CAMK2γ in intestinal epithelial cells modulates colitis-associated colorectal carcinogenesis via enhancing STAT3 activation.

Inflammation is one of the major risk factors for cancer. Here, we show that calcium/calmodulin-dependent protein kinase II gamma (CAMK2γ) in intestinal epithelial cells (IECs) modulates inflammatory signals and promotes colitis-associated cancer (CAC) in mice. We have identified CAMK2γ as a downstream target of colitis-induced WNT5A signaling. Furthermore, we have shown that CAMK2γ protects against intestine tissue injury by increasing IEC survival and proliferation. Calcium/calmodulin-dependent protein kinase II gamma knockout mice displayed reduced CAC. Furthermore, we used bone marrow transplantation to reveal that CAMK2γ in IECs, but not immune cells, was crucial for its effect on CAC. Consistently, transgenic over-expression of CAMK2γ in IECs accelerated CAC development. Mechanistically, CAMK2γ in IECs enhanced epithelial signal transducer and activator of transcription 3 (STAT3) activation to promote survival and proliferation of colonic epithelial cells during CAC development. These results thus identify a new molecular mechanism mediated by CAMK2γ in IECs during CAC development, thereby providing a potential new therapeutic target for CAC.

Role of CEACAM1 isoforms in an in vivo model of mammary morphogenesis: mutational analysis of the cytoplasmic domain of CEACAM1-4S reveals key residues involved in lumen formation.

CEACAM1 (carcinoembryonic antigen-related cell adhesion molecule 1) is a type I transmembrane glycoprotein expressed in epithelial cells with three or four extracellular domains (ECDs) and either long or short cytoplasmic domain isoforms. We have previously shown that the four extracellular domains, short cytoplasmic domain isoform, CEACAM1-4S, plays an essential role in lumen formation in an in vitro model of mammary morphogenesis. In this study, we transfected MCF-7 cells with either the long or short cytoplasmic domain isoforms of CEACAM1, and grew the cells in humanized mammary mouse fat pads in NOD/SCID mice. In this in vivo model, only the long cytoplasmic domain isoform, CEACAM1-4L, formed glands with lumen. On the basis of other studies that revealed phosphorylation of key Thr and Ser residues in the short cytoplasmic domain, we introduced phosphorylation mimic (for example, Thr or Ser to Asp) or null (Thr or Ser to Ala) mutations into the cytoplasmic domain of CEACAM1-4S and tested them in the in vivo model. Mutation of either Thr or Ser to Asp or the double mutant Thr+Ser to Asp, but not the null mutants, induced gland formation with a central lumen-containing apoptotic cells. Moreover, the phosphorylation mimic mutants of CEACAM1-4S induced downregulation of beta1-integrin, overexpression of beta2-integrin, inhibited phosphorylation of focal adhesion kinase (pTyr-397) and resulted in myofibroblast differentiation as characterized by expression of vimentin, alpha-smooth muscle actin and beta2-integrin, as well as the production of abundant extracellular matrix.

Protein epitopes in carcinoembryonic antigen. Report of the ISOBM TD8 workshop.

To characterize antigenic sites in carcinoembryonic antigen (CEA) further and to investigate whether there are differences between colon tumor CEA and meconium CEA (NCA-2) that can be detected by anti-CEA monoclonal antibodies (MAb), 19 new anti-CEA MAb were analyzed with respect to specificity, epitope reactivity and affinity. Their reactivities were compared with 10 anti-CEA MAb with known CEA-domain binding specificity that have previously been classified into five nonoverlapping epitope groups, GOLD 1-5. Cross-inhibition assays with antigen-coated microtiter plates and immunoradiometric assays were performed in almost all combinations of MAbs, using conventionally purified CEA (domain structure: N-A1B1-A2B2-A3B3-C) from liver metastasis of colorectal carcinomas, recombinant CEA, meconium CEA (NCA-2), truncated forms of CEA and NCA (CEACAM6) as the antigens. The affinity of the MAbs for CEA was also determined. The new MAbs were generally of high affinity and suitable for immunoassays. Three new MAbs were assigned to GOLD epitope group 5 (N-domain binding), 3 MAbs to group 4 (A1B1 domain), 1 to group 3 (A3B3 domain), 3 to group 2 (A2B2 domain) and 3 to group 1 (also the A3B3 domain). Three MAbs formed a separate group related to group 4, they were classified as GOLD 4' (A1B1 domain binding). The remaining 3 MAbs appear to represent new subspecificities with some relationship to GOLD groups 1, 2 or 4, respectively. Five MAbs, all belonging to epitope group 1 and 3, reacted strongly with tumor CEA but only weakly or not at all with meconium CEA, demonstrating that the two products of the CEA gene differ from each other, probably due to different posttranslational modifications.

