Cell culture assays for chemicals with tumor-promoting or tumor-inhibiting activity based on the modulation of intercellular communication

Abstract

The ability of chemicals with tumor-promoting or tumor-inhibiting activity to modulate gap junctional intercellular communication is reviewed. The two most extensively used types of assays for screening tests are (1) metabolic cooperation assays involving exchange between cells of precursors of nucleic acid synthesis and (2) dye-transfer assays that measure exchange of fluorescent dye from loaded cells to adjacent cells. About 300 substances of different biological activities have been studied using various assays. For tumor promoters/epigenetic carcinogens, metabolic cooperation assays have a sensitivity of 62% and dye-transfer assays 60%. Thirty percent of DNA-reactive carcinogens also possess the ability to uncouple cells. The complete estimation of the predictive power of these assays could not be made because the majority of the substances studied for intercellular communication effects in vitro have not yet been studied for promoting activity in vivo. Both metabolic cooperation assays and dye transfer assays respond well to the following classes of substances: phorbol esters, organochlorine pesticides, polybrominated biphenyls, promoters for urinary bladder, some biological toxins, peroxisome proliferators, and some complex mixtures. Results of in vitro assays for such tumor promoters/nongenotoxic carcinogens, such as some bile acids, some peroxides, alkanes, some hormones, mineral dusts, ascorbic acid, okadaic acid, and benz(e)pyrene, do not correlate with the data of in vivo two-stage or complete carcinogenesis. Enhancement of intercellular communication was found for 18 chemicals. Among these, cAMP, retinoids, and carotenoids have demonstrated inhibition of carcinogenesis. We examine a number of factors that are important for routine screening, including the requirement for biotransformation for some agents to exert effects on gap junctions. We also discuss the mechanisms of tumor promoter and tumor inhibitor effects on gap junctional permeability, including influences of protein kinase activation, changes in proton and Ca2+ intracellular concentrations, and effects of oxy radical production.

Modulated Gap Junctional Intercellular Communication as a Biomarker of PAH Epigenetic Toxicity: Structure-Function Relationship

“…To the contrary, the term epigenetic toxicity implies a mechanism of reversibly altering the genetic phenotype of a cell through biochemical pathways that ultimately turn genes on and off via intracellular pathways, a process under the homeostatic control of neighboring cells via intercellular communication through gap junctions (15,16). Because intracellular pathways often converge onto intercellular events (15), the development of in vitro assay systems that measure GJIC has been successfully used to detect many epigenetic carcinogens (27,28 (29). The potential human carcinogenicity of PAHs is based on many years of observation in animal and in vitro bioassays, epidemiology, and occupational medicine (29).…”

Reflections on the use of 10 IARC carcinogenic characteristics for an objective approach to identifying and organizing results from certain mechanistic studies

“…However, they are not mutagenic to the nuclear genome of cells but can reversibly inhibit GJIC. 44,45 The promotion process is potentially interruptible or even reversed. 46 Some of the successes of epidemiology included the detection of the association of smoking with lung cancer; alcohol was associated with liver cancer, and sun light was associated with skin cancer.…”

Mesenchymal Stem Cells: An Innovative Approach in Pharmacokinetics

“…The ability of chemicals with tumor-promoting or tumor-inhibiting activity to modulate gap junctional intercellular communication have been detected with two most extensively used assays, namely (1) metabolic cooperation assays and (2) dye-transfer assays [36]. In metabolic cooperation assays, a population of donor cells is incubated in the presence of an excess of a radiolabeled precursor (typically uridine) and then cocultured with unlabeled recipient cells.…”

“…These include the requirement of biotransformation for some agents to exert effects on gap junctions. The tumor promoters and tumor inhibitors affect gap junctional permeability that influences many physiological mechanisms like protein kinase activation, changes in proton and Ca 2+ intracellular concentration and oxyradical production [36]. Growth factors, hormones, extracellular matrix, and cytokines can also block GJIC [38].…”