Cytotoxicity of alpha-particle-emitting astatine-211-labelled antibody in tumour spheroids: no effect of hyperthermia.

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The high linear energy transfer, alpha-particle-emitting radionuclide astatine-211 (211At) is of interest for certain therapeutic applications; however, because of the 55- to 70-microm path length of its alpha-particles, achieving homogeneous tracer distribution is critical. Hyperthermia may enhance the therapeutic efficacy of alpha-particle endoradiotherapy if it can improve tracer distribution. In this study, we have investigated whether hyperthermia increased the cytotoxicity of an 211At-labelled monoclonal antibody (MAb) in tumour spheroids with a radius (approximately 100 microm) greater than the range of 211At alpha-particles. Hyperthermia for 1 h at 42 degrees C was used because this treatment itself resulted in no regrowth delay. Radiolabelled chimeric MAb 81C6 reactive with the extracellular matrix antigen tenascin was added to spheroids grown from the D-247 MG human glioma cell line at activity concentrations ranging from 0.125 to 250 kBq ml(-1). A significant regrowth delay was observed at 125 and 250 kBq ml(-1) in both hyperthermia-treated and untreated spheroids. For groups receiving hyperthermia, no increase in cytotoxicity was seen compared with normothermic controls at any activity concentration. These results and those from autoradiographs indicate that hyperthermia at 42 degrees C for 1 h had no significant effect on the uptake or distribution of this antitenascin MAb in D-247 MG spheroids.







Michael Rod Zalutsky

Jonathan Spicehandler, M.D. Distinguished Professor of Neuro Oncology, in the School of Medicine

The overall objective of our laboratory is the development of novel radioactive compounds for improving the diagnosis and treatment of cancer. This work primarily involves radiohalo-genation of biomolecules via site-specific approaches, generally via demetallation reactions. Radionuclides utilized for imaging include I-123, I-124 and F-18, the later two being of particular interest because they can be used for the quantification of biochemical and physiological processes in the living human through positron emission tomography. For therapy, astatine-211 decays by the emission of alpha-particles, a type of radiation considerably more cytotoxic that the beta-particles used in conventional endoradiotherapy. The range of At-211 alpha particles is only a few cell diameters, offering the possibility of extremely focal irradiation of malignant cells while leaving neighboring cells intact. Highlights of recent work include: a)
development of reagents for protein and peptide radioiodination that decrease deiodination in vivo by up to 100-fold, b) demonstration that At-211 labeled monoclonal antibodies are effective in the treatment of a rat model of neoplastic meningitis, c) synthesis of a thymidine analogue labeled with At-211 and the demonstration that this molecule is taken up in cellular DNA with highly cytotoxicity even at levels of only one atom bound per cell and d) development of
radiohalobenzylguanidines which are specifically cytotoxic for human neuroblastoma cells.

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