Molecular mechanisms of hepatic metastasis in colorectal cancer

Evaluation of hepatic-metastasis risk of colorectal cancer upon the protein signature of PI3K/AKT pathway

Liver is the most common organ of colorectal cancer (CRC) metastasis, and hepatic metastasis (HM) is regulated by complex protein network. Hence, we initiated a proteomic survey to seek interrelated multiplex markers related with HM. A total of 34 unique differential proteins were identified in the primary tumor tissues from 14 CRC patients with/without HM. A differential protein cluster, consisting of 17 proteins throughout PI3K/AKT pathway, was deduced and validated by Western blot. A three-protein signature elicited from the protein cluster, phosphorylated IkappaBalpha, TNFalpha and MFAP3L, was detected by immunohistochemistry on 105 pairs of CRC and normal samples. The positive protein signature was specifically correlated with HM (P < 0.001), and classified the HM risk of CRC patients with high sensitivity (92.85 +/- 4.87%) and specificity (94.94 +/- 2.5%). The high-risk group had significantly decreased overall survival (P < 0.001). Furthermore, RKO and HT29, two colon cancer cells with different expression status of the protein signature, were used to construct the nude mouse model of HM. And the HM occurrence of RKO cell (4/5) was dramatically higher than that of HT29 cell (1/5). Therefore, the protein signature derived from PI3K/AKT pathway is likely a promising multiplex biomarker for HM of CRC.

Integrin alpha v beta 6 mediates the potential for colon cancer cells to colonize in and metastasize to the liver

Integrin alpha v beta 6 (alpha v beta 6) is correlated with colon cancer progression. To detect the effects of alpha v beta 6 on liver metastasis, the specificity of alpha v beta 6 against the monoclonal antibody (mAb) 2G2 was examined by immunoprecipitation. Integrin alpha v beta 6-immunoreactivity (IR) in liver metastasis tissues (63 cases) and colon carcinoma (358 cases) were examined. These results showed that alpha v beta 6 was specifically recognized by the mAb 2G2, and that rates of alpha v beta 6 positivity in liver metastatic tissues (71.4%, 45/63) were higher than that for primary colon cancer (34.0%, 122/358) (P < 0.01). Patients who were alpha v beta 6-positive had higher liver metastasis rates (17%, 21/122) than those who were alpha v beta 6-negative (only 3%, 7/236) (P < 0.01). To examine the underlying mechanisms associated with alpha v beta 6 regulating colonic metastasis in the liver, experimental liver metastasis (intrasplenic injection of HT29 transfectants) and liver colonization assays (direct injection of WiDr transfectants into the liver) in nude mice were performed; these demonstrated that alpha v beta 6 contributed to the promotion of the metastatic potential and the survival of cancer cells in the liver. Matrix metalloproteinase-9 (MMP-9) levels in the cultures of both HT29 and WiDr cells were detected by the Biotrak MMP-9 activity assay system and gelatin zymography assay, and showed that suppression of alpha v beta 6-IR inhibited MMP-9 activity and secretion. Transwell migration assay in vitro also showed that alpha v beta 6 promoted migration on fibronectin for HT29/WiDr mock compared with HT29/WiDr antisense beta 6 transfects (P < 0.01). We concluded that alpha v beta 6 may mediate the potential for colon cancer cells to colonize in and metastasize to the liver. The mechanisms that alpha v beta 6 may be involved in include the promotion of MMP-9 secretion, the enhancement of migration on fibronectin, and the survival of cancer cells in the liver.

Is there a genetic signature for liver metastasis in colorectal cancer?

Even though liver metastasis accounts for the vast majority of cancer deaths in patients with colorectal cancer (CRC), fundamental questions about the molecular and cellular mechanisms of liver metastasis still remain unanswered. Determination of gene expression profiles by microarray technology has improved our knowledge of CRC molecular pathways. However, defined gene signatures are highly variable among studies. Expression profiles and molecular markers have been specifically linked to liver metastases mechanistic paths in CRC. However, to date, none of the identified signatures or molecular markers has been successfully validated as a diagnostic or prognostic tool applicable to routine clinical practice. To obtain a genetic signature for liver metastasis in CRC, measures to improve reproducibility, to increase consistency, and to validate results need to be implemented. Alternatives to expression profiling with microarray technology are continuing to be used. In the recent past, many genes codifying for proteins that are directly or indirectly involved in adhesion, invasion, angiogenesis, survival and cell growth have been linked to mechanisms of liver metastases in CRC.

Stromal fibroblasts in colorectal liver metastases originate from resident fibroblasts and generate an inflammatory microenvironment

Cancer-associated stromal fibroblasts (CAFs) are the main cellular constituents of reactive stroma in primary and metastatic cancer. We analyzed phenotypical characteristics of CAFs from human colorectal liver metastases (CLMs) and their role in inflammation and cancer progression. CAFs displayed a vimentin(+), alpha-smooth-muscle actin(+), and Thy-1(+) phenotype similar to resident portal-located liver fibroblasts (LFs). We demonstrated that CLMs are inflammatory sites showing stromal expression of interleukin-8 (IL-8), a chemokine related to invasion and angiogenesis. In vitro analyses revealed a striking induction of IL-8 expression in CAFs and LFs by tumor necrosis factor-alpha (TNF-alpha). The effect of TNF-alpha on CAFs is inhibited by the nuclear factor-kappaB inhibitor parthenolide. Conditioned medium of CAFs and LFs similarly stimulated the migration of DLD-1, Colo-678, HuH7 carcinoma cells, and human umbilical vein endothelial cells in vitro. Pretreatment of CAFs with TNF-alpha increased the chemotaxis of Colo-678 colon carcinoma cells by conditioned medium of CAFs; however, blockage of IL-8 activity showed no inhibitory effect. In conclusion, these data raise the possibility that the majority of CAFs in CLM originate from resident LFs. TNF-alpha-induced up-regulation of IL-8 via nuclear factor-kappaB in CAFs is an inflammatory pathway, potentially permissive for cancer invasion that may represent a novel therapeutic target.

