Introduction. The interaction between intracellular caspase-9 and PP2A proteins is critical to apoptosis. We designed PEP-010, a Cell Penetrating & Interfering Peptide, which specifically disrupts the interaction between caspase-9 and PP2A. We evaluated in vitro and in vivo its therapeutic properties to demonstrate its potential as an innovative approach to breast cancers treatment.

Material and Methods. In vitro evaluation was done by apoptosis (Annexin V) and cell viability (MTT) measurements on cancer cell lines from different origins. In vivo efficacy studies were conducted on patient-derived xenograft (PDX) mice models of triple-negative breast cancer (TNBC) and hormone-positive HER2-negative breast adenocarcinoma (BC). Pharmacokinetic and biodistribution studies were conducted on mice after administration by iv and ip route. Preliminary tolerance studies were done on mice and rats after repeated administration of PEP-010.

Results. First, we demonstrated that PEP-010 is able to penetrate into tumor cells and induces caspase-9-dependent apoptosis in several tumor cell types. Moreover, we demonstrated that PEP-010 specifically induces the death of cancer cells (CLL) without harm to healthy cells.After PEP-010 treatment, we observed a significant tumor growth inhibition in PDX mice models of TNBC, compared to the untreated control. In BC PDX mice models, we observed also a significant tumor growth inhibition with complete response after PEP-010 treatment. We also improved the stability and the pharmacokinetic parameters of PEP-010. Point mutations on a protease cleavage site clearly improved peptide stability while keeping the functional activity. Biodistribution studies demonstrated that the optimized peptide is able to reach the targeted tumor and accumulate there at higher concentration than the former peptide. Pharmacokinetic studies in mice administered with PEP-010 by iv and ip route were conducted as well as in vitro study of plasmatic clearance of PEP-010 in different species. We finally performed formulation studies to improve the solubility of PEP-010 and confirmed the efficacy of the drug product in a BC PDX mice model.Preliminary tolerance studies were done on mice and rats after repeated administration of PEP-010 without demonstrating any signs of toxicity. Moreover, no immunogenic response has be observed after repeated administration of PEP-010 in mice.

Conclusion. Using PEP-010, a CP&IP blocking caspase-9/PP2A interaction, we have demonstrated that this peptide has an interesting in vitro and in vivo therapeutic effect. PEP-010 constitutes a new innovative therapeutic approach for the treatment of human breast cancers. PEP-010 will enter GLP toxicity studies shortly in order to prepare the first in human clinical trial.

Citation Format: Sophie Lebel-Binay, Fariba Nemati, Leticia Dominguez-Berrocal, Justine Fleury, Adnan Naguez, Didier Decaudin, Angelita Rebollo. PEP-010, a cell penetrating & interfering peptide as a new therapeutic approach in breast cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3904.