A p21(Waf1/Cip1) carboxyl-terminal peptide exhibited cyclin-dependent kinase-inhibitory activity and cytotoxicity when introduced into human cells

In the present study, we report the cyclin-dependent kinase (Cdk)inhibitory activity of a series of p21(Waf1/Cip1) (p21) peptide fragments spanning th e whole protein against the cyclin D1/Cdk4 and cyclin E/Cdk2 enzymes. The m ost potent p21 peptide tested in our initial peptide series, designated Wil l, spanned amino acids 139 to 164, a region of p21 that has been found inde pendently to bind to proliferating cell nuclear antigen and also to inhibit Cdk activity. We go on to report the importance of putative beta-strand an d 3(10)-helix moths in Bile W10 peptide for cyclin-dependent kinase-inhibit ory activity. We also describe the cellular activity of W10 and derivatives that were chemically linked to an antennapedia peptide, the latter segment acting as a cell membrane carrier. We found that the W10AP peptide exhibit ed growth inhibition that resulted from necrosis in human lymphoma CA46 cel ls. Furthermore, regions in the W10 peptide responsible for Cdk-inhibition were also important for the degree of this cellular activity. These studies provide insights that may eventually, through further design, yield agents for the therapy of cancer.