Production and characterization of a mouse/human chimeric antibody directed against human neuroblastoma

Characterization of a novel T cell-engaging bispecific antibody for elimination of L1CAM-positive tumors

Neural cell adhesion molecule L1 (L1CAM) is a cell-surface glycoprotein involved in cancer occurrence and migration. Up to today, L1CAM-targeted therapy appeared limited efficacy in clinical trials although quite a few attempts by monoclonal antibody (mAb) or chimeric antigen receptor T-cell therapy (CAR-T) have been reported. Therefore, the development of new effective therapies targeting L1CAM is highly desirable. It has been demonstrated that T cell-engaging bispecific antibody (TCE) plays an effective role in cancer immunotherapy by redirecting the cytotoxic activity of CD3+ T cells to tumor cells, resulting in tumor cell death. In this study, we designed and characterized a novel bispecific antibody (CE7-TCE) based on the IgG-(L)-ScFv format, which targets L1CAM and CD3 simultaneously. In vitro, CE7-TCE induced specific killing of L1CAM-positive tumor cells through T cells. In vivo, CE7-TCE inhibited tumor growth in human peripheral blood mononuclear cell/tumor cell co-grafting models. To overcome the adaptive immune resistance (AIR) that impairs the efficacy of TCEs, we conducted a combination therapy of CE7-TCE with Pembrolizumab (anti-PD1 mAb), which enhanced the anti-tumor activity of CE7-TCE. Our results confirmed the feasibility of using L1CAM as a TCE target for the treatment of solid tumors and revealed the therapeutic potential of CE7-TCE combined with immune checkpoint inhibitors.

The affinity of antigen-binding domain on the antitumor efficacy of CAR T cells: Moderate is better

The overall efficacy of chimeric antigen receptor modified T cells (CARTs) remain limited in solid tumors despite intensive studies that aim at targeting multiple antigens, enhancing migration, reducing tonic signaling, and improving tumor microenvironment. On the other hand, how the affinity and engaging kinetics of antigen-binding domain (ABD) affects the CART's efficacy has not been carefully investigated. In this article, we first analyzed 38 published solid tumor CART trials and correlated the response rate to their ABD affinity. Not surprisingly, majority (25 trials) of the CARTs utilized high-affinity ABDs, but generated merely 5.7% response rate. In contrast, 35% of the patients treated with the CARTs built from moderate-affinity ABDs had clinical responses. Thus, CARTs with moderate-affinity ABDs not only have less off-target toxicity, but also are more effective. We then reviewed the effects of ABD affinity on the biology and function of CARTs, providing further evidence that moderate-affinity ABDs may be better in CART development. In the end, we propose that a fast-on/fast-off (high Kon and Koff ) kinetics of CART-target engagement in solid tumor allow CARTs to generate sufficient signaling to kill tumor cells without being driven to exhaustion. We believe that studying the ABD affinity and the kinetics of CART-tumor interaction may hold a key to designing effective CARTs for solid tumors.

Neuroblastoma Origin and Therapeutic Targets for Immunotherapy

Neuroblastoma is a pediatric solid cancer of heterogeneous clinical behavior. The unique features of this type of cancer frequently hamper the process of determining clinical presentation and predicting therapy effectiveness. The tumor can spontaneously regress without treatment or actively develop and give rise to metastases despite aggressive multimodal therapy. In recent years, immunotherapy has become one of the most promising approaches to the treatment of neuroblastoma. Still, only one drug for targeted immunotherapy of neuroblastoma, chimeric monoclonal GD2-specific antibodies, is used in the clinic today, and its application has significant limitations. In this regard, the development of effective and safe GD2-targeted immunotherapies and analysis of other potential molecular targets for the treatment of neuroblastoma represents an important and topical task. The review summarizes biological characteristics of the origin and development of neuroblastoma and outlines molecular markers of neuroblastoma and modern immunotherapy approaches directed towards these markers.

