Technetium-99m direct radiolabeling of monoclonal antibody ior egf/r3

Clinical Trials in a Molecular World

New therapies aimed at molecular abnormalities are often more efficacious and less toxic than nontargeted therapies; however, with current technology, major treatment decisions are being made with inadequate data. This problem needs to be fixed by molecular imaging technology, enabling he noninvasive establishment of the presence of a molecular target, its spatial distribution and heterogeneity, and how this changes over time. This article discusses the status of molecular imaging in clinical trails today, and looks forward to what physicians would like it to become.

[Direct and indirect labeling with 99mTc of an antireceptor monoclonal antibody of EGF]

INTRODUCTION

Radiolabeled monoclonal antibodies (MAbs) have been a useful tool for diagnostic imaging and therapy in Oncology. The aim of this study was to carry out the indirect 99mTc radiolabeling of ior egf/r3, monoclonal antibody (MAb) specific for epidermal growth factor (EGF) receptor, and the comparison with a direct 99mTc radiolabeling approach.

MATERIAL AND METHODS

Cyclic anhydride of the diethylenetriaminepentaacetic acid (ADTPA) was employed as bifunctional chelating agent in the indirect monoclonal antibody radiolabeling and it was coupled to MAb at molar ratios of 20:1, 50:1 and 200:1 (ADTPA:MAb). For the direct radiolabeling, the reduction of MAb was performed with 2-mercaptoethanol (2ME), based on Schwarz's method. Biological activity was measured by Flow Cytometry. Biodistribution studies were performed at 1, 3 and 24 h after injection of the radiolabeled antibody in Wistar rats.

RESULTS

After 30 min of 99mTc radiolabeling of the ior egf/r3 MAb, the radiochemical purity values were between 80.0 +/- 1.8 and 90.0 +/- 1.2 % for the indirect method using ADTPA, while it was 94.8 +/- 1.6 % for the direct approach using 2ME. Stability of the 99mTc-radiopharmaceuticals was similar for both methods. The biological activity was similar for both antibody formulations. There were no significant differences for the biodistribution to normal organs for both radiolabeled antibodies.

CONCLUSIONS

Use of ADTPA was shown to be an efficient method for the 99mTc labeling of the monoclonal antibody ior egf/r3. Radiolabeling using 2ME showed higher radiochemical purity.

Phase I clinical evaluation of a neutralizing monoclonal antibody against epidermal growth factor receptor

Ior egf/r3, a neutralizing monoclonal antibody (mAb) against Epidermal Growth Factor Receptor (EGFR) was generated at the Cuban Institute of Oncology. Immunoscintigraphic studies in 148 patients with this 99-m Technetium (99Tc) labeled mAb, showed a high sensitivity and specificity for in vivo detection of epithelial tumors. To study safety, pharmacokinetic and immunogenicity of ior egf/r3 at high doses, a phase I clinical trial was conducted. Nineteen patients with advanced epithelial tumors received 4 mAb intravenous infusions at 6 dose levels: from 50 to 500 mg. Previously, immunoscintigraphic images using the same mAb labeled with 99Tc were acquired. Blood samples were collected for pharmacokinetic analysis and HAMA response. After mAb therapy, objective response was classified according to WHO criteria. Ior egf/r3 was well tolerated in spite of the high-administered doses. Only a severe adverse reaction consisting of hypotension and lethargy was observed. In 13 patients, selective accumulation of 99Tc-labeled mAb was observed at the site of the primary tumor or the metastasis. Pharmacokinetic analysis revealed that elimination half-life and the area under the time-concentration curve increased linearly with dose. HAMA response was detected in 17 patients. After 6 months of mAb therapy, 4 patients had stable disease. One patient had a tumor partial remission after 3 cycles of ior egf/r3.

