PGP and osteosarcoma: Moreover, neither DOXO nor Caelyx® reduced the growth of these tumors, which were selected as models for CD44- and Pgp-overexpressing osteosarcomas, nor did they induce apoptosis in the tumor, whereas HALs-H2S-DOXO increased caspase-3 activation in the tumor and decreased Pgp expression in the tumor.