Intracellular redistribution of cell-penetrating peptide p28: A mechanism for enhanced anti-cancer activity

Cell-penetrating peptides (CPPs) have been studied as they provide an efficient strategy for the intracellular delivery of bioactive molecules in various biomedical applications such as cancer diagnosis and therapy. We have developed an anionic CPP, p28, that can preferentially enter cancer cells and induce cell cycle arrest and apoptotic cell death preclinically and that showed preliminary efficacy in humans. Yet, the underlying intracellular fate after cell entry remains largely uncharacterized. To better understand the intracellular trafficking of p28, we investigated more closely the role of endosomal acidification and retrograde transport in cancer cells. Here, we show that agents such as chloroquine (CQ), NH₄Cl, and nordihydroguaiaretic acid (NDGA) that alter discrete steps of endocytosis or Golgi-mediated transport remarkably increased p28 access to the cytosol and nucleus. Moreover, CQ significantly improved the antiproliferative effects induced by p28. Our findings suggest that inadequate intracellular localization is the major limiting factor for the efficacy of CPPs such as p28. Taken together, these results indicate that the effective and adequate alternation of intracellular localization of CPPs can be a promising drug-delivery strategy to specifically deliver the therapeutic molecule to its intracellular therapeutic active site or organelle that leads to potentiate the efficacy for cancer diagnosis and therapy.