Limited
drug penetration into
tumor tissue is one of the major factors causing clinical drug resistance in human solid
tumors. The multicellular layers (MCL) of human
cancer cells have been successfully used to study tissue pharmacokinetics of anticancer drugs. The purpose of this study was to develop a direct and simple method to evaluate vitality changes in situ within MCL using
calcein-AM. Human colorectal (DLD-1, HT-29) and bladder (HT-1376, J-82)
cancer cells were grown in Transwell inserts to form MCL and subjected to
paclitaxel exposure. The
drug distribution was evaluated using
paclitaxel-
rhodamine. Photonic attenuation and limited penetration of
calcein-AM prevented cellular vitality evaluation on optical sections under confocal microscopy in DLD-1 MCL. However, direct measurement of the fluorescence intensity on frozen sections of MCL allowed successful vitality assessment in more than 80% depth for HT-29 and J-82 MCL and in the upper 40% depth for DLD-1 and HT-1376 MCL. The penetration of
paclitaxel-
rhodamine was greater in HT-29 than DLD-1 and its distribution pattern was correlated to the spatial profile of vitality deterioration in both MCL, suggesting that tissue penetration may be an important determinant of
drug effect in
tumors. In conclusion, a novel method for vitality evaluation in situ within MCL was developed using
calcein-AM. This method may provide clinically relevant data regarding the spatial pharmacodynamics of
anticancer agents within avascular regions of solid
tumors.