Humanized versus murine anti-human epidermal growth factor receptor monoclonal antibodies for immunoscintigraphic studies

The anti-human epidermal growth factor receptor (EGF-R) humanized antibody h-R3 (IgG(1)), which binds to an extracellular domain of EGF-R, was used to evaluate the biodistribution on nude mice xenografted with A431 epidermoid carcinoma cell line. Results are compared with its murine version ior egf/r3 monoclonal antibody (mAb). Twenty-one athymic female 4NMRI nu/nu mice were injected intravenously with 10 microg/100 microCi of (99m)Tc-labeled mAbs. The mAb ior C5 that recognizes an antigen expressed preferentially on the surface of malignant and cytoplasm of normal colorectal cells was used as negative control. Immunoreactivity of (99m)Tc-labeled mAbs was measured by enzyme linked immunosorbent assay on A431 cell line and the immunoreactive fractions determined by Lindmo method. Among all organs significative accumulation was found in tumor (6.14 +/- 2.50 %ID/g, 5.06 +/- 2.61 %ID/g for murine and humanized mAbs, respectively) 4 h after injection. The immunoreactive fractions were found to be 0.88 and 0.81 for murine and humanized mAb, respectively. Thus, we expect better results using the humanized mAb h-R3 for diagnostic immunoscintigraphy.

Freeze-dried formulation for direct 99mTc-labeling ior-egf/r3 MAb: additives, biodistribution, and stability

Monoclonal antibodies (MAbs) have been useful for immunoscintigraphic applications in clinical diagnosis since they were introduced in nuclear medicine practice. The MAb ior egf/r3 developed at the Center of Molecular Immunology (Havana, Cuba) is a murine antibody that recognizes the human epidermal growth factor receptor (EGF-R) and has been used widely in the radioimmunodiagnosis of tumors of epithelial origin. Based on the direct Schwarz method, the present report describes the preparation of a freeze-dried formulation for radiolabeling the MAb ior egf/r3 with 99mTc for immunoscintigraphic applications. Radiolabeling efficiency, effects on immunoreactivity, biodistribution, pharmacokinetic, and stability of the formulation are reported. The study demonstrated that the freeze-dried formulation can be labeled with 99mTc at high yield. The resulting 99mTc-labeled ior egf/r3 MAb can be used to visualize in vivo human tumors of epithelial origin by immunoscintigraphy studies. The kit does not need any other addition or purification at the time of tagging other than the requisite amount of pertechnetate (40-50 mCi). Because the contents of the kit are lyophilized, no special storage or transportation is required.

Biodistribution of 99mTc-labeled anti-human epidermal growth factor receptor (EGF-R) humanized monoclonal antibody h-R3 in a xenograft model of human lung adenocarcinoma

The anti-human epidermal growth factor receptor (EGF-R) humanized monoclonal antibody (MAb) h-R3 is an (IgG1), which binds to an extracellular domain of EGF-R. It was used to evaluate the biodistribution on nude mice xenografted with H-125 human lung adenocarcinoma cell line. Results were compared with its murine version of the MAb ior-egf/r3. Twenty-one athymic female 4NMRI nu/nu mice were injected intraperitoneally with 10 microg/100 muCi of 99mTc-labeled MAbs. Immunoreactivity of 99mTc-labeled MAbs were measured by enzyme-linked immunosorbent assay (ELISA) on H-125 cell line and the immunoreactive fractions was determined by the Lindmo method. Among all organs, significant accumulation was found in serum (27.05 +/- 2.08 %ID/g) and tumor (3.903 +/- 0.89 %ID/g) at 4 h after injection. These values decreased to 5.03 +/- 0.50 %ID/g and 2.19 +/- 0.56 %ID/g for serum and tumor, respectively. The immunoreactive fraction was found to be 0.70, with a correlation coefficient r = 0.9984. With the good biodistribution and tumor uptake of the 99mTc-labeled humanized antibody h-R3, a phase I diagnostic clinical trial of tumor with epithelial origin should be pursued.