Chimeric 81C6 Research Articles

Phase 1 trial study of 131I-labeled chimeric 81C6 monoclonal antibody for the treatment of patients with non-Hodgkin lymphoma

AbstractWe report a phase 1 study of pharmacokinetics, dosimetry, toxicity, and response of 131I anti-tenascin chimeric 81C6 for the treatment of lymphoma. Nine patients received a dosimetric dose of 370 MBq (10 mCi). Three patients received an administered activity of 1480 MBq (40 mCi), and 2 developed hematologic toxicity that required stem cell infusion. Six patients received an administered activity of 1110 MBq (30 mCi), and 2 developed toxicity that required stem cell infusion. The clearance of whole-body activity was monoexponential with a mean effective half-life of 110 hours (range, 90-136 hours) and a mean effective whole-body residence time of 159 hours (range, 130-196 hours). There was rapid uptake within the viscera; however, tumor uptake was slower. Activity in normal viscera decreased proportional to the whole body; however, tumor sites presented a slow clearance (T1/2, 86-191 hours). The mean absorbed dose to whole-body was 67 cGy (range, 51-89 hours), whereas the dose to tumor sites was 963 cGy (range, 363-1517 cGy). Despite lack of a “blocking” antibody, 1 of 9 patients attained a complete remission and 1 a partial remission. These data demonstrate this radiopharmaceutical to be an encouraging agent for the treatment of lymphoma particularly if methods to protect the normal viscera are developed.

Human/murine chimeric 81C6 F(ab′) 2 fragment: preclinical evaluation of a potential construct for the targeted radiotherapy of malignant glioma

We have obtained encouraging responses in recent Phase I studies evaluating 131I-labeled human/murine chimeric 81C6 anti-tenascin monoclonal antibody (ch81C6) administered into surgically-created tumor resection cavities in brain tumor patients. However, because the blood clearance is slow, hematologic toxicity has been higher than seen with murine 81C6 (mu81C6). In the current study, a series of paired-label experiments were performed in athymic mice bearing subcutaneous D-245 MG human glioma xenografts to compare the biodistribution of the fragment ch81C6 F(ab′) 2 labeled using Iodogen to a) intact ch81C6, b) mu81C6, and c) ch81C6 F(ab′) 2 labeled using N-succinimidyl 3-[ 131I]iodobenzoate. Tumor retention of radioiodine activity for the F(ab′) 2 fragment was comparable to that for intact ch81C6 for the first 24 h and to that for mu81C6 for the first 48 h; as expected, blood and other normal tissue levels declined faster for ch81C6 F(ab′) 2. Radiation dosimetry calculations suggest that 131I-labeled ch81C6 F(ab′) 2 may warrant further evaluation as a targeted radiotherapeutic for the treatment of brain tumors.

Vascular targeted endoradiotherapy of tumors using alpha-particle-emitting compounds: theoretical analysis

Purpose : To establish the theoretical framework and study the feasibility of 211At-labeled anti-tenascin chimeric 81C6 monoclonal antibody (mAb) as anti-vascular endoradiotherapy for the treatment of glioblastoma multiforme (GBM) tumors. Methods and Materials : The morphology of blood vessels from histologic images was analyzed and used along with reaction-diffusion equations to assess the activity concentration of 211At-labeled chimeric 81C6 mAb in GBM tumor and normal-brain tissue. Alpha particle microdosimetry was then used to assess the survival probability and average absorbed dose for tumor and normal tissue endothelial cells (ECs) per unit vascular cumulated activity concentration q source (MBq-s g −1). In turn, these survival probabilities were used to assess the probability of failure Φ for a single vessel. Furthermore, using the vessel density, the specific tumor control probability per unit mass of tumor tissue ( tcp) and the specific normal-tissue complication probability per unit mass of normal-brain tissue ( ntcp) were estimated. The specific tumor control probability, tcp, was used to assess the overall tumor control probability ( TCP) as a function of tumor mass. Results : The levels of 211At-labeled ch81C6 mAb cumulated activity concentration in GBM tumor tissue were approximately five times higher than that in normal-brain tissue. Thus, the average absorbed dose to tumor ECs was higher than that of normal tissue ECs, and the survival probability for GBM ECs was lower than for normal-brain tissue ECs. Consequently, the resulting vessel-failure probability, Φ, for GBM tumor and for normal-brain tissue differ considerably, yielding a q source range between 10 3 and 10 4 MBq-s g −1. Conclusions : This theoretical analysis demonstrated that 211At-labeled chimeric 81C6 is an effective anti-vascular therapy for the treatment of GBM tumors, yielding a tcp higher than 0.999 for vascular cumulated activity concentrations q source higher than 1 × 10 4 MBq-s g −1, while yielding a low probability for normal-brain tissue damage.

Radiotoxicity of systemically administered 211At-labeled human/mouse chimeric monoclonal antibody: a long-term survival study with histologic analysis

Purpose: The antitenascin human/mouse chimeric monoclonal antibody labeled with the α-particle-emitting radionuclide 211At is of interest as an endoradiotherapeutic agent for the treatment of brain tumors. To facilitate the investigation of 211At-labeled chimeric 81C6 in patients, the long-term radiotoxicity of this radiopharmaceutical has been evaluated.Methods and Materials: Antibody labeling was performed using N-succinimidyl 3-[211At]astato-benzoate. After an initial dose-finding experiment, a second toxicity study was carried out at 4 dose levels in groups of 30 nonthyroid blocked B6C3F1 mice per group (15 males, 15 females). Male mice received either saline or 15–81 kBq/g and females received either saline or 16–83 kBq/g of 211At-labeled antibody. Ten animals (5 males, 5 females) were followed for 6 months and the remainder for 1 year.Results: The lethal dose in 10% of animals (LD10) for 211At-labeled chimeric 81C6 was 46 kBq/g in females and 102 kBq/g in males. Toxic effects—perivascular fibrosis of the intraventricular septum of the heart, bone marrow suppression, splenic white pulp atrophy, and spermatic maturational delay—generally were confined to a few animals receiving the highest doses of labeled antibody.Conclusions: The LD10 of 211At-labeled chimeric 81C6 in this mouse strain was about half that of [211At]astatide. These results establish the preclinical maximum tolerated dose of 211At-labeled chimeric 81C6 and define in the mouse the target organs for toxicity. These studies will be useful for determining starting doses for clinical studies with 211At-labeled chimeric 81C6.

