The carcinogenicity of nickel, chromium, arsenic,cobalt, and cadmium compou
nds has long been recognized. Nevertheless, the mechanisms involved in tumo
r formation are not well understood. The carcinogenic potential depends on
metal species; major determinants are oxidation state and solubility. Two m
odes of action seem to be predominant: the induction of oxidative DNA damag
e and the interaction with DNA repair processes, leading to an enhancement
of genotoxicity in combination with a variety of DNA-damaging agents. Nucle
otide excision repair (NER) is inhibited at low, non-cytotoxic concentratio
ns of nickel(II), cadmium(II), cobalt(II), and arsenic(III); the repair of
oxidative DNA base modifications is disturbed by nickel(II) and cadmium(II)
. One reason for repair inhibition appears to be the displacement of zinc(I
I) and magnesium(II). Potentially sensitive targets are so-called zinc fing
er structures present in several DNA repair enzymes such as the mammalian X
PA protein and the bacterial formamidopyrimidine-DNA glycosylase (Fpg prote
in); detailed studies revealed that each zinc finger protein exerts unique
sensitivities toward toxic metal ions. Taken together, toxic metal ions may
lower the genetic stability by inducing oxidative DNA damage and by decrea
sing the repair capacity towards DNA lesions induced by endogenous and exog
enous mutagens, which may in turn increase the risk of tumor formation.