Abstract 5326: Intracellular bacterial delivery of a NIPP1-peptide kills tumor cells

Abstract

Abstract Protein phosphatase-1 (PP1) is a cancer target because it is involved in many cell signaling pathways. Its activity is tightly regulated by its interaction partners, mainly via the RVxF-binding motif. RVxF-containing peptides deregulate PP1 and have therapeutic potential as antagonists of increased cancer kinase signaling. Because PP1 is responsible for more than half of the dephosphorylations on Ser/Thr sites, it is essential in all eukaryotic cells and it is difficult to target systemically. Moreover, delivering peptides to cells extracellularly is inefficient because of poor cell permeability and proteolytic instability. To specifically transport therapeutic peptides into cancer cells, we engineered bacteria to be intracellular delivery vectors. A bacterial delivery system (BDS) was designed by creating a strain that lyses after cell invasion and releases its contents into the cytoplasm of cancer cells. A BDS strain was then manipulated to express a peptide containing the RVxF motif of Nuclear Inhibitor of PP1 (NIPP1; AA 142-224). The therapeutic potential of this strain was tested on MCF-7 cell monolayers and on 3D tumor tissue. The BDS was cloned by inserting the bacterial phage lysis gene E under the control of the sseJ promoter, a Salmonella promoter that is activated after cell invasion. The specificity of the sseJ promoter was tested by inserting GFP under its control and infecting MCF-7 cancer cells with Salmonella containing the plasmid. All intracellular bacteria expressed GPF after 4 hours of infection, while no fluorescence was measured in the bacteria outside the mammalian cells. After infection, the created BDS lysed in 78% of invaded cells. BDS delivery of the NIPP1-peptide to MCF-7 cancer cells killed 41% of infected cells while infection with control, empty BDS did not result in any death. When treating tumor tissue with BDS expressing NIPP1-peptide, 39% of tumor tissue was killed after 9.5 hours, compared to 8% when treated with BDS alone. These results indicate that targeting phosphatases with intracellular peptide delivery by bacteria is feasible and reduces tumor tissue viability. Citation Format: Nele Van Dessel, Neil S. Forbes. Intracellular bacterial delivery of a NIPP1-peptide kills tumor cells. [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 5326. doi:10.1158/1538-7445.AM2015-5326