Competing interests C.J.D. is on the Scientific Advisory Board of Mirati Therapeutics. A.C.K. has financial interests in Vescor Therapeutics, LLC. A.C.K. is an inventor on patents pertaining to KRAS-regulated metabolic pathways, redox control pathways in pancreatic cancer, targeting GOT1 as a therapeutic approach, and the autophagic control of iron metabolism. A.C.K. is on the Scientific Advisory Board of Cornerstone/Rafael Pharmaceuticals.
Allele-specific signaling by different KRAS alleles remains poorly understood. The KRAS G12R mutation displays uneven prevalence among cancers that harbor the highest occurrence of KRAS mutations: it is rare in lung and colorectal cancers (~1%), yet relatively common (~20%) in pancreatic ductal adenocarcinoma (PDAC), suggesting context-specific properties. We evaluated whether KRAS G12R is functionally distinct from the more common KRAS G12D or KRAS G12V mutant proteins (KRAS G12D/V ). We found that KRAS G12D/V but not KRAS G12R drives macropinocytosis and that MYC is essential for macropinocytosis in KRAS G12D/V but not KRAS G12R -mutant PDAC. Surprisingly, we found that KRAS G12R is defective for interaction with a key effector, p110α phosphoinositide 3-kinase (PI3Kα), due to structural perturbations in switch II. Instead, upregulated KRAS-independent PI3Kγ activity was able to support macropinocytosis in KRAS G12R -mutant PDAC. Finally, we determined that KRAS G12R -mutant PDAC displayed a distinct drug sensitivity profile compared with KRAS G12D -mutant PDAC but is still responsive to the combined inhibition of ERK and autophagy.Hobbs et al.
Diffuse gastric cancer (DGC) is a lethal malignancy lacking effective systemic therapy. Among the most provocative recent results in DGC has been that of highly recurrent missense mutations in the GTPase RHOA. The function of these mutations has remained unresolved. We demonstrate that RHOA Y42C , the most common RHOA mutation in DGC, is a gain-offunction oncogenic mutant, and that expression of RHOA Y42C with inactivation of the canonical tumor suppressor Cdh1 induces metastatic DGC in a mouse model. Biochemically, RHOA Y42C exhibits impaired GTP hydrolysis and enhances interaction with its effector ROCK. RHOA Y42C mutation and Cdh1 loss induce actin/cytoskeletal rearrangements and activity of focal adhesion kinase (FAK), which activates YAP-TAZ, PI3K-AKT, and β-catenin. RHOA Y42C murine models were sensitive to FAK inhibition and to combined YAP and PI3K pathway blockade. These results, coupled with sensitivity to FAK inhibition in patient-derived DGC cell lines, nominate FAK as a novel target for these cancers. SIGNIFICANCE:The functional signifi cance of recurrent RHOA mutations in DGC has remained unresolved. Through biochemical studies and mouse modeling of the hotspot RHOA Y42C mutation, we establish that these mutations are activating, detail their effects upon cell signaling, and defi ne how RHOA-mediated FAK activation imparts sensitivity to pharmacologic FAK inhibitors.
SUMMARY We address whether combinations with a pan-RAF inhibitor (RAFi) would be effective in KRAS mutant pancreatic ductal adenocarcinoma (PDAC). Chemical library and CRISPR genetic screens identify combinations causing apoptotic anti-tumor activity. The most potent combination, concurrent inhibition of RAF (RAFi) and ERK (ERKi), is highly synergistic at low doses in cell line, organoid, and rat models of PDAC, whereas each inhibitor alone is only cytostatic. Comprehensive mechanistic signaling studies using reverse phase protein array (RPPA) pathway mapping and RNA sequencing (RNA-seq) show that RAFi/ERKi induced insensitivity to loss of negative feedback and system failures including loss of ERK signaling, FOSL1 , and MYC; shutdown of the MYC transcriptome; and induction of mesenchymal-to-epithelial transition. We conclude that low-dose vertical inhibition of the RAF-MEK-ERK cascade is an effective therapeutic strategy for KRAS mutant PDAC.
92 Background: The CCL2-CCR2 signaling axis may facilitate migration of myeloid derived suppressor cells to pancreatic cancer resulting in an immune suppressive tumor microenvironment. CCR2 inhibition in patients with non-metastatic pancreatic cancer was previously reported to decrease tumor-infiltrating macrophages/Treg cells and increase effector T cells (Nywening et al, 2016). Here, a CCR2 specific antagonist CCX872 was used in combination with FOLFIRINOX to treat subjects with locally advanced or metastatic, non-resectable pancreatic cancer in a multi-center study. Methods: Fifty subjects (ECOG score ≤ 2) were enrolled, receiving FOLFIRINOX (fluorouracil [5-FU], leucovorin, irinotecan, oxaliplatin) once every two weeks (maximum 12 cycles) plus 150 mg CCX872 QD or BID for 12 weeks. Subjects showing at least stable disease at the end of the 12-week treatment period were eligible to CCX872 treatment until disease progression. In this ongoing study, all subjects are followed for overall survival (OS). Blood samples were taken at baseline and at intervals throughout the active treatment period for hematologic and flow cytometric analysis of circulating immune cell populations. Results: The all-subjects OS at 18 months is 29%. This compares favorably with previously published data: i.e., OS of only 18.6% at 18 months for FOLFIRINOX regimen alone (Conroy et al, 2011). Peripheral blood monocyte counts at baseline inversely correlate with OS (p = 0.0071, Hazard ratio = 1.169) with CCX872 and FOLFIRINOX combination therapy. Overall, circulating monocytes, inflammatory monocytes and monocytic myeloid derived suppressor cells were reduced by treatment. Conclusions: CCX872-B plus FOLFIRINOX resulted in an OS of 29% at 18 months with no safety issues. Better OS was associated with lower peripheral blood monocyte counts at baseline. Clinical trial information: NCT02345408.
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