The soluble form of the cancer-associated L1 cell adhesion molecule is a pro-angiogenic factor

A soluble form of the L1 cell adhesion molecule (sL1) is released from various tumor cells and can be found in serum and ascites fluid of uterine and ovarian carcinoma patients. sL1 is a ligand for several Arg-Gly-Asp (RGD)-binding integrins and can be deposited in the extracellular matrix. In this study we describe a novel function of this physiologically relevant form of L1 as a pro-angiogenic factor. We demonstrated that the anti-L1 monoclonal antibody (mAb) chCE7 binds near or to the sixth Ig-like domain of human L1 which contains a single RGD sequence. mAb chCE7 inhibited the RGD-dependent adhesion of ovarian carcinoma cells to sL1 and reversed the sL1-induced proliferation, matrigel invasion and tube formation of bovine aortic endothelial (BAE) cells. A combination of sL1 with vascular endothelial growth factor-A (VEGF-A(165)), which is an important angiogenic inducer in tumors, strongly potentiated VEGF receptor-2 tyrosine phosphorylation in BAE cells. Chick chorioallantoic membrane (CAM) assays revealed the pro-angiogenic potency of sL1 in vivo which could be abolished by chCE7. These results indicate an important role of released L1 in tumor angiogenesis and represent a novel function of antibody chCE7 in tumor therapy.

The L1 cell adhesion molecule as a target for radioimmunotherapy

Monoclonal antibodies directed against the L1 cell adhesion molecule were shown recently to inhibit growth of target tumor cells in vitro and the growth of tumor cells in vivo in nude mice. The biologic functions of L1 in tumor cells, which include growth-promoting activity linked to endocytosis and cellular processing of the L1 cell surface protein, make this protein an attractive target for antibodies. This update deals with recent results on L1 expression in normal tissues and in the tumors that were investigated until now. L1 expression outside of the nervous system is highly restricted to peripheral nerve bundles and kidney-collecting tubule cells. In tumors, L1 overexpression is not ubiquitous. It is prevalent in neuroblastomas and in malignant ovarian tumors, and is also found in certain subtypes of other nonneuroendocrine and nongynecologic tumors, such as renal-cell carcinomas. The structure of the L1 protein and what is known about its functional role in tumors will be described in this paper. L1 is not only a novel tumor marker, but it appears to have growth-promoting and antiapoptotic functions and may contribute to a more malignant phenotype. The preclinical studies and the clinical study to evaluate tumor-targeting properties and potential for therapy of radiolabeled anti-L1 antibodies will be described to date. Some of these studies underline the importance of L1 endocytosis for the targeting of radiolabeled antibodies.

Hepatocyte growth factor-induced ectodomain shedding of cell adhesion molecule L1: role of the L1 cytoplasmic domain

The L1 cell adhesion molecule and its soluble form are tumor-associated proteins and potential markers for tumor staging as well as targets for therapeutic intervention. Soluble L1 is produced by metalloprotease-mediated ectodomain shedding of L1. We investigated effects of hepatocyte growth factor (HGF), a growth factor shown to increase invasiveness of renal carcinoma cells, on ectodomain shedding of L1 from these cells. All of the tested L1-positive renal carcinoma cell lines released a 180-kDa form of L1 into the medium. In the presence of serum, addition of HGF led to a dose-dependent increase in L1 shedding with a maximum reached at 5 ng/ml. In contrast, L1 shedding was inhibited by glial cell line-derived neurotrophic factor (GDNF). The tyrosine kinase inhibitor Genistein reduced basal and HGF-stimulated L1 shedding, indicating that protein phosphorylation is involved. To investigate the role of the L1 intracellular domain, two mutants of the L1 cytoplasmic part were constructed. L1trun lacking the complete intracellular domain showed enhanced basal shedding. In a L1YH mutant, containing the mutation tyrosine 1229 to histidine that deletes the ankyrin binding motif of L1, basal shedding was reduced. Disruption of actin assembly by cytochalasin D also reduced shedding of L1. These results indicate that the cytoplasmic domain regulates basal shedding of L1, and association with the cytoskeleton through the L1 ankyrin binding site is involved. HGF stimulated L1 shedding in both mutants, indicating that receptor-mediated phosphorylation in the L1 cytoplasmic domain is not required for HGF-stimulated shedding.