Controlling deamidation rates in a model peptide: effects of temperature, peptide concentration, and additives.

The rate of deamidation of the Asn residue in Val-Tyr-Pro-Asn-Gly-Ala (VYPNGA), a model peptide, was determined at pH 9 (400 mM Tris buffer) as a function of temperature and peptide concentration. Over the temperature range 5-65 degrees C, deamidation followed Arrhenius behavior, with an apparent activation energy of 13.3 kcal/mol. Furthermore, increasing the peptide concentration slows the rate of deamidation. Self-stabilization with respect to deamidation has not been reported previously. The rate of deamidation was also determined in the presence of sucrose and poloxamer 407 (Pluronic F127). In both cases, the rate of deamidation was retarded by up to 40% at 35 degrees C. In aqueous solutions containing poloxamer 407, the degree of stabilization is independent of formation of a reversible thermosetting gel. With sucrose, maximum reduction in the deamidation rate was attained with as little as 5% (w/v). Addition of sucrose results in a greater conformational preference for a type II beta-turn structure, which presumably is less prone to intramolecular cyclization and subsequent deamidation.

Carcinoembryonic antigen cell adhesion molecule 1 directly associates with cytoskeleton proteins actin and tropomyosin.

CEA cell adhesion molecule 1 (CEACAM1), a type 1 transmembrane and homotypic cell adhesion protein belonging to the carcinoembryonic antigen (CEA) gene family and expressed on epithelial cells, is alternatively spliced to produce four major isoforms with three or four Ig-like ectodomains and either long (CEACAM1-L) or short (CEACAM1-S) cytoplasmic domains. When murine MC38 (methylcholanthrene-induced adenocarcinoma 38) cells were transfected with human CEACAM1-L and stimulated with sodium pervanadate, actin was found to co-localize with CEACAM1-L at cell-cell boundaries but not in untreated cells. When CEACAM1-L was immunoprecipitated from pervanadate-treated MC38/CEACAM1-L cells and the associated proteins were analyzed by two-dimensional gel analysis and mass spectrometry, actin and tropomyosin, among other proteins, were identified. Whereas a glutathione S-transferase (GST) fusion protein containing the l-isoform (GST-Cyto-L) bound poorly to F-actin in a co-sedimentation assay, the S-isoform fusion protein (GST-Cyto-S) co-sedimented with F-actin, especially when incubated with G-actin during polymerization (K(D) = 7.0 microm). Both GST-Cyto-S and GST-Cyto-L fusion proteins bind G-actin and tropomyosin by surface plasmon resonance studies with binding constants of 0.7 x 10(-8) and 1.0 x 10(-7) m for GST-Cyto-L to G-actin and tropomyosin, respectively, and 3.1 x 10(-8) and 1.3 x 10(-7) m for GST-Cyto-S to G-actin and tropomyosin, respectively. Calmodulin or EDTA inhibited binding of the GST-Cyto-L fusion protein to G-actin, whereas calmodulin and G-actin, but not EDTA, stimulated binding to tropomyosin. A biotinylated 14-amino acid peptide derived from the juxtamembrane portion of the cytoplasmic domain of CEACAM1-L associated with both G-actin and tropomyosin with K(D) values of 1.3 x 10(-5) and 1.8 x 10(-5) m, respectively. These studies demonstrate the direct interaction of CEACAM1 isoforms with G-actin and tropomyosin and the direct interaction of CEACAM1-S with F-actin.

Chelators for radioimmunotherapy: I. NMR and ab initio calculation studies on 1,4,7,10-tetra(carboxyethyl)-1,4,7,10-tetraazacyclododecane (DO4Pr) and 1,4,7-tris(carboxymethyl)-10-(carboxyethyl)-1,4,7,10-tetraazacyclododecane (DO3A1Pr).

