Mutation of the Kirsten-ras (Ki-ras) proto-oncogene occurs frequently in colorectal cancers. alpha-Difluoromethylornithine (DFMO), an irreversible inhibitor of the polyamine biosynthetic enzyme, ornithine decarboxylase (ODC), inhibits Ki-ras transformation and colon tumorigenesis in carcinogen-treated animal models by mechanisms yet to be elucidated. Caco-2 cells transfected with an activated Ki-ras, but not parental cells, formed tumors in severe combined immunodeficient (SCID) mice. DFMO treatment (2% in drinking water) prevented tumor growth. Gene expression profiling was performed to identify Ki-ras-and DFMO-dependent patterns of gene expression. Microarray results were validated with real-time or semi-quantitative RT-PCR and/or Western blot analysis. Genes upregulated in Caco-2 cells expressing an activated Ki-ras encoded cytoskeletal-, transport-, protease-, and gap junction-associated proteins. These genes are important for normal development and maintenance of colonic epithelial tissue. Caco-2 cells transfected with an activated Ki-ras displayed increased expression of the integrin alpha 1 (INGA1) and enhanced cell migration on laminin. These parameters were unaffected by DFMO, but Ki-ras-dependent migration was inhibited by INGA1 antibodies. Other Ki-ras-dependent, but DFMO-independent, genes included transglutaminase (TGase) and kallikrein 6 (KLK6). Ki-ras-transfected cells also expressed increased levels of connexin43 (Cx43) (RNA and protein), tight junction protein, and endothelin 1. DFMO reversed these increases. The results indicated that the Ki-ras oncogene caused changes in experimental cell migration and cell-cell communication genes and that some of these changes could be reversed by DFMO.

Metastatic colon cancer is a major cause of deaths among colorectal cancer (CRC) patients. Elevated expression of kallikrein 6 (KLK6), a member of a kallikrein subfamily of peptidase S1 family serine proteases, has been reported in CRC and is associated with low patient survival rates and poor disease prognosis. We knocked down KLK6 expression in HCT116 colon cancer cells to determine the significance of KLK6 expression for metastatic dissemination and to identify the KLK6-associated microRNAs (miRNAs) signaling networks in metastatic colon cancer. KLK6 suppression resulted in decreased cells invasion in vitro with a minimal effect on the cell growth and viability. In vivo, animals with orthotopic colon tumors deficient in KLK6 expression had the statistically significant increase in survival rates (P = .005) and decrease in incidence of distant metastases. We further performed the integrated miRNA and messenger RNA (mRNA) expression profiling to identify functional miRNA-mRNA interactions associated with KLK6-mediated invasiveness of colon cancer.Through bioinformatics analysis we identified and functionally validated the top two up-regulated miRNAs, miR-182 and miR-203, and one down-regulated miRNA, miRNA-181d, and their seven mRNA effectors. The established miRNA-mRNA interactions modulate cellular proliferation, differentiation and epithelial–mesenchymal transition (EMT) in KLK6-expressing colon cancer cells via the TGF-β signaling pathway and RAS-related GTP-binding proteins. We confirmed the potential tumor suppressive properties of miR-181d and miR-203 in KLK6-expressing HCT116 cells using Matrigel invasion assay. Our data provide experimental evidence that KLK6 controls metastasis formation in colon cancer via specific downstream network of miRNA-mRNA effectors.

Pancreatic ductal adenocarcinoma is one of the most aggressive malignancies, characterized by the local invasion into surrounding tissues and early metastasis to distant organs. Oncogenic mutations of the K-RAS gene occur in more than 90% of human pancreatic cancers. The goal of this study was to investigate the functional significance and downstream effectors of mutant K-RAS oncogene in the pancreatic cancer invasion and metastasis. We applied the homologous recombination technique to stably disrupt K-RAS oncogene in the human pancreatic cell line MiaPaCa-2, which carries the mutant K-RASG12C oncogene in both alleles. Using in vitro assays, we found that clones with disrupted mutant K-RAS gene exhibited low RAS activity, reduced growth rates, increased sensitivity to the apoptosis inducing agents, and suppressed motility and invasiveness. In vivo assays showed that clones with decreased RAS activity had reduced tumor formation ability in mouse xenograft model and increased survival rates in the mouse orthotopic pancreatic cancer model. We further examined molecular pathways downstream of mutant K-RAS and identified RhoA GTP activating protein 5, caveolin-1, and RAS-like small GTPase A (RalA) as key effector molecules, which control mutant K-RAS-dependent migration and invasion in MiaPaCa-2 cells. Our study provides rational for targeting RhoA and RalA GTPase signaling pathways for inhibition of pancreatic cancer metastasis.

A significant percentage (~30%) of estrogen receptor-α (ERα)-positive tumors become refractory to endocrine therapies; however, the mechanisms responsible for this resistance remain largely unknown. Chronic exposure to arsenic through foods and contaminated water has been linked to an increased incidence of several tumors and long-term health complications. Preclinical and population studies have indicated that arsenic exposure may interfere with endocrine regulation and increase the risk of breast tumorigenesis. In this study, we examined the effects of sodium arsenite (NaAsIII) exposure in ERα-positive breast cancer cells in vitro and in mammary tumor xenografts. The results revealed that acute (within 4 days) and long-term (10 days to 7 weeks) in vitro exposure to environmentally relevant doses reduced breast cancer 1 (BRCA1) and ERα expression associated with the gain of cyclin D1 (CCND1) and folate receptor 1 (FOLR1), and the loss of methylenetetrahydrofolate reductase (MTHFR) expression. Furthermore, long-term exposure to NaAsIII induced the proliferation and compromised the response of MCF7 cells to tamoxifen (TAM). The in vitro exposure to NaAsIII induced BRCA1 CpG methylation associated with the increased recruitment of DNA methyltransferase 1 (DNMT1) and the loss of RNA polymerase II (PolII) at the BRCA1 gene. Xenografts of NaAsIII-preconditioned MCF7 cells (MCF7NaAsIII) into the mammary fat pads of nude mice produced a larger tumor volume compared to tumors from control MCF7 cells and were more refractory to TAM in association with the reduced expression of BRCA1 and ERα, CpG hypermethylation of estrogen receptor 1 (ESR1) and BRCA1, and the increased expression of FOLR1. These cumulative data support the hypothesis that exposure to AsIII may contribute to reducing the efficacy of endocrine therapy against ERα-positive breast tumors by hampering the expression of ERα and BRCA1 via CpG methylation, respectively of ESR1 and BRCA1.

Pancreatic cancer is a common cancer with poor odds of survival for the patient, with surgical resection offering the only hope of cure. Current surgical practice is time-consuming and, due to time constraints, does not sample the whole cut surface sufficiently to check for remaining cancer. Although microscopy with hematoxylin and eosin (H&E) stain is the gold standard for microscopic evaluation, multiphoton microscopy (MPM) has emerged as an alternative tool for imaging tissue architecture and cellular morphology without labels. We explored the use of multimodal MPM for the label-free identification of normal and cancerous tissue of the pancreas in a mouse model by comparing the images to H&E microscopy. Our early studies indicate that MPM using second-harmonic generation, third-harmonic generation, and multiphoton excitation of endogenous fluorescent proteins can each contribute to the label-free analysis of the pancreatic surgical margin.