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

Development of copper based drugs, radiopharmaceuticals and medical materials

Copper is one of the most interesting elements for various biomedical applications. Copper compounds show vast array of biological actions, including anti-inflammatory, anti-proliferative, biocidal and other. It also offers a selection of radioisotopes, suitable for nuclear imaging and radiotherapy. Quick progress in nanotechnology opened new possibilities for design of copper based drugs and medical materials. To date, copper has not found many uses in medicine, but number of ongoing research, as well as preclinical and clinical studies, will most likely lead to many novel applications of copper in the near future.

Evaluation of human major histocompatibility complex class I chain-related A as a potential target for tumor imaging

To investigate the feasibility of using human major histocompatibility complex class I chain-related A (MICA) as a target for tumor imaging diagnosis, 10C6, a monoclonal antibody (mAb) that specifically recognizes MICA in vitro, was labeled with (99m)Tc (technetium) and administered into mice bearing MICA-positive human ovarian epithelial carcinoma line SKOV3. Measurement of organ-specific radioactivity showed that tumor accumulated radioactivity continuously, while the uptake in the other organs decreased over time. Scintigram showed that the tumor became clearly visible at 24h post-injection of radio-labeled 10C6 mAb. These results suggest that MICA is a promising target for tumor imaging and mAb 10C6 may be used clinically for early tumor diagnosis.

Antibody-based immunotherapy in high-risk neuroblastoma

Although great advances have been made in the treatment of low- and intermediate-risk neuroblastoma in recent years, the prognosis for advanced disease remains poor. Therapies based on monoclonal antibodies that specifically target tumour cells have shown promise for treatment of high-risk neuroblastoma. This article reviews the use of monoclonal antibodies either as monotherapy or as part of a multifaceted treatment approach for advanced neuroblastoma, and explains how toxins, cytokines, radioactive isotopes or chemotherapeutic drugs can be conjugated to antibodies to enhance their effects. Tumour resistance, the development of blocking antibodies, and other problems hindering the effectiveness of monoclonal antibodies are also discussed. Future therapies under investigation in the area of immunotherapy for neuroblastoma are considered.

In vivo evaluation of 177Lu- and 67/64Cu-labeled recombinant fragments of antibody chCE7 for radioimmunotherapy and PET imaging of L1-CAM-positive tumors

PURPOSE

The L1 cell adhesion protein is overexpressed in tumors, such as neuroblastomas, renal cell carcinomas, ovarian carcinomas, and endometrial carcinomas, and represents a target for tumor diagnosis and therapy with anti-L1-CAM antibody chCE7. Divalent fragments of this internalizing antibody labeled with 67/64Cu and 177Lu were evaluated to establish a chCE7 antibody fragment for radioimmunotherapy and positron emission tomography imaging, which combines high-yield production with improved clearance and biodistribution properties.

EXPERIMENTAL DESIGN

chCE7F(ab')2 fragments were produced in high amounts (0.2 g/L) in HEK-293 cells, substituted with the peptide-linked tetraazamacrocycle 3-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate-triglycyl-L-p-isothiocyanato-phenylalanine, and labeled with 67Cu and 177Lu. In vivo bioevaluation involved measuring kinetics of tumor and tissue uptake in nude mice with SK-N-BE2c xenografts and NanoPET (Oxford Positron Systems, Oxford, United Kingdom) imaging with 64Cu-3-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate-triglycine-chCE7F(ab')2.

RESULTS

The 177Lu- and 67Cu-labeled immunoconjugates reached maximal tumor accumulation at 24 hours after injection with similar levels of 12%ID/g to 14%ID/g. Blood levels dropped to 1.0%ID/g for the 177Lu fragment and 2.3%ID/g for the 67Cu fragment at 24 hours. The most striking difference concerned radioactivity present in the kidneys, being 34.5%ID/g for the 177Lu fragment and 16.0%ID/g for the 67Cu fragment at 24 hours. Positron emission tomography imaging allowed clear visualization of s.c. xenografts and peritoneal metastases and a detailed assessment of whole-body tracer distribution.

CONCLUSIONS

67/64Cu- and 177Lu-labeled recombinant chCE7F(ab')2 revealed suitable in vivo characteristics for tumor imaging and therapy but displayed higher kidney uptake than the intact monoclonal antibody. The 67Cu- and 177Lu-labeled immunoconjugates showed different in vivo behavior, with 67/64Cu-3-(p-nitrobenzyl)-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate-triglycine-F(ab')2 appearing as the more favorable conjugate due to superior tumor/kidney ratios.

Monoclonal antibodies for brain tumour treatment

Conventional treatment of brain tumours includes surgical, radiotherapeutic and chemotherapeutic modalities. Nonetheless, the outcome of patients with brain tumours, in particular glioblastoma, remains poor. Immunotherapy with armed or unarmed monoclonal antibodies targeting tumour-specific antigens has emerged in the last two decades as a novel potential adjuvant treatment for all types of neoplasia. Many challenges to its implementation as a safe and viable therapy for brain tumours still need to be addressed; nevertheless, results from ongoing Phase I/II clinical trials are encouraging, as disease stabilisation and patient survival prolongation have been observed. Advances in preclinical and clinical research indicate that treatment of brain tumours with monoclonal antibodies can be increasingly adjusted to the characteristics of the targeted tumour and its environment. This aspect relies on the careful selection of the target antigen and corresponding specific monoclonal antibody, and antibody format (size, class, affinity), conjugation to the appropriate toxin or radioactive isotope (half-life, range), and proper compartmental administration.

