The department of translational TME Ligands focusses on the development of radiotracers targeting receptors within the tumor microenvironment (TME) for imaging and therapy. The cellular and molecular components of the TME represent interesting targets for cancer therapy. In addition, they can serve as imaging biomarkers for the early detection of tumor diseases and for monitoring treatment response. Non-invasive molecular imaging techniques such as PET and SPECT complement the classic immunohistochemical methods very well, since they can address the problem of heterogeneous receptor expression over time in vivo, e.g. when used in dynamic PET/CT. We are developing radiotracers by applying medical radiochemistry methods based on small organic molecules, low-molecular-weight peptides and peptidomimetics that are covalently labeled with a suitable radionuclide (e.g. fluorine-18, iodine-123) or with a radiometal via an attached chelator (e.g. gallium 68, lutetium-177). This usually involves heavy snthetic organic chemistry methods. These new radioligands will be evaluated both in vitro on tumor cell lines and in vivo in animal models (microPET, microSPECT and organ distribution in tumor-bearing small animals) with regard to their application in nuclear medicine. The combination of the above-mentioned radiotracer classes with optical imaging by incorporating tailor-made near-infrared dyes in the molecular structure plays an important role in translational research. In the field of bimodal imaging, e.g., in the later clinical theranostic application, this combination allows PET or SPECT imaging and fluorescence-guided robotic surgery with the same molecule.