Mechanisms of growth inhibition in human papillomavirus positive and negative cervical cancer cells by the chloromethyl ketone protease inhibitor, succinyl-alanine-alanine-proline-phenylalanine chloromethyl ketone

The chymotrypsin-like serine protease inhibitor, succinyl-alaninealanine- proline-phenylalanine chloromethyl ketone (AAPF_CMK), has been shown to have anticarcinogenic activity in a number of model systems and to be relatively selective for a nuclear protease. This inhibitor also has substantial effects on growth of tumorigenic human papillomavirus (HPV)-infected keratinocytes in organotypic raft cultures. Here, we examined the effects of AAPF_CMK on cell growth, cell-cycle kinetics, apoptosis induction, and DNA synthesis in two human cervical carcinoma cell lines: SiHa cells, which have integrated high-risk HPV-16; and C33a cells, which do not contain HPV DNA. AAPF_CMK inhibited growth of both cell lines in a time- and dose-dependent manner. Apoptosis studies showed no significant difference in drug-treated versus vehicle-treated cells in the C33a cell line. However, a significant dose-dependent increase in apoptosis occurred at a late time point in SiHa cells. Cell-cycle progression and DNA synthesis assays showed that the cellular mechanisms of growth inhibition by AAPF_CMK differ between the HPV16-positive and HPV-negative tumorigenic cell lines. Drug-treated C33a cells showed a significant accumulation of cells in the G2 phase of the cell cycle. In SiHa cells, growth inhibition produced by AAPF_CMK seemed to result from a global arrest of the cell cycle. Although the molecular mechanisms involved in AAPF_CMK-induced growth inhibition are distinct between the two tumorigenic cell lines, such differences may ultimately prove to have therapeutic utility. Novel therapies for treating established HPV infections are needed, because HPV is a causative agent in the development of multiple types of cancer.