Cytotoxicity of alpha-particle-emitting astatine-211-labelled antibody in tumour spheroids: no effect of hyperthermia.

The high linear energy transfer, alpha-particle-emitting radionuclide astatine-211 (211At) is of interest for certain therapeutic applications; however, because of the 55- to 70-microm path length of its alpha-particles, achieving homogeneous tracer distribution is critical. Hyperthermia may enhance the therapeutic efficacy of alpha-particle endoradiotherapy if it can improve tracer distribution. In this study, we have investigated whether hyperthermia increased the cytotoxicity of an 211At-labelled monoclonal antibody (MAb) in tumour spheroids with a radius (approximately 100 microm) greater than the range of 211At alpha-particles. Hyperthermia for 1 h at 42 degrees C was used because this treatment itself resulted in no regrowth delay. Radiolabelled chimeric MAb 81C6 reactive with the extracellular matrix antigen tenascin was added to spheroids grown from the D-247 MG human glioma cell line at activity concentrations ranging from 0.125 to 250 kBq ml(-1). A significant regrowth delay was observed at 125 and 250 kBq ml(-1) in both hyperthermia-treated and untreated spheroids. For groups receiving hyperthermia, no increase in cytotoxicity was seen compared with normothermic controls at any activity concentration. These results and those from autoradiographs indicate that hyperthermia at 42 degrees C for 1 h had no significant effect on the uptake or distribution of this antitenascin MAb in D-247 MG spheroids.

Tissue distribution and radiation dosimetry of astatine-211-labeled chimeric 81C6, an α-particle-emitting immunoconjugate

A paired-label study was performed in athymic mice bearing subcutaneous D-54 MG human glioma xenografts to compare the localization of human/mouse anti-tenascin chimeric antibody 81C6 labeled by reaction with N-succinimidyl 3-[ 211At]astatobenzoate and N-succinimidyl 3-[ 131I]iodobenzoate. Over the 48-h observation period, the distribution of 211At- and 131I-labeled antibody were quite similar in tumor and normal tissues except stomach. These data were used to calculate human radiation doses for both intravenously and intrathecal administered 211At-labeled chimeric 81C6 using a quality factor of 5 for α-emissions.

Chimeric anti-tenascin antibody 81C6: Increased tumor localization compared with its murine parent

When labeled using the Iodogen method, a chimeric antibody composed of the human IgG 2 constant region and the variable regions of murine anti-tenascin 81C6 exhibited superior uptake in human glioma xenografts compared with its murine parent. In the current study, three paired-label experiments were performed in athymic mice with subcutaneous D-54 MG human glioma xenografts to evaluate further the properties of radioiodinated chimeric 81C6. These studies demonstrated that (a) the enhanced tumor uptake of chimeric 81C6 is specific; (b) when labeling was performed using N-succinimidyl 3-iodobenzoate, chimeric 81C6 again showed preferential accumulation in tumor compared with murine 81C6; and (c) the tumor uptake advantage observed previously with murine 81C6 for N-succinimidyl 3-iodobenzoate compared with lodogen labeling did not occur with chimeric 81C6.

Generation and characterization of a mouse/human chimeric antibody directed against extracellular matrix protein tenascin.

The murine anti-tenascin monoclonal antibody 81C6, following iodination, has been shown to be an efficient localizing and therapeutic agent in both subcutaneous and intracranial human glioma xenograft models in athymic mice and rats. Similarly, effective monoclonal antibody 81C6 localization has been demonstrated in glioma patients, and Phase I trials with the intact murine IgG2b kappa molecule are currently in progress. In order to maximize the potential for repeated administration by minimizing murine Fc-mediated immunogenicity and reducing Fc-mediated immune effects, we created murine 81C6 variable region/human IgG2 chimeric monoclonal antibodies by the molecular cloning of the variable region genes of mouse 81C6 and their genetic linkage to human constant region exons. The resulting chimeric constructs were introduced into SP2/0 cells, and stable transfectomas were selected by G418 and mycophenolic acid resistance. The resistant clones were screened for anti-tenascin activity on tenascin-coated plates by enzyme-linked immunosorbent assay. The N-terminal amino acid sequence of both heavy and light chains of the purified chimeric 81C6 antibody matched exactly with that of the native mouse 81C6 as well as with that deduced from the nucleotide sequence. The production level of chimeric 81C6 (13.9 mg/ml) from ascites in the highest expressing transfectoma was much higher than that of native mouse 81C6 (2.5 mg/ml). The chimeric antibody showed the same specificity and equivalent affinity for human intact tenascin or tenascin-expressing cells as the native mouse 81C6 antibody. Direct comparison of radioiodinated chimeric and radioiodinated mouse 81C6 biodistribution in subcutaneous and intracranial xenograft-bearing mice showed higher tumor-to-normal tissue ratios for chimeric 81C6 as compared with native mouse 81C6. The improved localizing and clearance characteristics of chimeric 81C6 in xenograft model systems suggests that chimeric 81C6 would be an improved reagent for intracompartmental therapy of tenascin-expressing tumors in the human central nervous system.