CEP1612, a dipeptidyl proteasome inhibitor, induces p21(WAF1) and p27(KIP1) expression and apoptosis and inhibits the growth of the human lung adenocarcinoma A-549 in nude mice

The ubiquitin proteasome system is responsible for the proteolysis of impor tant cell cycle and apoptosis-regulatory proteins. In this paper we report that the dipeptidyl proteasome inhibitor, phthalimide-(CH2)(8)CH(cyclopenty l) CO-Arg(NO2)-Leu-H (CEP1613), induces apoptosis and inhibits turner growt h of the human lung cancer cell line A-549 in an in vivo model. In cultured A-549 cells, CEP1612 treatment results in accumulation of two proteasome n atural substrates, the cyclin-dependent kinase inhibitors p21(WAF1) and p27 (KIP1), indicating its ability to inhibit proteasome activity in intact cel ls. Furthermore, CEP1612 induces apoptosis as evident by caspase-3 activati on and poly(ADP-ribose) polymerase cleavage. Treatment of A-549 tumor-beari ng nude mice with CEP1612 (10 mg/kg/day, i.p. for 31 days) resulted in mass ive induction of apoptosis and significant (68%; P < 0.05) tumor growth inh ibition, as shown by terminal deoxynucleotidyltransferase-mediated UTP end labeling. Furthermore, immunostaining of tumor specimens demonstrated in vi vo accumulation of p21(WAF1) and p27(KIP1) after CEP1612 treatment. The res ults suggest that CEP1612 is a promising candidate for further development as an anticancer drug and demonstrate the feasibility of using proteasome i nhibitors as novel antitumor agents.