The serine protease inhibitors TLCK and TPCK inhibit the in vitro immortalization of primary human keratinocytes by HPV-18 DNA.

The human papillomaviruses (HPV) which are commonly found in anogenital malignancies express a viral E7 oncoprotein which possesses both immortalizing and transforming activities. The E7 protein forms a complex with the cellular tumor suppressor protein Rb and alters its interaction with transcription factor E2F, presumably interfering with cell cycle control and contributing to cellular transformation/immortalization. We demonstrated earlier that the serine protease inhibitors tosyl-L-phenylalanine chloromethyl ketone (TPCK) and tosyl-L-lysine chloromethyl ketone (TLCK) modified the HPV type 18 E7 protein in cell extracts as well as in living cells and abrogated its ability to form a complex with Rb. In the present study we evaluated the effect of TLCK or TPCK treatment on the immortalization of primary keratinocytes by transfected HPV-18 DNA. Supplementing the medium of primary foreskin keratinocytes with TLCK or TPCK during their immortalization with HPV 18 DNA demonstrated that either TLCK (5--10 microM) or TPCK (0.25 microM) could inhibit cellular immortalization by 50-100% without altering keratinocyte proliferation, suggesting that the topical application of these reagents in vivo could significantly interfere with HPV-mediated cellular transformation.