Peptide linkers lead to modification of liver metabolism and improved tumor targeting of copper-67-labeled antibody fragments

In order to determine if tumor/nontarget tissue ratios of 67Cu-labeled antibody fragments can be improved, modifying the DO3A copper chelate with tripeptide linkers was investigated. The peptide-linked chelates 1,4,7,10-tetraazacyclodecane-N,N',N",N"'-tetraacetate (DOTA)-triglycyl-L-p-isothiocyanato-phenylalanine (DOTA-R1-NCS), DOTA-glycyl-phenylalanyl-glycyl-L-p-isothiocyanato-phenylalanine (DOTA-R2-NCS), DOTA-glycyl-prolyl-glycyl-L-p-isothiocyanato-phenylalanine (DOTA-R3-NCS) and DOTA-glycyl-L-p-isothiocyanato-phenylalanine (DOTA-R4-NCS) were synthesized and coupled to F(ab')2 fragments of anti-colon carcinoma mAb35. In vitro, the 67Cu-labeled antibody fragments were fully immunoreactive and stable in human serum. In vivo in nude mice bearing human colon carcinoma xenografts the conjugates R1 and R3 showed improved tumor uptake and lower levels of radioactivity in the liver compared with the other conjugates. Biodistributions of the DOTA-R2-F(ab')2 showed at early time points after injection higher levels of radioactivity in the liver, lower levels of activity persisting in the blood and lower accumulation of activity in the tumor. When liver homogenates were analyzed 30 min post injection by SDS-PAGE or FPLC gel chromatography, it was found that radioactivity was released more slowly from the triglycine (R1)-F(ab')2 than from the immunoconjugates with the R2 or the R4 linker. The main radioactive metabolites were protein bands at 66 kD, 31 kD and low molecular weight fragments. The results show that the rate of cleavage of the copper complex from F(ab')2 fragments in vivo can be influenced by the amino acid sequence close to the complex, with significant consequences on biodistributions.

Cleavable linkers to enhance selectivity of antibody-targeted therapy of cancer

Radioimmunotherapy of cancer utilizes anti-tumor antibodies or antibody fragments conjugated to radionuclides to deliver radiation selectively to tumors. However, radiolabeled proteins deposit radioactivity in normal organs that metabolize or conserve proteins and peptides, primarily liver and kidneys. To accelerate the clearance of radioactivity from normal tissues, linkers between the antibody or antibody fragment and the radioactive moiety have been designed for cleavage in the liver and kidneys, to liberate low molecular weight radioactive species for rapid excretion. Modest success in improving the tumor-to-liver and tumor-to-kidney radiation dose ratios have been achieved in preclinical studies. Such changes when taken to clinical studies have suggested useful impact on therapeutic work. Recent advances in the development of cleavable linkers are described.

Increased binding affinity enhances targeting of glioma xenografts by EGFRvIII-specific scFv

Combinatorial variation of CDR3 of V(H) and V(L), followed by phage display, was used to select affinity mutants of the parental anti-epidermal growth factor receptor-vIII (EGFRvIII) scFv MR1. One mutant, MR1-1(scFv), had increased specific binding affinity for EGFRvIII. It was produced and radiolabeled, and its biodistribution was evaluated in human glioma-bearing athymic mice. MR1-1 targeted the same EGFRvIII epitope as MR1 with an approximately 15-fold higher affinity (K(d) = 1.5 x 10(-9) M) measured by surface resonance analysis. Labeling with (131)I or (125)I was performed, and the immunoreactive fraction of the labeled MR1-1(scFv) was 50% to 55%. After incubation at 37 degrees C for 4 days, the binding affinity was maintained at 60% of initial levels. The specificity of MR1-1 for EGFRvIII was demonstrated in vitro by flow cytometry and incubation of FITC-labeled scFv with the EGFRvIII-expressing U87MG. DeltaEGFR cell line or with the EGFRvIII-negative U87MG cell line in the presence or absence of competing unlabeled MR1-1(scFv). We also investigated the internalization and processing of MR1-1 compared with MR1; MR1-1 exhibited levels of both cell surface retention and internalization up to 5 times higher than those by MR1. In biodistribution studies performed in athymic mice bearing s.c. U87MG. DeltaEGFR tumor xenografts, animals received paired-label intratumoral infusions of (131)I-labeled MR1-1(scFv) and (125)I-labeled MR1(scFv). Our results showed an up to 244% +/- 77% increase in tumor uptake for MR1-1 compared with that for MR1. The improved tumor retention of MR1-1(scFv) combined with its rapid clearance from normal tissues also resulted in sustained higher tumor:normal organ ratios. These results suggest that the improved affinity of MR1-1 can significantly impact in vivo glioma-specific targeting and immunotherapy.

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.