ANPEP and neoplasm: According to this view, studies on the interaction of a cyclic CNGRC peptide with various CD13-expressing cells (endothelial cells, pericytes, tumor cells, and myeloid cells), by 2D Transferred Nuclear Overhouser Effect Spectroscopy (2D TR-NOESY) and by immunofluorescence techniques, showed that the expression of CD13 was necessary but not sufficient for the binding, as binding was observed to cells that form the tumor vasculature (endothelial cells and pericytes) and to some tumor cell lines, but not to myeloid cells [26].