Abstract A020: Combined inhibition of SHP2 and CDK4/6 is active in preclinical models of NF1-associated malignant peripheral nerve sheath tumor

Abstract Background: NF1 is an essential negative regulator of RAS activity and its function is lost in nearly 90% of malignant peripheral nerve sheath tumors (MPNST). Additional recurrent molecular changes include loss of function alterations in CDKN2A, TP53, EED and SUZ12, but molecular targeting of these genomic events represents a unique challenge. We previously reported that the efficacy of MEK inhibitor is limited by adaptive activation of receptor tyrosine kinases and the adaptor protein SHP2, and that combined inhibition of MEK and SHP2 is effective in MPNST. However, the clinical potential of combination MEK and SHP2 inhibitors may be limited by the overlapping toxicity induced by ERK pathway inhibition. Loss of CDKN2A, inactivation of RB1, and hyperactivation of cyclin dependent kinases (CDK) in MPNST also suggest that small-molecule CDK4/6 inhibitors (CDK4/6i) may be a potential therapeutic strategy, but monotherapy with CDK4/6i also demonstrates limited activity. We hypothesize that the anti-tumor response of SHP2i may be potentiated by agents targeting the cell cycle in combination. Methods: The effects of shRNA-mediated inducible SHP2 knockdown on RAS signaling, short-term and long-term cell growth, and response to CDK4/6i were examined using immunoblotting, high throughput proliferation assays, and colony formation assays. Combined effects of SHP2i plus CDK4/6i on signaling, cell cycle, apoptosis, cell and in vivo tumor growth were assessed. Pharmacodynamic (PD) assays were performed on tumors extracted following drug treatment in patient-derived xenograft (PDX) models of MPNST. Results: Despite a modest effect of SHP2 knockdown on ERK signaling, shPTPN11 reduced MPNST cell growth. SHP2 knockdown or SHP2i treatment alleviated activation of ERK signaling and cyclin D1 expression induced by CDK4/6i, and enhanced the sensitivity to CDK4/6i. Combination benefit was observed in in vitro cell growth and in vivo PDX. Although some PDX models demonstrated similar responses to SHP2i alone or SHP2i + CDK4/6i during the initial four weeks on treatment, we found sustained tumor growth inhibition exerted by the combination on longer therapy. PD studies demonstrated a decrease in p-ERK levels in tumors treated with either SHP2i alone or the SHP2i/CDK4/6i combination, as well as a synergistic suppression of cell cycle regulators by the combination. Conclusions: Our preliminary data demonstrate that the combined inhibition of SHP2 and CDK4/6 is active and produces deep and durable response in models of NF1-associated MPNST. This combination strategy may represent a novel treatment approach for patients with MPNST. Citation Format: Jiawan Wang, Ana Calizo, Kai Pollard, Lindy Zhang, John M. Gross, Nicolas Llosa, Angela C. Hirbe, Christine A. Pratilas. Combined inhibition of SHP2 and CDK4/6 is active in preclinical models of NF1-associated malignant peripheral nerve sheath tumor [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr A020.