Three-step monoclonal antibody tumor targeting in carcinoembryonic antigen-positive patients.

We describe a method to postlabel, in vivo, biotinylated monoclonal antibodies pretargeted onto tumor deposits when most of the non-tumor-bound antibodies have already been cleared as avidin-bound complexes. The application of this principle to tumor detection by immunoscintigraphy was tested in 20 patients with histologically documented cancer and increased circulating carcinoembryonic antigen levels. One mg of biotinylated anti-carcinoembryonic antigen monoclonal antibody (FO23C5) was administered i.v. (first step). After 3 days, 4-6 mg of cold avidin were injected i.v. (second step), followed 48 h later by 0.2-0.3 mg of a biotin derivative labeled with 111In (2-3 mCi) (third step). No evidence of toxicity was observed. Whole body radioactivity distribution was measured in five patients at various intervals postinjection by the conjugate counting technique. Tumors and metastases were detected in 18 of 19 patients (the remaining patient was a true negative) within 3 h after administration of 111In-biotin by planar or single photon emission tomography imaging. At the time of imaging, tumor/blood pool ratio was 5.5 +/- 3.2, and tumor/liver ratio was 6.7 +/- 3.9. Blood clearance of 111In-biotin was multiexponential, with the fast component having a t1/2 of 5 +/- 3 min. Urinary excretion of radioactivity over 3 h was 63.5 +/- 4.9% of the injected dose. Radioactivity at 3 h was 6.5 +/- 1.8% in blood, 1.6 +/- 0.3% in the kidney, and 2.4 +/- 0.6% in the liver. This approach represents an improvement in immunoscintigraphic techniques for tumor localization. The potential use for radioimmunotherapy is discussed.

A new enzymatic method to obtain high-yield F(ab)2 suitable for clinical use from mouse IgGl.

Four different proteases were screened for their capability of selectively digesting murine monoclonal IgGl to obtain active F(ab)2. For the screening, a series of five different mouse monoclonal antibodies (IgGl, k) was used, recognizing different tumor-associated antigens and currently used for radioimmunoimaging studies. The enzymes (pepsin, bromelain, ficin and elastase) showed different fragmentation capability and the fragments obtained showed different stability and immunoreactivity. No digestion was noticed using elastase. Pepsin gave discontinuous results, in that its activity ranged from reduction of IgG to small inactive fragments to an inability to digest the immunoglobulin. Pepsin activity was strongly pH-dependent and immunoreactivity of the obtained fragments was not always conserved. Bromelain and, in particular, ficin gave excellent results. Digestion was always rapid and stable, all five MAbs were reduced to F(ab)2 in a comparable time range and with high yields. Moreover, ficin-obtained F(ab)2 showed a highly conserved immunoreactivity. Therefore, ficin was selected as the murine monoclonal IgGl digestion enzyme to obtain active bivalent antibody fragments. The digestion procedure gave a uniform result for all five different MAbs and was easily scaled up to produce hundreds of milligrams of F(ab)2.

Radioimmunoscintigraphy of ovarian cancer with the MOv18 monoclonal antibody.

The monoclonal antibody (Mab) 131I-MOv18 was administered to 30 patients with ovarian carcinoma intravenously (n = 20) and intraperitoneally (n = 10). After intraperitoneal administration, higher tumour uptake (mean values 1.3% vs. 0.8%) and a better tumour/background ratio (mean values 2.8 vs. 1.9) than after intravenous injection were obtained. Moreover, after intraperitoneal administration the uptake in non-affected organs, such as liver and spleen, was lower. However, occasionally the favourable results of the intraperitoneal route were cancelled by persistent pelvic non-specific accumulations of 131I-MOv18. The possibility to change the biodistribution pattern in the latter cases with peritoneal washing was evaluated. 3 patients were submitted to this procedure and an improvement in the radiotracer biodistribution was obtained in 1 case. With regard to tumour detection, the average sensitivity (73%) showed a significant difference from the sensitivities for abdominal (61%) and pelvic lesions (90%). No false positive results were noted.

Radiolocalization of 99mTc-labeled fragments in a melanoma xenografted model.

A xenograft model of human malignant melanoma was used to compare, in terms of tumor localization, the specific antimelanoma monoclonal antibody (MoAb) 225.28S with an irrelevant antibody (4C4). Both specific and non-specific 99mTc-labeled fragments were injected in 12 nude mice bearing subcutaneous tumor. The animals were then sacrificed at 6 and 24 hours post-injection and immediately dissected. Radioactivity of the tumor and normal tissues was measured in a well scintillation counter and autoradiography of tumor, liver and kidneys was also obtained. Tumor localization of 99mTc-labeled MoAb 225.28S fragments was highly specific compared with 99mTc-labeled irrelevant antibody 4C4. With the exception of the kidneys, already at six hours there was a satisfactory tumor-to-normal tissue ratio, which improved at 24 hours. However, the percentage of injected dose per gram of tumor decreased with time, probably due to the weaker bond of radiolabeled Fab' fragments to tumor cells. These results would indicate 99mTc-fragments of the antimelanoma MoAb 225.28S as a suitable radiotracer in clinical nuclear medicine.

