Magnetic resonance imaging studies on nude mice grafted with colorectal adenocarcinoma using gadolinium-labeled monoclonal antibody.

A monoclonal antibody (Ab) 19.9 specific for colorectal carcinoma was labeled with a high number of gadolinium (Gd) atoms for its potential application as a contrast agent in magnetic resonance imaging (MRI). The DTPA was conjugated to 19.9 Ab via the bicyclic DTPA anhydride method (c. DTPA) using c. DTPA/Ab molar ratios between 5 and 150. The aggregates present in great amount at high c. DTPA/Ab ratios were systematically removed. Then the exact number of DTPA effectively conjugated, the immunoreactivity of the resulting 111In-DTPA-Ab were measured. The number of DTPA conjugated per antibody can be increased 20 to 25 with only a little loss of immunoreactivity. The 19.9 antibody conjugated with 16 and 25 DTPA was labeled with 153GdCl3 for pharmacokinetic studies on xenografted nude mice and with nonradioactive gadolinium to measure ex vivo the effect on the relaxation time T1 of the tumor. We found a 15 to 20% decrease of T1 on the tumor. In vivo experiments using a Bruker system and the same animal model showed a difference in the tumor contrast after the injection of 2 mg of Gd-labeled Ab.

Gd-25 DTPA-MAb, a potential NMR contrast agent for MRI in the xenografted nude mouse: preliminary studies.

Monoclonal antibodies (MAbs) 19-9 and 73-3 specific for human colon adenocarcinoma were labelled with a high number of gadolinium atoms. Twenty five DTPA were chelated per MAb, with only slight loss of immunoreactivity. The NMR contrast agent Gd-25 DTPA-MAb 19-9 or 73-3 ([Gd] 17 mumole/kg, [MAb] 60 microM) was injected into nude mice bearing human colon adenocarcinoma (SW948). Tumours were removed 24 hr after injection and T1 was measured in vitro. T1 relaxation time varied according to MAb specificity against tumour targets; T1 decreased 20% for MAb 19-9 and MAb 73-3 with SW948 tumour. Imaging was performed with this model. Very good contrast was obtained 24 hr after Gd-25 DTPA-MAb injection.

Selective modification of NMR relaxation time in human colorectal carcinoma by using gadolinium-diethylenetriaminepentaacetic acid conjugated with monoclonal antibody 19-9.

Monoclonal antibody 19-9 (mAb 19-9) against human colon adenocarcinoma was conjugated with gadolinium X diethylenetriaminepentaacetic acid (Gd X DTPA) and used as a contrast agent in nuclear magnetic resonance (NMR) in an effort to improve tumor target selectivity in nude mice. The data indicate that Gd X DTPA-mAb 19-9 in solution decreased the T1 relaxation of water protons at 90 MHz in direct proportion to the gadolinium concentration, and this effect was greater than in Gd X DTPA solutions. T1 relaxation time at 90 MHz, measured in tumors removed from nude mice 24 hr after injection of Gd X DTPA-mAb 19-9 (Gd, 20 mumol/kg; 16 DTPA molecules per mAb molecule), was significantly decreased (by 15%) as compared with the control group. Similar results were obtained in tumors from mice injected with Gd X DTPA-mAb 19-9 solutions in which Gd was used at 2, 6, or 10 mumol/kg (16 DTPA molecules per mAb molecule). These doses are lower than those commonly used for Gd X DTPA (10-100 mumol/kg) as contrast agent. Tumor localization by the Gd X DTPA-mAb 19-9 complex containing radioactive Gd (0.3 microCi/microgram of 153Gd) to confirm scintigraphy revealed significant concentrations of the complex (5% of the injected dose per gram of tissue) in the tumor. Scan images recorded in planar scintigraphy at day 5 showed good visualization of tumors.

A monoclonal antibody (Po66) directed against human lung squamous cell carcinoma immunolocalization of tumour xenografts in nude mice.

Po66, a mouse IgG1 monoclonal antibody, was produced by immunization against a patient lung squamous cell carcinoma. The tissue reactivity of the antibody was measured by a radioimmunological assay with enzymatically dissociated cells, by an immunofluorescence test on frozen tissue sections and by peroxidase-staining of paraffin sections. The antibody bound to lung squamous cell carcinoma, oesophagus carcinoma and, inconsistently to lung adenocarcinoma but not to the other tumours tested. Some normal tissues also reacted positively, in particular bronchial serous glands, oesophagus epithelium and renal distal and collecting tubules. In normal and malignant tissues showing epithelioid differentiation, Po66 bound to the intermediate maturation area. The antigen immunoprecipitated by Po66 from lung squamous cell carcinoma appeared as a single band with a molecular weight 47,000 to 50,000 daltons. Purified monoclonal antibody Po66 and an unrelated IgG1 immunoglobulin were labelled with radioactive iodine and injected i.v. into nude mice bearing subcutaneous xenografts of human lung squamous cell carcinoma. The localization index in the tumour was 3.3. Antibody labelled with 131I allowed gamma-scintigraphic imaging of the xenografts which were clearly outlined by days 9 to 11.