Abstract 5526: Deciphering the basis of CendR-mediated penetration into tumors

Abstract

Abstract Cell-penetrating peptides (CPPs) have proven their usefulness in overcoming barriers (such as the cell membrane) of drug delivery into tumor cells. We recently discovered a novel class of cell-penetrating peptides that also have tumor-penetrating properties. These so-called, CendR peptides,bind to neuropilin-1 (NRP1) and initiate an active endocytic process into tumor cells. Subsequent studies showed that CendR-initiated endocytosis is a receptor-dependent macropinocytosis process, and that its activity is stimulated by mTOR inhibition and nutrient deprivation. In vivo, CendR peptides penetrate across tumor vessels deeply into the extravascular tumor tissue, and show ability to improve the tumor accumulation and antitumor efficacy of coupled, and even co-administrated, drugs. Further understanding of the CendR-mediated cell and tissue penetration is of value to cell biology and cancer therapy. Here, we report ultrastructural studies to unveil the subcellular transport route for CendR peptide. After synchronized cell entry, transmission electron microscopy (TEM) imaging shows that CendR cargo is transported from early endosomes to late endosomes and lysosomes. We have also identified some of the genes important for this transport. Moreover, magnetic isolation of intracellular vesicles containing CendR cargo and proteomics analysis identified signature molecules associated with these vesicles. Studies with TAT peptide comprised of D-amino acids (D-TAT), included in these studies as a non-CendR CPP, indicate that D-TAT also penetrates into tumor cells through a variation of macropinocytosis independent of NRP1. The uniqueness of CendR pathway lies in the linkage of CendR endocytosis to mTOR and cellular nutrient status. We provide evidence that a transcription factor, Sp1, serves as a link between mTOR and CendR endocytosis by regulating the NRP1 level on the cell surface. Additionally, we have shown the intercellular transport of CendR cargo that affords tissue penetration and is also stimulated by nutrient deprivation. Here we identify genes critical to the export and re-entry of CendR cargo during intercellular transport. These results shed light into the mechanism of action of CPPs, and endocytosis in general. They also have implications in cancer metabolism and drug delivery. Citation Format: Hongbo Pang, Gary B. Braun, Tomas Friman, Erkki Ruoslahti. Deciphering the basis of CendR-mediated penetration into tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5526. doi:10.1158/1538-7445.AM2015-5526