Clonal analysis of the malignant properties of B16 melanoma cells treated with the DNA hypomethylating agent 5-azacytidine

Biosensors for metastatic cancer cell detection

Early detection and effective cancer treatment are critical to improving metastatic cancer cell diagnosis and management today. In particular, accurate qualitative diagnosis of metastatic cancer cell represents an important step in the diagnosis of cancer. Today, biosensors have been widely developed due to the daily need to measure different chemical and biological species. Biosensors are utilized to quantify chemical and biological phenomena by generating signals that are directly proportional to the quantity of the analyte present in the reaction. Biosensors are widely used in disease control, drug delivery, infection detection, detection of pathogenic microorganisms, and markers that indicate a specific disease in the body. These devices have been especially popular in the field of metastatic cancer cell diagnosis and treatment due to their portability, high sensitivity, high specificity, ease of use and short response time. This article examines biosensors for metastatic cancer cells. It also studies metastatic cancer cells and the mechanism of metastasis. Finally, the function of biosensors and biomarkers in metastatic cancer cells is investigated.

Mechanisms of metastasis

Metastasis is an enormously complex process that remains to be a major problem in the management of cancer. The fact that cancer patients might develop metastasis after years or even decades from diagnosis of the primary tumor makes the metastatic process even more complex. Over the years many hypotheses were developed to try to explain the inefficiency of the metastatic process, but none of these theories completely explains the current biological and clinical observations. In this review we summarize some of the proposed models that were developed in attempt to understand the mechanisms of tumor dissemination and colonization as well as metastatic progression.

Breast Cancer Metastasis Suppressor 1 (BRMS1) Forms Complexes with Retinoblastoma-binding Protein 1 (RBP1) and the mSin3 Histone Deacetylase Complex and Represses Transcription

Breast cancer metastasis suppressor 1 (BRMS1) suppresses metastasis of multiple human and murine cancer cells without inhibiting tumorigenicity. By yeast two-hybrid and co-immunoprecipitation, BRMS1 interacts with retinoblastoma binding protein 1 and at least seven members of the mSin3 histone deacetylase (HDAC) complex in human breast and melanoma cell lines. BRMS1 co-immunoprecipitates enzymatically active HDAC proteins and represses transcription when recruited to a Gal4 promoter in vivo. BRMS1 exists in large mSin3 complex(es) of approximately 1.4-1.9 MDa, but also forms smaller complexes with HDAC1. Deletion analyses show that the carboxyl-terminal 42 amino acids of BRMS1 are not critical for interaction with much of the mSin3 complex and that BRMS1 appears to have more than one binding point to the complex. These results further show that BRMS1 may participate in transcriptional regulation via interaction with the mSin3.HDAC complex and suggest a novel mechanism by which BRMS1 might suppress cancer metastasis.

Allelic diversity in the host genetic background may be an important determinant in tumor metastatic dissemination

Metastasis, the spread and growth of tumors at secondary sites, is an extremely important clinical event, since the majority of cancer mortality is associated with the metastatic tumors rather than the primary tumor. In spite of the importance of metastasis in the clinical setting, the actual process is extremely inefficient. Millions of tumor cells can be shed into the vasculature daily yet few secondary tumors are formed. To successfully colonize a distant site tumor cells must overcome a series of barriers. Failure to complete any single step in the metastatic cascade abrogates the ability to form a secondary lesion. A variety of theories have been proposed to explain the inefficiency of the metastatic process. The most commonly accepted, the progression theory, posits a series of random mutational occurs within a primary tumor to generate a small subpopulation that acquires full metastatic capability. While significant evidence supports this model, recent discoveries demonstrating the ability to predict metastatic propensity from gene expression profiles in bulk tumor tissue are not consistent with only a small subpopulation of cells in the primary tumor acquiring metastatic ability. A second theory of metastatic inefficiency, the transient compartment theory, is more consistent with the microarray data, but does not completely explain observations like metastasis associated loss-of-heterozygosity events. To reconcile the observed results additional variables need to be added to the model of metastatic inefficiency. One possible variable that might explain the discrepancies is genetic background effects. Studies have demonstrated that the genetic background a tumor arises on can have significant affects on the ability of the tumor to metastasize and on gene expression profiles. Thus the observations could be reconciled by combining the theories, with genetic background influencing both metastatic efficiency and predictive gene expression profiles, upon which subsequently occur metastasis-promoting mutational and epigenetic events. If the genetic background is an important determinant of metastatic efficiency it would have significant implications for the clinical prediction and treatment of metastatic disease, as well as for the design of potential prevention strategies.

