A Genome-scale CRISPR Screen Identifies the ERBB and mTOR Signaling Networks as Key Determinants of Response to PI3K Inhibition in Pancreatic Cancer.

KRAS mutation is a key driver of pancreatic cancer and PI3K pathway activity is an additional requirement for Kras-induced tumorigenesis. Clinical trials of PI3K pathway inhibitors in pancreatic cancer have shown limited responses. Understanding the molecular basis for this lack of efficacy may direct future treatment strategies with emerging PI3K inhibitors. We sought new therapeutic approaches that synergize with PI3K inhibitors through pooled CRISPR modifier genetic screening and a drug combination screen. ERBB family receptor tyrosine kinase signaling and mTOR signaling were key modifiers of sensitivity to alpelisib and pictilisib. Inhibition of the ERBB family or mTOR was synergistic with PI3K inhibition in spheroid, stromal cocultures. Near-complete loss of ribosomal S6 phosphorylation was associated with synergy. Genetic alterations in the ERBB-PI3K signaling axis were associated with decreased survival of patients with pancreatic cancer. Suppression of the PI3K/mTOR axis is potentiated by dual PI3K and ERBB family or mTOR inhibition. Surprisingly, despite the presence of oncogenic KRAS, thought to bestow independence from receptor tyrosine kinase signaling, inhibition of the ERBB family blocks downstream pathway activation and synergizes with PI3K inhibitors. Further exploration of these therapeutic combinations is warranted for the treatment of pancreatic cancer.

Correction: Suppression of interferon gene expression overcomes resistance to MEK inhibition in KRAS-mutant colorectal cancer.

A correction to this paper has been published and can be accessed via a link at the top of the paper.

Suppression of interferon gene expression overcomes resistance to MEK inhibition in KRAS-mutant colorectal cancer.

Despite showing clinical activity in BRAF-mutant melanoma, the MEK inhibitor (MEKi) trametinib has failed to show clinical benefit in KRAS-mutant colorectal cancer. To identify mechanisms of resistance to MEKi, we employed a pharmacogenomic analysis of MEKi-sensitive versus MEKi-resistant colorectal cancer cell lines. Strikingly, interferon- and inflammatory-related gene sets were enriched in cell lines exhibiting intrinsic and acquired resistance to MEK inhibition. The bromodomain inhibitor JQ1 suppressed interferon-stimulated gene (ISG) expression and in combination with MEK inhibitors displayed synergistic effects and induced apoptosis in MEKi-resistant colorectal cancer cell lines. ISG expression was confirmed in patient-derived organoid models, which displayed resistance to trametinib and were resensitized by JQ1 co-treatment. In in vivo models of colorectal cancer, combination treatment significantly suppressed tumor growth. Our findings provide a novel explanation for the limited response to MEK inhibitors in KRAS-mutant colorectal cancer, known for its inflammatory nature. Moreover, the high expression of ISGs was associated with significantly reduced survival of colorectal cancer patients. Excitingly, we have identified novel therapeutic opportunities to overcome intrinsic and acquired resistance to MEK inhibition in colorectal cancer.

Molecular profiling and combinatorial activity of CCT068127: a potent CDK2 and CDK9 inhibitor.

Deregulation of the cyclin-dependent kinases (CDKs) has been implicated in the pathogenesis of multiple cancer types. Consequently, CDKs have garnered intense interest as therapeutic targets for the treatment of cancer. We describe herein the molecular and cellular effects of CCT068127, a novel inhibitor of CDK2 and CDK9. Optimized from the purine template of seliciclib, CCT068127 exhibits greater potency and selectivity against purified CDK2 and CDK9 and superior antiproliferative activity against human colon cancer and melanoma cell lines. X-ray crystallography studies reveal that hydrogen bonding with the DFG motif of CDK2 is the likely mechanism of greater enzymatic potency. Commensurate with inhibition of CDK activity, CCT068127 treatment results in decreased retinoblastoma protein (RB) phosphorylation, reduced phosphorylation of RNA polymerase II, and induction of cell cycle arrest and apoptosis. The transcriptional signature of CCT068127 shows greatest similarity to other small-molecule CDK and also HDAC inhibitors. CCT068127 caused a dramatic loss in expression of DUSP6 phosphatase, alongside elevated ERK phosphorylation and activation of MAPK pathway target genes. MCL1 protein levels are rapidly decreased by CCT068127 treatment and this associates with synergistic antiproliferative activity after combined treatment with CCT068127 and ABT263, a BCL2 family inhibitor. These findings support the rational combination of this series of CDK2/9 inhibitors and BCL2 family inhibitors for the treatment of human cancer.

