Pretargeted ¹⁷⁷Lu Radioimmunotherapy of Carcinoembryonic Antigen–Expressing Human Colonic Tumors in Mice

Abstract

Pretargeted radioimmunotherapy (PRIT) with bispecific antibodies in combination with a radiolabeled peptide reduces the radiation dose to normal tissues, especially the bone marrow. In this study, the optimization, therapeutic efficacy, and toxicity of PRIT of colon cancer with a 177 Lu-labeled peptide was determined in mice with carcinoembryonic antigen (CEA)-expressing human tumors. Methods: To obtain the optimal therapeutic efficacy, several strategies were evaluated to increase the total amount of radioactivity targeted to subcutaneous LS174T colon cancer tumors in BALB/c nude mice. First, the maximum amount of bispecific anti-CEA and antihapten antibody TF2 and the peptide IMP288 that could be targeted was determined. Second, the tumor targeting of repeated administrations of radiolabeled IMP288 was investigated. Mice received 1 TF2 injection, followed by multiple IMP288 injections (3-h interval) or multiple cycles, with each IMP288 administration preceded by a new TF2 injection (72-h interval). PRIT was administered at maximum doses of TF2 and 177 Lu-labeled IMP288 in groups of 9 mice with subcutaneous LS174T tumors. Mice received 1, 2, or 3 successive cycles of treatment (26 MBq/mouse/cycle) or carrier only. The primary endpoint was survival; secondary endpoints were tumor growth, body weight, bone marrow, and renal toxicity. Results: The highest amount of radioactivity delivered to a subcutaneous colon tumor was achieved by the administration of 5.0 nmol of TF2 and 0.28 nmol of IMP288 in 3 successive cycles, with each IMP288 preceded by a new TF2 injection (72-h interval). PRIT effectively delayed tumor growth and prolonged survival significantly. Higher activity doses, administered in successive cycles, correlated with longer survival: the median survival of untreated mice was 13 d (range, 6-20 d), whereas that of mice treated with 1, 2, or 3 cycles of PRIT was 24 (range, 24-31 d), 45 (range, 38 $ 130 d), and 65 (range, 48 $ 130 d) days, respectively. Toxicity was limited: no significant changes in mean body weight were measured. Minimal changes in leukocyte counts were measured at 2 and 3 wk after injection, with full recovery within 7 wk after treatment. Platelet counts were unaffected. Serum creatinine levels were not increased significantly; thus, there was no indication of acute renal toxicity. Conclusion: This study indicates that PRIT in mice is an effective treatment modality against colon cancer, with limited toxicity.

Quantitative Immuno-SPECT Monitoring of Pretargeted Radioimmunotherapy with a Bispecific Antibody in an Intraperitoneal Nude Mouse Model of Human Colon Cancer

“…The activity in the tumor lesions as measured with SPECT correlated well with uptake measured with ex vivo biodistribution. In a previous study, we showed that successive administrations of PRIT within a 3-d interval resulted in similar uptake in the tumors (5). Therefore, images acquired after diagnostic or therapeutic administrations of PRIT can be compared quantitatively.…”

“…Subsequently, 10 mL of 50 mM ethylenediaminetetraacetic acid were added in order to complex any unbound 111 In or 177 Lu. Radiochemical purity of the radiolabeled IMP288 preparations was determined by reversed-phase high-performance liquid chromatography as described previously (5). In all experiments, the radiochemical purity of radiolabeled IMP288 exceeded 95%.…”

“…Chelate-metal complexes, such as diethylenetriaminepentaacetic acid-indium, have been used as haptens (4). More recently, peptides substituted with the hapten histamine-succinyl-glycine (HSG), in combination with anti-HSG antibody binding, have provided a more flexible system, because these HSG-substituted peptides can be conjugated with various chelators (e.g., DOTA, NODA/NOTA, or N 3 S-chelates), allowing stable complexes with many radionuclides, such as 111 In and 99m Tc for SPECT (5)(6)(7)(8), 68 Ga and 18 F for PET (9)(10)(11)(12)(13), or 90 Y and 177 Lu for pretargeted radioimmunotherapy (PRIT) (5,8). Including tyrosine in the peptide core also enables radioiodination (e.g., 124 I or 131 I) (7,14).…”

Phase II Trial of Anticarcinoembryonic Antigen Pretargeted Radioimmunotherapy in Progressive Metastatic Medullary Thyroid Carcinoma: Biomarker Response and Survival Improvement

“…The use of TF2, composed of a humanized anti-HSG Fab fragment derived from the 679 anti-HSG mAb and 2 humanized anti-CEA Fab fragments derived from the hMN-14 mAb (labetuzumab; Immunomedics, Inc.) by the dock-and-lock procedure, should reduce immunogenicity and facilitate repeated injections (22). Moreover, the HSG peptide allows facile and stable labeling with different radiometals, such as 177 Lu or 90 Y, having favorable physical features that could improve pRAIT efficacy (23).…”

Trial Watch: Monoclonal antibodies in cancer therapy

“…In the context of preclinical studies that yielded encouraging results, TF2 was pre-administered to mice and allowed to localize to CEA-expressing tumors, followed by the injection of 177 Lu-coupled IMP-288. 112 Similar approaches are now being evaluated in patients affected by CEA-expressing malignancies, including colorectal and small cell lung cancer ( Table 4).…”