TH and neoplasm: In order to further elucidate the introduced histidine analogs endue TH with the better pH-responsive capacity at acid tumor microenvironment for elevated cellular uptake and antitumor activity, the new TH analogs were attached to the 20-OH position of CPT by using a disulfide releasable carbonate linker, and the antiproliferation of these CPP-CPT conjugates were evaluated at different pH conditions in Hela cells.