The synthesis and evaluation of two cathepsin S-specific probes is described. For long-term retention of the probe at the target site and a high signal-to-noise ratio, we introduced a lipidation approach via the simple attachment of palmitoic acid to the reporter. After cathepsin S-specific cleavage in cultured cells and in a grafted tumor mouse model, fluorescence increased owing to dequenching and we observed an intracellular accumulation of the fluorescence in the target tissue. The lipidated probe provided a prolonged and strongly fluorescent signal in tumors when compared to the very similar non-lipidated probe, demonstrating that non-invasive tumor identification is feasable. The homing principle by probe lipidation might also work for selective administration of cytotoxic compounds to specifically reduce tumor mass.

The aim of this work was to measure optical properties of stool of mice to provide this relevant wavelength-dependent behavior for optical imaging modalities such as fluorescent molecular tomography and near-infrared optical tomography. BALB/c nude female mice were studied and optical properties of the stool were determined by employing the inverse adding-doubling approach. The animals were kept on chlorophyll-free diet. Nine stool samples were measured. The wavelength-dependent behavior of absorption and scattering in 550 to 1000 nm range is presented. The reduced scattering spectrum is fitted to the Mie scattering approximation in the near-infrared (NIR) wavelength range and to the Mie + Rayleigh approximation in visible/NIR range with the fitting coefficients presented. The study revealed that the absorption spectrum of stool can lead to crosstalk with the spectrum of hemoglobin in the NIR range.