“…There are several possibilities to explain this phenomena: 1) in vitro, a 1 M dose is not high enough to trigger apoptosis, although it is potent enough to elicit cell cycle arrest and inhibits EGFR and PKCs; 2) in vivo, at doses of 50 or 100 mg/kg, the real drug exposure for C2 is more than 1 M in tumor samples, hence, the apoptosisinducing effect is evident in the tumors; 3) it is possible that C2 can be metabolized after oral administration, and changed into modified derivatives. For instance, some 9-position modified acridine elicited apoptosis in numerous human cancers (20,21).…”