Abstract 2923: A novel cell-penetrating peptide targeting ATF5 (CP-d/n-ATF5) exerts anti-cancer activity in vitro and in vivo against a broad spectrum of human cancers

Abstract

Abstract Background The purpose of this study was to validate the anti-neoplastic activity of a novel ATF5-targeted therapeutic approach against various recalcitrant human malignancies. Activating transcription factor 5 (ATF5) is a member of the cAMP response element binding (CREB)/ATF subfamily of basic leucine zipper transcription factors and has been shown to be overexpressed in many human cancers. CP-d/n-ATF5 is a novel peptide specifically designed to contain a cell-penetrating domain and a domain inhibiting the function of ATF5 in a unique and novel targeted therapeutic approach. This therapeutic strategy was tested among a large panel of different therapy refractory human cancers including glioblastoma, melanoma, breast, prostate-, lung- and pancreatic cancer. Methods Cellular viability was assessed by MTT-assays. The induction of apoptosis was examined by staining for annexin V/propidium iodide or JC-1 (loss of mitochondrial membrane potential) prior to flow cytometric analysis. Western blotting was performed for further molecular analysis detecting caspase cleavage and expression of Bcl-2 family members. Subcutaneous xenograft models were used to examine the anti-neoplastic effects of CP-d/n-ATF5 in vivo. Results Our data show that CP-d/n-ATF5 yields a significant increase in apoptosis across a panel of 10 different cancer cell lines when compared to treatment with a mock-mutated control peptide or penetratin. On the molecular level, treatment with CP-d/n-ATF5 resulted in a marked down-regulation of the anti-apoptotic Bcl-2 family members Mcl-1 and Bcl-2. This effect was amplified in a synergistic manner by adding either ABT-263 or TRAIL to a combined targeted therapeutic approach. In vivo, treatment with CP-d/n-ATF5 resulted in a significant reduction of tumor growth in a heterotopic glioblastoma- and an orthotopic melanoma model. Conclusions The novel ATF5-targeting compound CP-d/n-ATF5 provides a broad and pronounced anti-neoplastic activity against human cancers in vitro and in vivo. On the molecular level, this effect is at least in part due to a shift of the cellular homeostasis towards a pro-apoptotic cellular phenotype by inhibiting anti-apoptotic Bcl-2 family proteins. Overall, CP-d/n-ATF5 may represent a promising novel anti-cancer agent. Citation Format: Georg Karpel-Massler, Chang Shu, Lily Chau, James M. Angelastro, Lloyd A. Greene, Markus D. Siegelin. A novel cell-penetrating peptide targeting ATF5 (CP-d/n-ATF5) exerts anti-cancer activity in vitro and in vivo against a broad spectrum of human cancers. [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 2923. doi:10.1158/1538-7445.AM2015-2923