The development of targeted anticancer drugs has been one of the most challenging goals of current research. Eukaryotic translation
initiation factor 4E (
eIF4E) is an oncogene that stimulates mRNA translation via binding to the 5' endcap structure. It is well documented that
eIF4E is overexpressed in many
cancers including breast, prostate, head and neck, and stomach
malignancies and leads to oncogenic transformation and
metastasis. One approach to block
eIF4E function in
cancer cells is based on the disruption of the interaction between
eIF4E and the
5' mRNA cap structure using cap analog inhibitors. Since analogs are cell-impermeable due to their anionic nature, we used a
cell penetrating peptide (
CPP) for delivery of model cap analogs into
cancer cells. The human immunodeficiency virus I (HIV-1)
transactivator of transcription derived
peptide (TAT) was conjugated with the analogs m7GMP and m7GpppG using click chemistry methodology. We observed that both conjugates (m7GMP-TAT and m7GpppG-TAT), contrary to TAT alone, did not translocate through the artificial
phospholipid membrane of giant
unilamellar vesicles. This suggests that passive transport is not the mechanism by which translocation of cap analogs occurs. In contrast, synthesized fluorescently labeled m7GpppG-TAT translocated into the human breast
adenocarcinoma cancer cell line MCF-7. Furthermore, we demonstrated that m7GMP-TAT and m7GpppG-TAT inhibited cap-dependent translation up to 30% both in vivo and in vitro while simultaneously not affecting cell growth and viability. These results demonstrate the usefulness of cell penetration
peptides as carriers for the internalization of cap analogs.