Alternative Genotoxicity Assays
Ames Assay: The simplest and most rapid assay is a bacterial
assay (the Ames Salmonella reverse mutation assay). However, it
is an imprecise assay that frequently gives false positive and false
negative results. It can only detect point mutations and is thus
incapable of detecting deletions which can lead to cancer. Thus
the FDA requires that a mammalian cell based mutation assay
also be used.
Mouse Lymphoma Assay (MLA) The mouse lymphoma TK+/-
assay (MLA) is based on detecting a mutation in the thymidine
kinase gene in mouse cells. In practice, cells are exposed to a
drug and then a period of time (2-3 days) elapses for expression of
a mutation in the TK gene. At this time, cells are exposed to a
special medium that kills non-mutant cells and allows mutant cells
to grow into colonies. This colony growth period requires an
additional 3-4 weeks. The MLA is the most widely used
mammalian cell genotoxicity assay and a considerable literature
attests to its value as a predictive assay for genotoxicity. The basis
for its use is that both small and large mutations are detectable
with this assay. Small colony mutants are often found to contain
large mutations that reduce the growth rate of the cells whereas
large colony mutants often contain smaller kinds of mutations,
such as point mutations. A limitation of the assay is that it is very
time consuming and labor intensive, and thus very expensive.
Furthermore, the assay cannot detect extremely large deletions
because they end up killing the cell rather than causing mutations.
Return to Technical Information.
Ames Assay: The simplest and most rapid assay is a bacterial
assay (the Ames Salmonella reverse mutation assay). However, it
is an imprecise assay that frequently gives false positive and false
negative results. It can only detect point mutations and is thus
incapable of detecting deletions which can lead to cancer. Thus
the FDA requires that a mammalian cell based mutation assay
also be used.
Mouse Lymphoma Assay (MLA) The mouse lymphoma TK+/-
assay (MLA) is based on detecting a mutation in the thymidine
kinase gene in mouse cells. In practice, cells are exposed to a
drug and then a period of time (2-3 days) elapses for expression of
a mutation in the TK gene. At this time, cells are exposed to a
special medium that kills non-mutant cells and allows mutant cells
to grow into colonies. This colony growth period requires an
additional 3-4 weeks. The MLA is the most widely used
mammalian cell genotoxicity assay and a considerable literature
attests to its value as a predictive assay for genotoxicity. The basis
for its use is that both small and large mutations are detectable
with this assay. Small colony mutants are often found to contain
large mutations that reduce the growth rate of the cells whereas
large colony mutants often contain smaller kinds of mutations,
such as point mutations. A limitation of the assay is that it is very
time consuming and labor intensive, and thus very expensive.
Furthermore, the assay cannot detect extremely large deletions
because they end up killing the cell rather than causing mutations.
Return to Technical Information.
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