Preparation and in vivo evaluation of a novel stabilized linker for 211At labeling of protein

Talanov, Vladimir S.; Garmestani, Kayhan; Regino, Celeste A.S.; Milenic, Diane E.; Plascjak, Paul S.; Waldmann, Thomas A.; Brechbiel, Martin W.

doi:10.1016/j.nucmedbio.2006.03.001

« Previous Next »Nuclear Medicine and Biology
Volume 33, Issue 4 , Pages 469-480, May 2006

Preparation and in vivo evaluation of a novel stabilized linker for ²¹¹At labeling of protein

Vladimir S. Talanov
- Radiation Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
- Corresponding authors. Radioimmune and Inorganic Chemistry Section, Radiation Oncology Branch, National Institutes of Health, Bethesda, MD 20892-1002, USA.
- Current affiliation: Department of Chemistry, Howard University, 525 College St. NW, Washington, DC 20059, USA.
Kayhan Garmestani
- Metabolism Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
Celeste A.S. Regino
- Radiation Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
Diane E. Milenic
- Radiation Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
Paul S. Plascjak
- Department of Nuclear Medicine, Clinical Center, National Institutes of Health, Bethesda, MD 20892, USA
Thomas A. Waldmann
- Metabolism Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
Martin W. Brechbiel
- Radiation Oncology Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
- Corresponding authors. Radioimmune and Inorganic Chemistry Section, Radiation Oncology Branch, National Institutes of Health, Bethesda, MD 20892-1002, USA.

Received 16 October 2005; received in revised form 26 February 2006; accepted 5 March 2006. published online 02 May 2006.

Abstract

Significant improvement of in vivo stability of ²¹¹At-labeled radioimmunoconjugates achieved upon employment of a recently reported new linker, succinimidyl N-2-(4-[²¹¹At]astatophenethyl)succinamate (SAPS), prompted additional studies of its chemistry. The ²¹¹At radiolabeling of succinimidyl N-2-(4-tributylstannylphenethyl)succinamate (1) was noted to decline after storage at −15°C for greater than 6 months. Compound 1 was found to degrade via a ring closure reaction with the formation of N-2-(4-tributylstannylphenethyl)succinimide (3), and a modified procedure for the preparation of 1 was developed. The N-methyl structural analog of 1, succinimidyl N-2-(4-tributylstannylphenethyl)-N-methyl succinamate (SPEMS), was synthesized to investigate the possibility of improving the stability of reagent–protein linkage chemistry. Radiolabeling of SPEMS with ²¹¹At generates succinimidyl N-2-(4-[²¹¹At]astatophenethyl)-N-methyl succinamate (Methyl-SAPS), with yields being consistent for greater than 1 year. Radiolabelings of 1 and SPEMS with ¹²⁵I generated succinimidyl N-2-(4-[¹²⁵I]iodophenethyl)succinamate (SIPS) and succinimidyl N-2-(4-[¹²⁵I]iodophenethyl)-N-methyl succinamate (Methyl-SIPS), respectively, and showed no decline in yields. Methyl-SAPS, SAPS, Methyl-SIPS and SIPS were conjugated to Herceptin for a comparative assessment in LS-174T xenograft-bearing mice. The conjugates of Herceptin with Methyl-SAPS or Methyl-SIPS demonstrated immunoreactivity equivalent to if not superior to the SAPS and SIPS paired analogs. The in vivo studies also revealed that the N-methyl modification resulted in a superior statinated product.