Cancer spread and micrometastasis development: quantitative approaches for in vivo models

The characteristics of disseminated tumor cells in pancreatic cancer: a black box needs to be explored

Despite recent advances in early diagnosis and surgical treatment, the clinical outcome of patients with pancreatic cancer has not been improved markedly. One of the reasons for the dismal outcome is early dissemination of tumor cells. Sensitive immunohistocytochemical and nucleic acid-based assays have detected disseminated tumor cells in the lymph nodes, bone marrow, peritoneal cavity or peripheral blood. Formation of the metastatic disease depends on the nature of the disseminated tumor cells. Standardization of protocols is mandatory to detect occult tumor cells in clinical practice. We present an overview of recent studies on the incidence, prognostic values and some characteristics of occult tumor cells disseminated in the secondary sites of patients with pancreatic cancer.

Simultaneous imaging of GFP, CFP and collagen in tumors in vivo using multiphoton microscopy

BACKGROUND

The development of multiphoton laser scanning microscopy has greatly facilitated the imaging of living tissues. However, the use of genetically encoded fluorescent proteins to distinguish different cell types in living animals has not been described at single cell resolution using multiphoton microscopy.

RESULTS

Here we describe a method for the simultaneous imaging, by multiphoton microscopy, of Green Fluorescent Protein, Cyan Fluorescent Protein and collagen in vivo in living tumors. This novel method enables: 1) the simultaneous visualization of overall cell shape and sub-cellular structures such as the plasma membrane or proteins of interest in cells inside living animals, 2) direct comparison of the behavior of single cells from different cell lines in the same microenvironment in vivo.

CONCLUSION

Using this multi-fluor, multiphoton technique, we demonstrate that motility and metastatic differences between carcinoma cells of differing metastatic potential can be imaged in the same animal simultaneously at sub-cellular resolution.

Increase in number of circulating disseminated epithelial cells after surgery for non-small cell lung cancer monitored by MAINTRAC(R) is a predictor for relapse: A preliminary report

Background

Lung cancer still remains one of the most commonly occurring solid tumors and even in stage Ia, surgery fails in 30% of patients who develop distant metastases. It is hypothesized that these must have developed from occult circulating tumor cells present at the time of surgery, or before. The aim of the present study was to detect such cells in the peripheral blood and to monitor these cells following surgery.

Methods

30 patients treated for lung cancer with surgery were monitored for circulating epithelial cells (CEC) by taking peripheral blood samples before, 2 weeks and 5 months after surgery and/or radiotherapy (RT) chemotherapy (CT) or combined RT/CT using magnetic bead enrichment and laser scanning cytometry (MAINTRAC^®) for quantification of these cells.

Results

In 86% of the patients CEC were detected before surgery and in 100% at 2 weeks and 5 months after surgery. In the control group, which consisted of 100 normal donors without cancer, 97 % were negative for CEC. A significantly higher number of CEC was found preoperatively in patients with squamous cell carcinoma than in those with adenocarcinoma. In correlation to the extent of parenchymal manipulation 2 weeks after surgery, an increase in numbers of CEC was observed with limited resections (18/21) whereas pneumonectomy led to a decrease (5/8) of CEC, 2 weeks after surgery. The third analysis done 5 months after surgery identified 3 groups of patients. In the group of 5 patients who received neo- or adjuvant chemo/radiotherapy there was evidence that monitoring of CEC can evaluate the effects of therapy. Another group of 7 patients who underwent surgery only showed a decrease of CEC and no signs of relapse. A third group of 11 patients who had surgery only, showed an increase of CEC (4 with an initial decrease after surgery and 7 with continuous increase). In the group with a continuous increase during the following 24 months, 2 early relapses in patients with stage Ia adenocarcinoma were observed. The increase of CEC preceded clinical detection by six months.

Conclusion

We consider, therefore, that patients with adenocarcinoma and a continuous increase of CEC after complete resection for lung cancer are at an increased risk of early relapse.

Mapping of the functional microcirculation in vital organs using contrast-enhanced in vivo video microscopy

A functional microcirculation is vital to the survival of mammalian tissues. In vivo video microscopy is often used in animal models to assess microvascular function, providing real-time observation of blood flow in normal and diseased tissues. To extend the capabilities of in vivo video microscopy, we have developed a contrast-enhanced system with postprocessing video analysis tools that permit quantitative assessment of microvascular geometry and function in vital organs and tissues. FITC-labeled dextran (250 kDa) was injected intravenously into anesthetized mice to provide intravascular fluorescence contrast with darker red blood cell (RBC) motion. Digitized video images of microcirculation in a variety of internal organs (e.g., lung, liver, ovary, and kidney) were processed using computer-based motion correction to remove background respiratory and cardiac movement. Stabilized videos were analyzed to generate a series of functional images revealing microhemodynamic parameters, such as plasma perfusion, RBC perfusion, and RBC supply rate. Fluorescence contrast revealed characteristic microvascular arrangements within different organs, and images generated from video sequences of liver metastases showed a marked reduction in the proportion of tumor vessels that were functional. Analysis of processed video sequences showed large reductions in vessel volume, length, and branch-point density, with a near doubling in vessel segment length. This study demonstrates that postprocessing of fluorescence contrast video sequences of the microcirculation can provide quantitative images useful for studies in a wide range of model systems.