Targeting of renal carcinoma with 67/64Cu-labeled anti-L1-CAM antibody chCE7: selection of copper ligands and PET imaging

In order to optimize radiocopper labeling of anti-L1-CAM antibody chCE7, five bifunctional copper chelators were synthesized and characterized (CPTA-N-hydoxysuccinimide, DO3A-L-p-isothiocyanato-phenylalanine, DOTA-PA-L-p-isocyanato-phenylalanine, DOTA-glycyl-L-p-isocyanato-phenylalanine and DOTA-triglycyl-L-p-isocyanato-phenylalanine). Substitution with more than 11 chelators per antibody molecule was found to influence immunoreactivity and biodistributions of (67)Cu-MAb chCE7 significantly. CPTA-labeled antibody achieved the best tumor to normal tissue ratios when biodistributions of the different (67)Cu-chCE7 conjugates were assessed in tumor-bearing mice. High resolution PET imaging with (64)Cu-CPTA-labeled MAb chCE7 showed uptake in lymph nodes and heterogeneous distribution in tumor xenografts.

Monoclonal antibody-based therapy for neuroblastoma

Dose-intensive combination chemotherapy can improve the clinical response of many pediatric solid tumors. However, cure remains elusive. Stage 4 neuroblastoma stands out as an exception. Part of this success is a result of antibody-based strategies, which include immunomagnetic purging of autologous marrow prior to autologous marrow transplantation and immunotherapy directed at minimal residual disease. It is striking that treatment with monoclonal antibodies, even when targeted at a single antigen, namely, ganglioside G(D2), can affect long-term progression-free survival among these patients. The potential role of the idiotype network in tumor control can be exploited clinically. The genetic engineering of these antibodies into novel forms holds great promise for more specific and effective targeting possibilities, including the delivery of cytokines and cells. Preclinical results are also promising. It is expected that the availability of novel antibodies directed at a broader spectrum of pediatric solid tumors will facilitate the successful application of this approach to more patients. Experience with metastatic neuroblastoma has provided proof of this principle. It is likely that other tumors will fall.

A triglycine linker improves tumor uptake and biodistributions of 67-Cu-labeled anti-neuroblastoma MAb chCE7 F(ab')2 fragments

The peptide-linked copper chelators CPTA-triglycyl-L-p-isothiocyanato-phenylalanine (CPTA-R1-NCS) as well as DOTA-triglycyl-L-p-isocyanato-phenylalanine (DOTA-R1-NCS) were synthesized and coupled to F(ab')2 fragments of the anti-neuroblastoma monoclonal antibody (MAb) chCE7. 67Cu-labeled conjugates were compared with the original CPTA- and DO3A-F(ab')2 in vitro and in vivo in mice bearing neuroblastoma xenografts. With the CPTA-R1-F(ab')2, biodistributions were improved, because radioactivity present in the kidney was reduced. With the DOTA-R1-F(ab')2, clearance from the blood was slower and tumor uptake was higher compared with the other conjugates. DOTA-R1-F(ab')2 achieved the best tumor/tissue ratios.

