-mouse antibody (HAMA) induced by the administration of radiolabeled mouse antibody. A competitive assay for HAMA was undertaken by incubation of these patients' sera with a high dose of nonspecific mouse immunoglobulin prior to CEA determinations, and subsequent CEA levels were normal. The presence of HAMA was confirmed by a noncompetitive solid-phase enzyme immunoassay in 73% of tested patients who received murine monoclonal antibodies for imaging. Identification of artifactual CEA elevations is important in the treatment of cancer patients.

Tumor uptake as a function of tumor mass: a mathematic model

Inverse correlations of tumor uptake (u), measured in percent injected dose per gram, with tumor mass (m) are demonstrated for phospholipid vesicle, nonspecific and specific monoclonal antibody tracers. Correlation coefficients implied u = B mA in 11 different animal experiments. Experimental exponent (A) values lay in the range -0.28-0.64 with a mean of -0.43 while intercept (B) values varied from 3 to 18. Spherical and cylindrical tumor models implied exponents of -0.33 and -0.5, respectively. Comparison of three implantation sites of the human LS174T xenograft revealed a narrow range of exponents (-0.38- -0.46) indicating a consistent geometry for this tumor. Blood flow to the lesion site and inside its volume (as dictated by tumor size) are factors in tumor uptake. Our results indicate that biodistribution data should include the variation of tumor uptake with mass. For less than 10 g lesions, we predict that radiation absorbed dose will be highly dependent upon tumor size.

Therapy of peritoneal carcinomatosis of human colon cancer xenografts with yttrium 90-labeled anti-carcinoembryonic antigen antibody ZCE025

The present study was undertaken to determine whether an anti-carcinoembryonic antigen (CEA) monoclonal antibody (MAB), labeled with the potent beta emitter yttrium 90, could alter the growth of diffuse intraperitoneal carcinomatosis of colon cancer. Nude mice bearing the CEA-producing human tumor line LS174T received therapy with the anti-CEA MAB ZCE025 90Y. Animals were evaluated 12 days after therapy. Untreated animals had a mean (+/- SEM) tumor burden of 3.99 +/- 0.10 g, while animals treated with ZCE025 90Y had 0.29 +/- 0.04 g present. This decrease was significant compared with the 1.31 +/- 0.16 g of tumor present in animals treated with a 90Y-labeled nonspecific antibody 96.5c. The therapeutic effects seen with ZCE025 90Y suggest a potentially useful role for 90Y-labeled anti-CEA MABs in the treatment of gastrointestinal carcinomatosis.