Jo-Sen Peng

Treatment of a patient with B cell lymphoma by I-131 LYM-1 monoclonal antibodies.

A patient with Richters syndrome, a malignant lymphomatous transformation of chronic lymphocytic leukemia, had become moribund with rapidly enlarging masses, granulocytopenia and thrombocytopenia despite the use of conventional chemotherapy and radiotherapy. Greater than ten percent of a test dose of I-131 Lym-1, a murine monoclonal antibody produced against Burkitts African B cell lymphoma, was accumulated by her tumor. The patient was subsequently treated with a series of injections of I-131 Lym-1 with dramatic clinical response, reduction of tumor volume by x-ray computerized tomography and progression of circulating cellular elements toward normality. Her course over the next ten months was not like that to be expected for Richters syndrome, which has an average survival of four months. This mode of treatment appears promising.

Non-dehalogenation mechanisms for excretion of radioiodine after administration of labeled antibodies.

In patients or mice with cancer the pharmacokinetic behavior of radioiodinated and radiometal chelated antibodies has been observed to be different. Rapid clearance from the tissues and excretion into the urine can occur after injection of radioiodinated antibodies. These observations have been interpreted to reflect in vivo dehalogenation of the antibody. This publication describes a variety of other mechanisms that can underlie these phenomena. These mechanisms include receptor uptake and catabolism of antibody and instability of the labeled antibody due to the labeling conditions. Specifically, the relative masses of chloramine-T and antibody in the iodination reaction mixture, the level of iodination of the antibody, and the amount of antibody administered to the recipient are all factors which can influence the clearance of radioiodinated antibody from the recipient. The final determinant for the different behavior of radioiodinated and In-111 metal chelated antibody relate to the different biologic pathways of indium when compared to iodine

EFFECTS OF PROTEIN MASS ON THE PHARMACOKINETICS OF MONOCLONAL ANTIBODIES (MoAb)

MoAb can be labeled with I-123 at high specific activities, so that only small amounts of protein are required for injection of large amounts of radioactivity for radioimmunoimaging or radioimmunotherapy. This can conserve antibody and decrease the possibilities of foreign protein reactions and target tissue binding site saturation. However, some investigators have suggested the use of milligram quantities of MoAb. In order to assess the effects on pharmacokinetics and imaging, we have administered microgram or milligram amounts of MoAb on separate occasions to 2 patients with a target tumor and 2 patients without a target tumor. Pharmacokinetics were observed in blood and urine by counting whole samples and HPLC fractions of these samples and in organs by serial imaging. Blood clearance and urinary excretion were faster during the early hours after injection of microgram amounts of MoAb, but subsequently were comparable to those obtained after milligram amounts. HPLC revealed rapid accumulation of radioiodide in the blood after microgram amounts, whereas the rate of accumulation and amount of radioiodide were less after milligram amounts. Complexes occurred earlier after milligram and later after microgram amounts of MoAb. Images confirmed rapid clearance of accumulation in stomach, thyroid and bladder. When a target cancer was present, there was also relatively greater activity in the lungs with microgram MoAb amounts compared to milligram amounts. This was not true in the absence of a target cancer. These observations have significant, but as yet, incompletely clear implications for radioimmunoimaging and radioimmunotherapy.

STABILITY OF RADIOIODIMATED MONOCLONAL ANTIBODIES (MoAb) AND THEIR F(ab')2 AND Fab FRAGMENTS IN VITRO

Knowledge of the stability of radioiodinated MoAb and their fragments in vitro is necessary for their practical application and commercialization. Using molecular-sieving (TSK-3000) high performance liquid chromatography (HPLC), cellulose acetate electrophoresis (CAE) at 11 and 45 minutes and solid phase immunoreactivity, we have observed the in vitro stability of a B cell lymphoma antibody (Lym-1, IgG2a) and its Fab fragment, and a mammary cancer antibody (B6.01, IgG1) and its F(ab‘)2 fragment. Each species was iodinated (I-125) with chloramine-T (C-T) at one microgram C-T per microgram of MoAb and one atom of iodine per molecule of MoAb, and were stored at 4°C. All four species showed mild degradation by 3 days, but this was only slowly progressive for the whole antibodies up to the final observation time of 21 days. F(ab’)2 more rapidly degraded between 6 and 14 days, and Fab between 3 and 6 days, as well as subsequently. The results by HPLC and CAE were comparable and were confirmed by tests of immunoreactivity. In summary, there was no significant difference in degradation in vitro between an IgG2a and an IgGl antibody iodinated in an identical manner, and these molecules were reasonably stable for 14–21 days at 4°C. Fragments of these MoAb iodinated in an identical manner were less stable, and this seemed to be size-related. This could be a reflection of the relatively greater impact of the addition of an atom of iodine to a smaller species, but more likely reflects an inherently reduced stability of the fragments.