RHO binding to FAM65A regulates Golgi reorientation during cell migration.

Directional cell migration involves reorientation of the secretory machinery. However, the molecular mechanisms that control this reorientation are not well characterised. Here, we identify a new Rho effector protein, named FAM65A, which binds to active RHOA, RHOB and RHOC. FAM65A links RHO proteins to Golgi-localising cerebral cavernous malformation-3 protein (CCM3; also known as PDCD10) and its interacting proteins mammalian STE20-like protein kinases 3 and 4 (MST3 and MST4; also known as STK24 and STK26, respectively). Binding of active RHO proteins to FAM65A does not affect the kinase activity of MSTs but results in their relocation from the Golgi in a CCM3-dependent manner. This relocation is crucial for reorientation of the Golgi towards the leading edge and subsequent directional cell migration. Our results reveal a previously unidentified pathway downstream of RHO that regulates the polarity of migrating cells through Golgi reorientation in a FAM65A-, CCM3- and MST3- and MST4-dependent manner.

DOCK10-mediated Cdc42 activation is necessary for amoeboid invasion of melanoma cells.

BACKGROUND: Tumor cells can move in a three-dimensional (3D) environment in either mesenchymal-type or amoeboid modes. In mesenchymal-type movement, cells have an elongated morphology with Rac-induced protrusions at the leading edge. Amoeboid cells have high levels of actomyosin contractility, and movement is associated with deformation of the cell body through the matrix without proteolysis. Because signaling pathways that control the activation of GTPases for amoeboid movement are poorly understood, we sought to identify regulators of amoeboid movement by screening an siRNA library targeting guanine nucleotide exchange factors (GEFs) for Rho-family GTPases. RESULTS: We identified DOCK10, a Cdc42 GEF, as a key player in amoeboid migration; accordingly, we find that expression of activated Cdc42 induces a mesenchymal-amoeboid transition and increases cell invasion. Silencing DOCK10 expression promotes conversion to mesenchymal migration and is associated with decreased MLC2 phosphorylation and increased Rac1 activation. Consequently, abrogating DOCK10 and Rac1 expression suppresses both amoeboid and mesenchymal migration and results in decreased invasion. We show that the Cdc42 effectors N-WASP and Pak2 are required for the maintenance of the rounded-amoeboid phenotype. Blocking Cdc42 results in loss of mesenchymal morphology, arguing that Cdc42 is also involved in mesenchymal morphology through different activation and effector pathways. CONCLUSIONS: Previous work has identified roles of Rho and Rac signaling in tumor cell movement, and we now elucidate novel roles of Cdc42 signaling in amoeboid and mesenchymal movement and tumor cell invasion.

Regulation of cell migration by the C2 domain of the tumor suppressor PTEN.

PTEN is a tumor suppressor protein that dephosphorylates phosphatidylinositol 3,4,5 trisphosphate and antagonizes the phosphatidylinositol-3 kinase signaling pathway. We show here that PTEN can also inhibit cell migration through its C2 domain, independent of its lipid phosphatase activity. This activity depends on the protein phosphatase activity of PTEN and on dephosphorylation at a single residue, threonine(383). The ability of PTEN to control cell migration through its C2 domain is likely to be an important feature of its tumor suppressor activity.