This work describes the modification of the chelating agent 1,4,7,10-tetraazacyclododecane-N,N',N' ',N' "-tetraacetic acid (DOTA) to improve the rate of metal loading for radioimmunotherapy applications. Previous ab initio calculations predicted that the compounds 1,4,7,10-tetra(carboxyethyl)-1,4,7,10-tetraazacyclododecane (DO4Pr) and 1,4,7-tris(carboxymethyl)-10-(carboxyethyl)-1,4,7,10-tetraazacyclododecane (DO3A1Pr) have a ca. 2000-fold improvement in yttrium metal loading rates compared to those of DOTA (Jang, Y. H.; Blanco, M.; Dasgupta, S.; Keire, D. A.; Shively, J. E.; Goddard, W. A., III. J. Am. Chem. Soc. 1999, 121, 6142-6151). In this study, we report the synthesis, purification, (1)H-NMR chemical shift assignments, pK(a) values, metal loading rate measurements, and additional ab initio calculations of these two compounds. The yttrium loading rates of DO3A1Pr are approximately twice those of DOTA, at pH 4.6 and 37 degrees C. The NMR data indicates that the DO4Pr analogue forms a stable type I complex but does not form a type II complex. The new ab initio calculations performed on DO4Pr and DO3A1Pr indicate that the rate-determining step is the deprotonation of the first macrocycle amine proton, not the second proton as assumed in the previous calculations. The new calculations predict an improvement in the rate of metal loading that more closely matches the experimentally observed change in the rate.

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.

Mammalian expression and hollow fiber bioreactor production of recombinant anti-CEA diabody and minibody for clinical applications.

Genetically engineered radiolabeled antibody fragments have shown great promise for the radioimmunoscintigraphy of cancer. Retaining the exquisite specificity of monoclonal antibodies yet smaller in molecular size, antibody fragments display rapid tumor targeting and blood clearance, a more uniform distribution in the tumor, and present a lower potential to elicit an immune response. However, one of the factors that has limited clinical evaluation of these antibody-derived proteins has been the difficulty in expressing and purifying the quantities necessary for clinical trials. This study outlines the capability of mammalian expression for the production of recombinant antibody fragments intended for clinical use. Two anti-carcinoembryonic antigen antibody fragments, the T84.66/212 Flex minibody (scFv-C(H)3) and the T84.66 diabody (scFv dimer) have been previously expressed and have shown excellent radioimaging properties in tumor bearing animals. To proceed toward human studies, these high affinity recombinant fragments and a second minibody version, the T84.66/GS18 Flex minibody, were expressed using a high-level mammalian expression system. Production of all three antibody fragments in a small-scale hollow fiber bioreactor resulted in 137-307 mg of crude antibody harvest. A purification protocol that employed ceramic hydroxyapatite and anion exchange chromatography resulted in 50-150 mg of purified T84.66 diabody and T84.66 minibody. The development of this level of research grade material established conditions for clinical production as well as provided material to complete pre-clinical studies and undertake protein crystallization studies. Scale-up for clinical studies produced 3.4 g of the T84.66 minibody in the harvest. A portion of this material was purified yielding 180 mg of highly purified T84.66 minibody intended for pilot radioimmunoscintigraphy studies of carcinoembryonic antigen (CEA) positive disease.

Fusion proteins of B7.1 and a carcinoembryonic antigen (CEA)-specific antibody fragment opsonize CEA-expressing tumor cells and coactivate T-cell immunity.

Genetic engineering can be used to generate antigen-specific molecules for improved tumor immunotherapy. We have constructed genes coding for fusion proteins consisting of a high-affinity antibody single-chain antibody fragment (scFv) specific for the human carcinoembryonic antigen (CEA) and the costimulation domain of the murine B7.1 molecule (mB7.1) linked to the antibody moiety by an IgG3 peptide linker. The hybrid genes were constructed in 2 orientations, one with the scFv located N-terminal to mB7.1 and one vice versa. Soluble proteins were expressed by CHO cells, purified using anti-idiotype-affinity chromatography and characterized by tumor-cell binding and costimulation activity. When tumor cells expressing CEA on the cell membrane were opsonized with the CEA-specific costimulators, both fusion proteins specifically stimulated murine T-cell preparations to proliferate in a similar manner. Our data suggest that "costimulation coating" of tumor cells may be a suitable approach for activation of a sustained cellular antitumor response. It also provides the opportunity to increase tumor immunogenicity using easily generated soluble fusion proteins that advantageously link biological functions of both the humoral and the cellular arm of the specific immune system.

Tumor targeting of radiometal labeled anti-CEA recombinant T84.66 diabody and t84.66 minibody: comparison to radioiodinated fragments.

