Utilization of a cell-penetrating peptide-adaptor for delivery of HPV protein E2 into cervical cancer cells to arrest cell growth and promote cell death

Cervical cancer is the second leading cause of cancer deaths in women worldwide. Human papillomavirus (HPV) is the causative agent of nearly all forms of cervical cancer, which arises upon viral integration into the host genome and concurrent loss of regulatory gene E2. E2 protein regulates viral oncoproteins E6 and E7. Loss of E2 upon viral integration results in unregulated expression and activity of E6 and E7, which promotes carcinogenesis. Previous studies using gene-based delivery show that reintroduction of E2 into cervical cancer cell lines can reduce proliferative capacity and promote apoptosis. However, owing in part to limitations on transfection in vivo, E2 reintroduction has yet to achieve therapeutic usefulness. A promising new approach is protein-based delivery systems utilizing cell-penetrating peptides (CPPs). CPPs readily traverse the plasma membrane and are able to carry with them biomolecular cargos to which they are attached. Though more than two decades of research have been dedicated to their development for delivery of biomolecular therapeutics, the full potential of CPPs has yet to be realized as the field is hindered by the tendency of CPP-linked cargos to be trapped in endosomes as well as having significant off-target potential in vivo. Using a CPP-adaptor system that reversibly binds cargo thereby overcoming the endosomal entrapment that hampers other CPP methods, bioactive E2 protein was delivered into living cervical cancer cells, resulting in inhibition of cellular proliferation and promotion of cell death in a time- and dose-dependent manner. The results suggest that this nucleic acid- and virus-free delivery method could be harnessed to develop novel, effective protein therapeutics for treatment of cervical cancer.