Rhenium complexes of 17Alpha-substituted estradiol capable of binding to the estrogen receptor

The gonadal steroids are implicated in hormone-dependent cancers of the breast and prostate.
In order to image estrogen receptor positive tumors by using ^99mTc based radiopharmaceuticals, we have synthesized novel rhenium(V), (III) and (i) complexes of 17Alpha-substituted estradiol. In our first investigations we used rhenium as a model for the radioactive technetium.

These complexes represent new classes of estrogen receptor-binding rhenium complexes.
The binding affinities (lamb-cytosol) at 0°C reveal RBA values of about 23% for the oxorhenium(V) complexes when X = O and 8% when X = S. The RBA values at 25°C are 10% for the oxorhenium(V) complexes when X = O and 15% when X = S. For the rhenium(III) and rhenium(I) complexes the RBA values are significantly lower for 0°C and 25°C, ranging from 0.6% to 2.5%.
Further studies will investigate the stability of these complexes under in vivo conditions using the corresponding ^99mTc-complexes.