Recombinant antibody fragments offer potential advantages over intact monoclonal antibodies in the radioimmunoscintigraphy (RIS) of solid tumors. Due to their smaller molecular size, antibody fragments have shown rapid tumor targeting and blood clearance, a more uniform tumor distribution and a lower potential to elicit a human immune response. Previously, we have expressed two genetically engineered antibody fragments, the T84.66 diabody (scFv dimer) and the T84.66 minibody (scFv-CH3 dimer), specific to carcinoembryonic antigen (CEA). When radioiodinated, both antibody fragments exhibited rapid tumor targeting and rapid blood clearance in xenografted mice. To extend and optimize their future clinical RIS utility with radiometals, these antibody fragments were conjugated with the macrocycle 1,4,7,10-tetraazacyclododecane N,N',N' ',N' "-tetraacetic acid (DOTA) and labeled with 111In. Tumor targeting and biodistribution studies were carried out in athymic mice xenografted with a human colorectal tumor cell line, LS174T. The [111In]T84.66 diabody (55 kDa) exhibited very rapid tumor targeting with 12.5 +/- 0.4% injected dose per gram (% ID g(-1) +/- standard error) at 2 h and reached a maximum of 13.3 +/- 0.9% ID g(-1) at 6 h. However, kidney uptake was observed to reached a peak of 183.5 +/- 21.0% ID g(-1) at 6 h, a result similar to that reported by others for other low molecular weight fragments labeled with radiometals. Preadministration of an oral dose of D-lysine resulted in a 59% lowering of the renal accumulation at 6 h, but was accompanied by a 31% reduction of tumor uptake to 9.2 +/- 1.2% ID g(-1). The second recombinant antibody fragment, the [111In]T84.66 minibody (80 kDa), displayed rapid tumor targeting of 14.2 +/- 6.1% ID g(-1) at 2 h, and reached a maximum activity of 24.5 +/- 6.1% ID g(-1) by 12 h. Renal uptake achieved a plateau of 12-13% ID g(-1) which cleared to 7.2% ID g(-1) at 72 h. However, hepatic uptake was elevated and reached a maximum of 26.0 +/- 1.0% ID g(-1) at 12 h in these xenograft-bearing mice. Experiments in nontumor bearing mice showed a reduction of hepatic activity at 12 h to 16.6 +/- 1.5% ID g(-1), indicative of an intrinsic hepatic accumulation of the [111In]DOTA-T84.66 minibody or metabolites. While the anti-CEA [111In]DOTA-T84.66 diabody and T84.66 minibody retain the rapid tumor targeting properties of the radioiodinated form, the normal organ accumulation (kidneys and liver, respectively) of the [111In]DOTA forms appeared problematic for RIS and RIT applications. Development of alternative blocking strategies or new metabolizable chelates are under investigation to enhance the utility of the radiometal form of these and other promising recombinant antibody fragments.

An improved method for conjugating monoclonal antibodies with N-hydroxysulfosuccinimidyl DOTA.

A simple, water-soluble procedure for conjugation of monoclonal antibodies to 1,4,7,10-tetraazacyclododecane-N,N',N",N"'-tetraacetic acid (DOTA) has been improved by optimizing pH, buffer, and temperature conditions for the preparation of N-hydroxysulfosuccinimidyl DOTA and its conjugation to the human/murine chimeric anti-carcinoembryonic antigen antibody cT84.66. This improved method results in a 6-fold increase in conjugation efficiency, a 3-7-fold decrease in antibody cross-linking, a more homogeneous population of conjugate species, and a 5-fold decrease in the quantities of reagents needed for conjugation. The cT84.66-DOTA conjugate was labeled to high specific activity with 111In, 90Y, 88Y, 64Cu, and 67Cu, affording near-quantitative incorporation of the majority of these radiometals. This improved conjugation procedure facilitates large-scale production and radiometal labeling of cT84.66-DOTA for clinical radioimmunotherapy trials.

Metabolism and renal clearance of 111In-labeled DOTA-conjugated antibody fragments.

Radiometal-labeled antibody fragments are promising reagents for radioimmunotherapy due to their high tumor uptake and rapid pharmacokinetics, but their therapeutic potentials are limited by high uptake and retention in the kidney. Identification of metabolic products is a first step in designing rationale approaches to lower kidney uptake. Previous studies in rats have shown that 111In-labeled DTPA-conjugated antibody fragments (via lysine residues) were degraded to an DTPA-epsilon-amino-lysine derivative and retained in the lysosomal compartments of the liver and kidney [Rogers et al. (1995) Cancer Res. 55, 5714s-5720s]. To determine the metabolic profile of another widely used metal-chelate, [111In]DOTA conjugated to lysines in antibody fragments via active ester chemistry, we analyzed kidney homogenates from nude mice injected with an [111In]DOTA-Fab generated enzymatically from the anti-lymphoma intact antibody Rituxan. The major kidney metabolite was identified as [111In]DOTA-epsilon-amino-lysine by comparison to an authentic synthetic standard. This end product was also identified in the urine, along with relatively small amounts of [111In]DOTA-Fab. Since injection of [111In]DOTA-epsilon-amino-lysine into nude mice resulted in rapid clearance into the urine without kidney retention, it is likely that the renal retention observed was due to kidney uptake of [111In]DOTA-Fab, followed by lysosomal degradation to [111In]DOTA-epsilon-amino-lysine, which is only slowly cleared from this compartment. This observation is supported by autoradiographs of the kidney showing rapid localization of radioactivity into the distal regions of the kidney cortex. To extend this analysis to clinical trials, we have also analyzed urine taken from a patient injected with the intact antibody [111In]DOTA-cT84.66. In that example, we found that the major radioactive species was also [111In]DOTA-epsilon-amino-lysine.

