Clastogen

A clastogen is a mutagenic agent giving rise to or inducing disruption or breakages of chromosomes, leading to sections of the chromosome being deleted, added, or rearranged. This process is a form of mutagenesis, and can lead to carcinogenesis, and tumorigenesis as cells that are not killed by the clastogenic effect may become cancerous. Known clastogens include acridine yellow, benzene, ethylene oxide, arsenic, phosphine, mimosine, actinomycin D, camptothecin, methotrexate, methyl acrylate, resorcinol and 5-fluorodeoxyuridine. 1,2-dimethylhydrazine also known as (DMH) is a known colon carcinogen and shows signs of possessing clastogenic activity. Exposure to clastogens increases frequency of abnormal germ cells in paternal males, contributing to developmental effects in the fetus upon fertilization.
Impact and DNA.
DNA synthesis can become obstructed by types of specific clastogens which have been seen due to radiation or alkylating agents, the effects that take place are known as chromosomal aberrations. There are also clastogens such as caffeine that don't show these effects of obstructing DNA synthesis and damaging DNA. Upon exposure to clastogens, the effects seen can consist of chromosomal rearrangements. The portions of deletions or inversions in chromosomes that take place are increasingly linked to cancer development. 
In terms of resistance, for a specific clastogen known as "Zeocin", a residue known as XLF-L115D mutant is flawed in terms of being resistant thus the clastogen activity shows no amount of decreasing.
In plants and mice cells studies have found that purine receptor agonists adenosine, ATP, ADP, cyclohexyladenosine, phenylisopropyladenosine and dimethylaminopurine riboside can lower the amount of clastogen damage seen in chromosomes and reduce the amount of micronuclei affected brought on by ethylmethane sulfonate and cyclophosphamide. Some ligands more than others can stop or reduce the clastogen activity of ethylmethane sulfonate such as adenosine, ADP or DAP. 
Assays.
There have been studies done that work with the usage of the DEL (deletion) assay to screen for clastogens. In vitro micronucleus assay (IVMN) can screen for clastogen activity. This is useful because an assay that can pick up clastogen activity can be used to foresee chromosome aberration activity. The IVMN assay can pick up on fragments that were membrane bound to DNA that were split from nuclei throughout the process of cell division. Micronuclei has been seen as a side product of clastogen activity or chromosome breakage.
The micronucleus test is another type of assay that uses gut cells to observe clastogens. The micronucleus test on gut cells is useful because in the case of the bone marrow micronucleus test there is not much activity seen after there has been oral exposure therefore more activity is seen in the gut cells. 
Telomeres.
There is a possibility of clastogens affecting telomeres. There can be uncertainty with telomeres that occur short term during the first round of cell division in which there can be chromosomal damage by clastogens. Clastogens (which break chromosomes) contribute to telomeric instability because it leads to chromosome end loss or true telomere loss. Clastogens can bring on issues with telomeres and cause them to not function as intended, most often seen anomalies seen occur in human lymphocyes, cancer cell lines and non-human established cell lines where there is telomere loss and copies of anomalies in the exposed cells, thus the problems that arise in telomeres can be duplicated and seen in exposed cells.
In addition, studies have shown that rat cells which were exposed to chemical clastogens express telomeric irregularities in function and can stay for several cell generations after treatment has been attempted. 
In Rats.
In a study where rats were treated with Brevetoxin B (PbTx2), there was a noticeable 2-3 fold growth in the amount of DNA seen in comet tails which tell us that Brevetoxin B shows in vivo clastogenic activity. This clastogen activity was seen after Brevetoxin B was injected by way of intratracheal administering in the rat. 