Clinical, biological, and molecular aspects of metastasis in colorectal cancer

Colorectal cancer is one of the most frequent malignant tumors with a still increasing incidence in Western countries. Currently, colorectal cancer is the second most common cancer in Europe both in terms of incidence and mortality. Approximately 90% of all cancer deaths arise from the metastatic dissemination of primary tumors. Thus, metastasis is the most lethal attribute of colorectal cancer. Today, colorectal cancer and metastasis thereof are understood as the results of early changes during tumor progression that determine the metastasis capacity. Much is known about molecules contributing to the metastasis phenotype, the pathways they control, and the genes they regulate. However, patient prognosis is mainly defined by histopathological staging, a static description of the anatomical extent of tumor spread within a surgical specimen. This review demonstrates the need for and possibilities of molecular-based staging as an essential prerequisite for improved diagnosis, prognosis, and therapy. Molecular determinants for progression and metastasis of colorectal cancer are discussed representing both potential markers for metastasis prognosis and targets for intervention strategies aiming at the ultimate goal of metastasis prevention.

The host inflammatory response promotes liver metastasis by increasing tumor cell arrest and extravasation

Inflammation can play a regulatory role in cancer progression and metastasis. Previously, we have shown that metastatic tumor cells entering the liver trigger a proinflammatory response involving Kupffer cell-mediated release of tumor necrosis factor-alpha and the up-regulation of vascular endothelial cell adhesion receptors, such as E-selectin. Here, we analyzed spatio-temporal aspects of the ensuing tumor-endothelial cell interaction using human colorectal carcinoma CX-1 and murine carcinoma H-59 cells and a combination of immunohistochemistry, confocal microscopy, and three-dimensional reconstruction. E-selectin expression was evident mainly on sinusoidal vessels by 6 and 10 hours, respectively, following H-59 and CX-1 inoculation, and this corresponded to a stabilization of the number of tumor cells within the sinuses. Tumor cells arrested in E-selectin(+) vessels and appeared to flatten and traverse the vessel lining, away from sites of intense E-selectin staining. This process was evident by 8 (H-59) and 12 (CX-1) hours after inoculation, coincided with increased endothelial vascular cell adhesion molecule-1 expression, and involved tumor cell attachment in areas of intense vascular cell adhesion molecule-1 and platelet endothelial cell adhesion molecule-1 expression. Nonmetastatic (human) MIP-101 and (murine) M-27 cells induced a weaker response and could not be seen to extravasate. The results show that metastatic tumor cells can alter the hepatic microvasculature and use newly expressed endothelial cell receptors to arrest and extravasate.

Increased Estrogen Sulfation of Estradiol 17β-D-Glucuronide in Metastatic Tumor Rat Livers

Changes in the disposition of estradiol 17beta-d-glucuronide (E(2)17G), a substrate of the organic anion-transporting polypeptide family (Oatp) and multidrug resistance-associated protein 2 (Mrp2), were examined in livers of male Wag/Rij rats that were injected with CC531 cells intraportally to induce metastatic tumors (n = 5) or with phosphate-buffered saline for sham-operated controls (n = 4). Multiple indicator dilution, single-pass liver perfusions revealed extremely high influx clearances of [(3)H]E(2)17G (>190 ml/min) in both groups. In recirculating liver perfusions, [(3)H]E(2)17G decayed monoexponentially in the reservoir perfusate, and the total (9.19 +/- 1.33 versus 8.18 +/- 0.94 ml/min) and biliary (4.94 +/- 1.07 versus 4.60 +/- 0.86 ml/min) clearances were similar in both groups (P > 0.05). The metabolic clearance of E(2)17G was higher in the tumor group (4.60 +/- 0.64 versus 3.23 +/- 0.23 ml/min, P < 0.05). E(2)3S17G, the 3-sulfate metabolite, whose identity was confirmed by mass spectrometry, appeared only in bile and not perfusate. Liver microsomal incubations of E(2)3(35)S17G and [(3)H]estrone sulfate revealed similar sulfatase activities between the tumor and sham livers, albeit the activities were much lower for E(2)3(35)S17G. Oatp1a1 and Oatp1b2 protein expression in liver membrane fragments was reduced by 42% and 38%, respectively, whereas that of cytosolic estrogen sulfotransferase (Sult1e1) was significantly increased (41%) with tumor (P < 0.05). All of the observations were captured by modeling. From modeling, we showed that reduction of the high influx clearance (546 to 283 ml/min) failed to lower the total clearance of E(2)17G, whereas up-regulation of Sult1e1 increased the E(2)17G sulfation clearance (2.56 to 3.69 ml/min) in livers with metastatic tumors.