Synthesis, physicochemical and biological evaluation of technetium-99m labeled lapatinib as a novel potential tumor imaging agent of Her-2 positive breast cancer

Chelators and metal complex stability for radiopharmaceutical applications

Diagnostic and therapeutic nuclear medicine relies heavily on radiometal nuclides. The most widely used and well-known radionuclide is technetium-99m (99mTc), which has dominated diagnostic nuclear medicine since the advent of the 99Mo/99mTc generator in the 1960s. Since that time, many more radiometals have been developed and incorporated into potential radiopharmaceuticals. One critical aspect of radiometal-containing radiopharmaceuticals is their stability under in vivo conditions. The chelator that is coordinated to the radiometal is a key factor in determining radiometal complex stability. The chelators that have shown the most promise and are under investigation in the development of diagnostic and therapeutic radiopharmaceuticals over the last 5 years are discussed in this review.

Radioiodinated Small-Molecule Tyrosine Kinase Inhibitor for HER2-Selective SPECT Imaging

One of the most clinically relevant molecular aberrations in breast cancer is overexpression of human epidermal growth factor receptor type 2 (HER2). We aimed to develop a radiolabeled tyrosine kinase inhibitor for HER2-targeted breast cancer imaging. In this study, a radioiodinated analog (^125/131I-IBA-CP) of the HER2-selective inhibitor CP724,714 was prepared and evaluated in HER2-positive or -negative subcutaneous human breast cancer xenografts. Methods: The CP724,714 analog IBA-CP was synthesized and assayed for its inhibitory activities against HER2 and 6 other tyrosine kinases. ^125/131I-IBA-CP was prepared using a copper-mediated radioiodination method with enhanced labeling yield and molar activity. In vitro biologic activity, including specific and nonspecific binding of ¹³¹I-IBA-CP to its HER2 kinase target, was assessed in different cell lines. In vivo small-animal ¹²⁵I-IBA-CP SPECT imaging and biodistribution studies were conducted on mice bearing HER2-positive, HER2-negative, or epidermal growth factor receptor (EGFR)-positive tumors. Nonradioactive IBA-CP and the EGFR inhibitor erlotinib were used as blocking agents to investigate the binding specificity and selectivity of ^125/131I-IBA-CP toward HER2 in vitro and in vivo. Additionally, ^125/131I-ICP was prepared by direct radioiodination of CP724,714 for comparison with ^125/131I-IBA-CP. Results: IBA-CP displayed superior in vitro inhibitory activity (half-maximal inhibitory concentration, 16 nM) and selectivity for HER2 over 6 other cancer-related tyrosine kinases. ^125/131I-IBA-CP was prepared in a typical radiochemical yield of about 65% (decay-corrected), radiochemical purity of more than 98%, and molar activity of 42 GBq/μmol at the end of synthesis. SPECT imaging revealed significantly higher uptake of ¹²⁵I-IBA-CP than of ¹²⁵I-ICP in the HER2-positive MDA-MB-453 tumors. Uptake in the HER2-negative MCF-7 tumors was much lower. Binding of ¹²⁵I-IBA-CP in the MDA-MB-453 tumors was blocked by coinjection with an excess amount of IBA-CP, but not by erlotinib. Conclusion: The radiolabeled HER2-selective inhibitor ^125/131I-IBA-CP is a promising probe for in vivo detection of HER2-positive tumors.

An improved 99mTc-HYNIC-(Ser)3-LTVSPWY peptide with EDDA/tricine as co-ligands for targeting and imaging of HER2 overexpression tumor

Overexpression of human epidermal receptor 2 (HER2) has given the opportunity for targeting and delivering of imaging radiotracers. The aim of this study was to evaluate the ^99mTc-HYNIC-(EDDA/tricine)-(Ser)₃-LTVSPWY peptide for tumor targeting and imaging of tumor with overexpression of HER2. The HYNIC-(Ser)₃-LTVSPWY was labeled with ^99mTc in presence of EDDA/tricine mixture as co-ligands. The in vitro and in vivo studies of this radiolabeled peptide were performed for cellular specific binding and tumor targeting. The high radiochemical purity of ^99mTc-HYNIC (EDDA/tricine)-(Ser)₃-LTVSPWY was obtained to be 99%. It exhibited high stability in normal saline and human serum. In HER2 binding affinity study, a significant reduction in uptake of radiolabeled peptide (7.7 fold) was observed by blocking SKOV-3 cells receptors with unlabeled peptide. The K_D and B_max values for this radiolabeled peptide were determined as 3.3 ± 1.0 nM and 2.9 ± 0.3 × 10⁶ CPM/pMol, respectively. Biodistribution study revealed tumor to blood and tumor to muscle ratios about 6.9 and 4 respectively after 4 h. Tumor imaging by gamma camera demonstrated considerable high contrast tumor uptake. This developed ^99mTc-HYNIC-(Ser)₃-LTVSPWY peptide selectively targeted on HER2 tumor and exhibited a high target uptake combined with acceptable low background activity for tumor imaging in mice. The results of this study and its comparison with another study showed that ^99mTc-HYNIC-(EDDA/tricine)-(Ser)₃-LTVSPWY is much better than previously reported radiolabeled peptide as ^99mTc-CSSS-LTVSPWY for HER2 overexpression tumor targeting and imaging.