Numerical selection of optimal tumor imaging agents with application to engineered antibodies.

Three analytic indicators were used to compare five members of a monoclonal antibody (Mab) family. The cognates consisted of the genetically engineered intact chimeric IgGI (cT84.66) and related engineered fragments [scFv, diabody, minibody, F(ab')2] reactive against the same epitope of carcinoembryonic antigen (CEA). All analyses were based on radioiodinated Mabs targeting to colorectal xenografts of LS174T tumors in nude mice. Affinity constants were evaluated initially. A second indicator was the imaging figure of merit (IFOM) which determines how rapidly a statistically significant tumor image can be acquired. Finally, deconvolution was used to determine tumor temporal response to an arterial bolus. This last analysis gave the possible tumor accumulation in the absence of normal tissue sequestration. Affinities were all in excess of 10(8) M-1 and were highest for the divalent Mabs. Using the IFOM criterion, an 131I label was best suited as a radiolabel for the intact (IgG) T84.66, while an 123I label indicated optimal imaging with either minibody or F(ab')2. Deconvolution analyses showed that divalent members behaved similarly while the univalent member (scFv) had a tumor residence time smaller by an order of magnitude. The diabody had the largest impulse response function, but renal uptake may limit its present usefulness.

A phase I radioimmunotherapy trial evaluating 90yttrium-labeled anti-carcinoembryonic antigen (CEA) chimeric T84.66 in patients with metastatic CEA-producing malignancies.

Chimeric T84.66 (cT84.66) is a genetically engineered human/murine chimeric IgG, with high affinity and specificity to carcinoembryonic antigen (CEA). The purpose of this Phase I dose escalation therapy trial was to evaluate the toxicities, biodistribution, pharmacokinetics, tumor targeting, immunogenicity, and organ and tumor absorbed dose estimates of cT84.66 labeled with 90Y. Patients with metastatic CEA-producing malignancies were first administered 5 mCi 111In-labeled DTPA-cT84.66 (5 mg), followed by administration of the therapy dose of 90Y-labeled DTPA-cT84.66 1 week later. The therapy infusion was immediately followed by a 72-h administration of DTPA at 250 mg/m2/24 h. Dose levels of administered activity ranged from 5 to 22 mCi/m2 with three to six patients per level. Serial nuclear scans, blood samples, and 24-h urine collections were performed out to 5 days after infusion. Human antichimeric antibody response was assayed out to 6 months. Patients were administered up to 3 cycles of therapy every 6 weeks. Radiation absorbed doses to organs were estimated using a five compartment model and MIRDOSE3. Twenty-two patients received at least one cycle of therapy, with one individual receiving two cycles and two receiving three cycles of therapy. All were heavily pretreated and had progressive disease prior to entry in this trial. Reversible leukopenia and thrombocytopenia were the primary dose-limiting toxicities observed. Maximum tolerated dose was reached at 22 mCi/ m2. In general, patients with liver metastases demonstrated more rapid blood clearance of the antibody. Thirteen patients developed an immune response to the antibody. Average radiation doses to marrow, liver, and whole body were 2.6, 29, and 1.9 cGy/mCi 90Y, respectively. Dose estimates to tumor ranged from 66 to 1670 cGy (8.7 to 52.2 cGy/mCi 90Y) for each cycle of therapy delivered. Although no major responses were observed, three patients demonstrated stable disease of 12-28 weeks duration and two demonstrated a mixed response. In addition, a 41-100% reduction in tumor size was observed with five tumor lesions. 90Y-labeled cT84.66 was well tolerated, with reversible thrombocytopenia and leukopenia being dose limiting. Patients with extensive hepatic involvement by tumor demonstrated unfavorable biodistribution for therapy with rapid blood clearance and poor tumor targeting. Average tumor doses when compared with red marrow doses indicated a favorable therapeutic ratio. Stable disease and mixed responses were observed in this heavily pretreated population with progressive disease. This trial represents an important step toward further improving the therapeutic potential of this agent through refinements in the characteristics of the antibody and the treatment strategies used. Future trials will focus on the use of peripheral stem cell support to allow for higher administered activities and the use of combined modality strategies with radiation-enhancing chemotherapy drugs. Further efforts to reduce immunogenicity through humanization of the antibody are also planned. Finally, novel engineered, lower molecular weight, faster clearing constructs derived from cT84.66 continue to be evaluated in preclinical models as potential agents for radioimmunotherapy.

