Pancreatic stellate cells (PSCs) differentiate into cancer-associated fibroblasts (CAFs) that produce desmoplastic stroma, thereby modulating disease progression and therapeutic response in pancreatic ductal adenocarcinoma (PDA). However, it is unknown whether CAFs uniformly carry out these tasks or if subtypes of CAFs with distinct phenotypes in PDA exist. We identified a CAF subpopulation with elevated expression of α-smooth muscle actin (αSMA) located immediately adjacent to neoplastic cells in mouse and human PDA tissue. We recapitulated this finding in co-cultures of murine PSCs and PDA organoids, and demonstrated that organoid-activated CAFs produced desmoplastic stroma. The co-cultures showed cooperative interactions and revealed another distinct subpopulation of CAFs, located more distantly from neoplastic cells, which lacked elevated αSMA expression and instead secreted IL6 and additional inflammatory mediators. These findings were corroborated in mouse and human PDA tissue, providing direct evidence for CAF heterogeneity in PDA tumor biology with implications for disease etiology and therapeutic development.

The hilum (a transitional region) of the mouse ovary is identified as a stem cell niche of the ovarian surface epithelium, and its cells are prone to malignant transformation after inactivation of common tumour suppressor genes, suggesting that they may be the origin of ovarian carcinoma. The recent publication of integrated genomic analyses of ovarian carcinoma has provided an extensive catalogue of molecular aberrations of this deadly disease, but uncertainty about which epithelial cells the cancer originates in has complicated the application of such results. This study identifies a stem cell population in the hilum region of the mouse ovary as the origin of ovarian cancers induced by the loss of the RB1 and TRP53 tumour suppressors, whose pathways are altered frequently in the most aggressive and common types of human epithelial ovarian cancers. Epithelial ovarian cancer (EOC) is the fifth leading cause of cancer deaths among women in the United States, but its pathogenesis is poorly understood1,2,3. Some epithelial cancers are known to occur in transitional zones between two types of epithelium, whereas others have been shown to originate in epithelial tissue stem cells4,5,6. The stem cell niche of the ovarian surface epithelium (OSE), which is ruptured and regenerates during ovulation, has not yet been defined unequivocally. Here we identify the hilum region of the mouse ovary, the transitional (or junction) area between the OSE, mesothelium and tubal (oviductal) epithelium, as a previously unrecognized stem cell niche of the OSE. We find that cells of the hilum OSE are cycling slowly and express stem and/or progenitor cell markers ALDH1, LGR5, LEF1, CD133 and CK6B. These cells display long-term stem cell properties ex vivo and in vivo, as shown by our serial sphere generation and long-term lineage-tracing assays. Importantly, the hilum cells show increased transformation potential after inactivation of tumour suppressor genes Trp53 and Rb1, whose pathways are altered frequently in the most aggressive and common type of human EOC, high-grade serous adenocarcinoma7,8. Our study supports experimentally the idea that susceptibility of transitional zones to malignant transformation may be explained by the presence of stem cell niches in those areas. Identification of a stem cell niche for the OSE may have important implications for understanding EOC pathogenesis.

Purpose: The miR-34 family is directly transactivated by tumor suppressor p53, which is frequently mutated in human epithelial ovarian cancer (EOC). We hypothesized that miR-34 expression would be decreased in EOC and that reconstituted miR-34 expression might reduce cell proliferation and invasion of EOC cells. Experimental Designs: miR-34 expression was determined by quantitative reverse transcription-PCR and in situ hybridization in a panel of 83 human EOC samples. Functional characterization of miR-34 was accomplished by reconstitution of miR-34 expression in EOC cells with synthetic pre-miR molecules followed by determining changes in proliferation, apoptosis, and invasion. Results: miR-34a expression is decreased in 100%, and miR-34b*/c in 72%, of EOC with p53 mutation, whereas miR-34a is also downregulated in 93% of tumors with wild-type p53. Furthermore, expression of miR-34b*/c is significantly reduced in stage IV tumors compared with stage III (P = 0.0171 and P = 0.0029, respectively). Additionally, we observed promoter methylation and copy number variations at mir-34. In situ hybridization showed that miR-34a expression is inversely correlated with MET immunohistochemical staining, consistent with translational inhibition by miR-34a. Finally, miR-34 reconstitution experiments in p53 mutant EOC cells resulted in reduced proliferation, motility, and invasion, the latter of which was dependent on MET expression. Conclusions: Our work suggests that miR-34 family plays an important role in EOC pathogenesis and reduced expression of miR-34b*/c may be particularly important for progression to the most advanced stages. Part of miR-34 effects on motility and invasion may be explained by regulation of MET, which is frequently overexpressed in EOC. Clin Cancer Res; 16(4); 1119–28

Pancreatic ductal adenocarcinoma (PDAC) patients have a 5-year survival rate of only 8% largely due to late diagnosis and insufficient therapeutic options. Neutrophils are among the most abundant immune cell type within the PDAC tumor microenvironment (TME), and are associated with a poor clinical prognosis. However, despite recent advances in understanding neutrophil biology in cancer, therapies targeting tumor-associated neutrophils are lacking. Here, we demonstrate, using pre-clinical mouse models of PDAC, that lorlatinib attenuates PDAC progression by suppressing neutrophil development and mobilization, and by modulating tumor-promoting neutrophil functions within the TME. When combined, lorlatinib also improves the response to anti-PD-1 blockade resulting in more activated CD8 + T cells in PDAC tumors. In summary, this study identifies an effect of lorlatinib in modulating tumor-associated neutrophils, and demonstrates the potential of lorlatinib to treat PDAC.

Recent observations suggest that p53 mutations are responsible not only for growth of primary tumors but also for their dissemination. However, mechanisms involved in p53-mediated control of cell motility and invasion remain poorly understood. By using the primary ovarian surface epithelium cell culture, we show that conditional inactivation of p53 or expression of its mutant forms results in overexpression of MET receptor tyrosine kinase, a crucial regulator of invasive growth. At the same time, cells acquire increased MET-dependent motility and invasion. Wild-type p53 negatively regulates MET expression by two mechanisms: ( i ) transactivation of MET-targeting miR-34 , and ( ii ) inhibition of SP1 binding to MET promoter. Both mechanisms are not functional in p53 absence, but mutant p53 proteins retain partial MET promoter suppression. Accordingly, MET overexpression, cell motility, and invasion are particularly high in p53-null cells. These results identify MET as a critical effector of p53 and suggest that inhibition of MET may be an effective antimetastatic approach to treat cancers with p53 mutations. These results also show that the extent of advanced cancer traits, such as invasion, may be determined by alterations in individual components of p53/MET regulatory network.