Anti-neuroblastoma antibody chCE7 binds to an isoform of L1-CAM present in renal carcinoma cells

Immunoprecipitation after cell surface labeling of human neuroblastoma cells showed that the anti-neuroblastoma monoclonal antibody (mAb) chCE7 binds to a 200,000 M(r) cell surface protein. The protein was partially purified by immuno-affinity chromatography from a human renal carcinoma and a human neuroblastoma cell line, which both showed high levels of binding of MAb chCE7. NH(2)-terminal sequences of 18 and 15 amino acid residues were determined. Both sequences isolated from the renal carcinoma and the neuroblastoma cells showed strong homology to human cell adhesion molecule L1 (L1-CAM), and both were characterized by the NH(2)-terminal deletion of 5 amino acids, comprising exon 2 of L1-CAM. Reverse trancription-polymerase chain reaction (RT-PCR) analysis of the regions spanning exon 2 and exon 27 of L1-CAM indicated that in neuroblastoma cells both transcripts for the full-length and exon-deleted forms are present, whereas in the renal carcinoma cell lines only the exon-deleted L1-CAM isoform were detected. Western blot analysis showed that 6 of 7 tested renal carcinoma cell lines and 5 of 15 renal carcinoma tissues expressed L1-CAM. In normal adult kidney tissue, very low levels of protein expression were found. Northern blot analysis confirmed that in renal carcinoma and neuroblastoma cell lines L1-CAM mRNA levels are correlated with protein expression.

Engineered glycoforms of an antineuroblastoma IgG1 with optimized antibody-dependent cellular cytotoxic activity

The glycosylation pattern of chCE7, an antineuroblastoma chimeric IgG1, was engineered in Chinese hamster ovary cells with tetracycline-regulated expression of beta(1,4)-N-acetylglucosaminyltransferase III (GnTIII), a glycosyltransferase catalyzing formation of bisected oligosaccharides that have been implicated in antibody-dependent cellular cytotoxicity (ADCC). Measurement of the ADCC activity of chCE7 produced at different tetracycline levels showed an optimal range of GnTIII expression for maximal chCE7 in vitro ADCC activity, and this activity correlated with the level of constant region-associated, bisected complex oligosaccharides determined by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The new optimized variants of chCE7 exhibit substantial ADCC activity and, hence, may be useful for treatment of neuroblastoma. The strategy presented here should be applicable to optimize the ADCC activity of other therapeutic IgGs.

Evaluation of radioiodinated and radiocopper labeled monovalent fragments of monoclonal antibody chCE7 for targeting of neuroblastoma

Monovalent fragments of antineuroblastoma antibody mAb chCE7 were evaluated for their in vitro and in vivo tumor cell binding properties. Single chain fragments were constructed from the variable region genes cloned from hybridoma cells, expressed in E.coli and purified by metal chelate affinity chromatography. Radioiodinated CE7-scFv fragments were found to bind with high affinity (Kd approximately 10(-9) M) to target cells in vitro but formed aggregates at 37 degrees C, and bound to serum proteins in vitro and in vivo. Circular Dichroism spectra revealed the protein to be in a conformationally altered form and no permanent "refolding" could be achieved. In contrast, chCE7- Fab fragments were found to bind to target tumor cells with similar affinity than the parent mAb chCE7 (Kd approximately 10(-10) M), showed no tendency to aggregate and were stable in serum both in vitro and in vivo. Kinetics of association and dissociation of radioiodinated scFv and Fab fragments were found to be rapid. Radioiodination with the Iodogen method led to impaired immunoreactivity which was found to further increase the off- rates of radioiodinated fragments from tumor cells. Radioiodination with the Bolton-Hunter reagent as well as labeling of chCE7-Fab fragments with 67Cu via the macrocyclic CPTA ligand led to fully immunoreactive Fab fragments. Radioiodinated and radiocopper labeled monovalent CE7 fragments did not internalize into target tumor cells as the parent mAb and its F(ab')2 fragment. A comparison of the biodistribution in tumor bearing nude mice of the radiocopper labeled monovalent, non internalizing Fab fragments with the internalizing divalent F(ab')2 fragments showed in both cases high levels of radioactivity in the kidneys. Concerning tumor uptake, radioactivity from both internalizing and non internalizing fragments remained associated with tumor tissue for longer times than in case of the corresponding radioiodinated fragments. When compared with the radioiodinated forms, tumor uptake of radiocopper-labeled 67Cu-chCE7 and its F(ab')2 fragments was found to be higher. However in the case of the non internalizing 67Cu-chCE7-Fab fragment no increase in the absolute amount of radioactivity in tumor tissue compared with the radioiodinated Fab was observed, indicating an advantage of using radiocopper labeling in conjunction with internalizing antibody fragments for delivering high doses of radioactivity to neuroblastoma.