Targeting and therapy of carcinoembryonic antigen-expressing tumors in transgenic mice with an antibody-interleukin 2 fusion protein.

The purpose of this study was to engineer a bivalent single-chain anticarcinoembryonic antigen (CEA) antibody and an interleukin 2 (IL-2) fusion protein derivative for selective tumor targeting of cytokines. The variable domains of a high affinity anti-CEA antibody, T84.66, were used to form a single-gene-encoded antibody [single-chain variable fragment joined to the crystallizable fragment, Fc (scFvFc)]. The fusion protein (scFvFc.IL-2) consisted of mouse IL-2-fused to the COOH-terminal end of the scFvFc. The engineered proteins were assembled as complete molecules and were similar to the intact anti-CEA monoclonal antibody (Mab) in antigen-binding properties. Based on IL-2 content of the fusion protein, its ability to support proliferation of CTLL-2 cells was identical with that of IL-2. Despite a molecular size similar to that of the intact Mab, the blood clearance of the fusion protein was markedly faster than that of the intact Mab or scFvFc. Incubation of radiolabeled scFvFc.IL-2 but not the intact or scFvFc antibodies in mouse serum was accompanied by the appearance of complexes, suggesting that the latter may contribute to the accelerated clearance of the fusion protein. Biodistribution and tumor targeting studies were carried out in CEA-transgenic mice bearing CEA-positive murine tumors as well as the antigen-negative parental tumor. The bivalent anti-CEA scFvFc had tumor localization properties similar to those of the intact Mab. Although fusion of IL-2 to the COOH-terminal end of the bivalent scFvFc altered its pharmacokinetic properties, the fusion antibody was able to target tumors specifically. Maximum uptake of the intact Mab, scFvFc, and scFvFc.IL-2 in CEA-positive tumors was 29.3 +/- 5.0, 19.5 +/- 2.1, and 6.6 +/- 0.9% injected dose/g, respectively. Maximum tumor localization ratios (CEA-positive/CEA-negative tumor) were similar for all three antibody types (4.6-6.0), demonstrating the antigen specificity of the tumor targeting. Significant antigen-specific targeting to CEA-positive normal tissues of transgenic mice was not observed. Although the tumor-targeting properties of the fusion protein were low, the growth of CEA-expressing (P = 0.01) but not antigen-irrelevant (P = 0.22) syngeneic tumor cells was inhibited after treatment of transgenic mice with the anti-CEA-IL-2 antibody. Therapy of CEA-expressing tumors was improved after i.v. administration of the fusion protein (P = 0.0001). These studies indicate that anti-CEA antibody-directed cytokine targeting may offer an effective treatment for CEA-expressing carcinomas. The availability of an immunocompetent CEA transgenic mouse model will also help to determine the immunotherapeutic properties of these fusion proteins.

High-resolution microPET imaging of carcinoembryonic antigen-positive xenografts by using a copper-64-labeled engineered antibody fragment.

Rapid imaging by antitumor antibodies has been limited by the prolonged targeting kinetics and clearance of labeled whole antibodies. Genetically engineered fragments with rapid access and high retention in tumor tissue combined with rapid blood clearance are suitable for labeling with short-lived radionuclides, including positron-emitting isotopes for positron-emission tomography (PET). An engineered fragment was developed from the high-affinity anticarcinoembryonic antigen (CEA) monoclonal antibody T84.66. This single-chain variable fragment (Fv)-C(H)3, or minibody, was produced as a bivalent 80 kDa dimer. The macrocyclic chelating agent 1,4,7, 10-tetraazacyclododecane-N,N',N", N"'-tetraacetic acid (DOTA) was conjugated to the anti-CEA minibody for labeling with copper-64, a positron-emitting radionuclide (t(1/2) = 12.7 h). In vivo distribution was evaluated in athymic mice bearing paired LS174T human colon carcinoma (CEA positive) and C6 rat glioma (CEA negative) xenografts. Five hours after injection with (64)Cu-DOTA-minibody, microPET imaging showed high uptake in CEA-positive tumor (17.9% injected dose per gram +/- 3.79) compared with control tumor (6.0% injected dose per gram +/- 1.0). In addition, significant uptake was seen in liver, with low uptake in other tissues. Average target/background ratios relative to neighboring tissue were 3-4:1. Engineered antibody fragments labeled with positron-emitting isotopes such as copper-64 provide a new class of agents for PET imaging of tumors.

