Abstract 2940: Identifying the minimal region of the ING1 tumor suppressor capable of efficiently killing cancer cells

Abstract

Abstract ING1b is a type II tumor suppressor and a stoichiometric member of HDAC-containing protein complexes. ING1b overexpression promotes apoptosis, and decreased levels of ING1b are frequently observed in human tumors and cancer cell lines. Previously, we reported the identification of the regions of ING1b protein required for its pro-apoptotic function. Using deletion mutant analysis and transient expression in HEK293 cells we have determined that ING1b-derived peptides comprised of the NLS/NTS domain and the third alpha helix (A3H) of ING1b including the N-terminal portion of Lamin Interaction Domain (LID) are able to induce apoptosis at levels comparable to those of the full length ING1b, despite their lacking the PHD domain through which they affect the histone epigenetic code. Here, we report that adenoviral delivery of the A3H-NLS/NTS peptide led to a significant decrease in cell survival and induced apoptosis in a majority of tested cancer cell lines. The list of sensitive cancer cell lines was broad and included lines derived from both primary and metastatic tumor sources. As shown using an Annexin V binding assay, decreased survival of cells infected with adenovirus expressing A3H-NLS/NTS peptide was due to a large number of infected cells undergoing apoptosis. In fact, infecting triple negative tumorigenic MDA-MB-468 breast cancer line with 30 MOI of the Ad-A3H-NLS/NTS virus triggered rapid apoptosis in nearly 70% of infected cells. Importantly, these effects were time and dose dependent. Also, using a cell line carrying an inducible p53-expression system, we established that the ability of Ad-A3H-NLS/NTS to induce apoptosis is p53-independent. Next, we evaluated the cell death inducing properties of Ad-A3H-NLS/NTS using 10 breast cancer cell lines that were chosen based on their sensitivity to common HDAC inhibitors. While the overall sensitivity to Ad-A3H-NLS/NTS induced cell death varied among these lines, we observed no obvious correlation between the sensitivity to Ad-A3H-NLS/NTS and sensitivity/resistance to HDAC inhibitors. These findings suggest that Ad-A3H-NLS/NTS may have a broad application, including in those cancer cells lines that are normally resistant to conventional chemotherapy. Furthermore, combined application of Ad-A3H-NLS/NTS with either Trichostatin A (TSA) or Panobinostat (LBH-589) resulted in a strong additive, and possibly synergistic killing effect. Using the virus with either TSA or LBH-589 increased efficacy by nearly 3.5-fold as compared to the treatment with either TSA or LBH-589 along. Currently, the synergy between the Ad-A3H-NLS/NTS and common chemotherapeutics is being closely evaluated. Our long-term goal is to develop ING1b-based therapeutics that can be used as an adjuvant therapy in combination with existing cancer treatments. Citation Format: Oleksandr Boyko, Karl T. Riabowol. Identifying the minimal region of the ING1 tumor suppressor capable of efficiently killing cancer 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 2940. doi:10.1158/1538-7445.AM2015-2940