Characterization and biodistribution of a mouse/human chimeric antibody directed against pancreatic cancer mucin

BACKGROUND

Nd2 is a murine monoclonal antibody (MoAb) directed against purified mucins of the human pancreatic cancer cell line SW1990. The authors previously reported promising results with Nd2 for immunotargeting pancreatic cancer. However, murine MoAbs induce human anti-mouse antibodies (HAMAs), a serious problem for clinical use. Mouse/human chimeric antibodies may be less immunogenic and therefore reduce the incidence of HAMAs. In this study, the binding affinity, tumor specificity, biodistribution, and immunoimaging of chimeric Nd2 were evaluated.

METHODS

The affinity of chimeric Nd2 was evaluated by competition radioimmunoassay and Scatchard analysis using 125I-chimeric Nd2, 125I-murine Nd2, and SW1990 mucin. Immunoreactivity against pancreatic cancer tissues was examined histochemically by the avidin-biotin peroxidase complex method. The biodistribution of the MoAbs was examined in athymic nude mice bearing SW1990 xenografts that were administered intravenous 125I-labeled chimeric or murine Nd2. 111In-chimeric Nd2 was injected into the same xenograft models, and scintigrams were obtained on day 3.

RESULTS

Affinity analysis and immunohistochemical studies showed that chimeric Nd2 had the same affinity to SW1990 mucin and the same specificity for pancreas cancer tissues as murine Nd2. Intravenous administration of 125I-chimeric Nd2 resulted in a maximum tumor accumulation of 43% of the initial dose/gram of tumor, which was almost identical to the accumulation of 125I-murine Nd2. Distinct immunoscintigrams of tumors in nude mice were obtained with 111In-chimeric Nd2.

CONCLUSION

Chimeric Nd2 may have clinical potential in the radioimmunodetection and immunotherapy of pancreatic cancer.

Internalization and degradation of monoclonal antibody chCE7 by human neuroblastoma cells

Internalization and cellular degradation of a chimeric monoclonal anti-neuroblastoma antibody (MAb chCE7) is described. Immunofluorescence localization showed temperature-dependent redistribution of MAb chCE7 from the cell surface at 0 degrees C to vesicular structures after heating to 37 degrees C. SKN-AS cells which were pulse-labelled at 0 degrees C with radioiodinated chCE7 released 50% of the initial cell-bound radioactivity into the medium after 20 hr at 37 degrees C. Low-molecular-weight radioactivity in the medium was identified as iodotyrosine and the major intracellular degradation product was found to be an antibody fragment of 43 kDa. Degradation was blocked by chloroquine, an inhibitor of lysosomal function. MAb chCE7 binds to a carbohydrate epitope, as treatment with tunicamycin abolishes cell binding. In adherent cells in culture, inhibition of protein synthesis by cycloheximide affected cell-surface binding sites for chCE7 in a biphasic manner, with an initial increase followed by long-term decrease. Expression of binding sites was also found to be inhibited by sodium azide, by the lysosomotropic drug chloroquine and by Brefeldin A, a drug which prevents export of newly synthetized proteins to the cell surface. When cells were treated with high doses of chCE7 up to 24 hr and cell-surface binding sites were then measured after an acidic buffer wash, no loss of surface binding sites was found, indicating that pretreatment with MAb chCE7 does not induce down-regulation of its binding sites.