The chemistry of protein sequence analysis.

N-terminal sequence analysis by Edman chemistry continues to play an important role in the structural analysis of proteins and peptides. Improvements in the sensitivity of the method have been achieved mainly at the level of increasing the sensitivity of the on-line analysis of PTH amino acids by RP-HPLC (reverse phase high performance chromatography). Using microbore columns (0.8-1.0 mm), it is possible to run standards at the 0.5-1.0 pmol level and to sequence samples in the 1-5 pmol range. Due to constraints in current chromatographic methods, it is unlikely that further improvements in sensitivity will be achieved by this approach alone. Although alternative Edman reagents, including fluorescent chemistries, have promised to increase the sensitivity of sequencing into the low femtomole range, none of the methods have progressed into routine usage. These reagents and chemistries are critically evaluated in this review, and the problems which have prevented their further development discussed. Instrumental constraints are also considered. It is concluded that the development of more sensitive methods requires further research into both the chemistry and the instrumentation, and that alternative separation and detection methods may also play a role.

Biodistribution and radioimmunotherapy of human breast cancer xenografts with radiometal-labeled DOTA conjugated anti-HER2/neu antibody 4D5.

HER2/neu oncogene encodes a 185 kDa trans-membrane protein which is overexpressed in 20-30% of breast and ovarian cancers and portends a poor prognosis. We have studied the targeting and therapy of this oncoprotein with 4D5, a murine monoclonal antibody which recognizes a distinct epitope on the extracelluar domain of HER2/neu. We conjugated the antibody with an active ester of the macrocyclic chelating agent DOTA, radiolabeled the conjugate with either (111)In or (90)Y, and studied the antibody distribution and therapy, respectively, in athymic mice bearing xenografts of MCF7/HER2/neu, a human breast cancer cell line transfected with the HER2/neu oncogene. For the biodistribution of (111)In-labeled DOTA-4D5, a high specificity of tumor localization (30% ID/g) was seen with a tumor-to-blood ratio of greater than 2 at 48 h postinjection. Compared to a previously published study with (125)I-labeled 4D5 in beige nude mice bearing NIH3T3/HER2/neu xenografts [De Santes et al. (1992) Cancer Res. 52, 1916-1923], (111)In-labeled 4D5 antibody gave superior antibody uptake in tumor (30% ID/g vs 17% ID/g at 48h). In the therapy study, treatment of the nude mice bearing MCF7/HER2/neu xenografts with 100 microCi (3 microg) of (90)Y-labeled DOTA-4D5 caused a 3-fold reduction of tumor growth compared to untreated controls (injected with human serum albumin) in 40 days. Treatment of animals with 100 microCi of nonspecific antibody (90)Y-labeled DOTA-Leu16 (3 microg) had no tumor growth inhibition. Treatment with unlabeled DOTA-4D5 (3 microg) had a slight effect on tumor growth compared to untreated controls. When analyzed at the level of single animals, no effect was seen in seven of nine animals; however, in two of the animals, tumor growth inhibition was observed. Although a cold antibody therapeutic effect was unexpected at this dose level (3 microg), it may be possible that in some animals that 3 microg of antibody of (90)Y-labeled DOTA-4D5 augmented tumor growth reduction. To further explore the effects of cold antibody treatment alone, animals were treated with 100 or 400 microg of unlabeled 4D5 administered in two doses. These animals showed a 1.7-1.8-fold reduction in tumor growth over 28 days, a result less than that obtained with RIT only.

Evaluating changes in stable chromosomal translocation frequency in patients receiving radioimmunotherapy.

