Purpose: Cervical cancer cells are addicted to the expression of the human papillomavirus (HPV) oncoproteins E6 and E7. The oncogencity of E6 is mediated in part by targeting p53 and PDZ-family tumor suppressor proteins for rapid proteasomal degradation, whereas the E7 oncoprotein acts in part by coopting histone deacetylases (HDAC)1/2. Here, we examine the hypothesis that inhibition of proteasome function and HDAC activity would synergistically and specifically trigger cervical cancer cell death by the interruption of E6 and E7 signaling.
Experimental design: The sensitivity and molecular responses of keratinocytes and HPV-positive and HPV-negative cervical cancer cells and xenografts to combinations of proteasome and HDAC inhibitors were tested. The expression of HDAC1/HDAC2 in situ was examined in cervical cancer, its precursors, and normal epithelium.
Results: Cervical cancer cell lines exhibit greater sensitivity to proteasome inhibitors than do HPV-negative cervical cancers or primary human keratinocytes. Treatment of cervical cancer cells with bortezomib elevated the level of p53 but not hDlg, hScribble or hMAGI. Immunohistochemical analysis revealed elevated HDAC1/HDAC2 expression in cervical dysplasia and cervical carcinoma versus normal cervical epithelium. The combination of bortezomib and HDAC inhibitor trichostatin A or vorinostat shows synergistic killing of HPV-positive, but not HPV-negative, cervical cancer cell lines. Similarly, treatment of HeLa xenografts with the combination of bortezomib and trichostatin A retarded tumor growth significantly more effectively than either agent alone.
Conclusions: A combination of proteasome and HDAC inhibitors, including bortezomib and vorinostat, respectively, warrants exploration for the treatment of cervical cancer.