Cancer therapy with radiolabeled antibodies. An overview

Demonstration of highly specific toxicity of the alpha-emitting radioimmunoconjugate(211)At-rituximab against non-Hodgkin's lymphoma cells

The ability of an alpha-emitter conjugated to a chimaeric anti-CD20 monoclonal antibody to kill selectively human B-lymphoma cells in vitro is reported. Two B-lymphoma cell lines RAEL and K422, and normal haematopoietic progenitor cells from human bone marrow aspirates were incubated with(211)At-rituximab (Rituxan(R) or MabTheratrade mark) and plated in clonogenic assays for survival analyses. Following 1 h incubation with(211)At-rituximab, in concentrations which gave an initial activity of 50 kBq ml(-1), a high tumour cell to normal bone marrow cell toxicity ratio was obtained; 4.1 to 1.0 log cell kill. Biodistribution studies of(211)At-rituximab in Balb/c mice showed similar stability as that of the iodinated analogue. The data indicate that testing of(211)At-rituximab in human patients is warranted.

A new chemically modified chimeric TNT-3 monoclonal antibody directed against DNA for the radioimmunotherapy of solid tumors

In the last several years, our laboratory has developed a new approach to the radioimmunotherapy of solid tumors, designated Tumor Necrosis Treatment (TNT), that exploits the presence of degenerating and necrotic cells within tumors by utilizing MAbs directed against universal, intracellular antigens. The first TNT MAb developed by our laboratory, designated TNT-1, was directed against nucleosomal determinants consisting of histone H1 and DNA. Since absolute tumor accretion of MAb is a critical determinant of antitumor efficacy in radioimmunotherapy, we sought to identify new antinuclear antibodies that displayed high tumor localization properties. In the present study, we describe a murine antinuclear antibody, TNT-3, which demonstrates 3-fold higher tumor uptake than TNT-1. Because of this characteristic, a chimeric derivative designated chTNT-3 was developed and evaluated for antigen binding and tumor targeting. ELISA studies using a series of nuclear antigens confirmed that TNT-3 is directed against single-stranded DNA and does not cross react with TNT-1. Immunohistology reveals predominantly nuclear staining reactivity in human tissues and tumors. Since it was shown by our laboratory that charge modification can significantly improve the pharmacokinetic performance of monoclonal antibodies, chTNT-3 was chemically modified with biotin to generate an improved therapeutic reagent designated chTNT-3/B. Comparative studies with unmodified MAb demonstrated that biotinylation significantly shortened its clearance time in mice and produced lower normal tissue levels, while maintaining an equal amount of uptake in tumor xenografts for up to 10 days. These in vivo characteristics suggest that chTNT-3/B is an improved TNT reagent for the radioimmunotherapy of solid tumors.

Targeted radiotherapy of osteosarcoma using 153 Sm-EDTMP. A new promising approach

We report a case where targeted radionuclide therapy using 153Sm-EDTMP gave substantial palliative effect. A 35-year-old male with a primary osteosarcoma located in the first lumbar vertebra relapsed with progressive back pain after conventional treatment modalities had failed. He became bedridden, and developed paraparesis and impaired bladder function. On a diagnostic bone-scan intense radioactivity was localized in the tumor. He therefore was given 153Sm-EDTMP treatment twice, 8 weeks apart, 35 and 32 MBq/kg body weight respectively. After a few days the pain was significantly relieved and by the second radionuclide treatment the pareses subsided. For six months he was able to be up and about without any neurological signs or detectable metastases. Eventually, however, he experienced increasing local pain, developed paraparesis, was re-operated but died 4 months later. The dramatic transient improvement observed in this case warrants further exploration using 153Sm-EDTMP as a boost technique, supplementary to conventional external radiotherapy.