Abstract B27: Kinetochore-microtubule attachments as a precision therapy target

Abstract

Abstract Glioblastoma multiforme (GBM) is an aggressive and refractory cancer with limited therapeutic strategies and poor survival. One challenge in treating this disease is the ability of single glioblastoma stem-like cells (GSCs) to initiate tumors. To expand the therapeutic repertoire for GBM we performed RNAi screening in GSCs and a proposed cell of origin, neural crest stem cells (NSCs). In these screens we identified multiple regulators of kinetochore-microtubule attachments as specifically required for GSC survival. Kinetochores are composed of hundreds of proteins that form dynamic attachments between microtubules and chromosomes and are essential for genetic fidelity. Antimitotic agents, including those that target kinetochore proteins, are attractive therapeutics because cell division is essential for tumor expansion, but also because mitotic errors can trigger p53-independent apoptotic signals. However, as mitosis is an essential process, most antimitotic drugs have extremely limited therapeutic windows. We demonstrate that specific activities of the mitotic pseudokinase BubR1 are completely dispensable for non-transformed cells, yet become required for survival in a subset of GBM tumors. Through mutational studies we demonstrate that inactivating either BubR1's GLEBS or KARD domain causes lethal chromosome alignment defects in most GSCs and has no observable on-target toxicity in non-transformed cells. We further demonstrate that this cancer-specific requirement arises from oncogenic activation of the MAP kinase pathway, which ultimately hyperactivates Aurora B kinase at kinetochores. Increased phosphorylation of kinetochore proteins weakens their binding to microtubules and can be indirectly measured by a decrease in the distance between sister kinetochore pairs upon microtubule attachment. In limited samples, this measure serves as a functional biomarker for samples that require BubR1 for chromosome alignment. This work has identified multiple precision targets for GBM with dramatic therapeutic windows; moreover, we have initiated development of a biomarker to identify patients that would respond to such a therapy. Citation Format: Jacob A. Herman, Patrick J. Paddison, Jennifer DeLuca, James Olson. Kinetochore-microtubule attachments as a precision therapy target. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Cancer Cell Cycle - Tumor Progression and Therapeutic Response; Feb 28-Mar 2, 2016; Orlando, FL. Philadelphia (PA): AACR; Mol Cancer Res 2016;14(11_Suppl):Abstract nr B27.