Advancing RAS pathway targeted therapy in NF1-MPNST: effects of SHP2 and CDK4/6 inhibitors on the tumor and the tumor immune microenvironment

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PROJECT SUMMARY/ ABSTRACT There has been little advancement in overall survival for patients with malignant peripheral nerve sheath tumor (MPNST), despite decades of research and many clinical trials, and thus novel therapies are needed. While loss of NF1 GTPase-activating protein function suggests that targeting RAS may be a logical therapeutic approach, there is currently no approved drug that effectively and directly targets wild-type RAS. The design of novel therapeutic combinations requires a deep understanding of the signaling pathways regulated by hyperactive RAS and feedback that conditions the response to their inhibition. MEK, SHP2, and CDK4/6 are critical nodes in RAS effector signaling in MPNST tumors, and combinations of small molecule inhibitors that target them may have synergistic anti-tumor activity. Further, adaptive signaling changes in response to RAS effector pathway inhibition occurs not only in tumor cells but also in cells that comprise the tumor immune micro- environment (TIME). Thus, the characterization of the TIME in our murine model of MPNST, and its modulation via small-molecule inhibitors of the RAS pathway, will identify key immune pathways leading to the reprogramming of intratumoral myeloid cells, enhancing endogenous immune responses. We propose three Aims: 1. Identify and functionally validate mechanisms of acquired resistance to SHP2 inhibitors in MPNST in order to develop novel therapeutic combinations. We will determine how tumors become resistant to SHP2i, as well as to SHP2i +CDK4/6i in combination, and will perform genetic manipulation studies in order to functionally validate priority hits. 2. Determine the efficacy and tolerability of combination small- molecule inhibitors of RAS signaling, particularly SHP2i + CDK4/6i, in in vitro, patient-derived xenografts (PDX), and immune-competent syngeneic Nf1 -/-/Ink4a/Arf -/- mouse models. We will test the effects of SHP2i and CDK4/6i single agents or combinations as tools to probe the biochemical and biological changes that occur upon pathway perturbation, and will determine the mechanism and anti-tumor activity of these combinations, with a priority focus on the SHP2i+CDK4/6i combination, based on our advanced preliminary data. 3. Reprogram the intratumoral pathological myeloid cells via treatment with the combination of SHP2i and CDK4/6i in murine MPNST. Our preliminary data suggest that the landscape of MPNST is densely populated by tumor infiltrating myeloid cells. To evaluate the effects of these agents and their combinations on the TIME, we will utilize single cell transcriptional analysis, multiparameter flow cytometry and multiplex immunohistochemistry to decipher the specific effects of these drugs on cell types that comprise the tumor, including both immune-infiltrating and primary tumor cells. By determining the efficacy and mechanism of these rationally-designed therapeutic strategies in both PDX and immune-competent mouse models, our studies will provide mechanism-based, promising combinatorial approaches that may be rapidly and successfully translated to the clinic, and will inform effective patient selection strategies and the development of novel clinical trials for patients with MPNST.