Oncogenic alterations in the RAS/RAF/MEK/ERK pathway drive the growth of a wide spectrum of cancers. While BRAF and MEK inhibitors are efficacious against BRAF-driven cancers, effective targeted therapies are lacking for most cancers driven by other pathway alterations, including non-V600E oncogenic BRAF, RAS GTPase-activating protein (GAP) NF1 (neurofibromin 1) loss and oncogenic KRAS. Here, we show that targeting the SHP2 phosphatase (encoded by PTPN11) with RMC-4550, a small-molecule allosteric inhibitor, is effective in human cancer models bearing RAS-GTP-dependent oncogenic BRAF (for example, class 3 BRAF mutants), NF1 loss or nucleotide-cycling oncogenic RAS (for example, KRAS). SHP2 inhibitor treatment decreases oncogenic RAS/RAF/MEK/ERK signalling and cancer growth by disrupting SOS1-mediated RAS-GTP loading. Our findings illuminate a critical function for SHP2 in promoting oncogenic RAS/MAPK pathway activation in cancers with RAS-GTP-dependent oncogenic BRAF, NF1 loss and nucleotide-cycling oncogenic KRAS. SHP2 inhibition is a promising molecular therapeutic strategy for patients with cancers bearing these oncogenic drivers.

The ERK/MAP kinase cascade is a key mechanism subject to dysregulation in cancer and is constitutively activated or highly upregulated in many tumor types. Mutations associated with upstream pathway components RAS and Raf occur frequently and contribute to the oncogenic phenotype through activation of MEK and then ERK. Inhibitors of MEK have been shown to effectively block upregulated ERK/MAPK signaling in a range of cancer cell lines and have further demonstrated early evidence of efficacy in the clinic for the treatment of cancer. Guided by structural insight, a strategy aimed at the identification of an optimal diphenylamine-based MEK inhibitor with an improved metabolism and safety profile versus PD-0325901 led to the discovery of development candidate 1-({3,4-difluoro-2-[(2-fluoro-4-iodophenyl)amino]phenyl}carbonyl)-3-[(2S)-piperidin-2-yl]azetidin-3-ol (XL518, GDC-0973) (1). XL518 exhibits robust in vitro and in vivo potency and efficacy in preclinical models with sustained duration of action and is currently in early stage clinical trials. KEYWORDS: MAPK pathway, MEK, cancer, kinase inhibitor, XL518, GDC-0973 T he MAPK cascade, or mitogen-activated protein kinase signal transduction pathway, is a mechanism commonly subject to dysregulation in cancer, and constitutive or highly upregulated signaling is a frequent hallmark of oncogenic transformation and progression. Controlled by activation of RAS at the cell surface interior, the subsequent stimulation of Raf and then MEK and ERK serves to regulate a range of key intracellular effectors associated with cell proliferation, 1 invasion, 2 angiogenesis, 3 and apoptotic resistance. 4 Mutated RAS is associated with almost one-third of human cancers, and a majority of malignant melanomas and papillary thyroid cancers harbor B-Raf mutations. 5,6 Inhibitors of MEK have demonstrated efficacy against malignant tumors characterized by mutations in either RAS or Raf in preclinical models, and early development candidates including GSK1120212, In some tumors, activation of both the RAS driven ERK/ MAPK cascade and the PI3K-Akt pathway is observed, resulting in degenerate and convergent oncogenic signals, and upregulation or constitutive PI3K pathway activation is associated with resistance to MEK inhibitor single agent treatment.10 Several combination approaches using inhibitors of mTor, PI3K, Akt, and Raf have more recently been validated in preclinical models and are being pursued clinically. Herein, the discovery of XL518 (GDC-0973) (1), a potent and selective MEK inhibitor, is described. XL518 is currently in early stage clinical testing as both a single agent and in combination with the class I PI3K inhibitor GDC-0941. 11Our goal at the outset was the identification of a potent and selective MEK inhibitor with sustained duration of efficacy suitable for qd dosing and an optimized safety profile relative to clinical precursors. The diphenylamine series disclosed by the Pfizer/Warner Lambert groups served as a starting point for our effort. A key aspect tha...

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The protein tyrosine phosphatase SHP2 binds to phosphorylated signaling motifs on regulatory immunoreceptors including PD-1, but its functional role in tumor immunity is unclear. Using preclinical models, we show that RMC-4550, an allosteric inhibitor of SHP2, induces antitumor immunity, with effects equivalent to or greater than those resulting from checkpoint blockade. In the tumor microenvironment, inhibition of SHP2 modulated T-cell infiltrates similar to checkpoint blockade. In addition, RMC-4550 drove direct, selective depletion of protumorigenic M2 macrophages via attenuation of CSF1 receptor signaling and increased M1 macrophages via a mechanism independent of CD8 þ T cells or IFNg. These dramatic shifts in polarized macrophage populations in favor of antitumor immunity were not seen with checkpoint blockade. Consistent with a pleiotropic mechanism of action, RMC-4550 in combination with either checkpoint or CSF1R blockade caused additive antitumor activity with complete tumor regressions in some mice; tumors intrinsically sensitive to SHP2 inhibition or checkpoint blockade were particularly susceptible. Our preclinical findings demonstrate that SHP2 thus plays a multifaceted role in inducing immune suppression in the tumor microenvironment, through both targeted inhibition of RAS pathway-dependent tumor growth and liberation of antitumor immune responses. Furthermore, these data suggest that inhibition of SHP2 is a promising investigational therapeutic approach. Significance: Inhibition of SHP2 causes direct and selective depletion of protumorigenic M2 macrophages and promotes antitumor immunity, highlighting an investigational therapeutic approach for some RAS pathway-driven cancers.

A review on the syntheses of bioactive compounds published since 1995 using tartaric acid and its derivatives as synthons is presented.