Breast cancer seeking agents: basic approach

The knowledge of biochemical and physiological mechanisms involved in tissue localization is important so as to understand the information given by diagnostic nuclear medicine imaging, and eventually to design new radiopharmaceuticals. The cellular mechanisms which permit a high cancer uptake involve the perfusion and metabolism around the tumour tissue, the interference with normal function, the altered perfusion and/or metabolism within the tumour. All these phenomena can contribute to a high concentration of particular radiotracers in cancer and can create a favourable tumour/background ratio uptake sufficient for cancer imaging. Those molecules might be also powerful tools for reaching an advanced understanding of neoplastic and even "normal" cell biology. During these last years, some radiotracer specifically designed for different applications proved to be promising radiopharmaceuticals for breast cancer imaging. This is the case of monoclonal antibodies (Mabs) developed in the past against membrane cancer antigens. Other tracers, originally proposed for the study of vascular perfusion (cardiovascular tracers), have also revealed a capacity to be taken up by cancer cells. The radiopharmaceuticals mostly used as tumour seeking agents today (Radiothallium, Sestamibi, Tetrophosmin) were generated with other applications in mind. In this paper we review the mechanisms of uptake of the most relevant agents currently proposed for breast cancer imaging, including 18F-fluorodeoxyglucose (FDG). The radiotracers will be examined on the basis of the available scientific evidence regarding their cellular uptake and release. Moreover, we report our preliminary studies on the cellular uptake and release of these and other compounds recently introduced in clinical trials.