This invention is related to the Molecular Pharmacology field and especially to the development of peptides useful for treating epithelial tumors and mainly those associated to oncogenic types of HPVs. The main objective of this invention is to identify peptides whose structure permits to block the Casein Kinase II (CKII) phosphorylation domain by direct interaction with such a site. In the present invention it is shown eleven cyclic peptides with different aminoacid sequences which inhibit the CKII phosphorylation in vitro, exhibit cytotoxicity on HPV-16 transformed cells (CaSki) and also increase the sensitivity of these cells to the cytostatic effect of interferon (IFN). Furthermore, the invention relates to the use of these peptides conjugated or fused to other peptides and chemical compounds which penetrates into cells as well as with the use of both peptide and chemical mimetic molecules.