A Synthetic Cell-Penetrating Dominant-Negative ATF5 Peptide Exerts Anticancer Activity against a Broad Spectrum of Treatment-Resistant Cancers

Abstract

Purpose Despite significant progress in cancer research many tumor entities still have an unfavorable prognosis. Activating Transcription Factor 5 (ATF5) is up-regulated in various malignancies and promotes apoptotic resistance. We evaluated the efficacy and mechanisms of the first described synthetic cell-penetrating inhibitor of ATF5 function, CP-d/n-ATF5-S1. Experimental Design Preclinical drug testing was performed in various treatment-resistant cancer cells and in vivo xenograft models. Results CP-d/n-ATF5-S1 reduced the transcript levels of several known direct ATF5 targets. It depleted endogenous ATF5 and induced apoptosis across a broad panel of treatment refractory cancer cell lines, sparing non-neoplastic cells. CP-d/n-ATF5-S1 promoted tumor cell apoptotic susceptibility in part by reducing expression of the deubiquitinase Usp9X and lead to diminished levels of anti-apoptotic Bcl-2 family members Mcl-1 and Bcl-2. In line with this, CP-d/n-ATF5-S1 synergistically enhanced tumor cell apoptosis induced by the BH3-mimetic ABT263 and the death ligand TRAIL. In vivo, CP-d/n-ATF5-S1 attenuated tumor growth as a single compound in melanoma, glioblastoma, prostate cancer and triple-receptor-negative breast cancer xenograft models. Finally, the combination treatment of CP-d/n-ATF5-S1 and ABT263 significantly reduced tumor growth in vivo more efficiently than each reagent on its own. Conclusions Our data support the idea that CP-d/n-ATF5-S1, administered as a single reagent or in combination with other drugs, holds promise as an innovative, safe and efficient anti-neoplastic agent against treatment-resistant cancers.

Inhibition of Mitochondrial Matrix Chaperones and Antiapoptotic Bcl-2 Family Proteins Empower Antitumor Therapeutic Responses

“…For Annexin V/propidium iodide staining the Annexin V Apoptosis Detection Kit (BD Pharmingen) was used as previously described (24,25). For PI staining, cells were resuspended in 300 µl PBS and fixated by adding 1000 µl ice-cold ethanol prior to incubation over night at 4°C.…”

“…Patient-derived xenograft cells were stereotactically injected into 6–8 week-old male or female nude GFP or SCID SHO mice as previously described (22,24). A burr hole was positioned 2mm anterior and 2mm lateral of the bregma prior to introducing a Hamilton syringe under stereotactic guidance 3mm into the striatum.…”

Metabolic reprogramming of glioblastoma cells by L-asparaginase sensitizes for apoptosis in vitro and in vivo

“…A p ≤ 0.05 was considered statistically significant. The CompuSyn software (ComboSyn, Inc., Paramus, NJ - www.combosyn.com last accessed 06/01/15) was used for the drug combination analysis including the calculation of the combination index (CI) and isobologram as described before [58]. A CI < 1 was considered as synergistic, a CI = 1 as additive and a CI > 1 as antagonistic.…”

Mitochondrial dysfunction in cancer: Potential roles of ATF5 and the mitochondrial UPR

“…Interestingly, a cell permeable peptide, CP-d/n-ATF5-S1, has been developed as an ATF5-specific inhibitor. The inhibitory peptide impairs the growth of prostate cancer, glioblastoma, melanoma and triple receptor-negative breast cancer cells in cell culture and xenograft models by inducing apoptosis [134]. Lastly, ATF5 inhibition can selectively kill rat and human glioblastoma cells as well as human pancreatic cancer cells while sparing the neighboring normal cells in vivo [98, 99].…”