No abstract

Cancer-associated fibroblasts (CAFs) support tumorigenesis by stimulating angiogenesis, cancer cell proliferation, and invasion. We demonstrate that CAFs also mediate tumor-enhancing inflammation. Using a mouse model of squamous skin carcinogenesis, we found a proinflammatory gene signature in CAFs isolated from dysplastic skin. This signature was maintained in CAFs from subsequent skin carcinomas and was evident in mammary and pancreatic tumors in mice and in cognate human cancers. The inflammatory signature was already activated in CAFs isolated from the initial hyperplastic stage in multistep skin tumorigenesis. CAFs from this pathway promoted macrophage recruitment, neovascularization, and tumor growth, activities that are abolished when NF-kappaB signaling was inhibited. Additionally, we show that normal dermal fibroblasts can be "educated" by carcinoma cells to express proinflammatory genes.

Despite decades of research, efforts to directly target KRAS have been challenging. MRTX849 was identifi ed as a potent, selective, and covalent KRAS G12C inhibitor that exhibits favorable drug-like properties, selectively modifi es mutant cysteine 12 in GDPbound KRAS G12C , and inhibits KRAS-dependent signaling. MRTX849 demonstrated pronounced tumor regression in 17 of 26 (65%) KRAS G12C -positive cell line-and patient-derived xenograft models from multiple tumor types, and objective responses have been observed in patients with KRAS G12C -positive lung and colon adenocarcinomas. Comprehensive pharmacodynamic and pharmacogenomic profi ling in sensitive and partially resistant nonclinical models identifi ed mechanisms implicated in limiting antitumor activity including KRAS nucleotide cycling and pathways that induce feedback reactivation and/or bypass KRAS dependence. These factors included activation of receptor tyrosine kinases (RTK), bypass of KRAS dependence, and genetic dysregulation of cell cycle. Combinations of MRTX849 with agents that target RTKs, mTOR, or cell cycle demonstrated enhanced response and marked tumor regression in several tumor models, including MRTX849-refractory models. SIGNIFICANCE :The discovery of MRTX849 provides a long-awaited opportunity to selectively target KRAS G12C in patients. The in-depth characterization of MRTX849 activity, elucidation of response and resistance mechanisms, and identifi cation of effective combinations provide new insight toward KRAS dependence and the rational development of this class of agents.

Syndrome X, typified by obesity, insulin resistance (IR), dyslipidemia, and other metabolic abnormalities, is responsive to antidiabetic thiazolidinediones (TZDs). Peroxisome proliferator-activated receptor (PPAR) ␥, a target of TZDs, is expressed abundantly in adipocytes, suggesting an important role for this tissue in the etiology and treatment of IR. Targeted deletion of PPAR␥ in adipose tissue resulted in marked adipocyte hypocellularity and hypertrophy, elevated levels of plasma free fatty acids and triglyceride, and decreased levels of plasma leptin and ACRP30. In addition, increased hepatic glucogenesis and IR were observed. Despite these defects, blood glucose, glucose and insulin tolerance, and insulin-stimulated muscle glucose uptake were all comparable to those of control mice. However, targeted mice were significantly more susceptible to high-fat diet-induced steatosis, hyperinsulinemia, and IR. Surprisingly, TZD treatment effectively reversed liver IR, whereas it failed to lower plasma free fatty acids. These results suggest that syndrome X may be comprised of separable PPAR␥-dependent components whose origins and therapeutic sites may reside in distinct tissues.syndrome X

Lipid and carbohydrate homeostasis in higher organisms is under the control of an integrated system that has the capacity to rapidly respond to metabolic changes. The peroxisome proliferator-activated receptors (PPARs) are nuclear fatty acid receptors that have been implicated to play an important role in obesity-related metabolic diseases such as hyperlipidemia, insulin resistance, and coronary artery disease. The three PPAR subtypes, alpha, gamma, and delta, have distinct expression patterns and evolved to sense components of different lipoproteins and regulate lipid homeostasis based on the need of a specific tissue. Recent advances in identifying selective ligands in conjunction with microarray analyses and gene targeting studies have helped delineate the subtype-specific functions and the therapeutic potential of these receptors. PPARalpha potentiates fatty acid catabolism in the liver and is the molecular target of the lipid-lowering fibrates (e.g. fenofibrate and gemfibrozil), whereas PPARgamma is essential for adipocyte differentiation and mediates the activity of the insulin-sensitizing thiazolidinediones (e.g. rosiglitazone and pioglitazone). Recent evidence suggests that PPARdelta may be important in controlling triglyceride levels by sensing very low-density lipoprotein. Thus, uncovering the regulatory mechanisms and transcriptional targets of the PPARs will continue to provide insight into the pathogenesis of metabolic diseases and, at the same time, offer valuable information for rational drug design.