A BALB/c murine lung alveolar carcinoma used to establish a surgical spontaneous metastasis model

Line-1, a weakly immunogenic lung tumor cell line derived from the BALB/c mouse, metastasizes spontaneously to the lungs of mice following subcutaneous administration. The parameters that influence metastasis as well as the progression of metastatic lung disease following surgical resection of primary subcutaneous tumors were characterized. Histological analysis of the lungs obtained from mice bearing different size subcutaneous tumors demonstrated that >90% of the mice developed micrometastatic disease in the lungs when the tumor exceeded 650 mm3 in size. Surgical resection of subcutaneous tumors resulted in the cure of primary disease in 95% of the mice. Macroscopic tumor nodules were grossly visible in the lungs of 75% of the mice 5 weeks after surgery. Serum amyloid A level correlated with primary tumor burden and was diagnostic for the presence of metastatic disease. The efficiency of metastasis, post-surgical primary tumor recurrence and long-term survival were significantly different between BALB/c mice obtained from different suppliers. The Line-1-BALB/c surgical metastasis model provides a clinically relevant tool for the evaluation of anti-cancer therapies, especially those that are designed to target long-term suppression of minimal residual disease following surgical intervention.

Metastasis suppressor genes: signal transduction, cross-talk and the potential for modulating the behavior of metastatic cells

In the past decade, research from various disciplines has stimulated a re-evaluation of our ideas of how cancers metastasize. Two important findings have been fundamental to this re-evaluation: that cancer cells are subject to growth regulation at the secondary site and that a specific class of proteins suppresses the metastatic phenotype. These proteins are encoded by metastasis suppressor genes, which are operationally defined as genes that suppress in vivo metastasis without inhibiting primary tumor growth when transfected into metastatic cell lines and injected into experimental animals. Recent biochemical studies have shown that certain metastasis suppressor proteins participate in highly conserved signal transduction cascades that mediate cellular responses to growth factors, cytokines and cellular stresses. Further elucidation of the biochemical foundations of these pathways coupled with strong in vivo studies should give us insight into the mechanisms of cancer metastasis, and may hold important implications for the future of cancer staging and therapy, using both existing and novel modalities.

Periostin potently promotes metastatic growth of colon cancer by augmenting cell survival via the Akt/PKB pathway

Molecular mechanisms associated with tumor metastasis remain poorly understood. Here we report that acquired expression of periostin by colon cancer cells greatly promoted metastatic development of colon tumors. Periostin is overexpressed in more than 80% of human colon cancers examined with highest expression in metastatic tumors. Periostin expression dramatically enhanced metastatic growth of colon cancer by both preventing stress-induced apoptosis in the cancer cells and augmenting endothelial cell survival to promote angiogenesis. At the molecular level, periostin activated the Akt/PKB signaling pathway through the alpha(v)beta(3) integrins to increase cellular survival. These data demonstrated that the survival-promoting function is crucial for periostin to promote tumor metastasis of colon cancer.

Dynamic process of prostate cancer metastasis to bone

Prostate cancer metastasis to the bone occurs at high frequency in patients with advanced disease, causing significant morbidity and mortality. Over a century ago, the "seed and soil" theory was proposed to explain organ-specific patterns of metastases. Today, this theory continues to be relevant as we continue to discover factors involved in the attraction and subsequent growth of prostate cancer cells to the bone. These include the accumulation of genetic changes within cancer cells, the preferential binding of cancer cells to bone marrow endothelial cells, and the release of cancer cell chemoattractants from bone elements. A key mediator throughout this metastatic process is the integrin family of proteins. Alterations in integrin expression and function promote dissociation of cancer cells from the primary tumor mass and migration into the blood stream. Once in circulation, integrins facilitate cancer cell survival through interactions between other cancer cells, platelets, and endothelial cells of the target bone. Furthermore, dynamic changes in integrins and in integrin-associated signal transduction aid in the extravasation of cancer cells into the bone and in expansion to a clinically relevant metastasis. Thus, we will review the critical roles of integrins in the process of prostate cancer bone metastasis, from the escape of cancer cells from the primary tumor, to their survival in the harsh "third microenvironment" of the circulation, and ultimately to their attachment and growth at distant bone sites.

Microarrays bring new insights into understanding of breast cancer metastasis to bone

Using a microarray approach, Kang and colleagues identified several genes involved in the generation of breast cancer metastasis in bone and demonstrated their roles in bone colonization in vivo. Their findings and interpretations are reviewed in the context of recent array studies that compared gene expression in primary tumors and metastases. RNA expression array results have already demonstrated value in predicting whether metastases will develop in patients. They have also shown that expression patterns are similar in primary tumors and metastases. The latter data have invited re-examination of long-held notions related to mechanisms of metastasis. While the arrays show promise for improving diagnostic capability in breast cancers, ascribing mechanistic interpretations to correlative data should be done with extreme caution. Kang and colleagues' paper in Cancer Cell elegantly reinforces the concepts that efficiency of the metastatic process is dependent on the coordinated expression of multiple genes and that the expression of metastasis-associated genes is sometimes dependent on the microenvironment in which cells find themselves.