PURPOSE: The lack of any consistent correlation between radioimmunotherapy (RIT) dose and observed hematologic toxicity has made it difficult to validate RIT radiation dose estimates to marrow. Stable chromosomal translocations (SCT) which result after radiation exposure may be a biologic parameter that more closely correlates with RIT radiation dose. Increases in the frequency of SCT are observed after radiation exposure and are highly correlated with absorbed radiation dose. SCT are cumulative after multiple radiation doses and conserved through an extended number of cell divisions. The purpose of this study was to evaluate whether increases in SCT frequency were detectable in peripheral lymphocytes after RIT and whether the magnitude of these increases correlated with estimated radiation dose to marrow and whole body. METHODS AND MATERIALS: Patients entered in a Phase I dose escalation therapy trial each received 1-3 intravenous cycles of the radiolabeled anti- carcinoembryonic antigen (CEA) monoclonal antibody, 90Y-chimeric T84.66. Five mCi of 111In-chimeric T84.66 was co-administered for imaging and biodistribution purposes. Blood samples were collected immediately prior to the start of therapy and 5-6 weeks after each therapy cycle. Peripheral lymphocytes were harvested after 72 hours of phytohemagglutinin stimulation and metaphase spreads prepared. Spreads were then stained by fluorescence in situ hybridization (FISH) using commercially available chromosome paint probes to chromosomes 3 and 4. Approximately 1000 spreads were evaluated for each chromosome sample. Red marrow radiation doses were estimated using the AAPM algorithm and blood clearance curves. RESULTS: Eighteen patients were studied, each receiving at least one cycle of therapy ranging from 5-22 mCi/m2. Three patients received 2 cycles and two patients received 3 cycles of therapy. Cumulative estimated marrow doses ranged from 9.2 to 310 cGy. Increases in SCT frequencies were observed after each cycle for both chromosomes 3 and 4 in 16 of 18 patients and in at least one chromosome for the remaining 2 patients. Cumulative increases in SCT frequencies ranged from 0.001 to 0.046 with no major differences observed between chromosomes 3 and 4. A linear correlation between cumulative marrow dose and increases in SCT frequencies was observed for chromosome 3 (R2 = 0.63) and chromosome 4 (R2 = 0.80). A linear correlation was also observed between increases in SCT frequency and whole body radiation dose or administered activity (R2 = 0.67-0.89). There was less correlation between observed decrease in wbc or platelet counts and marrow dose, whole body dose, or administered activity (R2 = 0.28-0.43). CONCLUSIONS: Increases in SCT frequency were detectable in peripheral lymphocytes after low dose-rate RIT irradiation. A linear correlation was observed between increases in SCT and marrow dose, whole body dose, and administered activity. This correlation provides one of the strongest radiation dose-response and activity-response relationships observed with RIT. The detection of SCT may therefore have application as an in situ integrating biodosimeter after RIT. This biologic parameter should prove useful in comparing effects on marrow for different therapeutic radionuclides and in comparing effects of RIT and external beam radiation doses on a cGy per cGy basis. As a result, this should allow for a more direct comparison between different methods of irradiation and in further refinement of radioimmunotherapy dose estimates and dosimetry methodology.

Production of carcinoembryonic antigen (CEA) N-A3 domain in Pichia pastoris by fermentation.

Carcinoembryonic antigen (CEA) is a 180-kDa glycoprotein found on the surface of normal colon and malignant human adenocarcinomas. Recently, a fusion protein containing two of the seven Ig-like domains present in CEA (N and A3) has been constructed and expressed in Pichia pastoris [You, Hefta, Yazaki, Wu and Shively (1998) Anticancer Res. 18, 3193-3201]. Here, we report the generation and selection of a multi-copy clone expressing this fusion protein, the optimization of the shake-flask expression protocol and the upscaled production of CEA N-A3 using fermentation technology. P. pastoris transformants secreting the CEA N-A3 domain were generated by electrotransformation of the GS115 host strain with the pPIC9K vector containing the CEA N-A3 cDNA [You, Hefta, Yazaki, Wu and Shively (1998) Anticancer Res. 18, 3193-3201] then screened for CEA N-A3 expression and G418 resistance. The recombinant CEA N-A3 domain was detected in the culture supernatant using the monoclonal anti-CEA antibody T84.66. Optimization of methanol-induction conditions resulted in a high-methanol shake-flask expression protocol yielding significantly increased CEA N-A3 levels. Fermentation and culture conditions were optimized for 5-l working-volume fermentations and CEA N-A3 was affinity purified using Ni-IDA (imino di-acetic acid) affinity chromatography from the clarified fermentation supernatant. Peptide N-glycosidase F treatment revealed that the recombinant protein was heavily glycosylated but expressed as a single polypeptide of 28 kDa with no evidence of proteolytic degradation. Our results demonstrate that functional CEA N-A3 domain can be produced in sufficient quantities in P. pastoris for structural analysis or diagnostic applications. To our knowledge, this article represents the first report on the production of a human tumour antigen through fermentation.