CEP1612, a dipeptidyl proteasome inhibitor, induces p21WAF1 and p27KIP1 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 important cell cycle and apoptosis-regulatory proteins. In this paper we report that the dipeptidyl Proteasome Inhibitor, phthalimide-(CH2)8CH-(cyclopentyl) CO-Arg(NO2)-Leu-H (CEP1612), induces Apoptosis and inhibits tumor growth 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 natural substrates, the cyclin-dependent kinase inhibitors p21WAF1 and p27KIP1, indicating its ability to inhibit Proteasome activity in intact cells. Furthermore, CEP1612 induces Apoptosis as evident by Caspase-3 activation and poly(ADP-ribose) polymerase cleavage. Treatment of A-549 tumor-bearing nude mice with CEP1612 (10 mg/kg/day, i.p. for 31 days) resulted in massive induction of Apoptosis and significant (68%; P < 0.05) tumor growth inhibition, as shown by terminal deoxynucleotidyltransferase-mediated UTP end labeling. Furthermore, immunostaining of tumor specimens demonstrated in vivo accumulation of p21WAF1 and p27KIP1 after CEP1612 treatment. The results suggest that CEP1612 is a promising candidate for further development as an Anticancer drug and demonstrate the feasibility of using Proteasome inhibitors as novel antitumor agents.