Provided are anti-cancer compounds which act as a non-PGP substrate, same being compounds of formula I-1, or a pharmaceutically acceptable salt, a prodrug or a solvate thereof, and the medical use of these compounds in the treatment of cancers, tumors, conditions caused by cancers or tumors, or cell proliferative diseases. Also provided is a method for treating cancers, tumors, conditions caused by cancers or tumors, or cell proliferative diseases using the anti-cancer compounds which act as non-PGP substrates as described above.