Induction of invasive and metastatic potential in mouse T-lymphoma cells (BW5147) by treatment with 5-azacytidine

Non-invasive, non-metastatic mouse BW5147 T-lymphoma cells were treated with non-mutagenic concentrations of the hypomethylating agent 5-azacytidine (5-aza-C). Subsequently, invasive variants were selected on monolayers of rat embryo fibroblasts. The estimated frequency of induction of invasive variants was smaller than 1 in 10(6) cells. We obtained several independent clones that were stable in the expression of the invasive phenotype. In contrast to the parental cell line, the highly invasive clones produced widespread metastases upon tail vein injection in all the syngeneic AKR mice tested, whereas clones with an intermediate level of invasiveness formed metastases only in part of the mice tested. DNA analysis using the methylation-sensitive and insensitive restriction enzymes, Hpa-II and Msp-I, respectively, showed that the DNA of the invasive variants remained hypomethylated, up to 6 months after 5-aza-C treatment. 5-aza-C is thus able to induce invasive and metastatic potential in the BW5147 T-lymphoma cells, similar to the activated human c-Ha-ras oncogene or human chromosome 7, as studied previously. The acquisition of invasive and metastatic potential is presumably caused by DNA hypomethylation and thus activation of one or more silent invasion controlling genes.

Molecular oncogenetics of metastasis

Metastasis is a complex non-stochastic process that is most likely the result of genetic and epigenetic interactions of a wide variety of genes. The search for a single gene which can encompass such a pleiotropic response as to account for the observed phenotypic characteristics of metastatic tumour populations has been unsuccessful. Particular studies involving gene transfection, subtractive hybridisation and cell fusion are beginning to identify specific genes which contribute to metastasis in some cell types. However, such analyses are complicated by the inherent genetic instability and phenotypic heterogeneity present in tumour populations. A more detailed understanding of the metastatic process may require an abandoning of current generalised approaches to metastasis in favour of concentrating on key components of the metastatic cascade such as adhesion and invasion.

Use of the Membrane Invasion Culture System (MICS) as a screen for anti-invasive agents

The Membrane Invasion Culture System (MICS) assay was adapted for relatively rapid screening of compounds and used to identify anti-invasive drugs that inhibit human and murine tumor cell migration through a reconstituted basement membrane in vitro. Cell lines demonstrating low and high invasive and metastatic potentials were tested with all compounds for tumoricidal effects prior to evaluation in MICS at non-cytotoxic doses. The effect on invasive potential in the MICS assay was determined in 3 categories: (1) 48 hr drug pre-treatment prior to seeding in the MICS (exceptions: 90 min pre-treatment with pertussis toxin and, for some studies, continuous exposure for 2-7 days); (2) peptide or prostaglandins 2 hr after seeding and attachment to the membranes in MICS followed by continuous exposure; and (3) cells receiving neither drug nor peptide treatment and serving as controls in each MICS chamber. Since invasion involves cellular motility and deformability, some cytoskeleton disrupting agents were selected. Of these, vincristine, colcemid and colchicine inhibited invasion but taxol did not. Pre-treatment with cAMP agonists produced conflicting results: dibutyryl cAMP and 8-(4-chloro-phenylthio) cAMP resulted in 50% and 38% reduction in invasion, respectively, whereas 8-bromo cAMP stimulated invasive potential by 30%. Forskolin and cholera toxin both significantly reduced invasiveness. Pre-treatment with 5-azacytidine and araC, to consider the role of methylation and proliferations decreased invasive ability. Anti-metastatic drugs such as gamma-interferon and razoxane inhibited invasive potential but to varying degrees. Treatment of cells with prostaglandins E2, F2 alpha, A2, and D2 were ineffectual; however, indomethacin mildly inhibits invasion (less than 30%).(ABSTRACT TRUNCATED AT 250 WORDS)