[Renal accumulation of radioiodinated alpha-1-microglobulin increases in the mononephrectomised rat]. / L'accumulation rénale de alpha-1-microglobuline radioiodée augmente chez le rat mononéphrectomisé.

Alpha-1-microglobulin (alpha 1M) is highly accumulated by the kidneys of normal rats. Aim of this study has been to verify if uninephrectomy can modify this behaviour. For this purpose the radioactivity of the remaining kidney and those of plasma and urine have been measured in uninephrectomized rats after IV injection of radioiodinated alpha 1M. The experiments have been performed in 100 Sprague-Dawley male rats. Fifty animals underwent right nephrectomy, the others being the controls. Uninephrectomized rats and their controls have been divided in 3 groups, studied 4, 14 and 28 days after surgery, respectively. All the animals were injected with human alpha 1M labelled with iodine-131. They were sacrificed in part 18 minutes after the injection of labelled alpha 1M (time of highest kidney accumulation in the normal rat), and in part 28 minutes after the injection. Uninephrectomy increased plasma retention of labelled alpha 1M. Kidney uptake (total and per gram) was always higher in uninephrectomized animals. Similarly, urine radioactivity was higher in uninephrectomized rats. These results demonstrate that uninephrectomy remarkably increases the accumulation of alpha 1M in the remaining kidney.

Treatment of intracranial human glioblastoma by direct intratumoral administration of 131I-labelled anti-tenascin monoclonal antibody BC-2.

Ten patients with bulky brain glioblastoma, recurring after surgery, radiotherapy or chemotherapy, underwent direct intralesional radioimmunotherapy (RIT) using a monoclonal antibody (MAb), BC-2, raised against tenascin and labelled with 131I. Tenascin, the BC-2-recognized glycoprotein, is an antigen expressed by the stroma of malignant gliomas but not by normal cerebral tissue. Preliminary studies in animals have demonstrated the ability of anti-tenascin radiolabelled MAbs to detect and reduce tumours. A mean MAb dose of 1.93 mg (corresponding to 551.3 MBq of 131I) was injected directly into the tumour by means of a stereotaxic technique. Both systemic and local toxicity were negligible. After 24 hr, average tumour BC-2 uptake was 4.9% per gram and its effective half-life in neoplastic tissue was 66.5 hr: a mean radiation dose to target tissue of 36.48 cGy per MBq of injected 131I was delivered. Normal brain tissue and the major organs were spared. Most patients underwent multiple injections, reaching a cumulative tumour radiation ranging from 7,000 to 41,000 cGy. RIT failed to achieve any result in 4 of the 10 patients; in 3, the disease was stabilized; in the remaining 3, CT scan or NMR revealed 2 partial remission (greater than 50% reduction in tumour volume; PR) and I complete remission (CR). One patient with PR relapsed after II months; the other 2 patients were still maintaining their responses at the time of writing, 17 (CR) and 12 (PR) months after injection.

Human gliomas radioimmunoimaging with 131-I BC-2 murine IgG: preliminary report.

Ten patients with intracranial malignancies were studied by radioimmunoscintigraphy with I-131 BC-2 MoAb. Sensitivity and specificity of radioimmunoimaging were determined and compared with the results obtained with computed X-ray tomography and magnetic resonance imaging. BC-2 MoAb is a murine IgG1 anti-tenascin, which is not expressed by adult normal brain and has been found in large amount in gliomas and/or cerebral metastases, as well as other human tumors. Gamma-camera images obtained at 1 to 4 days exhibited increasing uptake of BC-2 in eight tumors, with varying degrees of contrast with the surrounding normal brain. Two lesions resulted negative to RIS: a meningioma and an oligodendroglioma. Specific tumor uptake of I-131 BC-2 was determined, by external gamma imaging, and ranged from 0.002 up to 0.007 percent of injected dose. Nonspecific uptake in the tumor was determined injecting 99m-Tc-FO23C5 (an isotype-matched control IgG1) in four patients and it was lower than 0.0001% ID. I-131 BC-2 tumor/nontumor ratios, measured using the geometric mean on digital images, ranged from 3 to 7.5:1. This study demonstrates that the tumor uptake of BC-2 in patients with glioma was due to specific processes.