Recombinant bispecific monoclonal antibodies prepared by the dock-and-lock strategy for pretargeted radioimmunotherapy

Abstract

The selective delivery of therapeutic radionuclides is a promising approach for treating cancer. Antibody-targeted radionuclides are of particular interest, with 2 products approved for the treatment of certain forms of non-Hodgkin lymphoma. However, for many other cancers, radioimmunotherapy has been ineffective, being limited by prolonged exposure to the highly radiosensitive bone marrow. An alternative approach, known as pretargeting, separates radionuclide from the antibody, allowing the radiation to be delivered on a small molecule that can quickly and efficiently migrate into the tumor, and then rapidly clear from the body with minimal retention in tissues. Several pretargeting methods have been developed that differ in the way they selectively capture the radionuclide. This review focuses on the development of a novel form of bispecific monoclonal antibody (bsMAb) pretargeting that uses a unique radiolabeled hapten-peptide system that can be modified to bind numerous therapeutic and imaging radionuclides. Together with a specialized recombinant humanized bsMAb prepared with by a technique known as the Dock-and-Lock method, this pretargeting procedure has been examined in many different animal models, showing a high level of sensitivity and specificity for localizing tumors, and improved efficacy with less hematologic toxicity associated with directly radiolabeled IgG. The bsMAb is a tri-Fab structure, having 2 binding arms for the tumor antigen and 1 capable of binding a hapten-peptide. Preclinical studies were preformed to support the clinical use of a bsMAb and a hapten-peptide bearing a single DOTA moiety (IMP-288). A phase 0 trial found an (131)I-tri-Fab bsMAb, TF2, that targets carcinoembryonic antigen was stable in vivo, quickly clears from the blood, and localizes known tumors. The first-in-patient pretargeting experience with the (111)In-IMP-288 also observed rapid clearance and low tissue (kidney) retention, as well as localization of tumors, providing initial promising evidence for developing these materials for radioimmunotherapy.

Copyright 2010 Elsevier Inc. All rights reserved.

Figures

Figure 1

Schematic representation of the Dock-and-Lock modules and how the are assembled to form bispecific monoclonal antibodies.

Figure 2

Biodistribution of 131I-TF2 tri-Fab anti-CEA bsMAb in nude mice bearing the human colonic tumor xenograft, GW-39.

Figure 3

Comparison of the blood clearance kinetics of 131I-TF2 in mice and rabbits and to 131I-hMN-14 IgG in rabbits. TF2’s Fab CEA-binding arms are donated from hMN-14.

Figure 4

Evaluation of varying conditions to optimize pretargeting of 111In-IMP-288 di-HSG-DOTA-hapten-peptide. Nude mice bearing GW-39 human colonic tumor xenografts were injected iv with increasing amounts of TF2, and then at either 7, 16, or 50 h later, a fixed amount of 111In-IMP-288 was given (e.g., TF2/IMP-288 mole ratio at 470 µg of TF2 was ~80:1), and animals were then euthanized with determination of tumor (A) and tissue uptake. The bottom panel (B) shows uptake in the kidney in each of these groups of animals.

Figure 5

Blood and renal clearance of 111In-IMP-288 given to rabbits who received a fixed amount of TF2 (10:1 TF2/IMP-288 mole ratio) 3, 4, or 5 days later, or to rabbits who were only given 111In-IMP-288. (A) Blood clearance over the first 24 h showed more than 99% (dark line) had cleared before 18 h under the various conditions examined. Bars represent the range found in 2 to 4 rabbits that were studied. (B) Regions of interest analysis for the kidneys derived from whole-body images taken over 3 days, which provided an estimate of the percentage of the total injected activity that was given (biological values).

Figure 6

Linear (top) and log (bottom) plots of the blood clearance of 131I-TF2 in 2 colorectal cancer patients.

Figure 7

Anterior whole-body images of a patient given 131I-TF2 anti-CEA × anti-HSG tri-Fab bsMAb. Initial images at 1 h showed the activity mainly in the heart (H) with some uptake in the liver (Lv). By 24 h, evidence of catabolic activity was observed with uptake in sinuses, and activity in stomach (S) and urinary bladder (UB). There was also activity in the transverse colon (TC) leading into the descending colon, but also there was distinct uptake in the cecum (arrow), where initial colonoscopy and later surgery had indicated a newly diagnosed 5.0 cm lesion. Heart activity was able appreciably less at 24 h, and by 72 h, the only activity remaining was in the thyroid, again likely representing catabolized radioiodine uptake.

Figure 8

Blood clearance of TF2 by ELISA (A) and whole-body distribution of 111In-IMP-288 (B) in a patient with extensive metastatic colorectal cancer. The patient was given 75 mg of TF2 followed 5 days later with 100 µg (~69 nmoles) of 111In-IMP-288 (5 mCi). TF2’s blood clearance, as determined by ELISA, in this patient (open squares) was similar to that of 2 earlier patients who had received ~1.2 mg of TF2 (open and closed triangles). The biodistribution of 111In-IMP-288 showed evidence of rapid dispersion through the body within 10 minutes. The heart (H), liver, lungs, and kidneys (K) can be discerned. Regions of interest indicated that 18% of the injected activity was already present in the urinary bladder (UB). By 24 h, most of the activity had been cleared from the blood and body, with only a small amount of activity in the urinary bladder. Known metastatic sites in the lungs and liver were disclosed (arrows), and there was residual activity in the kidneys.