Skip to main content

Advertisement

Log in

Therapeutic advantages of Auger electron- over β-emitting radiometals or radioiodine when conjugated to internalizing antibodies

  • Original article
  • Published:
European Journal of Nuclear Medicine Aims and scope Submit manuscript

Abstract.

Recent studies suggest a higher anti-tumour efficacy of internalizing monoclonal antibodies (MAbs) when labelled with Auger electron emitters, as compared with β-emitters. The aim of this study was to compare the anti-tumour efficacy and toxicity of the internalizing MAb, CO17-1A, labelled with Auger electron emitters (125I, 111In) versus conventional β-emitters (131I, 90Y) in a colon cancer model, and to assess whether the residualizing radiometals may have therapeutic advantages over the conventionally iodinated conjugates. Biodistribution studies of 125I-, 111In- or 88Y-labelled CO17-1A were performed in nude mice bearing subcutaneous human colon cancer xenografts. For therapy, the mice were injected with either unlabelled or 125I-, 131I-, 111In- or 90Y-labelled CO17-1A IgG2a, whereas control groups were left untreated or were given a radiolabelled isotype-matched irrelevant antibody. The influence of internalization was assessed by comparing the results with those obtained with an anti-carcinoembryonic antigen (CEA) antibody which does not internalize to a relevant extent. The maximum tolerated activities (MTA) and doses (MTD) of each agent were determined. Myelotoxicity and potential second-organ toxicities, as well as tumour growth, were monitored. Bone marrow transplantation (BMT) was performed in order to enable dose intensification. Radiometals showed significantly better tumour-to-blood ratios than the respective iodinated conjugates. The MTAs of 131I- and 125I-CO17-1A without artificial support were 11.1 MBq (300 µCi) and 111 MBq (3 mCi), respectively; the MTA of the metals was reached at 4 MBq (100 µCi) for 90Y-, and at 85 MBq (2.3 mCi) for 111In-CO17-1A. Myelotoxicity was dose limiting in all cases. BMT enabled an increase in the MTA to 15 MBq (400 µCi) of 131I-labelled CO17-1A, to 4.4 MBq (120 µCi) of 90Y-labelled CO17-1A, and to 118 MBq (3.2 mCi) of 111In-labelled CO17-1A, while the MTA of 125I-CO17-1A had not been reached at 185 MBq (5 mCi) with BMT. Whereas no significant therapeutic effects were seen with unlabelled CO17-1A, tumour growth was retarded significantly with its radiolabelled forms. The therapeutic results were significantly (P<0.01) better with both Auger electron emitters (125I and 111In) than with the β-emitters, and, in accordance with the biodistribution data, a trend towards better therapeutic results was found with radiometals (more complete remissions) as compared with radioiodine. In contrast, at equitoxic doses, no significant difference was observed in the therapeutic efficacy of 131I- versus 125I-labelled non-internalizing anti-CEA antibody, F023C5. These data suggest that, at equitoxic doses, the therapeutic efficacy of internalizing MAbs labelled with Auger electron emitters, such as 125I or 111In, is superior to that of internalizing MAbs labelled with conventional β-emitters. The lower toxicity of Auger electron emitters may be due to the short path length of their low-energy electrons, which can reach the nuclear DNA only if the antibody is internalized (as is the case in antigen-expressing tumour tissue, but not in the stem cells of the red marrow).

This is a preview of subscription content, log in via an institution to check access.

Access this article

Price excludes VAT (USA)
Tax calculation will be finalised during checkout.

Instant access to the full article PDF.

Institutional subscriptions

Similar content being viewed by others

Author information

Authors and Affiliations

Authors

Additional information

Received 1 October 1999 and in revised form 15 March 2000

Rights and permissions

Reprints and permissions

About this article

Cite this article

Behr, T., Béhé, M., Löhr, M. et al. Therapeutic advantages of Auger electron- over β-emitting radiometals or radioiodine when conjugated to internalizing antibodies. Eur J Nucl Med 27, 753–765 (2000). https://doi.org/10.1007/s002590000272

Download citation

  • Issue Date:

  • DOI: https://doi.org/10.1007/s002590000272

Navigation