Overexpression of estrogen receptors
(ERs) is one of the important
characteristics of most breast cancers. We aim to develop a new type
of ER-specific radioiodine-labeled estrogen derivative ([131I]IPBA-EE), which was modified with an albumin-specific ligand 4-(p-iodophenyl) butyric acid (IPBA) to improve the metabolic
stability and enhance the ER-targeting ability of estrogen. [131I]IPBA-EE can effectively bind to albumin in vitro, and
its dissociation constant (Kd = 0.31 μM)
is similar to IPBA (Kd = 0.30 μM).
The uptake of [131I]IPBA-EE in ER-positive MCF-7 cells
(41.81 ± 3.41%) was significantly higher than that in ER-negative
MDA-MB-231 cells (8.78 ± 2.37%, ***P < 0.0005)
and could be significantly blocked (3.92 ± 0.35%, ***P < 0.0005). The uptakes of [131I]IPBA-EE
in rat uterus and ovaries were 5.66 ± 0.34% ID/g and 5.71 ±
2.77% ID/g, respectively, at 1 h p.i., and these uptakes could be
blocked by estradiol (uterus: 2.81 ± 0.41% ID/g, *P < 0.05; ovarian: 3.02 ± 0.08% ID/g, *P <
0.05). SPECT/CT imaging showed that ER-positive MCF-7 tumor uptake
of [131I]IPBA-EE reached to 6.07 ± 0.20% ID/g at 7
h p.i., which was significantly higher than that of ER-negative MDA-MB-231
tumor (0.87 ± 0.08% ID/g, **P < 0.005) and
could be blocked obviously with fulvestrant (1.65 ± 1.56% ID/g,
*P < 0.05). In conclusion, a novel radioiodinated
estradiol derivative, [131I]IPBA-EE with albumin-binding
property and good metabolic stability, was developed to image the
ER in breast cancer. This promising ER-targeted probe has the potential
to warrant further preclinical investigations.