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SMAD4 is inactivated in the majority of pancreatic ductal adenocarcinomas (PDAC) with concurrent mutational inactivation of the INK4A/ARF tumor suppressor locus and activation of the KRAS oncogene. Here, using genetically engineered mice, we determined the impact of SMAD4 deficiency on the development of the pancreas and on the initiation and/or progression of PDAC-alone or in combination with PDAC-relevant mutations. Selective SMAD4 deletion in the pancreatic epithelium had no discernable impact on pancreatic development or physiology. However, when combined with the activated KRAS G12D allele, SMAD4 deficiency enabled rapid progression of KRAS G12D -initiated neoplasms. While KRAS G12D alone elicited premalignant pancreatic intraepithelial neoplasia (PanIN) that progressed slowly to carcinoma, the combination of KRAS G12D and SMAD4 deficiency resulted in the rapid development of tumors resembling intraductal papillary mucinous neoplasia (IPMN), a precursor to PDAC in humans. SMAD4 deficiency also accelerated PDAC development of KRAS G12D INK4A/ARF heterozygous mice and altered the tumor phenotype; while tumors with intact SMAD4 frequently exhibited epithelial-to-mesenchymal transition (EMT), PDAC null for SMAD4 retained a differentiated histopathology with increased expression of epithelial markers. SMAD4 status in PDAC cell lines was associated with differential responses to transforming growth factor-␤ (TGF-␤) in vitro with a subset of SMAD4 wild-type lines showing prominent TGF-␤-induced proliferation and migration. These results provide genetic confirmation that SMAD4 is a PDAC tumor suppressor, functioning to block the progression of KRAS G12D -initiated neoplasms, whereas in a subset of advanced tumors, intact SMAD4 facilitates EMT and TGF-␤-dependent growth.[Keywords: Smad4; pancreatic cancer; epithelial-to-mesenchymal transition mouse models; TGF-␤] Supplemental material is available at http://www.genesdev.org. PDAC (pancreatic ductal adenocarcinoma) ranks as the fourth leading cause of cancer mortality in the United States and carries a median survival of <6 mo (Li et al. 2004). Hallmarks of this disease include the infiltration of the tumor with a proliferative stroma (desmoplasia), early invasion and metastasis, and pronounced genomic instability (Solcia et al. 1995). PDAC is characterized by a highly recurrent pattern of genetic lesions consisting of activating mutations of KRAS and inactivation of INK4A (via mutation, deletion, or promoter methylation) in virtually all cases, inactivation of the p53-ARF pathway in ∼87% of cases (including tumors with deletions of the INK4A/ARF locus), and SMAD4 inactivation in ∼53% (Hansel et al. 2003). Hence, SMAD4 status can be considered as a distinguishing molecular feature of two major classes of PDAC. Significant ongoing efforts are being directed toward the elucidation of how specific signature mutations contribute to the genesis and progression of PDAC and influence its tumor biological features.

The metabolic syndrome is a collection of obesity-related disorders. The peroxisome proliferator-activated receptors (PPARs) regulate transcription in response to fatty acids and, as such, are potential therapeutic targets for these diseases. We show that PPAR␦ (NR1C2) knockout mice are metabolically less active and glucoseintolerant, whereas receptor activation in db͞db mice improves insulin sensitivity. Euglycemic-hyperinsulinemic-clamp experiments further demonstrate that a PPAR␦-specific agonist suppresses hepatic glucose output, increases glucose disposal, and inhibits free fatty acid release from adipocytes. Unexpectedly, gene array and functional analyses suggest that PPAR␦ ameliorates hyperglycemia by increasing glucose flux through the pentose phosphate pathway and enhancing fatty acid synthesis. Coupling increased hepatic carbohydrate catabolism with its ability to promote ␤-oxidation in muscle allows PPAR␦ to regulate metabolic homeostasis and enhance insulin action by complementary effects in distinct tissues. The combined hepatic and peripheral actions of PPAR␦ suggest new therapeutic approaches to treat type II diabetes.fatty acid and glucose metabolism ͉ insulin sensitivity