Abstract 1771: Pre-clinical validation of a novel anti-tumor strategy using cell penetrating peptides blocking caspase-9/PP2A interaction (2011)

Abstract Background: Dysfunction in the regulation of apoptosis is associated with important pathologies, including cancers. While apoptosis is known to rely on the Bcl-2 family members and caspases, recent data suggest that the serine/threonine phosphatase PP2A is a key actor in regulating both Bcl-2 family members and caspases for cell life or cell death decision. Cell penetrating peptides are molecules that can translocate into cells without causing membrane damage, leading to their proposed use as vector for delivering therapeutic cargo. Focusing on both caspase-9 and PP2A, our goal was to develop cell penetrating peptides specifically designed against the caspase-9/PP2A interaction and evaluate their in vitro and in vivo therapeutic potential in various cancer cells and tumors. Materials and Methods: We have published the Drug Phosphatase Technology (DPT) based on the design of cell penetrating peptides obtained by association of a cell permeable shuttle, DPT-sh1 to a sequence of interest. We have also shown a direct interaction of human caspase-9/human PP2Ac, detected by co-immunoprecipitation and confirmed by far western. We decided to generate a peptide containing the previously published penetrating sequence (DPT-Sh1) associated to the site of interaction of human caspase-9 (DPT-C9h), in order to disturb the interaction caspase-9/PP2Ac. Using breast cancer, non-small cell lung cancer, and uveal melanoma cell lines, and well characterized primary human breast cancer (BC) xenografts, we have then investigated the effect of DPT-C9h in in vitro apoptosis induction using the Annexin V-FITC and propidium iodide approaches, and in ex vivo tumor growth inhibition (TGI). DPT-C9h peptide was intraperitonealy administered at doses ranging from 1 to 25 mg/kg/day for 5 weeks. Tumor volume was measured twice per week and Relative Tumor volume (RTV) was calculated from the beginning of the treatment. Results: We have demonstrated that DPT-C9h specifically blocked in vitro, in vivo, and ex vivo caspase-9/PP2A interaction, and induced apoptosis in all tested cancer cell lines. We have also showed that DPT-C9h induced a TGI of 80% and 60% in one luminal (HBCx-5) and one triple negative (HBCx-10) BC xenografts, respectively. Other in vivo experiments using different breast cancer xenografts models are ongoing. Finally, no toxicity has been observed in treated mice, as well as no immunogenic response in immunodeficient mice. Conclusions: We have identified an interaction between caspase-9/PP2A that may be used as a new therapeutic target. Using the cell penetrating peptide DPT-C9h blocking this interaction, we have demonstrated that DPT-C9h had an impressive in vitro and in vivo therapeutic effect and therefore constitutes a new therapeutic approach of human cancers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 1771. doi:10.1158/1538-7445.AM2011-1771