Abstract 68: Tumor operational signaling pathways in an Nf1 mutant mouse model system

Abstract

Abstract Purpose/Objectives: NF1 is recognized as a tumor suppressor, via its role as a Ras GTPase activating protein. However, the precise mechanisms critical to tumor development in NF1 patients remain unclear. NF1 heterozygosity confers susceptibility to tumorigenesis, promoted by genotoxins such as radiation. We mutagenized Nf1 heterozygous mice using radiation to generate a diverse panel of Nf1 null tumors. Using these novel reagents we interrogated signaling pathways essential for tumor development and propagation towards identification of potential targets for therapeutic approaches. Materials/Methodology: Cell lines were derived from solid tumors developing after focal irradiation of Nf1 heterozygous mice. Radiation-induced tumors included mammary carcinomas, squamous carcinomas, and sarcomas. We employed a high-throughput toxicity screen of 94 conventional and targeted FDA-approved chemotherapeutics directed across diverse core cellular signaling pathways. Drug sensitivity profiles were determined by quantifying cell numbers after a 72 hour drug exposure, and tumor cell lines, non-transformed wild-type and Nf1 null MEFs, and mutant Ras-transformed cell lines (added as controls) were compared. Validation of identified drug sensitivities was performed by enzyme activity assays, phosphoprotein analysis, and soft-agar colony formation. Results: Nf1 mutant tumors failed to demonstrate a common drug sensitivity signature, but instead revealed a heterogeneous pattern of differential sensitivities, with subgroups clustering independent of tumor histology. However, radiation-induced Nf1 null tumor lines exhibited increased sensitivity to inhibition of the Ras-Erk and PI3K-mTOR axis as compared to non-transformed controls. Enhanced sensitivity to agents targeting cell cycle and survival pathways was also observed selectively within the Nf1 null tumor cell lines. Conclusions: These studies indicate that Nf1 null tumors, even those of the same histology, do not intrinsically share a signature sensitivity profile to pharmacologic inhibition. This suggests that therapeutic targeting of signaling pathways in Nf1 mutant tumors is not likely to be defined strictly by Nf1 loss alone. Notably, these Nf1 null tumors evidence varied operational dependence upon PI3K-mTOR and Raf-MEK activity. Current efforts are directed towards further resolving essential mediators, with the goal of more precisely defining signaling pathways which drive progression of the malignant state. Citation Format: Steve Braunstein, Rana Mroue, Brian Huang, Sourav Bandyopadhyay, Jean Nakamura. Tumor operational signaling pathways in an Nf1 mutant mouse model system. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 68. doi:10.1158/1538-7445.AM2014-68