Listeriolysin O enhances cytoplasmic delivery by Her-2 targeting liposomes

Abstract

To enhance cytoplasmic delivery of liposomal contents to breast cancer cells, the authors have attached the pore-forming protein, listeriolysin O (LLO), to thermosensitive liposomes. The antibody trastuzumab (Herceptin^®) was also conjugated with the outer surface of the liposomes, resulting in highly specific binding and internalization into mammary epithelial cells that overexpress the human epidermal growth factor receptor 2 (Her-2). The liposomes were preloaded with a marker fluorescent dye, and the effect of LLO on the distribution of dye within the cells was monitored using fluorescence microscopy. Owing to the thermosensitive nature of the liposomes, hyperthermia at 42°C triggered the release of the encapsulated fluorescent calcein from the endocytosed liposomes into the interior of the endosomes. LLO, when conjugated to these liposomes, subsequently formed pores in the endosomal membrane, allowing calcein to flow out of the endosomal compartment into the cytoplasm. Her-2–targeted liposomes bearing LLO delivered a 22-fold greater concentration of calcein to mammary epithelial cells that overexpress Her-2 compared to cells with normal Her-2 expression. Thus, the addition of LLO to preformed liposomes offers a method for significantly enhancing delivery of liposomal contents to the cytoplasm of targeted cells.

Keywords::

• Cancer
• controlled drug delivery
• immunoliposomes
• Her-2
• ErbB2
• trastuzumab
• listeriolysin O
• thermosensitive liposomes
• Herceptin©

Acknowledgments

The authors thank Kristian Sexton, Brooke Kullberg, and Holly Martinson for their technical support and Dr Richard Kullberg for his critical review of the manuscript.

Declaration of interest: The authors are extremely grateful to Dr. Max Rabinowitz at Alaska Oncology and Hematology for generously donating trastuzumab. This work was funded by grants from the Alaska Run for Women, the Alaska Men’s Run, and the WWAMI program at the University of Alaska Anchorage. The authors alone are responsible for the content and writing of the paper.